Improving fuel cell vehicle efficiency: Exploring dynamic cooling strategies for stack radiators with intermittent spray cooling

Advancements in stack cooling via air-cooled radiators for fuel cell (FC) electric vehicles have attracted significant attention. In this study, continuous spray cooling (CTSC) and intermittent spray cooling (IMSC) approaches for FC vehicles were developed at a lab-scale level. Additionally, the thermo-evaporation performance of various IMSC strategies, involving different spray intervals (0–120 s), continuous spray periods (10–60 s), and duty cycles (25–100 %), was investigated. Steady-state analysis revealed that, compared to conventional stack radiators, the CTSC approach using Nozzle#2 achieved superior thermal efficiency (η_th) with an improvement of 36.6–83.8 %, and enhanced spray evaporation efficiency (η_ev) by 18.2–23.9 %. In contrast, Nozzle#1 yielded only a 16.2–52.5 % increase in η_th and an 11.4–18.6 % improvement in η_ev. Compared to CTSC, IMSC extended the low-temperature operating range of the radiator even during the spray-off periods, leading to improved spray evaporation performance. However, excessive coolant exit temperature and heat rejection rate fluctuations were observed at higher spray periods with longer intervals (IMSC-60-60I and IMSC-40-40I) and lower duty cycles (<50 %). On the other hand, the IMSC strategy with shorter intervals and spray periods, i.e., IMSC-30-20I, was identified as optimal, offering a 55.7 % improvement in η_ev compared to CTSC, despite a 2.8 % reduction in η_th. Overall, the optimal IMSC configuration exhibited a 69.4 % higher heat rejection capacity compared to conventional air-cooled stack radiators. Furthermore, variations in η_th were validated using existing correlations, and new empirical correlations for both η_th and air-side heat transfer coefficient were developed, with prediction accuracies of approximately 86 % and 85 %, respectively. Additionally, the radiator's heat transfer area could be reduced by up to 76.2 %, despite a 7.5 % increase in vehicle curb weight. In summary, this study highlights the potential of using IMSC strategies for stack radiators in FC vehicles. The findings provide valuable insights for designing and implementing IMSC-enhanced radiators in real-world applications.