| 1. |
- Albernaz, Daniel L., et al.
(författare)
-
Droplet deformation and heat transfer in isotropic turbulence
- 2017
-
Ingår i: Journal of Fluid Mechanics. - : Cambridge University Press. - 0022-1120 .- 1469-7645. ; 820, s. 61-85
-
Tidskriftsartikel (refereegranskat)abstract
- The heat and mass transfer of deformable droplets in turbulent flows is crucial. to a wide range of applications, such as cloud dynamics and internal combustion engines. This study investigates a single droplet undergoing phase change in isotropic turbulence using numerical simulations with a hybrid lattice Boltzmann scheme. Phase separation is controlled by a non-ideal equation of state and density contrast is taken into consideration. Droplet deformation is caused by pressure and shear stress at the droplet interface. The statistics of thermodynamic variables are quantified and averaged over both the liquid and vapour phases. The occurrence of evaporation and condensation is correlated to temperature fluctuations, surface tension variation and turbulence intensity. The temporal spectra of droplet deformations are analysed and related to the droplet surface area. Different modes of oscillation are clearly identified from the deformation power spectrum for low Taylor Reynolds number Re, whereas nonlinearities are produced with the increase of Re A, as intermediate frequencies are seen to overlap. As an outcome, a continuous spectrum is observed, which shows a decrease in the power spectrum that scales as similar to f(-3) Correlations between the droplet Weber number, deformation parameter, fluctuations of the droplet volume and thermodynamic variables are also developed.
|
|
| 2. |
- Albernaz, Daniel L., 1984-, et al.
(författare)
-
Lattice Boltzmann Method for the evaporation of a suspended droplet
- 2013
-
Ingår i: Interfacial phenomena and heat transfer. - : Begell House. - 2167-857X. ; 1, s. 245-258
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper we consider a thermal multiphase lattice Boltzmann method (LBM) to investigate the heating and vaporization of a suspended droplet. An important benefit from the LBM is that phase separation is generated spontaneously and jump conditions for heat and mass transfer are not imposed. We use double distribution functions in order to solve for momentum and energy equations. The force is incorporated via the exact difference method (EDM) scheme where different equations of state (EOS) are used, including the Peng-Robinson EOS. The equilibrium and boundary conditions are carefully studied. Results are presented for a hexane droplet set to evaporate in a superheated gas, for static condition and under gravitational effects. For the static droplet, the numerical simulations show that capillary pressure and the cooling effect at the interface play a major role. When the droplet is convected due to the gravitational field, the relative motion between the droplet and surrounding gas enhances the heat transfer. Evolution of density and temperature fields are illustrated in details.
|
|
| 3. |
- Albernaz, Daniel L., 1984-, et al.
(författare)
-
Simulation of a suspended droplet under evaporation with Marangoni effects
- 2016
-
Ingår i: International Journal of Heat and Mass Transfer. - : Elsevier. - 0017-9310 .- 1879-2189. ; 91, s. 853-860
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the Marangoni effects in a hexane droplet under evaporation and close to its critical point. A lattice Boltzmann model is used to perform 3D numerical simulations. In a first case, the droplet is placed in its own vapor and a temperature gradient is imposed. The droplet locomotion through the domain is observed, where the temperature differences across the surface is proportional to the droplet velocity and the Marangoni effect is confirmed. The droplet is then set under a forced convection condition. The results show that the Marangoni stresses play a major role in maintaining the internal circulation when the superheated vapor temperature is increased. Surprisingly, surface tension variations along the interface due to temperature change may affect heat transfer and internal circulation even for low Weber number. Other results and considerations regarding the droplet surface are also discussed.
|
|
| 4. |
- Albernaz, Daniel L., et al.
(författare)
-
Thermodynamics of a real fluid near the critical point in numerical simulations of isotropic turbulence
- 2016
-
Ingår i: Physics of fluids. - : American Institute of Physics (AIP). - 1070-6631 .- 1089-7666. ; 28:12
-
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.
|
|
| 5. |
- Albernaz, Daniel, et al.
(författare)
-
Multirelaxation-time lattice Boltzmann model for droplet heating and evaporation under forced convection
- 2015
-
Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - 1539-3755 .- 1550-2376. ; 91:4
-
Tidskriftsartikel (refereegranskat)abstract
- We investigate the evaporation of a droplet surrounded by superheated vapor with relative motion between phases. The evaporating droplet is a challenging process, as one must take into account the transport of mass, momentum, and heat. Here a lattice Boltzmann method is employed where phase change is controlled by a nonideal equation of state. First, numerical simulations are compared to the D-2 law for a vaporizing static droplet and good agreement is observed. Results are then presented for a droplet in a Lagrangian frame under a superheated vapor flow. Evaporation is described in terms of the temperature difference between liquid-vapor and the inertial forces. The internal liquid circulation driven by surface-shear stresses due to convection enhances the evaporation rate. Numerical simulations demonstrate that for higher Reynolds numbers, the dynamics of vaporization flux can be significantly affected, which may cause an oscillatory behavior on the droplet evaporation. The droplet-wake interaction and local mass flux are discussed in detail.
|
|
| 6. |
- Aldaeus, Fredrik, et al.
(författare)
-
Multi-step dielectrophoresis for separation of particles
- 2006
-
Ingår i: Journal of Chromatography A. - : Elsevier BV. - 0021-9673 .- 1873-3778. ; 1131:1-2, s. 261-266
-
Tidskriftsartikel (refereegranskat)abstract
- A new concept for separation of particles based on repetitive dielectrophoretic trapping and release in a flow system is proposed. Calculations using the finite element method have been performed to envision the particle behavior and the separation effectiveness of the proposed method. As a model system, polystyrene beads in deionized water and a micro-flow channel with arrays of interdigited electrodes have been used. Results show that the resolution increases as a direct function of the number of trap-and-release steps, and that a difference in size will have a larger influence on the separation than a difference in other dielectrophoretic properties. About 200 trap-and-release steps would be required to separate particles with a size difference of 0.2%. The enhanced separation power of dielectrophoresis with multiple steps could be of great importance, not only for fractionation of particles with small differences in size, but also for measuring changes in surface conductivity, or for separations based on combinations of difference in size and dielectric properties.
|
|
| 7. |
- Aldaeus, Fredrik, et al.
(författare)
-
Superpositioned dielectrophoresis for enhanced trapping efficiency
- 2005
-
Ingår i: Electrophoresis. - : Wiley. - 0173-0835 .- 1522-2683. ; 26:22, s. 4252-4259
-
Tidskriftsartikel (refereegranskat)abstract
- One of the major applications for dielectrophoresis is selective trapping and fractionation of particles. If the surrounding medium is of low conductivity, the trapping force is high, but if the conductivity increases, the attraction decreases and may even become negative. However, high-conductivity media are essential when working with biological material such as living cells. In this paper, some basic calculations have been performed, and a model has been developed which employs both positive and negative dielectrophoresis in a channel with interdigitated electrodes. The finite element method was utilized to predict the trajectories of Escherichia coli bacteria in the superpositioned electrical fields. It is shown that a drastic improvement of trapping efficiency can be obtained in this way, when a high conductivity medium is employed.
|
|
| 8. |
- Amberg, Gustav
(författare)
-
Detailed modelling of contact line motion in oscillatory wetting
- 2022
-
Ingår i: NPJ MICROGRAVITY. - : Springer Nature. - 2373-8065. ; 8:1
-
Tidskriftsartikel (refereegranskat)abstract
- The experimental results of Xia and Steen for the contact line dynamics of a drop placed on a vertically oscillating surface are analyzed by numerical phase field simulations. The concept of contact line mobility or friction is discussed, and an angle-dependent model is formulated. The results of numerical simulations based on this model are compared to the detailed experimental results of Xia and Steen with good general agreement. The total energy input in terms of work done by the oscillating support, and the dissipation at the contact line, are calculated from the simulated results. It is found that the contact line dissipation is almost entirely responsible for the dissipation that sets the amplitude of the response. It is argued that angle-dependent line friction may be a fruitful interpretation of the relations between contact line speed and dynamic contact angle that are often used in practical computational fluid dynamics.
|
|
| 9. |
- Amberg, Gustav
(författare)
-
Semisharp phase field method for quantitative phase change simulations
- 2003
-
Ingår i: Physical Review Letters. - 0031-9007 .- 1079-7114. ; 91:26
-
Tidskriftsartikel (refereegranskat)abstract
- The standard phase field model for simulation of phase change requires an asymptotic analysis in a vanishing interface width, in order to connect the model parameters to the sharp interface parameters, which has hampered the quantitative usefulness of the method. In this Letter the method is simplified to the point that the relevant reduced problem can be solved analytically, allowing the sharp and phase field parameters to be identified, in principle, without restrictions on the model parameters. The scheme is tested for standard cases of two-dimensional solidification, showing excellent agreement with sharp interface kinetics.
|
|
| 10. |
|
|
