CLEANING OF THE MILKING PIPELINE USING A 2-PHASE FLOW

Because of their special tasks (transport of the milk from the milking equipment to the receiver under the influence of gravitational force alone without flooding the pipeline cross section, transfer of the low pressure required for milking to the milking equipment) milking pipelines in milking installations must have larger dimensions than pipelines in contact with the product, e.g. in installations used in food technology or in dairies. In attempting to reduce the operating cost for cleaning of the milking pipeline required at least once a day, consequent application of a multiphase-gas/liquid flow by utilizing the low pressure achievable with the milking vacuum installation appears to be a suitable way. It is known that a gas-/liquid flow forms, under defined conditions, ''slugs'' passing through the pipeline system with high velocity, if the whole pipeline cross section is in contact with the milk. Because of their high velocity these slugs possess a high kinetic energy, which is concentrated on relatively small sections of the flow system. This excess kinetic energy could be utilized during cleaning as component ''mechanics'' in the form of wall friction losses. After a first theoretic consideration of the behaviour of the slug flux in a horizontal pipeline, practical experiments using a tubular loop of 75 m in length (nominal width 73 mm) were performed to determine the main physical data how the slug flux is brought about and maintained, the low pressure achievable with the existing milking vacuum installation being used as motive power for the slugs. The installation of suitable, mobile measuring points within the tubular loop has enabled the measurement of the local slug length (1-7 m), its velocity of migration (5-17 m/s) and the local wall shearing stress (50-250 N/m2). Additionally, cleaning trials using pipe elements coated, in the interior, with butterfat were performed and the residual tat quantities, which had not been removed by the slug flux, determined. In the tests the volumes of the cleaning solutions could be reduced to approximatively 125 I respectively, the total volume of the pipeline system to be cleaned being 450 I; hence, compared with conventional circulation cleaning with total flooding of the cleaning circuit, considerable savings can be realized concerning the cleaning chemicals used and energy cost.