Pdf dropwise condensation has superior heat transfer efficiency than. Recurrent filmwise and dropwise condensation on a beetle. Droplet nucleation and condensation are ubiquitous phenomena in nature and industry. Difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. Abstract engineering the dropwise condensation of water on surfaces is critical in a wide range of applications from thermal management. Engineering the dropwise condensation of water on surfaces is critical in a wide range of applications from thermal management e.
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. Promotion of dropwise condensation of ethyl alcohol, methyl alcohol, and acetone by polytetrafluoroethylene by cecil e. Excess promoter on the tube surface significantly reduces heat transfer but appears to be slowly removed by draining. Vertical surface dropwise condensation heat transfer using. It was an honor to receive the max jakob memorial award for 2018. Condensation heat transfer enhancement in the presence of non. Drop size distributions and heat transfer in dropwise. A thick film of water, which has low thermal conducti vity, acts as an insulating blanket in filmwise conden sation. In standard dropwise condensation, liquid droplets forming on a subcooled non wetting surface are. The authors consider the heattransfer arising from condensation on a single drop, and by means of an assumed distribution of drop sizes. 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.
Mathematical modeling on dropwise condensation 1mr. The 1effect of relative humidity on dropwise condensation dynamics julian e. In film wise condensation, the cooled surface is smooth and frictionless which results in quick. Stable dropwise condensation for enhancing heat transfer via the initiated chemical vapor deposition icvd of grafted polymer films. Following rapid advances in surface engineering, the last years have seen an unprecedented interest in dropwise condensation research. Condensation is the process of transition from a vapour to the liquid or solid state. Stable dropwise condensation for enhancing heat transfer via.
Dropwise condensation on textured surfaces presents a holistic framework for understanding dropwise condensation through mathematical modeling and meaningful experiments. Apr 21, 2018 difference between filmwise and dropwise condensation heat transfer at in dropwise is 10 times larger than in filmwise. Dropwise and filmwise condensation of water vapor on gold. 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.
When dropwise surfaces degrade, they convert to filmwise condensation. In dropwise condensation on surfaces, small droplets appear on nucleation sites and grow. In this work, we report the development of a bioinspired hybrid surface with high wetting contrast that allows for seamless integration of filmwise and dropwise condensation modes. Dropwise condensation is achieved by adding a promoter chemical into the vapor, andor roughened surfaces and surface and surface coated with hydrophobic impurities like fatty acids and organic compounds, known as dropwise promoters. To improve the thermal performance and durability of steam surface condensers, a selfhealing, replenishable filmforming amine ffa coating deposited on the condenser tubing is proposed. Howard pearlman, 3rd thermal and fluids engineering conference tfec, fort lauderdale, fl, march 47, 2018. This is a direct comparison of two common modes of condensation, filmwise and dropwise. Condensation heat transfer enhancement in the presence of. Dropwise condensation of water vapor on long vertical tubes was investigated as to in situ cleaning and promoting techniques for a variety of tube materials. The paper presents a new theory of heattransfer by dropwise condensation in the absence of noncondensing gases. However, the necessity for nonwetting to achieve dropwise condensation is unclear. Unlimited viewing of the articlechapter pdf and any associated.
Dropwise condensation of vapor on and underneath horizon. Dropwise condensation article about dropwise condensation. So most condensers are designed on the assumption that film condensation will take place on the surface eventually. Overall heat transfer coefficients are reported for filmwise and dropwise condensation. In this study, we conducted aircooled condensation experiments inside bare and tetrafluoroethylene tfecoated pyrex glass tubes. Jun 05, 2016 vapour may condense onto a cooled surface in two distinct modes known as filmwise and dropwise. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. Effect of contact angle on steam dropwise condensation. Dropwise condensation on advanced functional surfaces.
In dropwise a large area of solid surface is directly exposed to vapour. In this mode, when steam condenses, the droplets are formed. A nonthermal gliding arc plasma reformer for syngas production. The process is accompanied by liberation of heat energy due to the change 10 phase. Dropwise condensation on solid hydrophilic surfaces science. In this work, we study the growth of water droplets on hydrophobic convex surface textures such as bumps and concave surface textures such as dimples with a. The critical radius for onset of droplet condensation is determined in the preceding paper part i, leading to a more accurate determination of droplet nucleation density and the coalescence radius in this paper part ii. Lancaster, pennsylvania, usa abstract dropwise condensation has shown the ability to increase condensation heat transfer coefficients by an order of magnitude over filmwise condensation. Dropwise condensation on hydrophobic bumps and dimples. Condensation heat transfer enhancement in the presence of noncondensable gas using the interfacial effect of dropwise condensation. Which gives more heat transfer, filmwise condensation or. Jan 10, 2020 download fulltext pdf download fulltext pdf dropwise condensation on solid hydrophilic surfaces article pdf available in science advances 62. Filmwise and dropwise condensation and boiling thermodynamics.
Motivated by previous reports of substrate softening increasing droplet nucleation rate, here. Particular attention is given to heat transfer measurements, theory, transition and effects of surface. Dropwise condensation on rough hydrophobic cylinders of different diameter d. Recurrent filmwise and dropwise condensation on a beetle mimetic surface. On the right half of the frame is a bare silicon wafer, on which water wets readily. Promotion of dropwise condensation of ethyl alcohol. This reaction appears in the droplet receding and advancing. Studies on condensing droplet morphology and growth dynamics have been conducted 20 in the past.
Using infrared thermometry and sideview visualization with a chargecoupled device ccd camera, highresolution local wall temperature distributions on the tubes and the formation of filmwise and dropwise condensation inside the tubes could be determined. Dropwise condensation on inclined textured surfaces. Ar dr fraction of the surface area covered by drops with a base radius in. Pdf dropwise and filmwise condensation ahtisham ul haq. 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. The process at the vaporliquid interface during condensation is first discussed. Dropwise condensation is provoked artificially with the help of silicons, teflon, assortment of waxes, and fatty. Dropwise condensation occurs when a vapor condenses on a surface not wetted by the condensate.
Despite intensive efforts over the past few decades, almost all studies have focused on the dropwise condensation enabled by superhydrophobic surfaces. Dropwise condensation on solid hydrophilic surfaces. The equipment heats and condenses water, and includes a separate control module with a digital display. Pdf dropwise condensation studies on multiple scales. 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. Mathematical modeling and numerical simulation of dropwise. In dropwise condensation, droplets must grow until they reach the critical departure diameter, which is several millimeters for gravitydriven, quiescent cases rose, 1981. Dropwise definition of dropwise by the free dictionary. Pdf dropwise condensation heat transfer process optimisation on. Dropwise condensation on surfaces with graded hydrophobicity richard w. Dropwise condensation 2019 max jakob memorial award paper.
Apr 10, 2018 in particular, in contrast to the wellknown capillary condensation effect, we report an unexpectedly less favorable condensation on smaller, millimeterscale dimples where the capillary condensation effect is negligible. View the article pdf and any associated supplements and figures for a period of 48 hours. An improved dropwise condensation heat transfer model modified from previous models is proposed in this paper. Department of chemical engineering, university of california and bodega marine laboratory, berkeley, california 94720. Simultaneous dropwise and filmwise condensation behavior on a completely hydrophilic configuration.
Scale effect on dropwise condensation on superhydrophobic. 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 vapour and the surface, dropwise condensation is several more times effective than filmwise. It is now generally accepted that phase change, whether homogeneous or. Dropwise condensation of vapor is a phasechange process. Jul 28, 2014 to attain efficient shedding of liquid droplets in condensation on a superhydrophobic surface, a bond number a dimensionless number for appraising dropwise condensation and a solidliquid fraction smaller than 0. Over the past century, research has shown that heat transfer rates during steam dropwise condensation on nonwetting e. Consequently, a lot of effort has been dedicated to finding durable materials that could sustainably promote dwc as well as finding routes to enhance the heat transfer rate during this phase change process.
Vapour may condense onto a cooled surface in two distinct modes known as filmwise and dropwise. Article information, pdf download for dropwise condensation theory and. Surface topography plays an important role in promoting or suppressing localized condensation. Abstract this film and dropwise condensation unit is used to observe the process of heat. Dropwise condensation on surfaces with graded hydrophobicity. Pdf dropwise condensation on solid hydrophilic surfaces. Film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface. A majority of the work devoted to surface engineering for promoting dropwise condensation heat transfer has focused on steam. 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. Less attention has been dedicated to the condensation of lowsurfacetension fluids such as hydrocarbons and refrigerants, which are used in several industrial processes including hvac, refrigeration, lng storage, and organic rankine cycles. Pdf recurrent filmwise and dropwise condensation on a.
Comparison of experimental results with the correlation shows a. Dropwise condensation of steam on gold surfaces dropwise condensation of. On the right half of the frame is a bare silicon wafer. The chapter covers four main areas of condensation heat transfer. Bonner, dropwise condensation in vapor chambers 26th ieee semitherm symposium condensation can be maintained in heat pipes and vapor chambers as long as the coating does not wear or degrade. 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. Apr 22, 2012 this is a direct comparison of two common modes of condensation, filmwise and dropwise. The phenomenon of dropwise condensation, in which the condensate forms. Dropwise and filmwise condensation saurabh pandey abstract. In a traditional rankine cycle, the condenser system for coalfired power plants uses a pumped cooling water system to reject heat to a wet or dry cooling tower. Garimella2 cooling technologies research center, an nsf iucrc school of mechanical engineering and birck nanotechnology center purdue university, 585 purdue mall, west lafayette, in 47907 abstract. Dropwise condensation phenomena wilkins 1973 aiche.
Dropwise condensation modeling suitable for superhydrophobic. Droplet growth kinetics during dropwise condensation. Unlimited viewing of the articlechapter pdf and any associated supplements and figures. A sensitive test for the presence of organic contamination has been developed.
Alternatively, you can download the file locally and open with any standalone pdf reader. Dropwise condensation of steam on gold surfaces dropwise condensation of steam on gold surfaces. The aim of this work is to investigate chemical composition, crystalline structure, and barrier properties of inorganic films on the carbon steelpolyaniline interface formed with pani prepared by two different procedures. It can be homogeneous, namely, distributed in the vaporphase, or heterogeneous, as in the presence of a cooler solid substrate 12. To attain efficient shedding of liquid droplets in condensation on a superhydrophobic surface, a bond number a dimensionless number for appraising dropwise condensation and a solidliquid fraction smaller than 0. 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. Dropwise condensation, which collects the condensate liquid in the form of droplets on the cold substrate, has attracted a growing interest due to much higher heat transfer coefficient since the. Dropwise condensation, the first stage of frosting, is enhanced on the peaks and suppressed in the valleys when the serrated surface is exposed to humid air, causing frosting to initiate from the.
Experimental investigation of filmwise and dropwise. Download fulltext pdf download fulltext pdf dropwise condensation on solid hydrophilic surfaces article pdf available in science advances 62. Nanograssed micropyramidal architectures for continuous. Borlepwar 1,2mechanical department,maharashtra institute of technology,aurangabad, m.
Simultaneous dropwise and filmwise condensation on hydrophilic. Dropwise condensation takes place when the surface over which condensation takes place is non wetable. The effect of relative humidity on dropwise condensation. View enhanced pdf access article on wiley online library html view download pdf for offline viewing. Dropwise condensation occurs on nonwettable surface while filmwise occurs on wettable surfaces. 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. Stable dropwise condensation for enhancing heat transfer. The thickness of the film formed depends on many parameters including orientation of the surface, viscosity, rate of condensation etc.
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