Background Oriented Schlieren (BOS) imaging of condensation from humid air on wettability-engineered surfaces

Gupta, R. , Das, C., Datta, A. and Ganguly, R. (2019) Background Oriented Schlieren (BOS) imaging of condensation from humid air on wettability-engineered surfaces. Experimental Thermal and Fluid Science, 109, 109859. (doi: 10.1016/j.expthermflusci.2019.109859)

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Condensation of water vapor in presence of non-condensable gas is observed in several engineering applications ranging from power generation to water harvesting. Non-intrusive optical diagnostics of the thermal and vapor concentration boundary layers on a condensing surface can offer a veritable means of predicting the condensation heat transfer coefficient (CHTC), but the literature in this field is far from being well-developed. Here we perform a Schlieren imaging-based mapping of the thermogravitational density boundary layer during condensation from humid air on vertical surfaces of three different wettability, i.e., superhydrophilic, hydrophilic (control) and superhydrophobic. A lens-free, Background Oriented Schlieren (BOS) technique is used to cross-correlate the refraction of light and quantify the density gradient fields near the condenser plates for three different humidity ratios (13.5, 15.5 and 17.5 g/kg dry air) at a constant degree of subcooling (19.5 °C). CHTC measurement from condensate collection data is used to validate the non-intrusive data. The mean refraction angle and the mean density gradient near the plate are found to scale linearly with the CHTC and the condensate mass flux, respectively. The study clearly shows the potential of BOS technique in predicting the condensation heat transfer rates from humid air.

Item Type:Articles
Additional Information:The work has been supported by Department of Atomic Energy – Board of Research in Nuclear Sciences (DAE-BRNS), India through Project No. 36(1)/14/24/2016-BRNS. The authors gratefully acknowledge the support received from DAE-BRNS, India.
Glasgow Author(s) Enlighten ID:Gupta, Mr Rohit
Authors: Gupta, R., Das, C., Datta, A., and Ganguly, R.
Subjects:T Technology > TJ Mechanical engineering and machinery
College/School:College of Science and Engineering > School of Engineering > Systems Power and Energy
Journal Name:Experimental Thermal and Fluid Science
ISSN (Online):1879-2286
Published Online:26 June 2019

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