Experimental investigation of a header-integrated thermosyphon heat exchanger for sealed enclosure cooling

In this study, the thermal performance of a two-row, 18-tube thermosiphon heat pipe heat exchanger specifically designed for enclosure cooling is experimentally investigated. Unlike conventional multi-row heat pipe exchangers, all tubes in the present system are interconnected through a common liquid header and a common vapor header, resulting in uniform saturation pressure and causing the entire bundle to behave as a single-stage heat exchanger. Experiments were performed using R236fa and R1234ze(E), under three heating-power levels and four air-velocity settings. Thermal resistances, evaporator- and condenser-side effectiveness, and overall effectiveness were obtained from steady-state measurements using energy-balance correlations. For evaporator air velocities between 1.89 and 4.72 m/s, the overall effectiveness of the thermosyphon heat exchanger using R1234ze(E) exceeds that of R236fa by approximately 10–34%, depending on heat input, with larger gains observed at lower thermal loads. The measured overall effectiveness ranges between 19% and 37%, in agreement with single-stage analytical predictions and significantly higher than comparable multi-row systems reported in the literature. The results demonstrate that common-header thermosyphon configurations constitute a robust and efficient passive cooling strategy for sealed electrical enclosures.