Performance Investigation of a Multi-stage Bubble Column Humidifier for Air Humidification

Conventional packed bed humidifiers (PBH) are often employed in the humidification–dehumidification desalination system. However, these humidifiers need a considerable packing volume due to low heat and mass transfer characteristics. Injecting air into the water column in a bubble column humidifier (BCH) to improve heat and mass transfer is receiving increasing attention. Hence, this paper proposes a novel design of BCH for multi-stage air heating and humidification. The proposed multi-stage BCH is theoretically and experimentally investigated. The feasibility is further assessed by comparing the performance with those of PBH. Mathematical models based on the heat and mass transfer process have been developed for BCH and PBH. The simulation results revealed that the theoretical models agreed well with the experimental data. Experimental results showed that the water height in the column has a negligible effect on BCH efficiency; however, feedwater mass flow rate, superficial velocity, and coil length have a significant effect. Furthermore, findings demonstrated that two-stage BCH efficiency is about 16–21% and three-stage BCH efficiency is about 25–30% higher than single-stage BCH. Single-stage BCH achieved a vapor content difference of 27–43% higher than PBH, while two-stage and three-stage BCH achieved vapor content differences of 81–115% and 111–162% higher than PBH, respectively.