Based on the rigid plastic theory; the load-deflection functions with and without considering the effect of strain hardening are respectively derived for an elliptical tube under quasi-static compression by two parall...Based on the rigid plastic theory; the load-deflection functions with and without considering the effect of strain hardening are respectively derived for an elliptical tube under quasi-static compression by two parallel rigid plates. The non-dimensional load-deflection responses predicted by the present theory and the finite element simula- tions are compared, and the favorable agreement is found. The results show that strain hardening may have a noticeable influence on the load-deflection curves of an elliptical tube under quasi-static compression. Compared with the circular counterpart, the ellip- tical tube exhibits different energy absorption behavior due to the difference between the major axis and the minor axis. When loaded along the major axis of a slightly oval tube, a relative even and long plateau region of the load-deflection curve is achieved, which is especially desirable for the design of energy absorbers.展开更多
An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardenin...An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardening effect. The four-hinge collapse mechanism is used, and the governing equation is derived from Lagrange equations of the second kind. The numerical simulation of the dynamic response of the elliptical tube under impact using the finite element explicit code LS-DYNA is performed. The reaction force-displacement curve and displacement-time curve of the plate obtained from the two methods are in good agreement.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 contact melting process of solid phase change material(PCM)has essential applications in some energy storage systems,which is related closely to the heat resource’s geometry and thermal boundary conditions.The co...The contact melting process of solid phase change material(PCM)has essential applications in some energy storage systems,which is related closely to the heat resource’s geometry and thermal boundary conditions.The contact melting of PCM in a horizontal elliptical tube under the second kind of thermal boundary condition,namely the constant surface heat flux,was investigated analytically.The analysis model is proposed based on the contact melting lubrication theory,and the model deduces the basic dimensionless equations.The variation rules of parameters such as contact melting speed,melting completion time,and boundary layer thickness distribution are obtained for the different heat fluxes.The influences of the elliptical heat resource geometry boundary and the compression coefficient on these melting parameters were also analyzed.The results include the contact melting inside a horizontal circular tube.Compared with the contact melting under the first kind of thermal boundary condition,the constant surface temperature,some significant conclusions are drawn.展开更多
Based on experimental data,numerical simulations by turbulent air flowing across staggered tube bundle composed of twisted elliptical tube(TET)with constant tube wall temperature are conducted in present study.Paramet...Based on experimental data,numerical simulations by turbulent air flowing across staggered tube bundle composed of twisted elliptical tube(TET)with constant tube wall temperature are conducted in present study.Parametric study on the thermal-hydraulic characteristics of air crossflow in TET bundles is investigated with physical parameters and Reynolds number(Re).The results show that spiral channels created by spiral deformation of TETs have a diversion effect on the air flow,which changes the flow direction of the air near the tube wall.The air in the near wall region is a three-dimensional flow,consisting of a flow perpendicular to the normal direction of the elliptical cross section and a spiral flow along the helicoid on the downstream side and the upstream side.And the interaction of the spiral channels makes the two flows and their mixing more complicated.The excellent heat transfer performance of staggered TET bundles is confirmed by the comparison of the comprehensive heat transfer performance with that of circular tube bundles.The average Nusselt number(Nu)increases with the increase of the aspect ratio(A/B)and with the increase of Re while decreases as the twist pitch(S)increases.The average Euler number(Eu)increases as A/B increases,while it decreases as Re increases and as S increases.Due to the fact that the suitable correlations for staggered TET bundles are not reported,correlations for Nu and Eu obtained from experimental data and numerical results are presented in the multiple forms.展开更多
基金Project supported by the National Natural Science Foundation of China(No.11472035)
文摘Based on the rigid plastic theory; the load-deflection functions with and without considering the effect of strain hardening are respectively derived for an elliptical tube under quasi-static compression by two parallel rigid plates. The non-dimensional load-deflection responses predicted by the present theory and the finite element simula- tions are compared, and the favorable agreement is found. The results show that strain hardening may have a noticeable influence on the load-deflection curves of an elliptical tube under quasi-static compression. Compared with the circular counterpart, the ellip- tical tube exhibits different energy absorption behavior due to the difference between the major axis and the minor axis. When loaded along the major axis of a slightly oval tube, a relative even and long plateau region of the load-deflection curve is achieved, which is especially desirable for the design of energy absorbers.
基金Project supported by the National Natural Science Foundation of China(No.11032001)
文摘An analytical model is developed to study the crushing behavior and energy absorption capability of a single elliptical tube impacted by two parallel rigid plates, with and without consideration of the strain hardening effect. The four-hinge collapse mechanism is used, and the governing equation is derived from Lagrange equations of the second kind. The numerical simulation of the dynamic response of the elliptical tube under impact using the finite element explicit code LS-DYNA is performed. The reaction force-displacement curve and displacement-time curve of the plate obtained from the two methods are in good agreement.
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.
基金supported by the National Natural Science Foundation of China(Project number 12175311).
文摘The contact melting process of solid phase change material(PCM)has essential applications in some energy storage systems,which is related closely to the heat resource’s geometry and thermal boundary conditions.The contact melting of PCM in a horizontal elliptical tube under the second kind of thermal boundary condition,namely the constant surface heat flux,was investigated analytically.The analysis model is proposed based on the contact melting lubrication theory,and the model deduces the basic dimensionless equations.The variation rules of parameters such as contact melting speed,melting completion time,and boundary layer thickness distribution are obtained for the different heat fluxes.The influences of the elliptical heat resource geometry boundary and the compression coefficient on these melting parameters were also analyzed.The results include the contact melting inside a horizontal circular tube.Compared with the contact melting under the first kind of thermal boundary condition,the constant surface temperature,some significant conclusions are drawn.
基金supported by National Natural Science Foundation of China(No.51806060,No.51876055,and No.51706061)CAS Key Laboratory of Renewable Energy(No.E029kf0401)Doctoral Research Startup Fund of Henan University of Science and Technology.
文摘Based on experimental data,numerical simulations by turbulent air flowing across staggered tube bundle composed of twisted elliptical tube(TET)with constant tube wall temperature are conducted in present study.Parametric study on the thermal-hydraulic characteristics of air crossflow in TET bundles is investigated with physical parameters and Reynolds number(Re).The results show that spiral channels created by spiral deformation of TETs have a diversion effect on the air flow,which changes the flow direction of the air near the tube wall.The air in the near wall region is a three-dimensional flow,consisting of a flow perpendicular to the normal direction of the elliptical cross section and a spiral flow along the helicoid on the downstream side and the upstream side.And the interaction of the spiral channels makes the two flows and their mixing more complicated.The excellent heat transfer performance of staggered TET bundles is confirmed by the comparison of the comprehensive heat transfer performance with that of circular tube bundles.The average Nusselt number(Nu)increases with the increase of the aspect ratio(A/B)and with the increase of Re while decreases as the twist pitch(S)increases.The average Euler number(Eu)increases as A/B increases,while it decreases as Re increases and as S increases.Due to the fact that the suitable correlations for staggered TET bundles are not reported,correlations for Nu and Eu obtained from experimental data and numerical results are presented in the multiple forms.
