Answer:
Heat transferred from the refrigerated space = 95.93 kJ/kg
Work required = 18.45 kJ/kg
Coefficient of performance = 3.61
Quality at the beginning of the heat addition cycle = 0.37
Explanation:
From figure
is heat rejection process
is heat transferred from the refrigerated space
is high temperature = 50 °C + 273 = 323 K
is low temperature = -20 °C + 273 = 253 K
is net work of the cycle (the difference between compressor's work and turbine's work)
Coefficient of performance of a Carnot refrigerator is calculated as
From figure it can be seen that heat rejection is latent heat of vaporisation of R-12 at 50 °C. From table
From coefficient of performance definition
Energy balance gives
Vapor quality at the beginning of the heat addition cycle is calculated as (f and g refer to saturated liquid and saturated gas respectively)
From figure
Replacing with table values
Quality can be computed by other properties, for example, specific enthalpy. Rearrenging quality equation we get
By energy balance, turbine's work is
Finally, compressor's work is