Research On Engineering Calculation Methods Of Heat Transfer And Flow Resistance For Small Reactors Once-through Steam Generator

Based on the helical tube experimental data,the heat transfer and flow resistance models for helical tube have been developed in program RELAP5.With the program code in RELAP5,existed helical tube empirical formula of heat transfer and flow resistance had been studied.With the experimental data provided by CGN,Suitable model was obtained by nonlinear fitting by setting the relation with undetermined coefficients in MATLAB.Finally,appropriate model to describe the new empirical formula for helical tube was rebuilt in RELAP5 based on the original model.The thermal equilibrium gas rate was used to determine the helical tube heat transfer partitions.The heat transfer area was divided into four parts with suitable formula including single-phase fluid heat transfer,two-phase boiling heat transfer,lack liquid zone heat transfer and single-phase gas heat transfer.Also the single–phase and two-phase pressure drop correlations were modified on the basis of original form.With input parameters,New formula was compared with calculation results by original RELAP5 program and some conclusion was obtained:Compared with straight tube,the subcooled boiling in helical tube is shorter.And The local dry-out point of helical tube is associated with the geometric shape.When dry-out occurs,the heat transfer coefficient behind the dry-out point will decline smoothly replacing dispersion flow.And the heat exchange capacity is stronger than straight tube.New fitting for the helical tube heat transfer equation in the program is built and the result shows new relation can calculate helical tube heat transfer and pressure drop with different thermal equilibrium gas rate.Compare with experimental data,heat transfer coefficient variation curve have a good match.Compared with original RELAP5 program,the heat transfer coefficient from experiment is 63.7% more than original program result.Original RELAP5 cannot show the performance of helical tube without geometric parameters of helical tube as coil diameter.With the high gas rate calculation,the analysis of heat transfer deterioration is CHF-DNB judgment which underestimate the helical tube in the lack liquid heat transfer performanceThe pressure drop model of helical tube in program use straight tube formula while single-phase and two-phase pressure drop is 52% higher than straight tube numerically.The geometrical parameters of helical tube mainly affect the friction pressure drop and having no effect on the gravity pressure drop while the critical position influence acceleration pressure drop.