| 1. |
- Albernaz, Daniel L., et al.
(författare)
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Thermodynamics of a real fluid near the critical point in numerical simulations of isotropic turbulence
- 2016
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Ingår i: Physics of fluids. - : American Institute of Physics (AIP). - 1070-6631 .- 1089-7666. ; 28:12
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the behavior of a fluid near the critical point by using numerical simulations of weakly compressible three-dimensional isotropic turbulence. Much has been done for a turbulent flow with an ideal gas. The primary focus of this work is to analyze fluctuations of thermodynamic variables (pressure, density, and temperature) when a non-ideal Equation Of State (EOS) is considered. In order to do so, a hybrid lattice Boltzmann scheme is applied to solve the momentum and energy equations. Previously unreported phenomena are revealed as the temperature approaches the critical point. Fluctuations in pressure, density, and temperature increase, followed by changes in their respective probability density functions. Due to the non-linearity of the EOS, it is seen that variances of density and temperature and their respective covariance are equally important close to the critical point. Unlike the ideal EOS case, significant differences in the thermodynamic properties are also observed when the Reynolds number is increased. We also address issues related to the spectral behavior and scaling of density, pressure, temperature, and kinetic energy.
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| 2. |
- Carlson, Andreas, et al.
(författare)
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Short and long time drop dynamics on lubricated substrates
- 2013
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 104:3, s. 34008-
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Tidskriftsartikel (refereegranskat)abstract
- Liquid infiltrated solids have been proposed as functional solvent-phobic surfaces for handling single and multiphase flows. Implementation of such surfaces alters the interfacial transport phenomenon as compared to a dry substrate. To better understand the interface characteristics in such systems we study experimentally the dynamics of a pendant water drop in air that contacts a substrate coated by thin oil films. At short times the water drop is deformed by the oil that spreads onto the water-air interface, and the dynamics are characterized by inertial and viscous regimes. At late times, the the oil film under the drop relaxes either to a stable thin film or ruptures. In the thin film rupture regime, we measure the waiting time for the rupture as a function of the drop equilibrium contact angle on a dry substrate and the initial film height. The waiting time is rationalized by lubrication theory, which indicates that long-range intermolecular forces destabilize the oil-water interface and is the primary mechanism for the film drainage.
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| 3. |
- Shen, Biao, et al.
(författare)
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Early Onset of Nucleate Boiling on Gas-covered Biphilic Surfaces
- 2017
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Ingår i: Scientific Reports. - : Nature Publishing Group. - 2045-2322. ; 7:1
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Tidskriftsartikel (refereegranskat)abstract
- For phase-change cooling schemes for electronics, quick activation of nucleate boiling helps safeguard the electronics components from thermal shocks associated with undesired surface superheating at boiling incipience, which is of great importance to the long-term system stability and reliability. Previous experimental studies show that bubble nucleation can occur surprisingly early on mixed-wettability surfaces. In this paper, we report unambiguous evidence that such unusual bubble generation at extremely low temperatures-even below the boiling point-is induced by a significant presence of incondensable gas retained by the hydrophobic surface, which exhibits exceptional stability even surviving extensive boiling deaeration. By means of high-speed imaging, it is revealed that the consequently gassy boiling leads to unique bubble behaviour that stands in sharp contrast with that of pure vapour bubbles. Such findings agree qualitatively well with numerical simulations based on a diffuse-interface method. Moreover, the simulations further demonstrate strong thermocapillary flows accompanying growing bubbles with considerable gas contents, which is associated with heat transfer enhancement on the biphilic surface in the low-superheat region.
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| 4. |
- Bredenberg, Johan, et al.
(författare)
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Modeling zinc sulfhydryl bonds in zinc fingers
- 2001
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Ingår i: International Journal of Quantum Chemistry. - : Wiley. - 0020-7608 .- 1097-461X. ; 83:3-4, s. 230-244
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Tidskriftsartikel (refereegranskat)abstract
- Molecular dynamics simulations have been carried out employing three different model descriptions of the zinc sulfhydryl interactions in class II fingers. One bonded and two nonbonded models were studied. Two variant structures of the glucocorticoid receptor DNA-binding; domain and a NMR structure from a fragment of methionyl-tRNA synthetase were subjected to long-time MD simulations with these models. Our analysis is focused on comparison with experimental and quantum mechanical data, concerning the local Zn-finger and overall structural and dynamic properties for these models. All models performed M ell, but the nonbonded models appeared to reproduce the protein dynamics in better agreement with experimental data than does the bonded description.
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| 5. |
- Carlson, Andreas, et al.
(författare)
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Dissipation in rapid dynamic wetting
- 2011
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Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press (CUP). - 0022-1120 .- 1469-7645. ; 682, s. 213-240
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Tidskriftsartikel (refereegranskat)abstract
- In this article, we present a modelling approach for rapid dynamic wetting based on the phase field theory. We show that in order to model this accurately, it is important to allow for a non-equilibrium wetting boundary condition. Using a condition of this type, we obtain a direct match with experimental results reported in the literature for rapid spreading of liquid droplets on dry surfaces. By extracting the dissipation of energy and the rate of change of kinetic energy in the flow simulation, we identify a new wetting regime during the rapid phase of spreading. This is characterized by the main dissipation to be due to a re-organization of molecules at the contact line, in a diffusive or active process. This regime serves as an addition to the other wetting regimes that have previously been reported in the literature.
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| 6. |
- Do-Quang, Minh, et al.
(författare)
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When and how surface structure determines the dynamics of partial wetting
- 2015
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Ingår i: Europhysics letters. - : IOP Publishing. - 0295-5075 .- 1286-4854. ; 110:4
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Tidskriftsartikel (refereegranskat)abstract
- The motion of a three phase contact line, as in a droplet spreading over a dry surface, is ubiquitous in nature and common in technology, but is still not well understood. As has been recently shown, line friction may play an important role in rapid dynamic wetting. Recognizing this as a sometimes dominating factor, we identify the possible scenarios for dynamic wetting of a partially wetting fluid, given the fluid and substrate properties. In doing so, we also reconcile the seemingly different interpretations of dynamic wetting that have been put forward in the recent literature. Copyright (C) EPLA, 2015
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| 7. |
- Kekesi, Timea, et al.
(författare)
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Drop deformation and breakup in flows with shear
- 2016
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Ingår i: Chemical Engineering Science. - : Elsevier. - 0009-2509 .- 1873-4405. ; 140, s. 319-329
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Tidskriftsartikel (refereegranskat)abstract
- A Volume of Fluid (VOF) method is applied to study the deformation and breakup of a single liquid drop in shear flows superimposed on uniform flow. The effect of shearing on the breakup mechanism is investigated as a function of the shear rate. Sequential images are compared for the parameter range studied; density ratios of liquid to gas of 20, 40, and 80, viscosity ratios in the range 0.5-50, Reynolds numbers between 20, a constant Weber number of 20, and the non-dimensional shear rate of the flow G = 0-2.1875. It is found that while shear breakup remains similar for all values of shear rate considered, other breakup modes observed for uniform flows are remarkably modified with increasing shear rate. The time required for breakup is significantly decreased in strong shear flows. A simple model predicting the breakup time as a function of the shear rate and the breakup time observed in uniform flows is suggested.
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| 8. |
- Knaust, Stefan, 1985-, et al.
(författare)
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Influence of flow rate, temperature and pressure on multiphase flows of supercritical carbon dioxide and water using multivariate partial least square regression
- 2015
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Ingår i: Journal of Micromechanics and Microengineering. - : Institute of Physics Publishing (IOPP). - 0960-1317 .- 1361-6439. ; 25:10
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Tidskriftsartikel (refereegranskat)abstract
- Supercritical carbon dioxide (scCO(2)) is often used to replace harmful solvents and can dissolve a wide range of organic compounds. With a favorable critical point at 31 degrees C and 7.4 MPa, reaching above the critical point for scCO(2) is fairly accessible. Because of the compressible nature of scCO(2) and the large changes of viscosity and density with temperature and pressure, there is a need to determine the behavior of scCO(2) in microfluidic systems. Here, the influence of how parameters such as flow rate, temperature, pressure, and flow ratio affects the length of parallel flow of water and scCO(2) and the length of the created CO2 segments are investigated and modeled using multivariate data analysis for a 10 mm long double-y channel. The parallel length and segment size were observed in the laminar regime around and above the critical point of CO2. The flow ratio between the two fluids together with the flow rate influenced both the parallel length and the segment sizes, and a higher pressure resulted in shorter parallel lengths. Regarding the segment length of CO2, longer segments were a result of a higher Weber number for H2O together with a higher temperature in the channel.
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| 9. |
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| 10. |
- Liu, Jiewei, et al.
(författare)
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Diffuse interface method for a compressible binary fluid
- 2016
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 93:1
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Tidskriftsartikel (refereegranskat)abstract
- Multicomponent, multiphase, compressible flows are very important in real life, as well as in scientific research, while their modeling is in an early stage. In this paper, we propose a diffuse interface model for compressible binary mixtures, based on the balance of mass, momentum, energy, and the second law of thermodynamics. We show both analytically and numerically that this model is able to describe the phase equilibrium for a real binary mixture (CO2 + ethanol is considered in this paper) very well by adjusting the parameter which measures the attraction force between molecules of the two components in the model. We also show that the calculated surface tension of the CO2 + ethanol mixture at different concentrations match measurements in the literature when the mixing capillary coefficient is taken to be the geometric mean of the capillary coefficient of each component. Three different cases of two droplets in a shear flow, with the same or different concentration, are simulated, showing that the higher concentration of CO2 the smaller the surface tension and the easier the drop deforms.
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