| The shortage of energy has increased the demand for energy conservation in many industries and has become the most important research field in recent years.Many industrial applications require high-performance heat exchanger to achieve efficient energy transfer,such as chemical industry,automotive industry,metallurgy,etc.However,while many heat exchangers strengthen heat exchange,the flow resistance has also doubled,which limits the industrial development prospects of these heat exchangers.Therefore,further reducing the flow resistance of the heat exchanger and improving its work efficiency have become the focus of research by scholars.The research on enhanced heat transfer technology of convection in the tube aims to enhance the heat exchange of the fluid between the wall region and the core area,and obtain a higher comprehensive heat transfer efficiency with lower energy consumption.In order to explore the enhanced heat transfer characteristics of the fluid in the tube and reduce the flow resistance,the main work is as follows:First of all,the structure of the commonly used triangular wing vortex generator is remolded under the condition that the projected area of the vortex generator is the same as that of the circular tube.The effects of the opening angle(β = 90 °,60 °,45 °)and inclination angle(θ = 90 °,60 °,45 °)of the new vortex generator(symmetrical triangular wing)on the thermal performance are explored respectively.The results show that the smaller the angle β of the symmetrical triangular wing is,the smaller the flow resistance is,and the lower the comprehensive heat transfer efficiency is,and the smaller the inclination angle θ of the symmetrical delta wing is,the lower the flow resistance is.In case G(θ = 45 °),due to the streamlined structure of its vortex generator,the reflux area is effectively suppressed,the flow resistance is reduced by20%,and the comprehensive heat transfer efficiency is improved by 8%.The field synergy principle is used to explain the results,and the average field coordination angle of case D(β = 90 °,θ = 60 °)is the smallest.Secondly,from the point of view that it is beneficial to the generation of longitudinal vortex,a new type of symmetrical trapezoidal wing vortex generator is proposed by changing the boundary characteristics of symmetrical delta wings,and the effects of flank length L of symmetrical trapezoidal wing L(6mm 8mm)and inclination angle(θ = 90 °,60 °,45 °)on flow and heat transfer characteristics are studied.The numerical results show that the new symmetrical trapezoidal wing vortex generator can guide the fluid to produce local longitudinal vortices,which can further reduce the flow resistance and enhance the comprehensive heat transfer efficiency.The shorter the flank length L of the symmetrical trapezoidal wing is,the stronger the longitudinal vortices is and the smaller the flow resistance is.The effect of the inclination angle θ on the flow resistance is the same as that of the symmetrical delta wing.When the flank length L is 6mm,the comprehensive heat transfer efficiency is the highest,which is 1.22.Compared with symmetrical delta wings and delta wings,the flow resistance is reduced by 2.7% and 21.3% respectively,and the thermal enhancement factor is increased by 0.9% and 8.9%,respectively.The field synergy results show that the inclination angle of the symmetrical trapezoidal wing is 45 °,and the field synergy angle of L=6mm is the smallest.Finally,the heat transfer experimental platform is built with air as the working medium,and the experimental data are monitored and recorded.The results show that the experimental results are in good agreement with the numerical simulation results.Among them,the maximum error of Nu and f is 3.51% and 10.22%.In addition,the uncertainty analysis and repeatability analysis of the experiment are carried out,and the maximum uncertainty of Re,Nu and f are 2.0%,5.9% and 3.0%,respectively.in the repeatability analysis,the maximum errors of Nu and f are 7.00% and 5.1%,respectively. |
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