Research And Application Of New Type Compound Refrigeration

With the development of science and technology,traditional vapor compression refrigeration has been unable to meet the growing demand for refrigeration technology,and the large-scale use of this technology has caused and exacerbated many global environmental problems.To cope with the ozone hole and global warming crisis brought about by traditional refrigeration,it is urgent to develop new environmentally friendly refrigerants.Solid-state refrigeration based on the caloric effect of ferrous materials has attracted widespread attention due to its environmentally friendly and efficient characteristics.At present,the research on solid-state refrigeration has just begun,and there are still many issues worthy of in-depth study.This paper focussed on solid-state refrigeration technology,and carried out related research on new composite refrigeration technologies such as new materials and new systems.The purpose is to provide a reference for the development of efficient compound refrigeration technology.Firstly,（C₂H₅NH₃）₂CuCl₄（EA₂CuCl₄）crystals were prepared by slow evaporation of the solution.Early research has found that it has large magnetocaloric effect at low temperatures.In this paper,its electrocaloric properties were obtained by studying the ferroelectric phase transition process in the room temperature region.The study showed that EA₂CuCl₄ has a large pyroelectric coefficient p and phenomenological coefficientβ,which can be considered as a new type of electrocaloric material.Because it exhibits different caloric effects in different temperature regions,it is expected to achieve efficient cooling in different temperature regions and exert the characteristics of multicaloric refrigeration.Secondly,P（VDF-TrFE）/Metglas ferroelectric thin film composites were prepared by Sol-gel method and spin coating method.Using the magnetostrictive property of Metglas to apply stress to P（VDF-TrFE）,the effect of stress on the electrocaloric cooling performance of P（VDF-TrFE）,which has a large electrocaloric effect,was studied.During the magnetic field changed from 0 to 200 Oe,the maximum polarization strength P_max increased from 4.84μC/cm² to 5.63μC/cm²,and the maximum entropy changeΔS_max increased from 14.2 J K^-1kg^-1 to 16.5 J K^-1 kg^-1,a total increase of 16.78%and the optimal temperature reduced from360 K to 340 K,which proved that the stress can significantly enhance the electrocaloric performance of P（VDF-TrFE）and effectively regulate its operating temperature.Finally,starting from the problem of improving the low heat exchange efficiency of solid-state refrigeration fluids,a variety of composite refrigeration theoretical models were established with magnetic refrigeration as a representative.The advantages of fast response and large heat flux of thermoelectric refrigeration were used to solve the solid-state refrigeration heat transfer problem.Analysis of the simulation calculation results showed that the Gd/Bi₂Te₃ composite structure cannot improve the cooling performance of the system,because the charge as the heat carrier in thermoelectric refrigeration cannot absorb continuous energy changes like the fluid medium.And the application of Peltier elements in magnetic refrigeration systems is one of the feasible ways,which can solve the system loss caused by the reciprocating motion of the heat exchange fluid to a certain extent.However,the power consumption of the system increased after adding the Peltier elements.The balance between the two is future research content.