基于混合格子玻尔兹曼方法的二维多孔介质冷凝
CONDENSATION IN TWO-DIMENSIONAL POROUS MEDIA BASED ON HYBRID LATTICE BOLTZMANN METHOD
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摘要: 采用混合格子玻尔兹曼模型开展了二维多孔介质中蒸汽冷凝的数值模拟研究, 揭示了其中涉及的多相流-相变-传热耦合作用机理. 首先对饱和蒸汽在竖直亲水与水平疏水过冷壁面上进行冷凝模拟, 验证了混合格子玻尔兹曼模型的准确性. 将该模型应用在二维均匀多孔介质冷凝模拟中, 发现高温蒸汽遇到过冷多孔介质后先以液滴状冷凝, 而后汇聚连通形成液面. 当冷凝液在不同固体层间的孔隙沿流向流动时, 气液界面由于毛细力作用呈现“凹-凸”周期性变化. 受粘性阻力影响, 冷凝液在孔隙内流动缓慢, 甚至出现液体阻塞. 进一步研究了多孔介质表面润湿性、孔隙率、孔隙排布形式、流体热力学参数对冷凝行为的影响, 结果表明: 壁面接触角从53°减小为29°时, 冷凝量提高约10.9%, 且液体阻塞现象被抑制. 当孔隙率提高9.37%时, 冷凝量增加约28.07%. 具有较大热扩散系数的液体能够提高热量传递效率, 使得冷凝加快; 在导热率及系统输入热量固定、流体比热容增大时, 用于相变的热量减小, 导致冷凝难以发生. 在对比分析四种不同孔隙结构对冷凝过程的影响机理后, 提出了“进出口大孔隙率、中间段小孔隙率”的孔隙排布, 实现提高蒸汽冷凝量约5.11%的同时抑制阻塞.Abstract: A hybrid lattice Boltzmann model is developed to numerically investigate vapor condensation in two-dimensional porous media, aiming to elucidate the underlying coupling mechanisms among multiphase flow, phase change, and heat transfer. To verify the accuracy of the hybrid lattice Boltzmann model, simulations of saturated vapor condensing on vertically oriented hydrophilic and horizontally oriented hydrophobic subcooled walls are first conducted. It is then applied to simulate condensation in uniform porous structures. The results indicate that high-temperature vapor initially condenses into discrete droplets upon contact with subcooled porous media, which subsequently coalesce into continuous liquid films. As the condensate flows through pore spaces between solid layers, the gas-liquid interface exhibits periodic "concave-convex" deformations due to capillary effects. The transport of condensate is significantly hindered by viscous resistance, and liquid blockage may occur within the pores. Parametric studies are conducted to explore the effects of surface wettability, porosity, fluid thermophysical properties, and pore arrangement on the condensation behavior. It is found that reducing the wall contact angle from 53° to 29° enhances the total condensate volume by approximately 10.9% and effectively suppresses liquid blockage. An increase in porosity by 9.37% leads to a 28.07% increase in condensation mass. Fluids with higher thermal diffusivity promote more efficient heat transfer, thereby accelerating the condensation process. In contrast, when thermal conductivity and heat input are fixed, increasing the fluid’s specific heat capacity reduces the amount of energy available for phase change, thus hindering condensation. Based on a comparative analysis of four different pore structures, an optimized design featuring higher porosity at the inlet and outlet and lower porosity in the central region is proposed. This configuration increases the condensate yield by approximately 5.11% while mitigating flow obstruction.
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