TAILIEUCHUNG - Heat Transfer Handbook part 111

Heat Transfer Handbook part 111. The Heat Transfer Handbook provides succinct hard data, formulas, and specifications for the critical aspects of heat transfer, offering a reliable, hands-on resource for solving day-to-day issues across a variety of applications. | ACTIVE TECHNIQUES 1097 to 3 by weight of 1-pentanol in saturated pool boiling of water. In another study van Stralen 1970 reports up to 80 improvement in the film boiling coefficient in a 4 1 weight percent mixture of 2-butanone and water. Bergles and Scarola 1966 and Pabisz and Bergles 1997 have considered subcooled flow boiling of water a 1-pentanol by weight mixture and found a distinct reduction in CHF at low subcooling. Contrarily with the addition of a surfactant to seawater the overall heat transfer coefficient was found to be doubled in vertical upflow boiling in a desalination application. ACTIVE TECHNIQUES A variety of active techniques including mechanical aids stirring surface scraping and rotating surfaces surface vibration fluid vibration electrostatic electric and magnetic fields injection suction and jet impingement have been investigated in the literature Bergles 1998 . As indicated earlier all of these methods and devices require the input of external power to promote the desired enhancement which should be accounted for appropriately when evaluating the improved thermal-hydraulic performance. For stirring and surface scraping devices Uhl 1970 and Hagge and Junkhan 1974 provide early reviews and the applications include both single-phase and boiling heat transfer. Rotating surfaces commonly preexist in cooling of rotating electrical machinery and gas turbine rotor blades and substantial enhancement of up to 350 in heat transfer coefflcients for laminar flows in straight tubes routing around their own axis or a parallel axis have been reported Mori and Nakayama 1967c McElhiney and Preckshot 1977 Vidyanidhi et al. 1977 . Tang and McDonald 1971 have reported that with high-speed rotation of heated cylinders in saturated pools the convective coefficients are so high that boiling can be suppressed. Enhanced steam condensation on a rotating vertical cylinder has been documented by Nicol and Gacesa 1970 . In most recent studies however compound

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