Numerical investigation of the falling film thickness and heat transfer characteristics over horizontal round tube

The numerical investigation was performed to analyze the film thickness and heat transfer characteristics over the horizontal round tube of the falling film evaporator. A three-dimensional model for the falling film flow and heat transfer was established, and the volume of fluid (VOF) method was applied to track the gas-liquid interface. The effects of different spray densities, saturation temperatures, and longitudinal inter-tube spacings (gamma, T-sat, s) on the falling film thickness (delta) and local heat transfer coefficient (h) were analyzed. Asymmetric circumferential distribution of delta is captured by the simulation results. The h reduces first and then rises slightly as the phi increases, and the maximum value appears in the impact point. Moreover, in the circumferential direction, phi = 70 & LCIRC; is the critical value for the variation of delta under different s, and the increment of gamma and T-sat leads to the increase in delta and h. In the axial direction, with increasing the gamma, the delta and the h increase, and the axial size of the crest zone tends to narrow. In addition, the increase of s promotes the rise of h. Meanwhile, the delta varies slightly in the crest zone, and it decreases obviously in the stable zone.

Automated summary

In this study, numerical simulations were conducted to investigate the film thickness and heat transfer characteristics of a falling film evaporator over a horizontal round tube. The results showed that the film thickness had an asymmetric circumferential distribution, and the heat transfer coefficient reached its maximum value at the impact point. Increasing the spray density, saturation temperature, and longitudinal inter-tube spacing led to an increase in the film thickness and heat transfer coefficient.