Numerical analysis of absorption enhancement of falling film absorbers using specialized geometries

This work discusses the use of Computational Fluid Dynamics (CFD) simulations to improve the absorption efficiency of vertical plate falling film absorbers. The goal of this work is to reduce the size of the absorber while keeping the air-side pressure drop low.
Two geometries are analyzed to achieve this goal. In the first geometry, wires are inserted into the air gap between the vertical plates of the falling film absorber. These wires create vortices that mix the airflow and move moist air from the core to the interface with the falling film, resulting in improved absorption. The second geometry utilizes a stacked arrangement of successive falling films, allowing the moist core of the airflow from the previous absorber step to directly contact the falling film of the next step.
The results indicate that for typical absorption conditions in cold store applications, the size of the falling film absorber can be reduced by about 20% with the wire geometry and by about 30% with the stacked arrangement. However, the air-side pressure drop increases for both geometries compared to a conventional falling film absorber. This increase depends significantly on the diameter of the wires used, the number of wires, the number of absorber steps, and the distance between the falling films.
In conclusion, the use of special geometries in falling film absorbers can increase the absorption efficiency and thus minimize the size of the absorber. However, an increase in air-side pressure drop must be accepted.