What is the difference between a refrigerator and heat pump? Expression for the performance factor for both if they are running on reversed Carton cycle.

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 In a heat engine, heat is transferred from a higher temperature level called source to a lower temperature level called sink. A heat pump is similar to a refrigerator. The only point of difference between the two is of the operating temperatures.

Difference between Refrigerator and Heat pumps

  1. Transfer of heat: Both the refrigerator and the heat pumps carry the heat from low temperature reservoir or the sink to the high temperature reservoir or source. The main purpose of the refrigerator is to chill or cool or freeze the substance, by maintaining very low temperature in the freezer. It absorbs the heat from the freezer or evaporator and throws it to the atmosphere which is at high temperature.

The main purpose of the heat pump is to heat the room during winter seasons or when the atmospheric temperature is very low. It absorbs the heat from the atmosphere which is at low temperature and throws it to the room which is at high temperature and which is to be heated.

    2. Location of the evaporator: In the refrigerator the evaporator is located in the freezer section. The evaporator absorbs the heat from the substance, which is to be cooled. In the heat pump the evaporator is located outside the room which is to be heated. The evaporator absorbs the heat, which is later thrown inside the room for heating it.

    3. Location of the condenser: In the refrigerator the condenser is located outside the refrigerator and it is exposed to the atmosphere. It is through the condenser that the heat is thrown to the atmosphere. In the heat pump the condenser is located inside the room and it acts as the heating devise.

   4. Working of evaporator and condenser: In the refrigerator the evaporator performs the main function of chilling or freezing, while the condenser performs the function of delivering the heat to the atmosphere. In the heat pump, it is the condenser that performs the main function of heating the room, while the evaporator performs the function of absorbing the heat from the atmosphere.



                                            
                                                                       p-V diagram




                                                                    T-s diagram

Since the co-efficient of performance (C.O.P) means the ratio of the desired effect in kJ/kg to the energy supplied in kJ/kg, therefore C.O.P in case of Carnot cycle run either as a refrigerating machine or a heat pump or as a heat engine will be as ...

1. For a reversed Carnot cycle refrigerating machine: 

              (C.O.P) ref     ͇   Heat extracted from the cold body/cycle
                                                    Work done per cycle


                                ͇      T 2 ⨯ pn               ͇       T 2     
                                    (T 1  x T 2) x pm       T 1 - T 2

2. For a Carnot cycle heat pump: 
     
     ( C.O.P) heat pump  ͇   Heat rejected to the hot body/cycle
                                               Work done per cycle
                                     

                                     ͇         T 1 ⨯ lm         ͇        T 1 ⨯ pn   
                                       (T 1 - T 2) ⨯ pn        (T 1 - T 2) ⨯ pn 

                                         
                                   ͇        T 2      
                                       T 1- T 2

                                ͇  1+         T 2     
                                           T 1 -T 2


3. For a Carnot cycle heat engine : 

      (C.O.P) heat engine   ͇     Work obtained / cycle     ͇       (T 1 - T 2) ⨯ pn 
                                              Work supplied / cycle                T 1 ⨯ lm




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