How fins and flow redesign boost hydrogen storage

Charging capacity contours and hydrogen pathlines for the four different geometry designs

As hydrogen becomes an increasingly important part of global decarbonisation strategies, the need for efficient, compact and safe storage systems is growing rapidly. Metal hydrides (MH) are a promising option because they can store hydrogen at relatively low pressures with high volumetric density. However, one of their major limitations is slow absorption rates caused by heat accumulation inside the reactor.

A new study led by Dae Yeob Lee, with co-authors Dr Yasser Mahmoudi, Dr Vincenzo Spallina and Dr Amir Keshmiri (Founder and Technical Director of Mansim), addresses this challenge using advanced computational fluid dynamics (CFD) to understand how reactor design influences heat and mass transfer during hydrogen absorption.

The key challenge: removing heat quickly

During hydrogen charging, metal hydrides release heat. If this heat is not removed effectively:

• absorption slows dramatically

• reactor efficiency drops

• cycle times increase

• storage capacity is under-utilised

The study explores how internal fins and a water-jacket heat-exchanger can be engineered to accelerate heat removal and significantly improve performance.

Using CFD to optimise reactor geometry

The research applies a transient CFD model, treating the metal hydride bed as a porous medium and using a turbulent conjugate heat-transfer model for the water jacket.

The team analysed a range of parameters:

• fin arrangements  inline vs. staggered

• fin materials, stainless steel vs. copper

• water-jacket flow rate, Reynolds numbers from 5,100 to 22,000

• hydrogen inlet pressure, 5 to 20 bar

• reactor design variations, four geometries compared

This parametric approach allowed the researchers to quantify how each design choice affects hydrogen charging time.

Staggered fins dramatically boost performance

One of the most striking findings was the impact of fin arrangement:

• staggered fins achieved a 30% reduction in absorption time at Re = 5100

• raising the flow rate to Re = 22,000 shaved off a further 27%

• increasing the hydrogen inlet pressure to 20 bar produced a 61% reduction in absorption time

Copper fins outperformed stainless steel due to their higher thermal conductivity, showing the importance of enhanced heat-transfer pathways inside the hydride bed.

Balancing performance and practical constraints

While adding more fins improves cooling, the study highlights important trade-offs:

• increased pressure drop in the water jacket

• added reactor mass

• reduced available hydride volume

• diminishing returns beyond a certain fin density

The four reactor designs assessed demonstrate that maximum cooling does not always mean maximum efficiency. A balanced design approach is essential for industry adoption. Source: https://www.sciencedirect.com/science/article/pii/S0360319925012509