Question

A precision flow adjustment valve (needle valve) is used to control the flow of steam in a ½ inch diameter (0.0127 m) pipe that is 60 m long. The pressure drop across the pipe is 16.71 kPa when the valve is half closed. Determine the loss coefficient, KL , of the valve. The average volumetric flow rate through the pipe is 0.00206 m³/s.

(Steam at 200 kPa and 300 C, 0.086*10^-3 Pa*s)

Answer 1

We are given a precision flow adjustment valve (needle valve) is used to control the flow of steam,

The diameter of the pipe as D = 0.0127 m

Cross sectional area of the pipe,

Length of pipe, L = 60 m

Pressure drop across the pipe is given = 16.71 kPa , when the valve is half closed.

The volumetric flow rate through the pipe is q=0.00206 m3/s

The viscosity of the steam is =0.086*10-3 Pa.s

Lets assume the steam to be ideal gas to calculate its density,

We know calculate velocity of the steam throught the pipe,

Let's see wether the flow is in turbulent or laminar region,

so,

Which is below 2100, So the flow of steam is laminar so we can use the following formulae to calculate the fanning friction factor,

Now we can use the bernoulli's eqn. to find the loss coeffecient of valve,

Kv represents the loss coeffecient of the valve.

So,

So the loss coffecient of a precision flow adjustment valve (needle valve) when the valve is half closed is 1.078