Introduction
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Introduction: In the present days when technology has so improved that all the product become compact and more effective. One of the best example is size of computer become so small and more effective. Automobile manufacturer and designers want to reduce the size and weight of different parts of automobile components. Companies are striving to shorten the design cycles and to cut engineering as well as prototype cost, so that they can reduce the overall weight, analysis time and manufacturing cost of the car and improve the performance of car. Thus customer satisfaction would be improved. By conventional design and analysis process it is very difficult to make an actual radiator and make changes for improving the efficiency of radiator and reducing the size of radiator. But with the help of advance design softwares (Commercial s/w) like Pro/Engineer, CATIA & ANSYS etc. It is become possible to create an accurate model of any part of automobile. For analyzing the complex cooling, air flow characteristics and resulting thermal performance of the radiator and other heat generating components in the engine compartment can be easily understand by utilize cost effective numerical tools such as computational Fluid dynamics (which is a part of ANSYS). The radiator of a Maruti 800 (MB308) car is studied and modeled to determine the heat transfer rates, temperature profiles and overall efficiency. The actual radiator is measured and a model is made native in Pro/Engineer. All the features of the row including the hollow water tubes and the fins are recreated to ensure the most accurate model. The analysis is done with air, when traveling at different speeds across the radiator. ANSYS is used to calculate the air velocity distribution over the radiator. The objective is to show how CFD can be used as a practical engineering tool to complement and enhance the design process. So, by using these advance commercial softwares environment we can improve the effectiveness and overall performance of any part (radiator) of the car.
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Need of Analysis: Automotive companies are trying to shorten design cycles and to cut engineering as well as prototype costs. The condition demand a better understanding of the complex cooling air flow characteristics and resulting thermal performance of the radiator and other heat generating components in the engine compartment. Here we use cost effective numerical tool COMPUTATIONAL FLUID DYNAMICS (CFD) as a part of the systems engineering. It is used as a practical engineering tool to complement and enhance the design process.
Computer simulation: Simulation is a broadly used and somewhat ill-defined term from the engineering point of view. According to Webster’s international dictionary “To simulate” means “To feign, to attain the essence without the reality”. However, the simplest meaning of simulation is “imitation”. These dictionary meanings don’t bring out a clear picture of the word “Simulation” for engineering applications. Therefore, a definition of the word “Simulation” is more appropriate in this context. With some trepidation, the author defines simulation as follows: “Simulation is the process of designing of a model of a real system and conducting experiments with it, for the purpose of understanding the behavior of the system.” Computer simulation has gained greater importance these days because of the availability of fast digital computers. It can be defined as follows: Computer simulation is the process of formulating a model of physical system representing actual processes and analyzing the same. Usually, the model is a mathematical one representing the actual processes through set of algebraic, differential or integral equations and the analysis is made using a computer. In modern research, computer simulation has become a powerful tool that saves time and is also economical when compare to experimental study. A propose theory can be analyzed quickly using a computer and the cost of setting up an experimental apparatus can be postponed until the optimization is achieved. However, it may be noted that simulation is only a step prior to experimentation and the results obtained from simulation studies must be validated with experimental results to establish the reliability. Once validated, computer
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simulation can provide a deep insight into the performance characteristics of the system. This statement is particularly true for the case of radiator studies. A computer simulation or a computer model is a computer program that attempts to simulate an theoretical model of a particular system. Computer simulations have become a useful part of modeling many process of engineering new technology .
Types of computer simulation: Computer models can be classified according to several criteria including: •
Stochastic or deterministic (and as a special case of deterministic, chaotic)
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Continuous or discrete (and as an important special case of discrete, discrete event or DE models).
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Local or distributed.
For example: •
Stochastic models use random number generators to model the chance or random events; they are also called Monte Carlo simulations.
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A discrete event simulation (DE) manages events in time. Most computer, logic-test and fault-tree simulations are of this type. In this type of simulation, the simulator maintains a queue of events sorted by the simulated time they should occur. The simulator reads the queue and triggers new events as each event is processed. It is not important to execute the simulation in real time. It's often more important to be able to access the data produced by the simulation, to discover logic defects in the design, or the sequence of events.
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A continuous simulation uses differential equations (either partial or ordinary), implemented numerically. Periodically, the simulation program solves all the equations, and uses the numbers to change the state and output of the simulation. Most flight and racing-car simulations are of this type. This may also be used to simulate electrical circuits. Originally, these kinds of simulations were actually implemented on analog computers, where the differential equations could be represented directly by various electrical components such as op-amps. By the late 1980s, however, most "analog" simulations were run on conventional digital computers that emulate the behavior of an analog computer.
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A special type of discrete simulation which does not rely on a model with an underlying equation, but can nonetheless be represented formally, is agent-based simulation. In agent-based simulation, the individual entities (such as molecules,
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cells, trees or consumers) in the model are represented directly (rather than by their density or concentration) and possess an internal state and set of behaviors or rules which determine how the agent's state is updated from one time-step to the next. •
Distributed models run on a network of interconnected computers, possibly through the Internet. Simulations dispersed across multiple host computers like this are often referred to as "distributed simulations". There are several military standards for distributed simulation, including Aggregate Level Simulation Protocol (ALSP), Distributed Interactive Simulation (DIS) and the High Level Architecture (HLA).
Computer simulation in Engineering: Generic examples of types of computer simulations in engineering, which are derived from an underlying mathematical description: •
a numerical simulation of differential equations which cannot be solved analytically, theories which involve continuous systems such as phenomena in cosmology, fluid dynamics (e.g. climate models, roadway noise models, roadway air dispersion models) fall into this category.
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a stochastic simulation, typically used for discrete systems where events occur probabilistically, and which cannot be described directly with differential equations (this is a discrete simulation in the above sense). Phenomena in this category include genetic drift, biochemical or gene regulatory networks with small numbers of molecules. (see also: Monte Carlo method).
Advantage of computer simulation in Radiator Analysis: •
It serves as a tool for a better understanding of the variables involved and their effect on radiator performance.
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It reduces considerably the time-consuming tests by narrowing down the variables that must be studied.
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It helps in optimizing the radiator design for a particular application, reducing cost and time.
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Objective of the Project: •
Predict temperature distribution over the radiator tubes and fins.
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Determine the heat transfer rate from the radiator.
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Predict velocity distribution over the radiator tube.
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Determine the efficiency of fins.
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Determine the effectiveness of radiator.
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Graphical outputs from the simulation included the velocity vectors and the contour plots detailing the flow characteristics around the front end of the car and over the radiator.
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Developing the program in C++ language.
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Principle of the cooling system & Heat Transfer
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Principle of the cooling system:
Cooling system
Figure 1
The purpose of the cooling system is to do three things: •
To maintain highest and most operating temperature with in the engine.
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To remove excess heat from the engine.
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To bring the engine up to operating temperature as quickly as possible. If the engine is not at the highest operating temperature, it will not run
efficiently, fuel mileage will decrease and wear on the engine components will increase. With in the gasoline or diesel engine, energy from the fuel is converted to power for moving the vehicle .Not all of the energy however is converted to power Referring to Figure 2. •
25% and to push the vehicle (output)
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9% radiant loss
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33% exhaust loss
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Remaining 33% must be removed by cooling system
Most of the energy approximately 70% in the gasoline engine is converted into heat.
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.
.
If the engine temperature is too high, various problems will occur, these include: •
Overheating of lubricating oil-this will result in the lubricating oil breaking down.
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Over heating of the parts-This may causes loss of strength of the metal.
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Excessive stress between engine parts- This may cause increase in friction, which may cause excessive wear.
If the engine temperature is too low, various problems will occurs, this includes: •
Poor fuel mileage-The combustion process will be less efficient.
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Increase in carbon built up-As the fuel enters the engine, it will condense and cause excessive built up on the intake valves.
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Loss of the power if the combustion process is less efficient, the power output will be reduced.
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Fuel not being burned completely, this will cause fuel to dilute the oil and cause excessive engine wear.
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Heat transfer: Heat transfer occurs when a temperature difference exists. As a result of combustion, high temperatures are produced, inside the engine cylinder. Considerable heat flow occurs from gases to the surrounding metal walls. However, the heat transfer on this account is quite small. Hence, the cylinder wall must be adequately cooled to maintain safe operating temperatures in order to maintain the quality of the lubricating oil. Heat transfer from gases to the cylinder wall may occur predominantly by convection and radiation whereas the heat transfer through the cylinder wall occurs only by conduction. Heat is ultimately transferred to the cooling medium by all the three modes of heat transfer. The temperature profiles across the cylinder barrel wall are shown in figure 3 for water-cooled engine. In this case, Tg, is mean gas temperature which may be as high as 8500C. This may not be confused with the peak temperature of the cycle which may be two or three times this value. Largest temperature drop, however, occurs in the boundary layer of the gas which lies adjacent to the cylinder wall. There is a corresponding boundary-layer in the cooling medium on the outer side of the cylinder. However, because of fins in the air-cooled engines the effect of external boundary layer is reduced. The conduction of heat through cylinder walls with corresponding temperature gradients is illustrated in the figure 3. The gas film, being of low conductivity, offers a relatively high resistance to the heat flow, whilst on the water jacket side there is usually a layer of corrosion products, scale etc, which the poor conductors of heat. The least resistance to the heat flow occurs through the metal cylinder wall, as shown by the temperature gradient there. In actual practice because of the cyclic operation of engines, there is a cyclic variation of the gas temperature with in the cylinder the effect of which is to cause a decrease of heat to travel into the metal which gradually dies out and after warm up period a steady flow condition prevails. It has been experimentally established that in internal combustion engine the cyclic temperature variation die out fast before fluctuations reach the outside surface of the cylinder. Maximum temperature of the cylinder walls, in a properly designed engine, seldom exceeds 100C above the mean temperature.
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Figure 3
The cooling system works on the principle of heat transfer. Heat will always travel from a hotter to cooler object. Heat transfer is in three ways 1. Conduction 2. Convection 3. Radiation Conduction is defined as transfer of heat between two solid object .for examples referring to figure 4, heat must be transferred from valve stem to valve guide. Since both objects are solid, heat is transferred from hotter stem valve to cooler valve guide by conduction. Heat is also transferred from the valve guide to cylinder head by conduction.
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Valve Guide
Valve Stem
Figure 4
Heat is transferred by conduction from the valve guide. Both objects are solid. Heat can be transferred by convection; convection is defined as the transfer of heat by circulation of heated parts of a liquid gas. When the hot cylinder block transfers heat to the coolant, it is done by convection. Convection also occurs when the hot radiator parts transfers heat to the coolant air surrounding the radiator. Radiation is another way that heat is transferred. Radiation is defined as transfer of heat by converting heat energy to radiant energy. Any hot object will give off radiation. The hotter the object, the greater the amount of radiant energy. When the engine is hot ,some of the heat is converted to radiant(about 9%).The cooling system relies on these principles to remove the excess heat within the engine.
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Variation of gas temperature: There is an appreciable variation in the temperature of the gases inside the engine cylinder during different processes of the cycle. Temperature inside the engine cylinder is almost the lowest at the end of the suction stroke. During combustion there is a rapid rise in temperature to peak value which again drops during the expansion. This variation of the gas temperature is illustrated in figure 5 for various processes in the cycle.
Figure 5
Figure 6
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Piston temperature distribution: The piston crown is exposed to very high combustion temperature. Figure-7 gives typical values of temperature at different parts of a cast iron piston. It may be noted that maximum temperature occurs at the centre of the crown and decrease at the outer edge. The temperature is the lowest at the bottom of the skirt. Poor design may result in the thermal overloading of the piston at the centre of crown. The temperature difference between piston outer edge and centre of the crown is responsible for the flow of heat to the ring belt through the path offered by metal section of the crown. It is therefore, necessary to increase the thickness of the crown from the centre to the outer edge in order to make a path of greater cross-section available for increasing the heat quantity. The length of the path should not be too long or the thickness of the crown crosssection is too small for the heat to flow. This may even lead to cracking of the piston during overload operation.
Figure 7
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Cylinder temperature distribution: Whenever a moving gas comes in to contact with a wall, there exists a relatively stagnant gas layer which act as a thermal insulator. The resistance of this layer to heat flow is quite high. Heat transfer from the cylinder gases takes place through the gas layer and through the cylinder walls to the cooling medium. A large temperature drop is produced in the stagnant layer adjacent to the walls. The peak cylinder gas temperature may be 2800K while the temperature of the cylinder inner wall surface may be only 450K due to cooling. Heat is transferred from the gases to the cylinder walls when the gas temperature is higher than the wall temperature. The rate and direction of flow of heat varies depending upon the temperature differential. If no cooling is provided there could be no heat flow, so that the whole cylinder wall would soon reach an average temperature of the cylinder gases. By providing adequate cooling, the cylinder wall temperature can be maintained at optimum level.
Figure 8
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Figure 9
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Theory of engine heat transfer: In spite of its high temperature, the cylinder gas is poor radiator and almost all the heat transfer to the cylinder walls from combustion space is by convection. In order to understand the engine heat transfer, a simple analysis can be followed for the flow of heat gases through the pipe. For gases in pipes it can be shown by dimensional analysis and also through experiments that hL/k = Z×( ρCL/µ)n×(Cpµ/k)m
(1.0)
Where h= coefficient of heat transfer L= any characteristic length k= thermal conductivity of the gases Z= constant ρ= mass density of gases C= velocity of gases µ=viscosity of gas n, m=exponents The term (ρCL/µ) can be recognized as Reynolds no. for cylinder gases. The term (Cpµ/k)is called the Prandtl number and is nearly constant for gases. Therefore, Prandtl number can be absorbed in the constant Z in equation 1.0 so thathL/k = Z×( ρCL/µ)n
(1.1)
Since prandtl number is constant, k α Cpµ and substituting Cpµ for k in equation 1.0. hL/Cpµ = Z×(ρCL/µ)n
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h=Z×Cp×(ρC)n×(L/ µ)n-1
(1.3)
The rate of heat transfer can be written asq=h×A×∆T Where ∆T is the temperature difference between the gas and wall. Substituting the value of h from equation (1.3) we get q= Z×Cp×(ρC)n×(L/ µ)n-1× A×∆T
(1.4)
In the above expression, A is the area of the heat transfer which is proportional to L2 and S is the mean piston speed which is proportional to gas velocity C. when the average gas temperature is considered Cp and µ can be assumed to have constant values, then q= Z× (ρS)n×Ln+1×∆T
(1.5)
Piston speed is proportional to the product of L and N where N is the rpm of the engine. Volumetric efficiency, ηv is proportional to the density of charge ρ, then q= Z× (ηvN)n×L2n+1×∆T
(1.6)
The average temperature of the cooling medium, the fuel-air ratio of the mixture and the compression ratio of the engine directly influence the value of ∆T.The density is mainly affected by the intake pressure, compression ratio and the volumetric efficiency,ηv. Those engines which have nearly equal value of ∆T, the heat transfer rate depends on the product of ηvN and the size of the engine. For engines when ∆T is assumed to be invariantq= Z× (ηvN)n×L2n+1
(1.7)
The value of Z and n are determined from the experiments on a particular type of engine under various operating conditions. The constants so obtained can be used for calculating heat transfer rate for other operating conditions of the same engine or for geometrically similar engine.
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Parameters Affecting Engine Heat Transfer: The engine heat transfer depends upon many parameters. Unless the effect of these parameters is known, the design of a proper cooling system will be difficult. In this section, the effect of various parameters on the engine heat transfer is briefly discussed. 1. Fuel-Air Ratio: A change in fuel-air ratio will change the temperature of the cylinder gases and affect the flame speed. The maximum gas temperature will occur at an equivalence ratio of about 1.12 that is at a fuel-air ratio about 0.075. At this fuel-air ratio ∆T will be a maximum. However from experimental observations the maximum heat rejection is found to occur for a mixture, slightly leaner than this value. 2.
Compression Ratio: An increase in compression ratio cause only a slightly increase in gas
temperature near the top dead centre, but because of the greater expansion of the gases, there will be a considerable reduction in gas temperature near bottom dead centre where a large cylinder wall is exposed. The exhaust gas temperature will also be much lower because of greater expansion so that the heat rejected during blow down will be less. In general, as compression ratio increases there tend to be a marginal reduction in heat rejection. 3.
Spark Advance: A spark advance more than the optimum as well as less than the optimum
will result in increased heat rejection to the cooling system. This is mainly due to the fact that spark timing other than MBT value (Minimum spark advance for Best Torque) will reduce the power output and thereby more heat is rejected. 4.
Preignition And Knocking: Effect of preignition is the same as advancing the ignition timing. Large
spark advance might lead to erratic running and knocking. Though knocking cause large change in local heat transfer conditions, the overall effect on heat transfer due to knocking appears to be negligible. However no quantitive information is available regarding the effect of preignition and knocking on engine heat transfer.
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5.
Engine Output: Engines which are designed for high mean effective pressure or high piston
speeds, heat rejection will be less. Less heat will be lost for the same indicated power in large engines. 6.
Cylinder Wall Temperature:
The average cylinder gas temperature is much higher in comparison to the cylinder wall temperature. Hence, any marginal change in cylinder gas temperature will have very little effect on the temperature and thus on heat rejection. A typical temperature distribution (figure 8) which would be found in an I.C. engine operating at steady state, three of the hottest points are: 1. Around the spark plug. 2. The exhaust valve and port. 3. The face of the piston. Not only are these places exposed to the high temperature gases, but they are difficult places to cool. Highest gas temperature during combustion occurs around the spark plug. This creates a critical heat transfer problem area. The spark plug fastened through the combustion chamber wall creates a disruption in the surrounding water jackets, causing a local cooling problem. On air-cooled engines the spark plug disrupts the cooling fin pattern, but the problem may not be as severe. The exhaust valve and port operate hot because they located in the pseudo steady flow of hot exhaust gases and create a difficulty in cooling similar to the one the spark plug creates. The valve mechanism and connecting exhaust manifold make it very difficult to route coolant or allowed a finned surface to give effective cooling. The piston face is difficult to cool because it separated from the water jackets or outer finned cooling surface.
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Heat transfer in combustion chamber: Once the air-fuel mixture is in the cylinders of an engine, the three primary modes of heat transfer (conduction, convection, radiation) all play an important part for smooth steady state operation. In addition the temperature with in the cylinders is affected by a phase change-evaporation of the remaining liquid fuel. The air-fuel mixture entering the cylinder during the intake stroke may be hotter or cooler than the cylinder wall, with the resulting heat transfer being possible in either direction. During the compression stroke, the temperature of the gas increases, and by the time combustion starts, there is already a convective heat transfer to the cylinder walls. Some of this compressive heating is lessened by the evaporating cooling which occurs when the remaining liquid fuel droplets vaporize. During combustion peak gas temperature on the order of 3000K occur within the cylinders, and effective heat transfer is needed to keep the cylinder walls from overheating. Convection and conduction are the main heat transfers modes to remove energy from the combustion chamber and keep the cylinder walls from melting. The basic idea is that according to Foriour law for small ∆x, q=-k (∆T/∆x) Heat transfer through a cylinder wall. Heat transfer will be Q= (Tg-Tc)/ [1/hgAg+ {ln (rc/rg)/ (2πkL)} +1/Achc]
(1.8)
Where Tg- gas temperature in the combustion chamber Tc- coolant temperature hg- convection heat transfer coefficient on the gas side. hc- convection heat transfer coefficient on the coolant side. Ag-inside area of cylinder Ac-area of cooling jacket around the cylinder rg –radius of piston rc-radius of cooling jacket k- Thermal conductivity of the cylinder wall. Heat transfer through the combustion chamber cylinder wall of an I.C. engine. The cylinder gas temperature Tg and convection heat transfer coefficient hg vary over large ranges for each engine cycle, while the coolant temperature Tc and heat transfer coefficient
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hc are fairly constant, as a result of this, heat conduction is cyclic for a small depth in to the cylinder wall on the combustion chamber side. Heat transfer in above equation (1.8) is cyclic. Gas temperature Tg in the combustion chamber varies greatly over an engine cycle, ranging from maximum values during combustion to minimum during intake. It can even be less than wall temperature early in the intake stroke, momentarily reversing heat transfer direction. Coolant temperature Tc is fairly constant, with any change occurring over much longer cycle times. The coolant is air for air-cooled engines and antifreeze solution for water cooled engine. The convection heat transfer coefficient hg on the cylinder gas side of the wall varies greatly during an engine cycle due to change in gas motion, turbulence, swirl, velocity etc. this coefficient will also have large spatial variation with in the cylinder for same reasons. The convection heat transfer coefficient on the coolant side of the wall will be fairly constant, being dependent upon coolant velocity. Thermal conductivity k of the cylinder wall is a function of wall temperature and will be fairly constant. Convection heat transfer on the inside surface of the cylinder isq= Q/A =hg (Tg-Tc)
(1.9)
Wall temperature Tw should not exceed 1800C-2000C to assure thermal stability of the lubricating oil and structural strength of the wall. There are a number of ways to identifying a Reynolds number to use for comparing flow characteristics and heat transfer in engines of different sizes, speed and geometrics. Choosing the best characteristic length and velocity is sometimes difficult. One way of defining a Reynolds no for engines which correlates data fairly well is Re= ((ma+mf)D)/(Ap*µg)
(1.10)
Where ma=mass flow rate of air in to cylinder mf= mass flow rate of fuel in to cylinder D=bore Ap=area of piston face µg =dynamic viscosity of gas in the cylinder A nusselt number for the inside of the combustion chamber can be defined using this Reynolds number. Nu=hgD/kg=C1(Re)C2
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Where C1 and C2 = constant Kg=thermal conductivity of cylinder gas hg=average value of the convection heat transfer coefficient to be used in eqn(1.8).
Types of cooling system: Engine manufacturers today commonly used two types of cooling system. •
Air cooled system
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Liquid cooled system
Air-cooled engine: Several producers have designed engines that are air cooled. Certain foreign manufacturers still use air cooled engines. Air cooled engines have fins or ribs over the outer surfaces of the cylinder and cylinder heads. These fins are cast directly to the cylinder and heads. The fins increase the surface area of the object which, in turn, increases the amount of convection and radiation available for heat transfer. The heat produced by the combustion transfers from the internal parts of the engine by conduction to outer fins. Here the heat is dissipated to the passing air. In some cases, individual cylinders are used to increase air circulation around the cylinder. Air cooled engines require air circulation around the cylinder block and heads. Some sort of fan is usually used to move the air across the engine. A shroud is also used in some cases to direct or control the flow of air across the engine. Air cooled engine usually do not have exact control over engine temperature, however they do not use a radiator and water pump. This may reduce maintenance on the engine over along period of time. The basic principle involved in this method to have current of air flowing continuously over a heated metal surface from where the heat is to be removed. The heat dissipated depends upon following factors •
Surface area of metal into contact with air.
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Mass flow rate of air.
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Temperature difference between the heated surface and air.
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Conductivity of metal. Thus for an effective cooling the surface area of the metal which in
contact with the air should be increased. This is done by using fins over the cylinder
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barrels. These fins are either cast as an integral part of the cylinder or separate finned barrels are inserted over the cylinder barrel. Sometimes, particularly in the case of aero engine, the fins are machined from the forged cylinder blanks. To increase the contact area still further, baffles are used sometimes. Use of copper and steel alloy has also been made to improve heat transfer because of their better thermal conductivity.
Advantages: •
Air cooled engines are lighter because of the absence of the radiator, the cooling jackets and the coolant.
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They can be operated in extreme climates, where the water may freeze.
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In certain areas where there is scarcity of cooling water, the air cooled engine has an advantage.
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Maintenance is easier because the problem of leakage is not there.
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Air cooled engine get warmed up earlier than the water cooled engine.
Disadvantages: •
It is not easy to maintain even cooling all around the cylinder, so that the distortion of the engine takes place. This defect has been remedied sometimes by using fins parallel to the cylinder axis. This also helpful where a no. of cylinders in row are to be cooled. However, this increases the overall engine length
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As the coefficient of the heat transfer for air is less than that for water, there is less efficient cooling in this case and as a result the highest useful compression ratio is lesser in the case of air cooled engines than in the water cooled ones.
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The fan used is very bulky and absorbs a considerable portion of the engine power (about 5%) to drive it.
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Air cooled engines are more noisy, because of the absence of the cooling water which acts as sound insulator.
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Some engine components may become inaccessible easily due to guiding baffles and cooling, which makes the maintenance difficult.
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The cooling fins around the cylinder may vibrate under certain conditions due to which noise level would be considerably enhanced.
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Liquid-cooled engines: In a liquid cooled engine the heat from the cylinder is transferred to a liquid flowing through jackets surrounding the cylinders. The liquid then pass through a radiator. Air passing through the radiator removes the heat from liquid to the air. Liquid cooling systems usually have better temperature control than air cooled engine. They are designed to maintain a coolant temperature of 820C-980C. The engine runs best when its coolant is about 200 degrees Fahrenheit (93 degrees Celsius).
Liquid coolant flow: When the vehicle is started, the coolant pumps begin circulating the coolant. The coolant goes through the cylinder block from the front to the rear. The coolant circulates around the cylinders, and passes through the cylinder block. The coolant then passes up into the cylinder head through the hole in the head gasket. From there, it moves forward to the front of the cylinder head through internal passages. These passages permit cooling of high heat areas like spark plug and exhaust valve areas. As the coolant leaves the cylinder head, it passes through a thermostat on the way to the radiator. As long as the coolant temperature remains low, the thermostat stays closed. Under these conditions the coolant flows through the by-pass tube and returns to the pump for recirculation through the engine. As the coolant heats up, the thermostat gradually opens to allow enough hot coolant to pass through the radiator. This will maintain the engine’s highest operating temperature.
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Figure 10
From the thermostat, the coolant flows to the internal passages in the radiator. There are tubes in the core with small fins on them. The coolant is now being cooled by the air passing through the radiator. From there it returns to the outlet of the radiator and back to the pump. It then continues its circulation through the engine.
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Maruti 800 (MB 308) coolant characteristics
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Maruti800 (MB308) coolant characteristics: Ethylene glycol (monoethylene glycol (MEG)) IUPAC name: Ethane-1, 2-diol Ethylene glycol is an alcohol with two -OH groups (a diol), a chemical compound widely used as an automotive antifreeze. In its pure form, it is an odorless, colorless, syrupy liquid with a sweet taste. Ethylene glycol is toxic, and its accidental ingestion should be considered a medical emergency. Water is one of the most effective fluids for holding heat, but water freezes at too high a temperature to be used in car engines. The fluid that most cars use is a mixture of water and ethylene glycol (C2H6O2), also known as antifreeze. By adding ethylene glycol to water, the boiling and freezing points are improved significantly. The temperature of the coolant can sometimes reach 2500F to 2750F (1210C to 1350C). Even with ethylene glycol added, these temperatures would boil the coolant, so something additional must be done to raise its boiling point. The cooling system uses pressure to further raise the boiling point of the coolant. Just as the boiling temperature of water is higher in a pressure cooker, the boiling temperature of coolant is higher if you pressurize the system. Maruti 800 car radiator has a pressure limit not exceed than 0.9 kgf/cm2. Antifreeze also contains additives to resist corrosion. Water has been the most commonly used engine coolant. This is because it has good ability to transfer heat and can be readily obtained. Water alone, however is not suitable for today engines for a number of reasons . water has a freezing point 320F (00C). Engines must operate in colder climates also water has a boiling point of 2120F (1000C). Engine coolant temperature often exceeds this point. In addition, water can be very corrosive and produce rust with in a coolant system. To over come these problems, anti-freeze added to the coolant. An ethylene glycol type anti-freeze coolant is used. This anti freeze includes suitable corrosion inhibitors. The best percentage of anti-freeze to water to use is about 50% antifreeze mixed with 50% water.
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Freezing point: Figure 11 shows what happens to the freezing point of a coolant when different percentages of anti-freeze are used. For example, when 100% water is used, the freezing point is 320F (00C). When 25% antifreeze and 75% water is used, the freezing point of the coolant is about 100F. At 68% antifreeze, the freezing point of the coolant is about -920F. As the amount of anti freeze percentage increases from this point, the freezing point goes back towards 00F.
Boiling points: The addition of anti freeze in the cooling system increases the boiling point. The boiling point of a fluid is the temperature at which a liquid becomes vapor. Any coolant that becomes a vapor has very poor conduction and convection properties. Therefore, it is necessary to protect it from safety against engine cooling system overheating failure. Properties of antifreeze solutions: Ethylene Glycol-Water Mixture: %Ethylene
Sp.Gravity
Freezing
Boiling pt.
Glycol by
At 101 Kpa &
pt. at
at 101 kpa
volume
15 0C
101 kpa 0 0
C
0
C
0
F
F
0
1.000
0
32
100
212
10
1.014
-4
24
-
-
20
1.029
-9
15
-
-
30
1.043
-16
3
-
-
40
1.056
-25
-14
-
-
50
1.070
-38
-37
111
231
60
1.081
-53
-64
-
-
100
1.119
-11
12
197
386
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Table I
Thermal Properties: Most heat is transferred in a cooling system by convection from hot metal to a cooler liquid as in the engine block or from a hot liquid to cooler metal surfaces, as in the radiator. The convection coefficient of liquids in a tube is a complicated relationship between the thermal conductivity, viscosity of the liquid, and the tube diameter, which determines the amount of turbulent flow. With almost 2.5 times greater thermal conductivity than glycol-based coolants, water has amazingly efficient heat transfer properties compared to virtually any other liquid cooling medium. Mixtures of glycol and water have nearly proportional improvement due to the addition of water.
Figure 11
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Production: Ethylene glycol is produced from ethylene, via the intermediate ethylene oxide. Ethylene oxide reacts with water to produce ethylene glycol according to the chemical equation : C2H4O + H2O → HOCH2CH2OH This reaction can be catalyzed by either acids or bases, or can occur at neutral pH under elevated temperatures. The highest yields of ethylene glycol occur at acidic or neutral pH, with some of a large excess of water present. Under these conditions, ethylene glycol yields of 90% can be achieved. The major byproducts are the ethylene glycol oligomers diethylene glycol, triethylene glycol, and tetraethylene glycol.
Applications: The major use of ethylene glycol is as an engine coolant and antifreeze. Due to its low freezing point, it has also been used as a deicing fluid for windshields and jet engines.
Safety: The major danger from ethylene glycol is from its ingestion. Due to its sweet taste, children and animals will sometimes consume large quantities of it if given access to antifreeze. Symptoms of ethylene glycol poisoning follow a three-step progression doses as small as 30 milliliters (2 tablespoons) can be lethal to adults
Corrosion: Corrosion in the cooling system can be vary damaging to the engine. Corrosion can be produced in several ways. Direct attack means the water in the coolant is mixed with the oxygen from air. This process can produce rust particles, which can damage water pump seals and cause increased leakage. Electrochemical attack is a result of using different metals in an engine.
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Corrosion Protection: Modern automotive engines now use aluminium for heads, radiators, water pump housings, and nearly all hose fittings. These engines require significantly greater corrosion protection than cast iron counterparts of the past. Aluminium is an electro active metal that requires an impenetrable corrosion inhibitor film to prevent rapid corrosion. Acid neutralization capability is very important. Coolant left in a cooling system for several years can become acidic from the oxidation of the glycol to acids. Also, keeping the glycol concentration in the cooling system below 50% will help stability. Engine Coolant provides excellent protection from cavitation erosion in the water pump and cylinder head. Localized boiling in the cylinder head forms vapour bubbles, which collapse when they come in contact with cooler liquids. This collapse creates tremendous shock waves, which removes the inhibitor film from the aluminium surface and can cause catastrophic erosion of the aluminium if the inhibitor does not reform the film quickly. Another problem created by cavitation erosion is the deposition of the removed aluminium as a salt with poor heat transfer properties in the lower temperature radiator tubes. Engine Coolant prevents this corrosion through effective film formation and smaller vapour bubble formation which has a less violent collapse. Foam control is equally important since entrained air will cause cavitation erosion due to the collapse of foam bubble. Engine Coolant provides excellent control of foam with water alone and with glycol solutions.
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Parts of Liquid Cooling System
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Parts of Liquid Cooling System: •
Thermostat
•
Radiator
•
Pressure Cap
•
Hose pipes
•
Fan
•
Belt Drive
•
Water Pump
Figure 12
1. Cylinder Block 2. Cylinder Head 3. Bypass 4. Radiator Pressure cap 5. Radiator 6. Coolant Pump 7. Fan 8. Fan Blade 9. Thermostat
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Thermostats: Function: The thermostat is one of the most important part of the cooling system. It is designed to sense the temperature of the coolant. If the temperature of the coolant remains cold, the thermostat will be closed. The coolant then goes to the by-pass tube. This allows a small amount of the coolant to pass in to the radiator to be cooled. The remaining coolant flows through the by-pass tube. This coolant is recirculated without being cooled. If the engine is under heavier load, more cooling will be necessary. If the temperature of the coolant increases to opening temperature, the thermostat will open slightly. As the temperature of the coolant increases further, the thermostat opens more. This allows more coolant to reduce its temperature through the radiator. When the engine is under full load, the thermostat will be fully open .the maximum amount of the coolant will be sent to the radiator for cooling and a small amount of coolant will continue to flow through the bypass tube. Thermostat operates on a very simple principle. A wax pellet material with in the thermostat expands and causes the mechanical motion which opens the thermostat. This allows coolant to pass through to the radiator. It should be noted that the thermostat is opened only partially when the temperature reaches its opening point. As the coolant temperature increases, the thermostat opens further. Eventually, the coolant is hot enough to cause the thermostat to open fully to get maximum cooling. Thermostats are designed to open at different temperatures. Maruti 800 thermostat operating temperatures are 820C and 980C. Most thermostats in use are solid expansion “pill” type, basically a temperature sensitive valve. The thermostat is generally located between the front of the engine and top (inlet) hose of the radiator. The thermostat is commonly contained a metal housing connected to the hose.
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Figure 13
Wax Pallet Thermostat
Figure 14
Exploded View of Thermostat Assembly When we start a car the cooling system begins working instantly. Since the engine is cold, fast warm up-is critical, slow warm-up causes moisture condensation in the
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combustion chamber and ultimately affect engine life time. To assist engine warm-up, the thermostat shut off the flow of coolant. Every engine has an optimum working temperature 160F to 180F to 195F,185F to 228F, once the temperature sensitive valve reaches the correct range, the aperture open and allow normal flow of the coolant. The prime function of the thermostat is to promote fast warm-up and in doing so avoid overcooling. Once an engine is at working temperature, the thermostat remains open and regulate the temperature of the coolant. Avoiding excessive overheating is the responsibility of other parts of the cooling system.
Figure 15
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Thermostat coolant by-pass: The thermostat coolant bypass is an important bypass that permits coolant to reach the “hot” part of the engine during the warm up period. It allows coolant in the water jacket- a special passage located next to the combustion chamber- to be circulated where it is instantly needed. The thermostat remains closed so the only coolant moving is that in the water jacket. The bypass allows the coolant to circulate and pickup the heat created by combustion (before the engine overheats) but does not interfere with the thermostat preventing total circulation of the coolant. Once the optimum working temperature is reached, the work of the bypass is done. The thermostat opens permitting full flow of the coolant.
Figure 16
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Thermostat Model: The thermostat begins to open when the coolant temperature warms up to a certain level. The thermostat continues to open more up to the point that it is mechanically restricted. The engine coolant flow rate is dependent on the cross sectional area of the thermostat. This opening area can be simplified to a linear relationship of temperature from the thermostat opening coolant temperature to that which causes the opening of thermostat to be at its maximum. For, TengTstat_max, Athermostat =1 For, Tstat_min ≤Teng≤Tstat_ max, Athermostat= (Teng−Tstat_min)/ (Tstat_ max −Tstat_ min)
Where; Athermostat =Thermostat opening area coefficient Teng=Engine Coolant Model Temperature Tstat_min = is the engine coolant temperature causing the thermostat begins to open and Tstat_max = is the engine coolant temperature for maximum lift of the thermostat.
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Radiator (The Heart of Cooling)
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Radiator: The Heart of Cooling: Introduction: A radiator is a heat exchanger that removes heat from coolant passing through it, thereby maintaining the engine temperature. This is done by heat transfer from hot coolant coming from engine cooling jacket, flowing into the tubes via the Inlet tank. Heat rejected from coolant to the tube is transferred to the ram air (ambient) flowing over the fins. The radiator is the most important element of the cooling system and has the critical function of reducing temperature of the passing coolant. The “cooled” coolant continues recirculating throughout the engine, removing heat waste. The coolant carrying the heat waste from the engine moves into the radiator core via the inlet hose. •
Radiator Is a device which provides exchange of heat between two fluids are at different temperatures.
•
The function of the radiator is to transfer heat from the hot water flowing through the radiator tubes to the air flowing through the closely spaced thin plates outside attached to the tubes.
•
A radiator consists of an upper tank, core & the lower (Collector) tank. Hot coolant from the engine enters the radiator at the top & is cooled by the cross flow of the air , while flowing down the radiator .The coolant collects in the collector tank from where it is pumped to the engine for cooling.
•
Radiator is recuperator heat exchanger, in this case the fluids exchanging heat are on either side of dividing walls (in the form of pipes or tubes). These heat exchanger are used when two fluids cannot allow to mix i.e. the mixing is undesirable.
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Figure 17
Coolant moves through the interior of Al tubes that are bounded to rows of Al fins at many points. Heat, since it will always more to a cooler place-moves from the coolant to the Al tubes, to the fines ,and then to the outside air. The fins are designed to create a pause in air flow around the tubes and to asset in greater heat dissipation. The heat movement from metal to air occurs primarily at the points where the tubing and fines meet the exact points of heat dissipation. The cooler the radiation, the cooler the coolant and the cooler the engine. The coolant enters into the “hot” or inlet tank of the radiator, moves through the tubing to the “cool” or outlet tank is recirculated. During normal operation, between 7570 and 26500 litres of coolant will move through the radiator per driving hour. Since overheating causes an engine damage, the radiator must work quickly to transfer heat from the coolant into the air so that the cooled coolant can recirculated through the engine. There is an inlet and outlet tank bonded to header plates that hold the tubing and fines together on the inlet tank is a filler neck. The purpose of the radiator is to allow fresh air to reduce the temperature of the coolant .This is done by flowing the coolant through tubes, as the coolant passes through the tubes; air is forced around the tubes. This causes a transfer of heat from the hot coolant to the cooler air.
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This process is called heat exchange in this cease, heat is exchanged from the coolant, to air, this is called a liquid to air heat exchanger, note that the coolant flows through the tubes and air flows through the air fines. Radiator Construction: Radiators are classified by the direction in which the tubing is assembled in the core; two types of radiators are commonly used in the automobile. •
Down flow radiator.
•
Cross-flow radiator. Direction of Coolant flow
Cross Flow Radiator
Figure 18
Down Flow Radiator In the down flow radiator, coolant flows form the top of the radiator to the bottom .In the cross-flow radiator, the coolant flows from one side to the radiator to the other side. Maruti 800 used down flow radiator .Some automobile vehicle also and cross flow radiator because newer vehicles are lowers in front; the cross flow radiator has been used on most vehicles manufactured after 1970.
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Classification of Maruti Radiators According To Manufacturing Processes: There are two types of Radiators manufacturing Technologies used at CSIL (Climate Systems India Limited):Type 1: MAAR (Mechanically Assembled Aluminium Radiator) This technology involves joining of Tubes, fins, header, side support all together using mechanical operation in which a hydraulic press is used to expand the tubes over the header, there by providing a locking, this mechanical locking is further ensured by providing epoxy resin cx which form’s a firm joint between the header and tubes. It includes of: •
Round tubes
•
Flat Contoured fins
•
Sealing/joint obtained by mechanical interference, epoxy and rubber gaskets.
MAAR Type Radiators includes:•
Maruti 800
•
YE2 ( Zen )
•
OMNI
•
GYPSY 1L & GYPSY 1.3L
•
3BOX ( Esteem )
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Type 2: CABR (Controlled Atmosphere Brazed Radiator) This technology involves joining of Tubes, fins, header, side support all together using brazing operation in which a brazing material is sprayed over the radiator and then it is heated at controlled temperature so that the brazing material melts and results in brazed joints. It includes of:•
Elliptical tubes
•
Corrugated fins
•
Sealing/joint obtained by brazing and rubber gasket.
CABR Type Radiators includes: •
Model B ( Wagon R )
•
Model A ( Alto )
•
Model C ( Versa )
•
Model K ( under development )
•
Corsa ( under development )
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Maruti 800(MB308) Radiator Parts
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MAAR (Mechanically Assembled Aluminium Radiator): Maruti 800(MB308) Radiator Parts: Radiator are made of several parts 1. Core 2. Tanks 3. Side Support 4.
Gasket
5. Pressure Cap 6. Drain Cock Assembly
Core: A Heater Core is a Heat Exchanger that removes heat from coolant passing through it, thereby maintaining the engine temperature. This is done by Heat transfer from hot coolant coming from the engine cooling jacket, flowing into the tubes via the Inlet tank. Heat rejected from coolant to the tube is transferred to the ram air (ambient) flowing over the fins.
Figure 19
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Al tubes
Al fins
Figure 20
Radiator Core
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Parts of Core: Tubes, fins, header all together using mechanical operation in which a hydraulic press is used to expand the tubes over the header, there by providing a locking, this mechanical locking is further ensured by providing epoxy resin cx which form’s a firm joint between the header and tubes. •
Header
•
Tubes
•
Fins
•
Turbulatoes
Header: Function: There are two headers per radiator; headers are perforated plates through which each tube protrudes. Header hold the matrix of the fin and the tube together ultimately provide a mechanical mean to attach the tanks to the aluminium core. Design: A header should be strong enough to withstand the operation and burst pressure. Material of Header: Aluminium Thickness of sheet: 1.0 mm
Aluminium Header
Figure 21
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Round Tubes: Function: Carry coolant, hot from the engine, cold back to the engine. The heat exchange is done through the tube wall, transferred to the fin and removed by the air passing through the radiator.
Al Round Tube
Figure 22
Dimensions of tube: Internal Diameter:
6 mm
External Diameter:
6.82 mm
Thickness of tube:
0.41 mm
Length of Tube:
340 mm
Material of the tube:
Aluminium
Total No tubes used: 49(25 in one column & 24 in second column) Inner surface area: Outer Surface Area:
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Fins: Function: The Fin or spacer is Flat strip of aluminium between each tube. It is the mean to transfer heat from the tubes containing the coolant, to the air passing through the radiator. The louvers are the angular cuts on the fin surface that insure some turbulence to the air as it goes through, in order to increase the heat picked up by the air & therefore increase the heat rejected by the radiator. The louvers must be as big as possible to maximize the radiator efficiency but the airside pressure should be kept in mind, because it increases with increase in louver angle & can affect the radiator efficiency.
Aluminium foil fin
Material of fins: Al foil Thickness: 0.21 mm Total no of fins used: 227 Length of fin: 350 mm Width: 28 mm Pitch: 14 mm Transverse pitch: 12.82 mm Staggered offset: 7 mm Single Fin Surface Area: 6873.51 mm2
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Figure 23
Turbulators: Function: 1. To enhancing the turbulence in flow. 2. Increasing the surface area inside the tube.
Turbulator
Material: Aluminium Pitch: 2.8 mm Coil Dia.:5.25 mm Wire Dia.: 0.71 mm Pitch: 2.8 mm
Figure 24
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Figure 25
Tube –Turbulator Assembly
Figure 26
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Tanks: Function: A radiator tank besides containing coolant is an important structural member. It not only supports and connect a radiator core to the vehicle, but it also supports the fan , motor and shroud assembly (engine side),condenser and possibly transmission oil cooler , as well as sometimes a power steering , and hydraulic fan coolers as even as inter coolers. Each radiator has two tanks: Inlet Tank receiving hot coolant from engine, and an Outlet tank directing cooled coolant back to the engine. Design: All the tanks are designed as per the customer requirements with the help of 3D modeling software packages (Pro/Engineer etc.). Later on the mold flow analysis is done before finalizing the mold design.
Figure 27
Material: Nylon 6/6+30% GF (Coolant Resistance) Process: High Precision, High safety Injection Moulding.
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Upper Tank
Figure 28
Lower Tank
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Side Support: Function: There are two side supports per radiator. They run parallel to the tubes and get crimped, then brazed to the headers. Side Supports complete the frame that holds together the fin tube matrix, especially during the manufacturing process. It also protects the first & last fin of the radiator during handling before the radiator gets installed into a car. Side support in CAB radiator act as a fin shield & does not bear any structural load. Design: Side supports are on the shape of U channel.
Gasket: Function: There are two gaskets per radiator. A radiator gasket helps in maintaining a leak proof joint between tank and header.
Rubber Gasket
Figure 29
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Pressure Cap: Function: Pressure capes are placed on the radiator to do several things; They are designed to: •
Increase the pressure on the cooling system
•
Reduce cavitations
•
Protect the radiator hoses
•
Prevent or reduce surging. It is very important to maintain a constant pressure on the cooing system .The
pressure should be near 15 pounds/inch2 (103 kpa). In the case of Maruti 800 Pressure should not exceed 0.90 kgf/cm2. Pressure caps are placed on the radiator to maintain the correct pressure on the cooling system. Pressure on the cooling system changes the boiling point .As pressure is increased, the boiling point of the coolant also increases. This is shown in figure30. The bottom axis shows pressure, The vertical axis shows the boiling point .Different solution of antifreeze are also shown .For example ,using water ,the boiling point at o psig(pressure per inch2 ,on a gauge ) is 212 0
F (100 0C).
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Figure 30
If the pressure is increased to 15 psig (103.42 kpa),the boiling point increases to about 2500F(121.110C). Figure31 shows how pressures cap maintain the constant pressure. As the coolant increases in temperature, it begins to expand. As it expands, the coolant cannot escape. The spring holds a rubber washer against the filler neck.
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Figure 31
As the Pressure increases on the cooling system, the large spring eventually be lifted off its seat. This action releases any pressure over 0.9 kgf/cm2.
To Recovery Bottle
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Figure 32
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This keeps the fluid in the cooling system and increases the pressure. When the pressure reaches .9kgf/cm2, the rubber seal is lifted off the filler neck against spring pressure .The coolant then passes through the pressure cap to a tube that is connected to a recovery bottle .This type of is called a closed system. An open system allows the coolant to pass through the pressure cap directly to the road surface. The pressure cap also protects the hoses from expanding and collapsing. When the engine is shut down, the coolant starts to cool. As it cools, the coolant shrinks. Eventually, a vacuum is created in the cooling system .This means that the pressure outside the radiator is greater than the pressure inside the radiator. This causes the hoses to collapse. Continued expanding and collapsing of the hoses causes them to crack and eventually leak. The pressure cap has a vacuum valve which allows atmospheric pressure to seep into the cooling system where there is slight vacuum.
From Recovery Bottle
Figure 33
When the cooling system cools down, vacuum is produced in the system. The vacuum spring is opened and the system equalizes the pressure. During operation, a small spring holds the vacuum valve closed. When there is a vacuum inside the cooling system, the vacuum valve is pulled down and opened. The vacuum is then reduced with in the cooling system see figure-. Increasing the pressure also reduces cavitations, cavitations was defined earlier as small vacuum bubbles produced by the water pump action. Increased pressure reduced this action. Pressure on the cooling system also reduces surging. Surging is defined
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as sudden rush of water from the water pump. This could be caused by rapidly increasing the rpm of the engine. Surging can produce air bubbles and agitation of the coolant. Pressure on the cooling system tends to reduce this action.
Maruti 800 Pressure Cap
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Figure 34
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Pressure Spring
Vacuum spring
Exploded view of pressure cap assembly
Figure 35
Drain Cock Assembly: Function: Drain Cock assembly constitutes a drain cock stem with threads on it & a rubber O-ring. It is usually placed in the Outer tank & acts as a point for draining of coolant during servicing of radiator.
Outer Tank Drain Cock Figure 36
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Radiator Assembly
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Radiator Assembly:
Figure 37
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Exploded view of Radiator Assembly Figure 38
Figure 39
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Hoses: The Connectors Hoses, made either of an elastremeric, flexible compound or a molded rubber; are the connectors between the engine and the radiator and are the passages for coolant. The bottom or outlet hose is on the outlet tank of the radiator. “Cooled” coolant moves through this connector from the outlet tank of the radiator, through the water pump, and into the engine. The top or inlet hose is on the inlet tank of the radiator. Through it hot coolant returns from the engine for its recycling. The outlet hose often has a spiral wire reinforcement that helps prevent hose collapse due to excessive suction. The wire reinforcement can rust, causing rust particle to enter the engine passage. Since the problem is not visible from the outside, the inlet hose should be checked regularly. The one and only purpose of the hose is to provide a constant, uninterrupted flow of coolant. Either spring-screw clamps or wire clamps are used on hose ends.
Fans and Shrouds: Air flow Boosters Air, even in a liquid-based cooling system, is an important factor in dissipating heat. Radiators designed with maximum air flow, are the prime vessels for dissipating heat in the coolant to the outside air. The fan, sitting directly behind the radiator, is simply a booster pulling cooler outside air through the radiator core to assist heat throw-off. There are various types of fans; thermostatic, centrifugal, fluid coupling, flexible blade. Most are fixed, rigid blades attached directly to the water pump pulley (direct drive) by cap screw or stud and nuts. The rotation speed of the fan is determined by engine speed. In stop-and-go traffic, or slow driving, insufficient air for cooling is pulled through the radiator core (especially in large, high compression engine), and overheating can occur. Usually, when a car reaches a certain speed, natural air flow helps cool but does not eliminates the need for a fan. In case of Maruti 800, the fan operated through the electric motor controlled by the thermostat switch, thermostat acts as a feedback device in the system. Fan can also be variable pitch types using flexible blades that flatten out at high speeds and spin freely without using more horse power from the engine.
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With variable pitch fan, two types of fan clutches are used. Centrifugal fan clutches will automatically increase or decrease fan rotation depending on engine speed. Once adequate speed is reached, the centrifugal fan clutch will disengage the fan. Another fan clutch is thermostatically controlled by engine and ambient air temperature. Once the preset temperature is reached, the thermo viscous drive clutch disengages the fan. The number and size of the blades differ according to vehicle requirements. About the only problem that can occur is that one or all the blades becomes bent or broken, the only recourse is replacement. Depending on the vehicle, shrouds are installed to direct incoming air to the fan area. These maintain spoilers act to funnel the air through the radiator.
From Maruti 800 service Manual: Fan starts at 980C and runs until temperature decreases t0 920c. When temperature comes below 920C, the fan automatically turns off. Fan temperature limits: 920C to 980C Temperature sensor: Bourdan tube type and Electrically operated type. Fan Drive: By Electrical Motor Fan Controller: Thermostat switch No. of Blades: 4
Radiator fan & shrouds
Figure 40
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Material of fan: PA66 + 30% PF + GF Process: Precision Injection Moulding Material of shrouds: PA66 + 30% GF + MG Process: Precision Injection Moulding
Drive belt: the power connectors The drive belts, or belts, turns the fan and the water pump for the cooling system as well as for the generator, air conditioner compressor, and power steering pump. Depending on the vehicle and accessory options, there may be from one to four belts. All the belts are driven by a pulley attached directly to the crank shaft. The faster the engine turns, the faster the belt and accessory rotate. Incorrect belt tension invariably results in either overheating or premature component failure. Insufficient or too little tension on the belt causes inadequate action. The water pump does not rotate at the proper speed and the coolant circulates too slowly. Overheating is the result on the other hand, too much tension on the water pump belt causes excessive wear, and the water pump fails prematurely.
Water pump: The heartbeat The water pump, usually made of die cast aluminium or cast iron, circulate coolant into and through the cylinder block via the water jackets and through the thermostat and by-pass. The coolant that carries engine heat passes through the radiator, transferring this heat to the tubes and fins and then out to the out side air. When fuel is ignited and combustion starts, temperatures in the cylinder can reach 28000F plus, that is enough heat to melt an engine block and all its internal parts, around this part of the engine- the combustion chamber- is a water jacket that surrounds the block, head and intake manifold, and allows the coolant to these and other “hot” spots. Should it be impossible to transfer this heat, the resultant overheating will be the woe of the car owner. Seized pistons and bearings, burned values, and scored cylinders are the most common physical damages incurred from overheating. If the cooling system as faulty, or not in good working condition, the heat is throws off will cause the engine metal to expand and contract beyond the tolerance levels
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specified by the manufacturers. This expansion and contraction may cause gaps to form, which in turn, cause oil leaks and destroy head gaskets. A blown head gasket causes further problems by allowing exhaust gases to enter the water jackets creating excess pressure in the cooling system and allowing heat from the from the combustion chamber to more directly to the radiator. It also allows the air to enter the block, eventually causing rust and block deterioration. A cracked head or cylinder block creates similar problems.
Figure 41
Figure 42
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Analysis & Simulation
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Analysis ANALYSIS OF MARUTI 800 RADIATOR (MB308): Nomenclature: R
(L)
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R
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• Radiator is a type of compact heat exchanger. • Surface area density >= 700 m2/m3. • Radiator is a recuperator type heat exchanger. • Maruti 800 model is single pass cross flow type radiator. • Extended surface heat exchanger. • Single phase conversion on both sides-Two fluids used. • No phase change occurs in any of fluids in the exchanger; it is sometimes referred to as a sensible heat exchanger.
PARAMETERS: Coolant inlet Temperature (800C-1050C) =920C (From 2005 Maruti Suzaki Service Data Manual.) Coolant outlet Temperatures=? Air inlet Temperature(200C-400C)=270C. Air outlet Temperature=? Blend of Water+Ehylene Glycol (50/50).
DIMENSIONS OF TUBE: Internal Diameter: External Diameter: Thickness of tube: Length of Tube: Material of the tube: Total No tubes used: Inner surface area: Outer Surface Area:
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Figure 43
DIMENSIONS OF TURBULATOR: Material: Pitch: Coil Dia.: Wire Dia.: Pitch: Dhc:
Aluminium. 2.8 mm 5.25 mm 0.71 mm 2.8 mm 5.29 mm
DIMENSIONS OF FIN: Material of fins: Al foil Thickness: 0.21 mm Total no of fins used: 227 Length of fin: 350 mm Width: 28 mm Pitch: 14 mm Transverse pitch: 12.82 mm Staggered offset: 7 mm Single Fin Area: 6873.51 mm2 Surface area of single fin: 14380.9 mm2 Total surface area of 227 fins (AF): 3264464.3 mm2
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AF=3264464.3 mm2 AF= Total surface area of 227 fins Aw=Surface area of the tube between the fins=Nf×∏×Dr×leff Nf=No. of fins=227 leff=290-(.21×227)=242.33mm
Figure 44 Aw=1178602.307 mm2 A=AF+Aw=4443066.607mm2 AT=the total external area of the tube without fins AT=NT×L×∏×Dr=49×300×∏×6.82 =314957.2299mm2 Va=17m/s
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Mass flow rate of air (ma) = Va×ρa×AFR AFR=Frontal area of the radiator through the air passes AFR=(290×350)-(350×0.21×227)=84815.5mm2 ma=10×1.145×84815.5×10-6 =1.650934 kg/s The corresponding Reynolds no. Re a=Va× Dr× ρa/µ = (10×6.82×10-3×1.145)/ (1.895×10-5) =7005.345646 The air side heat transfer coefficient is obtained using the ESDU CORRELATION for high fin staggered array heat exchanger:
CALCULATION OF NUSSELT NUMBERS ON AIR FLOW: Nua=0.242× (Re a0.688) ×(s/h)0.297×(p1/p2)-0.91×Pr1/3 =0.242× (7005.3456460.688) ×(1.4/3.75) 0.297×(14/12.82)-0.91×(0.72681/3) =66.288228 Air side heat transfer coefficient: ha=ka×Nua/Dr =0.02625×46.00883/(6.82×10-3 ) =255.141639w/m2k Efficiency of the fins: ηf={tanh(√(2ha/(w× kf) ×Ψ)}/(√(2ha/(w kf) ×Ψ) Ψ= Dr/2[{(wf/2)/ Dr}-1][1+0.35ln{(wf/2)/ Dr}] =6.82×10-3/2[(14/6.82)-1][1+0.35ln(14/6.82)] =4.4936×10-3 W=2.1mm (width of fin) Kf=237 w/m.k (√ (2ha/(w kf) ×Ψ)=.0295156 ηf=.999885
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The effective air-side heat transfer coefficient based on total surface area is given byha!=( ηf×AF×Aw/A)ha =220.916239 w/m2.k The air side heat transfer coefficient referred to the external surface to the tube without fins: ha r= ha!(A/AT)=3116.441292 w/m2.k Coolant side heat transfer coefficient: CALCULATION OF NUSSELT NUMBERS ON COOLANT SIDE: The Nusselt number on coolant side depends primarily on coolant flow conditions. The coolant flow inside the radiator core can be considered as fluid flow in pipes. Thus, the coolant flow can be laminar, transitional or turbulent, each being characterized by the appropriate Reynolds number. The coolant flow is normally laminar when the Reynolds number is below about 2,100. In the range of Reynolds numbers between 2,100 and 4,000, the coolant flow is transitional. At a Reynolds number of about 4,000 the coolant flow becomes fully turbulent. The quoted Reynolds numbers are approximate and could vary under different radiator constructions. Nusselt Numbers for Laminar Coolant Flow: For laminar flow, the equation for laminar flow in tubes proposed by Hausen was used. Hausen's equation can be written as:
Nusselt Numbers for Turbulent Coolant Flow: For turbulent flow, the empirical equation developed by Dittus and Boelter in 1930 for fully developed turbulent flow in tubes was used. The Dittus and Boelter's equation can be expressed as:
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Nusselt Numbers for Transitional Coolant Flow: For transitional flow, a equation cited by Achaichia was also used to calculate the Nusselt Numbers in transitional flow. The equation can be written as:
ρc=1070 kg/m3 Vc=0.8 m/s µc=0.00156025 Ns/m2 internal dia of tube with turbulator=5.29mm Reynolds no: Re c=Vc×Dhc× ρc/µc =2902.252844 Prc =29.13 The Reynolds no. represents the flow is transient:
=35.879477 kc=.4685 w/m.k hc=(Nuc×kc)/ Dhc =3177.605847 w/m2.k Mass flow rate of coolant (mc) =NT× Vc×ρc×Atube, internal NT=No. of tubes mc=49 ×1×1070×∏/4× (5.29×10-3)2 =0.921873kg/s Fouling resistance for engine water: RF=0.000175 m2.k/w
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Overall heat transfer coefficient: Assumption: The thermal assumption at junction of fins & tubes are neglected. Hence, the value of Ur ,related to the external surface of the tube without fins, i.e. to dia. Dr 1/Ur=Rf+ 1/ha r+ (Dr/2ktube) ln(Dr/ Dhc)+1/hc Ur =1228.144626 w/m2k NTU=AUr/Cmin =4443066.607×10-6×1228.144626 / (1.650934 ×1007) =3.282262 R=Cmin/Cmax= (1.650934×1007)/ (0.921873×3383) =0.533072 RADIATOR HEAT TRANSFER EFFECTIVENESS: For a cross-flow heat exchanger with both fluids unmixed, the problem of determining the heat transfer effectiveness is very complicated even in the case of a single pass exchanger. Very little information about the heat transfer effectiveness for this kind of flow has been published. Mason [12] developed an analytical solution that is very difficult to use. Besides Mason's analytical solution, an approximate equation used By many authors to calculate the heat transfer effectiveness of a cross flow heat exchanger with both flows unmixed has been used.
R R =0.835025
=0.835025×(1.650934×1007) =1388.22 w/K
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In practical cases;
Q=.5×SD× (Thot, in- Tcold, in) =.5×1388.22× (92-27) =45.126 kW Tc, i-Tc,o=Q/Cmax Tc,out= Tc ,in- Q/Cmax =77.53 0C Ta,o-Ta,i=Q/Cmin Ta,o=54.144160C
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FEM Generation of Parts (Through pro/Engineer):
Fin
Round Tube
Header
Turbulator
Lower Tank
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Fan
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ANSYS Analysis
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ANSYS Analysis Air flow pattern over the round tubes (Through ANSYS) Velocity Distribution: Contour plot:
Figure B1
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Figure B2
Close view of contour plot
Figure B3 (Vsum)
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Figure B4
Vx Plot
Pressure Distribution over the tubes Figure B5
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Vector Plot:
Figure B6
Figure B7
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Flow Trace (particle flow):
Figure B8
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Temperature Distribution over the tubes: Contour Plots:
Figure B9
Tube with uniform temp 700C
Close view Figure B10
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Over the Aluminium fin: Heat Flux:
Figure B11
Contour Plot
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Contour Plot
Figure B12
Figure B13
Vector Plot
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Tube:
Contour Plot Figure B14
Figure B15 Vector Plot
(At entrance Region)
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Figure B16
(At exit Region)
(Temp Distribution) Figure B17
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Air Velocity/pressure distribution over the car:
Contour Plot
Figure B18
Vector Plot
Figure B19
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Pressure Distribution
Node representation
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Figure B20
Figure B21
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Particle flow
Figure B22
Figure B23
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Simulation Program
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Simulation Program #include #include #include #include void main() { clrscr(); int gdriver = EGA, gmode = EGAHI; initgraph(&gdriver, &gmode, "c:\\tc\\bgi"); setbkcolor(BLUE); outtextxy(200,30,"ALL THE DIMENSIONS ARE IN MM"); long float NT,L,Dr,Di,Lf,Tf,NF,AF=3264464.3,l_eff,A,Aw,Pi=3.141592,wf ,a,AT,di,Lc=300,SD ; coutNT; coutL; coutDr; coutDi; coutdi; coutLf; coutTf; coutwf; coutNF; l_eff=290-(Tf*NF); cout
