13468-11-11P AID: 1825 | 05/12/2014

Show the ideal vapor-compression refrigeration cycle, with refrigerant–134a as the working fluid, on diagram as in Figure (1).

For the given ideal vapor-compression refrigeration cycle, with refrigerant-134a as the

working fluid, the specific enthalpy, pressure, and specific entropy at state are , ,

and respectively. Also, the saturated liquid state is denoted by the subscript f, the saturated vapor is denoted by the subscript g, and the properties at latent stage are denoted by the subscript fg.

In an ideal vapor-compression refrigeration cycle, the compression process takes place in isentropic condition; the refrigerant comes into the compressor as a saturated vapor at the evaporator pressure, and leaves the condenser as saturated liquid at the condenser pressure.

Use “saturated refrigerant-134a pressure table”, to find and of refrigerant-134a, at

20 psia .

For isentropic process 1-2, specific entropy remains constant. Hence, .Use

“superheated refrigerant-134a table”, to find at 80 psia and at

. Use interpolation method to find .

Use “saturated refrigerant-134a pressure table”, to find of refrigerant-134a, at 80 psia

.

For the isenthalpic process 3-4, specific enthalpy remains constant. Hence and are equal.

Calculate the cooling load for the given ice-making machine .

Here, the mass flow rate of ice is , and the change in specific enthalpy for ice is

.

Substitute for , and for .

Find the mass flow rate of the refrigerant .

Substitute for , for , and for .

Calculate the power input to the given ice-making machine .

Substitute for , for , and for .

Also, convert to using suitable conversion factor.

Hence, the required power input to the given ice-making machine is .