Modeling of Energy and Heat Storage Fixed-Bed Reactors Using Discrete-Element Method

Abstract

This work is devoted to the modelling of heat storage device and energy storage reactors based on fixed-bed geometry. The interparticle discrete-element-method model is developed and used in this work. The model accounts for the interparticle heat exchange directly, which is most useful in a fixed bed where heat transfer between particles is significant. The DEM model can be coupled with one-dimensional or two-dimensional fluid flow and reaction or phase change intraparticle models. The model is used to prove two energy storage solution concepts numerically. The first concept is a new type of fixed-bed reactor for steam-methane reforming (SMR).The reactor consists of two sorts of spherical particles: electrically conductive particles and non-conductive catalyst particles. The main feature of this reactor is the application of electric resistance heating using the electrically conductive particles which heat the non-conductive catalyst particles and reacting gas inside the reactor. Steady-state particle temperatures are calculated based on the developed hybrid model with 3D discrete solid heat transfer and 1D fluid heat and momentum transfer. The modes of heat transfers include conduction between particles, forced convection and radiation. The catalyst size is selected to be 0.4 of radii of the conductive particles, based on the maximum radius at octahedral sites of closed packing. Analysis of simulations based on the electrical current and 3D temperature distribution revealed the optimal volume fraction of catalysts is determined to be between 0.27 and 0.30. The second concept is a heat storage device using encapsulated phase change material (PCM). The PCM considered in this work is paraffin with a melting temperature of 28 \degree C, which stores heat in the capsules as the PCM melts in a hot environment, and releases when the ambient temperature is cooled down. An intraparticle submodel for the heat rate is described in this work during melting and solidification. The equation for the heat transfer coefficient at the solid-liquid interface is found using direct numerical simulation and validated against published experimental data. A new method of increasing heat transfer is proposed that aluminum particles are mixed in with PCM capsules. The aluminum particles reduce overall charging/discharging time of the heat storage device and make the system more responsive. Numerical simulations using the hybrid model shows that the increase in heat transfer is achieved at the expense of volume efficiency. To reduce the charging/discharging time by 10%, the heat capacity per volume is reduced by 20%. bed geometry. The interparticle discrete-element-method model is developed and used in this work. The model accounts for the interparticle heat exchange directly, which is most useful in a xed bed where heat transfer between particles is signicant. The DEM model can be coupled with one-dimensional or twodimensional uid ow and reaction or phase change intraparticle models. The model is used to prove two energy storage solution concepts numerically. The rst concept is a new type of xed-bed reactor for steammethane reforming (SMR).The reactor consists of two sorts of spherical particles: electrically conductive particles and non-conductive catalyst particles. The main feature of this reactor is the application of electric resistance heating using the electrically conductive particles which heat the non-conductive catalyst particles and reacting gas inside the reactor. Steady-state particle temperatures are calculated based on the developed hybrid model with 3D discrete solid heat transfer and 1D uid heat and momentum transfer. The modes of heat transfers include conduction between particles, forced convection and radiation. The catalyst size is selected to be 0.4 of radii of the conductive particles, based on the maximum radius at octahedral sites of closed packing. Analysis of simulations based on the electrical current and 3D temperature distribution revealed the optimal volume fraction of catalysts is determined to be between 0.27 and 0.30. The second concept is a heat storage device using encapsulated phase change material (PCM). The PCM considered in this work is paran with a melting temperature of 28 C, which stores heat in the capsules as the PCM melts in a hot environment, and releases when the ambient temperature is cooled down. An intraparticle submodel for the heat rate is described in this work during melting and solidication. The equation for the heat transfer coecient at the solid-liquid interface is found using direct numerical simulation and validated against published experimental data. A new method of increasing heat transfer is proposed that aluminum particles are mixed in with PCM capsules. The aluminum particles reduce overall charging/discharging time of the heat storage device and make the system more responsive. Numerical simulations using the hybrid model shows that the increase in heat transfer is achieved at the expense of volume eciency. To reduce the charging/discharging time by 10%, the heat capacity per volume is reduced by 20%.