Average friction coefficient

Fig. 46—Average friction coefficient (from the 15th second to the 35th second) of the muitiiayers versus thickness of Fe-N layers. The average friction coefficient of Fe-N, Ti-N film and Si (111) wafer under the same condition is aiso shown in this figure. Load, 250 N. (a) Fe-N(40 nm)/Ti-N(2 nm) (b) Fe-N film, 450 nm (c) Ti-N fiim, 450 nm (d) Si(111) wafer.

It should be noted that the acceleration component is dominant in the last part of the pipe, where, because of the rapid pressure drop and the low absolute pressure, the specific volume of the gas increases sharply. This effect is more pronounced at high mass flow rates with large values of mass flow ratio, 3 (= mjm,). As shown in Figures 3.44a and 3.446, the average friction coefficient is affected by the mixture mass flow rate m, the mass flow ratio 3, and the diameter of the pipe D. The Re is defined as... 

Friction coefficients plotted here are average friction coefficients between station 1 and exit plane... 

Figure 3.44 Average friction coefficients (a) between station 1 and exit plane (b) between stations 1 and 6. (From Kopalinsky and Bryant, 1976. Copyright 1976 by American Institute of Chemical Engineers, New York. Reprinted with permission.)...

We use Eq. (5-56) to compute the friction coefficient and then calculate the drag force. An average friction coefficient is desired, so... 

The average-friction coefficient for a flat plate with a laminar boundary layer up to Recrii and turbulent thereafter can be calculated from... 

Nitrogen at 1 atm and 20°C is blown across a 130-cm-square flat plate at a velocity of 3.0 m/s. The plate is maintained at a constant temperature of lOO C. Calculate the average-friction coefficient and the heat transfer from the plate. 

For flat plates, the drag force is equivalent to friction force. The average friction coefficient Qcan be determined from Eq. 6-11,... 

The average friction coefficient and Nusselt number are expressed in functional form as... 

Once the average friction coefficient C is available, the drag (or friction) force over the surface can be determined from Rq. 7-1. In this case/1 is the surface area of the plate exposed to fluid flow. When both side.s of a thin plate are subjected to flow, A becomes the total area of the top and bottom surfaces. Note that the friction coefficient, in general, varies with location along the surface. 

The average friction coefficient over the entire plate is determined by substituting the relations above into Eq. 7-7 and performing the integrations (Fig. 7-7). We get... 

The first relation gives the average friction coefficient for the entire plate when the flow is laminar over the entire plate. The second relation gives the average friction coefficient for the entire plate only when Ihe flow is turbulent over the entire plate, or when the laminar flow region of the plate is too small relative to the tuibulent flow region (that is,. t < L). 

A curve fit of experimental data for the average friction coefficient in this regime is given by Schlichiing as... 

The average friction coefficient relations for flow over a flat plate are ... 

Figure 14. Average friction coefficient as a function of average normal load for sliding in the [772 ] crystallographic direction at 100 m/s at 300K. The friction coefficient in these simulations is taken to be the average friction force divided by the average normal force per rigid layer atom [34].

To anticipate the result, the introduction of a few branch points has little influence on the average friction coefficient C (101, 136, 7P6), doubtless because there are so few brandi points, but also because their effect on increasing C may be counterbalanced by the equal number of new chain ends characterized, generally, by a lower C-... 

Table II. Wear Rates and Average Friction Coefficients (fj ) at 316°C...

Table 6.4 Time Averaged Friction Coefficients as a Function of PEEK Content in PTFE ...

For this reason, PEEK-filled PTFE composites are attractive as solid lubricants. It is hypothesized that a synergistic effect shuts down the dominant wear mechanism of each constituent of the composite [29,30]. The time averaged friction coefficients as a function of compositions are shown in Table 6.4. 

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