Bending loss technique

Despite their flexibility in terms of the geometry of the formed waveguide and 3D structure capability, direct-writing techniques are restricted to low index contrast. The modes are generally large, and compact devices are not easily obtained due to bending loss. 

Vanes may be used to improve velocity distribution and reduce frictional loss in bends, when the ratio of bend turning radius to pipe diameter is less than 1.0. For a miter bend with low-velocity flows, simple circular arcs (Fig. 6-37) can be used, and with high-velocity flows, vanes of special airfoil shapes are required. For additional details and references, see Ower and Pankhurst The Mea.surement of Air Flow, Pergamon, New York, 1977, p. 102) Pankhurst and Holder Wind-Tunnel Technique, Pitman, London, 1952, pp. 92-93) Rouse Engineering Hydraulics, Wiley, New York, 1950, pp. 399 01) and Joreensen Fan Engineerinp, 7th ed., Buffalo Forge Co., Buffalo, 1970, pp. Ill, 117, 118). 

Ce and Nd, respectively. E and a have been measured by three-point bending techniques and the reported values are the mean of 4 or 5 data points. Figure 29.10 shows that for a Ce loading higher than 11% the mechanical properties drop. In the case of the Nd-loaded glass-ceramics, the loss of mechanical properties is progressive (Figure 29.11). 

After testing for as long as possible, the specimens are evaluated by mass loss, visual, and binocular examination and in some cases by metaUographic techniques. Generally, these tests can be accelerated only by severe bending or possibly by the application of a tight crevice, and the initiation of corrosion must be detected by careful weighing and examination. 

In treating pressure losses in bends, Rose and Duckworth (1969) have suggested an empirical technique that considers only the acceleration portion of the pressure loss. Other analyses such as that of Yang may also be employed to calculate this acceleration pressure loss. 

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