Studies on open loop and closed loop systems of humidification and dehumidification techniques for water desalination

Author(s): B.Niranjana Rao, M.Gangadhar

The humidification and dehumidification technique is an interesting one adopted for production of fresh water when the demand is centralized. This technique presents several advantages such as flexibility in capacity, installation and operating costs. Feasibility of the process can be justified economically because of the requirement of low heat energy by the process which can be obtained from various alternative energy sources like geothermal, solar, wind etc. The present work is a study of both theoretical and experimental approach to desalinationwith humidification and dehumidificationwhich is a promising technique of production of freshwater at small scale (fewliters/hr).Ageneral model based on heat and mass transfer balances in each component of the system was developed and used to optimize the system’s characteristics. The production of fresh water depends on the ratio between the salt water and the air mass flow rates. In this paper it is discussed that, if the ratio is continuously adjusted for optimum performance, it is possible to produce some quantity of fresh water daily per square meter of chamber surface on a typical time. The performances for open and closed air loop systems are presented. The installation consists of two compact units containing a closed loop which is an air cycle and the other is an open loop in which the air is taken fromthe atmosphere and heated.Air is heated and passed through sprinkled raw hot water chamber counter currently (humidifier), so that the air humidifies and the water vapour along with non-condensable air is dehumidified. Further it is passed through a refrigerator and condensed to recover fresh water.

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