Deflection and Stresses in Solar Central Receivers

Abstract

The aim of the design of central solar receivers is to withstand the high non-uniform solar-heat-flux and temperature during the solar-power-plant lifetime. This high non-uniform tube temperature causes high thermal stress, producing creep and fatigue damage. Therefore, is necessary to obtain an accurate estimation of the tube stresses during the receiver operation. In the same way, to ensure the panel integrity, the frontal and lateral tube deflections must be obtained to avoid excessive panel bowing and warpage, respectively. The huge number of simulations needed to perform the creep-fatigue analysis precludes the use of high time-consuming CFD-FEM simulations. To resolve this drawback, a reliable, accurate and fast procedure to obtain the tube stresses, using analytical stress estimation, is proposed. The procedure considers the temperature dependence of the thermo-mechanical properties. The temperature-dependent hoop stress is estimated using the solution for constant mechanical properties whereas the radial stress is estimated taking constant the Young modulus only. The temperature-dependent axial-bending stress is obtained using the non-homogeneous beam equation subjected to the movement restriction produced by tube clips. When the tube displacement is restricted by tube clips, the equivalent stress difference is less than 2% taking temperature-dependent properties and slightly higher than 10% for constant properties. The proposed stress estimation is enough accurate to perform a reliable fatigue-creep analysis and two order of magnitude faster than the CFD-FEM simulations. Finally, the tube deflection and displacement, restricted by tube clips, are derived straightforward using the temperature-dependent tube curvature and the beam theory.