Hydraulic Bench and Accessories

Hydraulic Bench and Accessories (Unit Operations Laboratory)

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LANSANG, Jelanie C. MAGSIPOC, Jay Anthony S. MAGSIPOC, Jay Anthony | Hydraulic Bench and accessories SABULAO, Vina B.

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1. INTRODUCTION

HYDRAULIC BENCH

2. DESCRIPTION 2.1 General Hydraulics Bench, its various accessories and the associated experimental equipment have been developed to provide a comprehensive range of experiments in fluid mechanics. Although the experiments are generally small in scale, they are manufactured to a high quality standard and are designed to produce experimental results which compare favourably with theoretical and empirical data.

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2.2 General Arrangement The bench consists of a steel frame which supports a fibre glass worktop with integral weir channel and volumetric measuring tank, a sump tank, variable speed centrifugal water pump with appropriate pipework and valves. The worktop is manufactured from fibreglass reinforced plastic, with additional balsa wood reinforcement, moulded to provide a recessed area for mounting experimental apparatus, an integral weir and a volumetric measuring tank equipped with sight glass and scale. The measuring tank is stepped with a 10 litre lower portion and 35 litre upper portion to ensure accurate measurements of both low and high flow rates. The measuring tank discharges into a fibreglass sump tank of approximately 120 litre capacity, via a quick acting ball valve located in the PVC pipework. An overflow pipe is provided in the volumetric measuring tank to prevent the sump tank from running dry. A V-notch weir, mounted at the discharge end of the weir channel is provided in clear acrylic plastic complete with a scale calibrated in litres per minute so that a continuous reading of flow rate can be made. A centrifugal pump delivers water to the outlet at the bench working surface, for connection to either individual experiments or to a flow stilling basket. Provision is made for fitting an additional pump. The flow is regulated by a chromium plated valve. The variable speed control box also provides a much more convenient method of regulating flow to experiments, particularly where the required flow rate is very low. A pressure gauge is provided coupled to a rotary selector switch mounted on the panel; pressure measurements can be made at the first and second pump delivery points, the experiment input point and at another external position when required. A vacuum gauge mounted in the pipework immediately prior to the pump is provided to read the pump suction pressure. The component parts are mounted on a robust stove enamelled steel frame, which is provided with castors for ease of mobility. 2.3 Water Circulation The circulation pump is mounted on a lower platform and this allows full accessibility to the unit. Water flows to the pump from the storage reservoir via a transparent suction pipe fitted with a stop valve at the reservoir outlet. Thus any cavitation taking place can be immediately seen in the transparent section. The water is delivered from the pump through a second transparent pipe passing through the panel above the pump. The pipe is connected to the bench regulating valve, the control knob of which is mounted on the left hand side of the instrument panel viewed facing the panel. 2.4 Electrical System A flexible electrical cable is provided for connection of main electricity. The cable is fitted with a connector which plugs into the speed control box located on the shelf 3

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under the working top. The speed control box incorporates a switched socket for the supply of electrical power to the water circulating pump and the second pump or an accessory. The connection to the mains supply should be carried out in accordance with the installation. 2.5 Pump and Motor Units The pump is a high speed centrifugal type manufactured by 'Stuart Turner’. The spilt flanged brass body is attached to the motor casing and the impeller is on an extension of the motor shaft giving the arrangement known as "close-coupled. At maximum speed of approximately 5400 rev/min the pump flow rate is 42 litres per minute against a head of approximately 5 metres and the maximum head at zero flow is approximately 20 metres. 2.6 Pressure Gauge and Selection Valve A Bourdon type pressure gauge mounted on the panel of the Hydraulic Bench Unit is connected via a special 4-way selector valve to various tapping points in the apparatus. a. First pump outlet b. Supply to the apparatus c. Auxiliary tapping - Do not turn the valve selector to 'Auxiliary' when this position is connected d. Second pump outlet - Where only one pump is fitted, connection (d) is plugged 2.7 Hydraulic Bench Accessories The basic bench unit can be augmented by a number of accessory units, some of which are essential for certain of the experiments which are described later. The available accessory units are listed below and, with the exception of the Auxiliary Pump P6101, are illustrated in figure 1. 2.7.1 Auxiliary Pump & Speed Control Unit A second variable speed centrifugal pump with associated pipework is available to increase the water flow capacity, enabling the Bench Unit to service a series of larger scale experiments The valving arrangements also enable the two pumps to be run in either series or parallel configuration. Figure 2 shows a hydraulics bench fitted with the auxiliary pump. The speed control units allow continuously variable speed control of both the main and auxiliary pumps so that pump characteristic curves may be obtained at different speeds. 2.7.2 Pump Speed Display

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This unit provides a constant display of the speed of either the main or auxiliary centrifugal pump. The method of connecting this display unit is shown in figure 3. The circuit diagram for this unit is shown on P6102/10 reproduced as figure. 2.7.3 Constant Head Inlet Tank The inlet tank provides a constant head of water for experiments requiring it, a two position overflow is arranged so that either a 250 or 500mm head can be provided to suit the experimental requirements. The tank is fitted with two screwed connection points, one in the base and one in the side, for the attachment of experiments. The tank is shown in figure 5. 2.7.4 Variable Head Outlet Tank The outlet tank is used in conjunction with the inlet tank P6103 to mount various experiments and to provide a regulated total head across the experiment. The discharge pipe on the variable head outlet tank can be set at any value between 50mm and 300mm above the experiment centre line height. The tank is shown in figure 5. 2.7.5 Feed Block The feed block is provided for use instead of the constant head inlet tank for those experiments which require more than 500mm inlet head. The feed block which is shown in figure 5 can supply the full head available from the pump(s). 2.7.6 Manometer The manometer is required for use with those experiments where the measurement of pressure drop or head loss is necessary. The unit, which is shown in figure 6, consists of four open vertical manometer tubes, thus enabling measurements to be made at four points simultaneously, and a water on mercury 'U'-tube for the measurement of higher values of differential pressure. The tubes are all mounted on a back board which locates onto fixing brackets mounted on the Bench Top. Connections to the experiments are made in clear flexible tube which should run from the manometer to the experiment without forming an inverted 'U' in order to prevent air traps. The manometer legs above mercury level are to be filled with water, any air bubbles being present are to be bled via the valve positioned at the top of the mercury manometer. This valve is a 3 position one, enabling equalisation between the legs, bleeding of air, and normal operation to take place. Allowance should be made for the relative specific gravity of 12.6 [i.e. (Hg - H2) = (13.6-1)] when measuring heads using the water on mercury manometer. 2.7.7 Hook Gauge and Scale The hook gauge enables vertical measurements to be made with a scale, at a series of points along the horizontal length of the weir tank. It is intended for use with P6223 and P6224 orifice experiments for plotting the trajectory of horizontal jets, 5

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and with P6225 and P6226 for determination of the water height above a weir. Precise positioning of the gauge is ensured by the use of accurate positioning rails onto which the gauge can be fitted. The positioning rails and the hook gauge are dual purpose having an orifice trajectory scale for use with the crosswire gauge, (datum point at the centre of the orifice), and a water level scale for use with the hook gauge, (datum point at the lowest point of the weir knife edge). Figure 7 illustrates the installation. 2.7.8 Rotameter A variable area flow meter can be supplied to be mounted from the front left hand leg of the frame between the pump delivery and the flow regulating valve, as shown in figure 1. The meter provides a direct reading of the flow rate obtained from the pump or pumps, rates from 0.4 - 4.0 m3/h can be measured. 2.7.9 Wattmeter The Wattmeter is used to measure the electrical power input to the pump motor. Figure 3A . 1-14A shows the installation of the Wattmeter and the circuit diagram is shown in figure 8.

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3. HYDRAULIC BENCH EXPERIMENTAL CAPABILITY. 3.1 Introduction A series of additional experimental apparatus are available which, when used in conjunction with Cussons hydraulics bench and its various accessories allows a very wide range of experiments to be conducted as illustrated below. 3.1.1

List of Symbols

A a ac B,

cross sectional area (major area) cross sectional area (minor area) cross sectional area at vena contractor Breadth

m2 m2 m2 m

b CP CC

specific heat at constant pressure coefficient of contraction

J/kgK dimensionles

Cd

coefficient of discharge

s dimensionles

Cm

meter coefficient

s dimensionles

Cv

coefficient of velocity

s dimensionles

D D,d E

characteristic dimension internal diameter of pipe or tube velocity approach factor

s m m dimensionles

F F

Force configuration constant (bends, elbows etc.)

s N dimensionles

f

friction factors

s dimensionles

& f’ g H,

acceleration due to gravity Head

s 9.807 m/s2 m

h hf ht Hm I i

friction head total or pitot head manometric head Current hydraulic gradient

m of fluid m of fluid m of fluid Amp dimensionles

K, k Constant

s dimensionles

L, l M M m

Length Mass mass flow rate area ratio

s m kg kg/s dimensionles

N Ns n

speed of rotation specific speed of rotation Constant

s rev/s rev/s dimensionles s 7

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P, p pt Q Q Re

Pressure total or pitot pressure Volume volume flow rate Reynold’s number

N/m2 N/m2 m3 m3/s dimensionles

R, r S T t V W W Wh Wi x y Z z

Radius reaction on vane Temperature Time Velocity work done Power hydraulic power input power Distance distance from centre height above datum correction factor

s m N  C or K s m/s J W W W m m m dimensionles

  

Density absolute viscosity Efficiency

s kg/m3 Ns/m2 dimensionles



h

hydraulic efficiency

s dimensionles



o

overall efficiency

s dimensionles

        3.1.2

shear stress Torque kinematic viscosity Angle Difference infinitesimal difference angular velocity function in dimensional analysis

rad/s

Abbreviations

B ac dc L

position of centre of buoyancy alternating current direct current length (dimensional analysis)

M T

mass (dimensional analysis) time (dimensional analysis)

3.1.3

s N/m2 Nm m2/s

Suffices

a,b,c

indices used in dimensional analysis

, d f m n s

Discharge Float Meter number of parts, pumps or elements Specific

3.2 Performance of a Centrifugal Pump 8

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This experiment utilises the pump supplied as part of the P6100 Hydraulics Bench. The experimental capability can be extended by using the P6102 Pump Speed Display Unit to indicate the pump speed and the P6109 Wattmeter to measure the electrical power input to the pump. The experiment allows the performance of the pump to be presented as characteristic curves of head plotted against flow rate. Refer to Part 2 for details of the theory, experiment and typical results. 3.3 Performance of Two Pumps Connected in Series or Parallel. By installing the Auxiliary Pump Unit P6101 onto the Hydraulics Bench it is possible, with the pipework and valving supplied, to operate the two pumps in series or in parallel. Part 2 of the manual also covers these experimental procedures. Figure 2 illustrates the installation of the Auxiliary Pump onto the Hydraulics Bench. The use of two pumps also allows the Hydraulics Bench to act as a service unit for larger items of experimental equipment, such as the wall mounted Friction in Pipes Apparatus P5160 and Flow Channel P6245. 3.4 Laminar and Turbulent Flow In A Pipe To carry out experiments on laminar and turbulent flow in a pipe Cussons P6220 Laminar Flow Experiment is required. This is mounted between the Constant Head Inlet Tank (P6103) and the Variable Head Outlet Tank (P6104) and requires the Manometer Board (P6106) to be mounted to the back of the bench for measuring differential head across the laminar flow tube. The arrangement of a similar experimental set up (P6221) can be seen in figure 1, which clearly shows the Inlet Tank, the experiment, the Outlet Tank and the Manometer Board. To allow experiments to be performed at higher flow rates than can be obtained with a 500mm inlet head it is necessary to use the P6105 Feed Block instead of the P6103 Inlet Head Tank. This experiment is discussed in detail in Part 3 of the manual 3.5 Losses In Pipes and Fittings Cussons P6221 provides two straight pipe lengths of different bore (7mm and 10mm), one 10mm bore pipe containing 90 bends, one 10mm bore pipe containing 4 90elbows, one length of pipe with a ball valve and one length of pipe with an angle seat valve. Any one of these pipes may be installed between the inlet and outlet head tanks (P6103 and P6104). The Manometer Board (P6106) is required for measuring head loss and to allow the relationship between head and flow to be investigated. To allow experiments to be performed at higher flow rates than can be obtained with a 500mm inlet head it is necessary to use the P6105 Feed Block instead of the P6103 Inlet Head Tank. Experimental details are given in Part 3. 3.6 Entry and Exit Losses to a Pipe The P6222 apparatus consists of two test pipes with an inlet bore of 10mm and an exit bore of 20mm, one with sudden transition the other with a 30 transition, 9

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these two pipes can be used to study either expansion or contraction losses. Adaptor pieces are also supplied to allow sudden and tapered entry and exit geometries to be obtained. The pipes and adaptors are again used between the inlet and outlet head tanks (P6103 and P6104). The Manometer Board (P6106) is required which allows the head-flow relationship to be investigated. Part 3 of the manual provides all the experimental details. 3.7 Orifices Cussons Elementary Orifice Set (P6223) comprises a set of three sharp edged orifices of 3, 5 and 8mm diameter. The Advanced Orifice Set (P6224) comprises square, triangular, Borda and bell mouthed orifices. The orifices are used in either the side or the base of the Inlet Head Tank (P6103) to study the discharge characteristics of orifices. When used in the side of the Inlet Head Tank the trajectory of the issuing jet of water can be studied with the aid of the accessory Hook Gauge (P6107). These experiments are presented in Part 4. 3.8 Weirs Cussons provide two sets of weirs: P6225 Elementary Weirs comprising a rectangular weir and two 'V' notch weirs (90 and 60 ); P6226 Advanced Weirs consisting of a trapezoidal (or Cippoletti) weir, a linear weir and a full width (or suppressed) weir. Any one weir can be attached to the end of the weir channel to replace the standard 60acrylic V notch weir supplied with the bench. The Hook Gauge (P6107) is an essential accessory for use with the weirs which enables accurate measurement of the head over the weir. Part 5 gives detailed information on experiments with weirs. 3.9 Flow Measurement by Tapered Area Meter The tapered area flow meter or Rotameter P6108 is an accessory to the Hydraulics Bench which, if purchased, may be permanently mounted between the pump delivery and the bench regulating valve. Once fitted not only can it be used to provide instantaneous reading of the flow rate but can also be used as an experiment in it’s own right. See Part 6 for a detailed treatment of this topic. 3.10 Flow Measurement by Venturi Cussons P6227 Venturi Meter is a classical 21 inlet conical venturi designed generally in accordance with British Standard BS 1042. The venturi is used between the inlet and outlet head tanks (P6103 and P6104) and can also be used with the feed block (P6105) to allow higher flow rates to be achieved. The manometer board (P6106) is essential for measuring differential pressure. The experimental work is presented in Part 6. 3.11 Flow Measurement by Orifice Plate

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The Orifice Plate Experimental Apparatus consists of two square edged orifice plates (8 and 12mm) which can be trapped between the flanges of a 22mm bore pipe installed between the inlet and exit head tanks (P6103 and P6104). The feed block (P6105) can also be used and the manometer board (P6106) is essential. The pipe is equipped with both corner tappings and D and D/2 tappings to allow both types to be compared. The design is otherwise in accordance with BS 1042. Part 6 contains full experimental details. 3.12 Flow Measurement by Turbine Meter The pulse producing turbine meter is installed in a 25mm bore pipe which is mounted between either the feed block (P6105) or the inlet head tank (P6103) and the outlet head tank (P6104). The manometer board is not required as an analogue display unit is provided. Part 6 of the manual discusses this method of flow measurement. 3.13 Flow Measurement by Pitot-Static Tube The pitot-static tube is installed in a 20mm bore tube which can be mounted between the inlet and outlet head tanks. Alternatively the feed block can be used. The manometer board is an essential requirement to measure the differential pitotstatic pressure. Part 6 provides experimental details. 3.14 Demonstration of Bernoulli’s Theorem The flow of water through a convergent-divergent clear acrylic passage of rectangular cross section is studied to demonstrate Bernoulli's Theorem. Fourteen manometer tappings and tubes are provided for the measurement of the static pressure distribution along the passage. The apparatus includes a dye injection system which may be used to demonstrate the onset of turbulent flow. Part 7 of the manual provides full details. 3.15 Hydraulic Ram The hydraulic ram is an example of an early design of hydraulic machine in which a large quantity of water falling through a small head is used to raise a small quantity of water through a large head. Refer to Part 8 of the manual. 3.16 Impact of Jets This apparatus is used to investigate the reaction of a jet of water on three interchangeable vanes. Two sizes of jet nozzle are supplied and three target vanes, namely:- one flat plate, one cone and one hemispherical bucket. Part 9 contains experimental details. 3.17 Calibration of a Pressure Gauge

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The apparatus consists of a simple but accurate dead weight calibration system which can be used to calibrate the pressure gauge fitted to the hydraulics bench. Refer to Part 10 of the manual. 3.18 Metacentric Height of Floating Vessels The floatation characteristics of floating vessels may be studied using Cussons Flat Bottomed Vessel P6235. The flat bottomed vessel is fitted with a detachable bridge piece and mast, which can also be used with Cussons Alternative Hull Sections P6236. A simple inclinometer is provided together with hull and bridge loading system. Experimental details are covered in Part 11 of the manual. 3.19 Centre of Pressure Apparatus Cussons Centre of Pressure Apparatus allows the force and centre of pressure acting on partially submerged and fully submerged rectangular planes to be determined. Part 12 of the manual presents the theory and experimental details concerned with this topic. 3.20 Free and Forced Vortices The Free and Forced Vortices Apparatus comprises a transparent cylindrical vessel in which both free and forced vortices can be established. The profile of the water surface can be measured as can the angular velocity of the vortex. Part 13 of the manual contains the details. 3.21 Pelton Wheel This hydraulic machine is fitted with a friction dynamometer to measure rotor torque. An optical tachometer (P4740) is available to measure the Pelton Wheel speed thus allowing the determination of power and efficiency. Part 14 of the manual specifies the experimental capability of this unit. 3.22 Large Scale Friction in Pipes This wall mounted unit allows a full range of experiments to be conducted on the loss of head due to friction in pipes of various diameters in an annulus, in a smooth and artificially roughened pipe, in various valves and fittings, and also features flow measurement by variable area flow meter, venturi meter, orifice plate meter and a pitot static tube. The hydraulics bench which is used to serve this experiment should be fitted with a second pump P6101. A separate manual is provided with this item of equipment. 3.23 Flow Channel Cussons flow channel has a 55mm wide by 175mm deep cross section and is 2500mm long. Used with a hydraulics bench fitted with two pumps the flow channel provides experiments in the uniform flow in open inclined channels, in the flow 12

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under a sluice gate and over sharp and broad crested weirs. The study of the flow over triangular hump weirs and long base weirs is provided for as is the study of hydraulic jumps. See Part 15 of the manual.

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OPERATING INSTRUCTIONS

4.1 Starting Procedure. a. Ensure that the pump inlet valve is fully open. b. Check the water level in the 'reservoir tank' and top up if required to within 20mm of the top. c. Either position the stilling basket in the left hand end of the weir channel or mount the required experimental apparatus on the working surface of the bench using the appropriate locating pegs. Connect the bench flexible water supply hose to either the apparatus or the stilling basket. d. Ensure that the bench regulating valve is in the closed position. e. Adjust the knob on the speed control unit to approximately mid-range. Connect the electrical supply to the bench and switch on. f. Adjust bench regulating valve and pump speed control to give the required water flow. 4.2 Flow Control. 4.2.1 Constant Speed Operation. Although there are two valves on the main pumping circuit, the control of flow should be made only with the valve on the instrument panel i.e. the bench regulating valve. The other valve (pump inlet valve) should be kept wide open at all times when the pump is running. The only exception to this is during the cavitation demonstration. 4.2.2 Variable Speed Operation. The pump speed can be varied from 30-7200 revs per min by using the pump speed control unit. The ac supply to the pump is varied using the control knob mounted on the unit. Speed is increased by turning clockwise. 4.3 Flow Measurement. Flow measurements may be obtained in 3 ways: 4.3.1 Volumetric Tank. a. Close the measuring tank outlet valve. b. Start the timing watch when the water level in the measuring tank is at zero or some other convenient level. c. Time the collection of a suitable quantity of water. For low flow rates, only the lower section of the measuring tank need be used. For high flow rates use the 15 litre mark as the starting point to ensure that hold up of water, as it flows across the tank, does not cause an error. d. After the measurement has been completed, open the measuring tank outlet valve completely. Note that an overflow valve for the measuring 14

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e. The mean volumetric flow rate can be calculated by dividing the volume collected by the time taken: The mass flow rate can then be obtained by multiplying by the density At normal ambient temperature may be taken as 1·00 kg/l 4.3.2 Weir Measurement. A scale calibrated in litres per minute is to be found on the weir notch. For readings above 10 litres per minute this scale may be used to give an instantaneous reading of flow rate. 4.3.3 Rotameter This too will give an instantaneous direct reading of flow rate for values above 0.4m3 per hour. 4.4 Pressure Measurements. Pressure at the pump delivery, supply hose delivery and at an auxiliary position can be monitored on the panel mounted pressure gauge by selecting the appropriate position on the selector switch. The pump suction pressure is measured directly by the in line pressure gauge mounted on the pump inlet pipework. Note that when pump delivery pressures are measured an allowance should be made for the fact that the gauge is positioned 0·7m higher than the tapping point i.e. 0.07 bar should be added to the gauge reading. Note that it is advisable to rotate the pressure selector switch anti-clockwise in order to minimise the possibility of a previously locked in jet of water being emitted from the auxiliary tapping point if this is not in use. 4.5 Stopping Procedure. a. Close the bench regulating valve. b. Ensure that the measuring tank outlet valve is open. c. Switch off the power supply on the hydraulic bench. d. Close the pump inlet valve. e. Turn the pump speed control to the minimum speed position. 4.6 Storage. If it is required to store the equipment the water should be drained from the unit. Most of the water can be drained from the unit using the pump with the flexible supply hose directed into a drain. For complete drainage a drain plug is provided 15

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underneath the reservoir tank. When storing the unit, leave all valves slightly open to prevent them seizing in the closed position. Cover the unit with a sheet of polythene or similar material in order to prevent it becoming dirty.

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HYDRAULIC BENCH AND ACCESSORIES Experiment No.1 THE HYDRAULIC BENCH

Introduction In most of the experiments in this laboratory you will use a hydraulic bench to determine the flowrate of water through various sets of apparatus. The purpose of the present experiment is to gain some familiarity with the used of the hydraulic bench. The hydraulic bench The operating principles of a hydraulic bench are surprising simple.

It consists of

the following • A tank that contains a reservoir of water. • A pump to remove water from the tank and direct it to a piece of fluid apparatus. • An on-off switch to start-stop the pump. • A valve to control the rate at which water is pumped from the tank. • An inlet in the top of the apparatus to collect water after it has been used. • A water-container immediately below the inlet in the top of the hydraulic bench. The water container also has a valve in its base that can be opened or closed by a handle set into the hydraulic bench. • A lever arm connected to water-container. The lever arm has a base upon which a set of weights can be placed. The lever arms have a 3:1 mechanical advantage, i.e. a 1.5 kg mass of water is required to lift a 4.5 kg mass placed on the balance. Note, the weights that come with the weighing tanks give the masses of the water in the containers. • There are some sensors connected to an LED to detect the motion of the lever arm past a reference point Front view of one of the hydraulic benches. The sets of weights are placed on the base connected to the lever arm in the centre of the photograph. The on-off switch is located to the top right of the bench with the control valve located immediately to its left.

The weighing container is the white plastic

container in the centre of the tank.

Side-view of the hydraulic bench. The lever arm is the metal bar sitting at 17

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an angle. The lever to open/close the base of the weighing tank is in middle of the tank towards the top of the weighing container.

The operation of the hydraulic bench is relatively simple. • The pump is started with the valve in the base of the weighing tank open. • Once you have got organized, close the valve in the base of the weighing tank. • The lever arm will rise and hit the sensor on the top rim of the bench. You should start the stop-watch the instant the arm hits the rim. • You should then place an appropriate mass on the hanger at the end of the lever arm. The lever arm will then go down. • The lever arm will start to rise again when the additional mass of water in the weighing tank approaches the mass placed on the hanger. • Stop the stop-watch when the lever arm triggers the sensor again. • The flow-rate is just the mass divided by the elapsed time. Experiment Set the flow rate using the outlet valve located at the front of the hydraulic bench. The valve should be about 55% open. Measure the actual flow rate using the weigh tank in the hydraulic bench and a stopwatch. Repeat this measurement ten times. There should be two independent measurements of the time taken to fill the weighing tank. You should record your readings in a table. A suggested Table design is shown below

• Determine the mean flow rate of water through the optical bench. • Determine the standard deviation of the flow rate? • To what precision do you think it is possible to determine the flow rate?

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• Was there any discernible change in your readings from run number 1 to number 10. Now open the valve fully and determine the maximum possible flow rate of the hydraulic bench. Equipment details Hydraulic benches. Stop-Watches (at least 2 per experimental group)

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Experiment No. 2 DEMONSTRATION OF VARIOUS PARTS OF HYDRAULIC BENCH. HYDRAULIC BENCH Hydraulic bench is a very useful apparatus in hydraulics and fluid mechanics it is involved in majority of experiments to be conducted e.g. to find the value of co efficient of velocity ‘Cv’, coefficient of discharge ‘Cd’ and contraction ‘C’ to study the characteristics of flow over notches, to find met centric height, in finding head losses through pipes, verification of Bernoulli’s theorem etc CENTIFUGAL PUMP Centrifugal pump is used for drawing water form sump tank and supply it for performing experiments. SUMP TANK The fluid used in hydraulic bench is stored in sump tank located at the bottom of hydraulic bench. The water from the sump tank is supplied through pump. Sump tank has the capacity of 160 liters. VERTICAL PIPE Water from the sump tank is supplied to the upper portion of bench through vertical transparent pipe using a pimp. CONTROL VALVE It is used to regulate the flow in the pipe i.e. to increase or decrease the inflow of water in hydraulic bench. CONNECTOR The connector allows flow for rapid substitution of accessories special purpose terminations may be connected to the pump supply by screwing connector. No hand tools are required for dong so. CHANNEL It is used in number of experiments .it provides passage in water for different experiments. DRAIN VALVE Drain valve is used for discharging of water form sump tank. SIDE CHANNELS Side channels are provided to support the accessory on test. VOLUMETRIC TANK 20

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Water discharging form the accessory (channels) on test is collected in a volumetric measuring tank .this tank is stepped to accommodate low or high flow rates. STILLING BAFFLE Volumetric measuring tank incorporates a stilling baffle inclined to reduce turbulence. SCALE AND TAPPING A sight tube and scale is connected to tapping in the base of the volumetric tank and glass an instantaneous indication of water flow. DUMP VALVE. Dump valve is in the base of the volumetric tank opening the dump valve allows the entrained water to return to the sump tank to recycling. ACTUATOR Dump valve is operated by a remote actuator lifting actuator opens the damp valve. When lifted and twisted through 90* .the actuator will retain the dump valve in the open position. OVERFLOW An over flow adjacent to the sump returns the water to the sump tank in the event of incorrect use of. MEASURING CYLINDER A measuring cylinder is provided to measuring a very small flow rater the cylinder is stored in the compartment house e.g. the sump. STARTER Electrical supply to the pump motor is via a starter.

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Experiment No. 3 CALIBRATION OF PESSURE GAUGE USING DEAD WEIGHT PRESSURE GAUGE CALIBRATION APPARATUS Dead weight calibrator, weights, hydraulic bench and calibrator. CALIBRATION To check error with comparison to some standard device is called calibration. ABSOLUTE PRESSURE The pressure that is taken with reference to absolute zero is called absolute pressure and at absolute zero there is a perfect vacuum means no air. P=rh GAUGE PRESSURE The pressure that is taken with reference to atmospheric pressure is called gauge pressure. Gauge pressure may be positive or negative . Gauge pressure when taken above the atmospheric pressure then it is positive and when taken below atmospheric pressure then its is negative. Gauge pressure is always measured with atmospheric pressure that is why when gauge pressure is at atmospheric pressure it results zero. Pabs=Patm + Pgauge PROCEDURE •

I placed the pressure gauge and calibrator assembly on bench top then I connected the inlet tube to the gauge manifold

•

A length of tube was connected to the calibrator drain and laid into the channel to prevent spillage of water on the bench top.

•

The calibrator was leveled by the adjustable feet level observing the sprit level

•

I removed the piston and accurately determine its mass and the mass of calibrator weights.

•

I closed the control valve of bench and open both corks then operate the pump starter, to open the valve and admitted water to cylinder

•

After the removal of air bubbles from the table connecting the gauge and calibrator I closed both corks simultaneously along with the flow control valve on bench and switched off the pump.

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HYDRAULIC BENCH AND ACCESSORIES

I noted the gauge reading corresponding to the piston mass of 0.5 kg while the piston is spinning (to minimize the friction effect).then I added .05kg of mass each time and noted the corresponding gauge readings using above procedure.

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Then a graph was plotted between percentage gauge error and cylinder.

OBSERVATIONS AND CALCULATIONS

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CHE 173.1

HYDRAULIC BENCH AND ACCESSORIES

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CHE 173.1

HYDRAULIC BENCH AND ACCESSORIES Experiment No. 4 EXPERIMENTAL STUDY OF LAMINAR, TURBULENT AND TRANSITIONAL FLOWS (VISUAL ANALYSIS)

APPARATUS Osborne Reynold apparatus, hydraulic bench and glass marbles. LAMINAR FLOW The flow in which fluid moves in liquid particles moves in form of thin sheets in which the particles are not intersecting the path lines of each other such type of flow is known as laminar flow. TURBULENT FLOW The flow in which liquid particles move in zig zag path and intersecting the path lines of each other is called as turbulent flow. TRANSITION FLOW The flow that takes place during the inter conversion of laminar and turbulent flow is called transition flow or Transition zone between laminar flow and turbulent flow is called transition flow.

REYNOLD’s NUMBER It is the ratio of inertial force to viscous force RN = Inertial force / viscous force RN =VL/F For Laminar flow Reynold number = 0—2000 For Transition flow Reynold number = 2000—4000 For Turbulent flow Reynold number = 4000— on ward. PIPE FLOW When liquid is touching a solid surface from all side then such type of flow is called as pipe flow. i.e. full flow in a pipe CHANNEL FLOW When the flowing liquid is not touching a solid boundary form any one side such kind of is called as channel flow, i.e. flow in a channel ,partial flow in a pipe. VISUAL ANALYSIS As it is a visual test is no need to take any reading the visual analysis of these flows is given below.

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CHE 173.1

HYDRAULIC BENCH AND ACCESSORIES

A device Osborne Reynolds is used in this test and is observed for different types of flow. The equipment operates in a vertical mode. A header tank containing stilling media A dye usually KMNO4 provides a constant head of water through a bellmouth entry to the flow visualization pipe. Flow through this pipe is regulated using a control valve at the discharge end. The operation of valve increases and decreases the flow through the visualization pipe. First it was observed that when the velocity of flow was small the dye appears like a very narrow needle flow in between the water showing laminar flow and when the velocity of water was increased gradually using control valve the dye appears to move little randomly showing transition flow and when velocity is more increased dye starts moving in zig zag path which show the turbulent flow.

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