A refrigeration plant with 5 Ton capacity is working 2 hours continuously. Estimate the total quantity of heat to be removed from the evaporator?
Answers
Answer:
4.1 Cooling capacity
Cooling capacity indicates the amount of heat the system can remove from the refrigerated space over time. It is equal to the change in the specific enthalpy of the refrigerant in the evaporator caused by the refrigeration load multiplied by the mass flow rate of the refrigerant. It is expressed in Equations (3a) and (3b) for Cases 1, 2 and 3. The cooling capacities of Cases 2 and 3 are based on the enthalpy of point 1, not 11, because the heat from the refrigeration load only increases the enthalpy from point 44 to point 1. The further change from point 1 to point 11 is caused by the HEX and therefore, should not be included in the cooling capacity calculation.
(3a)
(3b)
The values of the cooling capacities of various refrigerants at various evaporating temperature of all cases are plotted in Figure 4. As mentioned above, the volumetric flow rates at the compressor inlet are set as 0.001 m3/s. From the figure, it can be seen that R32 consistently produces the largest cooling capacity. It is also the only R22 substitute studied here that consistently produces higher cooling capacity than R22. This is consistent with the data shown in Figure 3, where R32 is also the only R22 substitute with a VFR less than unity which indicates a higher cooling capacity generation.
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Figure 4. – Cooling capacity of various refrigerants at various evaporating temperatures for cases without and with HEX
Figure 4 also shows the interesting behaviour of R744. It produces very small cooling capacities when used in a system without HEX. When the evaporating temperature is too high, it cannot even produce any positive cooling capacity. However, when a HEX with a 10 °C sub-cooling is used, its cooling capacity is increased significantly. If a HEX with a 10 °C superheating is used instead, the increase is less significant. This is because the amount of heat transferred through the HEX in Case 2 is more than that in Case 3, resulting in a more efficient system in Case 2.
Methodology of performance calculation of condensing unit thanks to the compressor
S. Colmek, in 7th International Conference on Compressors and their Systems 2011, 2011
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