Abstract:
Falling film micro-reactor (FFMR) has incomparable advantage in highly exothermic and fast reactions when compared with conventional reactors due to its characteristics of high specific surface area, easy separation of products and low scale-up effect. The superior chemical reaction performance exhibited by the FFMR strongly depends on the hydrodynamic behaviors of the liquid film and the heat transfer characteristics of gas-liquid interphase in the falling film microchannel. A transient computational fluid dynamics (CFD) model with the volume of fluid (VOF) method was employed to simulate the hydrodynamic behaviors of concentrated sulfuric acid
w=98 % in a home-made falling film microchannel reactor. The gas-liquid heat transfer behaviors of H
2SO
4-air in the FFMR was also simulated. Surface tension plays a significant role on film-forming process within the
Re and
Ca range of 0.001 33―0.066 7 and 7.00×10
−5―3.50×10
−3, respectively. The influences of liquid inlet velocity on the liquid film thickness and velocity distribution of the film were studied systematically. The results show that the liquid film thickness is proportional to the liquid inlet velocity and the velocity profiles across the film are parabolic curves. The simulated results match the Nusselt predicated results well within a deviation of 0.5%. The effects of gas inlet velocity, gas temperature and liquid inlet velocity on heat transfer coefficient were analyzed. Simulation results show that the increase of both gas inlet velocity and liquid inlet velocity exerts a positive effect on heat transfer coefficient, but the influence of gas temperature on heat transfer coefficient is negative for the increasing viscosity of gas with increasing temperature in FFMR, the heat transfer resistance strongly depends on the heat transfer resistance of gas side. The Nusselt number in FFMR is almost 8.77 times of that in the traditional reactors, which indicates that gas-liquid heat transfer can be intensified effectively by the FFMR. The results are scientific significance to discover the falling film behaviors and gas-liquid heat transfer in FFMR, and provide a theoretical basis for exploring and designing of new reactors.