02第二章 想气体的性质.ppt

第二章 理想气体的性质Chapter 2. Properties of Ideal Gas ;工程热力学的两大类工质;实际气体的特点 Characteristics of real gases includes: 由大量分子组成(consists of large quantities of molecular) 分子做无规则运动(molecules take random movement continuously) 分子间有作用力(interaction force among molecules ) 分子本身有体积(the volume of molecules) 以上特点决定了实际气体的性质很复杂。; 1. 两点假设 (Assumptions) 忽略分子的容积 (The volume of the gas molecule is negligible.)。 忽略分子之间的作用力 (The interaction forces between molecules are negligible);;哪些气体可当作理想气体;2.理想气体状态方程式 Equation of state for ideal gas (1). For 1 1kg working gas, Pv=RT P:绝对压力(absolute pressure )，Pa。 v:比容 (specific volume ), m3/kg。 T：热力学温度(Kelvin Temperature ),K。 R：气体常数(Gas constant) 与气体的种类有关。 (2) For m kg working gas, mPv=mRT or PV=mRT ; 摩尔质量(molar mass): the mass of 1mol substance (1mol 物质的质量)，M 摩尔体积(molar volume): the volume of 1mol substance (1mol物质占有的体积)，Vm。 阿伏假德罗定律(Avogadro’s hypothesis): 在同温同压下，各种气体的摩尔体积都相等。; Vm=Mrv/1000， Mr：分子量。 MrPv= MrRT PVm= RmT ; Rm与R的区别;(4) For n Mole working gas For n mol gas, PV=nRmT ;理想气体 (Definition of Ideal Gas)：;计算时注意事项实例 Attentions: ;The volume of the room is V= 4m× 5m× 6m =120 m3 The mass of air in a room is determined from the ideal gas relation to be ;Example. Determine the mass of air in a room whose dimensions are 4m× 5m× 6m at 100kPa and 25℃ Solution The mass of air in a room is to be determined. Analysis Air at specified conditions can be treated as an ideal gas. From table, the gas constant of air is R=0.287 kJ/kg.K and the absolute temperature is T=25+273.15=298.15 K. ;§3.2 比热和热容 Specific Heats and Heat Capacity 1.比热容（比热）的定义 Definition of Specific heat?? 将单位物量的物质温度升高1K所需加入的热量。 The energy required to raise the temperature of a unit quantity of a substance by one degree ; 2.基于不同物量单位的三种比热 (Three kinds of Specific heats based on different quantity