Transient Droplet Heating at High Peclet Number

1983 ◽  
Vol 105 (1) ◽  
pp. 83-88 ◽  
Author(s):  
H. A. Dwyer ◽  
R. J. Kee ◽  
P. K. Barr ◽  
B. R. Sanders
Keyword(s):  
Peclet Number ◽  
Good Accuracy ◽  
Reynolds Numbers ◽  
Adaptive Grids ◽  
Transient Heating ◽  
Low Reynolds Numbers ◽  
Péclet Number ◽  
Future Studies ◽  
Transient Period ◽  
Initial Heating

The transient heating of a spherical liquid particle at high Peclet number has been calculated with the use of adaptive grids for low Reynolds numbers. The use of adaptive grids greatly enhances the efficiency of the calculations and allows for the large Peclet numbers to be studied. The results of the calculations show that the transient period of internal isotherm redistribution represents a significant part of the droplet total heating. Even for the Pe = 1600 case, the initial heating period caused more than 50 percent of particle heating, and the asymptotic heating results cannot be used with good accuracy. The methods employed in the study have great potential, and will be applied to unsteady droplet evaporization and burning in future studies.

scholarly journals Turbulent flows in channels and pipes

2007 ◽  
Vol 29 (3) ◽  
pp. 385-396
Author(s):  
Khanh Le Chau
Keyword(s):  
Variational Principle ◽  
Viscous Fluid ◽  
Turbulent Flows ◽  
Good Accuracy ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Pipe Flows ◽  
High Reynolds Numbers ◽  
Friction Factors ◽  
High Reynolds

A variational principle for channel and pipe flows of incompressible viscous fluid is proposed. For low Reynolds numbers this variational principle reduces to the principle of minimum dissipation. For high Reynolds numbers it enables one to calculate the velocity profiles and the corresponding friction factors with reasonably good accuracy.

scholarly journals Surfactant-loaded capsules as Marangoni microswimmers at the air–water interface: Symmetry breaking and spontaneous propulsion by surfactant diffusion and advection

2021 ◽  
Vol 44 (2) ◽  
Author(s):  
Hendrik Ender ◽  
Ann-Kathrin Froin ◽  
Heinz Rehage ◽  
Jan Kierfeld
Keyword(s):  
Symmetry Breaking ◽  
Peclet Number ◽  
Reynolds Numbers ◽  
Water Soluble ◽  
Swimming Velocity ◽  
Water Interface ◽  
Péclet Number ◽  
Air Interface ◽  
Alginate Capsules ◽  
Air Water Interface

Abstract We present a realization of a fast interfacial Marangoni microswimmer by a half-spherical alginate capsule at the air–water interface, which diffusively releases water-soluble spreading molecules (weak surfactants such as polyethylene glycol (PEG)), which act as “fuel” by modulating the air–water interfacial tension. For a number of different fuels, we can observe symmetry breaking and spontaneous propulsion although the alginate particle and emission are isotropic. The propulsion mechanism is similar to soap or camphor boats, which are, however, typically asymmetric in shape or emission to select a swimming direction. We develop a theory of Marangoni boat propulsion starting from low Reynolds numbers by analyzing the coupled problems of surfactant diffusion and advection and fluid flow, which includes surfactant-induced fluid Marangoni flow, and surfactant adsorption at the air–water interface; we also include a possible evaporation of surfactant. The swimming velocity is determined by the balance of drag and Marangoni forces. We show that spontaneous symmetry breaking resulting in propulsion is possible above a critical dimensionless surfactant emission rate (Peclet number). We derive the relation between Peclet number and swimming speed and generalize to higher Reynolds numbers utilizing the concept of the Nusselt number. The theory explains the observed swimming speeds for PEG–alginate capsules, and we unravel the differences to other Marangoni boat systems based on camphor, which are mainly caused by surfactant evaporation from the liquid–air interface. The capsule Marangoni microswimmers also exhibit surfactant-mediated repulsive interactions with walls, which can be qualitatively explained by surfactant accumulation at the wall. Graphic Abstract

HAUSDORFF DERIVATIVE MODEL FOR CHARACTERIZATION OF NON-FICKIAN MIXING IN FRACTAL POROUS MEDIA

Fractals ◽  
2019 ◽  
Vol 27 (04) ◽  
pp. 1950063 ◽  
Author(s):  
YINGJIE LIANG ◽  
ZHI DOU ◽  
ZHIFANG ZHOU ◽  
WEN CHEN
Keyword(s):  
Decay Rate ◽  
Peclet Number ◽  
Radioactive Tracer ◽  
Fickian Diffusion ◽  
Scalar Dissipation ◽  
Scalar Dissipation Rate ◽  
Péclet Number ◽  
Future Studies ◽  
Structure Changes

This study investigates the scalar dissipation rate (SDR) and dilution index of non-Fickian mixing by using the Hausdorff derivative model for conservative and first-order decaying tracers under different boundary conditions. The expressions of SDR and dilution index are derived based on the analytical solution of the Hausdorff derivative model, in which the time and space Hausdorff derivative orders, respectively capture the complexity in transport trajectory and transport scale. The properties of SDR and dilution index are discussed for different cases of Peclet number, decaying rate of the radioactive tracer, and Hausdorff derivative order, respectively. We find that the SDR of non-Fickian mixing decays more slowly than that of the Fickian diffusion, and the time scale deviates from [Formula: see text]. The evolution of the SDR has a sharp peak and decays very fast to zero when Peclet number is large. For the radioactive tracer, the larger values of decay rate, the smaller values of SDR, which decays faster to zero. The Hausdorff derivative model with larger Peclet number leads to larger dilution index. The dilution index is larger for smaller decay rate before reaching the equilibrium state. Consequently, the two metrics can be satisfactorily used to describe non-Fickian mixing based on the Hausdorff derivative model. Future studies should be designed to examine the evolution of SDR and dilution index in real geological and hydrological systems undergoing structure changes and chemical reactions.

Heat transfer at high Péclet number from a small sphere freely rotating in a simple shear field

1971 ◽  
Vol 46 (2) ◽  
pp. 233-240 ◽  
Author(s):  
Andreas Acrivos
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Simple Shear ◽  
Peclet Number ◽  
Reynolds Numbers ◽  
Small Sphere ◽  
Péclet Number ◽  
Shear Field ◽  
Method Of Solution ◽  
Small Shear

The problem of heat transfer at high Péclet number Pe from a sphere freely rotating in a simple shear field is considered theoretically for the case of small shear Reynolds numbers. It is shown that the present problem is in many respects similar to that of heat transfer past a freely rotating cylinder which was recently solved by Frankel & Acrivos (1968). By taking advantage of the close analogy between these two problems, an approximate method of solution is developed according to which the asymptotic Nusselt number for Pe → ∞ is 9, i.e. 4½ times its value for pure conduction. As in the corresponding case of the cylinder, the fact that the asymptotic Nusselt number is independent of Pe results from the presence of a region of closed streamlines which completely surrounds the rotating sphere.

Investigation on the effect of leading edge tubercles of sweptback wing at low reynolds number

2020 ◽  
Vol 21 (6) ◽  
pp. 621
Author(s):  
Veerapathiran Thangaraj Gopinathan ◽  
John Bruce Ralphin Rose ◽  
Mohanram Surya
Keyword(s):  
Leading Edge ◽  
Reynolds Numbers ◽  
Sweep Angle ◽  
Laminar Separation ◽  
Low Reynolds Numbers ◽  
Flow Energy ◽  
Airplane Wing ◽  
Low Reynolds ◽  
Naca 0015 ◽  
Wing Performance

Aerodynamic efficiency of an airplane wing can be improved either by increasing its lift generation tendency or by reducing the drag. Recently, Bio-inspired designs have been received greater attention for the geometric modifications of airplane wings. One of the bio-inspired designs contains sinusoidal Humpback Whale (HW) tubercles, i.e., protuberances exist at the wing leading edge (LE). The tubercles have excellent flow control characteristics at low Reynolds numbers. The present work describes about the effect of tubercles on swept back wing performance at various Angle of Attack (AoA). NACA 0015 and NACA 4415 airfoils are used for swept back wing design with sweep angle about 30°. The modified wings (HUMP 0015 A, HUMP 0015 B, HUMP 4415 A, HUMP 4415 B) are designed with two amplitude to wavelength ratios (η) of 0.1 & 0.24 for the performance analysis. It is a novel effort to analyze the tubercle vortices along the span that induce additional flow energy especially, behind the tubercles peak and trough region. Subsequently, Co-efficient of Lift (CL), Co-efficient of Drag (CD) and boundary layer pressure gradients also predicted for modified and baseline (smooth LE) models in the pre & post-stall regimes. It was observed that the tubercles increase the performance of swept back wings by the enhanced CL/CD ratio in the pre-stall AoA region. Interestingly, the flow separation region behind the centerline of tubercles and formation of Laminar Separation Bubbles (LSB) were asymmetric because of the sweep.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

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