Evacuated Tube Reliability
After a year of operation several distinct patterns in the development of cracks in the evacuated tubes emerged. One of these involved the production sequence or, equivalently, the fin orientation and the other, the end of the tube where the crack occurred.
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Vertical and horizontal tube absorber orientations were produced in the first and second halves of the ICPC tube production run respectively. One year after installation 1.2 percent of the vertical fin orientation tubes and 9.8 percent of the horizontal tubes had developed cracks. This strongly suggests that there were distinct differences in the longevity of the vertically finned tubes versus that of the horizontally finned tubes (or, equivalently, of the first half of the production run versus
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Fig. 4 and 5depict the results of an animated Fig. 10: Rays Striking the Horizontal Fin
graphical ray tracing simulation that has been icpc at a Nominal Angle of 30 Degrees.
designed to investigate the optical perperformance of the ICPC. See Duff, et al [7]. Factors
incorporated are the transmittance of the glass tube, the reflectivity of the reflective surface, the gap between the tube surface and the fin and the absorptance of the fin. The sun ray is simulated as discrete uniform rays over a range of incident angles from 15 degrees to 165 degrees. The rays are followed through the glass envelope, to the reflector and to the absorber fin. The number of rays absorbed is recorded. The collector efficiency graph of Fig. 6 shows the amount of energy absorbed during a typical daytime period.
