English Abstract
Abstract :
This study presents an experimental and theoretical investigation of a novel cone-shaped desalination system. The system used gravity and atmospheric pressure to create a vacuum condition wherein water can be evaporated at relatively lower temperatures. This lowered temperature allows the use of low-grade heat sources to be used for the desalination process. The uniqueness of this study is the special inverted cone-shape geometry that allows the evaporator and condenser to be under the same roof.
The experimental setup including the tanks, piping and instrumentation has been designed and built as a part of this study. The main NVD (Natural Vacuum Distillation) tank which embodies the evaporation chamber as well as the fresh water chamber is placed at a height of 10.3 m above the ground level to balance the barometric height of water. The evaporation chamber is connected to the saline water feed tank, the brine disposal tank and the fresh water storage tank. All the storage tanks are at the ground level.
In this research, the process was studied theoretically and experimentally to investigate the effects of various operating conditions. Experimental studies were carried out on batch and continuous modes. The main factor that affects the production rate is the saline water temperature. Freshwater production rates of 24.4 L/day for the batch process and 15.65 L/day for the continuous process were measured using a heating temperature of 70 oC.
A theoretical model was also developed using the COMSOL simulation software, to simulate the performance of the system, which agreed with the experimental results. Freshwater production amount was found to be in direct proportion to the evaporation temperature and inversely proportional to the freshwater side temperature. The freshwater production amount was also found to increase non-linearly with the evaporation surface area. The recovery ratio and the thermal efficiency both increased with the increase in the heating temperature for the continuous operation while the increase in freshwater side temperature caused the production rate, recovery ratio and the thermal efficiency to fall. The brine withdrawal rate had a big impact on the system performance. The thermal efficiency showed a peak at a withdrawal rate of 5 kg/h. The depth of water in the evaporation chamber also affected the production rate in a directly proportional manner in the investigated range of 25 – 40 cm.
