Evaporative Wicking Phenomena on Nanotextured Surfaces for Heat Pipe Applications

2018 ◽  
Author(s):  
Duong Vy Le ◽  
Shiwei Zhang ◽  
Jonggyu Lee ◽  
Yoonjin Won
Keyword(s):  
Thin Film ◽  
High Speed ◽  
High Performance ◽  
Heat Dissipation ◽  
Thermal Conditions ◽  
Temperature Profiles ◽  
Textured Surfaces ◽  
High Speed Imaging ◽  
Thin Film Evaporation ◽  
Film Evaporation

Thermal management has become more important as high-performance electronics have concentrated heat loads with current cooling technologies. This motivates the implementation of new cooling solutions to dissipate high heat levels from high-performance electronics. Evaporative cooling is one of the most promising approaches for meeting these future thermal demands. Thin-film evaporation promotes heat dissipation through the phase change process with minimal conduction resistance. In this process, it is important to design surface properties and structures that can minimize meniscus thickness, increase liquid-vapor interface area, and enhance evaporation performances. In this study, we thereby investigate thin-film evaporation by employing nanotextured copper substrates for varying thermal conditions. Specifically, we visualize the liquid spreading on the nanotextured surfaces using a high-speed imaging technique to quantify evaporative heat transfer for various designs. The permeability is calculated using an enhanced wicking model to account for the evaporation effect. The mass balance measurements allow us to calculate evaporation rates. Then, we employ infrared thermography to examine two-dimensional temporal temperature profiles of the samples during the evaporative wicking with a given heat flux. The combination of time-lapse images, evaporation rate measurements, and temperature profiles will provide a comprehensive understanding of evaporation performances of textured surfaces.

Evaporative Wicking Phenomena on Nanotextured Surfaces

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Duong Vy Le ◽  
Quang N. Pham ◽  
Jonggyu Lee ◽  
Shiwei Zhang ◽  
Yoonjin Won
Keyword(s):  
Thin Film ◽  
High Speed ◽  
High Performance ◽  
Heat Dissipation ◽  
Thermal Conditions ◽  
Temperature Profiles ◽  
Textured Surfaces ◽  
High Speed Imaging ◽  
Thin Film Evaporation ◽  
Film Evaporation

AbstractAs modern electronics become miniaturized with high power, thermal management for electronics devices has become significant. This motivates the implementation of new cooling solutions to dissipate high-heat levels from high-performance electronics. Evaporative cooling is one of the most promising approaches for meeting these future thermal demands. Thin-film evaporation promotes heat dissipation through the phase change process with minimal conduction resistance. In this process, it is important to design surface structures and corresponding surface properties that can minimize meniscus thickness, increase liquid–vapor interfacial area, and enhance evaporation performances. In this study, we investigate thin-film evaporation by employing nanotextured copper substrates for varying thermal conditions. The liquid spreading on the nanotextured surfaces is visualized using a high-speed imaging technique to quantify evaporative heat transfer for various surfaces. The permeability is calculated using an enhanced wicking model to estimate the evaporation effect combined with the mass measurements. Then, infrared (IR) thermography is employed to examine two-dimensional temporal temperature profiles of the samples during the evaporative wicking with a given heat flux. The combination of optical time-lapse images, evaporation rate measurements, and temperature profiles will provide a comprehensive understanding of evaporation performances using textured surfaces.

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.

scholarly journals Experimental Study on the Heat Transfer Performance of Pump-Assisted Capillary Phase-Change Loop

2021 ◽  
Vol 11 (22) ◽  
pp. 10954
Author(s):  
Xiaoping Yang ◽  
Gaoxiang Wang ◽  
Cancan Zhang ◽  
Jie Liu ◽  
Jinjia Wei
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Vapor Pressure ◽  
Pressure Difference ◽  
Heat Dissipation ◽  
Vapor Pressure Difference ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Start Up ◽  
Liquid Vapor

To overcome the two-phase flow instability of traditional boiling heat dissipation technologies, a porous wick was used for liquid-vapor isolation, achieving efficient and stable boiling heat dissipation. A pump-assisted capillary phase-change loop with methanol as the working medium was established to study the effect of liquid-vapor pressure difference and heating power on its start-up and steady-state characteristics. The results indicated that the evaporator undergoes four heat transfer modes, including flooded, partially flooded, thin-film evaporation, and overheating. The thin-film evaporation mode was the most efficient with the shortest start-up period. In addition, heat transfer modes were determined by the liquid-vapor pressure difference and power. The heat transfer coefficient significantly improved and the thermal resistance was reduced by increasing liquid-vapor pressure as long as it did not exceed 8 kPa. However, when the liquid-vapor pressure exceeded 8 kPa, its influence on the heat transfer coefficient weakened. In addition, a two-dimensional heat transfer mode distribution diagram concerning both liquid-vapor pressure difference and power was drawn after a large number of experiments. During an engineering application, the liquid-vapor pressure difference can be controlled to maintain efficient thin-film evaporation in order to achieve the optimum heat dissipation effect.

scholarly journals Experimental Study on the Heat Transfer Performance of Pump-assisted Capillary Phase-change Loop

2021 ◽  
Author(s):  
Xiaoping Yang ◽  
Gaoxiang Wang ◽  
Cancan Zhang ◽  
Jie Liu ◽  
Jinjia Wei
Keyword(s):  
Thin Film ◽  
Heat Transfer ◽  
Vapor Pressure ◽  
Pressure Difference ◽  
Heat Dissipation ◽  
Vapor Pressure Difference ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Start Up ◽  
Liquid Vapor

To overcome the two-phase flow instability of traditional boiling heat dissipation technologies, a porous wick was used for liquid-vapor isolation, thus realizing efficient and stable boiling heat dissipation. A pump-assisted capillary phase-change loop with methanol as working medium was established to study the effect of liquid-vapor pressure difference and heating power on its start-up and steady-state characteristics. The results indicated that the evaporator undergoes four heat transfer modes including flooded, partial flooded, thin film evaporation and overheating. The thin film evaporation mode was the most efficient one with the shortest start-up period. Besides, the heat transfer modes were determined by liquid-vapor pressure difference and power. The heat transfer coefficient could be significantly improved and the thermal resistance could be reduced by increasing liquid-vapor pressure difference as long as it did not exceed 8 kPa. However, when the liquid-vapor pressure difference exceeded 8kPa, its influence on the heat transfer coefficient weakened. In addition, a two-dimensional heat transfer mode distribution diagram considering both liquid-vapor pressure difference and power was drawn through a great number of experiments. During engineering application, the liquid-vapor pressure difference can be controlled to maintain efficient thin film evaporation in order to achieve the optimum heat dissipation effect.

Ultra-High Speed Vitrification of Prostate Cancer Cells Based on Thin Film Evaporation

2019 ◽  
Author(s):  
Fengmin Su ◽  
Yiming Fan ◽  
He Xu ◽  
Nannan Zhao ◽  
Yangbo Deng ◽  
...  
Keyword(s):  
Thin Film ◽  
Survival Rate ◽  
Cell Survival ◽  
Cooling Rate ◽  
High Speed ◽  
Thin Film Evaporation ◽  
Film Evaporation ◽  
Freezing Method ◽  
Cell Survival Rate ◽  
Ultra High Speed

Abstract Thin film evaporation is an efficient phase change heat transfer style, and could achieve ultra-high cooling rate if it was applied for cells vitrification. In this paper, an experimental study for prostate cancer cells vitrification was done. The cells ultra-high speed freezing method was based on thin film evaporation of liquid nitrogen. In order to examine the feasibility of the new method, the comparison experiments, in which the other two generic approaches of cell cryopreservation were used, were done. The methods were respectively the equilibrium freezing method and the open pulled straws vitrification method. At the same time, the influences of the concentration of cryoprotectant on cooling rate and cell survival rate were analyzed. The results showed that the ultra-high speed freezing method based on thin film evaporation can obtain higher cooling rate and better cell survival rate than the other two conventional cryopreservation methods. It preliminarily proved the feasibility of this method applied to the cells vitrification process. In addition, both the cooling rate and the cell survival rate are affected by the concentration of the cryoprotectant in the cell suspension. The cooling rate decreases with the concentration of the cryoprotectant increasing, but cell survival rate increases first and decrease afterwards with the increase of the concentration of the cryoprotectant, in which an optimum value exists. This study will promote the practicality of the new ultra-fast cell freezing method.

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.

Cooling of High-Performance Server Modules Using Direct Immersion

2012 ◽  
Author(s):  
Aravind Sridhar ◽  
Sarah Styslinger ◽  
Christopher Duron ◽  
Sushil H. Bhavnani ◽  
Roy W. Knight ◽  
...  
Keyword(s):  
Heat Flux ◽  
High Speed ◽  
High Performance ◽  
Heat Dissipation ◽  
Heat Removal ◽  
Liquid Pool ◽  
Circuit Board ◽  
Air Cooling ◽  
High Speed Imaging ◽  
Close Proximity

An alternative to air-cooling of high performance computing equipment is presented. Heat removal via pool boiling in FC-72 was tested. Tests were conducted on a multichip module using 1.8 cm × 1.8 cm test die with multiple thermal test cells with temperature sensing capability. Measurements with the bare silicon die in direct contact with the fluid are reported. Additional testing included the test die directly indium-attached to copper heat spreaders having surface treatments. A screen-printed sintered boiling-enhanced surface (4 cm × 4 cm) was evaluated. Tests were conducted on an array of five die. Parameters tested include heat flux levels, dielectric liquid pool conditions (saturated or subcooled), and effect of neighboring die. Information was gathered on surface temperatures for a range of heat flux values up to 12 W/cm2. The highest heat dissipated from a circuit board with five bare die was 195 W (39 W per die). Addition of the heat spreader allowed heat dissipation of up to 740 W (from a five-die array). High-speed imaging was also acquired to help examine detailed information on the boiling process. Numerical modeling indicated that placing multiple boards in close proximity to each other did not degrade performance until board spacing was reduced to 3 mm.

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