HEAT TRANSFER ANALYSIS OF PHASE CHANGE MICROCAPSULES WITH THIN FILM EVAPORATION

A number of seawater desalination technologies have been developed and widely used during the last several decades. In the current investigation, a new approach of seawater desalination process is presented, which utilizes phase change microcapsules (PC mu Cs) and thin film evaporation. In this process, the PC mu Cs are placed into hot seawater. Then the hot seawater and the PC mu Cs containing the liquid phase change material (PCM) are ejected into a vacuum flash chamber. A thin liquid film of seawater is formed on the surface of the PC mu Cs, which subsequently vaporizes. This evaporation significantly increases the evaporation heat transfer coefficient and enhances desalination efficiency. Film evaporation on the PC mu Cs' surfaces decreases their temperature by releasing sensible heat. If their temperature is lower than the PCM phase change temperature, then the PC mu Cs change phase from liquid to solid releasing their latent heat, resulting in further evaporation. The PC mu Cs with solid PCM are pumped back into the hot seawater, and the salt residue left on the PC mu Cs can be readily dissolved. In this way, the efficiency can be increased and the corrosion reduced. A mathematical model was developed to determine the effects of PC mu Cs and thin film evaporation on the desalination efficiency. An analytical solution using Lighthill's approach was obtained. Results show that when PC mu Cs with a radius of 100 mu m and a water film of 50 mu m are used, the evaporation rate and evaporative capacity can be significantly increased.