An experimental investigation of salt-water separation in the vacuum flashing assisted with heat pipes and solid adsorption

A novel single stage vacuum evaporator, as a salt-water separator, is developed to fully use ultra-low grade heat source as low as 50 °C. The novel design incorporates several technologies, including heat pipes (HPs), spray flashing and solid adsorption. Its performance is evaluated by separating water from NaCl solution with 3%concentration. The results of the experiment study show that HPs transfer heat to the droplets rapidly to assist a second evaporation and maintain the superheat degree for the salt-water separation process after the flash evaporation. It is also found that, when the adsorbent beds are applied, the evaporation pressure decreases by 0.4-1 kPa compared to the early experiment results, which results in an increase of the superheat degree. The introduction of solid adsorption in the salt-water separator provides a new way to utilize ultra-low grade heat source, although it brings a mixed success to the whole device while the separation ratio is slightly lower than expected due to the fact that there are both improved and impaired effects of heat transfer during the whole adsorption process. The lower cooling water temperature of the adsorption process, leads to better desorption effect, which improves the overall performance of the salt-water separator.