scholarly journals Liquid Films Falling Down a Vertical Fiber: Modeling, Simulations and Experiments

Fluids ◽  
2021 ◽  
Vol 6 (8) ◽  
pp. 281
Author(s):  
Yadong Ruan ◽  
Ali Nadim ◽  
Lekha Duvvoori ◽  
Marina Chugunova
Keyword(s):  
Velocity Profile ◽  
Liquid Film ◽  
Control Volume ◽  
Plug Flow ◽  
Traveling Wave Solutions ◽  
Liquid Films ◽  
Physical Experiments ◽  
Theoretical Predictions ◽  
Viscous Liquid Film ◽  
Linear Drag

We provide a new framework for analyzing the flow of an axisymmetric liquid film flowing down a vertical fiber, applicable to fiber coating flows and those in similar geometries in heat exchangers, water treatment, and desalination processes. The problem considered is that of a viscous liquid film falling under the influence of gravity and surface tension on a solid cylindrical fiber. Our approach is different from existing ones in that we derive our mathematical model by using a control-volume approach to express the conservation of mass and axial momentum in simple and intuitively appealing forms, resulting in a pair of equations that are reminiscent of the Saint-Venant shallow-water equations. Two versions of the model are obtained, one assuming a plug-flow velocity profile with a linear drag force expression, and the other using the fully-developed laminar velocity profile for a locally uniform film to approximate the drag. These can, respectively, model high- and low-Reynolds number regimes of flow. Linear stability analyses and fully nonlinear numerical simulations are presented that show the emergence of traveling wave solutions representing chains of identical droplets falling down the fiber. Physical experiments with safflower oil on a fishing line are also undertaken and match the theoretical predictions from the laminar flow model well when machine learning methods are used to estimate the parameters.

scholarly journals Visualization of Surface Acoustic Waves in Thin Liquid Films

2016 ◽  
Vol 6 (1) ◽  
Author(s):  
R. W. Rambach ◽  
J. Taiber ◽  
C. M. L. Scheck ◽  
C. Meyer ◽  
J. Reboud ◽  
...  
Keyword(s):  
Liquid Film ◽  
Acoustic Waves ◽  
Low Cost ◽  
Thin Liquid Film ◽  
Surface Acoustic Waves ◽  
Liquid Films ◽  
Theoretical Description ◽  
Propagation Path ◽  
Microfluidic Channels ◽  
Potential Applications

Abstract We demonstrate that the propagation path of a surface acoustic wave (SAW), excited with an interdigitated transducer (IDT), can be visualized using a thin liquid film dispensed onto a lithium niobate (LiNbO3) substrate. The practical advantages of this visualization method are its rapid and simple implementation, with many potential applications including in characterising acoustic pumping within microfluidic channels. It also enables low-cost characterisation of IDT designs thereby allowing the determination of anisotropy and orientation of the piezoelectric substrate without the requirement for sophisticated and expensive equipment. Here, we show that the optical visibility of the sound path critically depends on the physical properties of the liquid film and identify heptane and methanol as most contrast rich solvents for visualization of SAW. We also provide a detailed theoretical description of this effect.

Dynamics of Developing Laminar Non-Newtonian Falling Liquid Films With Free Surface

1978 ◽  
Vol 45 (1) ◽  
pp. 19-24 ◽  
Author(s):  
V. Narayanamurthy ◽  
P. K. Sarma
Keyword(s):  
Liquid Film ◽  
Power Law ◽  
Mathematical Formulation ◽  
Liquid Films ◽  
Interfacial Shear ◽  
Newtonian Liquid ◽  
Power Law Model ◽  
Falling Liquid Film ◽  
Falling Liquid Films ◽  
Special Case

The dynamics of accelerating, laminar non-Newtonian falling liquid film is analytically solved taking into account the interfacial shear offered by the quiescent gas adjacent to the liquid film under adiabatic conditions of both the phases. The results indicate that the thickness of the liquid film for the assumed power law model of the shear deformation versus the shear stress is influenced by the index n, the modified form of (Fr/Re). The mathematical formulation of the present analysis enables to treat the problem as a general type from which the special case for Newtonian liquid films can be derived by equating the index in the power law to unity.

Study of the Fluid Dynamics of Thin Liquid Films Flowing Down a Vertical String With Counterflow of Gas

2015 ◽  
Author(s):  
Zezhi Zeng ◽  
Gopinath Warrier ◽  
Y. Sungtaek Ju
Keyword(s):  
Heat Transfer ◽  
Fluid Dynamics ◽  
Film Thickness ◽  
Liquid Film ◽  
Direct Contact ◽  
High Speed ◽  
Small Diameter ◽  
Liquid Films ◽  
Thin Liquid Films ◽  
Liquid Coolant

Direct-contact heat transfer between a falling liquid film and a gas stream yield high heat transfer rates and as such it is routinely used in several industrial applications. This concept has been incorporated by us into the proposed design of a novel heat exchanger for indirect cooling of steam in power plants. The DILSHE (Direct-contact Liquid-on-String Heat Exchangers) module consists of an array of small diameter (∼ 1 mm) vertical strings with hot liquid coolant flowing down them due to gravity. A low- or near-zero vapor pressure liquid coolant is essential to minimize/eliminate coolant loss. Consequently, liquids such as Ionic Liquids and Silicone oils are ideal candidates for the coolant. The liquid film thickness is of the order of 1 mm. Gas (ambient air) flowing upwards cools the hot liquid coolant. Onset of fluid instabilities (Rayleigh-Plateau and/or Kapitza instabilities) result in the formation of a liquid beads, which enhance heat transfer due to additional mixing. The key to successfully designing and operating DILSHE is understanding the fundamentals of the liquid film fluid dynamics and heat transfer and developing an operational performance map. As a first step towards achieving these goals, we have undertaken a parametric experimental and numerical study to investigate the fluid dynamics of thin liquid films flowing down small diameter strings. Silicone oil and air are the working fluids in the experiments. The experiments were performed with a single nylon sting (fishing line) of diameter = 0.61 mm and height = 1.6 m. The inlet temperature of both liquid and air were constant (∼ 20 °C). In the present set of experiments the variables that were parametrically varied were: (i) liquid mass flow rate (0.05 to 0.23 g/s) and (ii) average air velocity (0 to 2.7 m/s). Visualization of the liquid flow was performed using a high-speed camera. Parameters such as base liquid film thickness, liquid bead shape and size, velocity (and hence frequency) of beads were measured from the high-speed video recordings. The effect of gas velocity on the dynamics of the liquid beads was compared to data available in the open literature. Within the range of gas velocities used in the experiments, the occurrence of liquid hold up and/or liquid blow over, if any, were also identified. Numerical simulations of the two-phase flow are currently being performed. The experimental results will be invaluable in validation/refinement of the numerical simulations and development of the operational map.

Performing Fourier Transform on a Velocity Profile From Atmospheric Turbulence Studies

2021 ◽  
Author(s):  
Richard Adansi ◽  
Jose Terrazas ◽  
Arturo Rodriguez ◽  
V. M. Krushnarao Kotteda ◽  
Vinod Kumar ◽  
...  
Keyword(s):  
Fourier Transform ◽  
Velocity Profile ◽  
Size Distribution ◽  
Atmospheric Turbulence ◽  
Situational Awareness ◽  
Control Volume ◽  
The United States ◽  
Vertical Distance ◽  
Large Eddy ◽  
Computational Fluid Dynamics Cfd

Abstract Atmospheric Turbulence poses a challenge to land-based observatories operated by the United States Air Force (USAF) tasked with space situational awareness. By developing new methods for quantifying Turbulence, we intend to provide increased USAF capability in this domain. Current models for quantifying atmospheric Turbulence include Kolmogorov and Non-Kolmogorov methods. Through the nature of Fourier Transform, sinusoidal function, it is possible to determine the frequency at which velocities occur in a specified vertical distance and eventually determine eddy size in a control volume. First, an ANSYS Computational Fluid Dynamics (CFD) model will be created to simulate atmospheric Turbulence in a defined control volume. The simulation will include a one-dimensional flow over a flat plate. The data we acquired from the simulation were used to derive an equation relating the velocity to the vertical distance (velocity profile). We will perform a regression analysis to fit data from Large-Eddy Simulations (LES) and apply Fourier transformation from a time domain to a frequency domain. The objective is to use Fourier transform analysis to determine eddy size distribution and turbulent cascade dissipation in a control volume by analyzing the frequency of velocities. By calculating such eddy size distribution, we may quantify Turbulence in said control volume and compare results with the traditional Kolmogorov method.

Transient torque in stirred tanks

2017 ◽  
Vol 831 ◽  
pp. 554-578 ◽  
Author(s):  
K. Steiros
Keyword(s):  
Control Volume ◽  
Transient Dynamics ◽  
Momentum Balance ◽  
Shaft Speed ◽  
Body Rotation ◽  
Order Model ◽  
Stirred Tanks ◽  
Solid Body Rotation ◽  
Torque Measurements ◽  
Theoretical Predictions

The transient dynamics of stirred tanks whose impeller speed undergoes smooth or step changes is investigated. First, a low-order model is developed, linking the impeller torque with the ‘extent’ of the solid-body rotation in the tank, derived from an angular momentum balance in a control volume around the impeller. Utilisation of this model enables the prediction of the torque ‘spike’ appearing after an impulsive change of the shaft speed, and of the torque evolution during a quasi-steady transition. For the case of a small impulsive change in the shaft speed, a characteristic spin-up time is also proposed. Torque measurements performed in an unbaffled stirred tank show considerable agreement with the theoretical predictions.

scholarly journals Gravity-driven thin liquid films with insoluble surfactant: smooth traveling waves

2007 ◽  
Vol 18 (6) ◽  
pp. 679-708 ◽  
Author(s):  
RACHEL LEVY ◽  
MICHAEL SHEARER ◽  
THOMAS P. WITELSKI
Keyword(s):  
Free Surface ◽  
Traveling Waves ◽  
Surfactant Concentration ◽  
Piecewise Linear ◽  
Traveling Wave Solutions ◽  
Liquid Films ◽  
Insoluble Surfactant ◽  
Small Parameters ◽  
Gravity Driven ◽  
The One

The flow of a thin layer of fluid down an inclined plane is modified by the presence of insoluble surfactant. For any finite surfactant mass, traveling waves are constructed for a system of lubrication equations describing the evolution of the free-surface fluid height and the surfactant concentration. The one-parameter family of solutions is investigated using perturbation theory with three small parameters: the coefficient of surface tension, the surfactant diffusivity, and the coefficient of the gravity-driven diffusive spreading of the fluid. When all three parameters are zero, the nonlinear PDE system is hyperbolic/degenerate-parabolic, and admits traveling wave solutions in which the free-surface height is piecewise constant, and the surfactant concentration is piecewise linear and continuous. The jumps and corners in the traveling waves are regularized when the small parameters are nonzero; their structure is revealed through a combination of analysis and numerical simulation.

A comparative study on the breakup of Newtonian and viscoelastic liquid films

2018 ◽  
Vol 32 (12n13) ◽  
pp. 1840032
Author(s):  
Lijuan Qian ◽  
Shaobo Song ◽  
Lisha Jiang ◽  
Xiaolu Li ◽  
Jianzhong Lin
Keyword(s):  
Liquid Film ◽  
High Speed ◽  
Liquid Films ◽  
Viscoelastic Liquid ◽  
Ligament Length ◽  
Time Resolved ◽  
Liquid Bubble ◽  
Mean Size ◽  
The Difference ◽  
The Stability

The breakup of viscoelastic liquid films are investigated experimentally and analytically. The breakup phenomena of viscoelastic liquid film are recorded by the time resolved high speed camera. Video images reveal the difference behavior of liquid bubble breakup for Newtonian and viscoelastic liquid. For the Newtonian liquid, cylindrical ligaments are stretched into droplets with large distributions of drop size. For the viscoelastic liquid, the pinch-off point is located on the liquid connections to the nozzle and finally the main part of the ligament no longer elongates. Furthermore, a dispersion relation based on the stability analysis is involved to predict the ligament length and drop mean size after breakup for liquid film. The calculated ligament length is validated by the measured drop mean size at higher air-to-liquid mass flow ratio.

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