Chapter 6：热机

Summary

Second Law of themodinamie：Certain direction

Thermal energy reservoirs / heats reservoirs.热库:

  • can absorb or reject finite s aments of heat isothermally (等温吸收一定热量)

heat engine 热机

热机效率

\[ y_{\text {th }}=\frac{W_{\text {net, out }}}{Q_{H}}=1-\frac{Q_{L}}{Q_{H}} \]

Refrigerators 冷机

refrigerator 制冷

  • COP (coefficient of performance)

\[ \operatorname{COP}_{R}=\frac{Q_L}{W_{net, in}}=\frac{1}{Q_H / Q_L-1} \]

heat Pump 热泵

\[ {C O P_{H R}}=\frac{Q_n}{ W_{net. in}}=\frac{1}{1-Q_L / Q_H} \]

原理

Kelvin -Planck

  • No Heat Engine can produis a net amount of work whole exchanging heat with a sigh reservoirs only.
  • 任何热机不能在仅与一个热源进行热交换的情况下产生净功率。

Reversible

  • Si both the system and the surroundings can be restored. to. thar original condition:
  • 如果系统和周围环境都能恢复到原来的状态。

Cannot cycle

reversible 可逆

Carnot principal

\[ \left(\frac{Q_{H}}{Q_{L}}\right)_{\text {rev }}=\frac{T_{H}}{T_{L}} \]

Carnot heat engine

$$

\[\begin{aligned}&\eta_{\text {rev. th }}=1-\frac{T_{L}}{T_{H}}\\ & COP_{R,{\text {rev }}}=\frac{1}{T_{H} / T_{L}-1} \\ & COP_{HP,rev} =\frac{1}{1-T_{L} / T_{H}} \end{aligned}\]

$$

Scale 热力学温标

  • 开氏温标（Kelvin scal）