Flow boiling characteristics of R1233zd(E) in a horizontal square channel for fuel cell thermal management systems

Thermal management is a key challenge in developing aviation fuel-cell-based propulsion systems. However, comprehensive thermal–hydraulic studies for new low-global-warming-potential fluids remain limited under the low-pressure operating conditions and millimetric geometries relevant to low-temperature fuel-cell thermal management. The coupled influence of controllable operating parameters, particularly the pressure and the mass flux, on heat transfer performance, boiling inception, and hydraulic losses has not been systematically characterized for this application, limiting the validation of predictive models and design methods. To address this gap, this study investigates flow boiling of R1233zd(E) in a square channel (hydraulic diameter 5 mm) at inlet pressures of 2.5–3 bar, corresponding to a saturation temperature of 44 – 50 ° C . The experiments covered a mass flux range from 200 to 600 kg m − 2 s − 1 , heat flux from 0 to 20 W cm − 2 and an inlet subcooling of 5 ° C . The results show that increasing the inlet pressure from 2.5 to 3 bar reduces the wall superheat at boiling inception by approximately 40%, and enhances the heat transfer coefficient while reducing the hydraulic losses by 16%. The findings show that relatively small changes in operating pressure influence the heat transfer performance more strongly than comparable changes in mass flux, highlighting pressure as an effective regulating parameter for two-phase thermal management systems. The outcomes of this study provide an experimental basis for designing optimal operation of sustainable fuel cell thermal management.