工程热力学与传热学(英文) 第8章 热量传递的基本方式.pdf

Heat Transfer Chapter 8 Basic Modes of Heat Transfer Chapter 8 Basic Modes of Heat Transfer Contents  Conduction heat transfer and Fourier’s law of one- dimensional steady state heat-conduction  Convection heat transfer and Newton’s law of cooling  Radiation heat transfer and Stefan-Boltzmann Law  Heat transfer processes Basic Conceptions of Heat Transfer （传热的基本概念） Heat Transfer （传热） Heat transfer is the science that seeks to predict the energy transfer that may take place between material bodies as a result of a temperature difference. （传热是物质在温度差的作用下所发生的热量传递过程） Whenever there is a temperature difference in a medium or between media, heat transfer must occur. Basic Modes of Heat Transfer （热量传递的基本方式） Conduction （热传导） Convection （热对流） Radiation （热辐射） The difference between thermodynamics and heat transfer （传热学和热力学的关系） Consider the cooling of a hot steel bar that Exampl is placed in a pail of water. e （水桶内灼热钢棒的冷却过程） Thermodynamics • To predict the final equilibrium temperature of the steel bar- water combination. （钢棒和水这一体系最终的平衡温度） • To predict the energy transferred during the process. Heat transfer • To tell how long it takes to reach this equilibrium condition （需要多长时间达到平衡状态, 即热传播的速率） • To predict the temperature of both the bar and the water as a function of time. （钢棒和水的温度随时间的变化规律） 8-1 Conduction heat transfer （热传导） 8-1-1 Conduction Conduction is the transfer of energy from the more energetic particles of a substance to the adjacent less energetic ones as a result of interactions between the particles. 物体的各部分之间不发生相对位移时，依靠分子、 说 原子、自由电子等微观粒子的热运动而进行的热 明 量传递过程。  Conduction can take place in solids, liquids , or gases.