Heat Transfer Handbook part 99. 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. | 976 HEAT TRANSFER IN ELECTRONIC EQUIPMENT IO 3 IO 4 IO-5 IO 6 IO 7 IO 8 IO 6 IO 5 10-4 10-3 Figure Surface chemistry model of contact resistance. 1 SB p k km------- m 1 - B where km is the thermal conductivity of the continuous phase or base polymer y the particle volume fraction and S a shape parameter that increases with aspect ratio. Table provides the value of A for dispersed polymers. The constant B in eq. can be estimated using the expression kp km 1 B kp km S where kp is the thermal conductivity of the filler and TABLE Values of A for Several Dispersed Types Aspect Ratio of Dispersed Phase Length Diameter A Spheres 1 Randomly oriented rods 2 4 6 10 15 Source Cross 1996 . LENGTH-SCALE EFFECTS ON THERMOPHYSICAL PROPERTIES 977 1 vm where vm is the maximum packing fraction. Table lists values of vm for spheres and rods in different packing configurations. Another conmionly Lised mcdk l o r predtcting therm cl cduduvtivity of two-phase systems is effective medium transport EMT discussed by Devpura et al. 2000 . Both the EMT and Lewis-Nielsen models were developed for moderate filler density up to around 40 by volume and often fail to predict the thermal conductivity at higher perpcntapel ft tee flUer. nie Nielneri model donomeL lutstattp obeys a 40 volume fraction as shown by Devpura et al. 2000 whereas the EMT model underpredicts the thermal conductivity above 40 . Devpura et al. 2000 have proposed a new model based on the formation of a percolation network of the filler for calculating the thermal conductivity of high-volume-fraction particle-laden systems. The change in the conductivity of the matrix from its value at the percolation threshold percentage of filler particles at which percolation starts is given by Ak kf p - pc 0 95 0 5 where pc is the volume fraction at the percolation threshold and p is the volume fraction. The thermal conductivities calculated using the percolation
