1. 1 Second Law of Thermodynamics Engines and Refrigerators

2. 2 Heat Engine Any device that transforms heat partly into work or mechanical energy *working substance – matter inside the engine which undergoes inflow and outflow of heat, expansion and compression, and sometimes phase change

3. 3 how it works 1.Working substance absorbs heat from the hot reservoir 2.Performs some mechanical work 3.Discards the remaining energy in the form of heat into the cold reservoir *cyclic process Young

4. 4 1 st law applied to WS Q H >0: WS absorbs heat from HR Q C <0: WS discards heat into CR W>0: WS performs mechanical work U=0 after one cycle 1 st law: Q = U + W Q net = W Q H + Q C = W |Q H | - |Q C | = |W|

5. 5 thermal efficiency e = W/Q H = (|Q H |-|Q C |)/|Q H | = 1 –(|Q C |/Q H |)

6. 6 Refrigerator takes heat from a cold place and gives of heat to a warmer place requires a net input of mechanical work working substance – refrigerant fluid cold reservoir – inside of refrigerator hot reservoir – outside of refrigerator

7. 7 how it works 1.fluid absorbs heat from the cold reservoir 2.work is done on the fluid 3.energy from heat transfer and work done is discarded into the hot reservoir *cyclic process Young

8. 8 1.the fluid in the evaporator coil is colder than the inside of the ref, so it absorbs heat 2.the compressor takes in fluid and compresses it adiabatically (work is done on the fluid) 3.fluid is delivered to condenser at high pressure, fluid temperature is higher than that of surrounding air, fluid gives of heat and condenses 4.fluid expands adiabatically (expansion valve) into the evaporator and cools considerably Young

9. 9 1 st law applied to fluid Q C >0: fluid absorbs heat from CR Q H <0: fluid discards heat into HR W<0: work is done on fluid U=0 after one cycle 1 st law: Q = U + W Q net = W Q H + Q C = W -|Q H | + |Q C | = -|W| |Q C | + |W| = |Q H |

10. 10 coefficient of performance K = |Q C |/|W| = |Q C |/(|Q H |-|Q C |)

11. A heat engine takes in 1200 J of heat from the high-temperature heat source in each cycle and does 400 J of work in each cycle. How much heat is released into the environment in each cycle? A.400 J B.800 J C.1200 J D.1600 J

12. A heat engine takes in 1200 J of heat from the high-temperature heat source in each cycle and does 400 J of work in each cycle. What is the efficiency of this engine? A.¼ B.1/3 C.3 D.4

13. In one cycle, a heat engine takes in 900 J of heat from a high- temperature reservoir and releases 600 J of heat to a lower- temperature reservoir. How much work is done by the engine in each cycle? A.300 J B.600 J C.900 J D.1500 J

14. In one cycle, a heat engine takes in 900 J of heat from a high- temperature reservoir and releases 600 J of heat to a lower- temperature reservoir. What is its efficiency? A.3/9 B.6/9 C.3/15 D.6/15

15. In one cycle a heat engine does 400 J of work and releases 500 J of heat to a lower-temperature reservoir. How much heat does it take in from the higher- temperature reservoir? A.100 J B.400 J C.500 J D.900 J

16. In one cycle a heat engine does 400 J of work and releases 500 J of heat to a lower-temperature reservoir. What is the efficiency of the engine? A.4/9 B.4/5 C.5/9 D.1

17. In one cycle, a heat engine takes in 1000 J of heat from a high- temperature reservoir, releases 600 J of heat to a lower- temperature reservoir, and does 400 J of work. What is its efficiency? A.¼ B.1/3 C.2/5 D.3/5

18. A heat pump takes in 300 J of heat from a low-temperature reservoir in each cycle and uses 150 J of work per cycle to move the heat to a higher- temperature reservoir. How much heat is released to the higher-temperature reservoir in each cycle? A.150 J B.300 J C.450 J D.600 J

19. A heat pump takes in 300 J of heat from a low-temperature reservoir in each cycle and uses 150 J of work per cycle to move the heat to a higher-temperature reservoir. What is the coefficient of performance (COP)? A.1/3 B.1/2 C.2 D.3

20. In each cycle of its operation, a refrigerator removes 18 J of heat from the inside of the refrigerator and releases 30 J of heat into the room. How much work per cycle is required to operate this refrigerator? A.12 J B.18 J C.30 J D.48 J

21. In each cycle of its operation, a refrigerator removes 18 J of heat from the inside of the refrigerator and releases 30 J of heat into the room. What is the COP of this refrigerator? A.18/12 B.30/12 C.12/30 D.18/30