Mahbod Moein Jahromi

A novel active-passive hybrid heat sink design has been proposed and numerically analyzed for concentrated photovoltaic/thermal (CPV/T) units, using rotational concentric/eccentric annular tubes (CAT/EAT), in which water flows in the inner tube and a Phase Change Material (PCM) occupies the annulus. The thermal regulation strategy adopted for the CPV/T unit in this study consists of three consecutive phases: 1) stationary (PCM charging), 2) constant rotation, and 3) oscillatory rotation of the inner tube. Model accuracy is confirmed through grid and time-step independence and validation against benchmark experimental studies. Results show that during the first phase, the EAT configuration performs better due to lower thermal resistance, keeping CPV temperature at 368.7 K (under CR = 2.5), which is 5.7 K lower than the CAT one (374.4 K), yielding net electrical efficiencies of 13.61% and 13.13%, respectively. However, under the second and third phases, CAT outperforms EAT due to Taylor vortex formation and stronger convective mixing. In constant rotation, CPV temperature decreases to 353.02 K (CAT) and 357.1 K (EAT), while oscillatory rotation further reduces it to 337.8 K and 340.8 K, respectively. Transitioning from the first to the third phase improves the overall energy efficiency from 30.18% to 45.7% for the CAT configuration and from 31.59% to 39.11% for the EAT configuration. Meanwhile, the exergy efficiency increases from approximately 48% to 68% in both cases, demonstrating the effectiveness of the proposed hybrid thermal management strategy.

This paper presents a comprehensive evaluation of metal foam flow field application within polymer electrolyte fuel cells (PEFCs) and compares it with conventional serpentine channels from both computational fluid dynamics simulation and experimental viewpoints. The experiments are designed to investigate the effects of material, area density, compression ratio, and final thickness of metal foam. Additionally, the influence of housing plate material and relative humidity (RH) is tested here. The results reveal that at RH = 75%–100%, the best flow field design is nickel foam with a compression ratio of 70%, a final thickness of 0.5 mm, and an SS-304 housing plate, which delivers a great limiting current density. In comparison with the serpentine channel case, the PEFC with this foam flow field shows a 10% improvement in maximum power density (901 vs 989 mW cm−2) and a 45% improvement in limiting current density (2140 vs 3110 mA cm−2). While at RH = 30%, the same foam flow field with a final thickness of 1 mm is a superior option. The experiments also indicate that maximum power density increases by 23% (from 684 to 841 mW cm−2) as the compression ratio rises from 0% to 70% while reducing final thickness from 1 to 0.5 mm causes a 5.8% enhancement in (from 935 to 989 mW cm−2) cell performance. Simulation results reveal that metal foam is more effective in evenly distributing reactants, resulting in an average oxygen mass fraction at the cathode catalyst layer that is 38% higher than the serpentine channel case.