ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 1 Pitot Static Tube Aim To determine velocity of fluid at various points across the cross section of pipe. Apparatus Pitot tube to measure velocity Pointer gauge with Pitot tube attached at the end Transparent cross section Pump to circulate the fluid Stopwatch and sump tank to measure Q actual Theory The Pitot tube measures a fluid velocity by converting the kinetic energy of the flow into potential energy. The conversion takes place at the stagnation point, located at the Pitot tube entrance. A pressure higher than the free-stream (i.e. dynamic) pressure results from the kinematic to potential conversion. This static pressure is measured by comparing it to the flow's dynamic pressure with a manometer. Cross-section of a Typical Pitot Static Tube
Transcript
ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 1
Pitot Static Tube
Aim
To determine velocity of fluid at various points across the cross section of pipe.
Apparatus
Pitot tube to measure velocity
Pointer gauge with Pitot tube attached at the end
Transparent cross section
Pump to circulate the fluid
Stopwatch and sump tank to measure Qactual
Theory
The Pitot tube measures a fluid velocity by converting the kinetic energy of the flow into potential energy. The conversion takes place at the stagnation point, located at the Pitot tube entrance. A pressure higher than the free-stream (i.e. dynamic) pressure results from the kinematic to potential conversion. This static pressure is measured by comparing it to the flow's dynamic pressure with a manometer.
Cross-section of a Typical Pitot Static Tube
ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 2
Relationship between the velocity and pressure along a streamline can be give by Bernoulli’s equation.
Evaluated at two different points along a streamline, the Bernoulli equation yields,
If z1 = z2 and point 2 is a stagnation point, i.e., v2 = 0, the above equation reduces to,
The velocity of the flow can hence be obtained,
Reynolds No=Re=ρvD/μ
Where, D=0.028 m
μ =.00098 at 210C
Vmax=2 x Average velocity
average theoretical velocity = ʃvdA/Atotal
Coefficient of pitot can be calculated as average vactual/average vtheoritical
Procedure
Check the level of CCl4 in the manometer tube. It should be up to half. If it is less, then fill it.
Close all pressure taps of Manometer connected to manometers.
Now switch on the main power supply (220 Volts AC, 50 Hz) and switch on the pump.
Operate the flow control valve to regulate the flow of water.
Open the pressure taps of the manometer slowly and remove the air bubbles (if any) from the manometer tube
Record the manometer readings and measure the discharge with the help of measuring tank and stop watch.
Now move the Pitot tube up and down tube for the same flow rate and note the manometer readings to estimate the velocity at different points in pipe.
Take readings at sufficient number of points to plot the velocity profile across the cross section. Repeat the same procedure for different flow rates of water by operating the control valve, and by-pass valve.
When the experiment is over, close all manometer pressure taps first and switch off the pump.
ME-313, IIT Gandhinagar, Dept. of Mechanical Engineering Page 3
Switch off the power supply to panel.
Drain the water from sump tanks using the drain valves.
Data
Area of sump tank= 0.1 m2. Cross sectional area of pipe = 0.0006157 m2
Density of manometric fluid ( CCl4 )=1590 kg / m3
Observation
Sr ΔP-9 ΔP-5 ΔP0 ΔP5 ΔP9 Height(cm) time(sec)
1 169 192 196 207 203 19.7 30
2 159 173 178 183 188 19.3 30
3 118 135 136 134 133 16.7 30
Calculation
Velocity profile for various distances from centre of pipe.
