Development of a dimensionless engineering correlation for calculating the diodicity of an asymmetric membrane hydrodiode

Modeling passive safety loops in the system thermal-hydraulic codes RELAP5 and TRACE requires explicit calculation dependencies that describe the behavior of hydraulic components. Hydrodiodes are passive devices providing different flow resistance in forward and reverse directions without moving parts. Hydrodiodes are key components of reactor emergency core cooling systems during loss-of-coolant accidents. The aim of the research is to formulate an analytical, dimensionless correlation that approximates the diodicity of an asymmetric diaphragm hydrodiode in the self-similar regime and is suitable for direct implementation into user-defined tables of system thermal-hydraulic codes for nuclear power plants. Based on 54 computational fluid dynamics points (RANS, k–ω ∙ SST) and full-scale experimental data for the optimal configuration, the author obtains a dimensionless correlation for the diodicity of an asymmetric diaphragm hydrodiode using Buckingham's π-theorem, symbolic regression and nonlinear least squares. The formula relates the diodicity to the flow section similarity number, relative eccentricity, and plate inclination angle. On the training dataset, the coefficient of determination is R2 = 0.88 with a root mean square error of RMSE = 0.16; the mean absolute percentage error MAPE is 8.2 %; the discrepancy compared to full-scale experiment is 3,9 %. The derived relationship exhibits scale invariance, correctly reproduces the symmetry boundary conditions, and is suitable for implementation into the user-defined tables of RELAP 5 and TRACE system codes via the Form Loss component. The range of applicability corresponds to the self-similar regime where diodicity is independent of the Reynolds number.