The effect of relative humidity on dropwise condensation dynamics. On hydrophobic surfaces, dropwise condensation may form and increase heat fluxes by 510 times compared to filmwise condensation figure 1b. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a pdf plugin installed and enabled in your browser. Temperatures and the condensate heat resistance in dropwise. In standard dropwise condensation, liquid droplets forming on a. If condensate tends to wet the surface and there by forms a liquid film, then processes of condensation is. If you do not see its contents the file may be temporarily unavailable at the journal website or you do not have a pdf plug. Reos show sustained dropwise condensation behavior for over 100 hours at accelerated saturated steam conditions without compromising structural integrity or hydrophobicity, and produce an almost tenfold enhancement in the heat transfer coefficient 103 5. Filmwise and dropwise solteq equipment for engineering. Megaridisa, a department of mechanical and industrial engineering, university of illinois at chicago, chicago, il 60607, usa b nbd nanotechnologies, 8 saint marys st.
Drop distributions and numerical simulation of dropwise. Dropwise condensation realises heat transfer coefficients which are about one order of magnitude higher than those for filmwise condensation koch, 1997. 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. The authors consider the heattransfer arising from condensation on a single drop, and by means of an assumed distribution of drop sizes. The process at the vaporliquid interface during condensation is first discussed. Significantly, heat transfer rates in dropwise condensation can be much higher than in filmwise condensation. The limiting heat transfer mechanisms of dropwise condensation. It can be homogeneous, namely, distributed in the vaporphase, or heterogeneous, as in the presence of a cooler solid substrate 12. Supporting information recurrent filmwise and dropwise condensation by patterned high wetting contrast youmin hou, miao yu, xuemei chen, zuankai wang, and shuhuai yao, department of mechanical and aerospace engineering, the hong kong university of science and technology, kowloon, hong kong. In the current work, the effect of dropwise condensation at the microscopic level was analyzed using geometrical optics and optical simulation.
Optimization of superhydrophobic surfaces to maintain. Enhancing filmwise and dropwise condensation using a hybrid. Here, we also investigate the effect of nucleation site density, varied from 104cm2 to 107cm2. In dropwise condensation, vapor condenses in the form of distinct drops. An evaluation of polymer coatings for the promotion of dropwise condensation of steam. Dropwise condensation 2019 max jakob memorial award paper. The unit itself contained bench top unit, with an integrated steam generator and air extraction system. Drop spatialdistributions has become the main obstacle to the direct numerical simulation of dropwise condensation heat transfer. Dropwise condensation characteristics of permanent. Dropwise condensation article about dropwise condensation. Vertical surface dropwise condensation heat transfer using self.
A study of dropmicrostructured surface interactions. Enhancing dropwise condensation through bioinspired wettability patterning aritra ghosh,a sara beani,b bong june zhang,b ranjan ganguly,a,c constantine m. Jan 10, 2020 dropwise condensation on solid hydrophilic surfaceseaax0746. The equipment heats and condenses water, and includes a separate control module with a digital display. Report includes historical background, experiments with elements and dropwise condensation, economic considerations, and publications that came from his program. Design and fabrication of a hybrid superhydrophobic. Supporting information recurrent filmwise and dropwise. Condensation on the atomic scale dropwise condensation of vapor is a phasechange process. Dropwise condensation of low surface tension fluids on. There is not a specific approach in choosing the size of the roughness of the superhydrophobic surfaces and it was mostly selected arbitrarily to investigate the behavior of condensates on these surfaces. Hydrophobicity of rareearth oxide ceramics and their. A mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic contact angle greater than 150 deg features. Dropwise condensationfurther heat transfer measurements proceedings of the fourth international heat transfer conference, parisversailles, france, aug.
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. Request pdf enhancing filmwise and dropwise condensation using a hybrid wettability contrast mechanism. Moreover, researchers have focused their attention on micro and nanostructured surfaces displaying superhydrophobic characteristics 6 which may lead to even higher heat transfer coefficients promoting the phenomenon of jumping droplets. Dropwise condensation of steam on gold surfaces dropwise condensation of steam on gold surfaces.
Enhancing dropwise condensation through bioinspired. 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. Dropwise condensation has been of interest to the heat transfer community since its earliest published work in 1930. Drop nucleation, growth, and condensation have important practical consequences. 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. All content on this website, including dictionary, thesaurus, literature, geography, and other reference data is for informational purposes only. When dropwise surfaces degrade, they convert to filmwise condensation.
The process of droplets jumping, against adhesive forces, from a solid surface upon coalescence has been studied using both experimental and. 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. Gold surfaces for condensation heat transfer gold surfaces for condensation heat transfer. It is now generally accepted that phase change, whether homogeneous or heterogeneous condensation, is induced by. The chapter covers four main areas of condensation heat transfer. 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. In the current work, we analyze the effect of the dropwise condensation at the microscopic level using geometrical optics and optical simulation. 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. 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. In the past decade, the condensation on superhydrophobic surfaces has been investigated abundantly to achieve dropwise condensation.
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 aerodynamic surfaces, to list a few. The main components in the unit are the specially designed condensers for the observation of. If condensate tends to wet the surface and there by forms a liquid film, then processes of condensation is known as film wise condensation. National security internet archive nsia additional collections. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. It is the aim of the present work to put forward the random fractal model describing the drop size and spatial distributions. 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. Design and fabrication of a hybrid superhydrophobichydrophilic surface that exhibits stable dropwise condensation. May 03, 2011 a mathematical model is developed to represent and predict the dropwise condensation phenomenon on nonwetting surfaces having hydrophobic or superhydrophobic contact angle greater than 150 deg features. The steam condensation heat transfer performance on the optimum hybrid surface is about 23% higher than that of complete dropwise condensation at surface subcooling of 2. Although it has been known for decades that dropwise condensation outperforms filmwise condensation in heat transfer owing to the droplet. 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. In order to predict and evaluate the performance of systems reliant on condensation, it is equally important to understand how these external conditions affect the dynamics of dropwise condensation.
The detection of dropwise condensation in the camera field is a complex problem that requires an interdisciplinary approach in order to build an accurate model for image formation. Dropwise condensation detection in a single image by tarik. 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. A theory of dropwise condensation at large subcooling. Dropwise condensation heat transfer process optimisation. 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. Which gives more heat transfer, filmwise condensation or. The present work deals with dropwise condensation on flat. Dropwise condensation on surfaces with graded hydrophobicity. 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. Promotion of dropwise condensation of ethyl alcohol.
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. Dropwise condensation heat transfer process optimisation on superhydrophobic surfaces using a multidisciplinary approach z. Existing durable materials such as metals and ceramics are generally hydrophilic and require polymeric modifiers to render them hydrophobic, but these. In this research, we are optimizing the size of the. Dropwise condensation of vapor on and underneath horizon. Report regarding the development of a new approach to dropwise condensation, understanding the role of nucleation in the process, and the possibility of permanent dropwise condensing surfaces.
Dropwise definition of dropwise by the free dictionary. The temperature variations occurring in dropwise condensation at condenser plates of a compact, polymer heat exchanger are studied using instantaneous. Enhancing filmwise and dropwise condensation using a. Pdf dropwise condensation studies on multiple scales. Modeling of dwc involves modeling heat transfer through a single drop and applying it. The drop spatialdistributions on dropwise condensations are less well understood till now. 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. Pdf recent advances in nanotechnology, chemicalphysical texturing and thin film coating. Dropwise and filmwise condensation saurabh pandey abstract. Bikash mondal, marc mac giolla eain, qianfeng xu,vanessa m. Filmwise and dropwise condensation experiments were carried out at atmospheric pressure varying the condensing plates, their inclinations and orientations. The effect of relative humidity on dropwise condensation. Dropwise condensation of water vapor on long vertical tubes was in vestigated as to in situ.
Pdf dropwise condensation on solid hydrophilic surfaces. Mathematical modeling and numerical simulation of dropwise. Dropwise condensation detection in a single image by. Condensation of vapor is a crucial part of a wide range of industrial processes from power generation and distillation to liquefaction and refrigeration. The use of steam surface condensers typically results in low thermal performance on the steamside due to the filmwise mode of condensation. Using basic principles, an analytical model for dropwise condensation is devised, which takes into account the elementary processes that make up the dropwise condensation cycle. Pdf dropwise condensation heat transfer process optimisation on. On the right half of the frame is a bare silicon wafer, on which water wets readily. The results shows that pixels from a region within foggy image area. In film wise condensation, the cooled surface is smooth and frictionless which results in quick.
So most condensers are designed on the assumption that film condensation will take place on the surface eventually. The model is established by synthesizing the heat transfer through a single droplet with the drop size distribution. Promotion of dropwise condensation of ethyl alcohol, methyl. The 1effect of relative humidity on dropwise condensation dynamics julian e. Similarly as in the previous chapter, in this chapter we will discuss heat transfer with phase change, but in this case we will discuss condensation of gas phase vaportoliquid phase change. Dropwise condensation of vapor is a phasechange process. In dropwise condensation the condensate liquid collects in the form of countless droplets of varying diameters on the condensing surface, instead of forming a continuous film, and does not wet the solid cooling surface.
There are mainly two mode of condensation processes known as film wise condensation and dropwise condensation. This is a direct comparison of two common modes of condensation, filmwise and dropwise. Circular patterns condensation surfaces using a wettability contrast mechanism is one of. Transfer coefficient through dropwise condensation and. Filmwise and dropwise condensation and boiling thermodynamics. It is now generally accepted that phase change, whether homogeneous or. For the same temperature difference between the vapour and the surface, dropwise condensation is several more times effective than filmwise. Alternatively, you can download the file locally and open with any standalone pdf reader. Critical insight into the industrial application of dropwise condensation. Vapour may condense onto a cooled surface in two distinct modes known as filmwise and dropwise.
Similarly as in the previous chapter, in this chapter we will discuss heat transfer with phase change, but in this case we will discuss condensation of gas phase vaportoliquid phase change in general, condensation is the change of the physical state of matter from gas phase into liquid phase, and is the reverse. Dropwise condensation on rough hydrophobic cylinders of different diameter d. Correlation for dropwise condensation heat transfer. Film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface. Apr 22, 2012 this is a direct comparison of two common modes of condensation, filmwise and dropwise. The effect of sweeping by the departing droplets on the heat transfer coefficient in dropwise condensation is studied analytically here. Dropwise condensation on solid hydrophilic surfaces. On the right half of the frame is a bare silicon wafer. Mar 03, 2020 it was an honor to receive the max jakob memorial award for 2018. Dropwise condensation modeling suitable for superhydrophobic. The paper presents a new theory of heattransfer by dropwise condensation in the absence of noncondensing gases.
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