Matched asymptotic expansions, are used to describe turbulent Couette–Poiseuille flow (plane duct flow with a pressure gradient and a moving wall). A special modification of conventional eddy-diffusivity closure accounts for the experimentally observed non-coincidence of the locations of zero shear stress and maximum velocity. An asymptotic solution is presented which is valid as the Reynolds number tends to infinity for the whole family of Couette–Poiseuille flows (adverse, favourable, and zero pressure gradients in combination with a moving wall). It is shown that plane Poiseuille flow is a limiting case of Couette–Poiseuille flow. The solution agrees with experimental data for plane Couette flow, for the limiting plane Poiseuille flow, and for a special case having zero net flow and an adverse pressure gradient. The asymptotic analysis shows that conventional eddy diffusivity closures are inadequate for general Couette–Poiseuille flows.

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Equations are formulated for the two-dimensional, anisotropic conduction of heat in space radiator fins. The transverse temperature field is obtained by the integral method, and the axial field by numerical integration. A shape factor, defined for the heat-pipe interface boundary condition, simplifies the analysis and renders the results applicable to general heat-pipe/conduction-fin designs. The thermal results are summarized in terms of the fin efficiency, a fin length parameter, and a radiation/axial-conductance number. These relations, together with those for mass distribution between fins, heat pipes, and headers are used in formulating a radiator mass/heat-rate criterion function. Minimization of the criterion function results in asymptotic solutions for the optimum radiator geometry and conditions. The effect of physical properties on the optimum design is determined; in particular, performance is found to vary with fin conductivity to the 1/3 power for large conductivity values.

The numerical conduction of heat in packed beds of particles is investigated, including the effects of inter-particle microasperity gaps and deformation contacts. A detailed numerical model of two half spheres in contact with interstitial fluid is constructed, including asperity (roughness) gaps and deformation contacts on the respective orders of 5 pm and 100 pm for 1 mm particle diameters. The resulting heat flux distributions at the diametrical planes of the particles are integrated to yield the overall thermal conductance, K , or resistance, R = 1/K, between the two diametrical planes. The results show K to be strongly dependent on the interstitial fluid gap and the deformation contact diameter, as well as on fluid and solid conductivities. The effective bed conductivity, k,, is determined as a function of K and the void fraction, and correlated in terms of bed parameters. The resulting k, correlation agrees well with published experimental data over a wide range of substances and temperatures.On etudie la conduction numerique de la chaleur dans des lits gamis de particules, incluant les effets des ecarts de microasperite inter-particules et les contacts de deformation. Un modele numerique detaille de deux demi-sp&res en contact avec un fluide interstitiel est mis au point, qui inclut les asperites (rugosite) et les contacts de deformation respectivement de 5 pm et 100 pm pour des diametres de particules de 1 mm. Les distributions de flux de chaleur resultant dans le plan diametral des particules sont integrees afin d'etablir la conductance thermique, K, ou la resistance, R = 1/K, entre les deux plans diametrals. Les resultats montrent que K est fortement dependant de l'espace fluide interstitiel et du diametre de contact de deformation, et des conductivites du fluide et des solides. La conductivite effective du lit, k,, est determinee en fonction de K et de la fraction de vide et correlee en termes de parametres de lit. La correlation k, resultante concorde bien avec des donnees experimentales publiees pour une vaste g a m e de substances et de temperatures.Keywords: conduction, radiation, packed beds, thermal, effective conductivity, correlation, particle contact. opular bed conduction models, based on axial 1-D con-P duction in the sphere and interstitial fluid, were developed by Y agi and Kunii (1 957), Dixon (1 985), and Hayashi, et al. (1987). More exact analyses using radial and angular conduction, with solutions by relaxation methods, were performed by Deissler and Boegli (1958), Krupiczka (1967), and by Wakao and Kato (1969). A harmonic method was used by McPhedran and McKenzie (1978) for spheres in very close proximity, but not touching. Chan and Tien (1973) considered contacting spheres in vacuum, with Hertzian contact deformation, whereas Wakao and Kato (1 969) used 1 -D conduction at the contact point, but without size variation of the contact region. Batchelor and O'Brien (1 977) investigated theoretically both contacting and noncontacting spheres for thermal and electrical conduction. In the pr...

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