Pdf dropwise condensation on solid hydrophilic surfaces. Dropwise condensation on surfaces with graded hydrophobicity. They found that all promoters which gave ideal dropwise condensation contained a nonpolar hydrocarbon chain. The chapter covers four main areas of condensation heat transfer. A thick film of water, which has low thermal conducti vity, acts as an insulating blanket in filmwise conden sation. Droplet nucleation and condensation are ubiquitous phenomena in nature and industry. However, the necessity for nonwetting to achieve dropwise condensation is unclear. In standard dropwise condensation, liquid droplets forming on a subcooled non wetting surface are removed from the. Steam may condense onto a surface in two distinct modes, known as the filmwise and the dropwise condensation.
For instance, the heat transfer coefficient for dropwise condensation of steam is around 10 times that for film condensation at power station condenser pressures and more than 20 times that for film condensation at. Several different spacings were examined for the horizontal orientation, arranging a dropwise section above a filmwise one, to make clear the effect of the drops falling down to the filmwise section. Oct 14, 2016 dropwise condensation dwc on hydrophobic surfaces is attracting attention for its great potential in many industrial applications, such as steam power plants, water desalination, and deicing of. Improvement of heat transfer by promoting dropwise. This invited paper is based on the award lecture and is written in an informal style expanding on the lecture and focusing on work in which i have been involved over the past 60 years. Filmwise condensation occurs on a vertical or horizontal plane when a film of condensate is formed on surface and flows by action of gravity. In the first series, the pattern design consists of hydrophobic. Dropwise condensation has shown the ability to increase condensation heat transfer coefficient by an order of magnitude over conventional filmwise condensation. The condensation heat transfer rates were compared to that of the complete dropwise condensation dwc and complete filmwise condensation fwc, respectively. Dropwise condensation occurs on nonwettable surface while filmwise occurs on wettable surfaces. Correlation for dropwise condensation heat transfer.
Dropwise definition of dropwise by the free dictionary. Author links open overlay panel karim egab a c mohammed alwazzan a benli peng a saad k. Film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface. A study of dropmicrostructured surface interactions during. The paper presents a new theory of heattransfer by dropwise condensation in the absence of noncondensing gases. For this reason, several research groups around the. Dropwise condensation occurs when small drops formed on surface. Poor dropwise condensation was obtained with promoters composed of two approximately equal polar and nonpolar groups, and complete filmwise condensa.
Generally, film wise condensation results in low heat transfer rates as the film of. In filmwise condensation a laminar film of vapour is created upon a surface. Enhancing filmwise and dropwise condensation using a hybrid wettability contrast mechanism. Over the past century, research has shown dropwise condensation heat transfer on nonwetting surfaces to be an order of magnitude higher than filmwise condensation heat transfer on wetting substrates. The authors consider the heattransfer arising from condensation on a single drop, and by means of an assumed distribution of drop sizes, deduce the mean heattransfer rate for the whole surface. Overall heat transfer coefficients are reported for filmwise and dropwise condensation. The steamside heat transfer coefficient with dropwise condensation was estimated to be over 0. Dropwise and filmwise condensation saurabh pandey abstract. Over the past century, research has shown that heat transfer rates during steam dropwise condensation on nonwetting e. This steam flows upwards to the dropwise and filmwise condensers where it is condensed by transferring heat to. In dropwise then flow downwards, accumulating static droplets below them along the way. The effect of relative humidity on dropwise condensation dynamics.
This unit contained with an integrated steam generator boiler and. Particular attention is given to heat transfer measurements, theory, effect the presence of air in the condenser has on the heat flux and surface heat transfer coefficient. Difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. Condensation heat transfer can be optimized by using surfaces in which dropwise condensation dwc occurs, and even further optimized using superhydrophobic surfaces. The process at the vaporliquid interface during condensation is first discussed. Request pdf enhancing filmwise and dropwise condensation using a hybrid wettability contrast mechanism. Dropwise condensation of steam on gold surfaces dropwise condensation of steam on gold surfaces. This film can then flow downwards, increasing in thickness as additional vapour is picked up along the way. Circular patterns condensation surfaces using a wettability contrast mechanism is one of. Dropwise condensation article about dropwise condensation.
The film and dropwise condensation module h102k is used with the h102 heat exchanger service unit which supplies both electrical power and instrumentation for the module via a control console that is supplied with the h102k module. Vertical surface dropwise condensation heat transfer using. Enhancing filmwise and dropwise condensation using a. Apr 22, 2012 this is a direct comparison of two common modes of condensation, filmwise and dropwise. Recurrent filmwise and dropwise condensation on a beetle mimetic surface. Despite this effect, a comparison of h during filmwise and dropwise condensation of water and octane, shown in figure 1b as the slope of q. Dropwise and filmwise condensation of water vapor on gold. Jan 10, 2020 download fulltext pdf download fulltext pdf.
Transfer coefficient through dropwise condensation and. Pdf filmwise and dropwise condensation of steam on short. International journal of heat and mass transfer 2017, 114, 187197. Simultaneous dropwise and filmwise condensation on hydrophilic microstructured surfaces. The equipment heats and condenses water, and includes a separate control module with a digital display. A study of dropmicrostructured surface interactions. Clean metal surfaces are normally wetted and the mode of condensation is filmwise, where the condensate forms as continuous film on the surface. Dropwise condensation on solid hydrophilic surfaces science. Apr 21, 2018 difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. Hydrophobic and superhydrophobic surfaces promote dropwise condensation in vaporfilled environments and increase their heat transfer coefficients more than fil. Selfshedding and sweeping of condensate on composite nanosurface under. Dropwise condensation on advanced functional surfaces theory and experimental setup.
Dropwise condensation on carbon steel surface asme. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. The first model argues that liquid droplets only form heterogeneously at nucleate sites. Current dropwise condensation research is focused on cu and other special metals, the cost of which limits its application in the scale of commercial power plants. Promotion of dropwise condensation of ethyl alcohol, methyl. Enhancing filmwise and dropwise condensation using a hybrid.
Continuous dropwise condensation achieved without the assistance of a hydrophobic coating. Dropwise condensation of low surface tension fluids on. Compared to filmwise condensation on conventional condenser surfaces, heat transfer can be significantly enhanced by tuning the wettability of the surface to promote dropwise condensation. Pdf filmwise and dropwise condensation experiments were carried out at atmospheric. Dropwise condensation is preferred over filmwise condensation due to the higher rates of heat and mass transfer that may be achieved 6. On the right half of the frame is a bare silicon wafer, on which water wets readily. So most condensers are designed on the assumption that film condensation will take place on the surface eventually. Grafted nanofilms promote dropwise condensation of. Dropwise condensation dwc on hydrophobic surfaces is attracting attention for its great potential in many industrial applications, such as steam power plants, water desalination, and deicing of. On hydrophobic surfaces, dropwise condensation may form and increase heat fluxes by 510 times compared to filmwise condensation figure 1b.
Pdf dropwise and filmwise condensation ahtisham ul haq. This is a direct comparison of two common modes of condensation, filmwise and dropwise. Following rapid advances in surface engineering, the last years have seen an unprecedented interest in dropwise condensation research. Filmwise and dropwise condensation and boiling thermodynamics. All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only. Dropwise condensation on solid hydrophilic surfaces. Dropwise condensation can be promoted by applying i suitable organic promoter ii thin layer of special metal iii coating with polymer film on condenser surface. When dropwise surfaces degrade, they convert to filmwise condensation. Vapor condensation is a crucial part of a broad range of industrial applications including power generation, water harvesting, and air conditioning. Nov 28, 2016 film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface.
Dropwise condensation has been of interest to the heat transfer community since its earliest published work in 1930. Dropwise condensation on advanced functional surfaces. The heat flux of the filmwise part increased with increasing the height of the dropwise part up to 2 mm, but then decreased above that. Condensation in order to use boundary layer theory to describe the condensation problem, the following assumptions must be made. In film wise condensation, the cooled surface is smooth and frictionless which results in quick. Condensation heat transfer can be optimized by using surfaces in which dropwise condensation. This ongoing interest is motivated by the observation that dropwise condensation promoted surfaces typically exhibit heat transfer coefficients at least five times higher often exceeding 10 times higher than filmwise condensation at similar operating. Four videos showing the filmwisetodropwise transition, spatial control and coalesceinduced droplet jumping on hybrid surfaces, as well as further information on hybrid wettability verification, droplet growth model, droplet wetting and coalescence dynamics, evolution of droplet adhesion, supplementary analysis of figureofmerit for condensation performance on hybrid. In dropwise a large area of solid surface is directly exposed to vapour. For superhydrophobic condensation, a structured silicon surface with pillars 2. Filmwise and dropwise solteq equipment for engineering. Introduction filmwise and dropwise are two forms of condensation. The effect of a novel coating technique on filmwise and. In many cases it is adequate to assume equilibrium at the interface but in dropwise condensation and condensation of metals the interface temperature discontinuity plays and important role.
Four videos showing the filmwise to dropwise transition, spatial control and coalesceinduced droplet jumping on hybrid surfaces, as well as further information on hybrid wettability verification, droplet growth model, droplet wetting and coalescence dynamics, evolution of droplet adhesion, supplementary analysis of figureofmerit for condensation performance on hybrid surface and filmwise. High heat transfer enhancement using dropwise condensation dwc has been of interest since the earliest published work in 1930, which reported an order of magnitude higher heat transfer coefficients compared to filmwise condensation for comparable conditions 8. Dropwise condensation 2019 max jakob memorial award paper. It was an honor to receive the max jakob memorial award for 2018. The area ratio of dropwise regions and filmwise regions in the present study was fixed at 50%. Selfshedding and sweeping of condensate on composite nanosurface under external force field. May 15, 2019 converting from filmwise condensation, where the condensate spreads to cover the entire condenser surface, to dropwise condensation, a more efficient form of condensation where this film is broken up into discrete mobile droplets, as shown in figure 1a, has been explored for usage in steam turbine condensers, which are prolific in electricity. Article information, pdf download for dropwise condensation theory and. Recurrent filmwise and dropwise condensation on a beetle. In film wise condensation, the surface over which the steam condenses is wetable and hence, as the steam condenses, a film of condensate is formed. However, the necessity for nonwetting to achieve dropwise. The greater heat transfer performance of the simultaneous dropwise and filmwise condensation behavior when compared to filmwise condensation is owed to the thin liquid film kept between pillars and to the continuous. Simultaneous dropwise and filmwise condensation behavior on a completely hydrophilic configuration. The light blue and light red shaded regions represent dropwise and filmwise condensation, respectively.
During processes of this set up visually observe the exchange of heat during dropwise and filmwise condensation. Pdf recurrent filmwise and dropwise condensation on a. The effect of a novel coating technique on filmwise and dropwise condensation of steam on horizontal tubes helen p. Study on dropwise condensation curves dropwise to filmwise transition of propylene glycol, ethylene glycol and glycerol vapors on a copper surface using a monolayer type promoter part 2. For the same temperature difference between the steam and the surface, dropwise condensation is several times more effective than filmwise, and for this reason the former is desirable although in practical plants, it seldom occurs for. The effect of relative humidity on dropwise condensation.