从流型,压降和传热三个方面综述了以前研究者在U型管中所做的研究.指出了180°弯头对整个U型管的流型及其流型转变,压降损失及其预测方法和增强换热的影响.同时提出了今后关于U型管可能的研究方向:(1)细化曲率比等几何因素对流型压降传热的影响；(2)关注低温介质的U型管中的流动与传热；(3)以180°弯头加上距其一定距离的上下游为一个单元考虑其整体的压降损失；(4)量化气液两相流在U型管中的传热.%A review was conducted to elaborate the influence of 180 degree return bend on U - tubes from three aspects; flow pattern, pressure drop and heat transfer. The secondary flow induced in the 180 degree return bend changed the incoming flow pattern, increased the pressure loss and enhanced the heat transfer in U - tubes. It is advised that there four possible research directions of the U - tubes. ( 1) Refining the influence of geometric factors such as the curvature ratio on the flow pattern transition and pressure drop and heat transfer. (2) Focus on the low temperature fluid medium flowing in U - tubes. ( 3 ) Reconsider the pressure loss of U - tube taking the 180 degree return bend and its up - and downstream section as a unit. (4) Qualify the heat transfer of gas - liquid two - phase flow in U - tubes.
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