Effective thermal conductivity of a compacted pebble bed in a stagnant gaseous environment: An analytical approach together with DEM

An analytical estimate of the effective thermal conductivity of a pebble bed with mono-sized pebbles in the presence of a stagnant gas is presented. The Discrete Element Method (DEM) is used to simulate granular assemblies under uniaxial compression and Resistor Network (R-N) model is applied for estimating the effective thermal conductivity numerically. In this paper, two heat transfer paths, i.e., conduction through pebble-pebble contact and pebble-gas-pebble interface are considered. The effect of the cutoff range for gap and the strain on the effective conductivity is studied. The validity of the analytical model is verified with the results from the R-N Model for different solid-to-gas thermal conductivity ratios and for different packing fractions. The analytical and numerical models show a good agreement with the experimental results of the effective thermal conductivity for lithium orthosilicate pebble beds in the presence of helium and air at different temperatures.