Thermalhydraulic analysis and heat transfer correlation for an intermediate heat exchanger linking a SuperCritical Water-cooled Reactor and a Copper-Chlorine cycle for hydrogen co-generation

This paper presents the development of a new heat-transfer correlation for the flow of SuperCritical Water (SCW) in bare circular tubes, and its applicability to thermalhydraulic analysis for Heat eXchanger (HX) designs, linking a SuperCritical Water-cooled nuclear Reactor (SCWR) and a Copper-Chlorine (Cu–Cl) cycle-based hydrogen co-generation facility.A large set of experimental data, obtained in SCW flowing upwards in a 4-m long vertical bare tube with a 10-mm Internal Diameter (ID), was analyzed. The data were collected at pressures of about 24 MPa, inlet temperatures from 320 to 350 °C, values of mass flux ranging from 200 to 1500 kg/m2·s and heat fluxes up to 1250 kW/m2, for several combinations of wall and bulk-fluid temperatures that were below, at, or above the pseudocritical temperature.A dimensional analysis was conducted, using the Buckingham Π-theorem, to derive a general form of the empirical SCW heat-transfer correlation for the Nusselt number, which was finalized based on the experimental data obtained within the Normal Heat-Transfer (NHT) and Improved Heat-Transfer (IHT) regimes.The derived correlation showed the best fit for the experimental data within a wide range of flow conditions. This correlation has an uncertainty of about ±25% for Heat Transfer Coefficient (HTC) values and approximately ±15% for calculated wall temperatures.Subsequently, this correlation was used to calculate HTCs in support of preliminary thermalhydraulic calculations for HXs with SCW and SuperHeated Steam (SHS) as the operating fluids. The HXs are to be designed for integration into the No-Reheat or Single Reheat SCW Nuclear Power Plant (NPP) cycles and provide a link to support hydrogen production through the Cu–Cl cycle. Thermal energy will be transferred from the SCWR to an intermediate SHS loop operating at 5 MPa and delivered to the hydrolysis and oxygen-production process steps of the Cu–Cl cycle facility, which operates at temperatures of up to 530 °C. The analyzed HXs are of a double-pipe, counter-flow design.Calculations involved numerical solutions to identify HX outlet flow temperatures, required pipe lengths, number of pipes for each HX unit, mass flow rates and other relevant heat transfer parameters. Various test conditions have been assessed in support of a database to determine feasible configurations for an HX design.