Question

The procedure to be followed in solving for discharge in a simple pipe problem, when $h_f,L,D,V\text{and}\epsilon \text{are given is to}$
[Note: Re is Reynolds number,
f = friction coefficient,
$\frac{\epsilon }{D}=\text{relative roughness}$
V = velocity]

• A. assume f, compute: V, Re,$\frac{\epsilon }{D}$ and calculate f; and repeat if necessary
• B. assume Re, compute f, check $\frac{\epsilon }{D}$
• C. assume V, compute Re and calculate f, V again
• D. assume $\epsilon \text{compute V, Re, and calculate f}$

Answer 1

The correct option is C assume V, compute Re and calculate f, V again

$\text{(i) Assume f(It is function of Re and}\frac{\epsilon }{D}$

$\text{Head Loss,}{h}_f=f\frac{L}{D}\frac{V^2}{2g}$


(ii) From head loss formula compute V.

$\text{(iii) Find}\frac{\epsilon }{D}\text{from given data.}$

$\text{Reynolds number,}Re=\frac{VD}{\nu }$

(iv) Now again find 'f'. (say from Colebrook equation)

(v) If the computed 'f' is same as assumed 'f', then stop, otherwise repeat the procedure with new value of 'f'.