Study on heat transfer characteristics of ultra-thin flat heat pipes at different liquid filling rates and heat loads

Abstract

The boiling characteristics of flat heat pipes greatly affect their heat transfer performance, but the research on micro-scale ultra-thin steam chamber is still unclear. The heat transfer performance of ultra-thin plate heat pipe (UTFHP) was investigated by analyzing the boiling heat transfer characteristics under various operating conditions through both theoretical analysis and visualization experiments. The findings demonstrate that the heat transfer process of UTFHP can be classified into three stages based on changes in bubble behavior and heat transfer characteristics. Additionally, we conducted a comprehensive examination of the heat transfer mechanism. The study identifies key factors that affect bubble heat transfer in UTFHP, including temperature, pressure, working fluid properties, and gas–liquid interface area. The impact of heating power on the merging point and turning point of the UTFHP is discussed, while the liquid filling rate is found to have an insignificant effect. The start-up time of the UTFHP is delayed by the liquid bridge, which can be improved by introducing multiple air bubbles and liquid bridges. The study also investigates factors affecting the heat transfer capacity of UTFHP during stable operation, revealing that as heating power increases, the temperature of the evaporator and condenser increases linearly, while the thermal resistance initially increases, decreases, and then increases.