Pitch to diameter ratio

The individual objects that compose the model are screws which simulate the molecules of the helical polymer their individual chirality is responsible for the spontaneous formation of the overall helical structure. In the model, the screws are left-handed and have a rather compact thread, that is, the pitch-to-diameter ratio of the individual screws is small In this case, left-handed screws generate a left-handed overall helical structure. If instead the thread is loose, left-handed screws may generate a right-handed superstructure (see discussion in Section 3). 

Figure 7.4 Simplified macroscopic model for cholesteric (a) lateral and (b) top view of left-handed superhehx (photographs display a half-pitch length) composed of left-handed helical screws with pitch-to-diameter ratio much smaller than Jt. (Reprinted with permission of John Wiley Sons from Circular Dichroism—Principles and Applications, 2nd ed., N. Berova, K. Nakanishi, R. W. Woody, Eds., Copyright 2000.)...

Figure 7.9 Different handedness of packing of right-handed helices with different pitch-to-diameter ratios. Right-handed helices with p/d < n interact to give right-handed superhelix, while when p/d > it, superhelix is left-handed. (Reprinted with permission of Wiley-VCH from Chemistry—A European Journal, Vol. 6, p. 3249 ad ff., copyright 2000.)...

Kettle reboilers consist of a bundle of tubes in an oversize shell. Submergence of the tubes is assured by an overflow weir, typically 5-15 cm higher than the topmost tubes. An open tube bundle is preferred, with pitch to diameter ratios in the range of 1.5-2. Temperature in the kettle is substantially uniform. Residence time is high so that kettles are not favored for thermally sensitive materials. The large shell diameters make kettles uneconomic for high pressure operation. Deentraining mesh pads often are incorporated. Tube bundles installed directly in the tower bottom are inexpensive but the amount of surface that can be installed is limited. 

For eight three-bladed propellers tested, with diameters from 3.6 to 12.4 in. and pitch-to-diameter ratios in the range 0.92-1.54, these authors found that the discharge flow was directly proportional to rotational speed and about proportional to the square of the diameter. Thus ... 

The perforations in sieve trays are seldom less than of an inch in diameter and they are located on equilateral triangles such that the pitch to diameter ratio is greater than 2 but less than 5 with an optimum of about 3.8. The trays are generally designed with tray thickness to hole diameter of 0.1 to 0.7. 

In the study of Miyatake and Iwashita [256], the relationship of local Nusselt number and Graetz number is formulated for developing longitudinal flow between a triangular array of cylinders with a uniform heat flux and various pitch-to-diameter ratios. For PID = 1.01-1.1 ... 

Rgure 6.4 Graphical relationship between fractional hole area and hole pitch to diameter ratio (From J. David Chase, excerpted by special permission from Chemical Engineering, July 31, 1967, copyright by McGraw-Hill, Inc., New York, NY 10020.)... 

Lead cooled fast reactor design assumes the subassembly with fuel pins arranged in square lattice with large pitch-to-diameter ratio (s/d 1.4-1.5). In LMFR a more tight arrangement of fuel pins is adopted (s/d 1.1-1.18) ... 

In Table 6.2 and Fig. 6.3 relationships Nu=f(Pe) taken for triangular and square lattice with fixed pitch-to-diameter ratio (x=1.4) are compared. 

Core Fuel rod pitch-to-diameter ratio Cladding outer diameter Cladding thickness Fuel pellet-cladding bond Fuel smear density Fuel pellet outer diameter Active core height Active core diameter Above core fission gas Open-lattice of cylindrical fuel rods on a triangular pitch lattice. 1.121 2.5 cm 1 mm Pb 0.90 2.18 cm 0.8 m 1.02 m 1.4 m... 

PITCH-TO-DIAMETER RATIO AND HYDRAULIC DIAMETERVERSUS FUEL PIN DIAMETER... 

FIG. XXII-9. Relationship between fuel pin diameter and triangular pitch-to-diameter ratio. 

Rail transportability imposes a size limitation upon the reactor vessel and guard vessel of 6.1 m in diameter and 18.9 m in height [XXIII-25]. The fission gas plenum height is based upon an assumed conservative gas release from nitride fuel of 2.5% per atom % of bum-up. The fuel volume fraction was held fixed in the thermal hydraulic design analyses at the value of 0.215 determined by the core design. The fuel rod outer diameter and pitch-to-diameter ratio were varied to determine an optimum combination. Figure XXIII-5 shows the relationship... 

PITCH-TO-DIAMETER RATIO VERSUS FUEL ROD DIAMETER (FUEL VOLUME FRACTION = 0.215 SMEARED DENSITY = 0.78)... 

FIG. XXIII-5. Pitch-to-diameter ratio versus fuel rod outer diameter for triangular lattice with fuel volume fraction equal to 0.215 andfuel smeared density of 78%. 

The four modular HXs provide for counter-current heat exchange. The S-CO2 flows upwards through the inside of 1 cm inner diameter tubes while the Pb flows downwards over the exterior of the tubes (Fig. XXIII-13). The tube inner diameter of 1.0 cm was chosen to preclude occlusion of the lead flow channels due to growth upon the structure of protective oxide layers or plugging by contaminants. A triangular tube array having a pitch-to-diameter ratio of 1.75 was determined to be optimal. 

The standard full-pitch screw has a pitch-to-diameter ratio of 1 this configuration is satisfactory only when the maximum hopper opening does not exceed 1 to 1.5 pitches. Using larger opening leads to serious flow problems in the bin and unnecessarily high horsepower requirements. 

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