Shear cell method

There are several different methods available for determining the flow properties of powders. Shear cell methods provide an assessment of powder flow properties as a function of consolidation load and time. There are a number of types of shear cells available, the most common being the Jenike shear cell [21]. 

Approaches used to model ozone formation include box, gradient transfer, and trajectoty methods. Another method, the particle-in-cell method, advects centers of mass (that have a specific mass assigned) with an effective velocity that includes both transport and dispersion over each time step. Chemistry is calculated using the total mass within each grid cell at the end of each time step. This method has the advantage of avoiding both the numerical diffusion of some gradient transfer methods and the distortion due to wind shear of some trajectory methods. 

The wave-front shearing interferometric method can be applied to transparent melts which do not attack cell windows made of silicate glass. The principle of this method has been given by Gustafsson. " A thin foil is placed vertically, a laser beam passing in the -direction along the plane. The heat is transferred in a melt in the direction of x. The slope of the... 

Amidon and Houghton [48] completed a comparative study of several common methods of characterizing powder flow. Table 2 contains experimental results for a number of commonly used pharmaceutical excipients. Compressibility index, angle of repose, flow rate through an orifice, and shear cell data are presented. 

Shear cell measurements offer several pieces of information that permit a better understanding of the material flow characteristics. Two parameters, the shear index, n, and the tensile strength, S, determined by fitting simplified shear cell data to Eq. (6), are reported in Table 2. Because of the experimental method, only a poor estimate of the tensile strength is obtained in many cases. The shear index estimate, however, is quite reliable based on the standard error of the estimate shown in parenthesis in Table 2. The shear index is a simple measure of the flowability of a material and is used here for comparison purposes because it is reasonably reliable [50] and easy to determine. The effective angle of internal... 

A direct comparison of the results obtained by the simplified shear cell methodology and the Flowfactor Tester of Jenike and associates is difficult since the experimental procedures differ. Figures 10 and 11 show the yield loci obtained using both methods. For free flowing spray-dried lactose the yield loci are very similar (Fig. 10) and nearly linear, as is generally observed [45]. Bigger... 

Hua J, Erickson LE, Yiin T-Y, Glasgow LA. A review of the effects of shear and interfacial phenomena on cell viability. Grit Rev Biotechnol 1993 13(4) 305-328. Tramper J, de Gooijer KD, Vlak JM. Scale-up considerations and bioreactor development for animal cell cultivation. Bioprocess Technol 1993 17 139-177. Griffiths B, Looby D. Scale-up of suspension and anchorage-dependent animal cells. Methods Mol Biol 1997 75 59-75. 

Standard Shear Testing Method for Bulk Solids Using the Jenike Shear Cell. ASTM Standard D6128-00. ASTM International, 2000. 

The weaknesses associated with the flow through an orifice and angle of repose measurements limit their application for powder flow studies and hopper designs. Consequently, several powder shear testers and methods that permit a more thorough and precisely defined assessment of powder flow characteristics were developed. Shear testers that measure the frictional characteristics of a powder bed under load yield valuable information with regard to powder flow in high-speed tablet equipment. A number of types of shear cell testers are available, but the most common types used in the pharmaceutical industry are the Jenike shear cell and the Schulze ring shear tester.61,62... 

Some work has shown a direct correlation between shape factor and the flow properties of powders. The flowability of fine powders, as measured by a shear-cell as well as by Carr s method, was found to increase with increasing sphericity, where the sphericity is indicated by a shape index approaching one, as measured by an image analyzer. Huber and co-workers derived an equuation in which flow rate was correlated to the volume specific surface as measured by laser diffractometry. Reasonable predictions were made for individual powders as well as binary and ternary mixtures. 

Heistand and Carstensen related the repose angle to the intrinsic cohesion and frictional coefficient of powders. As mentioned previously, the dependence on the technique used makes this method much less reliable for this purpose than a shear cell. In addition, the repose angle does not quantitatively treat the compressive forces of the flow process in the same... 

The applicability of the flow property test used is highly dependent on what the user is trying to capture. As an example, if there is concern that a certain batch of material may arch when transferred into a bin, a shear test may be the most comprehensive QC test. However, a quantitative test such as a shear test may require more time/resources to conduct than is practical, so faster test methods are often desired. One option is abbreviated shear cell testing (1). 

Bausch A. Hausmann R. Bongaitz C. Zinn T. Measurement of flowability with a ring shear cell, evaluation and adaptation of the method for use in pharmaceutical technology. In Proceedings of the 2nd World Meeting APGI/APV. Paris. May 1998 135-6. 

The angle of internal friction can be measured indirectly, in shear cells for example, or directly, by the grooved plate method. There... 

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