Question

10) An open channel flow in a hydraulic lab is designed to line artificially with corrugated metal. To keep the shape and all other conditions the same, the designer can simply replace the corrugated metal with brass and the flow rate (Q, in m/s) of the channel will a. Decrease by 50% b. Increase by 50% c. Double d. Quadruple

Answer 1

Answer

The correct a answer of this question is option number C.

means flow rate will be double

Explaination:

In case of open channels flow the flow rate is given as below

AR2/3 1/2 n

This equation is manning equation and n is known as the manning coefficient.

Manning cofficient is different for different materials

Value of n for corrugated material and brass is given below

n for corrugated metal: .022

n for brass: .011

here S is hydraulic gradient which is generally based on bed slope.

So as given all the other parameters remains same as only manning cofficient will change so we as we can also see that the manning cofficient of brass is half of that of corrugated metal so from flow rate equation we can say that as the manning number is half so the flow rate will be double as flow rate is inversely proportional to manning number