Heat Transfer of Near Pseudocritical Nitrogen in Helically Coiled Tube for Cryogenic Energy Storage
Heat Transfer of Near Pseudocritical Nitrogen in Helically Coiled Tube for Cryogenic Energy Storage
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DOI：
10.3390/en15082752
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发表时间：
2022-04
期刊：
影响因子：
3.2
通讯作者：
Yi Wang;Tiejun Lu;Xianglei Liu;A. Sciacovelli;Yongliang Li
中科院分区：
文献类型：
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作者：
Yi Wang;Tiejun Lu;Xianglei Liu;A. Sciacovelli;Yongliang Li
本文研究了在准临界条件、浮力和盘管曲率共同作用下，氮气在螺旋管内流动的低温换热现象。最终目标是设计最优的液空储能换热器。局部换热系数是通过管子的横截面沿圆周方向计算的。考察了压力、质量流量和热流密度对换热的影响。用一个无量纲数Ψ解释了浮力和盘管曲率对换热系数的双重影响，该数表示两者的比值。结果表明，换热系数随质量流量的增大而增大，随压力和热流密度的减小而减小。当流体温度低于准临界温度(例如35bar时的−温度为146.3°C)时，浮力效应主导换热，而在较高温度下，线圈曲率诱导的离心力效应主导换热。当流体温度低于准临界温度时，螺旋盘管的换热系数比直管低约13%，但在较高温度时，两者的差值缩小(±6%)。这是因为热物性的变化和浮力效应抵消了盘曲和改进湍流混合对换热的好处。
This paper investigates the cryogenic heat transfer phenomena of nitrogen flowing in helically coiled tubes under the combined effects of pseudocritical conditions, buoyancy, and coil curvature. The ultimate goal was to design optimum heat exchangers for liquid air energy storage. Local heat transfer coefficients were evaluated peripherally across tube cross sections. The pressure, mass flux, and heat flux effects on the heat transfer were examined. The dual effect of buoyancy and coil curvature on heat transfer coefficients was interpreted via a dimensionless number Ψ, which denotes a ratio between the two effects. Results reveal that the heat transfer coefficients increase with increasing mass flux but decreasing pressure and heat flux. The buoyancy effect dominates the heat transfer at fluid temperatures below the pseudocritical temperature (e.g., −146.3 °C at 35 bar), while the coil curvature-induced centrifugal effect dominates at higher temperatures. The heat transfer coefficients for the helical coil were approximately 13% lower compared with those in straight tube at fluid temperatures below the pseudocritical temperature, but their difference shrinks (<±6%) at higher temperatures. The reason is that the benefits of coil curvature and improved turbulent mixing on heat transfer are counteracted by the thermophysical property variation and buoyancy effect.