EFFICIENT MODELING OF COUPLED TRANSFER IN PACKED BEDS. APPLICATION AS MOISTURE BUFFER FOR INTERMITTENT DRYING
Résumé
With the rise of renewable energy in the energy mix, the drying process has to adapt to the availability of energy, in terms of power and cost. Packed beds of hygroscopic particles are likely to play a role in moisture buffers, levelling the energy available by storing latent heat. In this work, a macroscopic formulation able to treat non-local equilibria within the particles was used to model a packed bed. A full implicit method computational method is used to solve to set of coupled and non-linear equations. A full Newton-Raphson strategy was adopted to advance in time. The dual-scale fields embedded in the kernel function together with the efficient computational solution allow a packed-bed to be simulated in a few seconds for a whole cycle (adsorption-desorption). The computational software allows the time-evolution of the spatial fields of temperature, relative humidity of the air and moisture content of the particle to be obtained. Two contrasted hygroscopic products were characterised by experiments in a DVS (sorption isotherm and dynamic of moisture change to define the kernel function). Finally, several simulations are presented with the two contrasted hygroscopic products and operating conditions representative of a solar dryer. These simulations allow clear conclusions to be drawn regarding the potential of such packed beds as energy buffers for drying: pros and cons of each product, sizing of the system (bed and particle size).