These calculations suggest that an absorber mass of less than 300 kg may be possible, which compares favorably with the 650 kg of the previous sensible-heat axial- flow receiver [7], and with the 1040 kg (PCM + canisters) of the reference receiver [9], However, not all of the above materials lead to practical geometries; thus, the low conductivity of Boron results in a receiver length of only 5.5 cm (and yet a diameter of 5.7 m); by contrast, the high conductivity of Pyrolytic Graphite results in a more practical length of 0.8 m and a diameter of 0.25 m. Conclusions The attenuation concept for thermal energy storage was introduced; it was shown that the higher-order response of this concept leads (in principle) to improved performance, relative to a first-order response (see Appendix A). A receiver geometry based on the concept was modeled, including typical input flux and radiative loss, subject to specified receiver 1) total energy input, 2) fluid average temperature rise, 3) thermal efficiency, and 4) fluid outlet oscillation amplitude. The dynamic response of the receiver was determined by analytical transfer functions and numerical Fourier transforms. The results of the analysis indicate that a reduced mass is possible, relative to previous receivers and equal constraints, with the new designs tending to smaller sizes operating at higher temperatures. With some materials the thickness b may be of the same order as the length L, in which case a two-dimensional analysis should be done. Because of the radial gradient, it is anticipated that such analysis would show even better results. The indicated smaller receivers require investigation of the attainable input flux distribution, and of the effects on reflector geometry. A benefit unaccounted for here is the lower shell mass associated with the smaller receivers. Thus, the indicated improved performance of the attenuation receiver warrants further evaluation with two-dimensional effects, and (possibly) with composite-designed materials. Acknowledgment This paper was presented at the ASME/JSME/JSES International Solar Energy Conference, San Francisco, March 27-30, 1994. References [1] Kerslake, T. W. and Ibrahim, M. B., 1990, "Analysis of Thermal Energy Storage Material with Change-of-Phase Volumetric Effects," Proc. ASME Int'l. Solar Energy Conf., Miami, FL, April 1-4, pp. 315-325. [2] Strumpf, H. J. and Coombs, M. G., 1987, "Advanced Heat Receiver Conceptual Design Study." Final Report (NASA CR-180901). Strumpf, H.J.. and Coombs, M.
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