Cf fluid heat capacity rate (m-dot-Cp), W/K Db absorber element inside diameter, m £ absorber-base solid-fluid heat exchange effectiveness f nondimensional axial variation of source flux f mass fraction (Appendix A) G FEI of g(T), transfer function (Appendix A) g nondimensional time-variation of source flux i imaginary unit (^-1) J source-flux/base-temperature transfer function K thermal conductance (Appendix A) k conductivity, W/m-K L length of absorber element, m N axial conduction no. transfer units (kA/LCf= (Tfo a-Tfl)/r|Ts) N' transfer units effectiveness ratio (N/S) P period of orbit (1.56 hr), s Qs c constant (average) heat input, W, kW q heat flux, W/m2 qs c source input heat flux (Qs yA^, W/m2 R thermal resistance (Appendix A) rs source temperature ratio (Ts/Tfl) rf fluid average temperature rise ratio (Tfo a/Tfl - 1) rg fluid outlet oscillation temperature ratio (|Tfo v|/(Tfo a-Tfl)) s transform variable (iq) T temperature, absorber local temperature, K Ts scaling source temperature (LQS c/kA = tcQsyMc), K t time, s tc time constant (L2/a = LMc/kA), s U base overall heat exchange coefficient (W/m2K) U variable temperature component (Appendix A) X axial coordinate, m x nondimensional axial coordinate (X/L) x fractional energy loss (Appendix A)
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