Thermal modelling and performance evaluation of LmNi4.91Sn0.15 hydride bed configurations for space-constrained thermal applications

Abstract

• Quantified WR, TP and sorption rate of reactors of identical sizes and conditions. • MH reactor sorption dynamics improves in order: ECT ≈ 3HCR < 4HCR < TBR < CBR. • MH reactor static performance improves in order: TBR < ECT < 3HCR < CBR < 4HCR. • Optimal design is factored by a mixture of TP, WR, and 90/100% sorption time ratio. • 253CBR_d3mm layout is ∼2 times faster than 60ECT_d6.35 mm in sorption rate. An appropriate thermal management system design in the reaction bed is undoubtedly needed to achieve the optimum thermal performance of the metal hydride-based hydrogen storage reactor. The developed 3D thermal model examined the hydrogen sorption performance of diverse heat exchanger configurations, namely, (i) capillary bundled reactor (CBR), (ii) tubular bundled reactor (TBR), and (iii) helical coiled reactor. The performance of these heat exchanger configurations of identical reactor size was compared with an embedded cooling tube bed comprising 2.75 kg LmNi 4.91 Sn 0.15 under homogeneous and pragmatic operating conditions. Relying on the sequential simulations performed in COMSOL Multiphysics® 5.6, a CBR assembly consisting of 253 tubes of 3 mm diameter outperforms smaller diameter CBRs in aspects of flexible fabrication and relatively quick sorption. Furthermore, helically coiled reactors exhibit faster absorption and desorption than embedded cooling tubes (ECT) with a comparatively better weight ratio. It is observed that coils of smaller diameter (4 spiral tubes of 3.175 mm diameter) with a pitch of 8 mm can produce 420–500 W/kg MH of thermal power under 320 s. Subsequently, a sensitivity analysis was conducted to scrupulously explore and evaluate the five reactors with various heat exchanger layouts, demonstrating that the CBR (3 mm diameter, 253 tubes) sorption performance was ∼2.3 times faster than the 60 tubes ECT reactor. The present work offers a cautious understanding of how to improve the thermal performance of the reactor without lowering the hydride content based on the bed configurations when used for accurate space-constrained applications.