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Index

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A B C D E F G H I J K L M
McNaught, J M, Macdonald equation, for fixed-bed pressure drop, Mach number, Macleod-Sugden method for surface tension Macrolayer consumption model for critical heat flux in pool boiling, Maddox, R N Magnetic fields, effect on properties of rheologically complex materials, Magnetic devices, for fouling mitigation, Magnetohydrodynamcs, inaugmentation of heat transfer in microfluidic systems, Margarine manufacture, crystallization of edible oils and fats in, scraped surface heat exchangers for, Marlotherm, heat transfer media, Martensitic stainless steels, Martin, H Martinelli and Boelter equations for combined free and forced convection, Martinelli and Nelson correlations: Mass absorption coefficient, Mass extinction coefficient, Mass fraction, in multicomponent mixtures, Mass scattering coefficient, Mass transfer: Mass transfer coefficient: Materials of construction, for heat exchangers, Low temperature operation, ASME VIII code guidelines for, Matovosian, Robert, Matrix inversion techniques, in radiative heat transfer, Maximum drag reduction Maximum velocities (in shell-and-tube heat exchangers) Maxwell model, for non-Newtonian fluid, Maxwell-Stefan equations, for multicomponent diffusion, Maxwell's equations, for electromagnetic radiation, Mean beam length concept, in radiative heat transfer: Mean phase content, Mean temperature difference: Measurement of fouling resistance, Mechanical design of heat exchangers: Mechanical draft cooling towers, Mechanical loads, specifications in EN13445, Mechanical vapour compression cycles in refrigeration, Mediatherm, heat transfer medium, Melo, L F, Melting, thermal conduction in, Melting point: Mercury: Merilo correlation, for critical heat flux in horizontal tubes, Merkel's equation, in cooling tower design, Mertz, R, Metais and Eckert diagrams, for regimes of convection: Metals: Metallurgical industry, kilns and furnaces for, Metastable equilibrium, of vapor and liquid, Methane: Methanol: Methyl acetate: Methylacetylene: Methyl acrylate: Methyl amine n-Methylaniline: Methyl benzoate: 2-Methyl-1,3-Butadiene (Isoprene): 2-Methylbutane (isopentane): Methylbutanoate: 2-Methyl-2-butene: Methylcyclohexane: Methylcyclopentane: Methylethylketone: Methyl formate: Metallurgical slag, use of submerged combustion in reprocessing of, Methyl fluorate: 2-Methylhexane: Methylisobutylketone: Methylmercaptan: 1-Methylnaphthalene: 2-Methylnaphthalene: 2-Methylpentane: 3-Methylpentane: 2-Methylpropane (isobutane): 2-Methylpropene: Methyl propionate: Methylpropylether: Methylpropyl ketone: Methyl salicylate: Methyl-t-butyl ether: Microbubbles, for drag reduction, Microchannels (see also microfluidics) Micro-fin tubes: Microfluidics, enhancement of heat transfer in, Mie scattering, in pulverized coal combustion, Miller, C J Miller, E R Mineral oils, as heat transfer media, physical properties of, Mineral wool production, submerged combustion systems for, Minimum fluidization velocity, Minimum heat flux in pool boiling: Minimum tubeside velocity, in shell-and-tube heat exchangers, Minimum velocity for fluidization, Minimum wetting rate, for binary mixtures, Mirror-image concept, in radiative heat transfer, Mirrors, spectral characteristics of reflectance from, Mishkinis, D, Mist flow: Mitigation of fouling, Mixed convection occurrence in horiozntal circular pipe, Metais and Eckert diagram for, Mixing (shell-side), in twisted tube heat exchangers, Mixing length, in turbulent flow, Mixtures: Modelling, of fouling: Models, theory of, Modulus of elasticity: Moffat, R S M, Molecular gas radiation properties, Molecular weight: Mollier chart, for humid air, Momentum equation: Monitoring, on line, of fouling, Monochloroacetic acid: Monte Carlo methods, in radiative heat transfer, Moody chart: Morris, M Mostinski correlations: Moving bed, heat transfer to, Muchowski, E, Mueller, A C Muller-Steinhagen, H Multicomponent mixtures: Multidimensional systems, heat conduction in, Multiflux methods, for radiative heat transfer in nonisothermal gases, Multipass shell-and-tube heat exchangers, Multiphase fluid flow and pressure drop: Multiple duties, in plate heat exchangers, Multiple effect evaporation, Multiple hairpin heat exchanger, Multistage flash evaporation (MSF) Multizone model, for furnaces,
N O P Q R S 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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