Analysis of Galinstan-Based Microgap Cooling Enhancement Using Structured Surfaces

2015 ◽  
Vol 137 (9) ◽  
Author(s):  
Lisa Steigerwalt Lam ◽  
Marc Hodes ◽  
Ryan Enright
Keyword(s):  
High Surface ◽  
Liquid Cooling ◽  
Structured Surfaces ◽  
Low Viscosity ◽  
Cassie State ◽  
Gas System ◽  
Hydrodynamic Slip ◽  
Cooling Enhancement ◽  
Convective Resistance ◽  
Gas Layer

Analyses of microchannel and microgap cooling show that galinstan, a recently developed nontoxic liquid metal that melts at −19 °C, may be more effective than water for direct liquid cooling of electronics. The thermal conductivity of galinstan is nearly 28 times that of water. However, since the volumetric specific heat of galinstan is about half that of water and its viscosity is 2.5 times that of water, caloric, rather than convective, resistance is dominant. We analytically investigate the effect of using structured surfaces (SSs) to reduce the overall thermal resistance of galinstan-based microgap cooling in the laminar flow regime. Significantly, the high surface tension of galinstan, i.e., 7 times that of water, implies that it can be stable in the nonwetting Cassie state at the requisite pressure differences for driving flow through microgaps. The flow over the SS encounters a limited liquid–solid contact area and a low viscosity gas layer interposed between the channel walls and galinstan. Consequent reductions in friction factor result in decreased caloric resistance, but accompanying reductions in Nusselt number increase convective resistance. These are accounted for by expressions in the literature for apparent hydrodynamic and thermal slip. We develop a dimensionless expression to evaluate the tradeoff between the pressure stability of the liquid–solid–gas system and hydrodynamic slip. We also consider secondary effects including entrance effects and temperature dependence of thermophysical properties. Results show that the addition of SSs enhances heat transfer.

Analysis of Galinstan-Based Microgap Cooling Enhancement Using Structured Surfaces

2013 ◽  
Author(s):  
Lisa Steigerwalt Lam ◽  
Marc Hodes ◽  
Ryan Enright
Keyword(s):  
Thermal Management ◽  
High Surface ◽  
Solid Contact ◽  
Structured Surfaces ◽  
Low Viscosity ◽  
Cassie State ◽  
Cooling Enhancement ◽  
Flow Through ◽  
Convective Resistance ◽  
Gas Layer

Analyses of conventional microchannel and microgap cooling show that galinstan, a recently developed non-toxic liquid metal that melts at −19°C, may be more effective than water for high flux thermal management applications. This is because its thermal conductivity is nearly 28 times that of water. However, since the specific heat per unit volume of galinstan is about half that of water and its viscosity is 2.5 times that of water, caloric, rather than convective, resistance is dominant. We analytically investigate the effect of using microgaps that incorporate structured surfaces to ascertain their efficacy in reducing overall thermal resistance of galinstan-based thermal management in the laminar flow regime. Significantly, the high surface tension of galinstan (10 times that of water) implies that it can remain in the non-wetting Cassie state at the requisite pressure differences for driving flow through microchannels and microgaps. The flow over the structured surface encounters a limited liquid/solid contact area and a low viscosity gas layer interposed between the channel walls and galinstan. Consequent reductions in friction factor result in decreased caloric resistance and reductions in Nusselt number produce an increase in convective resistance. These are accounted for by recently developed expressions in the literature for hydrodynamic and thermal slip.

Hierarchical Nano/Micro-structured Surfaces with High Surface Area/Volume Ratios

2021 ◽  
pp. 1-36
Author(s):  
Ketki Lichade ◽  
Yizhou Jiang ◽  
Yayue Pan
Keyword(s):  
Surface Structure ◽  
Surface Area ◽  
Light Trapping ◽  
High Surface ◽  
High Surface Area ◽  
Three Dimensional ◽  
Structure Design ◽  
Surface Structures ◽  
Structured Surfaces ◽  
Design And Manufacture

Abstract Recently, many studies have investigated additive manufacturing of hierarchical surfaces with high surface area/volume (SA/V) ratios, and their performance has been characterized for applications in next-generation functional devices. Despite recent advances, it remains challenging to design and manufacture high SA/V ratio structures with desired functionalities. In this study, we established the complex correlations among the SA/V ratio, surface structure geometry, functionality, and manufacturability in the Two-Photon Polymerization (TPP) process. Inspired by numerous natural structures, we proposed a 3-level hierarchical structure design along with the mathematical modeling of the SA/V ratio. Geometric and manufacturing constraints were modeled to create well-defined three-dimensional hierarchically structured surfaces with a high accuracy. A process flowchart was developed to design the proposed surface structures to achieve the target functionality, SA/V ratio, and geometric accuracy. Surfaces with varied SA/V ratios and hierarchy levels were designed and printed. The wettability and antireflection properties of the fabricated surfaces were characterized. It was observed that the wetting and antireflection properties of the 3-level design could be easily tailored by adjusting the design parameter settings and hierarchy levels. Furthermore, the proposed surface structure could change a naturally-hydrophilic surface to near-superhydrophobic. Geometrical light trapping effects were enabled and the antireflection property could be significantly enhanced (>80% less reflection) by the proposed hierarchical surface structures. Experimental results implied the great potential of the proposed surface structures for various applications such as microfluidics, optics, energy, and interfaces.

Rheological Properties of Liquid Metals and Semisolid Materials at Low Solid Fraction

2016 ◽  
Vol 256 ◽  
pp. 133-138 ◽  
Author(s):  
Marialaura Tocci ◽  
Christoph Zang ◽  
Ines Cadòrniga Zueco ◽  
Annalisa Pola ◽  
Michael Modigell
Keyword(s):  
Surface Tension ◽  
Rheological Properties ◽  
Liquid Metals ◽  
High Surface ◽  
Measuring System ◽  
High Surface Tension ◽  
Viscous Forces ◽  
Low Viscosity ◽  
Semi Solid ◽  
Low Shear

Rheological properties of liquid metals are difficult to investigate experimentally because of the extreme border conditions to consider. One difficulty is related to the low viscosity of liquid metals. Surface tension effects can cause forces that can be considerably higher than the viscous forces in the liquid metals. Evaluating the experimental data without considering these effects leads to an apparent shear thinning behavior of the material. In the present study, experiments were performed by means of a Searle rheometer changing the dimension of the measuring system with metals of high surface tension, as mercury and tin. It became evident that surface tension plays a significant role in the effects that falsify measurements at low shear rate. Conclusions can be drawn to what extent measurements of semi-solid metals are affected.

Bubble Injection to Enhance Heat Transfer in Microchannel Heat Sinks

2009 ◽  
Author(s):  
Amy Rachel Betz ◽  
Daniel Attinger
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Single Phase ◽  
Heat Fluxes ◽  
Heat Sinks ◽  
Segmented Flow ◽  
Liquid Cooling ◽  
Microchannel Heat Sinks ◽  
Convective Resistance ◽  
Parallel Microchannels

Liquid cooling is an efficient way to remove heat fluxes with magnitude of 1 to 10,000 W/cm2. One limitation of current single-phase microchannel heat sinks is the relatively low Nusselt number, because of laminar flow. In this work, we experimentally investigate how to enhance the Nusselt number in the laminar regime with the periodic injection of non-condensable bubbles in a water-filled array of microchannels in a segmented flow pattern. We designed a polycarbonate heat sink consisting of an array of parallel microchannels with a low ratio of heat to convective resistance, to facilitate the measurement of the Nusselt Number. Our heat transfer and pressure drop measurements are in good agreement with existing correlations, and show that the Nusselt number of a segmented flow is increased by more than a hundred percent over single-phase flow provided the mass velocity is within a given range.

Resins Materials as Alternative Insert for the Fabrication of Micro Structured Surfaces by Micro Injection Moulding

2014 ◽  
Vol 611-612 ◽  
pp. 909-914 ◽  
Author(s):  
Marco Sorgato ◽  
Gioia della Giustina ◽  
Erika Zanchetta ◽  
Giovanna Brusatin ◽  
Giovanni Lucchetta
Keyword(s):  
Epoxy Resin ◽  
Injection Moulding ◽  
High Volume ◽  
Mould Insert ◽  
Structured Surfaces ◽  
Low Viscosity ◽  
Micro Injection Moulding ◽  
High Volume Production ◽  
Resin Precursors ◽  
Micro Mixer

Micro injection moulding is a key technology for mass-production of micro structured surfaces, such as optical and microfluidic devices. The manufacturing of a microstructured master mould with traditional technologies poses challenges about durability, accuracy and high - volume production. This paper introduces a new approach to realize micro mould inserts in a fast and economical way. Suitable engineered materials as alternative inserts to the metallic one are proposed exploiting the following new strategy: a thermosetting epoxy resin from renewable sources was synthesized and used to realize the mould insert via casting. The initial low viscosity of the liquid epoxy resin precursors allows the achievement of a high fidelity replica of different micro structures and provides an inexpensive and convenient route for rapidly duplicate master mould. A staggered harringbone (SHM) micro-mixer geometry was replicated and the epoxy based resin insert withstood 900 moulding cycles showing good features replication and durability.

A photographic investigation into the disintegration of liquid sheets

1954 ◽  
Vol 247 (924) ◽  
pp. 101-130 ◽  
Keyword(s):  
Surface Tension ◽  
High Surface ◽  
Free Edge ◽  
High Viscosity ◽  
Liquid Sheet ◽  
Flow Rates ◽  
High Surface Tension ◽  
Liquid Sheets ◽  
Low Viscosity ◽  
Spinning Disk

The types of apparatus used to produce liquid sheets are classified according to the manner in which the energy is imparted to the liquid. The factors influencing the development, stability and manner of disintegration of a liquid sheet are examined more particularly with flat sheets produced from the single-hole fan-spray nozzle and the spinning disk. The development of the liquid sheet is influenced by the liquid properties. As the working pressure is raised the width of the sheet increases, but this development is hindered by high surface tension. It is shown that the effect of a surface-active agent on the development is only influential where the surface is not expanding or changing rapidly. Consequently its effect is more pronounced as the liquid moves farther away from the orifice. Increase of viscosity at the same pressure causes the region of disintegration to move away from the orifice, and high viscosity maintains the sheet undisturbed by air friction. Density has little effect on the area of the sheet. The effect of turbulence in the orifice is shown to be responsible for at least two types of disturbance in the sheet which results in holes being formed near the orifice. The depth of the disturbance in the sheet has to be equal to the thickness before disruption occurs. Similar disruption through the formation of holes can be caused by suspensions of unwettable particles. Wettable particles in low concentration, irrespective of their size, have no effect on the manner of disintegration. The most placid, stable and resistant sheet is obtained with a liquid of high surface tension, high viscosity, low density, giving low turbulence in the nozzle. Such a sheet will disintegrate when the velocity is raised and disintegration can occur through air friction. The easiest sheet to disintegrate is obtained with a liquid of low surface tension, low viscosity, low density and with low turbulence in the nozzle. Disintegration will occur near the nozzle at low velocities through waves caused by air friction. Disintegration through the formation of holes in the sheet can occur at low velocity with liquids of high surface-tension, low viscosity and high density where turbulence obtains in the nozzle. The formation of ligaments or threads is a necessary stage before the production of drops. Threads can be formed directly from any free edge or in the boundary. A free edge is formed when equilibrium exists between surface tension and inertia forces. In the spinning disk, at low flow rates, where the sheet is in contact with the surface of the disk, drops are formed at the ends of threads which break down into a limited number of sizes. At high flow rates a free edge of liquid exists outside the periphery of the disk with the formation of more irregular threads and a wider spectrum of drop sizes results. Where perforations occur in the sheet, expansion of the hole by surface tension occurs very regularly so that the holes remain nearly circular until they coalesce forming long threads. These long threads quickly become unstable and break down into drops. Threads being approximately uniform in diameter produce uniform drops, but the irregular areas of liquid which occur when a number of holes expand towards each other produce a wide variety of drop sizes. When the velocity of the sheet in the atmosphere is high, air friction causes slight variations in the sheet to develop rapidly into major wave disturbances, and these can result in holes being blown through the sheet so that disruption starts before the formation of a leading edge. With liquids having visco-elastic properties the sheet disintegrates through the formation of waves, but the rapid increase of viscosity, as the rate of shear is reduced, prevents further break-up of the threads into drops and a web of fine threads only is produced.

Scalable Manufacturing of Metal Nanoparticles by Thermal Fiber Drawing

2016 ◽  
Author(s):  
Jingzhou Zhao ◽  
Abdolreza Javadi ◽  
Ting-Chiang Lin ◽  
Injoo Hwang ◽  
Yingchao Yang ◽  
...  
Keyword(s):  
Metal Nanoparticles ◽  
High Surface ◽  
Continuous Manufacturing ◽  
Molten Metals ◽  
Fiber Drawing ◽  
Energy Applications ◽  
Low Viscosity ◽  
Thermal Drawing ◽  
Scalable Production ◽  
Glass Metal

Thermal fiber drawing has emerged as a novel process for the continuous manufacturing of semiconductor and polymer nanoparticles. Yet a scalable production of metal nanoparticles by thermal drawing is not reported due to the low viscosity and high surface tension of molten metals. Here we present a generic method for the scalable nanomanufacturing of metal nanoparticles via thermal drawing based on droplet break-up emulsification of immiscible glass/metal systems. We experimentally show the scalable manufacturing of metal Sn nanoparticles (<100 nm) in Polyethersulfone (PES) fibers as a model system. This process opens a new pathway for scalable manufacturing of most metal nanoparticles as well as composites with embedded metal nanoparticles, which may find exciting photonic, electrical, or energy applications.

Slip in the Presence of Semi-Circular Menisci Between Parallel Ridges

2020 ◽  
Author(s):  
Lisa Steigerwalt Lam ◽  
Yuri Muzychka
Keyword(s):  
Electronics Cooling ◽  
Internal Flows ◽  
Conformal Maps ◽  
Lab On Chip ◽  
Cassie State ◽  
Flow Curvature ◽  
Hydrodynamic Slip ◽  
On Chip ◽  
Oriented Parallel ◽  
Reducing Properties

Abstract Surfaces which are structured on the micro- and nanoscale to resist wetting are being considered for internal flows due to their drag reducing properties in applications such as electronics cooling and lab-on-chip. Here, an expression is developed to characterize the hydrodynamic slip in a laminar flow which occurs near the surface for the case when positive meniscus curvature is present. The surfaces considered are composed of ridges oriented parallel to the flow. Curvature of the meniscus, which resides between the liquid in the Cassie state and the gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. The meniscus is considered shear free. The no slip condition exists at the tips of the ridges. Conformal maps from the literature are used to derive an expression which is a function of cavity fraction of the surface. The positive protrusion angle is 90 degrees. Cavity fractions range from 0 to 75%.

Effect of Meniscus Curvature on Apparent Thermal Slip

2016 ◽  
Vol 138 (12) ◽  
Author(s):  
Lisa Steigerwalt Lam ◽  
Marc Hodes ◽  
Georgios Karamanis ◽  
Toby Kirk ◽  
Scott MacLachlan
Keyword(s):  
Slip Length ◽  
Constant Heat Flux ◽  
Perturbation Approach ◽  
Thermal Slip ◽  
Flux Boundary Condition ◽  
Structured Surfaces ◽  
Cassie State ◽  
Heat Flux Boundary Condition ◽  
Approximate Expressions ◽  
Good Agreement

We analytically consider the effect of meniscus curvature on heat transfer to laminar flow across structured surfaces. The surfaces considered are composed of ridges. Curvature of the menisci, which separates liquid in the Cassie state and gas trapped in cavities between the ridges, results from the pressure difference between the liquid and the gas. A boundary perturbation approach is used to develop expressions that account for the change in the temperature field in the limit of small curvature of a meniscus. The meniscus is considered adiabatic and a constant heat flux boundary condition is prescribed at the tips of the ridges in a semi-infinite and periodic domain. A solution for a constant temperature ridge is also presented using existing results from a mathematically equivalent hydrodynamic problem. We provide approximate expressions for the apparent thermal slip length as function of solid fraction over a range of small meniscus protrusion angles. Numerical results show good agreement with the perturbation results for protrusion angles up to ± 20 deg.

scholarly journals Dynamics of multiple protoplanets embedded in gas and pebble discs and its dependence on Σ and ν parameters

2018 ◽  
Vol 620 ◽  
pp. A157 ◽  
Author(s):  
M. Brož ◽  
O. Chrenko ◽  
D. Nesvorný ◽  
M. Lambrechts
Keyword(s):  
Surface Density ◽  
High Surface ◽  
Reverse Migration ◽  
Low Viscosity ◽  
Orbital Configuration ◽  
Low Mass ◽  
Convergence Zones ◽  
Hydrodynamical Simulations ◽  
Planetary Migration ◽  
Three Body

Protoplanets of super-Earth size may get trapped in convergence zones for planetary migration and form gas giants there. These growing planets undergo accretion heating, which triggers a hot-trail effect that can reverse migration directions, increase planetary eccentricities, and prevent resonant captures of migrating planets. In this work, we study populations of embryos that are accreting pebbles under different conditions, by changing the surface density, viscosity, pebble flux, mass, and the number of protoplanets. For modelling, we used the FARGO-THORIN two-dimensional (2D) hydrocode, which incorporates a pebble disc as a second pressure-less fluid, the coupling between the gas and pebbles, and the flux-limited diffusion approximation for radiative transfer. We find that massive embryos embedded in a disc with high surface density (Σ = 990 g cm−2 at 5.2 au) undergo numerous “unsuccessful” two-body encounters that do not lead to a merger. Only when a third protoplanet arrives in the convergence zone do three-body encounters lead to mergers. For a low-viscosity disc (ν = 5 × 1013 cm2 s−1), a massive co-orbital is a possible outcome, for which a pebble isolation develops and the co-orbital is further stabilised. For more massive protoplanets (5 M⊕), the convergence radius is located further out, in the ice-giant zone. After a series of encounters, there is an evolution driven by a dynamical torque of a tadpole region, which is systematically repeated several times until the co-orbital configuration is disrupted and planets merge. This may be a way to solve the problem that co-orbitals often form in simulations but they are not observed in nature. In contrast, the joint evolution of 120 low-mass protoplanets (0.1 M⊕) reveals completely different dynamics. The evolution is no longer smooth, but rather a random walk. This is because the spiral arms, developed in the gas disc due to Lindblad resonances, overlap with each other and affect not only a single protoplanet but several in the surrounding area. Our hydrodynamical simulations may have important implications for N-body simulations of planetary migration that use simplified torque prescriptions and are thus unable to capture protoplanet dynamics in its full glory.

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