Numerical simulation of a supercritical heat-exchanger using the lattice Boltzmann method

Recently, supercritical heat-exchangers have recovered the attention of researches to applications in GenIV supercritical water-cooled reactors (SCWR). As supercritical fluids have high heat capacity and low viscosity, they present an efficient heat exchange and reduce the overall energy requirements, resulting in more compact devices. However, when crossing the pseudocritical temperature, as it occurs for the water in both the core and in the primary heat exchanger, these fluids experience high variations in properties, which can affect the heat transfer and must be well understood. In this paper, a modified lattice Boltzmann method (LBM) to deal with supercritical flows near the pseudocritical point is proposed. It is based on modifications of existing models for conjugated heat transfer problems, enhancing the numerical scheme to deal with temperature-dependent properties. The new proposed model was employed to investigate a heat exchanger operating with water as both a hot (supercritical) and cold fluid, mimicking one possible scenario for the primary heat exchanger in a SCWR. The effects of the supercritical–subcritical transition were evaluated by performing a parametric evaluation of the hot fluid mass flow rate. The results evidenced the multi-dimensionality of the supercritical–subcritical transition, with the fluid flow presenting high thermal property variations in both x and y directions. It elucidates the importance of considering both temperature-dependent properties and more robust numerical methods when dealing with supercritical flows near the pseudocritical point. • An enthalpic LBM is proposed to deal with supercritical fluids. • Fluid properties variations are detrimental for simulating supercritical flows. • Heat transfer is sensitive to property variations in subcritical–supercritical transitions. • The transition is multi-dimensional, making 1D approaches potentially unsuitable. • The supercritical transition may occur locally while the bulk remains subcritical.