Numerical analysis of a solar tower receiver tube operated with liquid metals

• Forced convection turbulent conjugate heat transfer to liquid metal.
• Circumferentially and longitudinally non-uniform applied heat flux.
• Four-equation turbulence model to locally evaluate the turbulent Prandtl number.
• Parametric analysis by varying the governing parameters.
• Correlations for uniform heat flux valid also for non-uniform heat flux but not suited to evaluate local Nusselt numbers and temperature distribution.

Computational fluid dynamics is used in the present work to analyze the conjugate heat transfer in the receiver tube of a solar thermal tower operated with a liquid metal. A circumferentially and longitudinally non-uniform heat flux, due to solar irradiation, is applied on half the external surface while the other one is considered as insulated. The heat transfer mechanism of liquid metals differs from that of ordinary fluids. As a consequence, the Reynolds analogy, which assumes a constant turbulent Prandtl number close to unity, cannot be applied to these fluid flows. Therefore two additional equations, namely one for the temperature variance and one for its dissipation rate are additionally solved, in order to determine the turbulent thermal diffusivity. The effects of the wall thickness ratio, the solid-to-fluid thermal conductivity ratio, the Péclet number and the diameter-to-length ratio have been analyzed.The calculated average Nusselt numbers closely agree with those evaluated with appropriate correlations for liquid metals, valid for uniformly distributed heat flux. Nonetheless these are not suited to evaluate the local Nusselt number and wall temperature distribution.