Modeling of a Helical Coil Heat Exchanger for Sodium Alanate Based on-board Hydrogen Storage System

S. Kumar[1], and M. Raju[2]
[1]General Motors R&D Center, Warren, MI, USA
[2]Optimal CAE Inc., Detroit, MI, USA

Hydrogen refueling in a metal hydride based automotive hydrogen storage system is an exothermic reaction and hence an efficient heat exchanger is required to remove the heat for fast refueling. In this paper a helical coil heat exchanger embedded in a sodium alanate bed is modeled using COMSOL. Sodium alanate is present in the shell and the coolant flows through the helical tube. A three-dimensional COMSOL model is developed to simulate the exothermic chemical reactions and heat transfer. Due to memory limitations, only a few turns of the coil are included in the computational domain and periodic boundary conditions are applied at both ends. Practical difficulties encountered in modeling such three dimensional geometries in COMSOL as well as suitable approximations made to overcome such difficulties are discussed. A parametric study is conducted using COMSOL-Matlab interface. The distribution of temperature and hydrogen absorbed in the bed under various operating conditions is presented.