双U型管束模型换热器的流动和传热特性

为了研究双U型管束模型换热器的流动和传热性能,通过低速高温风洞的模型实验和Fluent-CFD数值计算,得到了换热器的管型和安装角对换热器压降和回热效率的影响规律。结果表明:在相同的双U型管管内气流平均流动速度下,椭圆管换热器的管内流动压降高于圆管换热器的,相对增加幅度在50%~60%之间;对于外部流动,换热器安装角度增大所诱导的外部流动压降显著增加,在换热器30°的安装角下,椭圆形管束的低阻流动型面得以充分体现,其外部流动压降较圆形管束换热器可以降低约50%;随着换热器安装角的增加,换热器回热效率具有明显的提高;相对换热器安装角,换热器管型对回热效率的影响较小,集气管的进气-出气方式对双U型管束换热器的回热效率具有较显著的影响。

Flow and heat transfer performance of double U-shaped-tubes modeled heat exchanger

In order to investigate the flow and heat transfer performances of double U-shaped-tubes modeled heat exchanger, model experiments were conducted in a low-speed high-temperature wind tunnel and numerical calculations were also conducted using Fluent-CFD software. The effects of tube cross-sectional shape and heat exchanger inclined angle on the pressure drop and recuperator effectiveness were obtained. The results show that the internal pressure drop for the elliptic-tube heat exchanger is increased by about 50%-60% relative to the circular-tube heat exchanger at the same averaged flow velocity inside the U-shaped tube. For the external flow, the pressure drop is significantly increased as the increase of heat exchanger inclined angle. At inclined angle of 30°, the pressure drop outside the elliptic-tube heat exchanger is significantly lower than that of the circular-tube heat exchanger with approximately 50% decrease. As the heat exchanger inclined angle increases, the recuperator effectiveness is significantly improved. By comparison with the effect of inclined angle, the tube shape has a weak influence on the recuperator effectiveness. The internal flow entering-gathering mode has moderate effect on the recuperator effectiveness of U-shaped-tubes heat exchanger.