tailieunhanh - Lecture Thermodynamics: An engineering approach (8/e): Chapter 5 (Part 1) - Yunus A. Çengel, Michael A. Boles

Chapter 5 (Part 1) - Mass and energy analysis of control volumes. We start this chapter with the development of the general conservation of mass relation for control volumes, and we continue with a discussion of flow work and the energy of fluid streams. | Chapter 5 Part 1 Mass and Energy Analysis of Control Volumes Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles Conservation of Energy for Control volumes The conservation of mass and the conservation of energy principles for open systems or control volumes apply to systems having mass crossing the system boundary or control surface. In addition to the heat transfer and work crossing the system boundaries, mass carries energy with it as it crosses the system boundaries. Thus, the mass and energy content of the open system may change when mass enters or leaves the control volume. Thermodynamic processes involving control volumes can be considered in two groups: steady-flow processes and unsteady-flow processes. During a steady-flow process, the fluid flows through the control volume steadily, experiencing no change with time at a fixed position. A heat exchanger, the heater . | Chapter 5 Part 1 Mass and Energy Analysis of Control Volumes Study Guide in PowerPoint to accompany Thermodynamics: An Engineering Approach, 8th edition by Yunus A. Çengel and Michael A. Boles Conservation of Energy for Control volumes The conservation of mass and the conservation of energy principles for open systems or control volumes apply to systems having mass crossing the system boundary or control surface. In addition to the heat transfer and work crossing the system boundaries, mass carries energy with it as it crosses the system boundaries. Thus, the mass and energy content of the open system may change when mass enters or leaves the control volume. Thermodynamic processes involving control volumes can be considered in two groups: steady-flow processes and unsteady-flow processes. During a steady-flow process, the fluid flows through the control volume steadily, experiencing no change with time at a fixed position. A heat exchanger, the heater core from a 1966 289 V8 Mustang, is another example of an open system. Cooling water flows into and out of the tubes and air is forced through the fin sturucture. Photo by M. A. Boles A hair drier is an example of a one entrance, one exit open system that receives electrical work input to drive the fan and power the resistance heater. Photo by M. A. Boles Let’s review the concepts of mass flow rate and energy transport by mass. One should study the development of the general conservation of mass presented in the text. Here we present an overview of the concepts important to successful problem solving techniques. Mass Flow Rate Mass flow through a cross-sectional area per unit time is called the mass flow rate . Note the dot over the mass symbol indicates a time rate of change. It is expressed as where is the velocity normal to the cross-sectional flow area. If the fluid density and velocity are constant over the flow cross-sectional area, the mass flow rate is where is