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# ch11-lec - Learning Objectives 1 Introduce the concepts of...

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Learning Objectives 1. Introduce the concepts of refrigerators and heat pumps and the measure of their performance. 2. Evaluate the maximum possible coefficient of performance for refrigerators and heat pumps based on the reversed Carnot cycle. 3. Analyze the ideal vapor-compression refrigeration cycle. 4. Analyze the actual vapor-compression refrigeration cycle.

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11-1 Refrigerators and Heat Pumps Refrigerator A device that transfers heat from a low- temperature region to a high-temperature region The objective of a refrigerator is to maintain the refrigerated space at a low temperature by removing heat from it Refrigerant The working fluid used in a refrigeration cycle Heat Pump Another device that transfers heat from a low- temperature region to a high-temperature region The objective of a heat pump is to maintain a heated space at a high temperature
11-1 Refrigerators and Heat Pumps Coefficient of Performance (COP) A measure of performance for refrigerators and heat pumps Tons of Refrigeration One ton of refrigeration is equivalent to 211 kJ/min or 200 Btu/min in net, R Input Work Effect Cooling COP W Q L = = Input Required Output Desired COP = in net, HP Input Work Effect Heating COP W Q H = = 1 COP COP R HP + =

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11-2 The Reversed Carnot Cycle Overview The Carnot cycle consists of four totally reversible processes: two isothermal and two isentropic The Carnot cycle has the maximum thermal efficiency for a given maximum and minimum cycle temperature It serves as a standard against which actual cycles can be compared All four processes that comprise the Carnot cycle can be reversed Reversing the direction of the processes also reverses the direction of any heat and work interactions The result is called the reversed Carnot cycle : a cycle that operates in the counter-clockwise direction on a T-s diagram
11-2 The Reversed Carnot Cycle Carnot Refrigerator or Carnot Heat Pump A refrigerator or heat pump that operates on a reversed Carnot cycle

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