Sliding coefficient of friction

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. 

The following variables can affect wall friction values of a bulk soHd. (/) Pressure as the pressure acting normal to the wall increases, the coefficient of sliding friction often decreases. (2) Moisture content as moisture increases, many bulk soHds become more frictional. (3) Particle size and shape typically, fine materials are somewhat more frictional than coarse materials. Angular particles tend to dig into a wall surface, thereby creating more friction. (4) Temperature for many materials, higher temperatures cause particles to become more frictional. (5) Time of storage at rest if allowed to remain in contact with a wall surface, many soHds experience an increase in friction between the particles and the wall surface. (6) Wall surface smoother wall surfaces are typically less frictional. Corrosion of the surface obviously can affect the abiUty of the material to sHde on it. 

However, if the diffusing molecules are much smaller than the solvent molecules, the coefficient of sliding friction is zero, i.e. the solute molecules can move freely in contact with the solvent molecule. In such cases kt is given by... 

Osborne and Porter have found that the Debye equation probably underestimates kiU because of a failure in the Stokes-Einstein dependence of diffusion coefficients on viscosity.185 The coefficient of sliding friction has always been assumed to be infinity. If it is zero, the Debye equation is increased by 50%. 

The coefficient of sliding friction fs of the solid equals the tangent of the angle of repose. For most substances this angle is 30-45° and... 

The angle of repose is a measure of the incline at which conveyors such as screws or belts can carry the material. The tangent of the angle of repose is the coefficient of sliding friction. This property is a factor in the power needed to transfer the material by pushing or dragging as in pneumatic, screw, flight, and Redler equipment. 

The physical properties of granular materials that bear particularly on their conveying characteristics include size distribution, true and bulk densities, and angle of repose or coefficient of sliding friction, but other less precisely measured or described properties are also of concern. A list of pertinent properties appears in Table 5.2. The elaborate classification given there is applied to about 500 materials in the FMC Corporation Catalog 100 (1983, pp. B.27-B.35) but is too extensive for reproduction here. For each material the table also identifies the most suitable design of screw conveyor of this... 

For the solid, take the coefficient of sliding friction to be fs = 1. Power loss is made up of four contributions. Assume no slip velocity ... 

Coefficient of sliding friction, 170 Collision, 165 bimolecular, 166 cross-section, 165, 167 (in) gas phase, 166 kinetic, 166 numbers, 165 optical, 165... 

Abrasion resistance, Taber CS-17, 0.5 kg load, mg/1000 cycles Coefficient of sliding friction to steel Thermal coefficient of linear expansion, per °C Thermal conductivity, at 25-160°C, W/(m K)... 

Figure 10.3 Effect of Negative DC Bias on Coefficient of Sliding Friction for Sputtered Molybdenum Disulphide (Ref.274)...

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