Particle Shape Influence on Heat Transfer in Cans Containing Liquid Particle Mixtures Subjected to End-over-end Rotation

Abstract

Overall heat transfer coefficients (U) and fluid-to-particle heat transfer coefficients (h fp) were evaluated using canned liquids of two different viscosities (oil and water) with suspended Nylon particles during end-over-end rotation. Data were gathered under various conditions: can rotation speed (10 to 20 rpm) and particle shape (sphere, cylinder and cube) with single particle and multiple particles (30% particle concentration) in cans. Particle transient temperatures were measured by installing a flexible thermocouple to the particle centre, allowing particle motion inside the can. Transient heat conduction equations were numerically solved to obtain h fpfor a given particle with a convective boundary condition at the fluid–particle interface. An overall heat balance equation was solved to obtain U. Average h fpvalues ranged from 170 to 1130 W/m 2·K with oil and 190 to 1430 W/m 2·K with water depending upon process conditions. U values varied from 130 to 200 W/m 2·K with oil and 520 and 800 W/m 2·K with water. Analysis of variance showed that particle shape effects on h fpwere significant ( P< 0.0001) with both single particle and multiple particles. With a single particle in the can, the spherical particle (19.05 mm diameter) showed the lowest h fp, followed in increasing order by the cylindrical particle (19.05 mm diameter and 19.05 mm length) and the cube-shaped particle (19.05 mm length). With multiple particles in the can an opposite trend was observed, giving the lowest values of h fpwith cubes and the highest values with spherical particles. With multiple particles in the can, the effects of particle shape on the U were similar to those obtained with h hf, but the magnitudes were lower.