Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was ...Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.展开更多
In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,hor...In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.展开更多
The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage....The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.展开更多
The thermal analysis of the annular rectangular profile fins with variable thermal properties is investigated by using the homotopy analysis method （HAM）. The thermal conductivity and heat transfer coefficient are a...The thermal analysis of the annular rectangular profile fins with variable thermal properties is investigated by using the homotopy analysis method （HAM）. The thermal conductivity and heat transfer coefficient are assumed to vary with a linear and power-law function of temperature, respectively. The effects of the thermal-geometric fin parameter and the thermal conductivity parameter variations on the temperature distribution and fin efficiency are investigated for different heat transfer modes. Results from the HAM are compared with numerical results of the finite difference method （FDM）. It can be seen that the variation of dimensionless parameters has a significant effect on the temperature distribution and fin efficiency.展开更多
As a simple and effective method of heat transfer enhancement,fins are widely used in latent heat storage systems.However,the choice of annular fins and longitudinal fins has always been controversial.In this paper,th...As a simple and effective method of heat transfer enhancement,fins are widely used in latent heat storage systems.However,the choice of annular fins and longitudinal fins has always been controversial.In this paper,the melting process of phase change material(PCM)in annular fins and longitudinal fins latent heat storage units with the same volume is numerically simulated.To ensure the same thermal penetration,three-dimensional spaces occupied with fins are specially controlled to be the same.Combined with finned structures,the effects of natural convection(NC),placement mode and heat transfer fluid(HTF)inlet direction on the melting process are studied.The results show that the melting time in annular finned structure is always 10%less than that in longitudinal finned structure,which demonstrates the superior of the annular fins in the latent heat storage unit.The melting time is the shortest in vertical unit with annular fins and HTF inlet at the bottom.Additionally,the correlation formulas of the liquid fraction are proposed in the vertical unit with HTF inlet at the bottom.展开更多
文摘Natural convection heat transfer from annular finned tubes was studied numerically. Effects of fin spacing, temperature difference and tube diameter on flow pathlines and local heat transfer were also studied. It was shown that pathlines remain mostly circular for different geometries. Moreover, the contributions of fin periphery, fin side and bare tube to heat transfer were specified. It was shown that the heat transfer per unit area of fin periphery can be several times that of other parts. Moreover, in higher finspacing, the heat transfer from the bare tube can be more important than fin sides.
文摘In this study,thermo-fluid characteristics of elliptical annular finned tube heat exchanger were numerically studied in detail.Transition SST model was utilized to simulate turbulent flow.Effects of air velocities,horizontal to vertical fin diameter ratios,and fin densities were examined in detail.The simulations indicate superior performance of elliptical fin layout.It was shown that pressure drop of annular elliptical fin can be only one half of that of a circular annular fin while containing comparable heat transfer performance.The vertical elliptical annular fin may even contain a higher heat transfer performance over circular fin.Correlations are proposed to estimate the Nu number and pressure drop based on the annular circular fin.The maximum deviations between the proposed correlations and simulations regarding pressure drop and heat transfer coefficient are 5.6%and 3.2%,respectively.For further elaboration of the superiority of the elliptical layout from the second law perspective,normalized entropy generation was also studied.In all cases,the entropy generation rate in circular fin was higher than that of an elliptical fin.
文摘The Green＇s function method is applied for the transient temperature of an annular fin when a phase change material （PCM） solidifies on it. The solidification of the PCMs takes place in a cylindrical shell storage. The thickness of the solid PCM on the fin varies with time and is obtained by the Megerlin method. The models are found with the Bessel equation to form an analytical solution. Three different kinds of boundary conditions are investigated. The comparison between analytical and numerical solutions is given. The results demonstrate that the significant accuracy is obtained for the temperature distribution for the fin in all cases.
文摘The thermal analysis of the annular rectangular profile fins with variable thermal properties is investigated by using the homotopy analysis method （HAM）. The thermal conductivity and heat transfer coefficient are assumed to vary with a linear and power-law function of temperature, respectively. The effects of the thermal-geometric fin parameter and the thermal conductivity parameter variations on the temperature distribution and fin efficiency are investigated for different heat transfer modes. Results from the HAM are compared with numerical results of the finite difference method （FDM）. It can be seen that the variation of dimensionless parameters has a significant effect on the temperature distribution and fin efficiency.
文摘As a simple and effective method of heat transfer enhancement,fins are widely used in latent heat storage systems.However,the choice of annular fins and longitudinal fins has always been controversial.In this paper,the melting process of phase change material(PCM)in annular fins and longitudinal fins latent heat storage units with the same volume is numerically simulated.To ensure the same thermal penetration,three-dimensional spaces occupied with fins are specially controlled to be the same.Combined with finned structures,the effects of natural convection(NC),placement mode and heat transfer fluid(HTF)inlet direction on the melting process are studied.The results show that the melting time in annular finned structure is always 10%less than that in longitudinal finned structure,which demonstrates the superior of the annular fins in the latent heat storage unit.The melting time is the shortest in vertical unit with annular fins and HTF inlet at the bottom.Additionally,the correlation formulas of the liquid fraction are proposed in the vertical unit with HTF inlet at the bottom.
