Calibration of Venturimeter
Calibration of Venturimeter
Calibration of Venturimeter
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CALIBRATION OF VENTURIMETER
AIM: To determine the Co-efficient of discharge Cd of the given venturimeter
APPARATUS:
Flow measurement device apparatus, Stop watch SPECIFICAIONS: * Area of Measuring tank, * Diameter of the Venturimeter (throat), * Diameter of the Venturimeter (Inlet) , DESCRIPTION OF APPARATUS: The apparatus has a measuring Tank to measure the flow rate, and pipe line with a Venturimeter. Tapping with Ball valves are provided at Inlet & Outlet of the Venturimeter and these are connected to manometer.A constant steady supply of water is provided using monoblock pump with a means of varying the flow rate A = 0.064 m2 d = 12.5 mm D = 25 mm
THEORY:
A Venturimeter is a device which is used for measuring the rate of flow of fluid through pipe line. The basic principle on which a venturimeter works is that by reducing the cross-sectional area of the flow passage, a pressure difference is created between the inlet and throat & the measurement of the pressure difference enables the determination of the discharge through the pipe. A Venturimeter consists of. 1. An inlet section followed by a convergent cone, 2. A Cylindrical throat & 3. A gradually divergent cone. The inlet section of the Venturimeter is of the same diameter as that of the pipe which is followed by a convergent cone. The convergent cone is a
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short pipe which tapers from the original size of the pipe to that of the throat of the Venturimeter. The throat of the venturimeter is a short parallel side tube having its cross-sectional area smaller than that of the pipe. The divergent cone of the venturimeter is gradually diverging pipe with its cross-sectional area increasing from that of the throat to the original size of the pipe. At the inlet section & the throat, of the venturimeter, pressure taps are provided through pressure ring. Venturimeter provides a constriction in the flow area which produces an accelerated flow. Consequently, there will be a fall in static pressure. Hence, the measurement of drop in static pressure provides an accurate measure of the flow rate in the pipe. The application of Bernoullis Equation between the inlet section and the throat section and the use of continuity equation leads to the following expression for the flow rate. Venturi Head is directly related to the flow rate. a1x a2 2g H ---------------------- (a12 - a22) ,Qth a1 a2 H Where H h Sm SW = = = = = = = = m3 /Sec
Qtheo =
Where,
Theoretical discharge c/s area of the inlet = c/s area of pipe c/s area of the throat Venturi head (in meters of fluid flowing through the pipe ) Sm h x ----- - 1 SW differential manometer reading Specific gravity of manometric liquid. Specific gravity of fluid in the pipe. (i.e; water & SW= 1)
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equation above because of frictional effects and consequent head loss between section at inlet and throat . In practice it is customery to account for this loss by insertion of an experimentally determined co-efficient of known as Coefficient of discharge . Thus the equation for actual discharge becomes Qact = Cd Qth The value of co-efficient of discharge -Cd depends on Renolds number (Re) of the flow and increases with increase in Reynoldss number for the same throat ratio . This has been observed experimentally to be true and the value of Cd is seen to vary from 0.95-0.99 for Re > 105.
PROCEDURE:
1. Fill-in the sump tank with clean water. 2. Keep the delivery valve closed. 3. Connect the power cable to 1 Ph, 220 V, 10 Amps with earth connection. 4. Switch-ON the Pump & open the delivery valve. 5. Open the corresponding ball valve of the Venturimeter pipe line. 6. Adjust the flow through the control valve of the pump. 7. Open the corresponding ball valves fitted to Venturi / Orifice tappings. 8. Note down the differential head reading in the Manometer. (Expel if any air is there by opening the drain cocks provided with the Manometer). 9. Operate the Butterfly Valve to note down the collecting tank reading against the Known time and Keep it open when the readings are not taken. 10. Change the flow rate & repeat the experiment.
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OBSERVATIONS:
MANOMETER READING mm of Hg D= 25mm d=12.5mm TIME TAKEN FOR 10cm RISE OF WATER t 'sec'
OPENINGS
CALCULATIONS: * Area of Measuring tank, * Acceleration due to gravity, * Diameter of the Venturimeter (throat), * Diameter of the Venturimeter (Inlet) , A = 0.064 m2 g = 9.81 m/sec2 d = 12.5 mm D = 25 mm
Qtheo =
m3 /Sec
Where, a1 a2
D2/4 d2/4
in m2 in m2
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2.
ACTUAL DISCHARGE, AR Qact = --------100 t Where, A R t = = = Area of measuring tank in m2 Rise of water level for timet secs in m. time taken in seconds for R mm rise of water. m3 /Sec
/
Theoretical discharge
Qact = ----Qtheo
TABLE OF CALCULATIONS:
TIME TAKEN FOR 10cm RISE OF WATER t 'sec
OPENINGS
MANOMETER READING mm of Hg
AREA (A)
AREA (a1)
AREA (a2)
Qth
Qact
Cd
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