换热器通道内反向旋转纵向涡间的干涉特性

纵向涡能以较小的压力损失获得较大程度的传热强化,在换热器空气侧强化传热中得到了广泛应用。换热器通道内通常存在多个纵向涡,纵向涡之间的干涉会不可避免地影响纵向涡的强度和强化传热性能。建立了换热器通道中旋转方向相反的两个纵向涡之间的干涉模型,通过数值方法分析了不同涡产生器横向间距下纵向涡之间的干涉现象。通过纵向涡强度定量研究了涡间干涉对纵向涡强度、流动阻力以及强化换热的影响。结果表明:旋转方向相反的两个纵向涡之间的干涉随着涡产生器间距的减小而增大;在涡产生器间距为零时纵向涡间干涉程度最大,纵向涡强度Se、Nu以及阻力系数f的变化量均达到最小值;在本文计算参数范围内,纵向涡引起的Se和Nu的变化量最大差别达到45%和50%,f的变化达到38%;纵向涡干涉并非一定不利于换热,纵向涡干涉后的流动结构影响其强化传热性能。在涡产生器横向间距为涡产生器底边横向投影长度的2倍时,可以利用纵向涡干涉获得最佳传热性能。

Interaction characteristics between longitudinal vortices with counter-rotating directions in heat exchanger channel

Longitudinal vortices can enhance heat transfer with small pressure loss penalty and has been widely applied in heat transfer enhancement of tube bank fin heat exchangers. Setting winglet vortex generator (VG) that can generate longitudinal vortices on the fin surface is a promising technique to enhance the airside heat transfer. In order to obtain better heat transfer performance, lots of VGs are punched out of the fin surface, so several longitudinal vortices appear in the flow channel. The interaction of vortices affects the intensity of longitudinal vortices and their effect on heat transfer enhancement. In this paper, the interaction of counter rotating longitudinal vortices generated by winglet VGs is quantitatively analyzed under different transversal distances between VGs. The effects of interaction of vortices on the intensity of vortices, flow field structure and heat transfer are discussed in detail by using the longitudinal vortex intensity parameter Se. The results show that the interaction of counter rotating longitudinal vortices increases with the decrease of transversal distance between VGs. When the distance between VGs is zero, the interaction between counter rotating vortices is the most serious, while the values of ΔSe, ΔNu and Δf get the minimum values. The maximum decreasing percentage of ΔSe, ΔNu and Δf are 45%, 50% and 38%, respectively. The interaction between counter rotating vortices does not necessarily decrease the heat transfer of longitudinal vortices. The heat transfer performance depends on not only the intensity of vortices but also their structure. The common flow region formed between counter rotating longitudinal vortices is beneficial for heat transfer enhancement. Due to the interactions of counter rotating longitudinal vortices and their effect on heat transfer enhancement, an optimum arrangement of VGs exists for better heat transfer performance. The best heat transfer performance can be obtained when the transversal distance between the VGs is twice the projected length of the base of VGs.