A first look at the performance of nano-grooved heat pipes

Abstract

Passive thermal spreaders utilizing liquid/vapor phase-change mechanism such as heat pipes, have been widely used in the macro-scale thermal management of electronic devices for many years. Micro-fabrication techniques enabled the fabrication micro-scale grooved heat pipes on semiconductors. Recent advances in fabrication techniques, on the other hand, enabled producing nano-andångström-scale capillaries and cavities, which renders the manufacturing of nanoscale heat pipes possible. In the present study, we have simulated nanoscale heat pipes composed of nano-grooves using molecular dynamics and evaluated their performance based on different operating parameters such as the filling ratio and heat load. Moreover, evaluation of size effect on the thermal performance is made by comparing proportionally scaled heat pipes. Simulation results reveal that efficient operation of nano-grooved heat pipes depend not only on the proper selections of filling ratio and heat load, but also on the geometrical parameters such as cross sectional dimensions and aspect ratio of the groove. The modeling strategy used in this study opens an opportunity for computational experimentation of nanoscale heat pipes. Nano-Grooved Heat PipesAkkus et al.cooling, on the other hand, is the major bottleneck for proper functioning of devices due to the formation of local hot spots with large on-chip temperature gradients [5,6].Thermal scientists have long been seeking efficient techniques to cool HHF devices. Singlephase cooling methods are impractical due to the high temperature difference and pumping needs [7]. Phase-change methods are desirable addressing their advantage in high latent heat of evaporation, which enables removal of high amount of heat with small temperature difference. Passive thermal spreaders utilizing liquid/vapor phase-change mechanism such as vapor chambers and heat pipes, are widely used in electronic cooling. Closed loop circulation of the working fluid is provided by the capillary pumping in liquid phase and density gradient in the vapor phase. While the vapor chambers have excellent hot spot removal ability by transporting the localized heat from a source to a large heat rejection surface, heat pipes function as superconductors to remove the waste heat away from the source.The first heat pipe was using wire mesh wick structure to pump the condensate to the evaporator section [8]. Then a single sealed non-circular micro-channel, whose sharp-angled corners work as liquid arteries, was proposed as micro heat pipes [9]. To increase the heat carrying capacity of a heat pipe, the number of liquid arteries should be maximized. Consequently, grooved heat pipes, which utilize multiple grooves machined on the inner wall of the base metal as the wick structures, have emerged and been widely studied in the literature due to the relative ease of their precise manufacturing and developing numerical solutions to estimate their performance [10,11,12,13,14,15,16,17]. Moreover, micro-electro-mechanical systems (MEMS) based micro-fabricat...

Drifting mass accommodation coefficients: in situ measurements from a steady state molecular dynamics setup

“…Beskok [61] and utilized in different applications [62][63][64], is used to investigate the steady state condensation process at a flat liquid-vapor interface. The computational setup consists of two parallel walls composed of Platinum (Pt) atoms (gray spheres in Fig.…”

Fast and Predictive Heat Pipe Design and Analysis Toolbox: H-Pat

“…Various types of heat pipes based on the routes of the phases exist, such as traditional heat pipes (cross flow of the phases along the same axis), loop heat pipes (different paths for the two phases) and pulsating heat pipes (conjugate flow of the phases along the same direction). Heat pipes can be manufactured in various geometrical shapes (Reay et al, 2013) and their size can range from nanometers to meters (Hoa et al, 2003;Peterson et al, 1993;Akkus et al, 2019). Regardless of their type, shape or size, all heat pipes share the same working principle: passive transport of the working fluid triggered by continuous phase change.…”

Interplay of capillary and Marangoni flows in micropillar evaporation

“…A thorough optimization demands control over both the design parameters and fabrication. Owing to the advances in micro and nano fabrication techniques, the high-resolution control of surface topography over length scales ranging from molecular-level to macro-level becomes possible, which allows numerous opportunities for the heat transfer enhancement via varying scale surface structures [3][4][5]. As opposed to the coating-based methods (e.g.…”