Numerical Investigation of Combined Effects of Thermocapillary Flows and Buoyant Convection in Self-Rewetting Fluids using Lattice Boltzmann method

Self-rewetting fluids (SRFs), such as aqueous solutions of high carbon content alcohols (e.g., n-butanol), show anomalous nonlinear (quadratic) variations of surface tension with temperature involving a positive gradient in certain ranges, leading to different thermocapillary convection compared to normal fluids (NFs). They have recently been used for enhancing thermal transport in a variety of applications. We use a robust lattice Boltzmann (LB) method based on central moments and multiple relaxation times to simulate the fluid motions and the transport of energy, and systematically study the combined effects of thermocapillary convection and buoyant convection in SRFs enclosed within a cavity. The attendant Marangoni stress condition as well as the imposed nonuniform heat fluxes on the free surface are both implemented using a novel moment-based boundary condition approach in the LB method. We investigate the effect of the dimensionless quadratic sensitivity coefficient of surface tension on temperature and other characteristic parameters at different Rayleigh numbers on the flow patterns and rates of heat transfer in SRFs and compare them with those arising in NFs.