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 pipel ines in milking installations must have larger dimensions than pipelin es in contact with the product, e.g. in installations used in food tec hnology or in dairies. In attempting to reduce the operating cost for cleaning of the milking pipeline required at least once a day, consequ ent application of a multiphase-gas/liquid flow by utilizing the low p ressure achievable with the milking vacuum installation appears to be a suitable way. It is known that a gas-/liquid flow forms, under defin ed 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 kineti c energy, which is concentrated on relatively small sections of the fl ow system. This excess kinetic energy could be utilized during cleanin g as component ''mechanics'' in the form of wall friction losses. Afte r 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 m ain physical data how the slug flux is brought about and maintained, t he low pressure achievable with the existing milking vacuum installati on being used as motive power for the slugs. The installation of suita ble, mobile measuring points within the tubular loop has enabled the m easurement 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). Addition ally, cleaning trials using pipe elements coated, in the interior, wit h butterfat were performed and the residual tat quantities, which had not been removed by the slug flux, determined. In the tests the volume s of the cleaning solutions could be reduced to approximatively 125 I respectively, the total volume of the pipeline system to be cleaned be ing 450 I; hence, compared with conventional circulation cleaning with total flooding of the cleaning circuit, considerable savings can be r ealized concerning the cleaning chemicals used and energy cost.