Atomization mechanism of a charged viscoelastic liquid sheet

In order to study atomization mechanism of a viscoelastic liquid sheet in an electric field, the spatial-temporal stability analysis of a viscoelastic liquid sheet injected into a dielectric station- ary ambient gas in the presence of a vertical electric field is conducted. The dispersion relations of both sinuous and varicose disturbance modes are solved to explore the spatial-temporal instability of a charged viscoelastic sheet, by setting both the wave number and frequency complex. A para- metric study is performed to test the influence of the dimensionless parameters on the absolute instability of the sheet. The results show that the increase of liquid Weber number and time constant ratio, or decrease of gas to liquid density ratio and Reynolds number, can damp the absolute insta- bility. The effect of the liquid elasticity depends on the value of time constant ratio： when time con- stant ratio is small, the increase of liquid elasticity could amplify absolute growth rate, but the effect is weak when the elasticity number is relatively large; when time constant ratio is large, the increase of liquid elasticity cannot affect the absolute growth rate. Moreover, the variation of electrical Euler number can hardly influence the absolute instability of a charged viscoelastic sheet.

SEDIMENTATION OF CYLINDRICAL PARTICLES IN A VISCOELASTIC LIQUID:SHAPE-TILTING

Aluminum and Teflon cylindrical particles with flat ends are dropped in aqueous Polyox solutions. The terminal equilibrium orientation of the particles is characterized by the tilt angle, a, formed by the major axis of the cyl-inder with the horizontal. It is observed that a is a function of the aspect ratio L=L/d, where L is the length and d is the diameter of the cylinder, and that it varies continuously from a certain angle, a0, to 90, as L increases toward a value L0. For a given shape, both a0 and L0 depend on the density of the cylinder and the properties of the liquid used. For the particles we have considered the value of L0 is of the order of 2. This 搕ilt-angle phenomenon?disappears as soon as the ends of the cylinder are round. Specifically, cylinders of the same density and with the same aspect ratio but with round ends, when dropped in the same polymeric solution will reach a final orientation with a=90. Therefore, this tilt-angle phenomenon seems to be tightly related to the shape of the particle.

Rayleigh–Taylor instability of viscoelastic self-rewetting film flowing down a temperature-controlled inclined substrate

Rayleigh–Taylor(RT) instability of gravity-driven viscoelastic self-rewetting film flowing under an inclined substrate uniformly heated or cooled is considered. The surface tension of self-rewetting film is considered as a quadratic function of temperature. The long wave hypothesis is used to derive a nonlinear free surface evolution equation of the thin viscoelastic film. Linear stability analysis shows that for a prescribed the viscoelastic coefficient, substrate cooling products instability,while substrate heating remains stability. Furthermore, we analyze the influence of viscoelastic coefficient on RT instability. Results show that the viscoelastic coefficient reinforces the RT instability whether the substrate is heated or cooled.Moreover, we use the line method to numerically simulate the nonlinear evolution equation and systematically examine the space-time variation of the film free surface. The numerical results illustrate that increasing the viscoelastic coefficient can enhance the disturbance amplitude and wave frequency. This means that the viscoelastic coefficient makes the system unstable, which is consistent with result of the linear stability analysis. In addition, the oscillation tends to accumulate downstream of the inclined substrate when the evolution time is long enough. Finally, the variation of film thickness with related parameters for different viscoelastic coefficients is investigated.

MHD flow of a visco-elastic fluid through a porous medium between infinite parallel plates with time dependent suction

This work provides a comprehensive theoretical analysis of MHD unsteady free convection viscoelastic fluid flow through a porous medium. The medium is treated as incompressible and optically transparent. The flow of the fluid is initiated by shearing action of the moving wall with time dependent suction. Radiative heat flow is considered in temperature equation. The coupled nonlinear problem has been solved asymptotically. Approximate solutions have been obtained for the mean velocity, mean temperature using multi parameter perturbation technique. The originality of the present study is to investigate the effect of viscoelastic property of the fluid（Walters B？ model） on the flow and heat transfer phenomena when the flow is permeated through a porous medium with uniform porous matrix subject to transverse magnetic field and time dependent fluctuative suction at the boundary surface. The case of viscous flow has been discussed as a particular case on comparison with the result reported earlier and it is in good agreement. Flow reversal is indicated incase of viscoelastic fluid with high heat capacity in the presence of magnetic field. The higher cooling of the plate in case of viscoelastic flow also causes a flow reversal.