Wall friction angle

In order to develop the proper dow pattern, knowledge of a material s dow properties is essential. Standard test equipment and procedures for evaluating sohds dow properties are available (6). Direct shear tests, mn to measure a material s friction and cohesive properties, allow determination of hopper wall angles for mass dow and the opening size required to prevent arching. Other devices available to evaluate sohds dowabiUty include biaxial and rotary shear testers. 

The angles (j) and ( )-. the effective angle and wall angle of friction, respectively. 

Wall angle of friction deg deg CT Powder normal stress during shear kg/cm" ... 

The angle p is related to the effective angle of friction p and the wall angle of friction p = arctan f by ... 

How Wall friction (degree) Bulk density (kg/m ) Shear strength (N/m ) Hausner ratio (—) Outlet size (cm) Mass flow wall angle (degree)... 

Wall Friction Angles. Wall friction values, important when characterizing the dow properties of a bulk soHd, are expressed as the wall friction angle or coefficient of sliding friction. The lower the friction, the less steep the hopper walls need to be to achieve mass dow. 

Fig. 5. Wall friction test (a) apparatus for measurement, and (b) results, where is the wall friction angle.

A material s flow function is usually measured on the same tester as the wall friction angle, although the cell arrangement is somewhat different (Fig. 6). ConsoHdation values are easily controUed, and the cohesive strength of the bulk soHd is determined by measuring interparticle shear stresses while some predeterrnined normal pressure is being appHed. 

Conica.1 Hoppers. Design charts for conical hoppers typically are plots of wall friction angles, ( ), vs hopper angle, 9. Charts such as that in... 

Because fluid slip occurs at highly water-repellent walls when the contact angle is about 150°, Watanabe et al. (1999) analyzed the friction factor of slip flow in a circular pipe. For a fully developed steady flow in a pipe, the Navier-Stokes equation can be written as... 

Most, if not all, velocity measurements in the bulk, other than NMR/MRI, make measurements through dear end-walls of either long or short cylinders. End-walls, because of friction with the particles, change the dynamic angle of repose near the end-wall and can also cause convections in long cylinders with components of velocity in the axial direction [34, 35], NMR/MRI experiments can avoid the end-wall effects by making measurements far from the end-walls in a long cylinder. 

SB Tan, JM Newton. Influence of capsule dosator wall texture and powder properties on the angle of wall friction and powder-wall adhesion. Int J Pharm 64 227-234, 1990. 

Ducts are used to transport the exhaust air and its contaminants to the collection area. An important feature of duct design is reduction of resistance to air flow from friction within the wall, aggravated by unnecessary curves and bends (particularly right-angled bends), as well as junctions with other ducts at sharp angles, collections of dust, and changes in duct diameter. 

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