Contribution of suspended particles to fluid mixing in recipro-mixing with a disk impeller

Measurements of power and mixing time were conducted in particle suspensions by using a mixing system with a disk impeller reciprocated up and down in a cylindrical vessel. In a dilute suspension of particle volume fraction, ϕ, less than 0.2, the power number was almost the same as that in mixing homogeneous liquids but the time required for fluid mixing was decreased with increasing ϕ. In the suspension of ϕ equal to 0.01, the mixing time was well correlated with the gravitational settling velocity of the suspended particles. In a dense suspension of ϕ larger than 0.3, the power number increased appreciably and more time was required for fluid mixing. From the variations of mixing time with the power input per volume, it has been confirmed that the energy required for fluid mixing in a dilute suspension of ϕ less than 0.2 is smaller than that for mixing liquids without particles. This suggests that the gravitational potential energy can be utilized for enhancing fluid mixing in the highly unsteady flow under reciprocation.