Forming method of micro heat pipe with compound structure of sintered wick on grooved substrate

Abstract

in chips and dramatically reducing reliability and performances [1][2][3]. So thermal control has become a hot issue for the high-power electronic components with high heatflux, which urgently needs solving. Miniature/micro heat pipes have become ideal radiating devices for high heatflux chips because of their high heat conductivity and no need for extra electronic driving. As a heat pipe's heat transfer performance is mainly determined by its wick structure, and the compound structure of sintered wick on a grooved substrate can have both sintered pipes' greater capillary force and grooved pipes' lower back-flow resistance to working fluid, therefore can better suit the trend of being light, thin, short and miniature for high heat-flux electronic devices [4][5][6]. But the key problems are how to fabricate ideal micro grooves in the inner wall of thin circular copper pipes to reduce the back-flow resistance to working fluid, and how to sinter a thin layer of copper powders on these micro grooves to boost capillary force, and consequently MHPs' heat transfer performances.The higher requirement for thermal control in so many industries has attracted more scholars to research on MHPs. In recent years, Suman [7] modelled surface tension gradient for grooved MHPs, analyzed the impacts of surface tension gradient on heat pipes' performances from the perspectives of working fluid's curvature radius, pressure and velocity, and concluded that heat transfer performances can be greatly enhanced by affixing appropriate surfactant or surface charge, which can decrease surface tension gradient of working fluid in heat pipes. Oh et al. [8] proposed a technique of laser-induced thermochemical etching, which can help fabricate triangle grooves with smooth surface in copper pipes' inner wall. Xin et al.[9] fabricated loop heat pipe (LHP) wicks through cold pressing and loose powder sintering respectively, tested the porosity, permeability and pore radius of two types of wicks, and discovered that the Abstract Micro heat pipes (MHPs) with excellent heat transfer performance have been the ideal radiating components to meet increasingly higher requirements posed by high heat-flux products. Based on MHPs' working principle, this study deduced capillary limit of a novel MHP with compound structure of sintered wick on grooved substrate, and probed into its forming mechanism: first, highspeed oil-filled spinning was applied to fabricating micro grooves, with optimal spinning and drawing speeds determined; then a mini-type vibration machine was used to help fill copper powders fast and uniformly, with appropriate sintering temperature and time fixed; the manufacturing method that integrates vacuum-pumping-cold-welding with secondary-degassing-cold-welding to increase vacuumizing efficiency. The results of experiments on its heat transfer performance show that the MHPs with sinteredwick-on-grooved-substrate structure fabricated through the proposed forming method can not only acquire much better heat transfer performance, but have advantag...

Characterisation of a grooved heat pipe with an anodised surface

“…Moreover, the contact angle plays a major role in enhancing the capillary pressure, since the capillary pressure is proportional to the contact angle. It is proven that the contact angle of an anodised surface is less than that of a nonanodised surface [16]. The capillary pressure generated in the grooved wick is represented as:…”

“…Li et al [16] tested an MHP by incorporating a compound structure of sintered wick on a grooved structure as the capillary material. From the studies [8][9][10][11][12][13][14][15][16], it is understood that the new kind of wick structures exhibited a significant effect on the heat transfer enhancement of heat pipes over the same with traditional wick structures. Although different wick structures are available for better heat transfer, the base materials of wick structures are mostly copperbased materials, which are slightly heavier than lightweight materials such as aluminium.…”

Plough-extrusion Forming for Making Micro-groove Heat Pipes on Hydrostatic Thrust Bearings of Heavy Machinery

“…The micro-sintered heat pipe has a high heat transfer capacity, but the manufacturing process is complicated. Moreover, the structure of sintered capillary wick is easily damaged, and the copper powder particles in the wick structure are prone to fall off when subjected to heavy load deformation [15]. However, the capillary wick structure of microgroove heat pipe is directly formed on the inner wall of the pipe [16].…”

Simulation Research on Ploughing Extrusion Angle Influence on Machinability

“…It is concluded that the plough-extrusion cutting performance of 60 degree extrusion angle cutter is the best.Nowadays, with the rapid development of microelectronic technology, the heat flux density of microelectronic products has increased dramatically. Because of the characteristics of high heat transfer efficiency, high heat dissipation property, good isotherm property and no need of extra power source, heat-pipes with wick micro-groove structure are widely used to solve the thermal control and conduction of products with high heat flux density [1][2][3][4][5]. The manufacturing forming of wick micro-groove structure is the key problem of micro heat pipe technology.…”