Microengineered Surfaces for Thin Film Evaporation for Enhanced Heat Dissipation

2009 ◽  
Author(s):  
Rong Xiao ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Liquid Film ◽  
Thermal Management ◽  
Heat Dissipation ◽  
Thin Liquid Film ◽  
High Heat ◽  
Heat Fluxes ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Micropillar Arrays

The increasing performance of integrated chips has introduced a growing demand for new thermal management technologies. While various thermal management schemes have been studied, thin film evaporation promises high heat dissipation rates (1000 W/cm2) with low thermal resistances. However, methods to form a thin liquid film including jet impingement and sprays have challenges associated with achieving the desired film thickness. In this work, we investigated novel microstructures to control the thickness of the thin film where the liquid is driven by capillarity. Micropillar arrays with diameters ranging from 2 μm to 10 μm, spacings between pillars ranging from 5 μm to 10 μm, and heights of 4.36 μm were studied. A semi-analytical model was developed to predict the propagation rate of the liquid film, which was validated with experiments. The heat transfer performance was investigated on the micropillar arrays with microfabricated heaters and temperature sensors. The behavior of the thin liquid film under varying heat fluxes was studied. This work demonstrates the potential of micro- and nanostructures to dissipate high heat fluxes via thin film evaporation.

High-Flux Thin Film Evaporation on Nanostructured Surfaces

2010 ◽  
Author(s):  
Rong Xiao ◽  
Kuang-Han Chu ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Liquid Film ◽  
High Performance ◽  
Heat Dissipation ◽  
Heat Removal ◽  
High Heat ◽  
Back Side ◽  
Nanostructured Surfaces ◽  
Thin Film Evaporation ◽  
Film Evaporation

The heat generation rates of high performance electronics motivate the development of new thermal management solutions. Thin film evaporation with a jet impingement or spray system promise high heat fluxes up to 1000 W/cm2 with low thermal resistances. However, challenges with implementation currently limit the ability to reach the theoretical limits. In this work, we investigated the utilization of micro-/nanostructured surfaces to control the liquid film thickness and provide a sufficient liquid flow rate to achieve high heat removal rates. We developed a model to predict the propagation rates of the liquid film, which accounted for the curvature of the liquid meniscus. We also fabricated test devices with pillar diameters ranging from 500 nm to 10 μm, spacings of 3.5 μm to 10 μm, and heights of 5 μm to 15 μm, and validated the model with confocal microscopy and high speed imaging. Heaters and temperature sensors were also integrated onto the back side of the chip to investigate heat transfer performance. When heat was applied, the structures significantly enhanced the heat dissipation rates and reduced the thermal resistance. The heat dissipation rate was also found to be positively correlated to the propagation rate of the liquid film. However, surface fouling in the experiments led to challenges to maintain a stable liquid film, and decreased the heat removal capability. This work provides insights to designing micro-/nanostructured surfaces for thin film evaporation to meet the heat dissipation demands of future high performance electronic systems.

Surface Temperatures and Heat Fluxes Associated With the Evaporation of a Liquid Film on a Semi-Infinite Solid

1971 ◽  
Vol 93 (4) ◽  
pp. 357-364 ◽  
Author(s):  
L. A. Hale ◽  
S. A. Anderson
Keyword(s):  
Thin Film ◽  
Boundary Value Problem ◽  
Liquid Film ◽  
Numerical Solution ◽  
Thin Liquid Film ◽  
Pool Boiling ◽  
Heat Fluxes ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Limiting Case

The boundary-value problem associated with the evaporation of a thin liquid film from a thick surface is presented in terms of several dimensionless parameters. A numerical solution is presented for a particular limiting case and the result is used to suggest criteria for determining the significance of thin-film evaporation in saturated pool boiling.

scholarly journals Thin Film Evaporation Using Nanoporous Membranes for Enhanced Heat Transfer

2012 ◽  
Author(s):  
Rong Xiao ◽  
Shalabh C. Maroo ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Thermal Management ◽  
High Heat ◽  
Heat Fluxes ◽  
Nanoporous Membranes ◽  
Transfer Coefficients ◽  
Thin Film Evaporation ◽  
Heat Transfer Coefficients ◽  
Film Evaporation

Recent advancements in integrated circuits demand the development of novel thermal management schemes that can dissipate ultra-high heat fluxes with high heat transfer coefficients. Previous study demonstrated the potential of thin film evaporation on micro/nanostructured surfaces [1–11]. Theoretical calculations indicate that heat transfer coefficients on the order of 106 W/m2K and heat fluxes of 105 W/cm2 can be achievable with water [1, 5–6]. However, in previous experimental setup, the coolant has to propagate across the surface which limits the increase in heat flux and the heat transfer coefficient, while adding complexity to the system design. This work aims to decouple the propagation of the coolant from the evaporation process through a novel experimental configuration. Thin nanoporous membranes of 13 mm diameter were used where a metal layer was deposited on the top surface to serve as a resistance heater. Liquid was supplied from the bottom of the membrane, driven through the nanopores by capillary force, and evaporated from the top surface. Heat transfer coefficient over 104 W/m2K was obtained with isopropyl alcohol (IPA) as the coolant, which is only two orders of magnitude smaller than the theoretical limit. This work offers insights into optimal experimental designs towards achieving kinetic limits of heat transfer for thin film evaporation based thermal management solutions.

Characteristics of Extended Evaporating Meniscus on Nanotextured Rough Solid Substrate for Wenzel States

2011 ◽  
Author(s):  
J. J. Zhao ◽  
Y. Y. Duan ◽  
X. D. Wang ◽  
B. X. Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Liquid Film ◽  
Thin Liquid Film ◽  
Disjoining Pressure ◽  
Roughness Effects ◽  
Maximum Heat ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Nanoscale Roughness

The surface nanostructure determines the system wettability and thus has significant effects on the thin liquid film spreading and phase change heat transfer. A model based on the augmented Young-Laplace equation and kinetic theory was developed to describe the nanoscale roughness effects on the extended evaporating meniscus in a microchannel. The roughness geometries in the model were theoretically related to the disjoining pressure and the thermal resistance across the roughness layer. The results show that the dispersion constant for the disjoining pressure increases with the nanopillar height when the solid-liquid-vapor system is in the Wenzel state. Thus, the spreading and wetting properties of the evaporating thin liquid film are enhanced due to the higher nanopillar height and larger disjoining pressure. Since the evaporating thin film length increases with the nanoscale roughness due to better surface wettability, the total liquid flow and heat transfer rate of the evaporating thin liquid films in a microchannel can be enhanced by increasing the nanopillar height. The effects of the nanopillar on the thin film evaporation are more significant for higher superheats. Hydrophilic nanotextured solid substrates can be fabricated to enhance the thin film evaporation and thus increase the maximum heat transport capability of the two-phase cooling devices.

Controlled Wetting in Nanoporous Membranes for Thin Film Evaporation

2016 ◽  
Vol 138 (8) ◽  
Author(s):  
Kyle L. Wilke ◽  
Banafsheh Barabadi ◽  
TieJun Zhang ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Liquid Film ◽  
Membrane Surface ◽  
High Heat ◽  
Nanoporous Membranes ◽  
Transfer Rates ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
High Heat Transfer ◽  
Controlled Flooding

With the ever increasing cooling demands of advanced electronics, thin film evaporation has emerged as one of the most promising thermal management solutions. High heat transfer rates can be achieved in thin films of liquids due to a small conduction resistance through the film to the evaporating interface. In thin film evaporation, maintaining a stable liquid film to attain high evaporation rates is challenging. We investigated nanoporous anodic aluminum oxide (AAO) membranes to supply liquid to the evaporating surface via capillarity. In this work, we achieved enhanced experimental control via the creation of a hydrophobic section within the nanopore. By creating a non-wetting section, the liquid is confined within the membrane to a region of well-controlled geometry. This non-wetting section also prevents flooding, where the formation of a thick liquid film degrades device performance. When heat flux is applied to the membrane surface, the liquid wicks into the membrane from the bottom and becomes pinned at the onset of the hydrophobic layer. As a result, the wetting in the membrane is controlled, flooding is prevented, and a stable evaporating surface in achieved. With this approach, thin film evaporation from nanoporous media can now be studied for varying parameters such as pore size, porosity, and location of the meniscus within the pore.

scholarly journals Capillary-Limited Evaporation From Well-Defined Microstructured Surfaces

2013 ◽  
Author(s):  
Solomon Adera ◽  
Rishi Raj ◽  
Evelyn N. Wang
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Phase Change ◽  
Thermal Management ◽  
Latent Heat ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Microstructured Surfaces ◽  
Latent Heat Of Vaporization

Thermal management is increasingly becoming a bottleneck for a variety of high power density applications such as integrated circuits, solar cells, microprocessors, and energy conversion devices. The performance and reliability of these devices are usually limited by the rate at which heat can be removed from the device footprint, which averages well above 100 W/cm2 (locally this heat flux can exceed 1000 W/cm2). State-of-the-art air cooling strategies which utilize the sensible heat are insufficient at these large heat fluxes. As a result, novel thermal management solutions such as via thin-film evaporation that utilize the latent heat of vaporization of a fluid are needed. The high latent heat of vaporization associated with typical liquid-vapor phase change phenomena allows significant heat transfer with small temperature rise. In this work, we demonstrate a promising thermal management approach where square arrays of cylindrical micropillar arrays are used for thin-film evaporation. The microstructures control the liquid film thickness and the associated thermal resistance in addition to maintaining a continuous liquid supply via the capillary pumping mechanism. When the capillary-induced liquid supply mechanism cannot deliver sufficient liquid for phase change heat transfer, the critical heat flux is reached and dryout occurs. This capillary limitation on thin-film evaporation was experimentally investigated by fabricating well-defined silicon micropillar arrays using standard contact photolithography and deep reactive ion etching. A thin film resistive heater and thermal sensors were integrated on the back side of the test sample using e-beam evaporation and acetone lift-off. The experiments were carried out in a controlled environmental chamber maintained at the water saturation pressure of ≈3.5 kPa and ≈25 °C. We demonstrated significantly higher heat dissipation capability in excess of 100 W/cm2. These preliminary results suggest the potential of thin-film evaporation from microstructured surfaces for advanced thermal management applications.

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