Temperature Effect on Capillary Flow Dynamics in 1D Array of Open Nanotextured Microchannels Produced by Femtosecond Laser on Silicon

Abstract

Capillary flow of water in an array of open nanotextured microgrooves fabricated by femtosecond laser processing of silicon is studied as a function of temperature using high-speed video recording. In a temperature range of 23–80 °C, the produced wicking material provides extremely fast liquid flow with a maximum velocity of 37 cm/s in the initial spreading stage prior to visco-inertial regime. The capillary performance of the material enhances with increasing temperature in the inertial, visco-inertial, and partially in Washburn flow regimes. The classic universal Washburn’s regime is observed at all studied temperatures, giving the evidence of its universality at high temperatures as well. The obtained results are of great significance for creating capillary materials for applications in cooling of electronics, energy harvesting, enhancing the critical heat flux of industrial boilers, and Maisotsenko cycle technologies.

Spreading and Drying Dynamics of Water Drop on Hot Surface of Superwicking Ti-6Al-4V Alloy Material Fabricated by Femtosecond Laser

“…The flow of a liquid in a capillary medium undergoes a sequence of regimes, including acceleration ( z ∝ t 2 ) [ 70 , 71 , 72 ], inertial ( z ∝ t ) [ 70 , 71 , 72 , 73 , 74 , 75 ], visco-inertial [ 36 , 76 ], classic Washburn’s regime ( z ∝ t 1/2 ) [ 77 ], and final stages [ 78 ]. In contrast to many previous works focused on the classic Washburn regime and other capillary flow stages occurring on the sub-second (0.1–1 s) and second (1–100 s) time scales [ 78 , 79 , 80 , 81 , 82 , 83 , 84 , 85 , 86 , 87 , 88 , 89 , 90 , 91 , 92 , 93 , 94 , 95 ], our study mainly focuses on the early capillary flow regimes on the millisecond time scale between 0 and 100 ms, understanding of which has recently become an important issue in fast remediation of dry-out spots in cooling high-heat flux electronics of 4G/5G telecom networks [ 96 , 97 ], Maisotsenko cycle (M-cycle) heat/mass exchangers [ 98 , 99 , 100 , 101 ], and miniaturization of microfluidic devices [ 102 ], where the classic Washburn regime and later capillary flow regimes do not occur because of the short length of capillary channels.…”

“…Our capillary system has a high hierarchical structural complexity. Furthermore, due to water supply from a pendant drop, the forces driving the liquid are more complicated and include the capillary pressure due to surface structure, Laplace pressure from the curvature of the drop remaining between the sample edge and needle, Laplace pressure from the curvature of the drop located on the sample, and gravitational force of the drop on the sample surface [ 36 , 103 , 104 ]. Therefore, the inertial regime of water behavior in our capillary system may differ from that in the capillary tubes.…”

“…A typical wicking medium currently used in heat pipes for cooling electronics is a porous material (mesh or sintered powder), performance of which degrades at high heat fluxes because of insufficient liquid transport and large thickness of the wicking medium (>0.5 mm) that limit the heat transfer [ 30 , 31 , 32 ]. Hierarchical wicking materials based on the surface capillary effect offer significantly enhanced cooling performance due to a high velocity of liquid transport, small thickness (<100 µm), and efficient evaporative functionality [ 33 , 34 , 35 , 36 , 37 , 38 ]. Prior studies also show that as compared with wire meshes, sintered powders, and microgroove structures, the micropillar arrays [ 39 , 40 ], especially hierarchical ones [ 41 , 42 ], provide superior heat transfer performance due to their good wicking, large surface area enhancement, and high evaporation rate owing to a large thin-film evaporation area [ 41 , 43 , 44 ].…”

“…Prior studies also show that as compared with wire meshes, sintered powders, and microgroove structures, the micropillar arrays [ 39 , 40 ], especially hierarchical ones [ 41 , 42 ], provide superior heat transfer performance due to their good wicking, large surface area enhancement, and high evaporation rate owing to a large thin-film evaporation area [ 41 , 43 , 44 ]. Previously, surface nano/microstructuring of materials [ 34 , 45 ] using direct laser ablation [ 46 , 47 , 48 , 49 , 50 ] has been successfully applied to fabrication of superwicking silicon [ 36 , 51 ], metals [ 10 , 14 , 33 , 37 , 52 ], glasses [ 53 , 54 ], and polymers [ 38 ] by producing an array of parallel microgrooves on a surface of a material. It has been demonstrated that this open capillary surface structure provides a strong capillary force capable of unidirectional transporting of water for a long distance, even against the force of gravity.…”

The effect of femtosecond laser fluence and pitches between V-shaped microgrooves on the dynamics of capillary flow

“…At present, there are many studies on using a femtosecond laser to fabricate the superwicking surface [21] , [22] , [23] , [24] , [25] , [27] , but few on the influence of laser processed surface structures on dynamics of superwicking action [28] , [29] , [30] . Besides, the excellent dynamics performance of sucking the liquid uphill against gravity on a superwicking surface is very important to meet more application requirements.…”