Experimental Studies and Comparative Analyses on Apparent Viscosity of Solid Particle, Droplet, and Bubble Suspensions

Background: Suspensions can be frequently seen in natural, industrial, and agricultural processes. The addition of dispersed phases (such as solid particles, droplets, and bubbles) greatly affects the rheological properties of matrix liquid. Therefore, it is very important to understand the rheological properties of particle suspensions for optimizing production processes and improving process efficiencies. Objective: To explore qualitatively the physical law and internal mechanism of the apparent viscosity of suspensions formed by a Newtonian liquid containing solid particles, droplets, and bubbles, respectively. Methods: The apparent viscosity of suspensions was measured and analyzed using a rotary rheometer (MCR302), and the evolution of particles was recorded using a highspeed camera (Revealer 2F01M). Results: When the deformation of deformable particles (such as bubbles or water droplets) is slight (close to a sphere in shape), or the arrangement of rigid particles is disordered, the relative viscosity of suspensions is greater than 1. When the deformation of deformable particles is large (greatly deviating from a sphere in shape) or rigid particles are arranged in order, the apparent viscosity of suspensions decreases and the relative viscosity of suspensions containing deformable particles is less than 1. Conclusion: The apparent viscosity of suspensions is closely related to particle shape, particle arrangement, and volume fraction. The higher volume fraction of particles significantly influences the apparent viscosity of suspensions.