| A large amount of food was wasted because of lack in effective preservation every year,which caused very significant economic losses.Freezing is the main method of food preservation.The faster freezing rate of the food,the more favorable it is for food preservation.In recent years,scholars from all over the world have devoted a lot in the research and development of quick freezing technology.However,the research of some new freezing technologies,such as high-pressure freezing and ultrasonic freezing,is still in the laboratory stage and cannot be applied in the industry.The quick-freezing technology used on domestic refrigerators is the traditional air blast freezing,and the food freezing rate is slow.This article takes the household refrigerator as the research object,and use the superior thermal conductivity characteristics of metal to improve the quick-freezing technology in household refrigerators.In this paper,a finned aluminum plate is added into the freezing process as an optimization measure.A series of aluminum plate assisted freezing experiments,designing and an improvement of quick-freezing technology is performed in a household refrigerator freezing room.A three-dimensional model of the freezer compartment of the refrigerator was established and meshed.The CFD software was used to simulate the flow field distribution in the refrigerator freezer during the experiment.Through the post-processing simulation results,the effect of different freezing modes on the flow field distribution in the freezer compartment of the refrigerator was obtained and the best freezing scheme was selected.The results show that:(1)The addition of finned aluminum plate at the bottom of the M package significantly accelerated the entire freezing process:compared with the control group,this method can shorten the time for 26%in the cooling stage and 29%in the crystallizing stage and 20%in the freezing stage.The average surface heat transfer coefficient increased by 42%,47%and 31%respectively.Adding aluminum plate at the bottom of the M package causes the rise of cold air on the left and right sides of the M package,which contributes to the convection heat transfer on the surface of the M package,and leads to a more uniform temperature gradient above the M package,which significantly increases the freezing rate.(2)The addition of aluminum plates to the upper part of the M package does not significantly improve the freezing rate during the entire freezing process:this method can only shorten the cooling stage,the crystallizing stage and the freezing stage by 6%,8%,and 4%,respectively.The average surface heat transfer coefficient only increased by 7%,10%and 6%,respectively.The aluminum plate in the upper part of the M package impedes the convective heat transfer between the upper surface of the M package and the cold air.However,the area and superior thermal conductivity of aluminum plate make up for the lack of convective heat transfer on the M package.(3)The addition of aluminum plates to both the upper and the bottom of the M package cause the most significant increase in the freezing rate:the time shortened of the above three stages are 34%,31%,and 20%respectively.The average surface heat transfer coefficient increased by 57%,50%,and 26%,respectively.The acceleration of this method is most obvious,but the up and down flow of cold air around the M package is hindered,resulting in uneven temperature distribution in the freezer compartment.(4)The steady state numerical simulation results show that when the heat of the freezing object is high,the heat transfer of the upper and lower aluminum plates is the best,when he heat of the freezing object is low,the heat transfer of the bottom aluminum plate is not much different from that of the upper and lower aluminum plate.Considering the fact that the food heat in the domestic refrigerator freezing room is not high in generally,as well as consumables and other factors,the selection of the bottom pad and aluminum plate is the optimal freezing scheme. |
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