The effect of translational and rotational relative velocity components on fluid-to-particle heat transfer coefficients in continuous tube flow

A liquid crystal technique was used to determine average fluid-to-particle heat transfer coefficients (hfp) for single spherical hollow aluminium particles heating in carboxymethylcellulose solutions in continuous tube flow. The particles' linear and rotational velocities were also measured by videotaping the particle motion at a bottom position. Particles with different diameter and density were used in solutions with different viscosities and at different flow rates (7 < Reynolds < 284; 144 < Prandtl < 1755). The values of the average heat transfer coefficient were between 334 and 1497 W/m²C. The results showed that both the relative fluid-to-particle velocity and the particle rotational velocity influence the heat transfer coefficients, although it is not possible to individualize their effects. However, the addition of the individual effects, predicted by using published dimensionless correlations, yielded a good fit with the experimental values.