IMPROVED SINGLE-STAGE REFRIGERATION UNITS TO REPLACE TWO-STAGE UNITS
DOI:
https://doi.org/10.15421/jchemtech.v33i2.325344Keywords:
throttling, compression work, compressor volume and energy losses, refrigeration coefficient, thermal pollution of the atmosphereAbstract
The ratio between the condensation pressure and the evaporation pressure of the working fluid in vapor-compressor refrigeration machines increases, the losses during throttling of the liquefied refrigerant and the work of adiabatic vapor compression increase. When this ratio π = ρcond / ρevap reaches a value of 8, to reduce the specified losses, they switch to a cycle with two-stage compression and intermediate vapor cooling and with double throttling of the liquefied refrigerant. However, such an improvement of vapor-compressor units complicates their operation. Therefore, in practice, single-stage refrigeration units are sometimes used even when π slightly exceeds the specified π value, and this leads to significant losses in the efficiency of the refrigeration cycle. The paper proposes to use improved single-stage refrigeration units as an alternative to two-stage refrigeration units. To verify the feasibility and effectiveness of this idea, a comparison of the efficiency indicators of two possible modifications of single-stage refrigeration units was performed to replace a two-stage one with a compression ratio π equal to 9. The calculations showed that the most effective substitute for two-stage refrigeration units is an improved single-stage unit with isochoric limit (maximum possible) regenerative superheating of steam and a polytropic process of its compression. Less effective, but more structurally simple, is a plant with isobaric superheating of steam. The reduction in the effective power of the compressors in these units relative to the indicator of a two-stage unit with limited regenerative heat exchange is 15 and 5 %, respectively, which means that the costs of electricity and fuel used for its generation are reduced. In addition, the thermal loads on the condensers of such plants are reduced, which means their weight and dimensions are reduced, and, most importantly, thermal pollution of the atmosphere is reduced (by 3 and 1 %, respectively).
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