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transfer media,

Index

HEDH
A B C D E F G H I J K L M N O P Q R S
Saddle supports, for heat exchangers, Safety factors, Safety, of heat exchangers: Salicyl aldehyde: Salts, heat transfer, as heat transfer media, Sand roughness, equivalent, Santotherm, heat transfer media, Sastri and Rao correlation for surface tension, Saturated boiling: Saturated density: Saturated fluids, tables of physical properties, Saturation pressure, Saturation temperature, Saunders, E A D Sauer, H J Jr, Scale formation in heat exchangers, Scaling approximations, in nonisothermal gas radiation, Scattering bed models, for radiative heat transfer from surfaces, Scattering, interaction phenomena with, Scattering coefficient, Schack wide-band model, for gas radiation properties, Schick and Prausnitz method, for critical volume of mixtures, Schlunder, E U Schmidt, F W Schmidt correlation, for heat transfer in in-line banks of high fin tubes, Schmidt number, Schneider, G E, Schrock and Grossman correlations, for forced convective heat transfer in two-phase flow, Schunk, M Schwier, K, Scraped surfaces: Scaling devices, in shell-and-tube heat exchangers, Seawater physical properties, Seider-Tate equation, for heat transfer in heat exchangers, Selection of heat transfer equipment: Semiconductors, thermal conductivity, Separated flow model: Separation, exergy analysis for, Separators, for use in association with evaporators, Series solutions, for one-dimensional transient conduction, Serrated fins, in plate fin heat exchangers, Shah correlation for boiling, Shah correlation, for boiling in horizontal tubes, Shape factor, in radiative heat transfer between diffuse surfaces, Shear flow, of non-Newtonian fluids, Shear free flow, of non-Newtonian fluids, Shear rate, in fluid, Shear stress: Sheffield, J W, Shelf dryer, Shell-and-tube heat exchanger: Shell-to-baffle clearance, in shell-and-tube heat exchangers, Shells, for shell-and-tube heat exchangers: Sherwood number Shipes, K V, Short-tube vertical evaporator, Sigma phase embrittlement, of stainless steels, Silicate scales, in heat exchangers, Silicone oils, as heat transfer media, physical properties of, Silver method, for calculation of multicomponent condensation, Similarity theory, Simonis, V, Single-phase fluid flow: Single stage flash evaporation (SSF): Singularities, two-phase gas-liquid pressure drop across, Sink, in radiation: Skid-mounted units, specification of, Skin friction coefficient, Skrinska, A, Slab: Sleeves, internal, for expansion bellows, Slot: Slug flow: Slugging, in fluidized beds, Smith, A A, Smith, R, Smith, R A Smith, O, Snell's law, in radiation, Software, for code design, Solar absorber, Solar reflector, Soldered fins, in double pipe exchangers, Solid fuels, properties of, Solids circulation, in fluidized beds, Solid-gas flow: Solid-liquid flow: Solidification: Solids: Solids circulation, in fluidized beds, Soot blowing, Sound velocity: Source, in radiation: Spacers, in shell-and-tube heat exchangers, Spalding, D B, Sparging: Specific enthalpy, Specific entropy: Specific heat capacity, Specific internal energy, Specific volume: Specification of heat exchangers, Spectral absorptivity: Spectral emissivity, in gases, Specular surface, Specular-walled passages, radiative heat transfer in, Spheres: Spherical coordinates, for finite difference equations for conduction, Spherical shells: Spheroids (oblate and prolate), free convective heat transfer from, Spine fins: Spiral heat exchanger: Spirally fluted tubes: Sponge rubber balls, in fouling mitigation, Spray dryers, Sprays, in heat exchangers, Square ducts: Stable equilibrium, of vapor and liquid, Staggered tube banks: Stainless steels, Stanton number Startup: State diagram, for fluidized beds, Static mixers, in heat exchangers, Statically stable foams, Steam, dropwise condensation of, Steam tables, Steam turbine exhaust condensers, Steels, as material of construction, Stefan-Boltzmann constant, Stefan's law, for blackbody radiation, Stegmaier, W, Steiner and Taborek correlation, for forced convective boiling, Stephan and Korner correlation, for boiling of binary mixtures, Stiffeners, PD5500 code guidelines for, Stiffeners, against external pressure, EN13445 guidance on, Stirred beds, heat transfer to, Stirred reactor model, for furnaces, Stone's strongly implicit method, Straight fins (longitudinal fins): Stratified gas-liquid flow: Stratified liquid-liquid-gas flow: Steam analysis methods, for shell-side heat transfer and pressure drop in shell-and-tube heat exchangers, Stress, compressive, in heat exchanger tubes, Stress corrosion cracking, of stainless steels, Stress equation models, for turbulent boundary layers, Stress-strain curve, for solids, Stress tensor: Stresses: Strip baffles, in tube bundles with longitudinal flow, Strouhal number, Subchannel analysis, for critical heat flux in rod bundles, Subcooled boiling: Subcooling: Sublayer, viscous, Submerged combustion, Successive over-under relaxation method for solution of implicit equations, Suction: Suction line exchangers in refrigeration, Sulfur: Sulfur compounds (organic): Sulfur dioxide: Sulfur hexafluoride: Sulfur trioxide: Supercritical fluids: Superficial velocity, in multiphase flow, Superheated gases: Superheated liquid, in metastable state, Superheated vapor, condensation of, on vertical surface, Supersaturation, as cause of fogging in condensers: Suppression of nucleate boiling, Surface catalysis, in augmentation of heat transfer, Surface condensers, Surface finish: Surface, hydraulically smooth, Surface material, effect on fouling, Surface models, in radiative heat transfer, Surface modification for drag reduction, Surface temperature, effect on fouling, Surface tension: Surfactants, in drag reduction, Suspension, radiation interaction phenomena in, Sutherland formula, for viscosity variation with temperature, Sutterby fluid (non-Newtonian), free convective heat transfer to, Swirling flow, in augmentation of heat transfer, Synthetic heat transfer media, Synthetic mixture heat transfer media,
T U V W X Y Z

Augmentation of Boiling and Evaporation

DOI 10.1615/hedhme.a.000199

2.7.9 Augmentation of boiling and evaporation

The augmentation of boiling heat transfer is one of the most exciting and dynamic areas of thermal engineering. Although utilization of enhanced boiling surfaces is now a standard practice of heat exchangers designers and manufacturers, especially for refrigeration and climatization industries, extensive research on this topic continues. Potentially, heat transfer augmentation techniques are capable of being applied to any heat exchanger having the following limiting parameters: reasonable manufacture processes and a favorable reduction in the initial and operational costs. Here, an overview is presented on the principal, commercially available heat transfer augmentation techniques used in evaporation, covering pool boiling, flow boiling within a tube and bundle boiling. The main techniques are identified, the literature on these topics described and, when available, pressure drop, heat transfer coefficients and CHF predictive methods are presented. The emphasis will be on more recent work while previous literature reviews will be cited for those interested in older work.

Other boiling enhancement techniques exist, such as the use of an aqueous surfactant or a polymeric additive, electric fields (EHD), etc. to enhance heat transfer, but these are still either not widely used or are not yet appropriate for practical application. Literature surveys by Cheng et al. (2007), Webb (1994) and Wasekar and Manglik (1999) on the use of surfactants and additives and by Eames and Sabir (1997) and Webb (1994) on electro-hydrodynamic (EHD) enhancement of boiling heat transfer are suggested here as reference studies.

A. Pool boiling

Over the past 70 years, the mechanisms of pool boiling heat transfer have been intensively investigated to better understand the boiling phenomenon of nucleate pool boiling, viz. nucleation site characteristics, pool boiling regimes, critical heat flux, bubble growth, bubble departure dynamics and the development of physical models and correlations to predict heat transfer. In addition to the studies for plain surfaces and tubes, there have been extensive efforts made to augment nucleate boiling heat transfer by means of special structures and plain surfaces covered with novel porous coatings. The joint effort by academic research, providing a better understanding of the boiling phenomenon, and by industry, providing both new geometries and technology for their fabrication, has led to the development and continuous improvement of commercially viable enhanced boiling surfaces.

Enhanced boiling surfaces are widely used in flooded evaporators, falling-film evaporators, direct-expansion evaporators, compact heat exchangers and cooling coils in refrigeration and air-conditioning systems, and to a lesser extent in reboilers in chemical processing plants. In these applications, the improvement of the heat transfer performance minimizes the evaporator size, resulting in reduced initial costs and space requirements, and can also be used to increase the evaporation temperature, improving the efficiency of the system. Moreover, the need for smaller and more effective heat exchangers has also motivated the development of enhanced surfaces for the electronics industry for cooling of high-power density components. Figure 1 shows schematically the structure of some earlier pool boiling enhanced surfaces. In this figure, it can be noted that the main point in the development of such surfaces is obtain a high density of reentrant grooves and tunnels interconnected below the surface to mimic that of metallic porous coatings.

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