scholarly journals Evaporation of a liquid sessile droplet subjected to forced convection

2021 ◽  
Vol 9 (5) ◽  
pp. 57-66
Author(s):  
A. Е. Korenchenko ◽  
A. A. Zhukova
Keyword(s):  
Gas Phase ◽  
Forced Convection ◽  
Mutual Influence ◽  
Density Wave ◽  
Sessile Droplet ◽  
Gaseous Media ◽  
Nonequilibrium Conditions ◽  
Rate Of Evaporation ◽  
Constant Contact Angle ◽  
The Mathematical Model

Experiments on measuring the rate of evaporation of liquid sessile droplets into air show that the rate of evaporation increases in the presence of forced convection flows. However, data on the effect of convection on evaporation are often contradictory and should be clarified. The paper presents a numerical analysis of evaporation from the surface of a water droplet subjected to forced convection in the gas phase. The drop is located on a smooth horizontal isothermal substrate; the mode with constant contact angle is considered. The shape of the drop has axial symmetry, the same for the velocities and pressure. Forced convection compatible with the symmetry conditions are represented by flows directed downward along the axis of the system and diverging along the sides near the drop and the substrate. The mathematical model is constructed for evaporation controlled by diffusion in the gas phase and takes into account surface tension, gravity, and viscosity in both media, buoyancy and Marangoni convection. The results indicate the existence of the mutual influence of liquid and gaseous media. Thus, a drop vibrates under the influence of movements in the atmosphere, which generates a density wave in the gas: the drop «sounds». The magnitude of the velocity in a liquid is 50 times less than the characteristic velocity in air. It is found that the evaporation rate does not change in the presence of forced convection flows, which contradicts most of the experimental works. The reason for the discrepancies is supposed to be the appearance of nonequilibrium conditions at the boundary of the condensed phase: under these conditions, the evaporation regime ceases to be diffusional.

Numerical modeling of the influence of bubbles on flow and heat transfer in the descending gas-liquid flow in a pipe

2012 ◽  
Vol 9 (1) ◽  
pp. 131-135
Author(s):  
M.A. Pakhomov
Keyword(s):  
Heat Transfer ◽  
Gas Phase ◽  
Liquid Flow ◽  
Bubble Diameter ◽  
Gas Content ◽  
Two Phase ◽  
Eulerian Description ◽  
Flow And Heat Transfer ◽  
Gas Liquid Flow ◽  
The Mathematical Model

The paper presents the results of modeling the dynamics of flow, friction and heat transfer in a descending gas-liquid flow in the pipe. The mathematical model is based on the use of the Eulerian description for both phases. The effect of a change in the degree of dispersion of the gas phase at the input, flow rate, initial liquid temperature and its friction and heat transfer rate in a two-phase flow. Addition of the gas phase causes an increase in heat transfer and friction on the wall, and these effects become more noticeable with increasing gas content and bubble diameter.

An experimental assessment of the evaporation correlations for natural, forced and combined convection regimes

2011 ◽  
Vol 226 (1) ◽  
pp. 145-153 ◽  
Author(s):  
A Jodat ◽  
M Moghiman
Keyword(s):  
Mixed Convection ◽  
Forced Convection ◽  
Evaporation Rate ◽  
Density Variation ◽  
Convection Regime ◽  
Combined Convection ◽  
Wide Range ◽  
The Difference ◽  
Rate Of Evaporation ◽  
Evaporation Models

In the present study, the applicability of widely used evaporation models (Dalton approach-based correlations) is experimentally investigated for natural, forced, and combined convection regimes. A series of experimental measurements are carried out over a wide range of water temperatures and air velocities for 0.01 ≤ Gr/Re2 ≤ 100 in a heated rectangular pool. The investigations show that the evaporation rate strongly depends on the convection regime's Gr/ Re2 value. The results show that the evaporation rate increases with the difference in vapour pressures over both forced convection (0.01 ≤ Gr/Re2 ≤ 0.1) and turbulent mixed convection regimes (0.15 ≤ Gr/Re2 ≤ 25). However, the escalation rate of evaporation decreases with Gr/ Re2 in the forced convection regime whereas in the turbulent mixed convection it increases. In addition, over the range of the free convection regime ( Gr/Re2 ≥ 25), the evaporation rate is affected not only by the vapour pressure difference but also by the density variation. A dimensionless correlation using the experimental data of all convection regimes (0.01 ≤ Gr/Re2 ≤ 100) is proposed to cover different water surface geometries and airflow conditions.

The Dissociation Equilibrium of Hydrogen and its Adsorption on Tungsten

1936 ◽  
Vol 32 (1) ◽  
pp. 152-157 ◽  
Author(s):  
J. K. Roberts
Keyword(s):  
Adsorption Isotherm ◽  
Statistical Method ◽  
Gas Phase ◽  
Approximation Formula ◽  
Dissociation Equilibrium ◽  
First Approximation ◽  
Adsorbed Atoms ◽  
Detailed Interpretation ◽  
Rate Of Evaporation ◽  
Detailed Balancing

The various processes occurring at the surface when hydrogen is adsorbed on tungsten are considered together with the dissociation equilibrium of hydrogen in the gas phase. The form of the adsorption isotherm is deduced from the principle of detailed balancing and is in agreement with that obtained by Fowler using a statistical method. A detailed interpretation of the experimental results now available shows that either (a) measurements of the rate of removal of the adsorbed film of oxygen on tungsten do not measure the rate of evaporation of oxygen atoms or (b) it is not possible to obtain a general first approximation formula giving the rate of evaporation of adsorbed atoms in terms of the heat of desorption. The desorption of hydrogen from tungsten is discussed and it is shown that the agreement between the temperature at which the film evaporates at an appreciable rate and that deduced from a desorption formula of the type mentioned in (b) assuming that the hydrogen evaporates as atoms must at present be regarded as a coincidence.

scholarly journals Young’s Equation vs. Sessile Drop Accelerometry: A Comparison Using the Interfacial Energies of Seven Polymer-water Systems

2018 ◽  
Author(s):  
Alfredo Calvimontes
Keyword(s):  
High Speed ◽  
Sessile Drop ◽  
Water Systems ◽  
Sessile Droplet ◽  
Droplet Shape ◽  
Drop Shape ◽  
Interfacial Energies ◽  
Balance Of Forces ◽  
Solid Liquid ◽  
The Mathematical Model

In this study, the values of the interfacial energies of seven different polymer-water systems obtained by Sessile Drop Accelerometry (SDACC) are compared with the values obtained by the Young’s-equation-based Owens-Wendt method. The SDACC laboratory instrument –a combination of a drop shape analyzer with high-speed camera and a microgravity tower- and the evaluation algorithms, are designed to measure the interfacial energies as a function of the geometrical changes of a sessile droplet shape due to the effect of “switching off” gravity during the experiment. The method bases on Thermodynamics of Interfaces and differs from the conventional aproach of the two hundred-years-old Young’s equation in that it assumes a thermodynamic equilibrium between interfaces, rather than a balance of forces on a point of the solid-liquid-gas contour line. A comparison of the mathematical model that supports the SDACC method with the widely accepted Young`s equation is discussed in detail in this study.

scholarly journals Controlling the metal-to-insulator relaxation of the metastable hidden quantum state in 1T-TaS2

2015 ◽  
Vol 1 (6) ◽  
pp. e1500168 ◽  
Author(s):  
Igor Vaskivskyi ◽  
Jan Gospodaric ◽  
Serguei Brazovskii ◽  
Damjan Svetin ◽  
Petra Sutar ◽  
...  
Keyword(s):  
Ground State ◽  
Electrical Resistance ◽  
Charge Density Wave ◽  
Density Wave ◽  
Fundamental Interest ◽  
Macroscopic Quantum ◽  
Nonequilibrium Conditions ◽  
Substrate Strain ◽  
Excitation Conditions ◽  
Optical Laser

Controllable switching between metastable macroscopic quantum states under nonequilibrium conditions induced either by light or with an external electric field is rapidly becoming of great fundamental interest. We investigate the relaxation properties of a “hidden” (H) charge density wave (CDW) state in thin single crystals of the layered dichalcogenide 1T-TaS2, which can be reached by either a single 35-fs optical laser pulse or an ~30-ps electrical pulse. From measurements of the temperature dependence of the resistivity under different excitation conditions, we find that the metallic H state relaxes to the insulating Mott ground state through a sequence of intermediate metastable states via discrete jumps over a “Devil’s staircase.” In between the discrete steps, an underlying glassy relaxation process is observed, which arises because of reciprocal-space commensurability frustration between the CDW and the underlying lattice. We show that the metastable state relaxation rate may be externally stabilized by substrate strain, thus opening the way to the design of nonvolatile ultrafast high-temperature memory devices based on switching between CDW states with large intrinsic differences in electrical resistance.

scholarly journals Numerical tracking of sorbent particles and distribution during gas desulfurization in pulverized coal-fired furnace

2017 ◽  
Vol 21 (suppl. 3) ◽  
pp. 759-769 ◽  
Author(s):  
Ivan Tomanovic ◽  
Srdjan Belosevic ◽  
Aleksandar Milicevic ◽  
Nenad Crnomarkovic ◽  
Dragan Tucakovic
Keyword(s):  
Gas Phase ◽  
Mutual Influence ◽  
Sulfur Removal ◽  
Pulverized Coal ◽  
Turbulent Dispersion ◽  
Boiler Furnace ◽  
Two Phase ◽  
Turbulence Modulation ◽  
Desulfurization Process ◽  
Sorbent Injection

Furnace sorbent injection for sulfur removal from flue gas presents a challenge, as the proper process optimization is of crucial importance in order to obtain both high sulfur removal rates and good sorbent utilization. In the simulations a two-phase gas-particle flow is considered. Pulverized coal and calcium-based sorbent particles motion is simulated inside of the boiler furnace. It is important to determine trajectories of particles in the furnace, in order to monitor the particles heat and concentration history. A two-way coupling of the phases is considered ? influence of the gas phase on the particles, and vice versa. Particle-to-particle collisions are neglected. Mutual influence of gas and dispersed phase is modeled by corresponding terms in the transport equations for gas phase and the equations describing the particles turbulent dispersion. Gas phase is modeled in Eulerian field, while the particles are tracked in Lagrangian field. Turbulence is modeled by the standard k-? model, with additional terms for turbulence modulation. Distribution, dispersion and residence time of sorbent particles in the furnace have a considerable influence on the desulfurization process. It was shown that, by proper organization of process, significant improvement considering emission reduction can be achieved.

scholarly journals TO THE QUESTION OF OPTIMISING THE DYNAMIC CHARACTERISTICS OF A VIBRATIONAL TREE UPROOTING MACHINE

2018 ◽  
Vol 45 (2) ◽  
pp. 149-157
Author(s):  
A. R. Mikhitarov ◽  
V. L. Savich ◽  
V. K. Khegai
Keyword(s):  
Mathematical Model ◽  
Root System ◽  
Dynamic Characteristics ◽  
Mutual Influence ◽  
Frequency Characteristics ◽  
Frequency Range ◽  
System A ◽  
Forest Sites ◽  
Tree Uprooting ◽  
The Mathematical Model

Objectives Following logging operations, tree stumps remain in the site of the former forest.While these may be uprooted by special machines in the course of forestry operations, the use of heavy forestry machines operated repeatedly on the forest sites not only lead to soil erosion, but also to considerable financial expense. Consequently, the development of machines combining cutting (logging) and uprooting operations – that is, uprooting the trees along with their roots – are of a great interest. As research has shown, the main disadvantages of the use of such technology by “conventional” logging or forestry machines are their excessive loading and energy intensity. The aim of the research is to investigate means of eliminating these drawbacks by using vibration.Methods The article deals with theproblem of ensuring the effectiveness of the vibration application – in particular, torsional vibrations, used to stub trees together with their roots. To solve this problem, a mathematical model of the “machine-tree-soil-root system” system was developed, which takes into account the mutual influence of the dynamic characteristics of the machine’s technological equipment and tree and soil-root system, which allows a rational (optimal) frequency range of vibration equipment to be selected by analysing the amplitude-frequency characteristics of a given system. To analyse the amplitude-frequency characteristics of a mechanical system, the Euler-Lagrange equationswere used.Results Based on the mathematical model of the “machine-tree-soil-root system (SRS)” system and an analysis of the amplitude-frequency characteristics of a given system, a rational range of vibration frequencies was determined. As shown by analysis, the work of vibrational equipment in a given frequency range can significantly reduce the dynamic loading of the machine and at the same time create appropriate conditions for the effective destruction of the soil-root system.Conclusion The proposed method allows the rational values of the frequency characteristic of vibration equipment for each calculated tree to be found depending on the soil type and the basic machine.

scholarly journals Numerical Analysis of an Impinging Jet Reactor for the CVD and Gas-Phase Nucleation of Titania

1993 ◽  
Vol 335 ◽  
Author(s):  
Suleyman A. Gokoglu ◽  
G. D. Stewart ◽  
J. Collins ◽  
D. E. Rosner
Keyword(s):  
Gas Phase ◽  
Impinging Jet ◽  
Gas Phase Reactions ◽  
Reactor Model ◽  
Deposition Rates ◽  
Numerical Predictions ◽  
Model Predictions ◽  
Phase Nucleation ◽  
Chemically Reacting ◽  
The Mathematical Model

AbstractWe model a cold-wall atmospheric pressure impinging jet reactor to study the CVD and gas-phase nucleation of TiO2 from a titanium tetra-iso-propoxide (TTIP)/oxygen dilute source gas mixture in nitrogen. The mathematical model uses the computational code FIDAP and complements our recent asymptotic theory for high activation energy gas-phase reactions in thin chemically reacting sublayers. The numerical predictions highlight deviations from ideality in various regions inside the experimental reactor. Model predictions of deposition rates and the onset of gas-phase nucleation compare favorably with experiments. Although variable property effects on deposition rates are not significant (∼11% at 1000K), the reduction of rates due to Soret transport is substantial (∼75% at 1000K).

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