MECHANICAL CLEANING EFFECT AND PRESSURE DROP OF AIR-WATER-FLOW IN HORIZONTAL GLASS TUBES (VACUUM DAIRY PIPELINES)

Mathematical models are presented which make it possible to calculate pressure drop and mechanical cleaning effect for plant design of vacuum dairy milking pipes. Experimentally, air-water mixtures were sent through a test plant, consisting of glass pipes 0.034 m in diameter and 60 m in length (93 m in some experiments), where a soiled piece of pipe could be inserted without disturbing the flow. The soiling was milk-based and dried on application. Light absorption of the soiled glass tube was measured before and after the cleaning operation, which was performed for 45 s with plain water at room temperature. To calculate the pressure drop, the so-called Dukler constant-slip-method was used. A holdup correlation according to Hughmark was improved to fit the pipe system used. Through linear regression analysis an equation was obtained, describing the cleaning effect as influenced by the Reynold number and the liquid fraction of the air-water mixture.