Performance enhancement of thermally regenerative flow battery by a novel design coupling Venturi-effect-inducing structure with nature-inspired flow distributors

The symmetric sinusoidal flow channel (SSFC), which can induce the Venturi effect, has been found to hold significant potential for enhancing the output performance and low-grade waste heat recovery efficiency of the thermally regenerative ammonia-based flow battery (TRAFB). However, this flow channel suffers from substantial mass transfer dead zones between adjacent constrictions. Inspired by the streamlined profile of water droplets in nature, four water droplet-like flow distributors (WFD Ⅰ-Ⅳ) are designed by this study and ingeniously coupled with the flow channel to address this issue and to achieve a higher performance thermally regenerative ammonia-based flow battery. The results indicate that the incorporation of these flow distributors not only significantly reduces the mass transfer dead zones but also further amplifies the Venturi effect, thereby diminishing reactant-starved regions and enhancing uniformity. The coupling of the symmetric sinusoidal flow channel with each of the four flow distributors enables the battery to achieve higher net power, electrical capacity, and thermoelectric conversion efficiency, as well as lower overpotential. Among these, the flow channel design scheme coupling symmetric sinusoidal structure with the flow distributor Ⅳ performs the best, realizing a peak net power increase of approximately 17.68 %, an ultimate electrical capacity increase of approximately 26.35 %, and a thermoelectric conversion efficiency increase of approximately 38.26 % compared to the original symmetric sinusoidal flow channel. To further evaluate the scalability and application feasibility of this scheme, it is applied to modify the structures of the three most commonly used flow fields. The modified flow fields all demonstrate better mass transfer, larger energy storage scale and higher efficiency, with the improvement becoming more pronounced at higher discharge currents. The highest Carnot-relative efficiency and net power are achieved by the modified serpentine flow field, reaching approximately 32.05 % and 317.14 W m⁻², respectively. However, the flow field with the most significant performance enhancement is the parallel flow field, which realizes a peak net power increase of approximately 27.47 % and a Carnot-relative efficiency increase of approximately 7.14 percentage points. Overall, the improvement effects are ranked as follows: parallel flow field > interdigital flow field > serpentine flow field.