tailieunhanh - Heat Transfer Handbook part 36

Heat Transfer Handbook part 36. 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 341 CLA roughness J IjWI dx m rms roughness J i y2 x dx m VL 0 where y x is the distance of poinss in the surfaee from the mnan plene Fig. and L is the length of a tacee tiPat oontams a suffieleni nembeo af aspeeities. For Gaussian asperity heights with respect to the mean plane these two measures of surface roughness are related Mikic and Rohsenow 1966 a CLA A second very important surface roughness parameter is the absolute mean asperity slope which is defined as Cooper et al. 1969 Mikic and Rohsenow 1966 and DeVaal et al. 1987 . a u a m m m Figure Typical joint between conforming rough surfaces. From Hegazy 1985. 342 THERMAL SPREADING AND CONTACT RESISTANCES 1 fL dy x m I ---------- L Jo dx dx rad The effective rms surface roughness and the eHeciive absolute mean asperity shipo for a typical joint formed by two conforming rough surfaces are defined as Cooper et al. 1969 Mikic 1974 Yovanovich 1982 a J 02 02 and m J m2 m2 Antonetti et al. 1991 reported approximate relationships for m as a function of a for several metal surfaces that were bead-blasted. The three deformation models elastic plastic or elastic-plastic give relationships for three important geometric parameters of the joint the relative real contact area Ar Aa the contact spot density n and the mean contact spot radius a in terms of the relative mean pl ie separation defined as X Y a. The mean plane separation Y and the effective surface roughness are illustrated in Fig. for the joint formed by the mechanical contact of two nominally f t rough surfaces. The models differ in the mode of deformation of the contacting asperities. The three modes of deformation are plastic deformation of the softer contacting asperities elastic deformation of all contacting asperities and elastic-plastic deformation of the softer contacting asperities. For the three deformation models there is one thermal contact conductance model given as Cooper et .

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