Enhanced heat flux in vertical natural convection by droplet-induced turbulence

Bubbles are typically used in engineering applications to promote mixing or to enhance heat transport. Using direct numerical simulations with immersed boundaries, we show that light rising droplets enhance the volume-averaged heat flux in vertical natural convection for Rayleigh numbers within one decade in separation and Prandtl number of 7. Specifically, we find that the heat flux can be manipulated by changing the volume fraction occupied by the droplets and the ratio of droplet density to fluid density. The underlying mechanism can be linked to the strength of droplet-induced turbulence, which can be quantified by the ratio of droplet buoyancy to the thermal buoyancy of vertical natural convection.