Comparative experimental study on condenser performance enhancement of a loop thermosyphon system with a microchannel condenser

Efficient condensation is essential for the performance and stability of loop thermosyphon (LTS) systems using low-surface-tension working fluids R1233zd(E) in passive thermal management applications. This study presents a comparative experimental investigation of condenser enhancement strategies based on microchannel structural optimization. Small-scale condensers with visualization capability were designed to systematically examine the effects of microchannel configuration, vapor-phase flow resistance, condensate drainage, non-condensable gases, and porous media on condensation heat transfer. The results demonstrate that interrupted microchannels effectively mitigate flow maldistribution and significantly enhance condensation heat transfer compared with conventional parallel microchannels. Reduction of vapor-phase flow resistance is identified as the dominant factor governing system-level performance, leading to improved condensate removal and delayed flooding. Visualization experiments reveal that accumulation of non-condensable gases severely degrades condensation performance in the downstream region of the condenser, emphasizing the necessity of effective venting. Porous media exhibit a dual effect: capillary-driven liquid film thinning enhances heat transfer at low heat fluxes, whereas increased flow resistance at high heat fluxes deteriorates performance. Modifications targeting only liquid-phase resistance provide limited overall improvement. Based on these findings, general and scalable design guidelines for enhanced LTS condensers are proposed, offering practical insights for high-performance passive two-phase thermal management systems. Graphical illustration of condensation enhancement mechanisms in a loop thermosyphon (LTS) system. The interrupted microchannel design improves flow distribution and condensate drainage, suppresses liquid accumulation, and reduces liquid film thickness, thereby enhancing condensation heat transfer.