A Study on the Frictional Pressure Drop Characteristics of Shell and Tube Side of Combined Heat Exchanger in a Sodium-cooled Fast Reactor

Abstract

The designing a more reliable decay heat removal (DHR) system to improve the safety is one of the most crucial issues in a pool-type sodium-cooled fast reactor (SFR). To achieving this goal, the newly developed design concept of the combined IHX-DHX unit, called CHX (Combined Heat eXchanger) was proposed. This new and innovative design concept combined IHX and DHX are composed of simplified flow path from the hot sodium pool to the cold pool through a serialized coolant path. The research of the pressure drop on the new geometry of the CHX is very important to evaluate the applicability of this innovative design. The frictional pressure drop characteristics of helically-coiled tube-side of the combined IHX-DHX unit (CHX) were totally investigated. The experimental study was performed to develop correlation for estimating frictional pressure drop of helical tubes in specific parameter ranges. Numerical simulations were carried out to investigate frictional pressure drop in the tube-side CHX and to verify experimental results. Based on the physical meaning of CFD results, friction factor model for predicting friction pressure drop of tube side CHX was presented. This correlation presented in this thesis can be applied to predict the frictional pressure drop of the helical tubes within the parameter range of the experiment performed. The frictional pressure drop characteristics of shell-side in the complicated geometry of the combined heat exchanger were generally investigated based on the experimental and CFD results. The CHX test section was constructed to evaluate the frictional pressure drop characteristics of the shell-side at low flow rates and the results were analyzed. Empirical correlation to predict frictional pressure drops in a flow across tube banks were implemented to the specific helical tube bundle geometry of the CHX unit, and the appropriateness of their application was numerically investigated as well. To figure out the thermo-hydraulic characteristics in the specified flow and geometry conditions, multi-dimensional CFD analyses were carried out and the results based on the physical meaning were thoroughly assessed with those from the empirical correlation. The analyses were performed for the specific operating conditions at i) the decay heat removal mode with very low flow rate as well as ii) the 100% normal operating mode with larger flow rate. Moreover, the flow distribution in each tubes was compared using CFD analysis results. The pressure drop characteristics of the shell and the tube side of the CHX were totally investigated. The overall review of the applicability to actual SFRs in terms of pressure drop has been completed. The results obtained from this study can be useful to adopt an innovative and challenging design concept development for the actual Generation-IV sodium cooled fast reactors.