The paper presents a theoretical study about turbulent film boiling on a horizontal tube with external flowing liquid. The high velocity flowing liquid is determined by potential flow theory. By using Colburn analogy,...The paper presents a theoretical study about turbulent film boiling on a horizontal tube with external flowing liquid. The high velocity flowing liquid is determined by potential flow theory. By using Colburn analogy, the present paper successfully addresses a new model to predict the vapor-liquid interfacial shear, applies the interfacial shear into the forced balance equation and then combines the forced balance equation, the energy equation and thermal energy balance equation. At last, both the film thickness and Nusselt number can be obtained. Besides, the present analysis also includes radiation effects, temperature ratio and eddy diffusivity. Finally, a comparison between the results of the present study and those reported in previous theoretical and experimental studies is provided.展开更多
Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and ventilation.This study numerically investigates the effect of vortex generators on the performance of ...Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and ventilation.This study numerically investigates the effect of vortex generators on the performance of elliptical fin-and-tube heat exchanger under different inclination angles.In this study,air flow that is in the transitional regime is selected as the working fluid.Reynolds numbers at the inlet are varied in a range of 1300 to 2100,and the shear stress transport k-ωturbulence model is selected to solve the non-closure of basic turbulence equations.The ellipticity ratios of the tubes which are used for the analysis are between 0.6 and 1.0,and the inclination angles are varied from 15°to 75°.The effects of different inclination angles of vortex generators on the Colburn factor j,friction factor f,and efficiency index j/f are analyzed.The friction and Colburn factors are observed to increase with increasing vortex generator inclination angles.It is found that the efficiency factors for a 15°vortex generator inclination angle at 0.6,0.7,0.8,and 0.9 ellipticity ratios improve compared to the corresponding cases with no vortex generator.However,the vortex generator cannot improve the efficiency factor of the circular tube heat exchanger.The 3 D CFD method employed by this study has great potential for use in optimally designing the arrangement of the vortex generators to enhance the performance of heat exchangers.展开更多
文摘The paper presents a theoretical study about turbulent film boiling on a horizontal tube with external flowing liquid. The high velocity flowing liquid is determined by potential flow theory. By using Colburn analogy, the present paper successfully addresses a new model to predict the vapor-liquid interfacial shear, applies the interfacial shear into the forced balance equation and then combines the forced balance equation, the energy equation and thermal energy balance equation. At last, both the film thickness and Nusselt number can be obtained. Besides, the present analysis also includes radiation effects, temperature ratio and eddy diffusivity. Finally, a comparison between the results of the present study and those reported in previous theoretical and experimental studies is provided.
基金the financial support by National Natural Science Foundation of China(Grant No.51879201,U1867215)。
文摘Elliptical fin-and-tube heat exchangers are commonly used in air conditioning,heating,refrigeration industries,and ventilation.This study numerically investigates the effect of vortex generators on the performance of elliptical fin-and-tube heat exchanger under different inclination angles.In this study,air flow that is in the transitional regime is selected as the working fluid.Reynolds numbers at the inlet are varied in a range of 1300 to 2100,and the shear stress transport k-ωturbulence model is selected to solve the non-closure of basic turbulence equations.The ellipticity ratios of the tubes which are used for the analysis are between 0.6 and 1.0,and the inclination angles are varied from 15°to 75°.The effects of different inclination angles of vortex generators on the Colburn factor j,friction factor f,and efficiency index j/f are analyzed.The friction and Colburn factors are observed to increase with increasing vortex generator inclination angles.It is found that the efficiency factors for a 15°vortex generator inclination angle at 0.6,0.7,0.8,and 0.9 ellipticity ratios improve compared to the corresponding cases with no vortex generator.However,the vortex generator cannot improve the efficiency factor of the circular tube heat exchanger.The 3 D CFD method employed by this study has great potential for use in optimally designing the arrangement of the vortex generators to enhance the performance of heat exchangers.
