Chapter 8, Problem 8.45CU

Figure 5.15 in the text gives a schematic of a Carnot cycle operating with a H2O liquid/vapor with a steady flow (constant mass flow rate) through each component. From the properties given below your cycle may or may not be a Carnot cycle. Kinetic energy and potential energy changes can be ignored in this problem. The cycle conditions are as follows: Process 4 – 1: constant pressure at 300 kPa from saturated liquid to saturated vapor Process 2 – 3: constant pressure at 30 kPa from x2 = 87.9% to x3 = 10.9% a) Determine the thermal efficiency using steam table data b) Compare the result of part a) with the Carnot efficiency using the boiler and condenser temperatures. c) State if the cycle is internally reversible, irreversible or impossible

An open feedwater heater is a direct-contact heat exchanger used in vapor power plants. Shown in the figure below are feedwater heater with H20 operating data for an open 31 °C as the working fluid operating at steady state, where T1 P2=3 bar = 0.92 +2 P3 3 bar Saturated liquid m380 kg/s T, PT=3 bar Open feedwater 3 heater Ignoring stray heat transfer from the outside of the heat exchanger to its surroundings and kinetic and potential energy effects, determine the rate of entropy production, in kW/K.

6.110 Figure P6.110 shows a simple vapor power plant operating at steady state with water as the working fluid. Data at key locations are given on the figure. The mass flow rate of the water circulating through the components is 109 kg/s. Stray heat transfer and kinetic and potential energy effects can be ignored. Determine a. the net power developed, in MW. b. the thermal efficiency. c. the isentropic turbine efficiency. t2 d. the isentropic pump efficiency. e. the mass flow rate of the cooling water, in kg/s. f. the rates of entropy production, each in kW/K, for the turbine, condenser, and pump. P = 100 bar T = 520°C %3D Power out Turbine P2 = 0.08 bar 2 = 90% %3D Steam Cooling water in at 20°C generator Condenser Pa= 100 bar T= 43°C Cooling water out at 35°C 4. Pump 3 P3 0.08 bar Saturated liquid Power in FIGURE P6.110 2. www