Experimental Device and Methods for Studying Milk Deposit Formation on Heat Exchange Surfaces

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Abstract
An experimental mini-heat-exchanger was developed in our laboratory. It can be inserted between the heating and holding sections of a pilot milk pasteurizer without modifying its temperature gradient. Representative soil samples from both heating and holding sections were obtained. Changes in soil composition according to running time were studied over a range of 1 min to 4 hours. Previously cleaned 0.4 mm thick stainless steel plates (304L) had to be cut into pieces before analysis. Different kinds of results were obtained. Scanning electron microscopy showed that the deposit was composed of two different types of soil. A dense deposit could be observed near the metal surface after only 1 min of treatment; the thickness of this deposit increased to 15 μm during the process. Over this layer, a spongy deposit only slightly bound to the former, could be observed Lightly fouled plates were analyzed by “in situ techniques” (X.P.S.) Thick deposits were embedded and sectioned for transmission electron microscopy and histochemical analyses. A microanalytical method was applied to deposits after removal and resulted in detection ranges exceeding 10 mg/cm2.