Pitch angle

The axial-flow fan is inherently a device for moving a consistent volume of air when blade setting and speed of rotation are constant. Variation in the amount of air flow can be obtained by adjusting the blade angle of the fan and the speed of rotation. The blade angle can be either (1) permanently fixed, (2) hand-adjustable, or (3) automatically adjusted. Air delivery and power are a direct function of blade pitch angle. 

Abstract—The geometrical conditions pertaining to closure, helicity, and interlayer distance between successive layers with circular cross-sections in carbon tubules (nanotubes) have been examined. Both the intralayer length of the C—C bonds and the interlayer distance between successive layers must vary with the radius of the layers. The division into groups of the sheets in nanotubes is found to be due to the reciprocal interaction of the interlayer distance variations and of the conditions required to maintain constancy of the pitch angle. 

Key Words—Carbon nanotubes, pitch angle, helix angle, interlayer distance, carbon-carbon intralayer distance. 

The pitch angle a, characteristic of this orientation of the hexagons is ... 

The only doublets consistent with this inequality, with the necessity of identical parity for p and q, and with values of r close to 0.34 nm, are given in Table 1 (from which the doublet (10,0) can be excluded since it is characteristic of a symmetrical, non-helical sheet). Hence, if br — 0, the necessary conditions for two successive helical cylindrical sheets to have strictly identical pitch angles are ... 

Table 1. (p,q) increments for obtaining identical successive pitch angles... 

Table 2. Computed characteristics of a five-sheet symmetric tubule with a nearly constant pitch angle Table 4. Group characteristics of the 28-sheet described in Table 3 nanotube...

Adjustable pitch fan A fan in which the pitch angle can be set to provide the required airflow rate. The pitch angle may be preset or controlled with the fan running. 

Figure 9-117. Diameter correlation for 16° pitch angle for fan blades. Used by permission of Whitesell, J., Chemical Engineering, Jan. (1955) p. 187, all rights reserved.

The blades are usually fixed pitch up to 48-in. diameter with applications for adjustable pitch above this size. Fixed pitch is used up to 60-in. diameter with aluminum fen blades when direct-connected to a motor shaft. Variable pitch is used with belts, gears, etc., between the fen shaft and the driver to allow for the possibilities of slight unbalance between blades due to pitch angle variation. Aluminum blades are used up to 300°F, and plastic is limited to about 160°-180°F air stream temperature. 

The hrst example is for a two-rail slider, the shape and dimensions of which are shown in Fig. 12. The input parameters are listed in Table 1. The direction of gas flow is along the rail directionX. The roll angle was set as zero. The calculated pressure distribution is plotted in Fig. 13. We can see that the air pressure quickly rises at the end of the wedge of the front taper, then gently increases to the pitch angle of the slider, and reaches the maximum near the end of the rails. At the tail, the pressure steeply drops to the ambient value. 

Fig. 15—Dimensionless pressure distributions of the gas film in the Q type slider under several different pitch angle conditions, (a) Pitch angle 0=0 /jirad, calculated floating force F=17.83g (b) Pitch angle 0=1O iirad, calculated floating force F=9.76g (c) Pitch angle 6 = 300 yurad, calculated floating force F = -0.75 g (d) Pitch angle 0=3,000 u,rad, calculated floating force F = 3.64 g.

Fig. 16—Influence of pitch angle on the floating force of a 2 type slider.

Fig. 17—A cross section of a 2 type slider with zero pitch angle.

Fig. 20—Effects of slider attitude on the floating force and moment. (a) influence of flying height on the floating force (b) Influence of pitch angle on the pitch moment.

Fig. 29—Effect of van der Waals force on loading capacity of a O type slider under different pitch angles. Input parameter was set as minimum film thickness ho=6 nm, roll angle =0, sliding speed u=25 m/s, length of the slider L=. 2S mm, width of the slider B = 1.1 mm, mass of the slider M=1.6 mg.

In further studies, Zastavker et al. established that the formation of helical ribbons with two distinct pitch angles is a general phenomenon observed in a wide variety of multicomponent systems containing a sterol.162 High-pitch (54°) and low-pitch (11°) helices were observed in almost all of the... 

Figure 5.43 Phase contrast optical micrographs of typical helical structures in chemically defined lipid concentrate system, (a) Low-pitch helical ribbon with pitch angle i r = 11 2°. (b) High-pitch helical ribbons with pitch angle t t = 54 2°. (c) Intermediate-pitch helical ribbons with pitch angle i r = 40.8 3.8°. Reprinted with permission from Ref. 162. Copyright 1999 by the National Academy of Sciences, U.S.A.

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