Ligament characterization of atomizing non-Newtonian liquid sheets: Fractal dimension

As gel propellants are increasingly used in rocket engines, non-Newtonian liquid atomization has emerged as a research subject of great interest. This paper addresses the atomization of flat sheets of aqueous xanthan gum solution, which are formed from two jets ejected from impinging injectors. Based on the experimental photos, it has been found that gel liquid sheets do not break up directly into droplets that can be characterized as spheres with Sauter mean diameter; instead, a mass of ligaments is observed. Therefore, this paper will introduce fractal dimension as a new parameter, related to the quality of atomization under these experimental conditions; and a power-law correlation between fractal dimension and Reynolds number of liquid jets has been achieved.

Analytical Model for the Deformation of Viscoelastic Non-Newtonian Drops Undergoing Secondary Atomization

While there is no single analytical model that accurately predicts all stages and modes of secondary atomization, many groups have developed models that predict deformation and oscillation of a single, isolated drop. The TAB (Taylor Analogy Breakup) model was chosen for this investigation, mainly due to its widespread use by Liu and Reitz [1], Hwang et al. [2], Tanner [3], and Lee and Reitz [4], among others. Since the TAB model is also the foundation for many other analytical models, it will also be used here as a starting point for the development of a viscoelastic non-Newtonian model to predict droplet deformed radii, droplet deformation time, and velocity at deformation time for viscoelastic xanthan gum - DI water solutions. Three additional improvements are made to this viscoelastic TAB model: the first is a change to a TAB coefficient; the second to the equation for the drag coefficient, and the third modification is to the breakup criterion. This model uses Carreau rheology and Zimm relaxation time. Non-dimensional drop diameter and initiation times are plotted against We; model results are compared to experimental results for a range of xanthan gum solution concentrations. Results show fair agreement between experimental results and model results for non-dimensional drop diameter, with the best match at low XG concentration and low-to-medium We (10–30). It was also noted that increased viscoelasticity seems to increase this drop diameter. Good agreement between experimental data and model results has been seen for initiation time, with increased viscoelasticity increasing this parameter as well.

A pair of bubbles’ rising dynamics in a xanthan gum solution: a CFD study

The motion and interaction of a bubble pair in a non-Newtonian fluid are numerically simulated by a volume of fluid method. The effects of initial horizontal bubble interval, oblique alignment and fluid rheological properties on the pair of rising bubbles are evaluated.

An Experimental Study on Heat Transfer Enhancement of Non-Newtonian Fluid in a Rectangular Channel With Dimples/Protrusions

Dimple and protrusion play important roles in the heat transfer enhancement and flow characteristic in cooling channels, which widely employed within electronic cooling systems. Non-Newtonian fluid has significant differences with Newtonian fluid, such as water, in fluid characteristic. In this study, an experiment on the viscosity of three different kinds of non-Newtonian fluids, i.e., xanthan gum solution, Carbopol 934 solution, polyacrylamide solution, was first accomplished to acquire the viscosity with different mass fractions. Then, experimental measurements on heat transfer and friction characteristics of non-Newtonian fluid in a rectangular channel with dimples and protrusions were conducted. The overall Nusselt numbers (Nu) and Fanning friction factors at different dimple/protrusion structures were obtained with various inlet flow rates and mass fractions. The results show that only xanthan gum solution has the significant shear thinning effect within the concentration range of this study, and the dimples/protrusions both have great effect on the heat transfer enhancement in the rectangular channel, and that the heat transfer of the case with the protrusions and crossing arrangement can be further enhanced with the higher Nu when compared to the case with the dimples and aligned arrangement. Moreover, an increase in Nu with the higher non-Newtonian fluid mass fraction is observed.