Nicolaie Dan Cristescu

A closed form solution for falling cylinder viscometers

The paper presents a theory of the flow of a viscous fluid in a falling cylinder viscometer. The velocity profile for the flow in infinite tube and finite tube are obtained in finite form. That allows us to determine quite easily the influence of various parameters involved on the fluid flow and on the motion of the cylinder. Also a formula written in finite form is obtained for the determination of the viscosity coefficient. All these formulae contain a term that can describe the influence of a magnetic field on the motion of the falling cylinder. A comparison of the viscosities determined according to the present theory and with a cone-plate viscometers show a good agreement.

Mechanical properties of microcrystalline cellulose. Part i. Experimental results

Abstract This paper describes a set of laboratory diagnostic tests performed in order to reveal the main mechanical properties exhibited by several cohesive powders. The laboratory tests were carried out on several powders, however only the results for microcrystalline cellulose, PH-105, mean particle size 20 μm will be mainly presented here. A few results of other materials will be incorporated as examples to explain the development of these diagnostic tests, as well as the development of improved methodologies. First, the powder was tested to see if it exhibits “instantaneous” response. For this purpose we have used a “quasi-static” procedure described later to determine the elastic parameters. All the elastic parameters were obtained experimentally by using an enhanced triaxial tester (Development of a New Technique for Measuring Volume Change of Dry Particulate Systems under Very Low Confining Pressures. IMECE: Recent Trends in Constitutive Modeling of Advanced Materials AMD-Vol. 239 (2000) 65). The tests were carried out at low to moderate confining pressures which are typical in storage and handling facilities such as bins and hoppers and mechanical feeders. Afterwards, we tried to see if the powder exhibits irreversible deformation and if this deformation is time dependent. We have found that the volume is either compressible or dilatant, and that irreversible volumetric deformation is taking place by creep. Compressibility is a transient phenomenon. Microcrystalline cellulose does not exhibit much dilatancy, but a rate effect was also recorded and this phenomena is of great importance for many industrial applications. Shortly, the diagnostic tests reveal that only elastic/viscoplastic non-associated constitutive equations are able to describe the mechanical properties discussed above. The paper describes all the data needed to determine such constitutive equations.

A New Experimental Setup for the Characterization of Bulk Mechanical Properties of Aerated Particulate Systems

This study introduces the development of a new experimental setup using an enhanced triaxial tester and a new methodology for the characterization of fine particulate systems in an aerated condition. Tests were performed using the new setup to study the effects of aeration on two different powders: a highly cohesive precompacted powder and a cohesionless powder, the former being microcrystalline cellulose PH-102, mean particle size 90 w m, and the latter alumina powder, mean particle size 100 µm. The degree of aeration was small and it was of the same order of magnitude as the velocities encountered during the entrapment of air in filling and during other handling processes. The superficial velocity for aeration was about three orders of magnitude lower than that required for fluidization. The immediate results have shown that even a small amount of interstitial air has a dramatic effect on the quasi-static strength and an obvious effect on the elastic parameters of the powder. The quasi-static strength of the alumina powder was reduced by about 20%, at a superficial air velocity of 0.02 m/s, whereas the quasi-static strength of microcrystalline cellulose was reduced by about 17%, at a superficial air velocity of 0.009 m/s. The Youngs modulus values were reduced by about 13% on average and the bulk modulus values by about 8% on average for microcrystalline cellulose for the air velocity given above. aerated dry particulate systems elastic parameters compressibility and/or dilatancy boundary failure envelope