Chapter 8, Problem 8.44P

Obtain the heat transfer to the engine Qh, the work done by the engine W, and the efficiency e.

1. Consider the scheme shown in the figure T, = 200°C for producing fresh water from salt water. The conditions are as shown in the figure. Assume that the properties of salt water are the same as those of pure water. The outer walls of heat exchanger, Heatem flash evaporator and pump can be considered as thermally insulated. The pressure drop of a continuous stream across the heat exchanger and heater are negligible. exc (ins a) Determine the ratio ("7/m.), which gives the mass fraction of salt water purified. 2 = 70 b) Determine the specific pump work, in kJ per kg of T2= liquid seawater. Liquid seawater in c) Determine the specific heat input for the heater, in kJ per kg of liquid seawater. d) Determine the specific entropy production for the flash evaporator and the heater, in kJ/K per kg of liquid seawater.

4. The condensing pressure for a Rankıne engine Is I Calculate the net work for 1 kg of steam and the thermal efficiency when the steam at the beginning of expansion is at 50 bar and (a) saturated, (b) 350°C, and (c) 640°C. Ans. (a) 627.2 kJ/kg, 26.4%; (b) 727.3 kJ/kg, 27.5%; (c) 1079.49 kJ/kg, 32.35% ot 2 15 MPà