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Instrumentation and Control Lab

Ex 5: Measurement of Flow Using Orificemeter and Venturimeter

5.1 Objective:

(i) To determine the coefficient of discharge of orificemeter and venturimeter
(ii) Determine the flow inside a pipe using orificemeter and venturimeter

5.2 Apparatus:

(i) Venturimeter orificemeter apparatus (ii) Stop watch (iii) Thermometer.

5.3 Procedure and Experimental Results:

(i) Open the bypass valve and start the motor.

(ii) Close the venturimeter valve and open the orificemeter valve fully.

(iii) Note the manometer displacement (hm) actual discharge rate (Qact in m3/s) and calculate theoretical discharge rate (Qth), discharge coefficient (Cd) and Reynolds number (Re.)

(iv) Vary the bypass valve position in steps from fully close to fully open. Note the readings and calculate the parameters described above.

(v) Now open the venturimeter valve and close the same of orificemeter. Follow the steps from (ii) to (iv).

(vi) Plot actual discharge rate (Qact) vs manometer height (hm) and discharge coefficient vs Reynolds number. You may also plot log(Qact) vs log(hm) to calculate the constants K and n in the Qact=K(hm)n.

5.4 Instrumental Details:

(i) Measuring tank dimensions 300x300x300 mm.
(ii) Test pipe diameter 28mm. Venturimeter throat and orifice diameter 14mm.

5.5 Few Questions for Viva Voce:

(i) Can you draw the flow profile of venturimeter and orificemeter?
(ii) What is vena contracta? What is head type flow measurement?
(iii) What is contraction coefficient?
(iv) What is Reynolds number? How the coefficient of discharge varies with Reynolds number?
(v) Do you know the other types of flow measurement device?
(vi) How could you measure the flow of a river?

3.5 Reference:

(i) E O Doebelin and D.N. Manik, “Measurement systems”, Tata McGraw Hill, special Indian edition, 2007.
(ii) B. G. Liptak, “Instrument Engineers’ Handbook: Process Measurement and Analysis”, vol 1, 4th edition, CRC, 2003.