3. Test procedures
The objective of the tests was to determine how the vapourcompression
refrigeration plant actually behaved when the different
types of refrigerant fluids were used. This way it was possible
to obtain adequate information on the plant with replacement fluids
other than R22 while working under different conditions.
The tests are intended to provide indications on the performance
of the refrigeration system designed and built to operate
with R22 when the original fluid has been replaced with other
HFC fluid mixtures.
The same thermostatic expansion valve with an exchangeable
orifice was used for all the tests. The orifice component was changed
with the different fluids in order to avoid swinging during
trials.
The thermostatic expansion valve was regulated in order to set
certain overheating parameters of the fluids (Dts = 5 C). The condensation
temperature was set at 38 C.
The experimental tests simulated a real running consistent with
the technical specifications of the evaporator. The inlet for the
water–glycol mixture was maintained at the constant temperature
of 12 C. The mass flow rate was chosen within a specific range in
order to have the outlet water–glycol mixture temperature between
4 and 10 C.
The mass flow rate was kept constant at a chosen value, and the
inlet and outlet temperatures were recorded in order to determine
the exchanged thermal power.
The tests were performed after reaching steady operating conditions.
The control parameters indicating the attainment of the
above conditions were: pressure and temperature in the inlet
and outlet evaporator sections. The working conditions were considered
steady when the temperature changes were smaller than
0.3 C and the pressure variations were 5 kPa and 20 kPa in the
low and high pressure circuit respectively.
In Fig. 2 a pattern thermodynamic cycle of the refrigerating machine
is shown below.
The COP is given by the relationship shown below
COP ¼
h1 h5
h3 h2
where ðh1 h5Þ is equal to the refrigerating effect and ðh3 h2Þ is
equal to the work required of the compressor per unit of working
fluid mass.