Duelling dry zones around hygroscopic droplets

2018 ◽  
Vol 853 ◽  
pp. 601-620 ◽  
Author(s):  
Saurabh Nath ◽  
Caitlin E. Bisbano ◽  
Pengtao Yue ◽  
Jonathan B. Boreyko
Keyword(s):  
Steady State ◽  
Surface Temperature ◽  
Vapour Pressure ◽  
Da Vinci ◽  
Sessile Droplet ◽  
Cellulose Fibres ◽  
Scaling Models ◽  
Dry Zone ◽  
Hygroscopic Material ◽  
Unique Ability

In the 1480s, da Vinci invented the first hygrometer using cellulose fibres to attract moisture from the atmosphere. Five hundred years later, Williams and Blanc showed that the depressed vapour pressure of a hygroscopic sessile droplet can inhibit condensation within an annular dry zone on the surface. What remains unresolved to this day is whether these regions of suppressed condensation around hygroscopic agents are due to inhibited nucleation versus inhibited growth of the condensate. We elucidate the competition between these two mechanisms by generating steady-state dry zones about frozen water droplets. The choice of ice as the hygroscopic material was motivated by its unique ability to remain undiluted as it attracts moisture from the air. Experiments, scaling models, and simulations where the ice droplet size, ambient humidity and surface temperature are systematically varied reveal that over the vast majority of the parameter space, the inhibited growth dry zone wins the duel over the nucleation dry zone.

Water Exchange in the Mantle of a Terrestrial Snail During Periods of Reduced Evaporative Loss

1972 ◽  
Vol 57 (1) ◽  
pp. 103-111
Author(s):  
J. MACHIN
Keyword(s):  
Steady State ◽  
Relative Humidity ◽  
Surface Temperature ◽  
Vapour Pressure ◽  
Pressure Difference ◽  
Water Exchange ◽  
Impermeable Barrier ◽  
Humidity Change ◽  
Evaporative Loss ◽  
Vapour Pressure Difference

1. Based on surface temperature, steady-state rates of evaporation of the mantle of inactive Otala lactea are very low even down to 1.5% relative humidity. 2. Mantle permeability is 0.016 mg/cm2/h per mmHg vapour pressure difference. 3. Marked peaks in surface temperature following humidity change are interpreted as net gain or loss of water to the mantle. 4. Smaller flucations in surface temperature are interpreted as limited mucusgland activity. 5. The existence of a superficial hygroscopic layer overlying an impermeable barrier in the mantle is discussed.

Steady-State Investigation of Vapor Deposited Micro Heat Pipe Arrays

1995 ◽  
Vol 117 (1) ◽  
pp. 75-81 ◽  
Author(s):  
A. K. Mallik ◽  
G. P. Peterson
Keyword(s):  
Thermal Conductivity ◽  
Steady State ◽  
Surface Temperature ◽  
Heat Pipe ◽  
Effective Thermal Conductivity ◽  
Heat Pipes ◽  
Temperature Gradients ◽  
Bottom Surface ◽  
Micro Heat Pipe ◽  
Micro Heat Pipes

An experimental investigation of vapor deposited micro heat pipe arrays was conducted using arrays of 34 and 66 micro heat pipes occupying 0.75 and 1.45 percent of the cross-sectional area, respectively. The performance of wafers containing the arrays was compared with that of a plain silicon wafer. All of the wafers had 8 × 8 mm thermofoil heaters located on the bottom surface to simulate the active devices in an actual application. The temperature distributions across the wafers were obtained using a Hughes Probeye TVS Infrared Thermal Imaging System and a standard VHS video recorder. For wafers containing arrays of 34 vapor deposited micro heat pipes, the steady-state experimental data indicated a reduction in the maximum surface temperature and temperature gradients of 24.4 and 27.4 percent, respectively, coupled with an improvement in the effective thermal conductivity of 41.7 percent. For wafers containing arrays of 66 vapor deposited micro heat pipes, the corresponding reductions in the surface temperature and temperature gradients were 29.0 and 41.7 percent, respectively, and the effective thermal conductivity increased 47.1 percent, for input heat fluxes of 4.70 W/cm2. The experimental results were compared with the results of a previously developed numerical model, which was shown to predict the temperature distribution with a high degree of accuracy, for wafers both with and without the heat pipe arrays.

Digital Microfluidic Device Using Ionic Liquids for Electronic Hotspot Cooling

2009 ◽  
Author(s):  
Hyejin Moon ◽  
Shreyas Bindiganavale ◽  
Yasith Nanayakkara ◽  
Daniel W. Armstrong
Keyword(s):  
Thermal Stability ◽  
Ionic Liquids ◽  
Surface Temperature ◽  
Hot Spot ◽  
Multiwall Carbon Nanotubes ◽  
Sessile Droplet ◽  
Electrowetting On Dielectric ◽  
Cooling Medium ◽  
Spot Area ◽  
Digital Microfluidic

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.

Numerical Simulation on the Evaporation of a Nonspherical Sessile Droplet

2019 ◽  
Author(s):  
Wenbin Cui ◽  
Benwei Fu
Keyword(s):  
Surface Temperature ◽  
Saturated Vapor ◽  
Surface Heterogeneity ◽  
Mass Transfer Process ◽  
Vapor Concentration ◽  
Curvature Radius ◽  
Sessile Droplet ◽  
Spherical Cap ◽  
Asymmetrical Shape ◽  
Evaporation Flux

Abstract When a droplet resting on a surface, its shape can be nonspherical or asymmetrical due to the surface heterogeneity, and surface temperature and evaporation flux may distribute asymmetrically during evaporation process thereafter. The evaporation of a nonspherical sessile droplet was simulated regarding heat and mass transfer process in this paper, which consists of part of a spherical cap and part of an ellipsoidal cap. Due to its asymmetrical shape, the surface temperature, saturated vapor concentration and evaporation flux distribute asymmetrically. The average surface temperature and average saturated vapor concentration are higher at ellipsoid side, but the average evaporation flux is higher at sphere side. Furthermore, due to the bigger curvature radius at ellipsoid side, the droplet evaporates faster at this side.

scholarly journals Attic Conversion – Hygrothermal Assessment of Historical Roof Truss

2020 ◽  
Vol 172 ◽  
pp. 15008
Author(s):  
Katerina Sojkova ◽  
Kamil Stanek
Keyword(s):  
Steady State ◽  
Relative Humidity ◽  
Boundary Conditions ◽  
Surface Temperature ◽  
Protection Agency ◽  
Critical Detail ◽  
Roof Truss ◽  
Project Phases ◽  
Heritage Protection ◽  
The City

In the City of Prague centre, an investor had the intention to convert the unused attic space of a historical palace into office and exhibition floor. It was necessary to design such a solution that would not worsen the humidity conditions and would not jeopardize the original Renaissance roof truss. The requirements of the heritage protection agency and the architect predetermined the use of very efficient thermal insulation above the rafters. The paper introduces and assesses several design solutions for: (1) new roofing layers and (2) the critical detail near the eaves, including variants with active heating elements. The assessment was based on results of 2D steady-state hygrothermal modelling using two criteria: (1) the interior surface temperature under winter design boundary conditions and (2) the relative humidity in the area of the timber elements under average January boundary conditions. The results showed hygrothermal implications of different design measures and helped to identify acceptable solutions for further project phases.

scholarly journals The Dependence of Temperature Profiles in Ice Sheets on Longitudinal Variations in Velocity and Surface Temperature

1978 ◽  
Vol 20 (82) ◽  
pp. 31-39 ◽  
Author(s):  
A. S. Jones
Keyword(s):  
Temperature Field ◽  
Steady State ◽  
Surface Temperature ◽  
Radial Flow ◽  
Ice Sheets ◽  
Temperature Profiles ◽  
Flow Lines ◽  
Temperature Variations ◽  
Longitudinal Variations ◽  
Surface Ice

Abstract Formulae for calculating temperature profiles in steady-state ice sheets are derived in terms of the horizontal and vertical velocities of the surface ice, and of the variation in surface temperature along the flow lines. Two models are considered: parallel flow and radial flow. In each case the result consists of a “stationary” term (equivalent to Robin's equation), a term dependent on the horizontal velocity, and a term arising from the temperature variations. This last term produces reversals in the temperature field such as are measured in practice.

Elastic, Plastic Stresses in Free Plate With Periodically Varying Surface Temperature

1958 ◽  
Vol 25 (4) ◽  
pp. 603-606
Author(s):  
Halil Yüksel
Keyword(s):  
Steady State ◽  
Surface Temperature ◽  
Constant Temperature ◽  
Thermal Stresses ◽  
Plastic Material ◽  
The Other ◽  
Perfectly Plastic ◽  
Temperature Oscillations ◽  
Steady State Temperature ◽  
Elastic Perfectly Plastic

Abstract The paper is concerned with a free plate that consists of an elastic, perfectly plastic material and is subjected to a harmonically varying temperature at one face, while the other face is kept at a constant temperature and the edge is perfectly insulated. The thermal stresses associated with the steady-state temperature oscillations are analyzed, and the development of plastic regions is discussed.

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