TAILIEUCHUNG - Heat Transfer Handbook part 37

Heat Transfer Handbook part 37. 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. | CONFORMING ROUGH SURFACE MODELS 351 X - fIn - In - V Hj HeJ p 3 ln . HeJ Sridhar and Yovanovich 1994 reviewed the plastic and elastic deformation contact conductance correlation equations and compared them against vacuum data Mi-kic and Rohsenow 1966 Antonetti 1983 Hegazy 1985 Nho 1989 McWaid and Marschall 1992a b for several metal types having a range of surface roughnesses over a wide range of ppparnnt contcct pressure. Srihhar and Yovanovich 119 a showed that the elastic deformation model was in better agreement with the vacuum data obtained for joints formed by conforming rough surfaces of tool steel which is very harde The elastic asperity contact and thermal conductance models of Greenwood and Williamson 1966 Greenwood 1967 Greenwood and Tripp 1967 1970 Bush et al. 1975 and Bush and Gibson 1979 are different from the Mikic 1974 elastic contact model presented in this chaptere However they predict similar trends of contact conductance as a function apparent contact pressuree Conforming Rough Surface Model Elastic-Plastic Deformation Sridhar and Yovanovich 1996c developed an elastic-plastic contact conductance model which is based on the plastic contact model of Cooper et al. 19969 and the elastic contact model of Mikcc 199741. The reunlts are uummarized below in terms of flee geometric patametets Ar Aa the real-to-apparent area ratio n the contact spot density a the mean contact spot radius and X the dimensionless mean plane separation Ar Aa X 2 1 m 2 exp -X2 16 o erfc X 2 fep - erfc 2 na hc y ksm 2 W2n r I--------------- - 1 -5 1 -yj fep 2 erfc XA 2 n a 1 352 THERMAL SPREADING AND CONTACT RESISTANCES X V2erfc 1 1 2P fep Hep The important elastic-plastic parameter fep is a function of the dimensionless contact strain e which depends on the amount of work hardening. This physiaal parameter lies in the range fep . The smallest and largest values correspond to zero and .

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