Ncees 2001 fluids #528

Question is asking hp required to drive a 2 pump system. First pump has a dp of 93.5 psi, mass flow rate of 340 Lbm/sec, efficiency of 60%. Second pump has dp of 956 psi, mass flow rate of 289 Lbm/sec, efficiency of 60%. Using pump hp equations and efficiency (delta p * mass flow rate/238.3*efficiency), I get 222.2 hp for pump 1 and 1932 hp for pump 2 for a total of 2155 hp. Answer in the book says 2370 hp. Any idea where I am going wrong?

You ignored the liquid densities at each pump. At pump 1 you need the density at p = 0.5 psi while at pump 2 you need the density at p = 94 psi. You can simply use the specific volume from the Sat. Water at pressure chart.

Thanks!