Question

An ice making machine operates on the ideal vapor compression cycle, using R-134a. The refrigerant

enters the compressor as saturated vapor at 140kPa and leaves the condenser as saturated liquid at

700kPa. Water enters the ice machine at 13 0 C and leaves as ice -4 0 C. For an ice production rate of 9kg/h,

determine the power input to the ice machine.

Answer 1

From the data given

$h_1 = 238.97 kJ/kg; h_2=267.51kJ/kg; h_3=h_4=77.67 kJ/kg$

Cooling load

$\dot{Q_L}=\dot{m_{ice}} \triangle{h_{ice}} = \frac{9}{3600}*455.896 =1.13974 kJ$

Refrigerant mass

$\dot{m_R}=\frac{\dot{Q_L}}{h_1-h_4}=\frac{1.13974}{238.97-77.67}=0.007066 kg/s$

The power input

$W_{in}=\dot{m_R}(h_2-h_1) = 0.007066(267.51-238.97)=0.20166 kJ/s = 0.27043 hp$