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1、Part 2. The Principles of Refrigeration ( 116 pages)Chapter 2. Thermodynamic Analysis of refrigeration cycle 2-1) The Laws of Thermodynamics and Their Relation to Refrigeration Thermodynamics are primarily concerned with two forms of energy: heat and work. Therefore Engineering Thermodynamics is the
2、 study of the interrelation between heat, work, and internal energy.There are two important concepts of thermodynamic analysis: System and Environment.A system （系统、体系）is defined as any quantity of matter or region of space to which attention is directed for purpose of analysis; and everything outsid
3、e the system boundary is referred to as the environment（环境）.1,2（1）The 0th Law of ThermodynamicsThe Zeroth Law of Thermodynamics states: 热平衡定律温度定义1. If two systems are each equal in temperature to a third system, then the temperatures of the two systems themselves are equal.2. If two closed systems (
4、together isolated), with different temperatures are brought into thermal contact, then the temperatures of the two systems will change to approach the same temperature. That is, the temperature of the system which is at a higher temperature will decrease and the temperature of the system with the lo
5、wer temperature will increase. They will eventually have the same temperature.热力学第零定律的重要性在于它给出了温度的定义和温度的测量方法。定律中所说的热力学系统是指由大量分子、原子组成的物体或物体系。它为建立温度概念提供了实验基础。这个定律反映出：处在同一热平衡状态的所有的热力学系统都具有一个共同的宏观特征，这一特征是由这些互为热平衡系统的状态所决定的一个数值相等的状态函数，这个状态函数被定义为温度。而温度相等是热平衡之必要的条件。（2）The 1st Law of Thermodynamics-能量守恒定律The
6、 energy of an isolated system remains constant. （isolated system孤立体系= 体系+环境）这里的环境：包括体系以外的全部冷源、热源和做功的机械Fig.1-2, Refrigeration and Heat PumpWithin an isolated system, where no other energy or material can enter or leave, energy can neither be created nor destroyed. Although energy cannot be created or
7、 destroyed, it can be transferred to work other forms of energy.The First Law of Thermodynamics can be expressed as a mathematical interpretation as (2-1)对一个循环来说， (2-2)In British System of Units, （abbr. British Thermal Unit）is still used as the unit of heat and inner energy, which was defined as the
8、 quantity of heat required to raise the temperature of one of water by from 63.to 64. The following relations exist.; (2-3)or Coefficient of Performance 性能系数 , is defined as the ratio of desired result to required input. for “refrigerator” (2-4a) for “heat pump” (2-4b)This values of may be larger th
9、an 100% for refrigerator or heat pump. And COP is expected to be as large as possible. （而热机的效率）（3）The 2nd Law of Thermodynamics -不可逆的自发过程；熵There are several alternate but equivalent ways to describe the 2nd Law:1. Heat Transfer: Heat flows spontaneously from a hot body to a cool body in absence of o
10、ther effects, not the opposite.2. Mass Transfer: Fluid flows spontaneously from a high pressure to low pressure in absence of other effects, not the opposite.3. Diffusion: Two gases, when placed in an isolated chamber, will mix uniformly throughout the chamber, but will not separate spontaneously on
11、ce mixed. 以上是3种不可逆的自发过程4. 4It is impossible to convert heat completely into useful work. 5. For an isolated system, any change over time of entropy S is either positive or zero, that is:熵的定义 (2-5)In the cases of refrigerator or heat pump, the heat is to be taken out from a cold body and transferred
12、into a hot body. According to the 2nd Law of Thermodynamics, heat Transfers from higher temperature to lower temperature is a spontaneous process, which can be reversed, but it will not reverse itself spontaneously. In order to reverse the process, i.e. heat transfers from lower temperature to highe
13、r temperature, some external inputs, energy or work, must be expended, as shown in Fig.1-2.To transfer of heat from a low-temperature medium to a high-temperature one requires special devices called refrigerators.（4）The 3rd Law of Thermodynamics 在0时，物质的熵为零。绝对零度不可达到。 There are several alternate but e
14、quivalent ways to describe the 3rd Law:1. The entropy of any pure substance in thermodynamic equilibrium approaches zero as the absolute temperature approaches zero.2. It is impossible to cool a body to absolute zero by any finite process. Although one can approach absolute zero as closely as one po
15、ssible, one cannot actually reach this limit.By liquefying and pumping on a container of helium-3, it is possible to produce a temperature of around 0.3 K.dilution refrigeration ：as low as 0.002 K.The lowest temperature produced for liquid helium is 90 micrkelvins.The adiabatic demagnetization and some other methods have been approached 0.001K or lower temperatures.2-2）The Refrigeration Cycle
