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A B C D E F G H I J K L M N O P Q R
Rabas and Taborek correlation, for heat transfer in banks of low fin tubes, Rackett equation (modified) for liquid density Radiation: Radiation shields, in radiation heat transfer, Radiation source analysis, Radiative heat transfer: Radiators, automotive, construction, Radiometers, application in gas radiation property measurement, Radiosity, Stephan's law for, Radiosity-irradiation formulations in radiative heat transfer, Rankine cycle in refrigeration, Rao, B K Raoult's law for partial pressure, Rating of heat exchangers, Rayleigh instability, in free convection, Rayleigh number Reay, D Reboilers: Reciprocal mode integrating sphere, for reflection and transmission measurements in radiation, Rectangles: Rectangular ducts: Rectangular enclosures, free convective heat transfer in: Rectangular fins, for plate fin exchangers Reduced pressure, correlations for pool boiling using, Reference temperature: Refinery processes, fouling in, Reflection, of thermal radiation, from solid surfaces: Reflectivity, of solid surfaces, Reflectometer, heated cavity, Reflux condensers, Refractories, density of, Refractory surfaces, Refrigerants: Refrigerant 11 (Trichlorofluoromethane): Refrigerant 12 (Dichlorodifluoromethane): Refrigerant 13 (Chlorotrifluoromethane): Refrigerant 21 (Dichlorofluoromethane): Refrigerant 22 (Chlorodifluoromethane): Refrigerant 116: Refrigerant plant, entropy generation in, Refrigeration, heat transfer in, Regenerators and thermal energy storage, Regimes of heat transfer, in ducts, single phase flow, Reidel method, for predicting enthalpy of vaporisation, Reinforcing rings, for expansion bellows, Relaminarization, of turbulent flow, Reichenberg method, for effect of pressure on gas viscosity, Relief system design for shell-and-tube heat exchangers with tube side failure, Removal of fouling deposits: Renewable fuels, properties of, Renotherm, heat transfer medium, Repair, of expansion bellows, Residence times, in dryers: Resistance network analysis, Resistance (thermal) due to fouling: Reversible (minimum) work, in Reynolds number, Reynolds stress models, for turbulence, Rheologically complex materials, properties of: Rheological properties of drag reducing agents Rheology, shear flow experiments used in, Rhine, J M, Ribatski, G, Riblets for drag reduction, Richardson number, Richie, J M, Ring cells, in free convection, RODbaffles, in tube bundles with longitudinal flow, Rod bundles: Rohsenow correlation, for nucleate boiling, Roll cells, in free convection, Roller expansion, of tubes into tube sheets, Rose, J W, Rossby number, Rotary dryer, Rotating drums, heat transfer to particle bed in, Rotating surface, in an annular duct Rotation, as device for heat transfer augmentation, Roughness, surface: Rough walled passages, radiative heat transfer down, Rubber (sponge) balls, in fouling mitigation, Ryznar index for water quality,
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Dropwise Condensation

DOI 10.1615/hedhme.a.000188

2.6.5 Dropwise Condensation

A. Introduction

This mode of condensation occurs when a vapour condenses on a surface which is not wetted by the condensate. It has long been recognised that, for non-metal vapours, dropwise condensation gives much higher heat-transfer coefficients titan found with film condensation. For instance, in the absence of non-condensing gases, the heat-transfer coefficient for dropwise condensation of steam is around ten times that for film condensation at power station condenser pressures and more than twenty times that for film condensation at atmospheric pressure. In circumstances where the filmwise coefficient is of similar magnitude to that on the cooling side, a change of mode to dropwise condensation offers a potential improvement in overall coefficient by a factor of around 2. This has been verified by experiment as shown in Figure 1.

Figure 1 Overall heat-transfer coefficient for steam at atmospheric pressure condensing on a water-cooled horizontal aluminium tube (I.D. 9.7 mm, O.D. 12.8 mm). Vapour velocity 0.7 m/s. Non-condensing gas content < 30 ppm. Coolant temperature 20 °C. Promoter — 9 μm copper plate, dioctadecyl disulphide. [From data in Rose (1978)]

Clean metal surfaces are wetted by non-metallic liquids and film condensation is the mode which normally occurs in practice. Non-wetting agents, known as dropwise promoters, are needed to promote dropwise condensation. Unfortunately, sufficiently reliable promoting techniques have not yet been developed and dropwise condensation has not so far been used on an industrial scale to any significant extent. On the laboratory scale, however, dropwise condensation can be reliably obtained for long periods for steam and a few high surface tension organic fluids. Reviews of dropwise condensation heat transfer have been given by Le Fevre and Rose (1969), Tanasawa (1991), and Marto (1994).

B. Dropwise promoters

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