No abstract

With demand for fresh water ever-increasing, it is essential to find ways for producing fresh water. Due to its abundance, sea water near coastal regions is a logical choice for desalination. Developing desalination systems that are scalable, energy efficient, and cost effective becomes imperative. A novel system combining dynamic flash evaporation and vapor separation for desalination in a single step was investigated in this work. Water from a primary tank at atmospheric pressure was pumped to higher pressure and simultaneously heated to temperature close to saturation. Heated water was injected tangentially into a separator tube section through two injection passages and injectors. Dynamic pressure drop due to friction and acceleration occurs when the initially subcooled water passes through the injection passages and injectors resulting in flashing. Flashing produces liquid-vapor two phase mixture which when tangentially injected results in centrifugal separation. A vapor core with liquid annulus forms in the separator tube. Vapor was removed with a retrieval tube placed in the vapor core and was directed to the condenser where condensation at atmospheric pressure take place. Thermal conversion efficiency based on the utilization of available superheat for vapor production and phase separation efficiency dependent on the mass-based quality of condensate were defined to evaluate the system. Thermal conversion efficiencies and phase separation efficiencies of up to 98% were achieved in the experiments. Parametric effects of flowrate, superheat, retrieval tube size on thermal conversion and phase separation efficiencies were studied. Experimental results with sea water as test fluid and purity of condensate achieving 98% by weight were reported.

A novel system combining dynamic flash evaporation and vapor separation for desalination has been investigated in this work. The feed water passes through injection tubes which are connected to injector passages installed tangentially onto a separator tube. Flashing in the injection tubes is initiated from pressure drop due to friction and acceleration resulting in a two-phase mixture. Centrifugal force from tangential injection separates the two-phase mixture. In this compact system, vapor production and phase separation occur on the order of several milli seconds. Tap water and sea water were used as inlet feed water for the system. Thermal conversion efficiency to analyze the vapor production efficacy and phase separation efficiency to evaluate the purity of the condensate were investigated to evaluate the system. Thermal conversion and phase separation efficiencies up to 98% were obtained with the single stage system. Further improvement in purity of condensate was achieved with a two-stage system. In the two-stage system the vapor captured along with some entrained droplets from the first stage was directed to a second set of injector passages connected in series to the first stage retrieval tube. With a two-stage system and sea water with salt concentration by mass of 2.5%, collected condensate with salt concentrations lower than 0.02% by mass were achieved, which is comparable to that of potable water. Thus, the novel dynamic flash evaporation and vapor separation system has been demonstrated to be very effective in producing potable water.