Numerical Research On Flow And Heat Transfer Of Power-law Fluid In Straight Tubes And Helical Tubes With Different Cross Sections

The flow and heat transfer phenomena of non-Newtonian power-law fluid widely exist in nature and production practice,especially in engineering practice,such as mixing technology,crude oil mining,coal water slurry transportation and so on.In recent years,the improvement of industrial level has intensified energy consumption,and “energy saving and efficiency improvement” has become a powerful measure to alleviate energy pressure.Fossil energy is the main energy source in China,and most of the fluids in fossil energy are non-Newtonian fluids.In addition,the rheological characteristics of non-Newtonian fluids are more complex and diverse than that of Newtonian fluids,so it is of great significance to systematically study the flow and heat transfer characteristics.In this paper,non-Newtonian power-law fluids are used as the main research media to study the variation of friction factor and convective heat transfer of power-law fluids in straight and helical tubes with different cross-sections.In this paper,the flow and heat transfer of power-law fluids in straight and helical tubes with different cross-sections are studied by numerical simulation.Firstly,the power-law model and turbulence model are validated by comparing the numerical simulation results with the the theoretical value of experimental correlations and classical experimental.Secondly,the flow and heat transfer of a specific power-law fluid in straight and helical tubes are numerically simulated and analyzed by using the verified power-law model and turbulence model.In this paper,the influence of cross-sectional shape,Reynolds number,power-law index,relative roughness and other factors on the flow and heat transfer of the fluid in the tube are mainly discussed.In addition,due to the slightly complex geometry of the helical tube,the influence of curvature and dimensionless pitch on the fluid flow and heat transfer in the helical tube is also considered.And the variation of velocity field,pressure field and temperature field on the cross section of Y=0 in the helical tube are analyzed and discussed in detail.Meanwhile,in order to show the flow and heat transfer characteristics ofpower-law fluid in helical tubes more clearly,the boundary conditions of adiabatic and constant wall temperature are set respectively for simulation calculation.The results show that cross-section shape,Reynolds number,power law index,relative roughness and other factors have a certain influence on the friction factor and convective heat transfer intensity of non-Newtonian power-law fluids in straight and helical tubes.And there are some correlations between these factors and the fluid flow and heat transfer.Besides the curvature and dimensionless pitch of the helical tube also have different effects on the flow and heat transfer of power-law fluid in the tube,and the curvature has a greater effect as is shown in the results.The reason is that the change of curvature will change the size of Dean number,which will affect the disturbance degree of secondary flow in the tube,and then affect the change of flow resistance and heat transfer capacity of power-law fluid in the tube.However,the dimensionless pitch change does not change Dean number and has little effect on secondary flow,so it have a little effect on the influence on flow and heat transfer relatively.In this paper,the flow resistance and convective heat transfer of non-Newtonian power-law fluids in straight and helical tubes with different cross-sections are discussed in some detail.The purpose of this paper is to provide some theoretical references for studying the flow and heat transfer characteristics of non-Newtonian power-law fluids caused by complex rheological characteristics.