2 edition of Drop-wise and film condensation of steam... found in the catalog.
Drop-wise and film condensation of steam...
Shea, Frederick L., jr.
Written in English
|Statement||[by] Frederick L. Shea, jr. ...|
|LC Classifications||TJ279 .S42 1940|
|The Physical Object|
|Number of Pages||27|
|LC Control Number||41000238|
Condensation of vapor is a crucial part of a wide range of industrial processes from power generation and distillation to liquefaction and refrigeration 1,2,3,4,5, the past eight decades, significant attention has been devoted to the study of underlying mechanisms, methods, and materials for enhancing the condensation heat transfer rate of steam by promoting dropwise condensation. Dropwise condensation realises heat transfer coefficients which are about one order of magnitude higher than those for filmwise condensation (Koch, ). For a long time, however, no adequate surfaces for dropwise condensation of steam had been found which satisfied industrial requirements with respect to stability and cost.
With ξ 0 = , Eq. (3) gives values of α i much higher than the heat transfer coefficient for the condensate in film condensation, except in the case of liquid metals. For example, for steam at 30°C, α i ≈ MW/m 2 K, which may be compared with typical values of the heat transfer coefficient in the range 10–50 kW/m 2 K for the condensate film during film condensation. Dropwise condensation. In dropwise condensation, the condensed vapor forms droplets on the surface instead of a continuous film. Dropwise condensation can occur when the surface is nonwetting or these droplets are taken away from the surface by external flow or by gravity. The vapour is in direct contact with the surface over most of the area.
Dropwise condensation. If the droplets of water on the heat transfer surface do not merge immediately and no continuous condensate film is formed, ‘dropwise’ condensation occurs. The heat transfer rates which can be achieved during dropwise condensation, are generally much higher than those achieved during filmwise condensation. Dropwise condensa tion of steam is a comparatively recent problem to attract the interest of investigators in the field of heat transfer. There is considerable advantage in obtaining and preserving dropwise condensation, since it has been shown by a number of workers that in dropwise condensation much higher rates of heat transfer occur.
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Film condensation may be analysed using Nusselt theory. The first analysis of film condensation was due to Nusselt and given in standard text books, e.g.
in Ref. . The theory considers condensation onto a vertical surface and the resulting condensed liquid film flows down the surface under the action of gravity and is assumed to be laminar.
15 results for "dropwise condensation". Skip to main search results. For nonmetal vapors, dropwise condensation gives much higher heat transfer coefficients than those found with film 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.
Dropwise and Filmwise condensation Filmwise condensation Unless specially treated, most materials are wettable as con-densation occurs a film condensate spreads over the thickness of the film depends upon a numbers of factors, e.g. the rate of condensation,the viscosity of the con-File Size: KB.
Drop-wise condensation. Drop-wise condensation takes place when the surface over which condensation takes place is non wet-able. In this mode, when steam condenses, the droplets are formed. When the drops become bigger, they simply fall under the gravity.
In drop wise condensation, high heat transfer rates are achieved and hence, many times. Pure vapor condenses when it contacts a solid surface whose temperature is below the saturation temperature of the vapor T se, filmwise and mixed forms of condensation with distinctly differing heat transfer performances can be observed, for example, the heat transfer coefficients for ideal dropwise condensation can be up to one order of Drop-wise and film condensation of steam.
book that is larger than. dropwise condensation is quite large compare with film wise condensation. The drop wise condensation of steam has heat transfer co-efficient 2 to 10 times as large as film condensation.
However, it has been difficult to sustain drop wise condensation commercially for long periods of time. This can be achieved in. Film-wise and drop-wise condensation experiments were carried out at atmospheric pressure varying the condensing plates, their inclinations and orientations (upward or downward facing), and the air concentrations.
As expected, dropwise condensation showed much higher heat transfer rates than corresponding film-wise condensation in the pure steam cases. In the pure steam cases, the drop-wise condensations showed much higher heat transfer rates than film-wise condensations, which showed good agreements with the Nusselt theory of natural convection condensation.
However in the steam and air mixture cases, as expected, both modes of condensations fell in similar range of heat transfer rates. Due. Film wise and Drop wise condensation are nothing but two different results of condensation of vapor/steam when gets into contact of cooled surface. In film wise condensation, the cooled surface is smooth and friction-less which results in quick.
Although it has been known since the s that heat transfer coefficients for dropwise condensation of steam are much higher than those for film condensation, there were, until the s, wide discrepancies between the results of different investigators.
Subsequently, more accurate measurements have shown good consistency and the. 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. To measure the thermal performance enhancement of these polymer coatings, a custom test apparatus was used to measure the local heat transfer coefficient.
A film of condensate inside plant will reduce the efficiency with which heat is transferred. When air dissolves into condensate, it becomes corrosive.
As can be seen, the steam and condensate system represents a continuous loop. Once the condensate reaches the feedtank, it becomes available to the boiler for recycling. Energy monitoring. For film wise condensation, the surface over which the steam condenses is wet-able and hence a film of condensate is formed as the steam condenses.
Generally, as the film of condensate impedes the heat transfer, film wise condensation will be resulted in low heat transfer rates. The thickness of the film formed depends on many parameters including orientation of the surface.
CONDENSATION HEAT TRANSFER OF STEAM ON VERTICAL DROPWISE AND FILMWISE COEXISTING SURFACES WITH A THICK ORGANIC FILM PROMOTING DROPWISE MODE. Experimental Heat Transfer: Vol. 16, No. 4, pp. b) False Dropwise condensation is a more effective way of heat transfer than filmwise condensation.
In film condensation, the surface is blanked by a liquid film of increasing thickness, and this view the full answer. Condensation may be of two types, filmwise condensation and dropwise condensation.
If the condensate wets the surface, a smooth film is formed and the process is called film type condensation. In this process, the surface is blocked by the film, w. Previous studies on dropwise condensation are primarily devoted to steam, with a few studies of fluids with high or moderate surface tens28,29,30,31 or Marangoni dropwise condensation of.
Steam condensation on corrugated tubes has been enhanced by using a hydrophobic coating to promote dropwise condensation. The coating was created with self-assembled-monolayers (SAMs) on gold and.
Tanner, D. Pope, C. Potter, and D. West, “ Heat transfer in dropwise condensation at low steam pressures in the absence and presence of non-condensable gas,” Int. Heat Mass Transfer 11(2), – (). DropWise coatings will have a massive effect on reducing power plant CO2 emissions, and will be a crucial part of reducing global CO2 emissions down to a survivable level.
This video explains how. It was an honor to receive the Max Jakob Memorial Award for 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.
Dropwise Condensation Technology - KURITA DW - Duration: Kurita Global 6, views. Daily Steam Boiler Maintenance in the Boiler Room - Boiling Point - Duration: