Model for determining the effective thermal conductivity of particle beds with high solid-to-gas thermal conductivity ratio

A model of thermal conductivity for planetary soils: 1. Theory for unconsolidated soils

“…A wealth of data has been acquired in laboratories to quantify and predict the thermal conductivity of particulate material in stagnant gases. The thermal conductivity of a two phase system made of solid spheres and gas at room temperature and below, is controlled by the gas contribution [ Bahrami et al , 2006a; Deissler and Boegli , 1958; Jaguaribe and Beasley , 1984; Masamune and Smith , 1963; Ofuchi and Kunii , 1965; Presley and Christensen , 1997b, 1997c; Raffray et al , 1989; Schotte , 1960; Slavin et al , 2002, 2004; Woodside and Messmer , 1961a; Yagi and Kunii , 1957]. These authors have established that the bulk conductivity of the two‐phase medium is mainly a function of the ratio between the gas pressure P (or mean free path λ ) and the pore size L. This ratio can be expressed with the Knudsen number Kn: with k B being the gas Boltzmann's constant and θ being the molecule collisional diameter (4.6 × 10 −10 m in the case of CO 2 molecules).…”

“…Experimental investigations have shown that natural particles are not ideal spheres and the contact areas between grains are enlarged by surface irregularities [ Batchelor and O'Brien , 1977; Buonanno and Carotenuto , 1997; Buonanno et al , 2003; Cooper et al , 1969; Melanson and Dixon , 1985; Meredith and Tobias , 1960] (Figure 2). Numerous techniques have been proposed to calculate or model the effective resistance to the heat flow by the joint regions, sometimes with loads that are not compatible with natural subsurface conditions [ Kaganer , 1966; Keller , 1963; Laraqi and Bairi , 2002; Mikić , 1974; Raffray et al , 1989; Shonnard and Whitaker , 1989; Slavin et al , 2004]. See a review presented by Bahrami et al [2006b].…”

New steam generation system for lead-cooled fast reactors, based on steam re-circulation through ejector

“…The choice of bayonet-tube steam generators is motivated by the possibility of introducing an efficient pipe rupture detection system consisting in the outer pipe of the bayonets equipped with two steel layers separated by a gap where pressurized helium (contained in a dedicated plenum) can permeate; the gap is filled with microspheres of conductive material, such as aluminum or industrial diamonds, in order to compensate for the gas low conductivity [16,17]. In case of failure, only one of the two metal layers composing the external pipe is expected to break, exposing the helium layer to the contact with either lead (in case of external layer rupture) or steam (in case of internal layer http://dx.doi.org/10.1016/j.apenergy.2014.…”