Simulation Optimization And Experimental Research Of Low-temperature System For Cell Storage

With the rapid development of life science,cell therapy has become a new hot spot,following the drug therapy and surgical treatment.However,the quality of cell cryopreservation has become a core element that limits the development of cell therapy technology.The key to ensuring the quality of cell cryopreservation is the cooling rate during the freezing process,the temperature uniformity during the storage process,and the normal operation of the robot during automated storing and retrieving.Therefore,based on the above problems in the process of cell storage,a low-temperature system is designed and the simulation optimization,theoretical calculations and experimental studies are carried out.By establishing a CFD model of the low temperature stratified test box,the structural parameters,including the nitrogen supply method,the height of the inlet and outlet,and the heat exchange method,are simulated and designed.The test box can achieve temperature stratification within the range of 120K?300K,in which the low-temperature region(120K?140K,0?300mm space)is used for cell storage,and the normal-temperature region(270K?300K,500?1160mm space)is used for automatic operation of mechanical arm.By optimizing operating parameters,including nitrogen flow and temperature,the temperature uniformity within the low-temperature region can be controlled within ±5K,which ensures that all stored samples have the same quality.In addition,by adjusting the flow ratio of liquid nitrogen to gaseous nitrogen in the heat exchanger to control the inlet temperature,the cooling rate within 5K/min?30K/min can be adjusted to meet the cryogenic storage for different types of cells.On the basis of simulation and optimization,this paper designs a low-temperature stratification test system through theoretical calculation.The system comprises a low-temperature supply system,a test box for low-temperature stratification simulation,a nitrogen delivery and exhaust system,and a data acquisition system.According to the calculation results,a low-temperature system test bench is built.The experiment was conducted using simulation-based optimization parameters.The experimental results show that the temperatures on the 300 mm,500mm,700 mm,and 900 mm height planes in the box at steady state reached 133.3K,193.3K,286.6K,and 290 K,which are in good agreement with the simulation data.The maximum steady-state temperature difference in the 300 mm height plane is 2?3K,and the temperature drop curves in the 300 mm plane at different azimuths basically coincide,indicating that the 300 mm height plane has good temperature uniformity during the cooling process.Therefore,a low-temperature area below 300 mm is used as a cell storage area,where good temperature uniformity can be ensured,and the cooling rate of cells on the same storage plane during the cooling process can be kept the same.The experimental study on the cooling rate is carried out using the simulated inlet temperature scheme.The experimental results are basically consistent with the simulated values.This indicates that the cooling rate can be controlled within the range of 5?40K/min by controlling the inlet temperature during the cooling process.