Experimental And Numerical Simulation Study On Flow Boiling Heat Transfer Of Propane In Helically Coiled Tube

With the increase of people’s awareness of environmental protection and the stricter environmental laws and regulations worldwide,the demand of clean energy is increasing.As one of the three major primary energy sources in the world,natural gas is an important clean energy source.Liquefied natural gas(LNG),as a cryogenic liquid,is a kind of efficient way for natural gas storage and transmission.Vaporizer is the key equipment in the utilization process of LNG.Intermediate Fluid Vaporizer(IFV)uses intermediate medium to avoid the direct heat transfer between corrosive seawater and high pressure LNG.Meanwhile,phase-change medium can reduce the circulation of medium and make the structure of heat exchanger more compact.It is very suitable for offshore floating storage and gasification devices.The intermediate fluid of IFV needs suitable boiling point and solidification point.Also,considering safety,availability,durability and environmental friendliness,propane is the best choice at present.Helical tube is an effective heat transfer enhancement tube.Compared with straight tube,helical tube has high heat transfer efficiency and compact structure.The two-phase flow in a helical tube is very complicated due to the torsional force and centrifugal force.At present,the law and mechanism of the two-phase flow in a helical tube are still being explored.Based on this background,the boiling heat transfer characteristics of propane in helical tube were studied experimentally and numerically in this paper.Firstly,according to the process of intermediate fluid vaporizer,a set of experimental system is designed in this paper.The main research is the analysis of the heat transfer between propane and water.The heat transfer section between propane and water is a double-pipe heat exchanger.The inner tube is a spiral tube,the outer tube is a straight tube,and the water goes through the outer tube to heat propane in the inner tube to make propane boiling.The temperature at the inlet and outlet of propane and water,the pressure at the inlet and outlet of propane and the volume flow of propane and water are measured.The boiling heat transfer coefficient of propane is calculated.In this paper,the experimental results are compared with some existing heat transfer correlations.By comparing with the existing heat transfer correlations of straight tube boiling,the results show that helical tube can enhance heat transfer.Comparisons with the existing correlations for boiling heat transfer of helical tubes show that the results of calculation are quite different due to the different application ranges of the existing correlations.In this paper,the Mixture multiphase flow model in Fluent software is used to simulate the boiling heat transfer of propane in a helical tube.Through the simulation results,we can understand the distribution of temperature,volume vapor fraction and velocity with cross section of propane boiling heat transfer in the helical tube,and the variation trend of boiling heat transfer coefficient with the cross-section radial and flow direction of the helical tube.The effects of various parameters on boiling heat transfer coefficient are analyzed by comparing the simulation results at different propane flow rates and heat flux.The difference of boiling heat transfer between helical tube and straight tube is also compared in the numerical simulation results,which shows that helical tube can enhance heat transfer.Comparing the simulation results with the experimental results under the same conditions,the relative deviation of most results is less than 40%,and the average deviation is 23.6%.