丝网型超薄热管结构参数影响的实验探究

Experimental research on structure parameters of the ultra-thin flattened heat pipe

随着电子器件朝着高性能化、集成化与微型化方向的快速发展,狭小空间内高热流密度的散热问题亟待解决.超薄热管作为相变传热元件,具有超高导热率和器件结构紧凑等优点,因此被广泛应用于微型电子器件的散热中.不同的电子元器件具有各不相同的器件结构与散热需求,因此超薄热管在实际应用中也存在各种各样的器件结构.在本课题组对丝网型超薄热管中丝网吸液芯结构参数(目数、丝径)对其传热性能影响的研究基础上,为迎合实际应用中散热部件结构多样化的要求,本研究选取了对超薄热管传热强化效果最优的丝网结构作为吸液芯,通过实验手段,进一步探究了超薄热管的器件结构(包括长度、宽度和厚度等)对其传热性能的影响规律.结果表明,器件长度对超薄热管性能的影响存在一个相互矛盾的因素,故存在一个最佳的长度值使得热管具有最优的传热性能.此外,器件宽度和厚度的增加,都可以不同程度地提升热管的工作性能.最后,基于实验数据,建立了可有效预测超薄热管工作性能的经验关联式.对比超薄热管蒸发端温度的预测值与实验值,发现其相对误差可控制在±10%以内.

With the rapid development of electronic devices in the direction of high performance, integration and miniaturization, the heat dissipation problem of high heat flux density in a narrow space needs to be solved urgently. Traditional single-phase flow cooling technologies, such as natural air cooling, forced air cooling, and liquid cooling, have been unable to meet the needs of practical applications due to their large size, complicated equipment, and low heat dissipation capability. Heat pipe is a type of heat transfer elements with extremely high thermal conductivity and excellent isothermality, thanks to its working mechanism of transports heat through a phase change process of internal working fluid. The continuous breakthrough of heat pipe technology in the direction of miniaturization and ultra-thinning has made the ultra-thin heat pipes(UTHPs) an ideal solution to solve the problem of high heat flux heat dissipation in narrow space of the electronic devices.As a research hotspot, researchers have conducted extensive studies on the internal capillary structure and the working fluid used in the UTHPs, which has made significant contributions to the performance improvement of UTHPs. Actually, in the practical applications of the UTHPs, it needs to meet the needs of various electronic device structures due to the diversity of electronic products, which causes the structure parameters of the UTHPs kaleidoscopic. However, the research and mechanism analysis of the influence of the shape and structure of the heat pipe on its thermal performance are rare.There are few models in this field that can effectively predict the working performance of ultra-thin heat pipes. In this paper, we focused on the most basic structural parameters including length, width and thickness of the UTHPs. A series of experiments were carried out to explore and summarize the influence of such parameters on the thermal performance of UTHPs. Combined with experimental phenomena and device parameters, the discussion and analysis on two-phase flow and phase change heat transfer enhancement are given. Besides, correlation for the evaporator temperature as a function of heat load and structure parameters of the UTHPs has been established to predict working performance of the UTHP based on the experimental data. The results show that there is a contradiction between the influence of the length of the UTHPs,that is, the flow resistance during the internal circulation and the filling mass of the working fluid. On one hand, the reduction of the length of the UTHP can shorten the flow distance of the working fluid to decrease its flow resistance. But on the other hand, the filling mass of the working fluid that the UTHP can contain is also reduced, which will weaken the maximum heat transfer capacity of the device. So, a reasonable coordination of this contradiction can effectively improve the heat transfer performance of ultra-thin heat pipes. In addition, the increase in the width and thickness of the UTHPs can expand the cross-sectional area of the device. Accordingly, the vapor flow channel is also enlarged, which can cause the flow velocity of the vapor fluid reduced to decrease its flow resistance. As a result, the thermal performance of the UTHP is promoted due to its increase of width and thickness. Finally, the relative error analysis of the established model is carried out. Comparing the predicted values and experimental values of the evaporator temperature of the UTHPs, it is found that the relative error can be controlled within ±10%. It shows that the model can accurately predict the working performance of the device and play an effective guiding role for the practical application of the device.