A gaggle of researchers in Thailand has outlined a brand new technique to establish the optimum temperature of a two-phase cascade warmth pump utilizing non-azeotropic refrigerants. Through their evaluation, the scientists discovered that the coefficient of efficiency for simultaneous heating and cooling is affected by the pinch level temperature of the cascade warmth exchanger, with the decrease temperature stage being accountable for the upper COP.
Researchers from Chiang Mai University in Thailand have proposed a brand new technique to search out the optimum temperature to extend the coefficient of efficiency (COP) of a two-stage cascade warmth pump utilizing non-azeotropic refrigerants.
Despite their restricted success in trade, non-azeotropic refrigerant mixtures are thought-about promising in warmth pump purposes as a result of they provide higher effectivity by way of coefficient of efficiency and compressor energy.
A two-stage cascade warmth pump system works as customary excessive temperature aspect (HS) cycle and low temperature aspect (LS) cycles connecting by way of a warmth exchanger. Each cycle consists of a condenser, an enlargement valve, an evaporator, and a compressor, with the general system together with a warmth exchanger and a warmth sink and with all of the elements in beneath fixed circulate, regular state.
During the LS cycle, the refrigerant is heated and vaporized within the evaporator to exit instantly as saturated vapor. This stress is elevated by the LS compressor beneath an isentropic course of and the vapor adjustments right into a saturated liquid, which undergoes irreversible adiabatic enlargement within the enlargement valve after which vaporizes once more by way of warmth absorption within the low- temperature evaporator.
During the HS cycle, the working fluid arrives on the warmth exchanger as saturated vapor after which strikes to the HS compressor beneath an isentropic course of. After condensation within the condenser, the working fluid adjustments to a saturated liquid, which then reduces the temperature and stress when re-entering the HS evaporator.
The teachers defined that figuring out the intermediate temperature of those warmth pump techniques, in addition to the condensing and evaporating temperatures of their HS and LS, is all the time a tough train. “In the case of non-azeotropic refrigerants, till now, there is no such thing as a basic technique obtainable to point out the optimum for a two-stage cascade warmth pump to attain the best COP.,” they declared.
“For sure values of the HS condensing and LS evaporating temperatures, a rise within the intermediate temperature results in a corresponding lower within the HS compression work and a rise within the LS compression work. Conversely, a lower within the intermediate temperature ends in the alternative impact. Then, the general COP for simultaneous heating and cooling is totally different at intermediate temperatures,” they added.
Through their evaluation, the scientists discovered that the COP for simultaneous heating and cooling is affected by the pinch level temperature of the cascade warmth exchanger, with a decrease temperature stage being accountable for a better COP. They additionally discovered intermediate temperature will increase in each the HS condensing temperature and the LS evaporating temperature. “Most of the optimum temperatures had been discovered to be decrease than the common values of HS condensing temperature and LS evaporating temperature,” in addition they defined.
They additionally concluded that the optimum temperature will be recognized by contemplating the correction issue correlation along with the common temperature between the HS condensing and LS evaporating temperatures as a reference. “Results from the newly developed mannequin are for optimum mid-temperature and most REVEALED by COPs present glorious settlement with these calculated utilizing the enthalpy technique, with deviations inside ± 7 % and ± 3 %, respectively,” they emphasised.
The proposed technique is described within the research “The optimum intermediate temperature two-stage cascade warmth pump with non-azeotropic refrigerants for simultaneous heating and cooling,” revealed in Engineering Results. Looking forward, the group stated it intends to check the method of multi-stage warmth pumps designed for very excessive temperature heating and low temperature cooling.
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