A heat exchanger heats oil using highpressure steam Steam en

A heat exchanger heats oil using high-pressure steam. Steam enters the heat exchanger at 500 psia and 700 F and leaves at 450 psia and 500 F with a mass flow rate= 22 lbm/s. Oil enters at a flow rate of 50 lbm/s and experiences a temperature increase of 70 F. Assuming the oil has a constant specific heat cp= 0.45 Btu/lbm*R, what is the efficiency of the heat exchanger? (%)

Solution

enthalpy of steam at 500 psia and 700 F = 1360 BTU / lb

enthalpy of steam at 450 psia and 500 F = 1240 BTU / lb

Heat available with steam   = mass flow rate * (1360 - 1240)   = 22 * (1360 - 1240) = 2640 BTU / s

Heat gained by Oil = m * Cp * (Tf - Ti)   = 0.45 * 50 * 70   = 1575 BTU/s

Efficiency of heat exchanger   = Heat gained / heat available   = 1575 / 2640   = 59.66 %