Analysis of thermal stresses in square ducts of solar receivers operated with liquid sodium

One of the failures in the solar receivers is usually produced by thermal stresses caused by the non-uniformity of the concentrated solar flux and the transient behavior of the climate. The use of liquid sodium as a heat transfer fluid allows to reach higher temperatures to feed more efficient power systems, however, this produces an increase in thermal stresses, putting the safety of the facilities at risk. The change of geometry is an alternative to improve the thermo-mechanical behavior of the receiver tubes. To compare the thermal and hydraulic characteristics, parameters such as the Reynolds number, the pressure loss, the internal heat transfer coefficient, and the mass flow are determined. With these, six equivalences are tested between conventional tubes and square ducts. The results show that for all the conditions of equivalence the thermal stress increases in comparison with a conventional tube, specifically in the corners of the square duct, however, the characteristics of heat transfer and pressure drop can be maintained and improved. These results imply that the use of other geometries can benefit the overall efficiency of the receiver as well as affect the levelized cost of electricity (LCOE).