Heat transfer profiles of a vertical, bare, 7-element bundle cooled with supercritical Freon R-12

Experimental datasets on simulated fuel bundles are very limited in availability. Supercritical water-cooled nuclear reactors (SCWRs), as one of the six concepts of Generation IV reactors, cannot be designed without such data. Therefore, a preliminary approach using modeling fluids such as carbon dioxide or refrigerants instead of water is practical. One of the supercritical modeling fluids typically used is Freon (R-12) with the critical pressure of 4.136 MPa and the critical temperature of 111.97 °C.A set of experimental data obtained at the Institute of Physics and Power Engineering (IPPE, Obninsk, Russian Federation) in a vertically oriented bundle cooled with supercritical Freon R-12 was analyzed. This dataset consisted of 20 runs. The test section was a 7-element bundle installed in a hexagonal flow channel with 3 grid spacers. Data were collected at pressures of approximately 4.65 MPa for several different combinations of wall and bulk-fluid temperatures that were below, at, or above pseudocritical conditions. Analysis of the data has confirmed that there are three distinct heat-transfer regimes for forced convention in supercritical fluids: (1) normal heat transfer; (2) deteriorated heat transfer; and (3) enhanced heat transfer. It was also confirmed that the effects of spacers are evident which was previously observed in sub-critical experimental data.