Experimental study of water evaporation at water seal under unsteady air pressure fluctuations

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Experimental study of water evaporation at water seal under unsteady air pressure fluctuations


Author: Lau, Chun-leung
Title: Experimental study of water evaporation at water seal under unsteady air pressure fluctuations
Degree: M.Eng.
Year: 2012
Subject: Evaporation (Meteorology)
Drainage, House
Hong Kong Polytechnic University -- Dissertations
Department: Dept. of Building Services Engineering
Pages: xiii, 71 leaves : ill. (some col.) ; 30 cm.
Language: English
InnoPac Record: http://library.polyu.edu.hk/record=b2525555
URI: http://theses.lib.polyu.edu.hk/handle/200/6640
Abstract: Water evaporation has already been studied for many applications. Numerous researches have focused on the prediction of water loss from steady free water body to an ambient environment, such as lakes, testing pans and swimming pools, as well as for different air velocity, temperature and humidity. However, only few studies have been conducted as regards the water surface conditions, including the disturbed water surface of swimming pools. A wide range of researches have studied the water loss from water bodies to ambient air for different applications, for example, lakes, water evaporation pans and swimming pools. These studies focused on the correlation between evaporation rate and air temperature, water temperature, relative humidity as well as horizontal air velocity of the water surface. Only a few researches mentioned the water evaporation in the drainage system fixtures. In this study, experiments were conducted with a 40mm diameter U-type water seal trap to study the evaporation characteristics under the influence of water surface undulation caused by air pressure fluctuation. Both ends of two U-type seal traps were connected together, in order to simulate a high relative humidity condition between the seal traps. It was aimed to create a zero net mass transfer at one end of the seal trap. The seal traps were located in a controlled environment with an air injection fan to create an air pressure variation, hence causing the water surface level to fluctuate. If the vapour pressure difference is increased, the evaporation flux is raised. This is consistent with the finding of the previous studies. The greater amount of evaporation could be caused by the higher water surface fluctuation level. The evaporation flux of the trap seal with air pressure fluctuation was higher than the evaporation flux at quiet water, which is an empirical model from other studies. That model could be considered as basic evaporation, and the additional evaporation might be attributed to other factors, such as water surface fluctuation. The significant evaporation was found at 0 to 0.25 Hz and 2.25 to 2 Hz of the water surface fluctuation.

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