| In twenty-first Century,cell therapy developed rapidly and is likely to gradually become the main way of human treatment.In order to have sufficient cells for cell therapy,the cells are stored for a rainy day.Cell storage usually involves two processes,one is the cooling process,the other is the heat preservation process.First,the cells are cooled down to reach the required storage temperature,and then stored in the cryogenic storage tank.Therefore,the two equipment for cell storage are cooling equipment and thermal insulation equipment.If the cooling process is unstable and there is too much temperature fluctuation,it will be a serious threat to the survival of biological cells.In order to ensure the rationality of the cooling process,the cooling system is designed to study the cooling equipment.The main purpose of this paper is to develop a control strategy for the temperature variation of the simulation system,which is to automatically obtain the change rule of the valve opening under the condition that the temperature change in the high and low temperature chamber is known.The ground high and low temperature simulation system mainly consists of high and low temperature cabinet,gasifier and plate heat exchanger.Vaporizer and plate heat exchanger are the important parts of the system,and only under full study can establish the control strategy for the entire system.First of all,based on the existing heat transfer coefficients of vapor phase,gasliquid phase and vapor phase in the evaporator during frost formation,the paper builds a physical model based on energy conservation principle and apply MATLAB to do simulation of the whole process in order to obtain different gasifier inlet liquid nitrogen flow and outlet refrigerant temperature curve.Secondly,the paper completes the plate heat exchanger selection according to the results of previous studies,and makes numerical analysis of heat transfer process for liquid nitrogen and nitrogen in the plate heat exchanger in order to obtain different outlet temperature variation curve under different inlet liquid nitrogen and refrigerant flow conditions,and thus,provides theoretical guidance to make the appropriate control strategy.Finally,based on the study of the heat transfer characteristics of the gasifier and the plate heat exchanger,the control strategy of the whole system is formulated.Taking the known internal temperature variation law as the input parameter,the corresponding valve control strategy would be obtained.The strategy could be applied to the actual operation process and the obtained results are compared with the known temperature variation to verify the accuracy of the model.Through the comparison of theoretical and experimental data,the trend of simulation and experimental value are basically the same.Due to the proper simplification in the numerical simulation,the numerical calculation and the experimental results have some discrepancies,but the maximum error does not exceed 10%,indicating that the model can better reflect the actual physical process. |
