Numerical simulation of the transport processes during drop impingement onto heated walls with special consideration of the evaporating three-phase contact line
When a liquid droplet impinges on a hot wall, the fluid dynamic and thermodynamic processes in the vicinity of the contact line play a significant role. The contact line defines the boundary between liquid, gas and wall. If the fluid approaches the critical state, the standard concept of an infinitely thin phase boundary between liquid and vapor is no longer valid. Therefore the modeling of the physical processes has to be optimized for the changed conditions.
The goal of the proposed project is to develop a comprehensive theoretical and numerical description of the dynamic processes occurring at a vaporizing contact line occurring during droplet impact. The local nano- and micro-phenomena have to be implemented in the VOF-Code (Volume Of Fluid) so that a drop impact can be simulated on a hot, dry or wetted surface. In particular the procedure of spreading, coalescence and disintegration of the film have to be modeled in physically correct way.
The existing model for the transport processes in the region of the contact line has to be extended in way that both the relative movement between the heating wall and the contact line as well as the not fully wetted systems can be considered. An essential element of the nano and micro Models near the line of contact is the concept of the adhesion pressure, where until now a relatively rudimentary approach is used the form of ∆p-3.
As part of the proposed project the existing concepts are to be extended in a way that allows to map the physical processes with enhanced realism. Particularly for evaporation processes close to the critical point it is assumed that the rudimentary approach describes the real processes inadequately, since the fluid phase boundary has to be described as a volume instead of a surface.
With this in mind the non local diffuse interface theory proves to be well suited for these conditions. The model for describing the processes in nano / micro-region is to be parametrized and then implemented to the VOF-Code. This can either be done in tabular form or in the form of correlations which take the saturation conditions, the overheating and the contact line speed into account.
The developed model will be used to simulate the dynamic heat- and mass transfer processes occurring during a droplet impact onto a hot wall with a not yet achieved accuracy. Initially the drop spreading dynamics and the temporal evolution of the contact angle will be investigated, and the results are then to be validated in a second step against experimental data. Once the model returns satisfying results the fingering, the rupturing of the film, the spreading of the dry spots and the development of cellular structures within the liquid film will be investigated. These quantities are of particular importance in the case of spray cooling, where the integral length and dynamics of the contact lines are of major relevance to the for the area-related cooling capacity.
Han, H., Schlawitschek, C., Stephan, P., Gambaryan-Roisman, T., Leroy, F., Müller-Plathe, F.:
Solid-liquid interface thermal resistance affects evaporation rate of droplets from a surface: A study of perfluorohexane on chromium using molecular dynamics and continuum theory.
Batzdorf, S., Breitenbach, J., Schlawitschek, S., Roisman, I., Tropea, C., Stephan, P., Gambaryan-Roisman, T.:
Heat transfer during simultaneous impact of two drops onto a hot solid substrate.
International Journal of Heat and Mass Transfer, eingereicht.
Batzdorf, S., Gambaryan-Roisman, T., Stephan, P. (2016):
Direct numerical simulation of the microscale fluid flow and heat transfer in the three-phase contact line region during evaporation.
ASME Journal of Heat Transfer, eingereicht.
Fischer, S., Gambaryan-Roisman, T., Stephan, P.:
On the development of a thin evaporating liquid film at a receding liquid/vapour-interface.
International Journal of Heat and Mass Transfer 88: 346-356, 2015.
Heat transfer and evaporation during single drop impingement onto a superheated wall.
Ph.D. Thesis, Technische Universität Darmstadt, 2015.
Herbert, S., Fischer, S., Stephan, P., Gambaryan-Roisman, T.
Local heat transfer and phase change phenomena during single drop impingement on a hot surface
International Journal of Heat and Mass Transfer, 61 (2013) 605-614
Herbert, S., Gambaryan-Roisman, T., Stephan, P.
Influence of the governing dimensionless parameters on heat transfer during single drop impingement onto a hot wall
Colloids and Surfaces A: Physicochemical and Engineering Aspects 432 (2013) 57-63
Kunkelmann, C.; Ibrahem, K.; Schweizer, N.; Herbert, S.; Stephan, P.; Gambaryan-Roisman, T.
The effect of three-phase contact line speed on local evaporative heat transfer: Experimental and numerical investigations.
International Journal of Heat and Mass Transfer 55 (7-8), pp. 1896-1904, 2012.
Ajaev, V.S., Klentzmann, J., Gambaryan-Roisman, T., Stephan, P.
Fingering instability of partially wetting evaporating liquids
Journal of Engineering Mathematics, 73 (2012) 31-38
van den Akker, E.A.T., Frijns, A.J.H., Kunkelmann, C., Hilbers, P.A.J., Stephan, P., von Steenhoven, A.A.
Molecular Dynamics simulation of the microregion
International Journal of Thermal Sciences, 59 (2012) 21-28
Raj, R., Kunkelmann, C., Stephan, P., Plawsky, J., Kim, J.
Contact line behavior for a highly wetting fluid under superheated conditions
International Journal of Heat and Mass Transfer, 55 (2012) 2664-2675
Ibrahem, K., Abd Rabbo, M.F, Gambaryan-Roisman, T., Stephan, P.
Experimental investigation of evaporative heat transfer characteristics at the 3-phase contact line
Experimental Thermal and Fluid Science, 34 (2010) 1036-1041
Ajaev, V.S., Gambaryan-Roisman, T., Stephan, P.
Static and dynamic contact angles of evaporating liquids on heated surfaces
Journal Colloid and Interface Science, 342 (2010) 550-558