Question

A horizontal venturimeter with inlet diameter of 30 cm and throat diameter of 15 cm is used to measure the flow of water. The reading on a differential manometer connected to the inlet and the throat is 20 cm of mercury. If $C_d=0.98$, the rate of flow is nearly

• A. 12.5 l/s
• B. 25 l/s
• C. 125 l/s
• D. 250 l/s

Answer 1

The correct option is C 125 l/s

In Venturimeter,
Rate of flow

$Q=\frac{C_d{A}_1{A}_2}{\sqrt{A_1^2-A_2^2}}\sqrt{2gh}$

Here, $h=20(\frac{\rho m}{\rho }-1)$

= 20 (13.6 - 1)
= 252 cm

$\therefore Q=\frac{0.98\times \frac{\pi }{4}\times {30}^2\times \frac{\pi }{4}\times {15}^2}{\sqrt{{[\frac{\pi }{4}\times {30}^2]}^2-{[\frac{\pi }{4}\times {15}^2]}^2}}\times \sqrt{2\times 981\times 252}$

$=\frac{0.98\times {30}^2\times \frac{\pi }{4}\times {15}^2}{\sqrt{{30}^4-{15}^4}}\times \sqrt{2\times 981\times 252}$

$=125.76l/sec$