In order to investigate the local heat and mass transfer characteristics in vapor absorption of falling film flow on a bundle of horizontal tubes in droplet and column flow mode

a transient computational fluid dynamics(CFD) model was developed. The model not only considered the simultaneous hydrodynamic characteristics and mass transfer of LiBr solution flowing on and between tubes

but also considered the real boundary condition for multi-rank tubes and the heat transfer between phases. Simulations were performed for the film Reynolds number varying from 11 to 38. The simulation results showed that the solution outlet concentration and temperature in different mass flow rates agreed well with the experimental data in reference

with deviations less than 2%. In both the droplet and column flow modes

the average concentration and temperature decreased rapidly in the falling-film regions

but increased then decreased in the inter-tube regions. The local absorption rates in the falling-film regions were about 10 times as much as that in the inter-tube regions in the droplet flow mode

and 7 times in the column flow mode. In the falling-film regions

the absorption rate in the column flow mode is obviously less than that in the droplet flow mode. However

in the inter-tube regions

the absorption rates in the two different flow modes were almost the same. When the absorption process reached a steady state

the variations of average concentration and temperature in the droplet flow mode were greater than that in the column flow mode. The average concentration variations of the falling-film regions on the four tubes increased in turn

but the average temperature variations decreased.