Schilling Sebastian, Glade Heike
Engineering Thermodynamics, University of Bremen, 28359 Bremen, Germany.
Membranes (Basel). 2023 Oct 22;13(10):842. doi: 10.3390/membranes13100842.
Membrane distillation (MD) is an attractive process for the concentration of seawater brines. Modelling and simulation of membrane distillation processes requires a better knowledge of the heat transfer coefficients in spacer-filled channels which are usually determined by applying empirical correlations for the Nusselt number. In this study, first, a comprehensive literature review on heat transfer correlations was conducted. It was found that the empirical correlations often used for MD simulation result in strongly varying Nusselt numbers that differ by up to an order of magnitude at low Reynolds numbers. Then, heat transfer in spacer-filled channels was investigated experimentally in a membrane distillation system using an aluminum plate instead of a flat-sheet membrane. Numerous tests were carried out with sodium chloride solutions in a wide range of salinities, between 1 g/kg and 95 g/kg, and temperatures, between 30 °C and 80 °C, yielding high heat transfer coefficients in a range of 1500 to 8300 W/(mK) at relatively low Reynolds numbers, between 100 and 1500, clearly showing the influence of the spacers on heat transfer. A new empirical Nusselt correlation (Nu=0.158Re0.652Pr0.277) was derived which represents the experimental data with a deviation of 10% and is valid for 100<Re<1500 and 2<Pr<7. Computational fluid dynamics simulations were performed to analyze the variations of the fluid properties across the boundary layer due to temperature differences. The simulations showed only minor deviations of the heat transfer coefficients in the hot and cold fluid channels for small driving temperature differences.
膜蒸馏（MD）是一种用于浓缩海水卤水的有吸引力的工艺。膜蒸馏过程的建模和模拟需要更好地了解填充间隔物通道中的传热系数，这些系数通常通过应用努塞尔数的经验关联式来确定。在本研究中，首先对传热关联式进行了全面的文献综述。结果发现，常用于MD模拟的经验关联式会导致努塞尔数变化很大，在低雷诺数下相差高达一个数量级。然后，在膜蒸馏系统中使用铝板代替平板膜，对填充间隔物通道中的传热进行了实验研究。使用氯化钠溶液在1 g/kg至95 g/kg的广泛盐度范围和30℃至80℃的温度范围内进行了大量测试，在相对较低的雷诺数（100至1500）下产生了1500至8300 W/(mK)范围内的高热传递系数，清楚地显示了间隔物对传热的影响。推导了一个新的经验努塞尔关联式（Nu = 0.158Re0.652Pr0.277），该关联式表示实验数据的偏差为10%，并且在100 < Re < 1500和2 < Pr < 7范围内有效。进行了计算流体动力学模拟，以分析由于温度差异导致的边界层内流体性质的变化。模拟结果表明，对于小的驱动温差，热流体通道和冷流体通道中的传热系数只有微小偏差。
