Hiromoto Usui

A thixotropy model for coal-water mixtures

Abstract The thixotropy model developed in this study is based on the phenomenological scheme proposed by Cheng and Evans, Brit. J. Appl. Phys., 16 (1965) 1599–1617. The idea of this model is based on the assumption that the thixotropic behavior of dispersed systems is well described by the coagulation process of the minimum sized particles contained in a dispersion system and the break-up process of coagulated clusters. Combined with the modified-cell model, the proposed thixotropy model can predict the complex rheological behavior of coal-water mixtures. This model can be applied to predict the viscosity of highly concentrated solid-liquid dispersion systems which have a wide particle-size distribution.

Drag reduction caused by the injection of polymer thread into a turbulent pipe flow

Drag reduction caused by the injection of concentrated polymer solutions into a turbulent pipe flow was studied. Measurements were made of the radial distribution of fluctuating velocities by means of video image analysis. The results showed that a higher velocity was observed for injected polymer threads and both the radial fluctuation and the Reynolds stress were significantly suppressed. It was suggested that the wall turbulence structure might be controlled by suppressing the large scale turbulent motion in the turbulent core region.

Rheological properties and some applications for rhamsan and xanthan gum solutions

The rheological properties of solutions of xanthan gum (Kelzan® D) and three rhamsan gums, S-60, S-130 and S-194, are examined. Effects studied include those of temperature, concentration and (for the rhamsan gums) extent of side chain branching. Solutions of greater viscosity and elasticity at most shear rates result as the degree of branching increases. When compared with xanthan gum, S-194 is found to be less temperature sensitive and more stable to excess shear. The use of these polymers in two commercial applications, i.e. coal–water mixtures and timber preservative emulsions, is also examined. Several advantages are identified when rhamsan gums are used instead of xanthan gum in both cases.

Elongational flow of dilute drag reducing fluids in a falling jet

An elongational flow of dilute polymer solution in a falling jet was studied. Measurements were made of the stress and velocity distribution along the falling jet by means of a photographic technique. The results show that the relaxation time in dilute drag reducing fluids is much longer than those predicted in a simple shear flow, and suggest the possibility of using a very high value of the relaxation time in a wall turbulence model. Also, the increase in Trouton ratios determined for a simple elongational flow is possibly as high as 27 000.

Drag Reduction Caused by the Injection of a Polymer Solution into a Pipe Flow

Drag reduction caused by the injection of concentrated polymer solutions into a turbulent pipe flow is reviewed. The experimental results obtained by means of a tracer particle method are examined in detail, and they are compared with the previous LDV measurements. It is suggested that the wall turbulence structure might be controlled by suppressing the large eddy motion in the turbulent core region.

Effect of Additives on the Fluidity and Stability of Coal Water Mixture

Publisher Summary This chapter describes the effect of additives on the fluidity and stability of coal water mixture (CWM). The establishment of the preparation technique for the highly loaded coal water mixture with the good fluidity and the enough stability is important in the increased use of coal slurries. The chapter presents flow characteristic curves obtained for the CWM with a Workworth coal. The experimental results indicate that the addition of a very small amount of polyacrylic acid (PSA) causes a drastic decrease in the shear stress level at lower shear rate region. Also, the rheological parameters indicate that the viscosity values are almost the same. The yield stress was drastically reduced by the small amount addition of PSA, and a considerable amount of the hard pack layer was observed at the bottom of the test cylinder. When the concentration of PSA is increased, the yield stress recovers and the hard pack depth decreases. The strongly adsorbed PSA molecule on the ash surface may cause the steric repulsion of the adsorbed layer, and the good dispersion of ash particles may result in the drastic decrease of the yield stress.

Statistical Measurements in the Turbulent Flow of Dilute Drag-Reducing Polymer Solutions in a Round Tube

The drag reduction phenomenon in a fully developed turbulent pipe flow was examined by measuring the longitudinal velocity by means of a laser-Doppler anemometer. Statistical analysis of the fluctuating velocity showed that the most significant effect of the polymer additive on the organized structure of wall turbulence was detected near the outer edge of a buffer layer. The typical ejection process was detected as the remarkable negative fluctuating velocity both through the buffer region and the inner part of turbulent core.