| In view of the fact that single-stage compression refrigeration cannot meet the requirements of the compound environment in the constant temperature and humidity chamber at low temperature,this paper determined the R507A/R23 cascade refrigeration cycle as the research object under the principle of energy conservation and emission reduction.The structural size and heat exchange effect of each part of the refrigeration cycle affect the spatial layout,operating status and economic benefits of the entire system.Therefore,computer simulation combined with forward design and local structure simulation provides a reliable means for research.The computer simulation provides the product performance to the forward selection design,the forward selection design is to establish the simulation test bed for the preparation,the local structure simulation is conducive to the complex structure parameters in the simulation.The specific research contents of this paper are as follows:(1)In order to study the characteristics of the stacked refrigeration system and provide a basis for the establishment of the test bed,the forward conventional design and MATLAB GUI were used to complete the overall rapid design,that is,the structural parameters and model of minicool constant temperature and humidity chamber with low temperature environment up to-50℃ were determined.COP analysis by GUI shows high consistency,which can meet the need of rapid design.(2)The evaporator and condenser models suitable for the environment were established by using the distributed parameter method,the micro-element was analyzed,the governing equation and the specific algorithm flow of the iterative method were given.The model of compressor was established by using the centralized parameter method.The S function in MATLAB was used to establish the refrigerant model such as R23,which made the invocation of physical parameters more accurate and rapid.The level 2 M S function in MATLAB was used to establish the visualization modules of evaporator,condenser,evaporative condenser,etc.,so as to facilitate the study of heat transfer flows in single-phase region and two-phase region.According to the simulation results,the refrigerant side heat transfer coefficient is low in the single-phase region,and generally shows a downward trend in the two-phase region,while the air side heat transfer coefficient is relatively stable.Based on the sequential module method,the overall simulation of the system was established by Simulink.The basic environmental conditions in the box were changed within the range allowed by the test conditions,and the measured data were compared with the simulation results.The comparison shows that the lower the setting temperature,the lower the overall performance and the greater the simulation error.After the accuracy of the model was verified,the structural parameters in the model were changed to observe their effects on performance.The results show that the overall heat transfer increases with the increase of inner and outer tube diameter,the fin spacing increases,the total heat transfer increases,but the heat transfer coefficient decreases.The fin thickness increases and the heat transfer volume increases slowly.For the specific condenser distribution parameter model,it is found that the refrigerant side heat transfer coefficient decreases with the increase of the flow as a whole,the air side heat transfer coefficient changes weakly,and the heat flow density increases in the overheated and two-phase zones,while the undercooled zone decreases.(3)Software Ansys and Fluent were used to simulate the condensed phase change flow in the shell of the bubble condenser.The results obtained by Lee model showed that the fluid was in a "Z" shape,the flow rate increased after passing through the baffle,and there was more condensate in the dead zone behind the baffle.Figure[70]Table[23]Reference[85]... |
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