双U形管束换热器压降和热效率模型实验

Model experiment on pressure drop and thermal efficiency of double U-shaped tubes heat exchanger

在低速风洞上实验研究了双U形管束换热器压降特性以及热效率,着重对比了U形管截面形状和换热器安装角的影响.结果表明:在相同的U形管管内平均速度下,椭圆管换热器的管内压降高于圆管换热器,在较高的管内平均速度下两者的差异更为明显;对于外部流动,换热器安装角增大所诱导的外部流动压降显著增加,在较小的换热器安装角下,椭圆管换热器的管外压降略大于圆管换热器,而在较大的换热器安装角下,椭圆管换热器的管外压降则显著低于圆管换热器;安装角为30°的换热器传热系数较安装角为10°时可以提高约50%,在密流比为0.4时,椭圆管换热器的热效率相对于圆管换热器约有6%的增加.

Pressure drop and thermal efficiency of double U-shaped tube heat exchanger, especially the effects of tube cross-sectional shape and heat exchanger inclined angle, were experimentally investigated in a low-speed wind tunnel. The results show that the internal pressure drop for the elliptical tube heat exchanger is bigger than the circular tube heat ex- changer under the same averaged flow velocity inside the U-shaped tube. The difference be- tween two different heat exchangers is more obvious under higher flow velocity inside the U- shaped tube. For the external flow, the pressure drop is significantly increased with the in- crease of the heat exchanger＇s inclined angle. Under small inclined angle, the external flow pressure drop for the elliptical tube heat exchanger is somewhat higher than the circular tube heat exchanger. However, the pressure drop outside the elliptical tube heat exchanger is sig- nificantly lower than the circular tube heat exchanger under big inclined angle. The overall heat transfer coefficient of heat exchanger with 30 degree inclination is about 50% higher than that with 10 degree. Under the density flow ratio of O. 4, the thermal efficiency of ellip- tical tube heat exchanger is increased about 6% in relative to the circular tube heat exchanger.