scholarly journals Microscale Temperature Measurements Near the Triple Line of an Evaporating Thin Liquid Film

2009 ◽  
Vol 131 (6) ◽  
Author(s):  
Hemanth K. Dhavaleswarapu ◽  
Suresh V. Garimella ◽  
Jayathi Y. Murthy
Keyword(s):  
Thin Film ◽  
Thin Liquid Film ◽  
Infrared Camera ◽  
Triple Line ◽  
Temperature Measurements ◽  
Confined Space ◽  
Two Phase ◽  
Thin Film Evaporation ◽  
Film Heat Transfer ◽  
Improved Accuracy

Thin-film evaporation from a meniscus in a confined space, which is the basis for many two-phase cooling devices, is experimentally investigated. The meniscus formed by heptane, a highly wetting liquid, on a heated fused quartz wafer is studied. Microscale infrared temperature measurements performed near the thin-film region of the evaporating meniscus reveal the temperature suppression caused by the intensive evaporation in this region. The high spatial resolution (∼6.3 μm) and high temperature sensitivity (∼20 mK) of the infrared camera allow for improved accuracy in the measurements. The effects of evaporation rate, applied heat flux, and channel width on the thin-film heat transfer distribution are also explored.

Microscale Temperature Measurements at the Triple Line of an Evaporating Thin Film

2007 ◽  
Author(s):  
Hemanth K. Dhavaleswarapu ◽  
Suresh V. Garimella ◽  
Jayathi Y. Murthy
Keyword(s):  
Thin Film ◽  
Quartz Substrate ◽  
Infrared Camera ◽  
Triple Line ◽  
Temperature Measurements ◽  
Confined Space ◽  
Two Phase ◽  
Thin Film Evaporation ◽  
Film Heat Transfer ◽  
Two Phase Cooling

Thin-film evaporation from a meniscus in a confined space, which is the basis for many two-phase cooling devices, is experimentally investigated. The meniscus formed by heptane, a highly wetting liquid, on a heated, fused quartz substrate is studied. Microscale infrared temperature measurements performed near the thin-film region of the evaporating meniscus reveal the temperature suppression caused by the intensive evaporation in this region. The high spatial resolution (∼6.3 μm) and high temperature sensitivity (∼20 mK) of the infrared camera allowed for accurate measurements. The effects of meniscus thickness and applied heat flux on the thin-film heat transfer distribution and rate are also explored.

scholarly journals Wicking and Thermal Characteristics of Micropillared Structures for Use in Passive Heat Spreaders

2011 ◽  
Author(s):  
Ram Ranjan ◽  
Abhijeet Patel ◽  
Suresh V. Garimella ◽  
Jayathi Y. Murthy
Keyword(s):  
Thin Film ◽  
Thermal Contact ◽  
Thermal Characteristics ◽  
Hydrodynamic Performance ◽  
Superior Performance ◽  
High Permeability ◽  
Two Phase ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Cooling Devices

The thermal and hydrodynamic performance of passive two-phase cooling devices such as heat pipes and vapor chambers is limited by the capabilities of the capillary wick structures employed. The desired characteristics of wick microstructures are high permeability, high wicking capability and large extended meniscus area that sustains thin-film evaporation. Choices of scale and porosity of wick structures lead to tradeoffs between the desired characteristics. In the present work, models are developed to predict the capillary pressure, permeability and thin-film evaporation rates of various micropillared geometries. Novel wicking geometries such as conical and pyramidal pillars on a surface are proposed which provide high permeability, good thermal contact with the substrate and large thin-film evaporation rates. A comparison between three different micropillared geometries — cylindrical, conical and pyramidal — is presented and compared to the performance of conventional sintered particle wicks. The present work demonstrates a basis for reverse-engineering wick microstructures that can provide superior performance in phase-change 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.

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.

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.

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.

Fluid Flow and Thin Film Evolution Near the Triple Line of Evaporative Sessile Droplet During Mixing Process

2019 ◽  
Author(s):  
Tengxiao Ma ◽  
Leping Zhou
Keyword(s):  
Thin Film ◽  
Fluid Flow ◽  
Film Thickness ◽  
Thin Liquid Film ◽  
Internal Flow ◽  
Triple Line ◽  
Mixing Process ◽  
Sessile Droplet ◽  
Mixing Processes ◽  
Strong Disturbance

Abstract Evaporation of a sessile droplet containing nanoparticles plays a crucial role in engineering. However, the internal flow of an evaporative droplet may be influenced by various factors. Therefore, it is necessary to explore the mechanisms of fluid flow, especially the evolution of thin liquid film near the triple line of an evaporating droplet. This paper describes an experimental study of fluid flow and thin film evolution near the triple line of a sessile droplet when it was mixed with another droplet of different size. The temporal and spatial evolution of thickness in the thin film near the triple line is obtained by using the sub-region method developed from the total internal reflection fluorescence microscopy. The experimental results show that the spatial variation of the local film thickness can be linear or oscillating depending on the mixing position of the droplets. When the mixing position is at the droplet apex, the film thickness near the triple line fluctuates drastically in an oscillating mode, indicating that the mixing of the small droplet causes a strong disturbance in the thin film region. By using the velocimetry technique, the distribution of near wall velocity in the sessile droplet during mixing process is obtained, which provides the basis for velocimetry near the triple line. This work helps to gain insight of the thin film evolution and the velocity field near the triple line on the mixing processes of droplets.

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.

Sign in / Sign up

Export Citation Format

Share Document