Question

A design related question.

1)design a walk in refrigerator and freezer with 10 ton and 30 ton cooling capacity respectively.
2) freezer must be maintained between (24 to 15 deg celcius) and refrigerator between (3-7 deg celcius)
3)ambient condition ( 38 deg celcius) and refrigeration compressor efficiency assumed at 75%.
4)heat exchanger maintained at 11 deg celcius.
5) emphasis on reducing operating cost, so one compressor can be used and also flash chamber
6) reducing compressor work input and increasing coefficient of performance.
7) power consumption must be in Kilowatt ( KW).

how would you do this?
can you write why you went with the choice you went with...just summarize and justify your findings. it's a open ended question and there is no right or wrong answer.

thank you, looking forward to learning this.

Answer 1

In this question all data (like pressure, mass flow rate, heat exchanger coefficient) has not been provided so can not solve this question with specific value to answer.

In general refrigerator or freezer design,

We used to find enthalpy of vapor at different temprature and pressure at various point in refrigerator cycle.

Heat exchanger is used to provide superheat vapor in compressor to reduce compressor work which in turn reduces power consumption.

In heat exchanger hot flow from condensor passed which will reject heat to evaporator flow vapor.

For 10 ton refrigerator,

Q = m*(h₆ - h₅), here h₆ = enthalpy at exit from evaporator, h₅ = enthalpy at entry from evaporator

We can get h₆ from calculation and from h₆ we can determine exit temperature from evaporator.

This temperature is input for heat exchanger calculation.

I hope your are aware of heat exchanger calculations, so you can calculate heat exhanger output temperature from cold flud.

Now this output temprature from heat exchanger is used for compressor and we can get compressor power required.

This how we design refrigerator with heat exchanger.