Noninvasive Monitoring by Ultrasound of Liquid Foodstuff to Ice Slurry Transitions Within Steel Ducts and Pipes

Ultrasound was assessed as a noninvasive method of detecting dynamic transitions occurring as a scouring high ice fraction ice slurry forces liquid food products through process lines. The attenuation of ultrasound waves passing through a test section was measured within a time window that captured waves with arrival time's characteristic of a direct path through the tubing and its contents. A recording transducer measuring the attenuated signal provided an output in volts, corresponding to the extent of attenuation. Water as a comparable substitute for a liquid food product gave typical values of 2.32 ± 0.07 V for mean amplitude of these waves. The passage of ice slurry reduced this value to 0.75 ± 0.03 V which represented a highly significant (P < 0.001) reduction in transmission. Tomato soup under similar circumstances gave values of 1.93 ± 0.09 V reduced to 0.64 ± 0.02 V when ice slurry flowed between the transducers. Dynamic transitions involving yoghurt and yoghurt mixtures were also detectable except when the yoghurt and the ice slurry shared similar degrees of signal attenuation. Pipe geometry was typically found to introduce systematic changes to recorded values but these did not detract from the basic finding that significant differences were always found between flowing food products and ice slurry, except in the case of pure yoghurt in a large channel. Noninvasive monitoring of dynamic product to ice slurry transitions in food grade steel pipes by ultrasound is readily achievable and could become a method of choice for product recovery systems.