Functionally graded materials application in solar central receivers.

In solar central receivers, temperature gradients arisen by incident heat flux are a key factor to their lifetime, since they cause thermal stresses on receiver tubes. In this work, a numerical analysis of how functionally graded materials could help to reduce thermal stresses, is carried out. Using an elastic modulus and thermal expansion coefficient variation throughout the tube radius, the influence of different material gradations between inner and outer tube walls have been studied. Results show how thermal expansion coefficient gradation may have a key role on thermal stress reduction, being necessary to have a material with a lower value at the outer radius compared with the inner radius material in order to homogenize the deformation of the cross section. Although a material with a lower elastic modulus in the outer radius reduces thermal stress, its influence is lower compared with thermal expansion coefficient. Optimizing the volume fraction of each constituent material also helps to enhance the stress reduction on solar receiver tubes. [ABSTRACT FROM AUTHOR]