Abstract:

To meet the heat dissipation requirements of highly integrated and high-power electronic devices in the 5G era, the use of ultra-thin heat pipes and ultra-thin vapor chambers is rapidly increasing. The extreme thinning of heat pipes/vapor chambers has become a hot research topic in the current industry and academia, as the heat generation of components is increasing and the space available for heat dissipation components inside electronic devices is becoming more compact. Some simulation studies have indicated that as the height of the vapor chamber is reduced to a certain extent, the flow resistance of vapor in the ultra-thin space increases sharply, consequently precipitating a steep decline in the thermal performance of ultra-thin heat pipes/vapor chambers.Hence, studying and analyzing the gas flow in extremely thin spaces is of great significance for exploring the pressure drop characteristics of vapor flow, assisting in solving the design challenges of ultra-thin heat vapor chambers/heat pipes, facilitating their further thinning and application. In this paper, the experimental apparatus for gas flow pressure drop in ultra-thin confined spaces was constructed, and preliminary air flow pressure drop experiments were conducted, obtaining data on air pressure drop changes under different channel heights (0.1—0.5 mm), surface mesh aperture (0.036—0.104 mm), and flow velocities (1—10 m/s). The results show that as the channel height increases, the Fanning friction factor f gradually decreases. The influencing factors of pressure drop were ranked by significance: channel height, flow velocity, mesh aperture. Flow velocity and channel height both have a significant impact on pressure drop, while mesh aperture has no significant effect. The pressure inside the channel gradually increases as the surface mesh aperture decreases. As the channel height decreases, the pressure drop inside the channel first increases slowly, and after decreasing to a critical height of 0.3 mm, the pressure drop inside the channel starts to increase significantly. As the air flow velocity increases, the pressure drop inside the channel increases, and the effect of air flow velocity on pressure drop follows an approximately proportional relationship. The Fanning friction factor f calculation correlation formula for rectangular microchannels was analyzed, and it was compared with the calculated values from the experimental results. Then, based on the commonly used laminar friction factor calculation formula f=64/Re, a correction was made, and it was found that the f calculation formula corrected based on the experimental data in this paper has better accuracy, and is more suitable for calculating gas pressure drop in microchannels with height ≤0.5 mm. Subsequently, the experimental apparatus was modified to include a steam generation device, but due to difficulties in adjusting the experimental setup, only a small amount of steam flow pressure drop data was obtained. Compared with the traditional calculation formula for laminar friction factor, the f correction relationship obtained through the air pressure drop experiment significantly improves the accuracy of calculating steam flow pressure drop.

Key words: microchannels, flow, friction coefficient, microscale, pressure drop, ultra-thin soaking plate, ultra-thin loop heat pipe

摘要：

随着超薄热管等元件进一步超薄化，蒸汽腔厚度减小导致蒸汽流动压降急剧增大，传热热阻增加，传输极限降低。搭建了超薄受限空间气体流动压降实验装置，开展空气流动实验，获得了不同通道高度（0.1~0.5 mm）、不同表面丝网孔径（0.036~0.104 mm）和不同流速（1~10 m/s）下的压降变化。结果表明：通道高度和流速对压降产生显著影响，而表面丝网孔径并不会；3个影响因素按显著程度依次为通道高度、流速、表面丝网孔径；随表面丝网孔径的减小，压降逐渐增大；随通道高度的减小，压降先缓慢增大，在减至0.3 mm后压降开始剧烈上升；随流速的增加，压降增大且近似呈正比例变化关系。最后基于实验数据修正了微通道层流情况下沿程阻力系数相关性预测关联式，以便更准确地预测气体压降。

关键词: 微通道, 流动, 摩擦因子, 微尺度, 压降, 超薄均热板, 超薄环路热管