Experimental Research On Heat Transfer Enhancement Of Molten Salt In Tubes

With the growth of population and economic development,the demand for energy is growing.Nuclear energy as a clean energy,has attracted more and more attention.Compared to the fossil fuel(coal,petroleum),nuclear energy has the following advantages:(1)the energy density of nuclear energy is large,(2)the nuclear reactor's security index is very high,(3)nuclear energy does not release harmful gases,such as carbon dioxide and sulfur dioxide.Thorium-based Molten Salt Reactor(TMSR)has being developed in Shanghai Institute of Applied Physics,Chinese Academy of Sciences since the year 2011.The molten salt reactor has the advantages of unique economic and inherent safety.In this advanced reactor,FLiBe is used as coolant,the heat energy is utilized by the Braytom Cycle,therefore it has good application foreground.In the thorium-based molten salt reactor system,the heat exchanger that is connected to the first and second loop is the indispensable process equipment of the energy transfer.In order to improve heat transfer,the measures of effective enhanced heat transfer can effectively increase the efficiency of heat exchangers and reduce the size of heat exchanger.In this work,the convective heat transfer characteristics of molten salt in the enhanced heat transfer tubes were studied by means of experimental investment.The main contents of this thesis include two aspects: one is experimental research on convective heat transfer characteristics in transversally corrugated tube;another is experimental research on convective heat transfer characteristics of finned tube.Based on the convective heat transfer experimental apparatus of molten salt and heat transfer oil,experimental study was executed for enhanced heat transfer of molten salt in transversally corrugated tube.Heat transfer coefficients of molten salt with the range of Reynolds number from 10,000 to 80,000 and the Prandtl number from 10 to 20 are evaluated according to the calculated overall heat transfer coefficients by Wilson plots.Based on the experimental data and correlation of smooth tube,the correlation for molten salt in transversally corrugated tube was developed by least-squares method.Our research indicated that the correlation for turbulent flow in transversally corrugated tube was in good agreement with experimental data.The ratio of the heat transfer coefficients Nu/Nus are used to evaluate the enhanced heat transfer.The average value of Nu/Nus is approximately 1.14.Based on the convective heat transfer experimental apparatus of molten salt and heat transfer oil,the heat transfer characteristics of molten salt of turbulent region in finned tube was also studied in this paper.Heat transfer coefficients of molten salt with the range of Reynolds number from 10,000 to 80,000 and the Prandtl number from 10 to 20 are evaluated according to the calculated overall heat transfer coefficients by Wilson plots.Based on the experimental data and correlation of smooth tube,the correlation for molten salt in transversally corrugated tube was developed by leastsquares method.Compared with the experimental data of molten salt in smooth tube,the results show that outside fins of finned tube do not have the effect of enhanced heat transfer.In order to study the characteristic of enhanced heat transfer of finned tubes,based on the theory of similarity criterion function,the convective heat transfer characteristics of the turbulent region in finned tube are studied by using the heat transfer oil instead of the molten salt.Heat transfer coefficients of heat transfer oil with the range of Reynolds number from 10,000 to 60,000 are evaluated based on the calculated overall heat transfer coefficients by Wilson plots.Besides,the convective heat transfer characteristics of molten salt in tube was also analyzed in the present work and a new correlation was proposed by the least-squares method.It is showed that the enhanced convective heat transfer effect of the finned tube is 2.32-3.63 times by using Dittus-Boelter convective heat transfer correlation.