185--Film Condensation of Pure Vapour

doi:10.1615/hedhme.a.000185

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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,

Discussion of Condenser Types design methods for multicomponent conduction in, flooding phenomena in

Film Condensation of Pure Vapour Discussion of Condenser Types

operational problems in,

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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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,

Discussion of Condenser Types design methods for multicomponent conduction in, flooding phenomena in

Film Condensation of Pure Vapour Discussion of Condenser Types

operational problems in,

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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Film Condensation of Pure Vapour

DOI 10.1615/hedhme.a.000185

2.6 CONDENSATION
2.6.2 Film Condensation of Pure Vapour

J. M. McNaught and D. Butterworth

A. Introduction

The various resistances to heat transfer during condensation are described in Section 184B. In condensation of a pure vapour, the main resistance is that of the film of condensate which forms on the cooled surface. With a laminar condensate film, heat transfer is by conduction so a thin film will give a lower resistance and therefore a higher heat transfer coefficient than a thick film. Turbulence in the film acts to increase the heat transfer coefficient. Vapour shear has the effect of thinning the film, inducing turbulence, and therefore of increasing the heat transfer coefficient. Other factors which affect the condensate heat transfer coefficient are waves on the film surface, droplet entrainment and deposition, condensate splashing, and condensate subcooling.

Section B provides methods for heat transfer with condensation on a vertical surface, which in a heat exchanger would normally be a vertical tube. Figure 1 illustrates condensation on a vertical surface when the vapour is considered to be stagnant and there is therefore no effect of vapour shear on the condensate film. The condensate drains vertically downwards under gravity, with a flowrate steadily increasing from zero at the top. At the very low film Reynolds numbers at the top of the surface the condensate flow is laminar and wave-free. At some point down the tube surface a transition occurs where waves form on the condensate film. This transition is due to instabilities at the vapour-liquid interface, and it can be characterised by the film Reynolds number. At a much higher Reynolds number there is a transition from laminar-type flow to turbulent flow. In the laminar region the heat transfer coefficient decreases as the Reynolds number increases. The rate of decrease becomes smaller in the laminar-wavy region because of the disturbances caused by the waves. In the turbulent region the higher effective viscosity causes the film to become thicker. However the overall effect in the turbulent region is that the heat transfer coefficient increases as the Reynolds number increases. This is because the increased convection due to turbulence more than compensates for the thickening film. Liquid metals can behave differently, as shown in Section F.

Figure 1 Condensation on a vertical surface in the absence of vapour shear

The effect of a downwards vapour velocity is to increase the heat transfer coefficient by both thinning the film and inducing turbulence (see Section B). An upward vapour velocity will tend to have the opposite effect. However a phenomenon known as flooding occurs before vapour velocities are high enough to affect heat transfer significantly. This phenomenon is where the upwards vapour flow prevents the condensate from draining from the bottom of the surface. This is discussed in Section B(e).

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