On Experimental and Computational Investigation of Heat Transfer Deterioration and Hydraulic Resistance in Annular Channel and SCWR 3-Rod Bundle

The experiments on upward flow of supercritical water in a vertical annuli and 3-rod tight bundle simulator made of 485-mm heated-length tubes of 5.2-mm OD and 4.5-mm ID with four helical ribs of 0.6-mm height, 1-mm width, and axial 400-mm pitch are presented. Heat transfer and pressure drop under various operating conditions (inlet pressure and temperature, flow mass rate and heat flux) were investigated. Longitudinal wall temperature profiles made it possible to determine the place and flow thermal state of heat transfer deterioration (HTD) onset. Analysis of the obtained data (about 200 regimes) proved their good enough agreement with the correlations previously derived by the authors both for the heat flux rate (q/G)b of HTD beginning and for pressure drop in round tubes and annular channels. These correlations were updated to correct the results of their prediction. Computational fluid dynamics and its counterpart computational heat transfer were used for modeling the above-mentioned thermohydraulic processes studied in the first part of the work by finding the most adequate flow turbulence model and optimized domain meshing. The accepted model was benchmarked by some data on heat transfer and pressure drop in tubes and annular channels cooled by SCW.

New Models of Droplet Deposition and Entrainment for Prediction of Dryout in Uniform and Non-Uniform Heated Annuli

In this paper, we present a phenomenological modeling of annular flow for dryout prediction in vertical annuli by adopting a new set of correlations of droplet deposition and entrainment. The performance of the new correlations is tested by using the experimental data of Becker and Letzter [1] measured in a 3000mm annulus under bilateral as well as unilateral heating conditions, and the experimental data of Becker et al. [2] obtained in a 3650mm long annulus in respect of eight different axial heat flux profiles. The applicability of two widely used correlations of droplet deposition and entrainment in annuli which were derived from flows in vertical tubes was also checked. It was shown that large discrepancies were observed for the tube-based correlations, while for our present model the predicted CHFs as well as the positions of dryout occurrence in the case of non-uniformly heated annuli agree well with the experimental data.