Diffuse-interface lattice Boltzmann simulation of nanofluid cooling for advanced battery thermal management

Abstract

A diffuse-interface lattice Boltzmann model (DI-LBM) is developed for cylindrical lithium-ion battery packs cooled by Al 2 O 3 / H 2 O nanofluids. A double distribution function (DDF) solves the flow and the temperature together on a uniform Cartesian grid, so heat passes correctly between the cell and the coolant without a body-fitted mesh. Three changes are made to the energy equation. First, the thermal collision rate is not modulated, so conduction inside the solid is not artificially slowed. Second, the thermal relaxation time changes with position through the local concentration field, so the solid and the coolant keep their own diffusivities. Third, the Dirichlet penalty source is replaced by a masked volumetric heat-generation term, which lets the cell heat itself from within and restores second-order accuracy in time. The Tiwari-Das nanofluid model and the Guo forcing scheme are used unchanged. The new terms are checked against an exact solution: in a uniformly heated cylinder, steady conduction gives a dimensionless centre-to-surface temperature difference of exactly one quarter, whatever the flow outside. A grid-refinement study shows that the interface thickness, not the grid spacing, controls the temperature jump at the interface. Agreement with published data is within 2.5% for the Nusselt number, the peak temperature and the surface-temperature standard deviation. Adding nanoparticles lowers the peak cell temperature by about 1 K at the heat-generation rate studied, and the benefit grows in proportion to that rate. Along the pack the heat-transfer rate falls because each cell receives coolant that is already warmer, not because the boundary layer changes. A composite figure of merit that also counts pumping power shows that adding nanoparticles is worthwhile only when peak temperature matters more than surface uniformity, because the richest suspension needs 4.75 times the pumping power of pure water. Because the geometry is set by a simple formula rather than by a mesh, the number, size and spacing of the cells can be changed without remeshing, which makes the method well suited to screening pack layouts. The masked source also accepts any heat-generation history, so an electrochemical model of the cell can be coupled in directly.