Application of Danckwerts-type boundary conditions to the modeling of the thermal behavior of metal hydride reactors

Journal
Chemical engineering science  
Volume
66
Issue
20
Start Page
4654
End Page
4662
Citation
Chemical Engineering Science 66 (20): 4654-4662 (2011)
Publisher DOI
10.1016/j.ces.2011.06.021
Scopus ID
2-s2.0-80051689989
The paper presents a model-based investigation of a metal hydride reactor applied as a solid state hydrogen storage device. The elements of a metal hydride reactor are hydrogen supply duct, internal hydrogen distribution, hydride bed, reactor shell and the flow domain of the heat transfer fluid. Internal hydrogen distribution and hydride bed are porous media. Therefore, hydrogen flows through non-porous and porous regions during its reversible exothermic absorption and endothermic desorption, respectively. The interface between porous and non-porous regions is a discontinuity with respect to energy transport mechanisms. Hence, Danckwerts-type boundary conditions for the energy balance equation are introduced. Application of the first and second law of thermodynamics to the interface reveals that temperature jumps may occur at the hydrogen inlet but are not allowed at the hydrogen outlet. Exemplarily the loading behavior of a metal hydride storage tank based on sodium alanate is analyzed. It is demonstrated and experimentally validated that only Danckwerts-type boundary conditions predict the important cooling effect of the inlet hydrogen on the exothermic absorption process correctly.
Subjects
Chemical reactors
Energy
Entropy
Heat transfer
Mathematical modeling
Porous media
DDC Class
540: Chemie