Cooling Tower Educational Standcairouniversity
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cw tower...
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Faculty of Engineering Cairo University Mechanical Power Departement
Cooling Tower Educational Stand B.Sc. Graduation Project
2008
Cairo University Faculty of Engineering Mechanical power department B.Sc. Graduation Project 2008
Cooling Tower Educational Stand
Project Supervisors: • Prof. Dr. Adel Khalil • Prof. Dr. Hany Khater • Dr. Galal Mostafa
I
Contents -
Acknowledgement. Project description. Nomenclatures. Page Chapter One: Introduction. 1. Objective. 2. Classification. 3. Components. 4. Water Treatment. Chapter Two: Literature review 1. Gunt. 2. Armfield. 3. P. A. Hilton. 4. Edibon. Chapter Three: Cooling Tower Design Calculation 1. Column. 2. Cooling tower performance 3. Tanks. i. Water tank. ii. Air tank. iii. Make up tank. iv. Drain tank. 4. Piping System and pump. 5. Blower and Butterfly Valve. 6. Water Injection Nozzle. 7. Stand. Chapter Four: Measuring devices and auxiliaries. 1. Temperature Measurements. 2. Humidity Measurements. 3. Flow Measurements. 4. Displays. 5. Data acquisition card. 6. Calibration. Chapter Five: Bill of Material and Cost. Chapter Six: Fabrication Procedure. 1. Welding. 2. Stand fabrication. 3. Painting and coating. 4. Pipes components and fittings. 5. The column. 6. Stand preparation. 7. Control panel. 8. Electronic and Electric devices installation. 9. Electric Connections. 10. Component assembly. II
1 1 2 6 7 8 8 10 12 14 16 20 21 21 23 23 24
25 29 30 31 32 32 34 34 37 38 46 48 51 51 55 56 57 59 61 62 62 63 64
Chapter Seven: Tests and Results. 1. Procedure 2. Results 3. Relations summery and conclusion -Appendices. -References
66 66 67 70 71 105
.
III
Acknowledgment First, we would like to thank Allah the merciful and compassionate for making all this work possible and for granting us with the best professors, family, friends, and colleagues that many people would wish and dream of having. We would like to thank our supervisors
• • •
Prof. Dr. Adel Khalil Prof. Dr. Hany Khater Dr. Galal Mostafa.
We are greatly indebted to them for their valuable supervision, kind guidance, and great help and effort to make this project possible. Words cannot express our deep gratitude and sincere appreciation to them.
Group Members:
Eng. Basel Amr Gouda Eng. Hebatallah Abdel Moniem Mohamed Eng. Mohamed El Sayed Rizk. Eng. Al Hussain Mohamed Kamel Eng. Ismail Gamal El Din Ismail. Eng. Ahmed Samir Abdallah. . Special Thanks to: • • -
Eng. Somya Mohamed Abdel Rehim For Supplying us with materials and support Colleague Ahmed waheed For his effort IV
- Project description The students affiliating with the present project will be required to study, design and fabricate a Water Cooling Tower Educational Stand. The Water Cooling Tower educational stand will eventually form a part of the undergraduate students “Heat Transfer Laboratory”. Step 1 : Water cooling tower fabrication. In this step, the following will be accomplished: Study the different heat and mass transfer mechanisms. Cooling tower heat load estimation. Design calculations of the water cooling tower showing different geometrical parameters and dimensions. Material selection of the different components. Working drawing sheets for the different cooling tower components. Fabricating the different components and assembling the cooling tower. Step 2 : Water cooling tower educational stand erection In this step, the following will be accomplished: Selecting and preparing the types of the measuring sensors, devices and data acquisition system. Assembling the cooling tower together with, the storage tank with heaters, the make-up tank, the air blower and air chamber, the water circulating pump, water injection nozzle, the column, valves and hoses, and the different measuring devices on the stand. Finalizing all mechanical, electrical and electronic works needed for the stand. Step 3 : Performance test on the water cooling tower educational stand In this step, the following will be accomplished: Assuring the validity of all stand measuring devices. Studying the effect of different parameters on the cooling tower performance. Comparing the experimental results with those calculated. V
-Nomenclatures
VI
VII
Chapter 1
Chapter One Introduction 1. Objective Cooling towers (Fig. 1) are heat removal devices used to transfer process waste heat to the atmosphere. They may either use the evaporation of water to remove process heat and cool the working fluid to near the wet-bulb air temperature or rely solely on air to cool the working fluid to near the dry-bulb air temperature. The objective of cooling towers can be divided into two categories: HVAC An HVAC cooling tower is a subcategory rejecting heat from a chiller. Water-cooled chillers are normally more energy efficient than air-cooled chillers due to heat rejection to tower water at or near wet-bulb temperatures. Air-cooled chillers must reject heat at the dry-bulb temperature, and thus have a lower average reverse-Carnot cycle effectiveness. Large office buildings, hospitals, and schools typically use one or more cooling towers as part of their air conditioning systems. Generally, industrial cooling towers are much larger than HVAC towers. Industrial Industrial cooling towers can be used to remove heat from various sources such as machinery or heated process material. The primary use of large, industrial cooling towers is to remove the heat absorbed in the circulating cooling water systems used in power plants, petroleum refineries, petrochemical plants, natural gas processing plants, food processing plants, semiconductor plants, and other industrial facilities. The circulation rate of cooling water in a typical 700 MW coal-fired power plant with a cooling tower amounts to about 71,600 cubic metres an hour (315,000 U.S. gallons per minute) and the circulating water requires a supply water makeup rate of perhaps 5 percent (i.e., 3,600 cubic metres an hour).
Fig. (1.1) cooling tower 1 Cooling Tower Educational Stand
B.Sc. Project 2008
Chapter 1
2. Classification Cooling towers can be classified into different categories as follows: Heat transfer mode • Wet cooling towers or simply cooling towers operate on the principle of evaporation. • Dry coolers operate by heat transfer through a surface that separates the working fluid from ambient air, such as in a heat exchanger, utilizing convective heat transfer. • Fluid coolers are hybrids that pass the working fluid through a tube bundle, upon which clean water is sprayed and a fan-induced draft applied. The resulting heat transfer performance is much closer to that of a wet cooling tower, with the advantage provided by a dry cooler of protecting the working fluid from environmental exposure. In a wet cooling tower, the warm water can be cooled to a temperature lower than the ambient air dry-bulb temperature, if the air is relatively dry. As ambient air is drawn past a flow of water, evaporation occurs. Evaporation results in saturated air conditions, lowering the temperature of the water to the wet bulb air temperature, which is lower than the ambient dry bulb air temperature, the difference determined by the humidity of the ambient air Air flow generation With respect to drawing air through the tower, there are three types of cooling towers: • Natural draft, which utilizes buoyancy via a tall chimney. Warm, moist air naturally rises due to the density differential to the dry, cooler outside air. Warm moist air is less dense than drier air at the same pressure. This moist air buoyancy produces a current of air through the tower (Fig. 2).
Fig. (1.2) Natural draft cooling tower
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Chapter 1 •
Mechanical draft, which uses power driven fan to force or draw air through the tower. − Induced draft: A mechanical draft tower with a fan at the discharge which pulls air through tower (Fig. 3). The fan induces hot moist air out the discharge. This produces low entering and high exiting air velocities, reducing the possibility of recirculation in which discharged air flows back into the air intake. This fan/fill arrangement is also known as draw-through.
Fig. (1.3) Induced draft fan cooling tower −
Forced draft: A mechanical draft tower with a blower type fan at the intake (Fig. 4). The fan forces air into the tower, creating high entering and low exiting air velocities. The low exiting velocity is much more susceptible to recirculation. With the fan on the air intake, the fan is more susceptible to complications due to freezing conditions. Another disadvantage is that a forced draft design typically requires more motor horsepower than an equivalent induced draft design. The forced draft benefit is its ability to work with high static pressure. They can be installed in more confined spaces and even in some indoor situations. This fan/fill geometry is also known as blow-through.
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Chapter 1
Fig. (1.4) Forced draft fan cooling tower Air-to-Water Flow -Cross flow: Is a design in which the air flow is directed perpendicular to the water flow (Fig 5). Air flow enters one or more vertical faces of the cooling tower to meet the fill material. Water flows (perpendicular to the air) through the fill by gravity. The air continues through the fill and thus past the water flow into an open plenum area. A distribution or hot water basin consisting of a deep pan with holes or nozzles in the bottom is utilized in a cross flow tower. Gravity distributes the water through the nozzles uniformly across the fill material. -Counter Flow: The air flow is directly opposite of the water flow (Fig 6). Air flow first enters an open area beneath the fill media and is then drawn up vertically. The water is sprayed through pressurized nozzles and flows downward through the fill, opposite to the air flow. Common to both designs: • The interaction of the air and water flow allow a partial equalization and evaporation of water. • The air, now saturated with water vapour, is discharged from the cooling tower. • A collection or cold water basin is used to contain the water after its interaction with the air flow. Both cross flow and counter flow designs can be used in natural draft and mechanical draft cooling towers.
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Chapter 1
Fig. (1.5) Cross Flow cooling tower
Fig (1.6) Counter Flow cooling tower
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Chapter 1
3. Components: Inlet water distributors: There are several types of water distributors, among them: 1. Gravity distributors: applied mainly for cross flow cooling towers and consist of vertical water riser that feed water into an open concrete basin, from which the water flows by gravity through orifices to the fill. 2. Spray distributors: used mainly with counter flow cooling towers and have cross pipe net with spray downward nozzles. 3. Rotary distributors: applied for cross flow cooling towers and consists of two slotted arms rotate about a central hub containing water supply pipe. The slots in the tow arms are directed downward but make small angle with the vertical direction to one side. The slots form a curtain angle and due to reaction force the arms rotate at a rotational speed of 25-to-30 rev/min. Drift eliminators: An assembly constructed of wood, plastic, cement board, or other material that serves to remove entrained moisture from the discharged air. Circulating Pump: The circulating pump transports the cooling water between the cooling tower and the condenser. The water is pumped from the cooling tower basin through to the condenser, where it is used as cooling medium. The water returns back for evaporative cooling in the cooling tower. Fan: A device for moving air in a mechanical draft tower. The fan design may be either an axial flow propeller or centrifugal blower. Also may be applied as induced draft or forced draft. Noticing that the induced type requires less power for same result. Fills: Is the heart of the cooling tower. The fill must provide good water-air contact area, high rates of heat and mass transfer and low air flow resistance. The fill also must be strong and deterioration resistant. The fill has mainly two forms − Splash fill: breaks falling water into small drops. This Type is made of bars stacked in desks and may be narrow-edged, square bars, rough bars and grids. Different materials are used, such as redwood, high-impact polystyrene or polyethylene, − Film fill: is made of vertical sheets that have a rough adsorbent surface and good wetness of water that allows water to fall as a film over the vertical surface. Film fill has different forms and materials; redwood battens, cellulose corrugated sheets, asbestos cement and waveform plastic. Water Basin: Is situated beneath the tower, collects and strains the water before pumped back to the circulating system. Large utility tower basins are generally made of concrete. Water leaves the basin via sloped canal at the bottom and through screens that prevent dust and foreign materials from entering the pump.
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Chapter 1
4. Water Treatment The large variety of alternative construction materials allows users to match unit construction to the water quality available for their systems, while helping to protect the tower from temporary upsets. Water treatment programs must be designed for three requirements: 1. Scale control; 2. Protection of system components against corrosion; and 3. Control of biological contaminants, such as Legionella pneumophilia, the bacterium that causes Legionnaires' disease. The first two requirements help to ensure energy efficiency and longevity of the cooling system, while the third ensures safe operation. Biological control is relatively easy to accomplish and is essential to the safe operation of the tower. Cooling towers can collect and concentrate airborne dirt and debris over time. To control this buildup, the cooling tower should be located so as to minimize contaminant induction and a proper blowdown rate should be maintained. Sidestream filters or separators have proven valuable in this regard by effectively removing dirt and debris from the tower water. These devices are coupled with a basinsweeping nozzle package, which is available either as original equipment in the tower or as a fieldinstalled aftermarket item. Cleaner tower water makes water treatment regimens more effective while keeping the cooling loop cleaner, saving energy, reducing maintenance, and improving reliability of the entire cooling system.
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Chapter 2
Chapter Two Literature review In this chapter we will introduce the specifications of the cooling tower educational stand that manufactured by different companies like Gunt, Armfield, P.A. Hilton, Edibon.
1. Gunt
Fig. (2-1) Gunt cooling tower educational stand. Column: Dimensions: 150x150x630 mm Pacing density: 110 m2/m3 Orifice diameter: 80 mm Approx. weight: 5 Kg Heaters: 3 stages 0.5-1-1.5 KW. Thermostat switches off at 50⁰c. Fan: Radial fan:
- Power consumption 0.25 KW.
-max. Differential pressure 430 pa.
-max. Flow rate 13 m3/min. 8
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Chapter 2 Pump: -Power consumption:
0.7 KW.
-max. Head: 34 m. -max. Flow rate: 34 L/min. Instrumentation: -Temp. Sensors at air inlet &outlet. -Temp Sensors at water inlet& outlet. -Water flow rate sensor. -Humidity sensors at air inlet& outlet. Dimensions: Height: 1.228 m. Length: 1.11 m. Width: 0.46 m. Weight: approx. 90 Kg. Service required: Electrical: -230 v, 50/60 HZ, 1 phase. or -230 v, 60 HZ, 3 phases. Computer& Data acquisition: Data acquisition with lab view software, h-w diagram and Windows X-P.
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Chapter 2
2. Armfield
Fig. (2-2) Armfield cooling tower educational stand. Column: Dimensions:150x150x600 mm Pacing density:110 m2/m3 (10 plates) Heaters: Maximum working temperature 50⁰c
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Chapter 2 Fan: Centrifugal fan: Maximum air flows: 0.06 Kg/s-1 Instrumentation: -thermocouple with digital read out. -Variable area flow meter with control valve. -Inclined manometer for orifice differential pressure measurement. Dimensions: Height: 1.2 m. Length: 0.95 m. Width: 0.6 m. Weight: approx. 130 Kg. Volume: 0.7 m3. Service required: Electrical: -220-240 v/1 ph/50 HZ. or -120 v/1 ph/60 HZ. Water: 2 L/hr distilled.
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Chapter 2
3. P. A. Hilton
Fig. (2-3) P.A.Hilton cooling tower educational stand Column: Dimensions: 150x150x60 mm Pacing density: 110 m2/m3 transparent P.V.C Orifice diameter: 80 mm Heaters: 0.5 &1 KW Instrumentation: -digital temp indicator with channel selector switch for all wet bulb, dry bulb & water temp variable area water temp flow meter & manometer air flow.
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Chapter 2 Dimensions: Height: 1.12 m. Length: 0.82 m. Width: 0.73m. Weight: approx. 56 Kg. Gross weight: app. 96 Kg. Volume: 0.76 m3. Service required: Electrical: -1.6 KW, 220-240 v, 1 ph, 50 HZ (with earth ground). or -1.6 KW, 110-220 v, 1 ph, 60 HZ (with earth ground). Water: demineralised or distilled approx 2 Kg/hr. Computer& Data acquisition: An optional Data Acquisition Upgrade HC892A comprising of an electronic data logger, menu driven software and all necessary transducers, allow all relevant parameters to be simultaneously displayed and recorded on a suitable PC.
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Chapter 2
4. Edibon
Fig. (2-4) Edibon cooling tower educational stand. Column: Dimensions: Total surface: 1.915 m2, Height of packaging: 650 mm. Pacing density: 58 m2/m3 (10 plates). Dimensions: Height: 1.4m. Length: 1 m. Width: 0.45 m. Weight: approx. 100 Kg. Service required: Electrical: -220V./50 Hz or 110 V. /60 Hz, directly from the mains.
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Chapter 2 Computer& Data acquisition: PCI Data acquisition board (National Instruments) to be placed in a computer slot. Bus PCI. Analog input: Number of channels= 16 single-ended or 8 differential. Resolution=16 bits, 1 in 65536. Sampling rate up to: 250 KS/s (Kilo samples per second). Input range (V)= 10V. Data transfers=DMA, interrupts, programmed I/0. Number of DMA channels=6. Analog output: Number of channels=2. Resolution=16 bits, 1 in 65536. Maximum output rate up to: 833 KS/s. Output range(V)= 10V. Data transfers=DMA, interrupts, programmed I/0. Digital Input/Output: Number of channels=24 inputs/outputs. D0 or DI Sample Clock frequency: 0 to 1 MHz. Timing: Counter/timers=2. Resolution: Counter/timers: 32 bits
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Chapter 3
Chapter Three Cooling Tower Design Calculation 1. Column The column is divided into two parts as follows: -The column body The column body Fig. (3.1) is an important component of the cooling tower at which the water and air interface where heat and mass exchange occur. The column material was manufactured from transparent plastic to allow viewing of water through the system. It is oppened from endes to allow the water and air movement inside it, also to insert and renise fill from it eassly. Column dimension estimation: The inlet air conditions: Tai=35⁰C=308 K. Pai=101.3 kPa. RHi=40%.
Fig.(3.1) columnbody
Where: ρai: Air inlet density,kg/m3. Pai: Air inlet pressure,kPa.
ρai =
Pai R × Tai
Tai: Air inlet temperature,K. R: universal constant,
101.3 × 103 yields ρai = �⎯⎯� ρai = 1.15 kg/m3 287 × 308
Assume air flow rate to be→
ṁ blower =
V̇ blower = 13 m3 /min
ṁ blower = V̇ blower × ρai
yields 13 × 1.15 �⎯⎯� 60
ṁ blower = 0.24 kg/s
From psychrometric chart at 35⁰c dry bulb temperature and 40% relative humidity;the humidity ratio ψai=0.01414 kg/kgda and wet bulb temperature wbtai=23.9⁰C. ṁ da = Cooling Tower Educational Stand
ṁ blower 1 + ψai
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Chapter 3 ṁ da =
0.24 1 + 0.01414
̇ = 0.238 kg/s mda
Where: ṁ da : Dray air mass flow rate, kg/s.
The cooling tower characteristics (KaV/L) specifies the size of the tower necessary to achevie the maximum possible effectiveness. The cooling tower characteristics,as a whole, are function of cooling range, tower approach, ambient wet bulb temperature and fluid flow ratio.these cooling tower characteristics represents also at the same time the fill characteristics required for a spacified job.the fill characteristics should be equal to the fill performance, which is a function of fluid flow ratio for a given matrix. As the evaluation of the cooling tower characteristics is time consuming procudure, in practice this is avoided by using the charts available by the Cooling Tower institute in Houston. In these charts the tower characteristic are expressed in terms of the cooling range,tower approach, ambient wet bulb temperature and the flow ratio. Design conditions: -
Twi=50⁰C. Two=45⁰C. Wbtai=23.9⁰C.
-
Vw=2 l/min. ρw=1000 kg/m3.
ṁ w = V̇w × ρw = Where:
2 × 10−3 × 1000 60
ṁ w = 0.0333 kg/s
V̇ w : Water volumetric flow rate, m3/s. ρw : Water density, kg/m3.
∴ L=0.0333 kg/s. G=0.238 kg/s.
“total water mass flow rate” “total air mass flow rate”
Where; L′ : Water loading, kg/m2 s. G′ : Air loading, kg/m2 s. Cooling Tower Educational Stand
L L′ 0.0333 = = = 0.14 G G′ 0.238
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Chapter 3 Note: The cross section area at which the air pass equal to that thwe water pass in counter flow L
cooling tower so → = G
L′
G′
Approach= Two-Wbtai Approach=35-23.9 Approach=21.1⁰C=38.16 ⁰F. Cooloing Range (CR)=Twi-Two=50-45 CR=5 ⁰C=9 ⁰F. From the characteristic curves Appendix (6) the required cooling range doesn’t exist, Hence, make interpolation. From Appendix (6) at From Appendix (6) at From Appendix (6) at
L′
G′ L′ G′ L′ G′
= 0.14 , Approach=38.16 ⁰F and CR=18 ⁰F=10 ⁰C → =0.14, Approach=38.16 ⁰F and CR=26 ⁰F=14.4 ⁰C →
L
= 0.17 →(1)
= 0.24
L KaV
= 0.14, Approach=38.16 ⁰F and CR=22 ⁰F=12.2⁰C →
By interpolation using Appendix (6) at CR=9 ⁰F=5 ⁰C. KaV
KaV
L KaV L
= 0.27
= 0.36
By using table (3.1) and assuming Height (Y)=3 ft=0.9144m we get; Constants C=0.5 m=0.09 n=0.91 Substituting in the following equation; K a = c (L)m (G)n K a =0.5 (0.0333)0.09 (0.238)0.91 K a =0.0997 →(2) By substituiting (2) in (1) we get; KaV = 0.17 L
yields 0.0997 × V = 0.17 �⎯⎯� V = 0.0568 m3 0.0333
A=
V=A×Y
0.0568 = 0.062 m2 0.9144
A ≅ 0.25 × 0.25 m2 So; the column dimensions will be 250×250× 900 mm3. 18
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Chapter 3 -The column cap It’s the upper component of the column. The spray nozzle, drift eliminator and the humidity and exit air tempreature sensors are located in the cap. Hence, the cap hieght mustn’t be long and it’s cross section equal to that of the column body. The cap dimensions=250×250×200 mm3.
Fig. (3.2) column cap. -The packing/fill and drift elimenator The packing(Fig. 3.3) used to increase the area of content between the air and water. The packing surface is corecated of P.V.C material. The fill spacing shown inFig. (3.4). The drift elimenator Fig.(3.5) is placed in the air exit way to decrease the water droplets carried by air.
Fig. (3.4) Fill spacing
Fig. (3.3) Packing
Fig. (3.5) Drift eliminator 19
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Chapter 3
2. Cooling tower performance Water: Air in:
Twi=50⁰C Tai=35⁰C
From psychrometric chart :
Two=45⁰C RHai=40% Wbtai=23.9⁰C
ṁ w = 0.0333 kg/s ṁ da = 0.238 kg/s
Cpw=4.18 kJ/kg C
Ψai=0.01414 kg/kgda
hai=71.49 kJ/kg
Cooling range and approach obtained CR=Twi-Two=50-45=5⁰C Approach= Two-Wbtai=35-23.9=21.1⁰C Q CT = ṁ w × Cp,w × CR
Where: Q CT : Cooling tower load. mẇ : Water flow rate. Cpw : specific heat at constant pressure
Q CT = 0.033 × 4.18 × 5 Q CT = 0.7 kW
Q CT = ṁ da × (hao − hai )
0.7 = 0.238 × (hao − 71.49) hao = 74.42 kJ/kg da
From psychrometric at hao = 74.42 kJ/kg da and RHao=100% Ψao=0.01877 kg/kgda Tao=23.9⁰C ṁ evap = ṁ da (ψao − ψai )
ϵ=
ṁ evap = 0.238(0.01877 − 0.01414)
ϵ=
ṁ evap = 1.10194 × 10−3 kg/s
Twi − Two Twi − Wbtai
50 − 45 × 100 45 − 23.9 ϵ = 23.697%
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Chapter 3
3. Tanks i. Water tank In the educational stand cooling tower the water tank considered as the heat load component (condenser), water is heated by an immersion heaters fitted from the back of tank. The heaters are metal tubes containing an insulated electric resistance heater which provide heat load about 1.5 kilowatts. The water return pipe contains twelve holes to provide good mixing of cold and hot water. The tank was attached with eye glass to determine the level of water in the tank. There is a baffle inside the tank to make good mixing of the hot water and cold water coming from the column. Tank capacity estimation 𝑄𝑄 = 𝑚𝑚̇ × 𝐶𝐶𝐶𝐶 × ∆𝑇𝑇 𝑚𝑚̇ = 𝜌𝜌 ×
𝑉𝑉 𝑡𝑡
Where: ρ: Water density, kg/m3 V: Water volume, m3 t: time need to heat the water, sec.
Q: Heaters power, kW 𝑚𝑚̇: Mass flow rate, kg/s CP: water specific heat, kJ/kg K ΔT: Temperature difference, ⁰C
Q=1.5 kW ∆𝑇𝑇 = 𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓𝑓 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟 − 𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖𝑖 𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 ∆𝑇𝑇 = 50 − 25 = 25°𝐶𝐶
Cp=4.18 kJ/kg K t=25 min.
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Chapter 3
1.5 = 1000 ×
Q = 𝜌𝜌 ×
𝑉𝑉 × 𝐶𝐶𝐶𝐶 × ∆𝑇𝑇 𝑡𝑡
𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦𝑦 𝑉𝑉 × 4.18 × 25 �⎯⎯⎯� 𝑉𝑉 = 0.0215 𝑚𝑚3 25 × 60
V ≅ 0.25 × 0.25 × 0.35 m3
The tank dimension = 250 × 250 × 450 mm3
Fig. (3.1) Water tank main dimensions(dimensions in cm).
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Chapter 3 ii. Air Tank Air tank is designed to deliver the air from the blower also to hold the column and allow air to be introduced into the column. So its dimensions must be suitable for carrying the column and also not large to force air to accelerate in the column (i.e. velocity is inversely proportional with area). Design requirements:• • • • • •
Air velocity inside the tank doesn’t exceed 4m/s to reduce the friction losses inside the tank. Take in consideration that the drain tank dimensions (25*25). Air flow upward around drain to the column and the area must be sufficient to the velocity not exceed 4 m/s. The air tank must be higher than the water tank to give the chance to support the drain inside to let the water flow the drain to the water tank. When the water tank have the water at level 40 cm from the ground and the drain must have at least 7 cm to let air flow from the air tank to the column. Hence the air tank will be 50 cm height and then the area around the drain as flow Q = Av
13 =A∗4 60
Aaround
A = .054167m2
drain
+ Adrai n = 0.341 ∗ 0.341
Let the air tank dimensions to be 0.4 ∗ 0.4 ∗ 0.5 m. And at this condition.
Acceptable velocity.
v=
13� 60 = 2.222 m⁄s 0.42 − 0.352
iii. Make up tank Is used to supply the system by the water loosest due to evaporation, drift, and blow down. The makeup water is piped to the water tank and at the end of the pipe a float valve exists to keep water level in the water tank constant. 23
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Chapter 3 Assume that the makeup tank support the system with makeup water for 1.5 hour, so the tank capacity can be calculated as follows.
1.1662 × 10−3 =
ṁ evap =
1000 × Vmakeup 1.5 × 60 × 60
ρ × Vmakeup t yields
�⎯⎯� Vmakeup = 6.3 × 10−3 m3
Vmakeup = 18.5 × 18.5 × 18.5 cm3
So let the makeup tank dimensions to be 20×20×20 cm3. iv. Drain tank
A tank that located in the air chamber under the column to collect the cooled water from the column and return it back to the water tank. The tank is designed to be with inclined base to accelerate the water over it to return quickly to the water tank to be heated and recirculated. Assume that the recirculated water to be stored in the drain tank for 2.5 minute so the drain tank capacity can be calculated as follows.
0.0322 =
ṁ circulated =
1000 × Vdrain 2.5 × 60
yields
ρ × Vdrain t
�⎯⎯� Vdrain = 0.005 m3
The drain tank dimensions are shown in figure (3.2) the base inclination is to force the water to be discharged from the pipe.
Fig. (3.2) drain tank main dimensions(dimensions in cm). 24
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Chapter 3
4. Piping system and pump -piping system Piping system conveys water between tanks to complete circulation. Piping system includes: • •
• •
Pipe Fittings - Three elbows. - One nibble. - Two boshes. - Two screwed union. - One T joint. Orifice plate with flanges. Valves - Check valve. - Gate valve. - Float valve.
Drain line :Design requirements:• •
Water velocity doesn’t exceed 0.07 m/sec Water flow rate 2lit/min
Hence when V=0.07m/sec & 𝑚𝑚𝑤𝑤̇ =(1/30)Kg/sec A=
̇ 𝑚𝑚 𝑤𝑤
𝜌𝜌 𝑉𝑉
=
(1/30)
1000∗0.07
Where 𝑚𝑚𝑤𝑤̇ is the water flow rate & A is the inner area of the pipe 𝐴𝐴 = 4.7619 ∗ 10−4 𝑚𝑚2
4
𝐷𝐷 = �4.7619 ∗ 10−4 ∗ = 0.0246 𝑚𝑚 𝜋𝜋
The nearest standard diameter 𝐷𝐷 = 1 𝑖𝑖𝑖𝑖 = 0.0254𝑚𝑚
Then
𝑚𝑚̇𝑤𝑤 = ̇ 𝜌𝜌 𝐴𝐴 𝑉𝑉
V= 0.06578 m/sec
25
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Chapter 3 Losses W.R.T. the velocity : ℎ𝑙𝑙 = ℎ𝑙𝑙𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 + ℎ𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + ℎ𝑙𝑙𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
Where L is the pipe length & 𝐹𝐹 =
1
ℎ𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 =
37 2
�2 log 𝑅𝑅 �
𝐾𝐾
𝑅𝑅 =
Also
𝐷𝐷
=
𝐹𝐹 𝐿𝐿 𝑉𝑉 2 2 𝑔𝑔 𝐷𝐷 .1
.0254
F = 0.26405
𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠ℎ𝑡𝑡 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙 = 2.0634 ∗ 10−3
For the orifice with 𝑛𝑛 = 12 ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
Design requirements:Orifice total area > pipe area. For holes exit velocity < in pipe velocity Let (1.25) * pipe area = ∑ holes area 𝜋𝜋 𝐴𝐴ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 = (1.25) 0.02542 4
𝐴𝐴_ℎ𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 = 6.334810−4 𝑚𝑚2
𝑡𝑡ℎ𝑒𝑒 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 𝑜𝑜𝑜𝑜 𝑒𝑒𝑒𝑒𝑒𝑒ℎ ℎ𝑜𝑜𝑜𝑜𝑜𝑜 = 8.2 ∗ 102 𝑚𝑚
Which gives a velocity 𝐴𝐴ℎ𝑜𝑜𝑜𝑜𝑜𝑜 ∗ 𝑣𝑣 = 𝑄𝑄ℎ𝑜𝑜𝑜𝑜𝑜𝑜 = Check the velocity through each hole
𝑣𝑣 = ℎ𝑙𝑙 =
𝑄𝑄𝑡𝑡𝑡𝑡𝑡𝑡 � 𝑛𝑛 𝐴𝐴ℎ𝑜𝑜𝑜𝑜𝑜𝑜
𝑞𝑞 𝑡𝑡𝑡𝑡𝑡𝑡 𝑛𝑛
= 0.0525 < 𝑣𝑣𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑚𝑚⁄𝑠𝑠
𝑘𝑘𝑣𝑣 2 𝑓𝑓𝑓𝑓𝑣𝑣 2 𝑛𝑛𝑛𝑛(𝑣𝑣 ⁄ℎ𝑜𝑜𝑜𝑜𝑜𝑜)2 ∗ 2 + + 2𝑔𝑔 2𝑔𝑔𝑔𝑔 2𝑔𝑔
0.29 ∗ (0.06968)2 12 ∗ 1 ∗ (0.0525)2 ∗ 2 −3 + 2.0634 ∗ 10 + 2 ∗ 9.81 2𝑔𝑔 ℎ𝑡𝑡𝑡𝑡𝑡𝑡 = 6.1717 ∗ 10−3 𝑚𝑚 26
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Chapter 3 Losses in make up tank:. . 𝑚𝑚𝑒𝑒𝑒𝑒 = 𝑚𝑚𝑚𝑚𝑚𝑚𝑚𝑚 = 4.635 ∗ 10−4 𝐾𝐾𝐾𝐾⁄𝑠𝑠2
𝑓𝑓𝑓𝑓𝑓𝑓 1�2 "𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣 𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑
𝑣𝑣 =
4 ∗ 4.635 ∗ 10−4
1000 ∗
𝑣𝑣 = 3.659 ∗ 10−3 𝑚𝑚⁄𝑠𝑠
𝑓𝑓𝑓𝑓𝑓𝑓 𝑡𝑡ℎ𝑒𝑒 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙𝑙ℎ = 0.5 𝑚𝑚
𝑅𝑅 =
𝑓𝑓 = ℎ𝑙𝑙 =
2 𝜋𝜋 1 � ∗ 0.0254� 4 2
0.1 ∗ 2 = 7.864 0.0254 1
37 2 �2 log � 𝑅𝑅
= 0.554
𝑓𝑓 ∗ 𝑙𝑙 ∗ 𝑣𝑣 2 0.554 ∗ 0.5 ∗ 3.6592 ∗ 10−6 = = 1.487 ∗ 10−5 𝑚𝑚 2𝑔𝑔𝑔𝑔 2 ∗ 9.81 ∗ 0.5 ∗ 0.0254
ℎ𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣𝑣
0.12 ∗ (3.659 ∗ 10−3 )2 = = 8.18855 ∗ 10−8 𝑚𝑚 2 ∗ 9.81 ℎ𝑙𝑙 𝑡𝑡𝑡𝑡𝑡𝑡 = ℎ𝑙𝑙𝑝𝑝 + ℎ𝑙𝑙𝑣𝑣 = 1.4952 ∗ 10−5 𝑚𝑚
Pump discharge pipe head loss Total head losses
𝐻𝐻𝑙𝑙 = ℎ𝑙𝑙 𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + ℎ𝑙𝑙𝑐𝑐ℎ 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 + ℎ𝑙𝑙𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 + ℎ𝑙𝑙𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜 + ℎ𝑙𝑙𝑇𝑇 + ℎ𝑙𝑙𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟𝑟
𝑓𝑓 =
1
�2 log
ℎ𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 =
ℎ𝑙𝑙𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝
37 � 𝑅𝑅
2
𝑓𝑓𝑓𝑓𝑣𝑣 2 = 2𝑔𝑔𝑔𝑔
= 0.26405 , 𝑤𝑤ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑅𝑅 =
ℎ 𝑜𝑜𝑜𝑜𝑜𝑜
+ ℎ𝑙𝑙𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛𝑛
0.1 0.0254
0.26405 ∗ 1.8 ∗ 0.06572 = 4.1167 ∗ 10−3 𝑚𝑚 2 ∗ 9.81 ∗ 0.0254 27
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Chapter 3
ℎ𝑙𝑙𝑐𝑐ℎ 𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒𝑒 ℎ𝑙𝑙𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 =
𝑘𝑘 ∗ 𝑣𝑣 2 2.5 ∗ 0.06572 = = = 5.5 ∗ 10−4 𝑚𝑚 2𝑔𝑔 2 ∗ 9.81
𝑘𝑘𝑣𝑣 2 , 2𝑔𝑔
ℎ𝑙𝑙𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔𝑔 = ℎ𝑙𝑙𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
𝑤𝑤ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑘𝑘 𝑎𝑎𝑎𝑎 𝑜𝑜𝑜𝑜𝑜𝑜 𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞𝑞 𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜𝑜
24 ∗ 0.06572 = 5.28 ∗ 10−3 𝑚𝑚 2 ∗ 9.81
8.2(0.0659)2 = = 1.8 ∗ 10−3 𝑚𝑚 2 ∗ 9.81
0.9(0.26287)2 ℎ𝑙𝑙𝑇𝑇 = = 3.16975 ∗ 10−3 2 ∗ 9.81
Head losses across the nozzle by using of hand pump and measuring the pressure in the nozzle line we find that ΔP=2 bar Using B.E. 𝑣𝑣12 𝑝𝑝2 𝑣𝑣22 𝑝𝑝1 + 𝑧𝑧1 + = + 𝑧𝑧2 + + ℎ𝑙𝑙 𝜌𝜌𝜌𝜌 2𝑔𝑔 𝜌𝜌𝜌𝜌 2𝑔𝑔
𝑤𝑤ℎ𝑒𝑒𝑒𝑒𝑒𝑒 𝑣𝑣1 = .0657 𝑚𝑚⁄𝑠𝑠
(𝑝𝑝1 − 𝑝𝑝2 ) 𝑣𝑣12 − 𝑣𝑣22 + (𝑧𝑧1 − 𝑧𝑧2 ) + = 𝐻𝐻𝑙𝑙 𝜌𝜌𝜌𝜌 2𝑔𝑔 𝑣𝑣2 = 18.83672 𝑚𝑚⁄𝑠𝑠 𝐷𝐷1 = 2.54 𝑐𝑐𝑐𝑐
𝐷𝐷2 = 0.15 𝑐𝑐𝑐𝑐 𝐻𝐻𝑙𝑙 = 1.763 𝑚𝑚
𝐻𝐻𝑙𝑙𝑡𝑡𝑡𝑡𝑡𝑡 = (4.1167 + 0.55 + 5.28 + 1.8 + 3.16975) ∗ 10−3 + 1.763 𝐻𝐻𝑙𝑙𝑡𝑡𝑡𝑡𝑡𝑡 = 1.77791645 𝑚𝑚
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Chapter 3
-pump Used to circulate the water through the system and also to overcome the losses in the pipes and valves. the suitable Pump specifications are: • • • • • •
Power Max. Flow Min. Flow Max. delivery head Min. delivery head Power supply
0.5 HP. 2.16 m3/hr. 0.6 m3/hr. 32.5 m. 5 m. 230v, 50Hz.
4. Blower and Butter fly valve -Blower The Blower has to overcome the system resistance, which is defined as the pressure loss, to move the air. The Blower output or work done by the Blower is the product of air flow and the pressure loss. Specifications:
Power supplies 230 V-50 HZ. • Power 100 W. • Flow rate 740 m3/hr. • Pressure 473 Pa.
Blower Size, mm Mass, Type of ventilator dimensions: Kg Φ d DΦ C A B L E VKMZ 160 200 344 240 25 25 350 40 6.6
Fig. (3.3) Blower main dimensions.
29
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Chapter 3 -Butterfly valve A butterfly valve figure (3.4) is from a family of valves called quarter-turn valves. The "butterfly" is a metal disc mounted on a rod. When the valve is closed, the disc is turned so that it completely blocks off the passageway. When the valve is fully open, the disc is rotated a quarter turn so that it allows an almost unrestricted passage of the process fluid. The valve may also be opened incrementally to regulate flow. The butter fly used was fabricated to suit the blower suction diameter.
Fig (3.4) butterfly valve
5. Water Injection Nozzles Two spray nozzles attached to sprinkler pipe. The nozzle atomizes water to increase the heat exchange and mass transfer between air and water; also the nozzle must provide good water distribution over the column fill. Fig(3.5) spray nozzles
The nozzle spray shape is cone 30⁰ angles with vertical.
Fig(3.6) testing angle of nozzle spray
30
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Chapter 3
6. Stand The table which will carry all cooling tower components.
Air Tank Water Tank Fits and Tolerance Display and Screen Column Connection Pipe Stand
Length(cm) 40 25
Width(cm) 40 25
Height(cm) 50 45
10
10
-
100
-
-
25 10
25 -
150 -
200
50
182
∑Length= 175 Cm (Length of air tank) < Length of Stand Max Width = 40 Cm (width of air tank) < width of Stand Max Height = 150 Cm (height of column) < Height of Stand 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊ℎ𝑡𝑡 = 𝑤𝑤𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡𝑡 + 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + 𝑤𝑤𝑝𝑝𝑝𝑝𝑝𝑝𝑝𝑝 + 𝑤𝑤𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑𝑑 + 𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤𝑤 + 𝑤𝑤𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠𝑠 𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑊𝑊𝑊𝑊𝑊𝑊𝑊𝑊ℎ𝑡𝑡 = 5 + 7 + 33.5 + 5 + 30 + 40 = 120.5𝐾𝐾𝐾𝐾 Max Weight for wheel=200Kg
𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇𝑇 𝑊𝑊𝑊𝑊𝑊𝑊𝑔𝑔ℎ𝑡𝑡 < Max Weight for wheel 𝑆𝑆𝑆𝑆𝑆𝑆𝑆𝑆 𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷𝐷
31
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Chapter 4
Chapter 4 Measurement devices and data acquisition system 1. Temperature measurements Three basic types of temperature measuring sensors • Thermocouples – Self Generating - Two metals joined together at a junction which generate a very small voltage (millivolts) which is a function of temperature. Voltage goes up as temperature goes up. • Resistance Temperature Devices (RTDs) – Resistive - Measuring the change of resistance in a piece of metal due to temperature. Resistance goes up as temperature goes up. • Thermistors – Resistive - Measuring the change in resistance in a semiconductor material due to temperature. Resistance goes down as temperature goes up. • Other methods exist – such as infrared detection and bimetallic strips
Characteristic
Thermocouple
RTD
Thermistor
Excitation
Self-Generating
External Required
External Required
Output Signal
millivolts
Typically volts for coarse measurements.. Can be millivolts for high accuracy
Typically Volts Can be millivolts for high accuracy.
Ground/Noise/Error
Floating, susceptibility to noise
Grounded, susceptible to lead wire resistance
Grounded, susceptible to lead wire resistance
Signal
Increase with temperature
Increases with temperature
Decreases with temperature if NTC, Increases with PTC
Range
- 200 deg c to +1200 deg C depending on type
-200 to +800 DegC for platinum
-100 to + 200 DegC
Pro’s
Inexpensive and rugged
Stability and linearity
High Sensitivity
Con’s
Floating measurement requires careful attention
Expense, Slow Response Time, Low Sensitivity, Self Heating
Smaller Temperature Range, NonLinear, Self Heating
Table (4.1) Comparison Of Sensing Methods 32
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Chapter 4
Resistance Temperature Detectors (RTDs) – a device used to relate change in resistance to change in temperature. Typically made from platinum, the controlling equation for an RTD is given by: 𝑅𝑅𝑇𝑇 = 𝑅𝑅𝑜𝑜 [1 + 𝛼𝛼 (𝑇𝑇 − 𝑇𝑇𝑜𝑜 )]
RT is the resistance of the RTD at temperature T (measured in °C) R0 is the resistance of the RTD at the reference temperature T0 (usually 0°C) 𝛼𝛼 s the temperature coefficient of the RTD PT100 Platinum wire-wound detectors comprise a pure platinum wire wound into a miniature spiral and located within axial holes in a high purity alumina rod. The freedom of movement of the platinum wire gives good long term stability. Specifications: Ro 100 Ohms Temperature range -200 to +800°C
Fig. (4.1) Resistance Temperature curve for PT 100.
Table (4.2) Resistance VS temperature and tolerance for PT100 33
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Chapter 4
2. Humidity sensors Is composed of a resistance where its ohm varies with the humidity of air.
General Description The EWHS 280 humidity sensor is a probe designed to be connected to a humidity measuring device. Output signal is a current signal (4...20 mA). Specifications Power input 9 – 28 Volt DC Measurement range 15 – 100 % Maximum Load 250 Ohm Accuracy +/- 5%
3. Flow Measurements 3.1 Pipe Flow rate Meters
Fig. (4.2) orifice plate Three of the most common devices used to measure the instantaneous flow rate in pipes are The orifice meter, the nozzle meter, and the Venturi meter. Each of these meters operates on the principle that a decrease in flow area in a pipe causes an increase in velocity that is accompanied by a decrease in pressure. Correlation of the pressure difference with the velocity provides a means of measuring the flowrate. In the absence of viscous effects and under the assumption of a horizontal pipe, application of both the Continuity and Bernoulli equations between points (1) and (2) shown in the following figure gave
Fig.(4.3) Typical pipe flow meter geometry 34
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Chapter 4
Qideal = A2 V2 = A2 �
2∆P ρ
A typical orifice meter is constructed by inserting between two flanges of a pipe a flat plate with a hole. The pressure at point (2) within the vena contracta is less than that at point (1). Nonideal effects occur for two reasons. First, the vena contracta area, (A2), is less than the area of the hole, (A0), by an unknown amount. Thus, A2=KA0, where Cc is the contraction coefficient (Cc
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