Milk Heat Exchanger Cleaning: Modelling of Deposit Removal

Abstract

The removal of solid deposits encrusted on heat transfer surfaces of milk heat exchangers using chemical cleaning agents is a complex procedure. It involves a number of physical and chemical parameters such as flow mechanics, working time, composition, concentration and temperature of the cleaning agents, composition of the deposits, and the condition (shape, roughness) of the surfaces. Due to the variety of influencing factors, the description of the deposit removal kinetics using a simple mathematical model appears to be extremely difficult. In a series of extensive cleaning trials on a computer-controlled experimental cleaning plant using standard test soils and various CIP-procedures, the removal of deposits was monitored using a video camera in combination with a computerized image processing system. The experimentally gained time functions for deposit removal were inserted into a new mathematical model. This model initially was developed for the removal of dust from floor carpets by vacuum cleaning. It consists of a two-parameter exponential function with a specific time constant (the time, at which a cleaning degree of cleaning of 63.2% is achieved) and a parameter that is called slope (in a special grid the equation is a straight line with this slope). The soil removal model using these two parameters, obtained by regression from the experimental data, correlated with the experimental values with a coefficient of correlation of up to 0.995. The derivation of the proposed model and its physical explanation are given in this paper.