Tatiana Gambaryan-Roisman

Technical University of Darmstadt | TU · Institute for Technical Thermodynamics (TTD)

In this paper, results of preparatory tests for a space experiment “Marangoni in Films” on board International Space Station are reported. The setup is thermalized at a setpoint temperature so that (thermal) Marangoni convection is exclusively a result of evaporative cooling of the film, here composed of a Hydrofluoroether (HFE)-7100, evaporating i...

Modeling of volatile droplets and rivulets on structured or rough surfaces requires detailed analysis of vapor diffusion and fluid flow near their edges where a significant amount of evaporation is expected based on both experimental data and theoretical considerations. We develop local analytical models of flow generated in these regions in both l...

With an increased need to solve fresh water scarcity for humanity in many places around the world, dew water harvesting is one promising approach to improve the situation. While condensation from humid air has been a research topic for many years, it is still unclear how surface wettability influences the condensation efficiency and the fresh water...

Spray cooling stands out as a suitable method for cooling of high-end electronic devices. Texturing of the surface can further increase the cooling performance. Understanding the flow dynamics and heat transport during the impingement of a single drop is crucial to gain an in-depth insight into complex phenomena governing spray cooling. In this stu...

Modification of surfaces to enable dropwise condensation (DWC) is a promising approach for achieving high condensation rates. In this work, we present an experimental study on condensation of water on copper surfaces coated with an ultrathin, 5-10 nm thick polydimethylsiloxane (PDMS) layer. This hydrophobic coating possesses a very low thermal resi...

Wetting of deformable surfaces is a highly debated topic in interface science. A classical approach employing the localized Young's traction γsinθ and curvature-induced traction following from the spherical cap assumption, is commonly used for the evaluation of the deformation - particularly, a wetting ridge - of the surface. This, however, does no...

One parameter frequently considered to be relevant for superspreading of trisiloxane surfactants is surface tension kinetics. In the scientific literature, some experimental results reported for trisiloxane surfactants are in contradiction with fundamental concepts of surfactant monomer diffusion. Therefore, maximum bubble pressure tensiometry has...

Controlling and improving processes like for example the production of organic semiconductors via printing depends on understanding the interplay of wetting and evaporation of complex fluids. Therefore, examination of the time dependent composition of complex fluid droplets during wetting or evaporation is of interest. The evaporation rate of sessi...

Drop impact on a hot surface heated above the saturation temperature of the fluid plays an important role in spray cooling. The heat transferred from the wall to the fluid is closely interrelated with drop hydrodynamics. If the surface temperature is below the Leidenfrost temperature, the heat transport strongly depends on the transport phenomena i...

In this study, hydrodynamics and heat transport during the impact of single and multiple drops onto a hot wall are studied numerically. The heat transfer in the vicinity of the three-phase contact line, where solid, liquid and vapour meet, contributes significantly to the global heat transfer. The microscale processes in the region of the three-pha...

Modeling the evaporation process of pinned urea-water solution (UWS) droplets sitting on a heated surface is of large interest for reducing the deposit formation in Selective Catalytic Reduction (SCR) systems, which can lead to a significant loss in efficiency. The kinetics of diffusion-governed evaporation of sessile droplets having the shape of a...

The geometry of rough, textured, fractured, and porous media is topologically complicated. Such media are commonly modeled as bundles of capillary tubes. However, angle-containing geometries can serve as a more realistic portrayal of their internal structure. A basic element inherent to all of these media is an open wedge-like channel. The classica...

Wetting of corner-containing geometries is ubiquitous, since the man-made surface and natural surfaces are usually not atomically smooth and contain pores, grooves, and cracks. In spite of the very long history of the research of capillary phenomena, the most attention was paid to capillary rise in cylindrical capillaries leaving the rich physics o...

The geometry of rough, textured, fractured and porous media is topologically complicated. Those media are commonly represented by bundles of capillary tubes when modeled. However, angle-containing geometries can serve as a more realistic portrayal of their inner structure. A basic element abidingly inherent to all of them is an open wedge-like chan...

The formation of solid deposits in exhaust treatment systems operating based on selective catalytic reduction is a major reason for the decline in system efficiency and possible damage. To reduce the amount of deposits, precise information about influencing variables but also about necessary preliminary processes is required. One such process is th...

Despite tremendous interest in the wetting dynamics at the microscale, attention to nanodroplets has started rising only over the last two decades. In the current work, we examine the dynamics of droplets of size comparable with the range of the surface force action spreading over wetting (adsorbed) films. We show that wetting exponents are strongl...

This paper presents an experimental study on hydrodynamics and heat transport during the horizontal coalescence of two drops impinging a hot wall. The study addresses the influence of distance between impact locations, the time interval between drop impact, and wall superheat on the transport processes. The experiments were conducted under a pure v...

Despite being intensively investigated, wetting at the nanoscale leaves a manifold of questions unresolved. In particular, the dependence of a contact angle on a droplet size for the droplets of the height of the order of a few nanometers is intensively debated. This effect is believed to be related to intermolecular (surface) forces. In the presen...

It is known that heat transfer resulting from the drop impact onto a hot substrate can be enhanced with the use of nanostructured coatings, such as nanofiber mats, on the substrate surface. One heat transfer enhancement mechanism is related to liquid imbibition into the porous structure and subsequent evaporation. The detailed mechanisms of liquid...

Liquid jet impingement is used for cooling and cleaning in various industrial branches. The advantages of jet impingement include high heat and mass transport rates in the vicinity of the impingement point. Pulsating liquid jets impinging on horizontal substrates with a pulsation frequency around 100 Hz have been shown to increase the cooling effic...

In this work, the wetting and evaporation behaviour of non-polar solvent droplets on thin soluble coatings is investigated experimentally. The wetting process on spin-coated polymer layers by toluene is captured using shadowgraphy. Initial spontaneous dynamic wetting as well as later stages of wetting are recorded and evaluated. Furthermore, struct...

Evaporation and deposit formation of a pinned urea-water drop on an initially smooth surface is modeled. Water evaporates from the two-component drop into the surrounding gas phase. This leads to an increase of the urea concentration inside the drop. At the three-phase contact line, high evaporation rates lead to a maximum of the urea concentration...

In this work, the wetting and evaporation behaviour of non-polar solvent droplets on thin soluble coatings is investigated experimentally. The wetting process on spin coated polymer layers by the solvent is captured using shadowgraphy. Initial spontaneous dynamic wetting as well as later stages of wetting are recorded and evaluated. Furthermore, st...

We describe the aims and content of this issue.

Wetting of surfaces with porous coating is relevant for a wide variety of technical applications, such as printing technologies and heat transfer enhancement. Imbibition and evaporation of liquids on surfaces covered with porous layers are responsible for significant improvement of cooling efficiency during drop impact cooling and flow boiling on s...

The present work addresses the influence of the wall superheat, drop impact velocity, and impact diameter on hydrodynamics, heat transport, and evaporation during drop impingement onto a heated solid wall in a pure vapor atmosphere. A generic experimental setup has been designed and built with a temperature-controlled cell that allows investigation...

In this study, hydrodynamics and heat transport during the vertical coalescence of multiple successive drops impacting a hot wall are analyzed experimentally. This study addresses the influence of wall superheat and the frequency of drop generation on the hydrodynamics and heat transport. The experiments are conducted under a pure vapor atmosphere...

Nanofluids hold promise for a wide range of areas of industry. However, understanding of wetting behavior and deposition formation in course of drying and spreading of nanofluids, particularly containing surfactants, is still poor. In this paper, the evaporation dynamics of quantum dot-based nanofluids and evaporation-driven self-assembly in nanoco...

Nanofluids hold promise for a wide range of areas of industry. However, understanding of wetting behavior and deposition formation in course of drying and spreading of nanofluids, particularly containing surfactants, is still poor. In this paper, the evaporation dynamics of quantum dot-based nanofluids and evaporation-driven self-assembly in nanoco...

Wetting of surfaces with porous coating is relevant for a wide variety of technical applications, such as printing technologies and heat transfer enhancement. Imbibition and evaporation of liquids on surfaces covered with porous layers are responsible for significant improvement of cooling efficiency during drop impact cooling and flow boiling on s...

In this work a two‐step model to investigate a thin liquid film sheared by a turbulent gas flow is presented. In a first step, a direct numerical simulation of the gas phase is conducted. The turbulent shear stress at the lower wall is stored and used as a boundary condition for the long‐wave evolution of the liquid film, which is calculated in a s...

Liquid jet impingement is used in industries for cleaning or cooling the surfaces, since this process is characterized by high heat or mass transport rates. The impinging jet spreads radially outwards and creates a wall film flow, which is bounded by a hydraulic jump. The existing models describing the extent of the radial flow zone and the positio...

This study is aimed at experimental investigation of hydrodynamics and convective heat transfer in gravity and gas-driven thin liquid wall films. The liquid film has been annularly applied on a vertically aligned heated tube mounted in a flow channel. In the arranged two-phase flow domain, both the liquid film flow and co-current air flow were ther...

Wetting and spreading of surfactant solutions play an important role in many technical applications. In printing processes, the size of individual droplets is typically on the order of a few tens of microns. The purpose of this study is to develop a better understanding of the interaction between spreading and surfactant transport on these small le...

Gas-driven liquid films are a promising candidate for heat up and evaporation of liquids in an efficient way. Many industrial fields benefit of this type of treatment, because of an intensive heat transfer, such as upcoming modern combustion chambers, reboilers, condensers or cooling applications, while gas-driven films represent a complex interact...

Vesicles have recently found widespread use in applications such as conditioning of textiles, paper and hair, as well as transdermal drug delivery. The mode of treatment in several such cases involves the application of droplets of aqueous dispersions of vesicles onto dry porous substrates like paper and textiles. One of the factors which affects t...

This study focuses on the influence of the system pressure on pool boiling regimes on a microstructured surface compared to a smooth surface. The microstructured surface consists of copper wires with diameters and lengths of 1 and 20 µm, respectively. The saturation pressure of FC-72 is varied between 0.5 and 1.8 bar. Boiling curves are determined...

Zero-gravity distillation (ZGD) is one of the few ways to establish a small-scale distillation process. In contrast to conventional distillation columns, capillary forces, e.g. induced by metal foams, are exploited to ensure liquid flow in ZGD units. In order to strengthen the knowledge basis necessary for the ZGD equipment design, understanding of...

In this work, the dynamics of a thin liquid film sheared by a turbulent gas flow are investigated numerically. It is known that even a constant interfacial shear stress affects film stability and dynamics. We are interested in the effect of turbulent fluctuations on the film development. A combination of a direct numerical simulation (DNS) of the t...

The evaporation and deposit formation process of a hydrocarbon drop on a heated aluminium surface is experimentally investigated and compared to a physico-mathematical model. To analyze the effect of wall temperature on deposit formation, the experiments are conducted for three substrate temperatures below, one temperature close to and one temperat...

Organomodified silicones (OMS), which conventionally find use in textile finishing processes, have recently become a very interesting prospect in the field of fabric softeners. Here, we present OMS-based fabric softener formulations in the form of classical emulsion (droplet size ≈0.1 μm – 10 μm) and microemulsions (droplet size ≈5 nm–50 nm) using...

Phenomena of drop impact have been studied extensively due to their importance in many industrial applications like spray cooling, ink-jet printing and spray coating. Different outcomes of drop impact have been identified: deposition, corona and prompt splash, full and partial rebound. The outcome is determined by parameters like drop diameter and...

For many industrial applications it is important to control the outcome of drop impact. One of the means of passive control for such processes is in the application of smart, deformable, rheologically complex surfaces. In this experimental work an impact of a viscous Newtonian drop onto a substrate coated by a thin visco-elastic layer is investigat...

This paper examines the evolution and rupture of a thin liquid film evaporating on a structured wall and the concomitant heat and mass transport. The heat is supplied either from the side of the wall or from the hot ambient gas. An evolution equation for the film thickness is derived in the framework of the long-wave theory under the assumption tha...

Hypothesis: Colloidal deposition on porous substrates is a complex process influenced by both, (i) characteristics of colloidal permeation into porous substrates, and (ii) mechanism of colloidal deposition on solid surfaces. Such processes are quintessential to action of products such as hair conditioners and fabric softeners where the substrates...

The heat and mass transfer close to the apparent three-phase contact line is of tremendous importance in many evaporation processes. Despite the extremely small dimensions of this region referred to as the microregion compared to the macroscopic length scale of a boiling process, a considerable fraction of heat can be transferred in this region. Du...

A numerical method based on the Volume-of-Fluid approach has been used for simulating the simultaneous collision of two drops with a solid substrate. Heat transfer in the substrate and in the drop have been evaluated during the drop spreading and receding phases. The numerical model includes the liquid evaporation from the drop surface and especial...

Chemical reactions in thin liquid films are found in many industrial applications, e.g., in combustion chambers of internal combustion engines where a fuel film can develop on pistons or cylinder walls. The reactions within the film and the turbulent outer gas flow influence film stability and lead to film breakup, which in turn can lead to deposit...

An analytical approach is presented to describe pressure-driven streaming current (Istr) and streaming potential (Ustr) generation in geometrically complex samples for which the classical Helmholtz-Smoluchowski equation is known to be inaccurate. The new approach is valid under the same prerequisite conditions which are used for the development of...

We study the role of solid-liquid interface thermal resistance (Kapitza resistance) on the evaporation rate of droplets on a heated surface by using a multi-scale combination of molecular dynamics (MD) simulations and analytical continuum theory. We parameterize the nonbonded interaction potential between perfluorohexane (C6F14 ) and a face-centere...

Nanofiber coatings have shown a unique potential for heat transfer enhancement during drop impact cooling, nucleate boiling and flow boiling. In order to get insights into the mechanisms of heat transfer enhancement invoked by the nanofiber coating, we investigated evaporation of liquid in the vicinity of an apparent contact line of a single menisc...

In this study, the heat transfer in a granular medium due to a moving laser source is investigated numerically. A numerical model on laser energy absorption and its transport in granular media is presented. This process is especially relevant to laser melting/sintering of metal powders. The non-continuum approach is used to consider the discrete na...

A very simple numerical method is developed to determine the inter-particle radiation heat transfer in a granular powder bed. The method is completely independent of coordinate system and does not require any domain discretization. The solution procedure does not involve any matrix inversion, thus making it suitable candidate for radiation heat tra...

It has been recently shown that thermal treatment of polydimethylsiloxane (PDMS) films in air atmosphere leads to modification of wetting characteristics of the film surface. In the present work we studied the wettability and imbibition properties of substrates produced by thermal treatment of PDMS films of different thicknesses and elastic propert...

Sessile liquid droplets deposited on soft substrates may cause substrate deformation. The substrate elasticity affects the apparent contact angle and the spreading dynamics of the sessile drop. In the present work, a model for description of a droplet on an elastic substrate is developed using the disjoining pressure concept. A Finite Element Metho...

Deposition of vesicles on solid surfaces can in some cases result in the formation of assemblies of intact surface-bound vesicles known as supported vesicular layers (SVLs). Understanding the mechanism of SVL formation is thus important for effective utilization of vesicles in applications involving vesicle-substrate interactions such as drug deliv...

Hypothesis: Understanding the mechanism of intact vesicle deposition on solid surfaces is important for effective utilization of vesicles as active ingredient carriers in applications such as drug delivery and fabric softening. In this study, the deposition of large (davg=12μm) and small (davg=0.27μm) cationic vesicles of ditallowethylester dimeth...

To enhance heat transfer in forced convective boiling the mini-channel bottom was amended by nano-textured structures - periodic rectangular mats of electrospun polymer nanofibers. The fibers were about several hundreds of nanometer in diameter. The test fluid was FC-72. The flow in mini-channels contained trains of the Taylor bubbles. The role of...

In nucleate boiling two specific models are used to describe wall heat transfer to single bubbles: (i) The contact line model, in which evaporation close to the three-phase contact line is the dominating effect, and (ii) the microlayer model, in which evaporation of a thin liquid film below the bubble is the dominating effect. These models are disc...

Short-scale Marangoni flow in a film on an evenly heated horizontal wall with a structured surface is studied experimentally and numerically. The occurring two-dimensional convective rolls are fully visualized in the experiment for the first time, where a closed experimental environment allows to monitor the temperature and Biot number. For the num...

Non-isothermal liquid films are subject to short- and long-wave modes of Marangoni instability. The short-wave instability leads to the development of convection cells, whereas long-wave instability is one of the primary causes of the film rupture. In this paper different methods for modulation of Marangoni convection and Marangoni-induced interfac...

Wetting of porous layers plays an important role in natural phenomena and in technical applications, including cooling technologies, ink-jet printing, functionalization of textile fabric and 3D-printing. In many technically relevant processes the complex wetting phenomena govern the transport of heat, mass and (nano)particles. A review of recent ad...

In the present paper a 3D non-stationary two-sided mathematical model of joint motion of evaporating liquid film and cocurrent gas flow in a microchannel with local heating has been developed. This model takes into account a deformable gas-liquid interface, convective heat transfer in the liquid and the gas phases as well as temperature dependence...

The cooling effectiveness of spray cooling is strongly influenced by droplet size and velocity as well as by the fluid properties. To enhance the understanding of the entire process, first of all basic processes occurring in the spray have to be addressed. Therefore, in this study the heat transfer during a single drop impingement onto a dry, super...

Coalescence of viscous particles with solid cores plays an important role in chemical and pharmaceutical industry, in agriculture and in production technology. Coalescence of metal particles, which are partially melted due the laser heating, is an important mechanism responsible for densification of metal powder during selective laser sintering pro...

Heat and mass transfer at a droplet impinging on a hot wall is investigated experimentally and numerically. The experiments are conducted with refrigerant FC-72 within a saturated vapour atmosphere. The droplet dynamics and the heater temperature very close to the solid–fluid interface are captured with high spatial and temporal resolution. The bou...

Shear-driven liquid film flows can occur in several locations of fuel preparation systems, e.g. inside air-driven atomizers or in Lean Pre-mixing Pre-vaporizing (LPP) combustion chambers of modern gas turbines. In LPP chambers the liquid fuel is primary atomized by a pressure nozzle and sprayed onto a pre-filmer. Fine fuel droplets accumulate at th...

One of the most commonly used methods of liquid atomization is the spinning disk atomization. This technique makes use of centrifugal forces to create a thin liquid film spreading radially over a disk. The film flowing along the disk is mostly wavy. The waves have a negative influence on the drop size distribution in the atomization process. It is...

One of the most commonly used methods of liquid atomization is the rotary atomization. In this process a radially spreading thin liquid film is created on a surface of a rotating disk, due to centrifugal forces. The liquid flows over the disk edge and disintegrates. The liquid film is mostly wavy. The radially propagating waves induce fluctuations...

Thin gas-driven liquid films find numerous industrial applications. They are used for fuel preparation in airblast atomizers of modern gas turbines. Strong shear forces at the gas-liquid interface destabilize the liquid-gas interface and lead to development of interfacial waves. In this study, the heat transfer in liquid films driven by turbulent g...

The flow of thin falling liquid films is unstable to long-wave disturbances. The flow instability leads to development of waves at the liquid-gas interface. The wave patterns depend on the properties of the liquid, the Reynolds number, the plate inclination angle, and the distance from the film inlet. The effect of the waves on heat and mass transf...

Marangoni convection plays an important role in hydrodynamics of evaporating liquid films and sessile drops. Evaporation of liquid films induces unsteady nonuniform temperature distribution across the liquid layer and in a substrate. If the substrate is composed of parts with different thermal properties, the interface temperature distribution beco...

In pool boiling or flow boiling devices or e.g. during meniscus evaporation within capillary structures the local heat flux and evaporation rate at the position where the liquid–vapor interface meets the solid wall can be extremely high. This three-phase contact line region is characterized by a thin liquid film with a very low heat resistance. Dep...