Research On Enhancement Method Of Jet Impingement Heat Transfer And Its Application In Vitrification Preservation

Vitrification preservation is one of the important methods for cryopreservation.By avoiding the biological injury caused by ice formation,the preservation effect of cells or tissues can be significantly improved.Ultra-rapid cooling and rewarming are the keys to achieve vitrification preservation,but the existing methods have low heat transfer efficiency,resulting in small throughput,low cell survival rate under low concentration of cryoprotectant,and limited application range.Jet impingement heat transfer is a kind of heat transfer method which impinges on solid surface with high velocity,thin boundary layer and high heat transfer efficiency.In this paper,the method of jet impingement is introduced into vitrification preservation,and a novel jet impingement heat transfer system for vitrification preservation is constructed.Various issues in the system are being studied to achieve further heat transfer of jet impingement system.The work carried out mainly includes the following aspects:(1)Study on vitrification preservation system based on jet impingement.By analyzing the typical heat transfer process of vitrification preservation,the key factors affecting the heat transfer efficiency are analyzed.The method of jet impingement vitrification is proposed.On this basis,an experimental platform for vitrification preservation by jet impingement was designed and built.(2)Study on heat transfer enhancement method for vitrification preservation system by jet impingement.According to the influencing factors of jet impingement heat transfer,the storage system is studied from the working medium and carrier.For the working medium,the heat transfer capacity of the working medium was enhanced by doping the liquid nitrogen with nanoparticles and constructing water-Al₂O₃ nano-fluid.For the carrier,the convective heat transfer effect between the working medium and the carrier surface was enhanced by constructing the microstructural surface,the super-hydrophilic/super-hydrophobic surface,and optimizing the structure of the jet generator.(3)Study on heat transfer characteristics of jet impingement heat transfer enhancement method.The heat transfer characteristics of the above enhanced heat transfer methods were studied by cooling or rewarming experiments with jet impingement,and the cooling/rewarming rate of the cell-free experiment was taken as the index to evaluate the heat transfer characteristics.The results show that doping 0.2g/L nano-Al₂O₃ particles into liquid nitrogen increases the cooling rate by 32.77%.The cooling rate and rewarming rate of the microchannel surface have increased by 5.38%and 42.58%compared with the smooth surface.After super-hydrophilic treatment,the cooling rate and rewarming rate of micro-pillar array surface are increased by 5.01%and7.44%respectively.(4)Study on biological application of jet impingement heat transfer enhancement.The developed method was applied to the vitrification of human bone marrow mesenchymal stem cells(HBMSCs).The survival rate of different kinds of low concentration cryoprotectants(less than 1M)was obtained.The highest survival rate was82.1±3.5%,and the lowest survival rate was 59.9±1.5%.The results showed that the vitrification method developed in this paper was effective in the preservation of HBMSCs under the condition of low concentration of cryoprotectant.In this paper,the enhancement method of jet impingement heat transfer is studied and applied to the vitrification preservation of biological samples.The experimental results show that the jet impingement method can improve heat transfer efficiency greatly.Compared with the traditional method,the jet impingement vitrification method has a larger throughput,can achieve vitrification at low concentration of cryoprotectant,and has a higher cell survival rate.The system can not only save cell suspensions,but also save tissue sections,expanding the application scenarios of the vitrification preservation method.Therefore,the jet impingement vitrification preservation system and its enhanced heat transfer method studied in this paper have better preservation performance,which provides more options for the cryopreservation of biomaterials.