Scraped Surface Heat Exchangers (SSHE) are widely used industrially for treating food products with high viscosity (cheese, ice cream…). In this kind of heat exchangers, the presence of spinning blades allows a regular renewal of the product surface, preventing clogging and improving heat transfer. However, if the body of the heat exchanger is relatively easy to clean, the entry and the exit of SSHE are poorly cleanable due to their particular geometry and the presence of seals which make cleaning difficult. A specific study was conducted in the entry bowl of a SSHE, whose design has been optimized by the manufacturer in order to minimize the risk of deposit eliminating the hydrodynamical dead zones. The main goal of this study is to extend the correlation previously identified on simple systems between the wall velocity gradient and the cleaning ability to optimize the hydrodynamic conditions leading to efficient cleanability. For this purpose, measurements of wall shear stress were made using the electrochemical method on the one hand, for different hydrodynamic conditions and especially in the presence of a pulsating flow. On the other hand, cleanability measurements after microbiological fouling and cleaning were performed. Two types of contamination were tested: spore-forming bacteria and biofilm. The clean in place protocol (0.5% NaOH, 60°C, 10 min.) is deliberately low in order to compare the different areas and allow an effective numbering of the colonies after culture. It follows that the geometry of the bowl tested presents no dead zones. However, the available space for flow significantly reduces the Reynolds number and turbulence intensity, which induces three areas of increasing contamination, corresponding to conditions of mean shears and low fluctuations. The use of a pulsating flow increases these fluctuations, and thereby reduces the residual contamination.
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