Microscale Layering of Liquid and Vapor Phases Within Microstructures for Self-Regulated Flow Delivery to Local Hot Spots

In this study, a new two-phase heat sink architecture is introduced that operates in two different phase change modes. At low wall superheat temperatures, the heat sink operates at the thin film evaporator mode and transitions to boiling when the wall superheat temperature is increased. This unique function is enabled through constraining the liquid and vapor phases into separate domains using capillary-controlled meniscus formed within a hierarchical 3D structure. The structure is designed to form thin layers of vertically oriented liquid films that directly evaporate into their neighboring vapor space. The dominant mode of heat transfer in this design is thin film evaporation, a very effective boiling sub-process. As the surface superheat temperature is increased and boiling starts, the capillary-controlled meniscus breaks down. A heat transfer coefficient of greater than 200 kW/m2K is achieved at less than 1 °C wall superheat temperature.

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Evaporation of Gravity- and Gas Flow-Driven Thin Liquid Films in Micro- and Minigrooves

ASME 2nd International Conference on Microchannels and Minichannels ◽

10.1115/icmm2004-2380 ◽

2004 ◽

Cited By ~ 1

Author(s):

T. Gambaryan-Roisman ◽

P. Stephan

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Gas Flow ◽

Thin Liquid Film ◽

Flow Region ◽

Wave Theory ◽

Liquid Films ◽

Wall Material ◽

Wall Structure ◽

Ultra Thin Film

Using microstructured wall surfaces may improve the heat transfer performance of falling film or shear-driven film cooling devices enormously. The advantages of the structured surface include the prevention of the formation of dry patches on hot surfaces, the promotion of ultra-thin film evaporation, and a wavy motion of the film that enhances mixing of the liquid. We develop a model describing the hydrodynamics and heat transfer by evaporation of gravity- and gas flow-driven liquid films on grooved surfaces. For low Reynolds numbers or low liquid mass fluxes the heat transfer is governed by the evaporation of the ultra-thin film at a micro region, in the vicinity of the three-phase contact line. We investigate the hydrodynamic stability of the film flow using the long-wave theory. In addition to the films completely covering the wall structure, we study the stability characteristics of a thin liquid film partly covering the grooved wall, so that the flow region is bounded by contact lines. Two cases are analyzed: fully wetting liquids and liquids which form a small but finite contact angle with the wall material.

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Boiling Heat Transfer in a Shallow Fluidized Particulate Bed

Journal of Heat Transfer ◽

10.1115/1.3248043 ◽

1987 ◽

Vol 109 (1) ◽

pp. 196-203 ◽

Cited By ~ 9

Author(s):

Y. K. Chuah ◽

V. P. Carey

Keyword(s):

Heat Transfer ◽

Thermal Conductivity ◽

Heat Flux ◽

Boiling Heat Transfer ◽

Pool Boiling ◽

Thin Layers ◽

Surface Nucleation ◽

Particle Layer ◽

Wall Superheat ◽

Flux Level

Experimental data are presented which indicate the effects of a thin layer of unconfined particles on saturated pool boiling heat transfer from a horizontal surface. Results are presented for two different types of particles: (1) 0.275 and 0.475-mm-dia glass spheres which have low density and thermal conductivity, and (2) 0.100 and 0.200-mm-dia copper spheres which have high density and thermal conductivity. These two particle types are the extremes of particles found as corrosion products or contaminants in boiling systems. To ensure that the surface nucleation characteristics were well defined, polished chrome surfaces with a finite number of artificial nucleation sites were used. Experimental results are reported for heat fluxes between 20 kW/m2 and 100kW/m2 using water at 1 atm as a coolant. For both particle types, vapor was observed to move upward through chimneys in the particle layer, tending to fluidize the layer. Compared with ordinary pool boiling at the same surface heat flux level, the experiments indicate that addition of light, low-conductivity particles significantly increases the wall superheat, whereas addition of heavier, high-conductivity particles decreases wall superheat. Heat transfer coefficients measured in the experiments with a layer of copper particles were found to be as much as a factor of two larger than those measured for ordinary pool boiling at the same heat flux level. The results further indicate that at least for thin layers, the boiling curve is insensitive to layer thickness. These results are shown to be consistent with the expected effects of the particles on nucleation, fluid motion, and effective conductivity in the pool at or near the surface. The effect of surface nucleation site density on heat transfer with a particle layer present is also discussed.

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Heat Transfer due to Microscale Thin Film Evaporation From the Steady State Meniscus in a Coherent Porous Silicon Based Micro-Columnated Wicking Structure

Volume 10: Heat and Mass Transport Processes, Parts A and B ◽

10.1115/imece2011-65057 ◽

2011 ◽

Cited By ~ 2

Author(s):

Navdeep S. Dhillon ◽

Jim C. Cheng ◽

Albert P. Pisano

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Porous Silicon ◽

Transfer Model ◽

Thin Film Evaporation ◽

Wall Superheat ◽

Rectangular Channels ◽

Rate Of Evaporation ◽

Energy Equations ◽

Liquid Vapor

A numerical fluid flow and heat transfer model is presented in order to study the evaporation characteristics of a stationary thin film liquid-vapor meniscus. The model is used to evaluate the evaporative heat transfer performance of micron-size rectangular channels on the surface of the secondary wick, inside a micro-columnated coherent porous silicon wick design. The shape of the liquid-vapor meniscus in the channel is obtained by solving the Young-Laplace equation, using a surface energy minimizing algorithm. Mass, momentum and energy equations are then solved in the liquid domain using a discrete finite volume method-based approach. The vapor is assumed to be fully saturated and evaporation at the liquid-vapor interface is modeled using kinetic theory. The effect of wall superheat and inlet-liquid subcooling on the rate of evaporation and associated heat transfer from the evaporating meniscus is characterized.

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Thermal Analysis on Finned Heat Sink with Thin Porous Layers

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.764-765.393 ◽

2015 ◽

Vol 764-765 ◽

pp. 393-397

Author(s):

Tzer Ming Jeng ◽

Sheng Chung Tzeng ◽

Dong Jhen Lin

Keyword(s):

Heat Transfer ◽

Free Convection ◽

Heat Sink ◽

Convection Heat Transfer ◽

Thin Layers ◽

Control Group ◽

Convection Heat ◽

Sintered Metal ◽

Free Convection Heat ◽

Radial Plate

This work experimentally explored the free convection heat transfer characteristics of finned heat sink with sintered-metal-beads layers. It has been proven that the metallic porous media can enhance the forced convection heat transfer efficiently. This work sintered the metal beads to adhere onto the both side surfaces of each radial plate fin of the metallic heat sink, and investigated whether the sintered-metal-beads layers promote the free convection heat transfer or not. The 0.5~0.85mm-diameetr bronze beads were employed. They were sintered smooth with the radial plate fins of the copper heat sink by thin layers at high temperature. The experimental groups were the plate-shape sintered-metal-beads and strip-shape sintered-metal-beads heat sinks. The pure copper finned heat sink was set as the control group. The results demonstrated that the thermal resistances of the experimental groups were separately 20.7% and 11.6% higher than that of the control group at the smaller temperature difference between the heated surface and the ambient (△T≈30°C); while the thermal resistances of the experimental groups were separately 15.3% and 6.9% higher than that of the control group at △T≈60°C. In general, the present sintered-metal-beads layers cannot strengthen the free convection heat transfer.

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Characteristics of an Evaporating Thin Film in a Microchannel

Heat Transfer, Volume 2 ◽

10.1115/imece2006-13899 ◽

2006 ◽

Author(s):

Hao Wang ◽

Suresh V. Garimella ◽

Jayathi Y. Murthy

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Capillary Pressure ◽

Order Differential Equation ◽

Initial Thickness ◽

Thickness Profile ◽

Wall Superheat ◽

Evaporation Heat ◽

Meniscus Profile

The thin-film region of an evaporating meniscus is investigated through an augmented Young-Laplace model and the kinetic theory-based expression for mass transport across a liquid-vapor interface. A fourth-order differential equation for the thickness profile is developed and the boundary conditions at the beginning of the thin-film region are discussed in detail. A perturbation on the initial thickness is employed to avoid the evaporation being totally suppressed all along the meniscus. The role of capillary pressure in controlling the meniscus profile and rate of liquid supply is detailed. The evaporation heat transfer coefficient is greatly suppressed at the beginning of the thin-film region due to disjoining pressure; in the intrinsic meniscus, evaporation is suppressed due to capillary pressure, especially for low wall superheat. The importance of the thin-film region in determining the overall heat transfer is shown to depend on the channel size and degree of superheat.

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A Compact Nanostructure Enhanced Heat Sink With Flow in a Rectangular Channel

ASME 2010 10th Biennial Conference on Engineering Systems Design and Analysis, Volume 2 ◽

10.1115/esda2010-25336 ◽

2010 ◽

Cited By ~ 1

Author(s):

Muhsincan Sesen ◽

Berkay Arda Kosar ◽

Ali Kosar ◽

Wisam Khudhayer ◽

Berk Ahmet Ahishalioglu ◽

...

Keyword(s):

Thin Film ◽

Heat Transfer ◽

Heat Flux ◽

Heat Sink ◽

Constant Pressure ◽

Rectangular Channel ◽

Constant Heat Flux ◽

Nanorod Arrays ◽

Constant Heat ◽

Copper Thin Film

This paper reports a compact nanostructure based heat sink. The system has an inlet and an outlet valve similar to a conventional heat sink. From the inlet valve, pressurized deionized-water is propelled into a rectangular channel (of dimensions 24mm×59mm×8mm). This rectangular channel houses a nanostructured plate, on which ∼600 nm long copper nanorod arrays with an average nanorod diameter of 150 nm are integrated to copper thin film coated on silicon wafer surface. Forced convective heat transfer characteristics of the nanostructured plate are investigated using the experimental setup and compared to the results from a flat plate of copper thin film deposited on silicon substrate. Nanorod arrays act as fins over the plate which enhances the heat transfer from the plate. Excess heat generating small devices are mimicked through a small heat generator placed below the nanostructured plate. Constant heat flux is provided through the heat generator. Thermocouples placed on the heater surface are utilized to gather the surface temperature data. Constant pressure drop across the heat sink and constant heat flux values are varied in order to obtain the correlation between heat removal rate and input power. Volumetric flow rate was measured as a function of the constant pressure drop. In this study, it was proved that nanostructured surfaces have the potential to be a useful in cooling of small and excessive heat generating devices such as MEMS (Micro Electro Mechanical Systems) and microprocessors.

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The effect of an aluminum heat-sink layer on the laser-induced amorphization of SiOx/TeGeSn/SiOx phase-change recording films

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100154846 ◽

1989 ◽

Vol 47 ◽

pp. 574-575

Author(s):

Matthew R. Libera ◽

Martin Chen

Keyword(s):

Thin Film ◽

Phase Change ◽

Heat Sink ◽

Multilayer Film ◽

Glassy Phase ◽

Film Structure ◽

Glass Forming ◽

Active Storage ◽

Dielectric Layers ◽

Amorphous States

Phase-change erasable optical storage is based on the ability to switch a micron-sized region of a thin film between the crystalline and amorphous states using a diffraction-limited laser as a heat source. A bit of information can be represented as an amorphous spot on a crystalline background, and the two states can be optically identified by their different reflectivities. In a typical multilayer thin-film structure the active (storage) layer is sandwiched between one or more dielectric layers. The dielectric layers provide physical containment and act as a heat sink. A viable phase-change medium must be able to quench to the glassy phase after melting, and this requires proper tailoring of the thermal properties of the multilayer film. The present research studies one particular multilayer structure and shows the effect of an additional aluminum layer on the glass-forming ability.

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