Abstract:
Various techniques are being researched to refrigerate our stored products at a
desired temperatures in supermarkets. In this report, via the exergy and energy
analyses, the 𝐶𝑂2/𝑁𝐻3 and 𝐶𝑂2/R134a cascade refrigeration systems were
compared to determine which of the system suited best the supermarket
application. The coefficient of performance (COP) was calculated as a measure of
the energy analysis while on the other side the sum of the individual exergy
destructions in each of the components which is equivalent to the total exergy
destruction was a measure of the exergy analysis. The cascade refrigeration
comprised of two refrigeration systems connected in series in which one of the
system will in lower temperature circuit (LTC) while the other will be in the higher
temperature circuit. The cooling space temperature and cooling capacity employed
in this report were -40°C and 40 kW. In both the exergy and energy analyses the
temperature at the LTC evaporator and condenser, cascade condenser temperature
difference and HTC condenser were varied individually to obtain the desired
results. The analyses result showed that 𝐶𝑂2/𝑁𝐻3 cascade refrigeration system was
more efficient than the 𝐶𝑂2/R134a system as it had lower values for the total
exergy destruction and higher COP values. Furthermore, in both cascade systems
maximum exergy destruction occurred in the condenser followed by the
compressor.
