Reserch On Flow Boiling Heat Transfer Characteristics And Thermal-Mechanical Coupling Effect Of Microchannels In Vitrification Preservation

Cryopreservation can effectively preserve tissues and cells and other biological materials for a long period of time.Currently,it has important application potential in life science research,species preservation,and clinical medicine.The vitrification preservation method can effectively avoid the low-temperature damage during the cooling process,and has a principle breakthrough compared to the traditional methods.The existing vitrification preservation method mainly improves the cooling rate through reducing sample volume,the operation is difficult and the heat exchange efficiency is limited.At the same time,the open operation method is easy to contaminate biological samples.In addition,the vitrification preservation objects are usually small in size,and the movement process is complicated.The experimental research has insufficient understanding of the complicated physical processes therein.In view of the above issues in vitrification preservation,this paper conducts research work in the following aspects(1)Numerical simulation method of flow boiling heat transfer in microchannelsIn this paper,the phase transition,heat transfer and other physical processes involved in the flow boiling process in the microchannel are analyzed theoretically,and the phase transition characteristics,flow morphology,heat transfer characteristics,mechanical properties,and fluid-solid and thermodynamic coupling properties at the microscale are studied.The corresponding control equations were established and the discrete methods were compared and determined to form a numerical simulation method for the flow boiling heat transfer characteristics in microchannels.This method lays a theoretical foundation for the subsequent chapters to establish a numerical calculation model for the flow boiling heat transfer process in microchannels of vitrification preservation.(2)Study on the cooling mechanism of flow boiling in microchannels of vitrification preservationBased on the numerical simulation method of the flow boiling heat transfer characteristics in microchannels,a numerical calculation model was established for the vitrificaiton preservation of biological samples,and the cooling mechanism was studied.Establish an experimental system for the cooling process during the vitrification preservation and verify the accuracy of the numerical simulation method.The influence of cooling flow rate,microchannel structure,sample layer thickness,and material of microchannel on the cooling rate was studied to provide a method for establishing the cooling rate control method of the vitrification preservation system.(3)Thermal-mechanical coupling effect of microchannel cooling system for preservation of phase change by vitrificationThe ultra-high cooling rate of microchannel flow boiling for vitrification preservation can overcome the rate limitation of traditional methods.However,microchannel chips and biological samples generate large thermal stress under a large temperature gradient,which may cause the microchannel structure to break or failed to save.In this paper,the thermal-mechanical coupling effect of the vitrified phase change microchannel system is studied.First,based on the thermal-mechanical coupling mechanism analysis of the phase change microchannel cooling system,the temperature field obtained by numerical analysis of the phase change microchannel cooling system is taken as the temperature load,and a thermal-mechanical coupling numerical calculation model is established.Then,the thermal stress of the microchannel chip and the biological sample under different flow conditions,microchannel chip parameters,and the material under vitrification preservation system were analyzed during the cooling process to determine the effect of each influencing factor on the thermal stress magnitude of the vitrification preservation system.It provides basic data for predicting the reliability of the system.(4)Optimized design of vitrification preservation cooling systemBased on the simulation method of the boiling heat transfer process in the microchannel,an orthogonal test method was used to design an example to determine the main parameters affecting the thermal stress and its range of values.Through the range analysis,the primary and secondary order of the factors affecting the cooling rate and the thermal stress in the temperature-saving cooling system of vitrification are obtained.The optimal parameter combination of the vitrified cooling system is obtained by the multi-index comprehensive balance method.According to the orthogonal test results,it was verified that the optimal parameter combination can ensure the structural strength of the chip and the successful preservation of the biological sample while satisfying the required cooling rate for vitrification preservation,and provides important support for the further development and application of vitrification preservation microchannel chip technology.Based on the above research content,the main innovations of this paper are summarized as follows,(1)Established simulation method suitable for vitrification preservation cooling systemIn this paper,based on the theoretical analysis of the physical processes involved in the flow boiling heat transfer in the microchannel,various characteristics of the flow boiling heat transfer process at the microscale are studied in detail,and the control equations of the boiling heat transfer process are established to form a numerical simulation method for the flow boiling heat transfer characteristics in the microchannel.The experimental verification shows that this method can accurately simulate the flow boiling heat transfer process of vitrified preservation microchannels.Breakthroughs Most of the research on vitrification preservation is limited to the current state of experimental research.(2)The influencing factors and laws of the flow boiling heat transfer and the thermal-mechanical coupling effect of the microchannels vitrification preserved are proposedFor different vitrification cryopreservation objects,there are different critical temperature drop rates for glass transition,and the thermal stress generated by the ultrahigh cooling rate used for vitrification preservation may cause the fracture of the system structure or the preservation failure of biological samples.This paper is based on the numerical simulation method for the vitrification preservation cooling process,and analyzes the influence of different factors on the cooling rate and thermal stress,provides a basis for controlling the cooling rate and thermal stress of vitrification preservation.It is of practical significance to break through the bottleneck of vitrification preservation technology.(3)Put forward an optimization method for vitrification preservation cooling systemBased on increasing the cooling rate of the vitrification preservation system,a breakthrough in the critical cooling rate of the vitrification preservation is achieved.At the same time,the system structure can meet the thermal stress limitation in the cooling process.In this paper,the optimization method of the system is proposed through the optimization design of the micro-channel structure.The optimized program can reach a higher cooling rate under the thermal stress limit of the micro-channel chip.The optimization method can help R&D personnel to optimize the system design,provide constructive suggestions for actual production and processing,and promote the application of vitrification preservation.