Evaluation of existing correlations for the prediction of pressure drop in wire-wrapped hexagonal array pin bundles

Abstract

Existing wire-wrapped fuel bundle friction factor correlations were evaluated to identify their comparative fit to the available pressure drop experimental data. Five published correlations, those of Rehme (REH), Baxi and Dalle Donne (BDD, which used the correlations of Novendstern in the turbulent regime and Engel et al. in the laminar and transition regimes), detailed Cheng and Todreas (CTD), simplified Cheng and Todreas (CTS), and Kirillov (KIR, developed by Russian scientists) were studied. Other correlations applicable to a specific case were also evaluated but only for that case. Among all 132 available bundle data, an 80 bundle data set was judged to be appropriate for this evaluation. Three methodologies, i.e., the Prediction Error Distribution, Agreement Index and Credit Score were principally used for investigating the goodness of each correlation in fitting the data. Evaluations have been performed in two categories: 4 cases of general user interest and 3 cases of designer specific interest. The four general user interest cases analyzed bundle data sets in four flow regimes – i.e., all regimes, the transition and/or turbulent regimes, the turbulent regime, and the laminar regime. The three designer interest cases analyzed bundles in the fuel group, the blanket and control group and those with P/D>1.06, for the transition/turbulent regimes. For all these cases, the detailed Cheng and Todreas correlation is identified as yielding the best fit. Specifically for the all flow regimes evaluation, the best fit correlation in descending order is CTD, BDD/CTS (tie), REH and KIR. For the combined transition/turbulent regime, the order is CTD, BDD, REH, CTS and KIR. In the turbulent regime alone, the order is CTD, BDD/REH, CTS and KIR. In the laminar regime, the order is CTD, CTS, KIR and BDD/REH. For fuel assemblies, the order is CTD, BDD, REH, CTS and KIR. For blanket and control assemblies, the order is CTD, CTS, KIR, REH and BDD. For bundles with P/D>1.06, the order is the same as that for the fuel group. Three supplemental evaluations have been performed, one being the 80 bundle set in the transition and/or turbulent regimes with 8 added CFD simulation results. The other two are based on the appropriate set of 109 bundles covering all flow regimes and 108 bundles covering the transition/turbulent regimes, respectively. In these supplemental evaluations the correlation order is CTD, CTS/BDD, REH and KIR for the CFD results added case; CTD, REH, BDD, CTS and KIR for the 109 bundle case and REH, CTD, BDD, CTS and KIR for the 108 bundle case. Several shortcomings were found in the most recently published evaluation for the best fit correlation by Bubelis and Schikorr. The twenty-two bundle set evaluated by Bubelis and Schikorr is reexamined by the methodologies in this study, resulting in the correlation order of REH, CTD, CTS, BDD and KIR.