Mixed convection of ferrofluids in a lid driven cavity with two rotating cylinders

Mixed convection of ferrofluid filled lid driven cavity in the presence of two rotating cylinders were numerically investigated by using the finite element method. The cavity is heated from below, cooled from driven wall and rotating cylinder surfaces and side vertical walls of the cavity are assumed to be adiabatic. A magnetic dipole source is placed below the bottom wall of the cavity. The study is performed for various values of Reynolds numbers (100 ≤ Re ≤ 1000), angular rotational speed of the cylinders (−400 ≤ Ω ≤ 400), magnetic dipole strengths (0 ≤ γ   ≤ 500), angular velocity ratios of the cylinders (0.25≤Ωi/Ωj≤4)(0.25≤Ωi/Ωj≤4) and diameter ratios of the cylinders (0.5≤Di/Dj≤2)(0.5≤Di/Dj≤2). It is observed that flow patterns and thermal transport within the cavity are affected by variation in Reynolds number and magnetic dipole strength. The results of this investigation revealed that cylinder angular velocities, ratio of the angular velocities and diameter ratios have profound effect on heat transfer enhancement within the cavity. Averaged heat transfer enhancements of 181.5 % is achieved for clockwise rotation of the cylinder at Ω = −400 compared to motionless cylinder case. Increasing the angular velocity ratio from Ω2/Ω1=0.25Ω2/Ω1=0.25 to Ω2/Ω1=4Ω2/Ω1=4 brings about 91.7 % of heat transfer enhancement.