连续螺旋折流板换热器流动与传热性能及熵产分析

Analyses on flow and heat transfer performance and entropy generation of heat exchanger with continuous helical baffles

采用数值模拟的方法,研究了螺旋角对连续螺旋折流板换热器流动与传热性能的影响,并以熵产数为指标对换热器性能进行了基于热力学第二定律的分析评价。结果表明,相同质量流量时壳程传热系数和压降均随螺旋角的增大而降低,且后者降低的幅度大于前者。连续螺旋折流板换热器壳程横截面上切向速度分布较弓形折流板换热器更加均匀。在靠近中心假管的内层区域,同一径向位置的轴向速度随螺旋角的增大而降低,而在靠近壳体壁面的外层区域则相反。螺旋角越大,不同径向位置的换热管间的换热量分布均匀性越好。壳程质量流量相等时,换热器中传热引起的熵产占总熵产的比重随着螺旋角的增大而增加,熵产数随着螺旋角的增大而降低。

A numerical simulation for heat exchanger with continuous helical baffles was carried out by using commercial codes of ANSYS CFX 12.0.The study focuses on the effects of helix angle on flow and heat transfer characteristics,and heat exchanger performance is evaluated by entropy generation number based on the analysis of the second law of thermodynamics.The results show that both the shell-side heat transfer coefficient and pressure drop decrease with the increase of the helix angle at certain mass flow rate.The latter decreases more quickly than the former.The tangential velocity distribution on shell-side cross section is more uniform with continuous helical baffles than with segmental baffles.The axial velocity at certain radial position decreases as the helix angle increases in the inner region near the central dummy tube,whereas it increases as the helix angle increases in the outer region near the shell.The heat exchange quantity distribution in tubes at different radial positions is more uniform at larger helix angle.The proportion of the entropy generation contributed by heat transfer in total entropy generation increases and the entropy generation number decreases with the increase of the helix angle at certain mass flow rate.