Investigation of Alkaline Cleaning-in-Place of Whey Protein Deposits Using Dynamic Gauging

A novel thickness measurement technique (DYNA-PROBE) allows the study of the behaviour of layers of soft material undergoing cleaning in flowing liquids, in situ and in real time without contacting the surface. The technique is demonstrated here in a study of the swelling and removal of whey protein films related to cleaning-in-place of dairy heat exchanger fouling deposits. The experimental protocol also allows the gauge to be calibrated in situ after each test, yielding measurement accuracies of ±10μm. Cleaning experiments also featured simultaneous measurement of the mass of protein removed and the thermal resistance of the foulant layer, via a commercial heat flux sensor. Experiments performed over a range of solution concentrations (0.3–2.0 wt% NaOH), temperatures (20–50°C) and velocities (0.03–0.30 ms −1; Re = 500–10,000) indicated the existence of an optimal cleaning solution concentration and several other features reported by previous workers. New information provided by the technique, including the sensitivity to shear of the swollen deposit, yields new evidence permitting integration of several conflicting earlier hypotheses on protein cleaning behaviour.