Three-dimensional surfactant-covered flows of thin liquid films on rotating cylinders

2018 ◽  
Vol 844 ◽  
pp. 61-91 ◽  
Author(s):  
Weihua Li ◽  
Satish Kumar
Keyword(s):  
Free Surface ◽  
Flow Visualization ◽  
Evolution Equations ◽  
Thin Liquid Film ◽  
Three Dimensional ◽  
Axial Direction ◽  
Liquid Films ◽  
Practical Applications ◽  
Rotation Rates ◽  
Visualization Experiments

The coating of discrete objects is an important but poorly understood step in the manufacturing of a broad variety of products. An important model problem is the flow of a thin liquid film on a rotating cylinder, where instabilities can arise and compromise coating uniformity. In this work, we use lubrication theory and flow visualization experiments to study the influence of surfactant on these flows. Two coupled evolution equations describing the variation of film thickness and concentration of insoluble surfactant as a function of time, the angular coordinate and the axial coordinate are solved numerically. The results show that surface-tension forces arising from both axial and angular variations in the angular curvature drive flows in the axial direction that tend to smooth out free-surface perturbations and lead to a stable speed window in which axial perturbations do not grow. The presence of surfactant leads to Marangoni stresses that can cause the stable speed window to disappear by driving flow that opposes the stabilizing flow. In addition, Marangoni stresses tend to reduce the spacing between droplets that form at low rotation rates, and reduce the growth rate of rings that form at high rotation rates. Flow visualization experiments yield observations that are qualitatively consistent with predictions from linear stability analysis and the simulation results. The visualizations also indicate that surfactants tend to suppress dripping, slow the development of free-surface perturbations, and reduce the shifting and merging of rings and droplets, allowing more time for solidifying coatings in practical applications.

Experimental Analysis and Flow Visualization of a Thin Liquid Film on a Stationary and Rotating Disk

1991 ◽  
Vol 113 (1) ◽  
pp. 73-80 ◽  
Author(s):  
S. Thomas ◽  
A. Faghri ◽  
W. Hankey
Keyword(s):  
Free Surface ◽  
Film Thickness ◽  
Liquid Film ◽  
Flow Visualization ◽  
Thin Liquid Film ◽  
Rotating Disk ◽  
Radial Spreading ◽  
Frictional Forces ◽  
The Mean ◽  
The Waves

The mean thickness of a thin liquid film of deionized water with a free surface on a stationary and rotating horizontal disk has been measured with a nonobtrusive capacitance technique. The measurements were taken when the rotational speed ranged from 0–300 rpm and the flow rate varied from 7.0–15.0 lpm. A flow visualization study of the thin film was also performed to determine the characteristics of the waves on the free surface. When the disk was stationary, a circular hydraulic jump was present on the disk. Upstream from the jump, the film thickness was determined by the inertial and frictional forces on the fluid, and the radial spreading of the film. The surface tension at the edge of the disk affected the film thickness downstream from the jump. For the rotating disk, the film thickness was dependent upon the inertial and frictional forces near the center of the disk and the centrifugal forces near the edge of the disk.

THE ANALYSIS OF THE BINARY HOMOGENEOUS SOLUTION FILM BEHAVIOR UNDER THERMAL ACTION

2021 ◽  
Vol 7 (2) ◽  
pp. 43-59
Author(s):  
Kseniia A. BORODINA
Keyword(s):  
Free Surface ◽  
Local Heating ◽  
Thin Liquid Film ◽  
Volatile Component ◽  
Experimental Studies ◽  
Homogeneous Solution ◽  
Liquid Films ◽  
Surface Shape ◽  
Pressure Jump ◽  
Capillary Flows

Studying the processes occurring in liquid films under thermal influence allows improving a variety of technological systems, since a thin layer aids in providing a high intensity of heat and mass transfer and a significant surface of phase contact with a minimum liquid consumption. Many Russian and international works wrote about theoretical and experimental studies of film flows, though paid insufficient attention to the study of the behavior of films of a binary homogeneous solution. This article studies the behavior of a thin liquid film containing a volatile component during local heating of a solid horizontal substrate. The presented calculations were performed for an aqueous solution of isopropanol. The author describes the formation of a specific surface shape, which is formed with a sufficient increase in the substrate temperature and the initial film thickness — the so-called “liquid drop”, separated from the main volume of the liquid by a thin extended layer, which is explained by the sequential occurrence of thermal and concentration-capillary flows. The results show a significant influence of the Laplace pressure jump on the character of the entire process. In addition, the cooling of the substrate leads to multidirectional flows, but in the opposite directions. The analysis of the functions of the temperature of the film free surface, the volatile component concentration in the solution, and the vapor density over the free surface at different times is carried out. The velocity field in liquid and gas during the evolution of thermocapillary and concentration-capillary flows is illustrated.

Computational Methods With Vortices—The 1988 Freeman Scholar Lecture

1989 ◽  
Vol 111 (1) ◽  
pp. 5-52 ◽  
Author(s):  
Turgut Sarpkaya
Keyword(s):  
Computational Methods ◽  
Evolution Equations ◽  
Operator Splitting ◽  
Three Dimensional ◽  
Separated Flow ◽  
Body Representation ◽  
Vortex Sheet ◽  
Personal View ◽  
Discrete Vortex ◽  
Practical Applications

A comprehensive review is presented of the computational methods based upon Helmholtz’s powerful concepts of vortex dynamics, making use of Lagrangian or mixed Lagrangian-Eulerian schemes, the Biot-Savart law or the Vortex-in-Cell methods. The ingenious approximations and smoothing schemes developed in search of predictive models, qualitative solutions, new insights, or just some inspiration in the simulation of often two-dimensional, occasionally three-dimensional, and almost always incompressible fluids are described in detail. One is forewarned at the onset that chaos awaits at the end of the road. The challenge is to produce results in the face of ever accumulating errors within a time scale appropriate for the investigation. The review is organized around two major sections: Theoretical foundations and practical applications of vortex methods. The first covers topics such as vorticity and laws of transportation, evolution equations for a vortex sheet, real vortices and instabilities, Biot-Savart law, smoothing techniques (cutoff schemes, amalgamation of vortices, subvortex methods), cloud-in-cell or vortex-in-cell methods, body representation (Routh’s rule, surface singularity distributions), operator splitting and the random walk method (description and convergence), and asymmetry introduction. The next section covers contra flowing streams, vortical flows in aerodynamics (vortex sheet roll-up; slender-body, two-vortex, multi-discrete vortex, and segment or panel methods; three-dimensional flow models, and vortex-lattice methods), separated flow about cylindrical bodies (circular cylinder, sharp-edged bodies, arbitrarily-shaped bodies), general three-dimensional flows (vortex rings, turbulent spots, temporally and spatially-growing shear layers, and other applications (vortex-blade interactions, combustion phenomena, acoustics, contour dynamics, interaction of line vortices, chaos, and turbulence). The review is concluded with a brief comparison of these methods with others used in computational fluid dynamics and a personal view of their future prospects.

Investigation and Analysis of the Flow Field Induced by a Symmetrical Suction Elbow at the Pump Inlet

2019 ◽  
Author(s):  
Sebastian Muntean ◽  
Alin Ilie Bosioc ◽  
Ionel Aurel Drăghici ◽  
Liviu Eugen Anton
Keyword(s):  
Flow Field ◽  
Cross Section ◽  
Three Dimensional ◽  
Axial Direction ◽  
Numerical Results ◽  
Vortex Center ◽  
Practical Applications ◽  
Curved Pipes ◽  
Annular Cross Section ◽  
Pump Inlet

Abstract The pump inlet casing deflects the fluid flow from the inlet pipe, mainly arranged normally to the axis, into the axial direction. The pump inlet casing can take a large variety of geometrical shapes from curved pipes to three-dimensional elbows. The hydrodynamic field induced by symmetrical suction elbow (SSE) at the pump inlet is experimentally investigated in order to quantify it effects at the pump inlet. The pump test rig and the experimental setup are detailed. A SSE model is installed at the pump inlet. Laser Doppler Velocimetry (LDV) measurements are performed on the annular cross section located at the pump inlet. As a result, the map of the velocity field is determined quantifying the non-uniformities induced by SSE. Next, the full 3D turbulent numerical investigation of the flow in the SSE is performed. The numerical results on the annular cross section are qualitatively and quantitatively validated against LDV data. A good agreement between numerical results and experimental data is obtained. The hydrodynamic flow structure with several pairs of vortices is identified examining the vorticity field. However, two pairs of vortices with largest contribution to the flow non-uniformity are examined. Three parameters are considered to quantify the evolution of each vortex center: two geometrical quantities (e.g. the radial and angular coordinates) and one hydrodynamic (the magnitude of vorticity). The largest values of the vorticity magnitude are identified in the center of both vortices located behind the shaft. The 3D distribution of the vortex core filaments is visualized. As a result, the 3D geometry of the SSE and the pump shaft are identified as the main sources of the flow non-uniformity at the pump inlet. This deep analysis of the 3D flow field induced by the SSE paves the way towards an improved geometry with practical applications to real pump and pump-turbines.

scholarly journals Effects of Gaps Between Side-Walls and60∘Ribs on the Heat Transfer and Rib Induced Secondary Flow Inside a Stationary and Rotating Cooling Channel

2001 ◽  
Vol 7 (6) ◽  
pp. 425-433
Author(s):  
Robert Kiml ◽  
Sadanari Mochizuki ◽  
Akira Murata
Keyword(s):  
Heat Transfer ◽  
Flow Visualization ◽  
Secondary Flow ◽  
Three Dimensional ◽  
Local Heat Transfer ◽  
Local Heat ◽  
Cooling Channel ◽  
Three Dimensional Flow ◽  
Side Walls ◽  
Visualization Experiments

The present study investigates the effects of gaps between the side-walls and60∘ribs on the local heat transfer distribution between two consecutive ribs. The heat transfer and flow visualization experiments were carried out inside a straight rib-roughened duct with the ribs mounted on two opposite side walls with and without the gaps. The results showed that the existence of the gaps appreciably enhances the Nu in the area between two consecutive ribs. It is caused by (1) the introduction of the fresh air through the gaps into this region, and (2) the improvement of the three-dimensional flow structure in the area between the two ribs.

Prediction of Ship Motions Via a Three-Dimensional Time-Domain Method Following a Quad-Tree Adaptive Mesh Technique

2020 ◽  
Vol 27 (1) ◽  
pp. 29-38
Author(s):  
Teng Zhang ◽  
Junsheng Ren ◽  
Lu Liu
Keyword(s):  
Free Surface ◽  
Incident Wave ◽  
Time Domain ◽  
Three Dimensional ◽  
Adaptive Mesh ◽  
Wave Profile ◽  
Time Domain Method ◽  
Ship Motions ◽  
Quad Tree ◽  
Mesh Technique

AbstractA three-dimensional (3D) time-domain method is developed to predict ship motions in waves. To evaluate the Froude-Krylov (F-K) forces and hydrostatic forces under the instantaneous incident wave profile, an adaptive mesh technique based on a quad-tree subdivision is adopted to generate instantaneous wet meshes for ship. For quadrilateral panels under both mean free surface and instantaneous incident wave profiles, Froude-Krylov forces and hydrostatic forces are computed by analytical exact pressure integration expressions, allowing for considerably coarse meshes without loss of accuracy. And for quadrilateral panels interacting with the wave profile, F-K and hydrostatic forces are evaluated following a quad-tree subdivision. The transient free surface Green function (TFSGF) is essential to evaluate radiation and diffraction forces based on linear theory. To reduce the numerical error due to unclear partition, a precise integration method is applied to solve the TFSGF in the partition computation time domain. Computations are carried out for a Wigley hull form and S175 container ship, and the results show good agreement with both experimental results and published results.

Three-dimensional Graphene Coated Shape Memory Polyurethane Foam with Fast Responsive Performance

2021 ◽  
Author(s):  
Tianjiao Wang ◽  
Jun Zhao ◽  
Chuanxin Weng ◽  
Tong Wang ◽  
Yayun Liu ◽  
...  
Keyword(s):  
Shape Memory ◽  
Polyurethane Foam ◽  
Three Dimensional ◽  
Shape Memory Polymers ◽  
Practical Applications ◽  
External Stimuli ◽  
Shape Memory Polyurethane

Shape memory polymers (SMPs) that change shapes as designed by external stimuli have become one of the most promising materials as actuators, sensors, and deployable devices. However, their practical applications...

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