A study of the bubble column evaporator method for improved thermal desalination

A bubble column evaporator (BCE) was used to study the enhanced evaporation of water from 0.5 m NaCl solutions, using a range of pre-heated carrier gases (air, CO2, Ar and He), each at an inlet temperature of 150 °C. Surprisingly, the use of hot helium as a carrier gas substantially improved water evaporation efficiency, by a factor of about 3 times, compared with, for example, dry air. It is suggested that this higher efficiency could be due to a slightly reduced water hydrogen bonding, and hence enthalpy of vaporisation, due to the continuous sparging of hot He gas atoms into the aqueous solution. These results suggest that this process could form a basis for the development of a more efficient, sub-boiling desalination process. The effect of added cationic and anionic surfactants on BCE water evaporation rate was also studied. The cationic surfactant myristyltrimethylammonium bromide (MAB) and the anionic surfactant Sodium dodecyl sulfate (SDS) each gave a slightly enhanced water evaporation rates, in agreement with previous studies, probably due to enhanced water vapor retention within surfactant coated bubbles.