Digital Microfluidic Device Using Ionic Liquids for Electronic Hotspot Cooling

Thermal management in electronics become more challenging as the size of electronics decreases, yet, the heat generated from electronics still increases. To enhance cooling efficiency of conventional cooling schemes such as heat pipes, we experimentally present a use of electrowetting on dielectric (EWOD) digital microfluidic technique to force the cooling liquid medium to move to hot spot area. In this paper, firstly, two different EWOD devices were compared in their cooling performance. One is a system using one plane device and sessile droplet of cooling medium and the other is a system using two parallel planes and liquid is sandwiched in between. Secondly, two types of liquids were used and compared as the cooling medium. De-ionized (DI) water and room temperature ionic liquid (RTIL) have been investigated. RTILs are thermally stable thanks to their low vapor pressure. In addition to thermal stability, RTIL can be tailored task specifically by altering cations and anions. Different experiments were conducted to study the capacity of IL’s to change the surface temperature of the hotspot generated and this was compared with that of DI water. The latter showed higher capacity to remove heat, while evaporation problem was predominant in the sandwiched setup. Three different ionic liquids, 1-butyl-3-methylimidazolium chloride or [BMIM]Cl, 1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)-imide or [BMIM]Ntf2, and [CMIM]FeCl4 showed less effect on changing the surface temperature compared to water. It is due to generally lower heat conductivity and higher viscosity of ILs than water. However, RTILs showed high thermal stability by resulting in no evaporation during cooling process while water had vigorous evaporation. Nanofluid of RTIL and multiwall carbon nanotubes (MWCNT) mixture has been tested as the first step toward enhancing thermal conductivity of RTIL.

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Stick–slip behavior during electrowetting-on-dielectric: polarization and substrate effects

Microfluidics and Nanofluidics ◽

10.1007/s10404-020-02374-y ◽

2020 ◽

Vol 24 (10) ◽

Author(s):

Russell C. Reid ◽

Marriner H. Merrill ◽

James P. Thomas

Keyword(s):

Charge Trapping ◽

Triple Line ◽

Microfluidic Chips ◽

Dielectric Polarization ◽

Sessile Droplet ◽

Stick Slip ◽

Electrowetting On Dielectric ◽

Charged Species ◽

Digital Microfluidic ◽

Substrate Surfaces

Abstract A novel triple-line stick–slip behavior, manifested by “sawtooth oscillations” of the contact angle (CA), was observed during sessile droplet advance by electrowetting-on-dielectric (EWOD) for DC voltages and during droplet retreat for AC voltages. The onset of stick–slip occurred on polished substrate surfaces when the applied potential approached the EWOD saturation voltage and at lower voltages on rougher surfaces. Stick–slip was reduced at higher AC frequencies (> 1 kHz), not significantly influenced by pH or voltage polarity and did not occur with AC polarization on substrates with a Parylene coating but no hydrophobic top-layer. The different triple-line pinning behaviors under DC and AC polarization are shown to be consistent with heterogeneous wetting associated with immobilization of charged species—referred to as charge trapping—near the triple-line at saturation. These experiments and insights offer a new approach for understanding and addressing EWOD device limitations related to CA saturation and charged species trapping leading to improved performance in micro-/nanofluidic pumps, digital microfluidic chips, and electret devices. Graphical Abstract

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Spatial Hotspot Analysis of Bucharest’s Urban Heat Island (UHI) Using Modis Data

Annals of Valahia University of Targoviste Geographical Series ◽

10.2478/avutgs-2018-0002 ◽

2018 ◽

Vol 18 (1) ◽

pp. 14-22 ◽

Cited By ~ 1

Author(s):

Georgiana Grigoraș ◽

Bogdan Urițescu

Keyword(s):

Surface Temperature ◽

Air Temperature ◽

Land Surface Temperature ◽

Hot Spots ◽

Land Surface ◽

Hot Spot ◽

Monitoring Network ◽

Residential Areas ◽

Hotspot Analysis ◽

The City

Abstract The aim of the study is to find the relationship between the land surface temperature and air temperature and to determine the hot spots in the urban area of Bucharest, the capital of Romania. The analysis was based on images from both moderate-resolution imaging spectroradiometer (MODIS), located on both Terra and Aqua platforms, as well as on data recorded by the four automatic weather stations existing in the endowment of The National Air Quality Monitoring Network, from the summer of 2017. Correlation coefficients between land surface temperature and air temperature were higher at night (0.8-0.87) and slightly lower during the day (0.71-0.77). After the validation of satellite data with in-situ temperature measurements, the hot spots in the metropolitan area of Bucharest were identified using Getis-Ord spatial statistics analysis. It has been achieved that the “very hot” areas are grouped in the center of the city and along the main traffic streets and dense residential areas. During the day the "very hot spots” represent 33.2% of the city's surface, and during the night 31.6%. The area where the mentioned spots persist, falls into the "very hot spot" category both day and night, it represents 27.1% of the city’s surface and it is mainly represented by the city center.

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The Microstructure of Fused Cast AZS Materials before, during and after the Use for Glass Melting

Advanced Materials Research ◽

10.4028/www.scientific.net/amr.39-40.607 ◽

2008 ◽

Vol 39-40 ◽

pp. 607-612

Author(s):

Bernhard Fleischmann

Keyword(s):

Glass Furnace ◽

Glass Melting ◽

Hot Spot ◽

Float Glass ◽

Vitreous Phase ◽

Spot Area ◽

Furnace Campaign ◽

Three Phases

A part of a soldier block, placed in a float glass furnace near the hot spot area, was investigated to learn about the changes in the microstructure during the production of the block, during the use for glass melting and after the shut down of the furnace and the cooling of the block. Beside the three phases after the production (baddeleyite, corundum, vitreous phase) during use as a soldier block mullite and secondary corundum as well as secondary zirconia may occure. Cooling down the used block after the furnace campaign the beginning of the crystallisation of feldspars may be seen.

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Thermal Stability and Decomposition Kinetics of 1-Alkyl-2,3-Dimethylimidazolium Nitrate Ionic Liquids: TGA and DFT Study

Materials ◽

10.3390/ma14102560 ◽

2021 ◽

Vol 14 (10) ◽

pp. 2560

Author(s):

Jianwen Meng ◽

Yong Pan ◽

Fan Yang ◽

Yanjun Wang ◽

Zhongyu Zheng ◽

...

Keyword(s):

Thermal Stability ◽

Density Functional Theory ◽

Ionic Liquids ◽

Density Functional ◽

Density Functional Theory Calculations ◽

Nitrogen Atmosphere ◽

Decomposition Kinetics ◽

Heating Rates ◽

Functional Theory ◽

Kinetics Of

The thermal stability and decomposition kinetics analysis of 1-alkyl-2,3-dimethylimidazole nitrate ionic liquids with different alkyl chains (ethyl, butyl, hexyl, octyl and decyl) were investigated by using isothermal and nonisothermal thermogravimetric analysis combined with thermoanalytical kinetics calculations (Kissinger, Friedman and Flynn-Wall-Ozawa) and density functional theory (DFT) calculations. Isothermal experiments were performed in a nitrogen atmosphere at 240, 250, 260 and 270 °C. In addition, the nonisothermal experiments were carried out in nitrogen and air atmospheres from 30 to 600 °C with heating rates of 5, 10, 15, 20 and 25 °C/min. The results of two heating modes, three activation energy calculations and density functional theory calculations consistently showed that the thermal stability of 1-alkyl-2,3-dimethylimidazolium nitrate ionic liquids decreases with the increasing length of the alkyl chain of the substituent on the cation, and then the thermal hazard increases. This study could provide some guidance for the safety design and use of imidazolium nitrate ionic liquids for engineering.

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