Flow Boiling Characteristics of R1233zd(E) in a Horizontal Square Channel

Thermal management is critical for the development of next-generation sustainable aviation propulsion systems, including fuel cells and battery-electric propulsion. Cooling technologies based on evaporative flows can dissipate higher heat fluxes within more compact volumes, thereby increasing the efficiency of thermal management systems. In order to design reliable components for advanced thermal management systems, the heat transfer and hydraulic characteristics associated with the selected coolant are needed.This article documents an experimental investigation on flow boiling heat transfer of refrigerant R1233zd(E) in a horizontal square channel with a hydraulic diameter of 5 mm.Experiments were performed by varying the mass flux from 200 to 600 kg · m-2 · s-1 andthe heat flux from 0 to 20 W· cm-2. The inlet pressure varied from 2.5 to 3 bar, while the inlet subcooling was kept constant at 5 ◦C. Flow visualization was performed to identify boiling regimes under different conditions. Results show that increasing mass flux enhances the two-phase heat transfer coefficient due to stronger convective effects and shifts the onset of nucleate boiling to higherwall superheating. The effect of pressure was also investigated. Higher pressure promotes nucleate boiling at lower wall superheat, with the wall superheating at the onsetof boiling decreasing from 12.1 to 7.3 ◦C as pressure increases from 2.5 to 3 bar at a mass flux of 400 kg · m-2 · s-1. At a heat flux of approximately 15 W· cm-2, the average heat transfer coefficient increases by up to 14 % with increasing flow pressure, while the corresponding pressure drop decreases by approximately 16 %. This provides relevant information that could be used to demonstrate the potential of two-phase cooling using low–global-warming-potential refrigerants for fuel cell thermal management in future aviation systems.