Selfshedding and sweeping of condensate on composite nanosurface under external force field. Article information, pdf download for dropwise condensation theory and. The surface is blanketed by a liquid film which serves as a resistance to heat transfer. Dropwise condensation article about dropwise condensation. On the right half of the frame is a bare silicon wafer, on which water wets readily. Dropwise condensation of low surface tension fluids on. Among dropwise condensation investigations, it has also been shown that smaller droplets result in higher heat. Selfshedding and sweeping of condensate on composite nanosurface under. On the right half of the frame is a bare silicon wafer. An experimental examination of the surface, using an optical method capable of detecting thin films of molecular dimensions, shows that no film greater than a monolayer in thickness exists on the area between the drops. Condensation curves for dropwise condensation of steam at atmospheric pressure were measured for the range of surface subcooling between 0. In all applications, the steam must be condensed as it transfers heat to a cooling medium which could be cold water in a condenser of generating station, hot water in a heating calorifier, sugar solution in a sugar refinery and etc. The drop wise condensation of steam has heat transfer coefficient 2 to 10 times as large as film condensation. Influence of processing conditions of polymer film on.
In filmwise condensation a laminar film of vapour is created upon a surface. Dropwise condensation occurs on nonwettable surface while filmwise occurs on wettable surfaces. Dropwise condensation 2019 max jakob memorial award paper. Apr 16, 20 excellent dropwise condensation of steam was observed on a polytethefluoroethylene ptfe coated plate. Visual display of key parameters and calculated values are displayed via a computer or optional hmi utilising the armfield ltd armbus software.
In this work, automated surface plasmon resonance imaging spri is used as a tool to study the existence of a thin film between the dropwise condensate. Dropwise condensation of steam on gold surfaces dropwise condensation of steam on gold surfaces. To measure the thermal performance enhancement of these polymer coatings, a custom test apparatus was used to measure the local heat transfer coefficient. A thick film of water, which has low thermal conducti vity, acts as an insulating blanket in filmwise conden sation. 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. Filmwise and dropwise condensation and boiling thermodynamics. Condensation in order to use boundary layer theory to describe the condensation problem, the following assumptions must be made. For the same temperature difference between the vapour and the surface, dropwise condensation is several more times effective than filmwise.
Dropwise condensation on surfaces with graded hydrophobicity. The effect of processing conditions of polymer film on dropwise condensation heat transfer of steam under atmospheric pressure is investigated to find an effective technique to prepare a viable polymer film sustaining longterm dropwise condensation pattern state. To understand the physics behind dropwise condensation, a microscopy technique must be able to measure a subnanometer film at a high temporal resolution 1,000 fps. 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. Pdf filmwise and dropwise condensation of steam on short. Which gives more heat transfer, filmwise condensation or. 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.
However, the need for nonwetting hydrophobic coatings in. Within the types of condensation that can form on a surface, dropwise condensation has been previously shown to produce condensation heat transfer coefficients up to an order of magnitude greater than film condensation. 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. Grafted nanofilms promote dropwise condensation of. Thin film condensation on nanostructured surfaces oh 2018. Structural and optical studies of cadmium sulfide quantum dotgraphene oxidechitosan nanocomposite thin film as a novel spr spectroscopy active layer. The surface is blanked by the film, which grows in thickness as it moves down the plate. Request pdf film and dropwise condensation the chapter covers four main areas of condensation heat transfer. In filmwise condensation liquid condensate forms a continuous film over the surface, this film flows down the surface under the action of gravity, shear force due to vapor flow, or other forces. The vapour is in direct contact with the surface over most of the area and heat transfer rates.
Film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface. The authors consider the heattransfer arising from condensation on a single drop, and by means of an assumed distribution of drop sizes. Over the past century, methods achieving dropwise condensation using a thin and acetone by polytetrafluoroethylene by cecil e. The traditional problems of laminar film condensation on plates and tubes are covered in some detail including natural and forced convection problems, the.
When considering surface is contaminated with substance which prevents condensate from the wetting surface,the vapour will condense in drops instead of a continuous film. Thin film condensation on nanostructured surfaces oh. Us3167927a us119169a us11916961a us3167927a us 3167927 a us3167927 a us 3167927a us 119169 a us119169 a us 119169a us 11916961 a us11916961 a us 11916961a us 3167927 a us3167927 a us 3167927a authority us united states prior art keywords surface condenser heat exchange section tube prior art date 19610623 legal status the legal status is an assumption and is. The experimental results indicated that the condensation heat transfer performance was increased by 30 to 47 times when compared with film condensation values at the same surface subcooling degrees. To improve the thermal performance and durability of steam surface condensers, film forming amine coatings were deposited on flat condenser surfaces to promote dropwise condensation. When dropwise surfaces degrade, they convert to filmwise condensation. Dropwise condensation the condensed vapor forms droplets on the surface.
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. Excellent dropwise condensation of steam was observed on a polytethefluoroethylene ptfe coated plate. Difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. In dropwise a large area of solid surface is directly exposed to vapour. Previous studies on dropwise condensation are primarily devoted to steam, with a few studies of fluids with high or moderate surface tension 27,28,29,30,31 or marangoni dropwise condensation of. The random fluctuation of the surface temperature was resulted from the high.
A study of dropmicrostructured surface interactions. Vapour may condense onto a cooled surface in two distinct modes known as filmwise and dropwise. A fluorcontaining organic film with thickness of more than 1. The equipment heats and condenses water, and includes a separate control module with a digital display. So most condensers are designed on the assumption that film condensation will take place on the surface eventually. Ppt condensation and boiling heat transfer powerpoint. This is a direct comparison of two common modes of condensation, filmwise and dropwise. The process at the vaporliquid interface during condensation is first discussed. On hydrophobic surfaces, dropwise condensation may form and increase heat fluxes by 510 times compared to filmwise condensation figure 1b. Solteq the use of steam both for power production to convey heat has a long history and its use in these fields is likely to continue into the foreseeable future. In 1930, for the first time, dropwise condensation was described in a scientific paper 1 and the heat transfer potential of this type of condensation, as compared to the filmwise condensation mode, was highlighted. Dropwise condensation on solid hydrophilic surfaces. The chapter covers four main areas of condensation heat transfer. Abstract this film and dropwise condensation unit is used to observe the process of heat.
Of ethyl alcohol, methyl alcohol, and acetone by polytetrafluoroethylene by cecil e. Dropwise condensation can be sustained for a long time by the combined effects of surface coating and periodic injection of the promoter into the vapor. Recurrent filmwise and dropwise condensation on a beetle. The observed drop growth kinetics suggests that smallest drops grow principally by the diffusion of water adsorbed on the substrate to the drop perimeter, while drops larger than about 50.
Dropwise condensation of water vapor from a naturally cooling, hot water reservoir onto a hydrophobic polymer film and a silanized glass slide was studied by direct observation and simulations. 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. Transfer coefficient through dropwise condensation and. Sep 19, 2006 dropwise condensation of water vapor from a naturally cooling, hot water reservoir onto a hydrophobic polymer film and a silanized glass slide was studied by direct observation and simulations. 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.
Vertical surface dropwise condensation heat transfer using. Dropwise condensation is usually obtained when the surface is hydrophobic. Dropwise condensation can occur when the surface is nonwetting or these droplets are taken away from the surface by external flow or by gravity. Pdf influence of processing conditions of polymer film on. A fluorcontaining organic film with thickness of more than 1 mum was coated on the dropwise regions of the external surface of a brass tube to promote dropwise condensation. Kirby langley research center summary the phenomenon of dropwise condensation, in which the condensate forms into drops rather than covering the entire cooling surface with a. However, the necessity for nonwetting to achieve dropwise condensation is unclear. 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. The main components in the unit are the specially designed condensers for the observation of. The th6 film and dropwise condensation unit demonstrates the concepts of film and dropwise condensation under variable pressure, vacuum, condition in a highly visual manner. Over the past century, methods achieving dropwise condensation using a thin dropwise.
The condensate film and binary vapor boundary layers both develop. Influence of processing conditions of polymer film on dropwise condensation heat transfer article pdf available in international journal of heat and mass transfer 4516. It was an honor to receive the max jakob memorial award for 2018. 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. Promotion of dropwise condensation of ethyl alcohol, methyl. Apr 22, 2012 this is a direct comparison of two common modes of condensation, filmwise and dropwise.
Correlation for dropwise condensation heat transfer. 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. The surfaces were divided horizontally into many regions according to the designed dropwise and filmwise condensation area ratio. Filmwise condensation when liquid formed by condensation wets the surface. The paper presents a new theory of heattransfer by dropwise condensation in the absence of noncondensing gases. Generally, film wise condensation results in low heat transfer rates as the film of.
Film and dropwise condensation request pdf researchgate. Dropwise condensation occurs on nonwettable surface while filmwise occurs on. Vapor condensation plays a key role in a wide range of industrial applications including power generation, thermal management, water harvesting and desalination. Subscribe to the latest product information, news and resources. In dropwise condensation, the condensed vapor forms droplets on the surface instead of a continuous film. Droplet nucleation and condensation are ubiquitous phenomena in nature and industry.
Mar 03, 2020 it was an honor to receive the max jakob memorial award for 2018. Dropwise condensation has been of interest to the heat transfer community since its earliest published work in 1930. The droplets develop at points of surface imperfections pit, scratch, called nucleation sites, and grow in size as more vapour condenses on its exposed surface. In the remaining lecture we now focus on indirect contact filmwise condensation. To improve the thermal performance and durability of steam surface condensers, filmforming amine coatings were deposited on flat condenser surfaces to promote dropwise condensation. The droplets slide down when they reach a certain size. Kirby langley research center summary the phenomenon of dropwise condensation, in which the condensate forms into drops rather than covering the entire cooling surface with a continuous film, produces heat. Although it has been known since the 1930s that heat transfer coefficients for dropwise condensation of steam are much higher than those for film condensation, there were, until the 1960s, wide discrepancies between the results of different investigators. The thickness of the film depends upon a numbers of factors, e.
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. Condensation heat transfer can be optimized by using surfaces in which dropwise condensation. However, it has been difficult to sustain drop wise condensation commercially for long periods of time. In standard dropwise condensation, liquid droplets forming on a subcooled non wetting surface are removed from the.
Apr 21, 2018 difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. Exploring the limits of dropwise condensation on nano. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. Filmwise and dropwise condensation experiments were carried out at atmospheric pressure varying the condensing plates, their inclinations and orientations. The unit itself contained bench top unit, with an integrated steam generator and air extraction system. Dropwise definition of dropwise by the free dictionary. Pdf influence of processing conditions of polymer film. Fast droplet nucleation and efficient droplet departure as well as low interfacial thermal resistance are important factors that determine the thermal performances of condensation.
Kim, dropwise condensation modeling suitable for superhydrophobic surfaces, asme. Filmwise and dropwise solteq equipment for engineering. Film condensation the condensate wets the surface and forms a liquid film. The condensate film and binary vapor boundary layers both develop from the leading edge of the vertical surface, x0.
Us2469729a us637768a us63776845a us2469729a us 2469729 a us2469729 a us 2469729a us 637768 a us637768 a us 637768a us 63776845 a us63776845 a us 63776845a us 2469729 a us2469729 a us 2469729a authority us united states prior art keywords silicon surface vapors organo halide prior art date 19451228 legal status the legal status is an assumption and is not a legal. 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. Th6 film and dropwise condensation demonstration unit. Enhancing filmwise and dropwise condensation using a. Over the past century, research has shown that heat transfer rates during steam dropwise condensation on nonwetting e. The vapour is in direct contact with the surface over most of the area and heat transfer rates are much higher more than 3 10 times higher as. From a study of surface phenomena, information is obtained about conditions under which net condensation can occur. 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.
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