旋流强度对气/雾两相传热传质的影响

为进一步提高发动机排气集水箱对高温烟气的降温性能，研究了旋流强度对高温烟气与冷却水雾两相流传热传质的影响．利用欧拉 拉格朗日方法和离散相模型对集水箱内横流喷雾冷却过程进行了三维数值模拟．对排气集水箱涡流室某一截面处的气流旋流数进行了理论推导，并将得到的旋流数解析解与数值解进行了比较．结果表明：集水箱涡流室内的旋流是强旋流动，理论解析解与数值解基本吻合；在集水箱排气室形成了一道“屏障”，在其上游区域内雾滴的有效运动行程比其下游区域内雾滴的有效运动行程长；提高烟气旋流强度，可增强两相掺混，延长液滴有效运动行程和蒸发时间；应使水雾雾滴进入烟气流场的初始位置位于“屏障”上游区域，以提高喷雾冷却效果．

Effect of Swirl Intensity on Heat and Mass Transfer in Gas-Droplets Two-Phase Flow

In order to further improve the cooling performance of a water-collecting box (WCB) for the high temperature exhaust gas in an engine exhaust system, a numerical simulation was performed to explore the effect of swirl intensity on the heat and mass transfer between the hot exhaust gas and the water droplets. The Eulerian-Lagrangian method and the discrete phase model were used in the three-dimensional simulation of the cross-flow spray cooling in the WCB. The swirl number was theoretically derived at a certain section of the vortex chamber in the WCB. The analytical swirl number was obtained using an analytical formula and was compared with the numerical solution. The results indicate that the swirling flow in the vortex chamber is strong and that the analytical swirl number agrees well with the numerical solution. A “barrier” is formed in the exhaust chamber, and the effective motion distance of the water droplets in the upstream zone of the “barrier” are longer than that of the droplets in the downstream zone. Raising the swirl intensity of gas flow will enhance the mix of two phases, and the effective motion distances and the evaporating time of the droplets will be prolonged. In order to enhance the spray cooling effect, the initial location where the water droplets enter the gas stream should be in the upstream zone of the “barrier”.