热力学与统计物理 金晓峰 复旦大学物理系 2005-3-16
2021/8/21 1 热力学与统计物理 金晓峰 复旦大学物理系 2005-3-16
Carnot's ideas
Carnot’s ideas Q W
2g-1
Carnot's Cycle FIGURE 20-5 The Carnot cycle Heat In a cyo the cycle for the Carnot engine begins at point expansion diagram (1)The gas is first panded isothermally, with addition of heat QH, along the path ab at temperature TH. (2)Next d→ the gas expands adiabatically Adiabatic Adiabatic from b to c-no heat is exchanged, compression lexpansion but the temperature drops to TL (3) B)The gas is then compressed at co stant temperature Ti, path c to d 0=0 and heat e. flows out. (4)Finally the gas is compressed adiabatically. path da, back to its original state. No Carnot engine actually exists, but as a theoretical engine it played c→d Isothermal Important role in the development of thermodynamics compression
Carnot’s Cycle
Carnot's theorem <All reversible engines operating between the same two constant temperatures tH and t have the same efficienc y An y irreversible engine operating between the same two fixed temperatures will have an efficiency less than this
“All reversible engines operating between the same two constant temperatures TH and TL have the same efficiency. Any irreversible engine operating between the same two fixed temperatures will have an efficiency less than this.” Carnot’s theorem
Clapeyron's Graph FIGURE 20-5 The Carnot cycle Heat In a cyo the cycle for the Carnot engine Isothermal begins at point a on this Pl expansion diagram (1)The gas is first panded isothermally, with addition of heat @), along path ab at temperature TH. (2)Next d→ the gas expands adiabatically Adiabatic Adiabatic from b to c-no heat is exchanged, compression lexpansion but the temperature drops to TL (3) B)The gas is then compressed at co stant temperature Ti, path c to d d 0=0 and heat e. flows out. (4)Finally the gas is compressed adiabatically. path da, back to its original state. No Carnot engine actually exists, but as a theoretical engine it played c→d Isothermal Important role in the development of thermodynamics compression
Clapeyron’s Graph
High Clausius, dea temperature, TH Engine Ow temperature, FIGURE 20-1 Schematic diagram of energy transfers for a heat engine
Clausius’ Idea
Clausius statement Not possible Q
Clausius statement Not possible
SECOND LAW OF THERMODYNAMICS (Kelvin-Planck statement h gh temperature leHI Engine FIGURE 20-4 Schematic diagram of a hypothetical perfect heat engine in which all the heat input would be used to do work
Clausius' ideas 热力学第一定律 8Q=du sW =dU t pdv
Q = dU + W = dU + pdV 热力学第一定律 Clausius’ ideas
