On the Enhancement of Filmwise Condensation Heat Transfer by Means of the Coexistence With Dropwise Condensation Sections

Abstract

This article describes work aimed at obtaining higher film wise condensation heat flux by distributing dropwise condensation surfaces of optimal width promoted by an organic coating among film wise surfaces, and to get higher mean overall heat transfer coefficients in condensing systems. Several different spacings were examined for the horizontal orientation, arranging a dropwise section above a film wise one, to make clear the effect of the drops falling down to the filmwise section. The heat flux of the filmwise pan increased with increasing the height ofthe dropwisepan up to 2 mm, but then decreased above that. The extent of the film wise pan that was augmented by drops was also tested by changing the width of the filmwise section sandwiched between dropwise sections of constant width. The heat flux of the film wise pan increased abruptly at a width between 5 and 3 mm. Consequently, it was shown that there exists an optimum widlh for each section for enhancing condensation heat transfer in the film wise sections.

Condensation on Surfaces With Biphilic Topography: Experiment and Modeling

“…Therefore, the state-of-the-art condensing surfaces cannot be applied to industrial applications due to their high manufacturing costs and difficulty in maintaining drop-wise condensation in long run. In order to tune the advantage of lower energy barrier accompanied with hydrophilic surfaces and higher drop mobility of super-hydrophobic surfaces, Kumagai et al (1991) entertained the possibility of using biphilic patterning of surfaces. Results showed a great potential of using such surfaces with heat transfer performance bounded by the two extreme cases, i.e., film and drop wise condensation.…”

Can Metal Matrix‐Hydrophobic Nanoparticle Composites Enhance Water Condensation by Promoting the Dropwise Mode?

“…Hydrophilic surfaces with millimeter scale hydrophobic patterns were first explored for condensation heat transfer enhancement by Tanaka and co‐workers . More recent work has focused on wetting[8a,b,e‐h] and condensation[6d],[8h‐u] of surfaces with both chemical and topological microscale features.…”

A model for calculating heat transfer coefficient concerning ethanol-water mixtures condensation

“…On the one hand, with change of subcooling, the condensation mode includes filmwise, dropwise and transitional mode between them, in fact, Marangoni condensation could be considered as combination of filmwise and dropwise (Utaka, 2004); on the other hand, even when HTC reach peak value, with condensation mode being dropwise, a thin film of condensate existed on the area among the droplets and a thin film of condensate still existed at the spots of droplet departure (Song, 1991). Kumagai (1991) had examined work aimed at obtaining higher filmwise condensation heat flux by distributing dropwise condensation surfaces. From two mentioned-above points, the calculation of the condensation could be applied in such a way that the total condensation proceed might be considered as combination of the filmwise and dropwise.…”

“…Utaka (2002) had measured thickness of the thin film which was always present on the condensation surface when the pseudo-dropwise condensation occurred. We shall introduce the characteristic parameter D p after a calculation for dropwise and filmwise have been completed, following Kumagai (1991), such that Marangoni condensation model may be expressed by the relations: For all experiments, the condensation HTC curve can be divided into three sections, that is, platform section (PS, A to B), ascension section (AS, B to C) and descent section (DS, C to D), as shown in Fig. Kumagai (1991) had examined work aimed at obtaining higher filmwise condensation heat flux by distributing dropwise condensation surfaces.…”