HEAT TRANSFER TO PARTICLES IN CANS WITH END‐OVER‐END ROTATION: INFLUENCE OF PARTICLE SIZE AND CONCENTRATION (%V/V)

Abstract

ABSTRACTThe heat transfer coefficients (U and hfp) associated with particulate fluids in cans were evaluated with suspended Nylon particles, during end‐over‐end rotation. Can rotation speed (10 to 20 rpm), particle diameter (19 to 25 mm) and particle concentration (single particle to 40% v/v) were studied as variables using fluids of two different viscosities (1.0 × 10−6 and 1 × 10−4m2/s). Particle transient temperatures were measured by placing a flexible thermocouple attached to the particle, allowing particle motion inside the can. Transient heat conduction equations for a spherical particle with convective boundary condition at fluid‐particle interface were numerically solved to obtain hfp. An overall heat balance equation was solved to obtain U. The hfp values varied from 170 to 1165 W/m2.K with oil and 175 to 1550 W/m2.K with water depending upon process conditions. The U values varied from 110 to 220 W/m2.K with oil and 480 to 800 W/m2.K with water. The hfp increased 10 to 60% with decreasing particle diameter from 25 to 19 mm while it increased about 3 folds as the particle concentration changed from a single particle to 30%. Further increase in panicle concentration to 40% decreased the hfp between 5 and 20% depending upon processing conditions. The effects of particle size and particle concentration on the U were similar to those obtained with hfp with lower magnitudes.