Being influenced by the turbulent structure, it is expected that the heat transfer can be enhanced by having ribs, spacers, grids, etc. placed in the flow. Some sources of the primary data on heat-transfer enhancement at supercritical pressures in various fluids are listed in Table 9.1. The main idea of these experiments was to find the most effective ways to enhance supercritical heat transfer and to delay or to avoid the deteriorated heat-transfer regimes in various flow geometries. These studies were important to supercritical "steam" generators where heat fluxes are quite high. Therefore, supercritical water flowing in circular tubes was the primary choice for investigations. Some studies were performed in supercritical carbon dioxide as the modeling fluid.