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Continuous Two-Phase Slug Flow Heat Exchanger for Ultra High-Temperature Short-Time Heating of Milk and Liquid Milk Products

Bureau of Foods, Food and Drug Administration, U. S. Department of Health, Education, and Welfare, Cincinnati, Ohio 45226

ABSTRACT

To facilitate research on thermal in-activation of enzymes and microorganisms, a slug flow heat exchanger was developed. Nitrogen compartmentalized liquid in the capillary tubing prevented laminar flow and enabled precise estimation of residence times of the fastest flowing fluids in the heating, holding, and cooling sections of the heat exchanger. Nitrogen-to-milk ratio of 1:4 or 1:5; fluid flow of 20 ml per min; holding at from 87.8 to 121.1 C, and from less than 1 to 60 sec, and heating and cooling times of 4 to 5 and 2 to 5 sec were used to evaluate instrument performance. Fresh milk and cream up to 30$ fat or homogenized cream up to 15% fat were processed satisfactorily. Residence time corrections due to heating and cooling sections were .73 and .0 sec, respectively, assuming z = 4.3 C. Holding time was computed from Y_sec = .0854 X_cm ± .57. When no holding section was used, heating time was 3.06 ± .04 sec and correction due to heating was .56 ± .01 sec.