Assessment of fluid-to-fluid similarity criteria to evaluate deterioration of heat transfer in flows of supercritical fluids

Abstract

In nuclear reactors, heat exchangers, and power cycles operating at supercritical thermodynamic conditions, heat transfer deterioration is a concern for the design and safety of primary heat removal components. Such deterioration can cause localized excursions in surface temperature, potentially compromising the integrity of the pressure boundary that contains the pressurized coolant. Therefore, accurately predicting flow conditions that lead to this deterioration is essential. To address this, numerous studies have investigated heat transfer at supercritical fluid states using various working fluids, including water. Building on previously published similarity criteria, this work evaluates deteriorated heat transfer predictive criteria against a more comprehensive dataset of over 480 tests. Unlike conventional approaches that normalize based on pressure at the critical state, the updated similarity criteria define surrogate fluid states using state-space similarity with peak Prandtl number, which arguably has more relevance to the flow. Additionally, dynamic flow criteria were examined by comparing the Richardson number with other buoyancy parameters and relevant ranges of Reynolds numbers were specified. The assessments were conducted for tubular geometries under upward flow, downward flow, and horizontal flow conditions. Particularly strong results are observed for the upward flow dataset, which comprises more than half of the database tests. Based on these evaluations, new predictive correlations for deteriorated heat transfer are proposed, applicable across broad ranges of Reynolds numbers and buoyancy parameters and fluids.