Abstract
ABSTRACT Residence times and residence time distributions in a scraped-surface heat exchanger were determined for single polystyrene spheres 10.00, 14.38, and 22.17 mm in diameter suspended in aqueous solutions of sodium carboximethylcellulose. The tests were conducted for solution consistency coefficient (m) ranges of 1.0 ±0.04, 4.5 ±0.09, and 8.0 ±0.16 Pa-s'* (flow behavior indices (n) of 0.84, 0.68, and 0.65, respectively), mass flow rates of 0.190, 0.298, and 0.428 kg/s, and blade speeds of 70 and 190 RPM. The standard deviation of the residence times decreased with increasing blade speed, mass flow rate, and sphere diameter and was unaffected by viscosity changes. Differences in viscosity, blade speed, and particle diameter levels did not affect the minimum and mean residence times. Mean particle residence times were equal to mean fluid residence times at the low and medium flow rate levels and only 16% shorter at the higher flow rate.
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