Chapter 10 - Vapor and combined power cycles. In Chapter 9 we discussed gas power cycles for which the working fluid remains a gas throughout the entire cycle. In this chapter, we consider vapor power cycles in which the working fluid is alternatively vaporized and condensed. We also consider power generation coupled with process heating called cogeneration. | Chapter 10 Vapor and Combined Power Cycles Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles We consider power cycles where the working fluid undergoes a phase change. The best example of this cycle is the steam power cycle where water (steam) is the working fluid. Carnot Vapor Cycle The heat engine may be composed of the following components. The working fluid, steam (water), undergoes a thermodynamic cycle from 1-2-3-4-1. The cycle is shown on the following T-s diagram. The thermal efficiency of this cycle is given as Note the effect of TH and TL on th, Carnot. The larger the TH the larger the th, Carnot The smaller the TL the larger the th, Carnot To increase the thermal efficiency in any power cycle, we try to increase the maximum temperature at which heat is added. Reasons why the Carnot cycle is not used: Pumping process 1-2 requires the pumping of a . | Chapter 10 Vapor and Combined Power Cycles Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles We consider power cycles where the working fluid undergoes a phase change. The best example of this cycle is the steam power cycle where water (steam) is the working fluid. Carnot Vapor Cycle The heat engine may be composed of the following components. The working fluid, steam (water), undergoes a thermodynamic cycle from 1-2-3-4-1. The cycle is shown on the following T-s diagram. The thermal efficiency of this cycle is given as Note the effect of TH and TL on th, Carnot. The larger the TH the larger the th, Carnot The smaller the TL the larger the th, Carnot To increase the thermal efficiency in any power cycle, we try to increase the maximum temperature at which heat is added. Reasons why the Carnot cycle is not used: Pumping process 1-2 requires the pumping of a mixture of saturated liquid and saturated vapor at state 1 and the delivery of a saturated liquid at state 2. To superheat the steam to take advantage of a higher temperature, elaborate controls are required to keep TH constant while the steam expands and does work. To resolve the difficulties associated with the Carnot cycle, the Rankine cycle was devised. The steam power plant is composed of several distinct componets. Steam generator or boiler Turbine and electric generator Condenser and cooling water system Pumps Rankine Cycle The simple Rankine cycle has the same component layout as the Carnot cycle shown above. The simple Rankine cycle continues the condensation process 4-1 until the saturated liquid line is reached. Ideal Rankine Cycle Processes Process Description 1-2 Isentropic compression in pump 2-3 Constant pressure heat addition in boiler 3-4 Isentropic expansion in turbine 4-1 Constant pressure heat rejection in condenser The T-s diagram for the Rankine cycle is
