Experimental investigation and modelling of steam-heated supercritical co2 compact cross-flow heat exchangers

Abstract As an answer to the reactor accidents in Fukushima, an additional safety concept is currently under development. The aim is a retrofitting of existing and installation in new nuclear power plants. The new concept is a self-propelling supercritical CO2-operated decay heat removal system based on the Brayton cycle. To be able to prove the functionality of such a system or to investigate next-generation power cycles, existing thermal-hydraulic system codes have to be extended and experimentally validated. In this publication, a novel modelling approach for thermal-hydraulic system codes is presented and validated. For model validation, we take results from our 82 experiments including heat transfer and pressure drop characteristics involving two different compact cross-flow heat exchangers with straight channel dimensions of 2x1 mm and 3x1 mm (width x height). On the heat source side, condensing steam flows downwards and on the heat sink side, sCO2 flows horizontally at pressures of 9.50 MPa and 7.75 MPa. At 9.50 MPa, the experimental results of the 3x1 mm CHX show a better thermal-hydraulic performance than the 2x1 mm CHX due to an improvement of the heat transfer rate of up to 6 % and an approximately 20 % lower pressure drop. The experiments at 7.75 MPa show a slight increase in the heat transfer rate compared to 9.50 MPa. By modelling just one representative plate and additional agglomeration of subvolumes, the approach enables fast and accurate calculations. Compared to the experimental results, most of the simulated cases show a deviation of less than 8 % in terms of the heat transfer rate. The simulated pressure drop is in all cases within 92 % of the experimental error band. This approach also enables to simulate large-scale cross-flow CHXs with limited numerical effort (low number of subvolumes). However, the impact of mass flow maldistribution, the choice of modelling options, and the effect of thermodynamic property variations need to be analysed in more detailed further investigations.