Future modelling concept for cleaning in the food industry

The hygienic state of process surfaces in food production plants crucially affects the quality of food products. Hygienic requirements must be included in the design of the process as well as when performing the cleaning procedure. Fluid flow plays an important role in both production and cleaning. Specific hydrodynamic parameters have been proved to control cleaning in closed process systems. The work pertains extension of flow modelling to be applicable for improvement of the hygienic state of closed process lines. The aim is to evaluate the suitability of computational fluid dynamics (CFD) simulations for estimation and improvement of cleaning and perform cleaning tests in pilot plant in order to establish a correlation to results for CFD simulations. The CIP-cleaning for test pipe was performed using a pilot plant cleaning system. The CIP-cleaning procedure consisted of prerinsing with cold water for 1 min, cleaning with 60°C detergent solution for 10 min and final rinsing with cold water for 1 min. The flow velocity in pipe inlet was adjusted to 1.5 m/s. The detection of microbial residues was performed by filling the pipe with SH-agar after cleaning. The pilot tests showed that some residuals of microbes were present at the dead end of the pipe. However, the smooth parts of the pipe did not have any microbial contamination after cleaning procedure according to detection methods used (the change of the colour of the agar from purple to yellow indicates microbial residues). CFD is used in many applications to model bulk parameters of fluid flows. Recently model developments have made it possible to resolve what happens in specific positions on and near walls, which is of interest when studying cleaning processes. The CFD simulation shows that the flow rate in dead end of the pipe is almost 0 m/s. A combination of knowledge in fluid dynamics and microbiology gives an excellent base for hygienic design of closed process lines and CIP cleaning systems.