Thermal performance of a flat microchannel heat pipe for convective cooling terminal under low-temperature differences

High-performance Heating, Ventilation and Air Conditioning (HVAC) terminal devices that use Flat Microchannel Heat Pipes reduce energy consumption and enhance indoor thermal comfort. With compact structures and excellent heat transfer, they have broad application prospects as cooling terminals. This study experimentally investigated the startup characteristics, condensation performance, and thermal resistance distribution under low-temperature-difference conditions. A combined experimental and numerical simulation approach was employed to analyze the influence of ambient temperature and humidity on system performance. The findings reveal that the simulation accurately predicts the local wall temperatures condensation section under various boundary conditions. Furthermore, the established heat transfer model shows good agreement with the experimental data, with deviations within ±1.5 %. This model effectively predicts key parameters such as the surface temperature and variations in the liquid film thickness. The results indicate that when the ambient temperature is 36 °C and the relative humidity exceeds 60 %, the condensate from dewing affects the surface temperature of the heat pipe and increases the heat transfer rate, while the thermal resistance in each zone remains relatively constant. The flat microchannel heat pipe is divided into three zones along the coolant flow direction. Due to non-uniform heat transfer, Zone 1 exhibits the lowest thermal resistance (0.08–0.13 K/W), whereas Zone 3 shows the highest (0.27–0.96 K/W). Increasing coolant flow rate improves overall heat transfer; lowering coolant temperature reduces total thermal resistance. This study provides a basis for the optimized design of cooling systems and validates the potential in improving building energy efficiency.