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Fluid Dynamic Relationships Involved in Circulation Cleaning¹

Departments of Food Science and Technology and Civil Engineering University of Massachusetts, Amherst

ABSTRACT

Removal of milk deposits on metal pipes using only fluid flow, without benefit of detergent materials, was studied. Soil removal rate was linear at flow rates between 4,000 and 30,000 kg/hour, representing Reynolds Numbers of from 85,000 to 600,000, demonstrating that cleaning effectiveness steadily improved as the pumping rate increased. Use of a spiral to produce convolute flow and the application of a water hammer were ineffective in improving removal of deposits.

A pressure-sensitive transducer, mounted flush with the pipe interior wall, coupled to an oscilloscope, demonstrated pressure changes averaging 0.06 kg/cm² at 2,240 cycles/second at the highest flow rate of 30,000 kg/hour, hut with both values falling as the flow rate was reduced. At 5,000 kg/hour the pressure change averaged 0.006 kg/cm² at 550 cycles/second.

As the laminar sublayer becomes progressively thinner with increasing flow rate it is progressively penetrated by soil protrusions. Thus, cleaning effectiveness is owing both to turbulent shear stress when the laminar sublayer is penetrated by the soil and to viscous shear stress when the soil is submerged in the sublayer.

¹ This study was supported in part by Researeh Grant no. EF-00317, Division of Environmental and Food Engineering, U.S. Public Health Service.