On the right half of the frame is a bare silicon wafer, on which water wets readily. 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. The chemical engineering journal, 12 1976 225231 elsevier sequoia s. 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. It is now generally accepted that phase change, whether homogeneous or heterogeneous condensation, is induced by. Printed in the netherlands on the heat transfer in dropwise condensation wen hai wu and jer ru maa chemical engineering department, cheng kung university, tainan taiwan, the republic of china received 6 january 1976. The process at the vaporliquid interface during condensation is first discussed.
Dropwise condensation on hydrophilic surfaces welcome to the ideals repository. It is now generally accepted that phase change, whether homogeneous or. Here, we demonstrate dropwise condensation of these liquids. If condensate tends to wet the surface and there by forms a liquid film, then processes of condensation is known as film wise condensation.
This is a direct comparison of two common modes of condensation, filmwise and dropwise. Surface science, wetting, condensation, engineered surfaces correspondence and requests for materials. Dropwise condensation dwc were first recognized by schmidt et al. Filmwise and dropwise condensation and boiling thermodynamics. Dropwise and filmwise condensation saurabh pandey abstract. Recurrent filmwise and dropwise condensation on a beetle. The instantaneous heattransfer performance of a surface is dictated by the number and sizes of drops on the surface. Promotion of dropwise condensation of ethyl alcohol. Stable dropwise condensation of ethanol and hexane on. Film wise and drop wise condensation are nothing but two different results of condensation of vaporsteam when gets into contact of cooled surface.
One surface promoted nearly perfect dropwise condensation for 2,400 hours. It is also essential in a range of industrial applications, such as power generation 4, water desalination 5,6, thermal management 7, and environmental control 8. For the same temperature difference between the vapour and the surface, dropwise condensation is several more times effective than filmwise. The authors consider the heattransfer arising from condensation on a single drop, and by means of an assumed distribution of drop sizes. Here, we also investigate the effect of nucleation site density, varied from 104cm2 to 107cm2. Dropwise condensation occurs when a vapor condenses on a surface not wetted by the condensate. When dropwise surfaces degrade, they convert to filmwise condensation. Dropwise condensation can improve heat transfer process and, consequently, leads to. Film boiling condensation full abstract the experiment. This reaction appears in the droplet receding and advancing. Dropwise condensation characteristics of permanent hydrophobic. The development of fabrication techniques to create surface structures at the micro and nanoscale using both bottom up and top down approaches has led to increased study of complex interfacial phenomena.
A majority of the work devoted to surface engineering for promoting dropwise condensation heat transfer has focused on steam. Hydrophobic and superhydrophobic surfaces promote dropwise condensation in vaporfilled environments and increase their heat transfer coefficients more than fil. The computer controlled film and dropwise condensation unit tcpgc has been specially designed for students use and to provide visual results and quantitative results related to heat transfer during condensation. On the heat transfer in dropwise condensation sciencedirect. In film wise condensation, the cooled surface is smooth and frictionless which results in quick. 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. In this research, we are optimizing the size of the. 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 on superhydrophobic surfaces with.
Such models describe the phenomena that take place during dropwise condensation. However, many industrial condensation processes such as hvac, refrigeration, and organic rankine cycles orcs condense lowsurfacetension fluids such as hydrocarbons and refrigerants. 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. Pdf dropwise condensation heat transfer process optimisation on. Apr 22, 2012 this is a direct comparison of two common modes of condensation, filmwise and dropwise. Dropwise condensation on superhydrophobic surfaces with twotier roughness chuanhua chen,a qingjun cai, chialun tsai, and chunglung chen teledyne scienti. Improvement of heat transfer by promoting dropwise. In order to enhance the dropwise condensation process, one must understand the hierarchal condensation process entirely. Click add files and select the files you want to include in your pdf. 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. Libraries government documents department to unt digital library.
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. Computer controlled film and dropwise condensation unit. 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. Selfcontained unit, which has its own steam generator. The condensation of steam occurs in many applications e. The equipment heats and condenses water, and includes a separate control module with a digital display. In this study, we conducted aircooled condensation experiments inside bare and tetrafluoroethylene tfecoated pyrex glass tubes. Pdf dropwise condensation has superior heat transfer efficiency than filmwise condensation. The lifetime of dropwise condensation on electroplated silver was also found to depend on the electroplating bath used and surface preparation prior to plating. So most condensers are designed on the assumption that film condensation will take place on the surface eventually. Dropwise definition of dropwise by the free dictionary. Dropwise condensation of vapor is a phasechange process. Vapor condensation is a crucial part of a broad range of industrial applications including power generation, water harvesting, and air conditioning. Dropwise condensation, where vapor condenses as droplets that partially wets.
There are mainly two mode of condensation processes known as film wise condensation and dropwise condensation. Several papers reported that dwc phenomena can be observed on stainless steel or coated substrate by hydrophobic. 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. The chapter covers four main areas of condensation heat transfer. Pdf dropwise condensation studies on multiple scales. Dropwise condensation modeling suitable for superhydrophobic. The 2nd openfoam user conference 2014, berlin germany numerical investigation of dropwise condensation with openfoam. Vapor condensation is a widely used industrial process for transferring heat and separating fluids. Development of constriction resistance model for dropwise. Some features of this site may not work without it. 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. In dropwise condensation the condensate liquid collects in the form of countless droplets of varying diameters on the condensing surface, instead of forming a. Effects of millimetric geometric features on dropwise condensation.
A portion of this surface was still condensing dropwise even after 3,450 hours of continuous condensation. Dropwise condensation studies on multiple scales article pdf available in heat transfer engineering 334. 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 the menu at the top, select view make sure thumbnails is checked in the dropdown menu. During condensation underneath an inclined substrate, initial nucleation happens at specific sites on the substrate. The phenomena that take place during dropwise condensation nucleation of droplets, growth, coalescence, departure and the relevant heat transfer mechanisms are addressed in this work. 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. Simulating heat transfer during transient dropwise. Transfer coefficient through dropwise condensation and. Microscale phenomena during dropwise condensation of.
The paper presents a new theory of heattransfer by dropwise condensation in the absence of noncondensing gases. Condensation on slippery asymmetric bumps kyoochul 1,2park, philseok 1kim2, alison grinthal 1, neil he, david fox1, james c. Numerical investigation of dropwise condensation with openfoam. Institute of aerospace thermodynamics itlr, university of stuttgart, 70569 stuttgart, germany. On the right half of the frame is a bare silicon wafer. Hydrophobic and superhydrophobic surfaces promote dropwise condensation in vaporfilled environments and. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film condensation. Grafted nanofilms promote dropwise condensation of low. In the past decade, the condensation on superhydrophobic surfaces has been investigated abundantly to achieve dropwise condensation. Gravitationally driven wicking for enhanced condensation heat. Depending on how much the pdf is damaged we will be able to recover it partially or completely. Despite progress in developing low surface energy hydrophobic and micronanostructured superhydrophobic coatings to enhance water vapor condensation, demonstration of stable dropwise condensation of lowsurfacetension fluids has not been achieved.
Dropwise condensation on micro and nanostructured surfaces. In dropwise condensation, droplets must grow until they reach the critical departure diameter, which is several millimeters for gravitydriven, quiescent cases rose, 1981. You can merge pdfs or a mix of pdf documents and other files. Computer controlled film and dropwise condensation unit, with. Modeling and simulating the growth of ellipsoidal droplets during. Dropwise condensation on rough hydrophobic cylinders of different diameter d. Optimization of superhydrophobic surfaces to maintain. Dropwise condensation on superhydrophobic surfaces with two. Promotion of dropwise condensation of ethyl alcohol, methyl alcohol, and acetone by polytetrafluoroethylene by cecil e. Experimental investigation of filmwise and dropwise. Heat transfer rates that are more than 10 times larger than those associated with film condensation can be achieved with dropwise condensation as there is no liquid film in this case to resist heat transfer. Vapour may condense onto a cooled surface in two distinct modes known as filmwise and dropwise. Promotion of dropwise condensation of ethyl alcohol, methyl. Abstract the experiment was carried out using the solteq film and dropwise condensation model.
An early dropwise condensation theory combined the heat transfer rate through a single drop with the expression for drop size distribution to obtain the condensation heat flux on the surface 14. Pdf recent advances in nanotechnology, chemicalphysical texturing and thin film coating technology generate definite possibilities for sustaining a. In the other hand, as well as gather experimental data for a better theoretical understanding. If your open pdf has more than a single page, select a thumbnail in the lefthand side where you want to insert another pdf file. Dropwise condensation characteristics of permanent. How to merge pdfs and combine pdf files adobe acrobat dc. Report includes historical background, experiments with elements and dropwise condensation, economic considerations, and publications that came from his program.
Figure 18 dropwise condensation of steam on a vertical surface. Mathematical modeling and numerical simulation of dropwise. It has been specially developed for use in students teaching which enable them to visually observe the process of heat transfer during condensation. Despite intensive efforts over the past few decades, almost all studies have focused on the dropwise condensation enabled by superhydrophobic surfaces. In dropwise condensation on surfaces, small droplets appear on nucleation sites and grow. If condensate tends to wet the surface and there by forms a liquid film, then processes of condensation is. Dropwise condensation article about dropwise condensation. Modeling dropwise condensation underneath unidirectional. Condensation on the atomic scale dropwise condensation of vapor is a phasechange process. While performance averaged over longer times is of interest from a technology standpoint, accurate simulation of the transient state is important in condenser design because the maximum heat rejection of the surface occurs in this range. 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. Studies on condensing droplet morphology and growth dynamics have been conducted 20 in the past.
Heterogeneous condensation of water vapor occurs in a variety of natural phenomena. This reaction appears in the droplet receding and advancing angles. Which gives more heat transfer, filmwise condensation or. Numerical investigation of dropwise condensation with. Gravitationally driven wicking for enhanced condensation. For this reason, several research groups around the world have tried to promote the dropwise condensation and to describe the underneath mechanisms. Typically, dwc was known as high heat transfer coefficient which has 57 times higher that of filmwise condensation fwc. Click, drag, and drop to reorder files or press delete to remove any content you dont want. Rearrange individual pages or entire files in the desired order. Primary view of object titled dropwise condensation characteristics of permanent hydrophobic systems. 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. It can be homogeneous, namely, distributed in the vaporphase, or heterogeneous, as in the presence of a cooler solid substrate 12. Droplet growth kinetics during dropwise condensation. Repair pdf file upload a corrupt pdf and we will try to fix it.
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