Analysis of output performance and low-grade heat recovery efficiency in thermal regeneration ammonia-based flow battery under various flow fields

The structure of the flow channel has a crucial impact on output capability and thermoelectric conversion efficiency of the Thermal Regeneration Ammonia-based Flow Battery (TRAFB) used for waste heat recovery. In this work, the three-dimensional numerical models of the battery with various flow channel configurations, which couple mass transfer and electrochemical reactions, have been established. Firstly, a comparative analysis of five classical flow channels (rectangular, parallel, interdigitated, serpentine, and spiral) is conducted to examine their influence on the battery's voltage, power, electrical capacity, energy density, active species concentration distribution, and uniformity. Subsequently, the effects of flow channel depth, width, and initial reactant molarity on the battery's output capability and energy storage performance are explored to optimize the flow channel structural parameters and battery operating parameters. In addition, the thermoelectric conversion capability of the battery is a key focus of the study. The research results indicate that the battery with a serpentine flow channel demonstrates the best performance. In terms of enhancing the battery performance, the order is serpentine > spiral > interdigitated > parallel > rectangular. Moreover, by reducing the depth and width of the flow channel, the peak power, energy density, and electrical capacity of the battery can be further enhanced. In addition, as initial Cu²⁺ molarity grows, the peak power, energy density, and electrical capacity of the battery all show a trend of first increasing and then decreasing, with the maximum values achieved at 0.4 M initial Cu²⁺ molarity. After enhancement by the serpentine flow channel with both depth and width of 0.5 mm, up to ∼50.00 % Carnot relative efficiency can be attained by the battery during low-power operation. Even when operating at limited power, it is still capable of achieving a Carnot relative efficiency of ∼11.22 %, which is significantly higher than the 5 % commercial benchmark.