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ARS Home » Research » Publications at this Location » Publication #84609
Title: MIXING OF DYE IN A MODEL SCALD TANK

Author
item CASON JR, JOHN
item SHACKELFORD, A.

Submitted to: Journal Of Poultry Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/25/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary: The water in a poultry scald tank is hot enough to kill suspended bacteria, but water mixing patterns are not known well enough to allow calculation of bacterial death during scalding. A method for calculating tank mixing characteristics would make it possible to set variables to maximize bacterial death or to design scald tanks for that purpose, thus reducing the numbers of bacteria on poultry carcasses. This experiment used dye mixing in water in a specially built tank to develop and test a computer program to predict mixing patterns in a poultry scald tank. The program successfully predicted movement of dye through the tank, indicating that water mixing in vigorously agitated tanks can be calculated successfully.

Technical Abstract: A model scald tank was constructed to study the mixing pattern of water in a poultry scalding system. Tank dimensions were approximately 6 m long by 10 cm wide with a water depth of 18 cm. Water was vigorously agitated with compressed air delivered through a 1.9 cm polyvinyl chloride pipe on the bottom of the tank. Food coloring was added to the tank at a single point and water samples were taken at distances of 0, 0.5, 1.0, 1.5, and 2.5 m every 30 s for 10 min, with 0 or 10 L/min water flow through the tank. Dye concentration was determined spectrophotometrically. A chain drive was then installed above the tank with aluminum paddles (area about 25% of tank cross-sectional area) attached to the chain every 15.2 cm to simulate the movement of carcasses through the water at 140 carcasses/min. Food coloring was added to the tank and water samples were taken every 15 s for 2.5 min, with 0 or 13.5 L/min water flow through the tank. A computer program based on perfect mixing of water in small slices or cells within the tank was adjusted until predicted dye movement matched sampling data, with correlations of 0.91 or better at all sampling points. For scalder designs with uniform mixing of water, the computer model can predict mixing patterns, including counterflow conditions in a single tank, well enough to yield realistic residence time patterns for bacteria suspended in scald water.