For the purpose of this paper, some rebuilding work was taken to the existing refrigeration system after the tests for
R502 were completed. The compressor and the system pipe lines were cleaned with chemical solvent and dry
nitrogen gas. The compressor lubricant oil was replaced with POE oil and the expansion valve was re-adjusted to
adapt R404A requirements. In order to measure the refrigeration capacity of the system, a flow meter to measure the
flow rate of refrigerant was added in the pipe line between the condenser and the expansion valve. Furthermore,
considering that many existing R502 systems use forced-cooling evaporators, a forced-cooling evaporator was
connected parallel to the original direct-cooling evaporator. Thus there are two parallel evaporators switched with
some valves in this system. Some other sensors for temperature and pressure measurements were also equipped into
the system. At last, the refrigerant of this system was changed to R404A.
Figure 1 shows the final refrigeration unit and the test system. A data acquisition system was used to accumulate
data and transmit them to the computer.
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