Volume-conserving method for dynamic contact line on complex surfaces

Contact angles in soap films from diffraction of light traversing a plateau border

Nanoparticles deposition patterns in evaporating nanofluid droplets on smooth heated hydrophilic substrates: A 2D immersed boundary-lattice Boltzmann simulation

Complexity upgrade and triggering mechanism of mixed-wettability: Comparative study of CO2 displacement in different phases

Conjugate heat transfer analysis of bubble growth during flow boiling in a rectangular microchannel

A kinetic treatment of glass formation V: Surface and bulk heterogeneous nucleation

Colloid retention at the meniscus-wall contact line in an open microchannel

Giant unilamellar vesicles (GUVs) composed of different phospholipid binary mixtures were studied at different temperatures, by a method combining the sectioning capability of the two-photon excitation fluorescence microscope and the partition and spectral properties of 6-dodecanoyl-2-dimethylamino-naphthalene (Laurdan) and Lissamine rhodamine B 1,2-dihexadecanoyl- sn-glycero-3-phosphoethanolamine ( N-Rh-DPPE). We analyzed and compared fluorescence images of GUVs composed of 1,2-dilauroyl- sn-glycero-3-phosphocholine/1,2-dipalmitoyl- sn-glycero-3-phosphocholine (DLPC/DPPC), 1,2-dilauroyl- sn-glycero-3-phosphocholine/1,2-distearoyl- sn-glycero-3-phosphocholine (DLPC/DSPC), 1,2-dilauroyl- sn-glycero-3-phosphocholine/1,2-diarachidoyl- sn-glycero-3-phosphocholine (DLPC/DAPC), 1,2-dimyristoyl- sn-glycero-3-phosphocholine/1,2-distearoyl- sn-glycero-3-phosphocholine (DMPC/DSPC) (1:1 mol/mol in all cases), and 1,2-dimyristoyl- sn-glycero-3-phosphoethanolamine/1,2-dimyristoyl- sn-glycero-3-phosphocholine (DMPE/DMPC) (7:3 mol/mol) at temperatures corresponding to the fluid phase and the fluid-solid phase coexistence. In addition, we studied the solid-solid temperature regime for the DMPC/DSPC and DMPE/DMPC mixtures. From the Laurdan intensity images the generalized polarization function (GP) was calculated at different temperatures to characterize the phase state of the lipid domains. We found a homogeneous fluorescence distribution in the GUV images at temperatures corresponding to the fluid region for all of the lipid mixtures. At temperatures corresponding to phase coexistence we observed concurrent fluid and solid domains in the GUVs independent of the lipid mixture. In all cases the lipid solid domains expanded and migrated around the vesicle surface as we decreased the temperature. The migration of the solid domains decreased dramatically at temperatures close to the solid-fluid→solid phase transition. For the DLPC-containing mixtures, the solid domains showed line, quasicircular, and dendritic shapes as the difference in the hydrophobic chain length between the components of the binary mixture increases. In addition, for the saturated PC-containing mixtures, we found a linear relationship between the GP values for the fluid and solid domains and the difference between the hydrophobic chain length of the binary mixture components. Specifically, at the phase coexistence temperature region the difference in the GP values, associated with the fluid and solid domains, increases as the difference in the chain length of the binary mixture component increases. This last finding suggests that in the solid-phase domains, the local concentration of the low melting temperature phospholipid component increases as the hydrophobic mismatch decreases. At the phase coexistence temperature regime and based on the Laurdan GP data, we observe that when the hydrophobic mismatch is 8 (DLPC/DAPC), the concentration of the low melting temperature phospholipid component in the solid domains is negligible. This last observation extends to the saturated PE/PC mixtures at the phase coexistence temperature range. For the DMPC/DSPC we found that the nonfluorescent solid regions gradually disappear in the solid temperature regime of the phase diagram, suggesting lipid miscibility. This last result is in contrast with that found for DMPE/DMPC mixtures, where the solid domains remain on the GUV surface at temperatures corresponding to that of the solid region. In all cases the solid domains span the inner and outer leaflets of the membrane, suggesting a strong coupling between the inner and outer monolayers of the lipid membrane. This last finding extends previous observations of GUVs composed of DPPE/DPPC and DLPC/DPPC mixtures (Bagatolli and Gratton, 2000, Biophys. J. 78:290–305).

Pentane drops on a water surface are predicted to have contact angles of the order of 1 degree or less in the phase of frustrated complete wetting. We have developed an optical method of measuring such small contact angles, applicable to cases where the refractive indices of the substrate and adsorbate are very similar and the fluid dynamics do not allow delay between image acquisitions, by using phase retrieval to map the surface profile of the drops. It is empirically shown that, with our method, a difference of nanometer order can be achieved for the phase-retrieved dimensions relative to their expected value. Results agree with numerical predictions by Weiss and Widom [Physica A292, 137 (2001)PHYADX0378-437110.1016/S0378-4371(00)00619-1].

The vehicle HVAC systems have a fundamental role for demisting operation, eventually even more important than assuring thermal comfort because it guarantees the correct visibility for the drivers in the respect of the global security, towards the passengers and the pedestrians. Fiat Auto regulation follows the Standard CEE 78/317 performance test that the HVAC systems must respect to assure windshield demisting. The performance is evaluated by means an experimental test in climatic chamber. This test usually requires either waste of time and of money, since it has to be performed in climatic chambers. Only afterwards, if this first test is satisfied, thermal comfort performances of the vehicle are analysed. The goal of the present work is to describe the CFD virtual model developed to predict the demist performance of an HVAC system coupled with the virtual vehicle cabin, once the cabin CAD surfaces are available (draft surfaces are enough), and not after the vehicle manufacturing. A suite of routines for the prediction of environment moist condensation and evaporation on solid surfaces is presented. The physical problems require the solution of the air flow field along a (cold) solid surface, the evaluation of the unsteady conduction through the solid itself, and the development of a suitable model for the heat and mass transfer within the thin water layer on the fogged surface. The routines for the unsteady simulation of the water layer evolution are designed as a purely interfacial procedure, minimizing the exchange of information with the flow and conductive solver. This allows the coupling with different solvers. Here, the model is used in connection with a commercial CFD solver, in order to predict the defogging process of a car windshield. The water layer is modelled as a collection of closely packed tiny droplets, leaving a portion of dry area among them. The effect of the contact angle is taken into account, and physical assumptions allow to define the local ratio between wet and dry surface for both the fogging and defogging process. The model for the misted layer simulation is derived from a numerical method developed for the aeronautical de-icing systems. Fluid domain, solid domain and liquid film are simultaneously solved, and the problem of the conjugated thermal exchange through solid-fluid domains is carried out by means of opportune interpolations and information exchange on the boundary conditions. Finally this model has been successfully validated with respect to the experimental results.

Investigation of extracellular polymer substances (EPS) and physicochemical properties of different activated sludge flocs under steady-state conditions

This study presents a novel, simplified model for the time-efficient simulation of transient conjugate heat transfer in round tubes. The flow domain and the tube wall are modeled in 1D and 2D, respectively and empirical correlations are used to model the flow domain in 1D. The model is particularly useful when dealing with complex physics, such as flow boiling, which is the main focus of this study. The tube wall is assumed to have external fins. The flow is vertical upwards. Note that straightforward computational fluid dynamics (CFD) analysis of conjugate heat transfer in a system of tubes, leads to 3D modeling of fluid and solid domains. Because correlation is used and dimensionality reduced, the model is numerically more stable and computationally more time-efficient compared to the CFD approach. The benefit of the proposed approach is that it can be applied to large systems of tubes as encountered in many practical applications. The modeled equations are discretized in space using the finite volume method, with central differencing for the heat conduction equation in the solid domain, and upwind differencing of the convective term of the enthalpy transport equation in the flow domain. An explicit time discretization with forward differencing was applied to the enthalpy transport equation in the fluid domain. The conduction equation in the solid domain was time discretized using the Crank–Nicholson scheme. The model is applied in different boundary conditions and the predicted boiling patterns and temperature fields are discussed.

In this paper, the in-house code based on the smoothed particle hydrodynamics is proposed to simulate a fluid-solid interaction (FSI) problem. This method is a Lagrangian, mesh-free method and it has a high ability to capture the free surface in two phase flows and also the interface in FSI problems. To compare ofweakly compressible SPH (WCSPH) and incompressible SPH (ISPH) schemes, fluid flow under a hypo-elastic gate is simulated in solid and fluid domains with both methods. At first fluid domain is simulated with ISPH method and solid domain is solved with WCSPH scheme. Another simulation is done with both fluid and solid parts solved with WCSPH method. The results of both methods are in a good agreement with each other and also with other researcher’s results. So it is concluded that it is easier to model the fluid flow with ISPH scheme and the solid part with WCSPH in coupling fluid-solid interaction problems with a good accuracy.

In this work, we use the immersed boundary method with four extensions to simulate a moving liquid–gas interface on a solid surface. We first define a moving contact line model and implements a static-dynamic friction condition at the immersed solid boundary. The dynamic contact angle is endogenous instead of prescribed, and the solid boundary can be non-stationary with respect to time. Second, we simulate both a surface tension force and a Young's force with one general equation that does not involve estimating local curvature. In the third extension, we splice liquid–gas interfaces to handle topological changes, such as the coalescence and separation of liquid droplets or gas bubbles. Finally, we re-sample liquid–gas interface markers to ensure a near-uniform distribution without exerting artificial forces. We demonstrate empirical convergence of our methods on non-trivial examples and apply them to several benchmark cases, including a slipping droplet on a wall and a rising bubble.

Adaptation of application of drop area method to characterize hydrophobicity of materials

A hydrodynamic theory of bilayer membrane formation