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.

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.

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.

The Visualization of Thin Film Evaporation on Thin Micro Sintered Copper Mesh Screen

2008 ◽  
Author(s):  
Chen Li ◽  
G. P. Peterson ◽  
Ji Li ◽  
Nikhil Koratkar
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Heat Flux ◽  
Thin Liquid Film ◽  
Heated Wall ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Sintered Copper ◽  
Mesh Screen ◽  
Copper Mesh

The thin film evaporation process through use of thin micro-scale sintered copper mesh screen was proven to be a very effective heat transfer mechanism with high critical heat flux (CHF). This efficient heat transfer mechanism is widely used in designing heat pipe, Capillary Pumped Loops (CPL), and drying process, however, the nucleation process and meniscus dynamics at the liquid-vapor-solid interface are not directly observed and systematically studied. Very few visual investigation in thin film evaporation has been conducted. In the existing two visual studies, the interface thermal resistance between coating and the heated wall was not seriously considered, and the heat flux was limited below 35 W/cm2. In this visualization investigation, the nucleation process and meniscus dynamics from initial condition to drying out were observed and well documented. To minimize the interface thermal resistance, the micro scale wicking was sintered to heated wall directly. High quality images were acquired through a well-designed visualization system. The majority of nucleate bubbles, whose diameters are at a magnitude of 10 μm, were found to form on the top wire surfaces instead of inside the porous media at moderate heat flux. Few large size bubbles were observed to grow inside capillary wicks, however, their presence did not seem to stop the evaporation process as reported before. The menisci receding process was visually captured for the first time. The minimum menisci radius was found to form at the smallest corners and pores. It is also illustrated the thin liquid area increases when the menisci recede and the thin liquid film evaporation is the dominant heat transfer mode at high heat flux. The present work visually confirms the heat transfer regimes of evaporation on micro porous media, which was proposed by Li and Peterson [2], and further improves the understanding to the nucleate boiling and thin liquid film evaporation on the surfaces of micro sintered copper mesh screen.

Analysis of Thin-Film Evaporation Through Sintered Wick Microstructures

2012 ◽  
Author(s):  
Karthik K. Bodla ◽  
Jayathi Y. Murthy ◽  
Suresh V. Garimella
Keyword(s):  
Thin Film ◽  
Particle Size ◽  
Pore Space ◽  
Heat Fluxes ◽  
Pore Scale ◽  
Particle Size Range ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Vof Model ◽  
Sintered Copper

Heat pipes are passive heat transport devices capable of transporting heat over long distances without a substantial drop in temperature. The topology and microstructure of the wick material play a crucial role in determining the thermal performance of such devices. Accurate modeling of pore-scale transport phenomena is thus important. In this study, pore scale analysis of thin-film evaporation through sintered copper wicks is performed. X-ray microtomography is employed to generate geometrically-faithful, feature-preserving meshes. Three commercially used sintered wicks of varying particle size ranges (45–60 μm, 106–150 μm and 250–355 μm) and with approximately 61% porosity are considered. The capillary pressure, effective pore radius, percentage thin film area and evaporative mass and heat fluxes are computed using the Volume of Fluid (VOF) model in FLUENT. Two different solution strategies are employed to stabilize the numerical solution and to improve convergence. After verifying that these strategies yield the correct solution, the VOF model is used to obtain static meniscus shapes in the pore space of the sintered wick samples. The meniscus shape is then held fixed and steady-state, thin-film evaporation analysis is performed. Liquid-vapor phase change heat transfer is modeled using a modified Schrage equation. Based on the present analysis, the best performing sample (particle size range) is identified along with the optimum contact angle.

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.

Heat Transfer Analysis of Flash Evaporation With MEPCM

2019 ◽  
Vol 11 (5) ◽  
Author(s):  
Yang Guo ◽  
Hongbin Ma ◽  
Benwei Fu ◽  
Yulong Ji ◽  
Fengmin Su ◽  
...  
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Phase Change ◽  
Thin Liquid Film ◽  
Heat Transfer Analysis ◽  
Seawater Desalination ◽  
Flash Evaporation ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Evaporation Heat

Several seawater desalination technologies have been developed and widely used during the last four decades. In the current investigation, a new approach to the seawater desalination process is presented, which utilizes microencapsulated phase change materials (MEPCMs) and thin film evaporation. In this process, the MEPCMs were placed into hot seawater. Then, the hot seawater and the MEPCMs containing the liquid phase change material (PCM) were ejected into a vacuum flash chamber. A thin liquid film of seawater was formed on the surface of the MEPCM, which subsequently vaporized. This evaporation significantly increased the evaporation heat transfer and enhanced the desalination efficiency. Film evaporation on MEPCM surfaces decreased their temperature by absorbing sensible heat. If their temperature was lower than the phase change temperature, the MEPCM would change phase from liquid to solid releasing the latent heat, resulting in further evaporation. The MEPCMs were then pumped back into the hot seawater, and the salt residue left on the MEPCMs could be readily dissolved. In this way, the desalination efficiency could be increased and corrosion reduced. A mathematical model was developed to determine the effects of MEPCM and thin film evaporation on desalination efficiency. An analytical solution using Lighthill's approach was obtained. Results showed that when MEPCMs with a radius of 100 µm and a water film of 50 µm were used, the evaporation rate and evaporative capacity were significantly increased.

Falling Films in Micro- and Minigrooves: Heat Transfer and Flow Stability

2003 ◽  
Author(s):  
Tatiana Gambaryan-Roisman ◽  
Peter Stephan
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Liquid Film ◽  
Heat Transfer Rate ◽  
Transfer Rate ◽  
Film Flow ◽  
Wall Structure ◽  
Falling Film ◽  
Thin Film Evaporation ◽  
Film Evaporation

Structured (in particular, micro- and minigrooved) wall surfaces may improve numerous industrial processes, including falling film evaporation, thin film evaporation in lean premixed prevaporized combustion technology (LPP), and spray and jet cooling. The advantages of such surfaces include the promotion of ultra-thin film evaporation at the apparent contact lines and the prevention of dry patches on hot surfaces. However, the behavior of thin film flow on structured surfaces has not yet been comprehensively studied. We derive a model describing the heat transfer in liquid film flowing down inclined micro- or minigrooved walls. The derived model accounts for peculiarities of the evaporation process in the vicinity of the liquid-vapor-solid contact line (“micro region”) and their effect on the overall heat transfer rate. It is shown that the effect of the micro region is to increase the overall heat transfer rate at the constant fluid flow rate. A long-wave stability analysis has been performed to quantify the effect of the capillary structure on the film stability properties. Sinusoidal and triangular longitudinal groove shapes have been considered. Two cases have been studied: (i) the film completely covers the wall structure; (ii) the film partly covers the wall structure. It is shown that the longitudinal grooves completely covered by the liquid have a stabilizing effect on the falling film flow. The performed analysis is a step towards modeling the wavy motion of the liquid film on grooved surfaces.

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