Technical Research On Precise Control Of Temperature In Indirect Cooling Refrigerators

Indirect cooling refrigerators have the advantages on auto-defrost,multitemperatrue compartment and large strorage capacity comparing with direct cooling refrigerators,and are increasingly favored by consumers.Consumer's requirements for the food preservation performance of refrigerators are constantly improving,and require refrigerators to have higher and higher performance on the precise control of compartment temperatures.However,the compartment temperatures of indirect cooling refrigerators will fluctuate violently during the auto-defrost process as the defrosting heat will enter the compartments;the compartment temperatures of conventional multi-compartment indirect cooling refrigerators(MIRs)are difficult to be precisely controlled as the cooling capacity cannot be independently delivered to each compartment;the temperature in large-volume compartment is difficult to obtain a high degree of uniformity due to the effect of cold air sinking and warm air rising as well as the heat leakage through the cabinet wall.These technical difficulties make the refrigertors fail to meet consumers' increasing requirements for high-quality food preservation.Therefore,this article proposed the following four technical studies on the precise control of compartment temperatures in indirect cooling refrigerators:(1)A high-efficiency defrosting method for indirect cooling refrigerators has been proposed,which is capable of reducing the amplitude of the fluctuation of compartment temperature during the defrosting process.The new method of defrosting is proposed based on the idea of making the frost absorb most of the heat generated by electric heater,and its principle is to make the defrosting process at different locations complete simultaneously by optimizing the frost mass distribution on the evaporator.In this method,the defrosting heat distribution on evaporator surface,the required frost mass distribution,the required air flow distribution and the structure of return air duct are determined,respectively.Application of this method in an actual household refrigerator shows that the defrosting efficiency is improved by 29.8%.(2)A frost reduction method for indirect cooling refrigerators has been proposed,which is capable of reducing the frequency of the fluctuation of compartment temperature during the defrosting process.The new method is proposed based on the idea of applying an enthalpy exchanger(EE)to reduce the amount of water vapor entering the evaporator.The influence of EE on air circulation and the change process of air humidity is analyzed,and it is indicated that the application of EE is able to reduce the frost accumulation.The design process of EE in frost-free refrigerator is illustrated.An experiment on a frost-free refrigerator shows that the application of EE decreases the frost accumulation by 18.8%.In addition,effects of EE on other main performances of frost-free refrigerator besides the frost accumulation are evaluated.(3)A method of independently delivering cooling capacity to each compartment in MIRs has been proposed,which realizes the independent control of temperatrue of each compartment.The method is proposed based on the idea of installing a novel air distributor in a MIR and changing the position of air supply dampers in the air distributor.The design method for the geometries of the novel air distributor is detailed illustrated.To validate the proposed method,a novel air distributor was designed in a typical MIR,and the temperatures of all compartments were measured and compared.It is found that the dynamic fluctuations of the FC temperature in the MIR without the air distributor excess the preset range at some working conditions,while those of the MIR with the novel air distributor are within the preset range at all working conditions,confirming the effectiveness of the proposed method for temperature control.(4)A method for improving temperature uniformity in a large-volume indirect cooling compartment has been proposed.Four basic methods are proposed at first,i.e.,using solid shelves to separate the large-volume compartment into several small compartments and sending cold air into each compartment;providing an cold air curtain to prevent heat leakage though front door;adjusting the flow direction of cold air to enhance convection in both sides of the compartment;and adding air outlets in different locations in the bottom of the compartment to distract the heat in the return air.Then a combination of these four methods is recommended as the optimal scheme.Practical application of the optimal scheme in a large-volume indirct cooling wine cabinet shows that the maximum temperature difference in the cabinet has decreased from 12.1? to1.9?,meaning that the effect is quite satisfied.