Measurement and analysis of reaction kinetics of La - based hydride pairs suitable for metal hydride - based cooling systems

摘要

The reaction kinetics of metal hydride pairs consisting of La_(0.9)Ce_(0.1)Ni_5, La_(0.8)Ce_(0.2)Ni_5, LaNi_(4.7)Al_(0.3) and LaNi_(4.6)Al_(0.4) were measured at different temperatures to determine their suitability for metal hydride - based cooling systems (MHCSs). The effect of operating conditions and compositional changes on driving potential and reaction rates during cooling and regeneration processes was studied. The reaction rates were increased with Ce content and decreased with Al content. The cooling and regeneration time of MHCS, for working temperature range of 140 ℃ (heat source), 25 ℃ (heat sink) and 10 ℃ (cooling), were measured for each pair. The estimated cycle time took the following trend (La_(0.8)Ce_(0.2)Ni_5 - LaNi_(4.7)Al_(0.3)) ＜ (La_(0.9)Ce_(0.1)Ni_5 - LaNi_(4.7)Al_(0.3)) ＜ (La_(0.8)Ce_(0.2)Ni_5 - LaNi_(4.6)Al_(0.4)) ＜ (La_(0.9)Ce_(0.1)Ni_5 - LaNi_(4.6)Al_(0.4)). Two reaction kinetics models namely Jander diffusion model (JDM) and Park - Lee model (PLM) were studied and employed for reaction kinetics analyses. The activation energies (E) of these hydrides were calculated using the Arrhenius plot. Estimated values of activation energies from these models were compared by substituting in the hydriding expression and accurate values of activation energies established for these hydrides.