Research On Heat And Mass Transfer Characteristics Of Fluids In Wavy-walled Tube

In order to enhance the heat transfer of fluid in the tube,many methods of enhanced heat transfer can be adopted,for example,apply pulsation,insert,treat heatt transfer surface and so on.Among those various methods,the use of shaped tubes to enhance heat transfer adds little complexity to the work system.It is more suitable for some industrial fields,such as heat exchanger in power plant,seawater temperature difference power generation heat exchange system.Due to its independent support,easy flow separation and low shear rate,the wave-walled tube is taken as the research object of this subject.Although some researches have been made on the mass transfer of the fluid in the wave-walled tube,and a few have been made on the heat transfer of the fluid in the wave-walled tube,the research on its structural parameters is not comprehensive.In the existing studies,it is not found that the overall heat transfer effect of wave-walled tube is analyzed from the aspect of radius ratio and comprehensive heat transfer factor,and no exploration on the application of the tube type in traditional tube-shell heat exchanger is found.Therefore,numerical simulation and experiment were combined to study the heat and mass transfer and flow characteristics of the fluid in the wave-walled tube.Firstly,the influence of wavelength and amplitude on velocity field,temperature field and vorticity field is analyzed by numerical simulation.It is found that as the wavelength of the wave-walled tube decreases,the heat transfer capacity,flow field turbulence and friction coefficient of the wave-walled tube increase,among which the friction coefficient increases slightly.It is also found that the turbulence of the fluid flow field in the wave-walled tube increases with the increase of the wave-walled tube amplitude,but the heat transfer capacity of the fluid in the wave-walled tube increases greatly.When the wave-wall tube wave-amplitude is less than 3.5mm,the fluctuation of the wave-amplitude has little influence on the friction coefficient.When the wave-amplitude exceeds 3.5mm,the friction coefficient increases sharply with the increase of the wave-amplitude.Secondly,the influence of the radius ratio of the wave-walled tube on the fluid flow and heat transfer in the tube is analyzed from pressure gradient and field synergy.It is found that the pressure gradient in the downstream pressure gradient zone is obviously higher than that in the inverse pressure gradient zone,and the convection heat transfer coefficient in the downstream pressure gradient zone is higher than that in the inverse pressure gradient zone.The smaller the radius ratio of the wave-wall tube,the greater the synergy between the velocity field and the temperature field,and the better the heat transfer effect.As the radius ratio increases,the friction coefficient of the fluid in the wave-walled tube increases first and then decreases,and reaches the maximum value when the radius ratio is 1.Thirdly,electrochemical experiments and visualization experiments were carried out on the heat and mass transfer and flow characteristics of the fluid in the wave-walled tube.The results of electrochemical experiments show that increasing the wave-amplitude or decreasing the wavelength of the wave-wall tube can enhance the heat and mass transfer rate of the fluid in the tube.The result of visualization experiment shows that the fluid in the wave crest of the wave-wall tube is easy to generate vortices,which makes the mass transfer mode change to vorticity diffusion.Finally,the wave-walled tube is applied to the shell and tube heat exchanger instead of the straight tube.The heat transfer and flow characteristics in the heat exchanger are analyzed by numerical simulation,and the flow field and temperature field of the fluid on the shell side are analyzed emphatically.The results show that the heat transfer efficiency of wave-wall tube heat exchanger is higher than that of straight wall tube heat exchanger,and the pressure drop of shell side is lower than that of straight wall tube heat exchanger.The comprehensive heat transfer capacity of wave-walled tube heat exchanger is higher than that of straight-walled tube heat exchanger,This can provide an important reference for the application of wave-wall tube in shell and tube heat exchanger.