David J. Tanner

An analysis of the influence of material structure on the effective thermal conductivity of theoretical porous materials using finite element simulations

Two-dimensional finite element simulations were used to examine the relative influences of selected porosity-related variables on effective thermal conductivity. The finite element models simulated a steady-state thermal conductivity measurement device performing measurements on theoretical materials with varying structures. The results indicated that the extent of contact between pores or particles and the designation of components as continuous or dispersed phases were more significant factors than the size or shape of individual pores or particles. The results suggested that materials with external porosity should be considered separately to materials with internal porosity for the purposes of effective thermal conductivity prediction, and that it is unrealistic to expect a model that is a function of the component thermal conductivities and volume fractions alone to provide accurate predictions for all porous materials. If an additional parameter is incorporated into an effective thermal conductivity model it should be related to the extent of contact between pores or particles.

A generalised mathematical modelling methodology for design of horticultural food packages exposed to refrigerated conditions: part 1, formulation

Abstract A generalised mathematical modelling methodology to predict rates of key heat and mass transfer processes within refrigerated horticultural packages is described. A novel zoned approach with flexible geometry descriptions and flexible unifying concepts are used to ensure wide-ranging model applicability. The model component hierarchy, which treats the in-pack fluid, packaging and product as equally important components, closely aligns the modelled system and the physical system. This, together with the flexible zone definition methodology and associated definitions of sub-models for intra- and inter-zonal heat and mass transfer pathways support the use of an object-oriented simulation computer programme design. In Part 2, the heat transfer sub-models are presented, and the total model system tested against experimental data for several package-product combinations. In Part 3, the mass transfer sub-models are presented and further test results reported.