Exercise-3

in an air duct of circular cross section (0.5m in diameter), a venturi meter of throat diameter 0.25m is installed. The duct carries  of gas measured at 298k and 1 atmospheric pressure. Determine the maximum pressure drop that a manometer can handle. Take the discharge coefficient as 0.98.

Solution

 

(1)

In this equation 1 and Y both are unknowns. One way is to assume some value of  and then show that our assumption is correct. Let us assume .

(2)

Now we have to show that . We use equation 7.

 and

 since gas is diatomic

Calculation yields . Hence our assumption of Y is ok.

you are proposing now an orifice instead of a venturi meter to measure 50 mm of water as the maximum pressure drop. Calculate the diameter of sharp-edged orifice to measure the full reading at maximum flow. Take coefficient of discharge 0.62 for the orifice.