Research on the performance of multi-stage bubble column humidification-dehumidification solar desalination system

To enhance the humidification and dehumidification process by bubbling, we designed a multi-stage bubble column (BC) solar desalination system, composing a humidifier and a condenser that are both M-layers. The air is circulated by the air pump inside the device, which generates a lot of bubbles after passing through the perforated plate, so that the device has a huge heat and mass transfer area. In order to enable the system to operate stably within the selected working conditions and increase the heat transfer coefficient, the structural parameters of the condensing coil and the perforated plate were designed. A steady-state heat transfer model of the system involving a stepwise diversion of seawater was developed to explore an effective method to increase the system’s performance ratio (PR). Based on the structural design and analysis of the calculation results, a “4-layers+4-layers” BC was fabricated and tested. The experimental results show that the system has a productivity of 27.2 kg/h and a PR of 1.38 at an operating temperature of 65.6°C. The theoretical model was verified by comparison with experimental values. Based on the theoretical model, further analysis found that: 1) under given flow rate of seawater and air, adjusting the seawater inlet temperature can make the PR reach a local maximum value (PRmax); 2) by selecting a smaller seawater flow rate, reducing the air flow rate and preheating the imported seawater to a specific temperature can further improve PRmax; 3) The effect of seawater diversion on increasing PRmax is more pronounced, a diversion at the final layer of the condenser can increase the PRmax by 25.2% relative to no diversion.