Cleaning in place of plate heat exchangers – Removal behavior of whey protein fouling

• Beyond a threshold, an increased amount of fouling does not increase cleaning time. • Even with uniform fouling, the CIP flow tends to form preferential paths through the equipment. • At the stage where cleaning is dominated by NaOH diffusion, fouling removal remains consistent across different PHEs. Maintaining hygiene is critical in food manufacturing, and Cleaning-in-Place (CIP) is the standard method used. In this study we examine the CIP process to remove whey protein fouling in plate heat exchangers (PHEs). Fouling layers, representative for typical manufacturing processes, were generated through a controlled fouling process. The effects of temperature, velocity, pH, and amount of fouling on the cleaning process were assessed by measuring protein mass in the CIP effluent. Regardless of the cleaning conditions, removing the last 2 % of fouling mass takes up almost 50 % of the total cleaning time. To further investigate this slow second stage, the cleaning process was paused, and PHE channels were disassembled to quantify the residual fouling distribution on the plates. The cleaning solution (80 °C of 0.5 wt% NaOH at velocity 27.5 cm·s −1 ) formed preferential pathways through the PHE channel rather than following the plate’s liquid-distribution pattern, thus limiting contact with the residual fouling layer. The subsequent fouling removal was primarily driven by NaOH diffusion. A cleaning mathematical model was developed and validated against experimental data, effectively estimating the cleaning process in two distinct PHE systems.