FLOW CHARACTERISTICS OF VISCOUS, NON-NEWTONIAN FLUIDS IN HOLDING TUBES OF HTST PASTEURIZERS

The type of flow and ratio of maximum to average velocity in the holdi ng tube was studied for viscous, non-Newtonian fluids, Appropriateness of the salt test in water for holding time determinations was also st udied. Sucrose and guar solutions were used to model rheological chara cteristics typical of ice cream mixes. Flow was observed using a dye s tream and video photography. In straight-line flow, maximum velocity w as 1.6 to 2 times faster than bulk-flow velocity for typical industria l settings (Re-g from 70 to 1900). When elbows were added, the dye str eam was displaced from its centerline position and the ratio of dye st ream to bulk-flow velocity decreased. No extrapolation could be made f rom salt tests in water to minimum holding time for viscous, non-Newto nian fluids.