Experimental evaluation of a cascade refrigeration system

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A prototype of a cascade refrigeration system using NH3 and CO2 as refrigerants has been
designed and built. The prototype is used to supply a 9 kW refrigeration capacity horizontal
plate freezer at an evaporating temperature of
50 C as design conditions. The prototype
includes a specific control system and a data acquisition system. The experimental
evaluation started with the real conditions within the design operating parameters.
Subsequently， several tests were performed fixing four CO2 evaporating temperatures (
50，

45，
40 and
35 C). At each one of the evaporating temperatures evaluated， the CO2
condensing temperature was varied from
17.5 to
7.5 C and an experimental optimum
value of CO2 condensing temperature was determined. The discussions on the experimental
results include the influence of the operating parameters on the cascade systems
performance. In addition， the experimental results are compared with two common double
stage refrigeration systems using NH3 as refrigerant.