Numerical Simulation On Heat Performance Of Finned Tube Heat Exchanger

With the rapid development of economy, the energy demand is increasing surprisingly in China. Energy short supply has been one of the principal elements restricting the development of economy and society, which makes energy-saving and emission-reduction becomes an urgent task. In industrial processes, almost 50% of thermal energy transforms into low-grade waste heat discharged directly, which leads to energy waste and environmental pollution. In aluminum electrolysis enterprises, the main energy consumers, nearly 30% of input energy transforms into low temperature (100-200℃) flue waste heat and is discharged after the dust collection process. Recycling and utilizing those waste heat energy to generate power is of great significance for energy-saving in the aluminum electrolysis industrials.Based on the program "The research of key technologies in the power generation system using low temperature flue waste heat" supported by the high-tech plan in the industrial filed in Hunan province, the thermal performance of finned tube heat exchanger was studied by using the numerical simulation method in this dissertation.The main contents and conclusions are as following:(1) The calculation model of heat transfer in the finned tube heat exchanger was established by using the computational fluid dynamics software-FLUENT. In present model, comparisons were performed synthetically and finned tube with unit length was chosen to be calculated. In order to avoid the difference between the actual situation and the situation in which the constant heat flux boundary condition or constant wall temperature boundary condition was set on the tube wall, the coupling calculation method was applied to investigate the convective heat transfer performance of waste flue outside the tube and working fluid inside the tube.(2) The influences of temperature and velocity on thermal performance were researched among waste flue, liquid and gaseous working fluid. The results of numerical simulation show that as the velocity increased, for waste flue and working fluid, the average surface heat transfer coefficient increases and heat transfer performance is promoted. As the temperature increases, the average surface heat transfer coefficient of waste flue and liquid working fluid increase, however, that of gaseous working fluid decreases due to the difference property parameters between the liquid and gas. In the calculation zone, the average surface heat transfer coefficient on waste flue side ranges from 50 to 130 W/(m2·K), and ranges from 190 to 1900 W/(m2·K) on working fluid side.(3) According to experimental study, the result data of numerical simulation under various operating conditions is usually arranged into the form of Nu. The characteristic curve of heat transfer was obtained and dimensionless equations of heat transfer were fitted by least square method. An experimental platform was built and a calculation program was programmed based onε-NTU method. Finned tube units were accumulated using programming, by which numerical solutions and experimental conclusions were compared. Conclusions show the max relative error of results between program and experiment is below 20%. The results show the reliability of the numerical simulation.