Real-time estimation of the transient thermomechanical behaviour of solar central receivers

Solar radiation variability requires the use of simplified low-computational-cost analytical models for the thermo-mechanical analysis of molten-salt solar receivers. Thus, an analytical quasi-steady 1D-conduction solution for temperature-dependent thermal conductivity is proposed. It is compared against an analytical 2D-conduction expression relying on constant properties and FEM simulations, for various tube thicknesses and convective coefficients during steady-state operation and cloud passages. Small tube-thicknesses and high molten-salt velocity during operation make the Biot number large enough to neglect the angular diffusion: during a steady state, the maximum error in the dimensionless temperature gradient of the 1D-conduction expression against FEM is -0.16% for the regular-operation convective coefficient and 7.37% for a reduced one. Moreover, the high Fourier number for molten-salt receiver-tubes dimensions enables to use the quasi-steady assumption to determine the tubes transient temperature, with a maximum tube-crown dimensionless temperature error around 0.38%. Yet, it is ill-advised for thicker tubes, such as the ones required in sCO2 applications, which present a greater azimuthal heat transfer rate and heat accumulation during transients. Thus, opposite to the transient 2Dconduction solution for constant properties, the quasi-steady radial-conduction expression for variable conductivity is suitable to obtain the transient tube temperature with confidence and to monitor the damage due to high non-uniform purely transient solar-flux in molten-salt receivers.