tailieunhanh - Lecture Thermodynamics: An engineering approach (8/e): Chapter 9 - Yunus A. Çengel, Michael A. Boles

Chapter 9 - Gas power cycles. The objectives of Chapter 9 are to: Evaluate the performance of gas power cycles for which the working fluid remains a gas throughout the entire cycle; develop simplifying assumptions applicable to gas power cycles, review the operation of reciprocating engines, analyze both closed and open gas power cycles,. | Chapter 9 Gas Power Cycles Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles Our study of gas power cycles will involve the study of those heat engines in which the working fluid remains in the gaseous state throughout the cycle. We often study the ideal cycle in which internal irreversibilities and complexities (the actual intake of air and fuel, the actual combustion process, and the exhaust of products of combustion among others) are removed. We will be concerned with how the major parameters of the cycle affect the performance of heat engines. The performance is often measured in terms of the cycle efficiency. Carnot Cycle The Carnot cycle was introduced in Chapter 5 as the most efficient heat engine that can operate between two fixed temperatures TH and TL. The Carnot cycle is described by the following four processes. Carnot Cycle Process Description 1-2 Isothermal . | Chapter 9 Gas Power Cycles Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles Our study of gas power cycles will involve the study of those heat engines in which the working fluid remains in the gaseous state throughout the cycle. We often study the ideal cycle in which internal irreversibilities and complexities (the actual intake of air and fuel, the actual combustion process, and the exhaust of products of combustion among others) are removed. We will be concerned with how the major parameters of the cycle affect the performance of heat engines. The performance is often measured in terms of the cycle efficiency. Carnot Cycle The Carnot cycle was introduced in Chapter 5 as the most efficient heat engine that can operate between two fixed temperatures TH and TL. The Carnot cycle is described by the following four processes. Carnot Cycle Process Description 1-2 Isothermal heat addition 2-3 Isentropic expansion 3-4 Isothermal heat rejection 4-1 Isentropic compression Note the processes on both the P-v and T-s diagrams. The areas under the process curves on the P-v diagram represent the work done for closed systems. The net cycle work done is the area enclosed by the cycle on the P-v diagram. The areas under the process curves on the T-s diagram represent the heat transfer for the processes. The net heat added to the cycle is the area that is enclosed by the cycle on the T-s diagram. For a cycle we know Wnet = Qnet; therefore, the areas enclosed on the P-v and T-s diagrams are equal. We often use the Carnot efficiency as a means to think about ways to improve the cycle efficiency of other cycles. One of the observations about the efficiency of both ideal and actual cycles comes from the Carnot efficiency: Thermal efficiency increases with an increase in the average temperature at which heat is supplied to the system or with a decrease in the average