Clausius statement of the Second Law of Thermodynamics: It is impossible to construct a device that, operating in a cycle, has no effect other than the transfer of heat from a cooler to a hotter body. Thus, the Clausius statement tells us that heat will not flow from cold to hot regions without assistance of outside agents. The devices that provide this assistance are called refrigerators and heat pumps. The working of refrigerator and heat pump is shown in Figure 8.1. The distinction between refrigerator and heat pump is one of purpose more than technique. The refrigeration unit transfers heat from cold to hot regions for the purpose of cooling the cold region while the heat pump does the same thing with the intent of heating the hot region.
Figure 8.1 Working of Refrigerator and Heat Pump
The performance of the refrigerators and heat pump is expressed in terms of the Coefficient of Performance (COP), which is defined as
Tones of Refrigeration (TR): The cooling effect produced is quantified as tons of refrigeration, also referred to as ‘chiller tonnage’.
where Q Mass flow rate of coolant in kg/h
Cp Coolant specific heat in kcal/kg °C
Ti Inlet temperature of coolant to evaporator (chiller) in °C
To Outlet temperature of coolant from evaporator (chiller) in °C
1 TR of refrigeration = 3,024 kcal/h heat rejected
Power of refrigerator = QL/C.O.P
Capacity of refrigeration plant = Heat removal rate in tons
The heat absorbed from a body or space to be cooled, equivalent to the latent heat of fusion of 1 ton of ice from 0°C in 24 hours is called 1 ton of refrigeration.
Leave a Reply