Answer to Question #206536 in Chemical Engineering for raghad

Question

] n-heptane (ρ = 39.9 lbm/ft³) at 25 ^oC is being pumped from one tank to another as shown in the figure below. All pipes have 3 in internal diameters. Assume that the overall frictional loss in the pipes is given by:

 

      V = average velocity in the pipe, ft/s

 

If the average velocity in the pipe V is 25 ft/s, determine the following:

a)  The power required to drive the pump in kW knowing that it has an efficiency of 75%

b) The pressure at the inlet of the pump (in psia)

c)  NPSH available at the pump inlet knowing that the vapor pressure of n-heptane at 25 ^oC is 10.3 psia. Comment on your result. For simplicity you may ignore the friction in the short length of pipe between the supply tank and the inlet of the pump.

d)  The pressure at the pump exit (in psia)

Answer 1

i) Power = $\Delta$ PQ

and Q = $\pi$ /4 x D²V and Δ P = 2f(L/D)pV²

Q = 3.142/4 x 3² x 25 = 176.7375

Δ P = 2 x 1/75 (14.78/3) x 25² x 39.9 = 3276.23

power = 176. 7375 x 3276.23 = 579.032kW

ii) Pressure at the inlet = hpg

= 4.5 x10 x 39.9 = 1795.5pasi

P = 1795.5