July 17, Week 7 Today: Heat Pumps and Engines, Chapter 11 Final Homework #7 now available. Due Monday at 5:00PM. Thermodynamics 21st July 2014
First Law of Thermodynamics First Law of Thermodynamics: W + Q = ∆ E th Thermodynamics 21st July 2014
First Law of Thermodynamics First Law of Thermodynamics: W + Q = ∆ E th There are two ways to change the thermal energy of on object - Work being done to the object ( W ) and heat ( Q ) Thermodynamics 21st July 2014
First Law Signs In applying the first law of thermodynamics, we have to think about the “system” = the object that is of interest. Everything else is called the environment Thermodynamics 21st July 2014
First Law Signs In applying the first law of thermodynamics, we have to think about the “system” = the object that is of interest. Everything else is called the environment Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature remains constant) Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature 0 − − − remains constant) Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature 0 − − − remains constant) An expanding gas inflates a balloon Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature 0 − − − remains constant) An expanding gas inflates a balloon ? ? ? − Heat depends on how the gas expands Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature 0 − − − remains constant) An expanding gas inflates a balloon ? ? ? − Heat depends on how the gas expands After 30 minutes of baking, a pan is removed from the oven and sits on a counter Thermodynamics 21st July 2014
First-Law Followup Process Q ∆ E th ∆ T W Steam is used to spin a turbine. (Assume the turbine’s temperature 0 − − − remains constant) An expanding gas inflates a balloon ? ? ? − Heat depends on how the gas expands After 30 minutes of baking, a pan is removed from the oven and sits on a 0 − − − counter Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th The system is the engine Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th The system is the engine W = − W out Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th The system is the engine W = − W out Q = Q H − Q C Thermodynamics 21st July 2014
Heat Engine Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th The system is the engine W = − W out Q = Q H − Q C ∆ E th = 0 (In a perfect situation, the engine simply uses heat to do work. It doesn’t absorb the heat itself.) Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th − W out + Q H − Q C = 0 Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th − W out + Q H − Q C = 0 W out = Q H − Q C Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th − W out + Q H − Q C = 0 W out = Q H − Q C Better Form: Q H = W out + Q C Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th − W out + Q H − Q C = 0 W out = Q H − Q C Better Form: Q H = W out + Q C Efficiency: e = W out Q H Thermodynamics 21st July 2014
Heat Engine II Heat Engine - Device that uses the transfer of heat from a higher temperature to lower temperature to extract work W + Q = ∆ E th − W out + Q H − Q C = 0 W out = Q H − Q C Better Form: Q H = W out + Q C Efficiency: e = W out Q H e = Q H − Q C = 1 − Q C Q H Q H Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? H OT 100 J 75 J C OLD Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT 100 J 75 J C OLD Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% 100 J 75 J C OLD Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% 100 J 50% (c) 75 J C OLD Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% 100 J 50% (c) (d) 75% 75 J C OLD Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% 100 J 50% (c) (d) 75% 75 J C OLD (e) 100% Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% 100 J 50% (c) (d) 75% 75 J C OLD (e) 100% Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% Q H = 100 J 50% (c) W out (d) 75% Q C = 75 J C OLD (e) 100% Thermodynamics 21st July 2014
Heat Engine Exercise What is the efficiency ( W out /Q H ) of the following heat engine? (a) 0% H OT (b) 25% Q H = 100 J 50% (c) W out = 25 J (d) 75% Q C = 75 J C OLD (e) 100% Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot W + Q = ∆ E th = 0 Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot W + Q = ∆ E th = 0 W = W in Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot W + Q = ∆ E th = 0 W = W in Q = Q C − Q H Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot W + Q = ∆ E th = 0 W = W in Q = Q C − Q H W in + Q C − Q H = 0 ⇒ W in + Q C = Q H Thermodynamics 21st July 2014
Heat Pump Heat Pump - Device that does work in order to move heat from cold to hot W + Q = ∆ E th = 0 W = W in Q = Q C − Q H W in + Q C − Q H = 0 ⇒ W in + Q C = Q H Coefficient of Performance: COP = Q C Q C = W in Q H − Q C Thermodynamics 21st July 2014
Heat Pump Exercise If the COP ( Q C /W in ) of the following heat pump is 2 , how much heat was removed from the cold reservoir and how much heat was released to the hot reservoir? H OT 20 J C OLD Thermodynamics 21st July 2014
Heat Pump Exercise If the COP ( Q C /W in ) of the following heat pump is 2 , how much heat was removed from the cold reservoir and how much heat was released to the hot reservoir? (a) Q C = 10 J , Q H = 30 J H OT 20 J C OLD Thermodynamics 21st July 2014
Heat Pump Exercise If the COP ( Q C /W in ) of the following heat pump is 2 , how much heat was removed from the cold reservoir and how much heat was released to the hot reservoir? (a) Q C = 10 J , Q H = 30 J H OT (b) Q C = 10 J , Q H = 10 J 20 J C OLD Thermodynamics 21st July 2014
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