A study of the bubble column evaporator method for thermal desalination

• High temperatures do not affect inhibition of bubble coalescence in salt solutions.
• Enhanced bubble column evaporation was observed using high inlet gas temperatures.
• Surfactant monolayer coatings were found to improve the evaporation rate.
• Latent heats of vaporization can be obtained even at high inlet gas temperatures.

A simple bubble column evaporator can be used to evaporate water from concentrated salt solutions without boiling. The process is made more effective by the inhibition of bubble coalescence caused by the presence of some concentrated salts, such as NaCl. This work examines the effects of high bubble temperatures on this coalescence inhibition and its effects on the efficiency of water vapor collection. A continuous flow of hot dry air, at 275 °C, produced about 10% higher rate of water vaporization than that expected from the equilibrium vapor pressures. Also, the use of a non-ionic surfactant monolayer bubble coating further improved the evaporation efficiency, by up to 18%, apparently due to supersaturation. In addition, the steady state temperature of the bubble column evaporator can be used to estimate the latent heat of vaporization even for inlet air temperatures of up to 275 °C.