The section Energy Technology performs research on heat transfer and thermofluids engineering. One of the research topics is Heat Storage. Thermo-chemical heat storage is the storage of heat using the endothermic reaction of chemical compounds. During the inverse exothermic reaction the stored thermal energy is released again, generally at a different temperature level.
An important class of materials constitutes of solid or powdery hydro-sorbents like salt-hydrates and zeolites (with a typical length scale of about 100 μm) characterized by a network of interconnecting microscopic pores through which water vapor is transported. The water vapour is attached to or incorporated in the crystal lattice of the hydro-sorbent. Theoretical heat storage capacities can easily be 10 times higher compared to sensible heat storage in water. However, up till now, the realized efficiencies are low and strongly fluctuating.
Tasks
For the purpose of the development of solid sorption materials, micro- and meso-scale models will be developed for the hydration and dehydration processes taking place in powdery samples. These processes are a combination of heat and vapor transport in the grains constituting the powdery sample and in the voids between the grains of the powdery sample. The micro-scale model for the hydration and dehydration processes on grain level will be based on a Monte-Carlo simulation technique using a stochastic model for the nucleation sites, followed by isotropic growth.
The model will be temperature and pressure dependent. Besides, the influence of local defects, like fractures/dislocations and cracks, on the hydration and dehydration processes will be studied, resulting in anisotropic behavior. The micro scale model will be used to derive relations for conversion speeds on grain level to be used in the meso-scale model. For the meso-scale calculations a powdery sample will be considered with a Coarse-Grained Monte-Carlo technique for the hydration and dehydration processes in the grains and a CFD-model for the heat and mass transfer processes in the porous structure of the powdery sample.
The models developed will be validated with micro-scale experiments on grain level (both single- and multi-crystalline) and meso-scale experiments on powdery level carried out in a parallel-running ADEM-project at ECN. Lithium sulfate, a mono-hydrate, and copper sulfate, a penta-hydrate, will be used as model materials because of their well established and relatively simple hydration and dehydration reactions. In a later stage of the project the focus will be on more complex materials, like magnesium and calcium chloride, more suitable for real applications.
The developed meso-scale model will be used to study the transport properties of heat and vapor of various materials as function of several structure properties of those materials.
PhD student-Meso-scale models for heat and vapor transport in storage mate
