真空滤油机流场的数值模拟

Simulation of Flow Field in Vacuum Oil Purifier

为了获取真空滤油机蒸发脱水的动态特性,考虑了油水汽三相流、水滴蒸发相变等因素,建立了真空滤油机的流场的RSM模型以及水滴运动蒸发的相变方程;分析了滤油机内部的蒸汽体积浓度分布、压力分布以及轴向和径向速度分布的规律,结果表明滤油机内部分离塔板上部的中心附近压力梯度较大,而靠近壁面附近压力梯度较小,有助于蒸汽有向壁面运移的趋势,,实现液汽分离;分离塔板内部压力梯度趋缓,增大了油水在塔板内的停留时间;油水混合液的最大径向速度面把滤油机内部的流场分为了准强制涡和准自由涡;而其轴向速度呈对称分布;进一步揭示了油水分离的特性,并计算了滤油机的蒸发效率,计算值与实测值吻合较好,验证了该模型的有效性,对深入研究真空滤油机的油水分离机理奠定前期基础。

The flow-field of the liquid in the vacuum oil purifier was approximated with Reynolds Stress model （RSM）, and simulated to understand the dynamic behavior of vacuum evaporation and dehydration of water droplets mixed in the oil. In the simulation,the influencing factors,including the coexistence of the oil, water,and vapor phases,and evaporation of water droplets, were considered. The realistic situation of water vapor, such as its density and partial pressure distributions, its radial and axial velocities distributions, were calculated. The results included： i） When the pressure gradient near the center of the upper separation plate is larger than that close to the wall of the purifier, the flowing of vapor towards the wall results in a separation of vapor from liquid; ii）. A smaller pressure gradient inside the separation plate increases the residence time of the liquid inside the plate; iii） The surface, moving at the highest radial velocity, divides the flow field into a quasi-forced vortex and a quasi-free vortex; and iv）, Its axial velocity distributes symmetrically.The calculated evaporation rate of the purifier was found to agree fairly well with the measured one.