Нестаціонарне теплоперенесення в аеродисперсній системі з щільним шаром гравію в каналі ґрунтового регенератора

The paper investigates the space-time evolution of the temperature field in the aerodisperse system “air–dense gravel bed” realized in the channel of a soil regenerator for greenhouses. Aerodisperse systems with dense granular layers are widely used in heat power units, regenerative heat exchangers, and seasonal thermal energy storage devices, but the physics of unsteady heat transfer between the gas flow and a fixed bed of particles has not been fully clarified. Special attention is paid to the sequential heating of the bed along the channel and to the interaction between the thermal front in the solid phase and the temperature field of the gas phase, which are characteristic features of aerodisperse systems under charging conditions of heat storage units. The aim of this study is to analyze the temperature field in the channel of a soil regenerator with a dense gravel bed considered as an aerodisperse system and to quantify coupled heat transfer between the gas and solid phases under transient conditions. The physical model is formulated as a two-component quasi-homogeneous medium, where the gas flow and the dense granular layer are treated as interacting components of the aerodisperse system. The governing equations include the heat transfer equation for the solid phase with effective thermal conductivity and a convective energy equation for the gas flow with an intercomponent heat transfer term describing the energy exchange between the gas and dispersed subsystems. The numerical implementation is performed in Matlab using finite-difference schemes: gas temperature along the channel is calculated sequentially in space, while the temperature of the granular bed is obtained by an implicit time-stepping scheme. The calculations employ thermophysical properties of a gravel bed typical for regenerators with dense granular packing, including porosity, density, specific heat, effective thermal conductivity, and specific particle surface area. The results are presented as two-dimensional temperature fields T(x,t) and Tg(x,t), temperature profiles of the bed and gas along the channel at characteristic times, and time dependences at selected cross-sections. It is shown that a pronounced heating front is formed in the “air–dense gravel bed” aerodisperse system, which gradually propagates from the inlet region of the channel towards the outlet due to gas cooling and heat accumulation in the granular layer. The obtained regularities provide deeper physical insight into heat transfer in aerodisperse systems with dense packing and can be used to optimize geometric and operating parameters of soil regenerators and other regenerative heat exchangers with granular beds.