Range Of Solids Concentrations Research Articles

Investigation of solid—liquid pipe flow with regard to turbulence modification

Based on laser—Doppler anemometry, a special measuring system has been developed with which investigation of undisturbed suspension pipe flow is possible, even close to the wall. For turbulent flowing suspensions with mean particle size of d p 50 = 53 μm in the range of solids concentration up to 5.6% by volume both local mean values and turbulence quantities were measured. The experimental results show that the intensity of turbulence is significantly affected by the solid particles. Depending on solids concentration as well as on wall distance, the solid particles increase or damp the intensity of turbulence. Turbulence data calculated on the basis of the experimental results show that the turbulence modifications can be explained by fluid—particle interaction. Thus the results of previous heat transfer measurements in suspension flow can be interpreted by the measured fluid—particle interaction.

Investigation of solid-liquid pipe flow with regard to turbulence modification

Based on laser-Doppler anemometry, a special measuring system has been developed with which investigation of undisturbed suspension pipe flow is possible, even close to the wall. For turbulent flowing suspensions with mean particle size of d p50 = 53 μm in the range of solids concentration up to 5.6% by volume both local mean values and turbulence quantities were measured. The experimental results show that the intensity of turbulence is significantly affected by the solid particles. Depending on solids concentration as well as on wall distance, the solid particles increase or damp the intensity of turbulence. Turbulence data calculated on the basis of the experimental results show that the turbulence modifications can be explained by fluid-particle interaction. Thus the results of previous heat transfer measurements in suspension flow can be interpreted by the measured fluid-particle interaction.

Particle abrasion at high solids concentration in stirred vessels

A model of particle abrasion at high solids concentration is developed for agitated vessels and is tested experimentally using copper sulphate and nickel ammonium sulphate crystals abrading in two non-solvent liquids. For two scales of operation, an 8-fold range of energy dissipation rates, a 3-fold range of solids concentration and three sizes of particle between 1.2 and 1.8 mm, the experimental results and the model are in good agreement. In addition, the dependence of abrasion rate on particle concentration is in agreement with the predictions of earlier models based on particle-particle impacts. However the effect of the non-solvent fluid is not adequately accounted for by the model and it appears that this may be due to it over-compensating for the effect of viscosity. The “energy/unit area of new surface” E required to produce abrasion fragments increases rapidly at first as the corners and edges of the crystals are removed but once this process is complete, E remains constant (at E∞). The ratio of the E*infin;. values for the two crystalline materials is found to be approximately the same as the ratio of their hardnesses.

Thermal conductivity of polymers filled with particulate solids

AbstractThe thermal conductivities of polystyrene and polyethylene containing several different particulate solids were measured over a range of solid concentrations. Experimental data were compared with results predicted by theoretical models for two‐phase media. The equations of Bruggeman and Cheng‐Vachon both gave reasonable agreement with measured results. The applicability of these equations does not appear to depend upon the structure of the polymer.

Retention of volatile compounds in freeze‐drying slabs of malto‐dextrin

SummaryA study was made of the effect of a number of process variables on the retention of some volatile compounds during freeze‐drying of ‘model’liquid foods. As a model liquid food, aqueous solutions of malto‐dextrin were chosen. To these solutions acetone, methanol, n‐propanol and n‐pentanol were added in low concentrations.The retention of volatiles strongly increased with increasing molecular size of the volatiles but was independent of the relative volatility. For constant dissolved solids concentration and constant temperature at the sublimation front in drying slabs or granules, process conditions leading to a maximum drying rate always resulted in maximum volatile retention. Retention increased with decreasing freezing rate when solids concentration, sublimation front temperature, and drying rate were constant. Retention always increased with decreasing temperature of the sublimation front. In drying granules, retention exhibited a maximum with respect to particle diameter, and increased with decreasing layer thickness. In the dissolved solids concentration range between 5 and 20% (w/w) the retention strongly increased with increasing concentration, whereas above 20% the retention became independent of initial solids concentration.The observed effects of process variables on volatile retention can be explained qualitatively with the selective diffusivity concept.

Aggregation of silica dispersions by iron(III)

Abstract The coagulation and restabilization of silica dispersions by iron(III) has been studied as a function of pH, applied metal ion concentration (Ct), and the surface area of the dispersed phase (S). Understanding and interpretation of these phenomena in the iron(III)-silica system requires a knowledge of the interrelationships among Ct, pH, and S. Results are presented graphically as log Ct-pH and log Ct-log S domains of coagulation and restabilization. Hydrolyzed iron(III) is observed to be a better coagulant than nonhydrolyzed ferric ions and is also able to restabilize silica dispersions. Adsorption of hydrolyzed iron(III) species is responsible for the influence of the surface area of the solid silica phase on coagulation and restabilization. The observed dependence on surface area is in agreement with that predicted by a Langmuir model. Light scattering and refiltration rate measurements are shown to provide complementary quantitative measures of coagulation and restabilization, permitting these phenomena to be studied over a wide range of solid phase concentrations.

SURFACE ELECTRICAL CONDUCTANCE AND ELECTROKINETIC POTENTIALS IN NETWORKS OF FIBROUS MATERIALS

Stream-current, permeability, and conductance measurements were made on cylindrical pads of randomly oriented Dacron, glass, Nylon, and Orlon fibers over a range of electrolyte and solid concentrations. Values of the specific surface conductivity were computed from the conductance data, using equations which were derived from a capillary network theory.The measured conductance values were independent of pad concentration, increased with increasing electrolyte concentration, and were higher than values calculated from electrical double-layer theory using the measured values of ζ-potential. A number of plausible reasons for the discrepancies are advanced.

Electroosmosis and streaming in natural and synthetic fibers

A critical comparison of the electroosmotic flow rate and stream current over a wide range of solid concentrations was made using softwood bleached sulfite, cotton, cellulose acetate, and glass fibers in the presence of 2.5 × 10 −5 N KCl. ξ E showed a good agreement with ξ S with the sulfite and glass fibers, but was lower than ξ S for the cotton and acetate fibers. It was also found that the electroosmotic flow rate F was not directly proportional to the applied potential at low values of F. It was shown conclusively that the discrepancy was due to the unexpectedly large effect of the air bubble in the capillary flowmeter in resisting electroosmotic flow. When allowance is made for the bubble effect, F is independent of the applied potential and ξ E and ξ S agree within 1%. A series of measurements of electroosmotic pressures is reported. With the glass fibers, agreement between ξ E and ξ S was obtained at solid fractions at low as 0.009, in a region where the resistance to flow of fluid approaches the Stokes resistance of single particles. This is taken to be evidence of an equivalence of the electroosmotic, electrophoretic, and streaming functions.

ELECTROKINETIC PROPERTIES OF CELLULOSE FIBERS: II. ZETA-POTENTIAL MEASUREMENTS BY THE STREAM-COMPRESSION METHOD

A new technique of measuring the ζ-potential of cellulose fibers, in which stream current potential measurements are carried out over a range of solid concentrations on a single pad, is described. In employing the stream potential method it is necessary to measure the d-c. resistance of the pad, since a pronounced dispersion effect yields a-c. resistance values which are in considerable error. Reversible electrodes must therefore be used and since stream current measurements can then be carried out, this simpler method is preferred. Degrees of swelling calculated from the stream data are consistently higher than those calculated from permeability measurements. This discrepancy indicates a serious limitation of the conventional electrokinetic theory when applied to swollen cellulose. A model of the fiber–liquid interface, consisting of partially dissolved electrically charged cellulose chains accounting for the observed discrepancy, is discussed. If this model is applicable, the physical significance of the ζ-potential becomes extremely complex.