Flow Rate Measurement.pdf 42s15

American University of Sharjah College of Engineering Mechanical Engineering Department P. O. Box 26666 Sharjah, UAE

LI : Sayem Zafar Office EB2-45 Tel: 06-5152609 e-mail: [email protected]

  Experiment: Flow Rate Measurement  OBJECTIVES To show the application of Bernoulli equation for the flow rate measurement and demonstrate the existence of losses in pipe.

THEORY Various ways exist of measuring volumetric flow rate. One way to measure the flow rate directly is called cubing. It works by filling a measuring chamber with a known volume of fluid and keeping track of the volume of the liquid per unit time. However, most flow meters measure the flow rate indirectly i.e. by measuring the average velocity ‘V’ to determine the volumetric flow rate ‘Q’ from Q = AV, where A is cross sectional area of flow. The ratio of ‘direct’ and ‘indirect’ volumetric flow rate is called the discharge coefficient. Venturi Meter Venturi Meter is a device the measures the flow rate by obstructing the flow at a throat. Theoretical ideas behind these flow meters are the conservation of mass and the Bernoulli equation. Applying conservation, the reduction in cross sectional area will contribute to an increase in velocity. Thus, from Bernoulli equation, this will lead to a decrease of static pressure. Venturi meter measures the drop in static pressure while the velocity can be calculated using Bernoulli equation and conservation of mass.  

 + z +   =   + z + 

…………………………………..……….. (e.q.1)

Where

 + z

h=

Note: Since there are looses in pipes, station-1 values do not perfectly add up to station-2 values.

Data Required Area of the pipe Area of the throat h1 h2 Volume of liquid in the collecting chamber Time of measurement

Results • • • • •

Measured volumetric flow rate i.e. through cubing Calculated volumetric flow rate The percent error Compare the results and determine the discharge coefficient Discuss why there is a discrepancy in the results