Increase In Fluid Viscosity Research Articles

On the formation of bubbles in gas-particulate fluidized beds

The method of characteristics is applied to the nonlinear equations describing two-phase flow in a fluidized bed. The method shows how a small disturbance changes with time and distance and can, eventually, produce a flow discontinuity similar to a shock wave in gases. The parameters entering the analysis are the amplitude of the initial disturbance, the wavelength of the original disturbance, the particulate pressure function, the particulate size, the uniform fluidization voidage, the uniform fluidization velocity, the fluid viscosity, the particulate density, and the fluid density. A parametric study shows that the following factors delay shock formation: a decrease in particulate size, an increase in bed density, an increase in fluid viscosity, and a decrease in particulate density. Experimental data on bubble formation in gas-particulate fluidized beds show that these same factors delay bubble formation. It is concluded, therefore, that the shock front and the bubble front are one and the same thing.

Drag experiments with cylinders of varying roughness related to flow around thunderstorm cells

The drag on a storm by environmental winds, which vary with height, is considered by analogy with a hydrodynamic experiment of vortex shedding due to flow past smooth and rough cylinders. The vortex shedding rate for rough cylinders is shown experimentally to be smaller than that for smooth cylinders, and this difference is equivalent to an increase in fluid viscosity. This result is at variance with earlier predictions that roughness-induced turbulence would destabilize the flow and cause transition to occur at a lower Reynolds number. The eddy viscosity influences the drag on a storm during its growth. If the hydrodynamic analogy between the rough cylinder experiment and the storm cloud is valid, then increased roughness at the storm cloud edge increases the eddy viscosity locally, which would be indicative of increased mixing. The increased mixing at the periphery of the storm between ambient air and storm air causes the storm motion to respond more to the momentum of the flow. The vertical variation in ‘roughness’ of the storm may cause a number of different responses in the direction of motion.

Formulas for Phase Velocity and Damping of Longitudinal Waves in Thick-Walled Viscoelastic Tubes

The frequency equation for longitudinal waves in a viscoelastic tube of infinite length filled with a viscous fluid is solved for the complex wavenumber, k(=k1+ik2). Thus for two modes, Young's mode and Lamb's mode, an explicit expression for k is obtained which yields the phase velocity c(=ω/k1, ω=radial frequency) and the damping constant k2. The formulas for k, c, and k2 are valid for wall thicknesses up to the size of the inner radius of the tube. The approximation as compared with results obtained numerically with an IBM 7040 digital computer from the original frequency equation involves an error which in almost all cases is considerably less than 1.5%. For Lamb's mode, as it was found earlier for the torsional mode, an increase of the fluid viscosity increases the damping at the higher frequencies but decreases the damping at the lower frequencies. The theoretical results are compared with those of experiments in which the longitudinal waves are generated in the fluid and the fluid in its turn moves the wall. The experimental curves thus obtained show the pattern of Young waves, and the agreement with the Young curves obtained from the formulas mentioned above is satisfactory. For torsional waves, formulas for k, c, and k2 analogous to these for longitudinal waves are given.