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.

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.

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.

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.

Design of a New Reactor to Work at Low Volume Liquid/Surface Solid Ratio and High Pressure and Temperature: Dissolution Rate Studies of UO2 Under Both Anoxic and Reducing Conditions.

2014 ◽  
Vol 1665 ◽  
pp. 303-309
Author(s):  
A. Martínez-Torrents ◽  
J. Giménez ◽  
I. Casas ◽  
J. de Pablo
Keyword(s):  
Hydrogen Peroxide ◽  
High Pressure ◽  
High Pressures ◽  
Liquid Surface ◽  
High Surface ◽  
High Pressure And Temperature ◽  
Solid Ratio ◽  
Reducing Conditions ◽  
Flow Through ◽  
Low Volume

ABSTRACTA flow-through experimental reactor has been designed in order to perform studies at both high pressure and high temperature conditions. A chromatographic pump is used to impulse the leachant throughout the reactor in order to work at very low flows but high pressures. Therefore, high surface solid to volume leachant ratios, similar to the ones predicted in the final repository, can be obtained. The reactor allows working at different atmospheres at pressures up to 50 bars. The temperature inside the reactor can be set using a jacket.Using this new reactor the evolution of uranium concentrations released from an UO2 sample was studied at different conditions.The results show that at hydrogen pressures between 5 and 7 bars, hydrogen peroxide does not seem to significantly oxidize the uranium (IV) oxide. Uranium concentrations in those experiments remain between 10-8 mol·l-1 and 10-9 mol·l-1.

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.

Thermo-Wetting and Friction Reduction Characterization of Microtextured Superhydrophobic Surfaces

2011 ◽  
Author(s):  
Tae Jin Kim ◽  
Phillip Glass ◽  
Carlos H. Hidrovo
Keyword(s):  
Thermal Management ◽  
Channel Flow ◽  
Liquid Layer ◽  
Microfluidic Channel ◽  
Friction Reduction ◽  
Superhydrophobic Surfaces ◽  
Microfluidic Channels ◽  
Textured Surface ◽  
Flow Measurements ◽  
Gas Layer

Microtextured superhydrophobic surfaces have become ubiquitous in a myriad of engineering applications. These surfaces have shown potential in friction reduction applications and could be poised to make a big impact in thermal management applications. For instance higher heat transfer rate with less pumping power might be achievable through the aid of superhydrophobic surfaces. However, past and current research on superhydrophobic surface has focused mainly on modifying either the chemical component or the roughness factors of such surfaces. The purpose of this paper is to account for the thermal effects of the heated fluid flowing in superhydrophobic microfluidic channels. Herein we characterize the wetting behavior as a function of temperature of microtextured superhydrophobic surfaces, for both active and passive thermal management applications. A series of PDMS microtextured samples were fabricated using micromachining and soft lithography techniques. Flow measurements were performed using the superhydrophobic microfluidic channel. The channel surface roughness was large enough to induce the Cassie-Baxter state, a phenomenon in which a liquid rests on top of a textured surface with a gas layer trapped underneath the liquid layer. This gas layer induces a two-phase flow, and friction reduction can be achieved for the liquid channel flow. With this channel, flow rates were measured by varying the equilibrium temperature of the substrate. The temperature in the constant pressure source was controlled by circulating the water through a water-bath. As the heating reached a certain threshold the curvature of the liquid-gas interface was reversed and dewetting of the penetrated liquid layer was observed. This result suggests that the Cassie state in fluid flow can be prolonged even under increased pressure drops by increasing the temperature in the gas layer.

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