CONSIDERATIONS ON A FLUID TO FLUID SCALING THEORY FOR HEAT TRANSFER TO SUPERCRITICAL FLUIDS: RECOMMENDATIONS FOR NON-UNIFORM HEAT FLUX CONDITIONS

A fluid to fluid scaling similarity theory has been recently proposed and validated against numerical results. Dimensionless groups initially adapted from concepts at the basis of boiling channel stability were considered and further developed identifying their impact on the flow and heat transfer conditions. Once a reference heat transfer case is selected, to be represented in similarity with a different fluid, a sound procedure for the definition of scaled boundary conditions is now available: the obtained level of similarity in quantitative and phenomenological terms, as assessed by RANS analyses, is very high and involves both bulk, wall, axial and radial distributions of the most relevant quantities. The theory was initially developed for uniform heating along the flow duct. In the present paper, the capabilities of the proposed similarity theory are further analysed considering non-uniform heat flux distributions along the heated length. In particular, a sinusoidal distribution, in similarity with the one postulated for simple reactor cores, is considered. The present analyses confirm and extend the capabilities of the proposed rationale; these results may help experimentalists in setting up counterpart tests in their facilities, showing that some degree of freedom is required in order to obtain trends showing a high level of similarity with different fluids. The present theory, validated against numerical results, seems sufficiently solid to be considered for further validation against experimental data. The present paper aims at raising the interest of the research community for the rationale at its basis, being convinced that a common effort would help in shading light on this very complex and interesting topic.