Comparison of heat and mass transfer in falling film and bubble absorbers of ammonia-water

An experimental analysis of ammonia-water absorption process was performed for the falling film and bubble modes in a plate-type absorber. The experiments were made to examine the effects of solution flow rate and gas flow rate on the performance of the absorber. It was found that the bubble mode is superior to the falling film mode for mass transfer performance, and more heat was generated in the bubble mode. Increase of solution flow rate rarely affected the mass transfer, but improved the heat transfer. As the gas flow rate increased, fluidization occurred in the bubble mode and influenced the thermal boundary layer. However, channeling appeared in the falling film mode and decreased the heat transfer area. Increase of the gas flow rate greatly enhanced the performance of heat transfer in the bubble mode but made it worse in the falling film mode. Finally, the results were converted into dimensionless numbers to elucidate physical phenomena and we plotted Sherwood number versus Reynolds number for mass transfer performance and Nusselt number versus Reynolds number for heat transfer performance.