Attenuation Thermal Energy Storage in Sensible-Heat Solar-Dynamic Receivers Kurt O'Ferrall Lund * Summary: Solar dynamic receiver designs are investigated and evaluated for possible use with sensible energy storage in single-phase materials. The designs are similar to previous receivers having axial distribution of concentrated solar input flux, but differ in utilizing axial conduction in the storage material for attenuation of the solar flux "signal", and in having convective heat removal at the base of the receiver. One-dimensional, time-dependent heat transfer equations are formulated for the storage material temperature field, including radiative losses to the environment, and a general heat exchange effectiveness boundary condition at the base. The orbital periodic input solar flux is represented as the sum of steady and oscillating components, with the steady component solved numerically subject to specified receiver thermal efficiency. For the oscillating components the Fast Fourier Transform algorithm (FFT) is applied, and the complex transfer function of the receiver is obtained and evaluated as a filter for the input flux spectrum. Inverse transformation results in the amplitudes and mode shapes of the oscillating temperatures. By adjustment of design parameters, the amplitude of the oscillating component of the outlet gas temperature is limited to an acceptable magnitude. The overall result of the investigation is the dependence of the receiver M-c product (mass times specific heat) on the conduction transfer units, which leads to lower weight designs than comparable previous single- and two-phase designs, when all constraints are included. As these attenuation designs also offer improvements in cost reduction and reliability they warrant further detailed investigation. NOMENCLATURE A cross-sectional area ([(Db+b)2 - Db2]7c/4 ), m2 As surface area (nDbL). m2 A B integration constants a thermal diffusivity, m2/s b thickness of absorber element, m Bi base Biot number (UL/k) c absorber specific heat, J/kgK * Center for Energy and Combustion Research 0310, University of California. La Jolla, CA 92093-0310 Tel: 619/534-5573 FAX: 619/534-5354
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