Optimization of the cleaning efficiency by pulsed flow using an experimentally validated CFD model

摘要

The enhancement of the cleaning efficiency of CIP systems is playing a key role in improving food production. Higher efficiency leads to both, better hygienic conditions as well as to shorter downtimes and, hence, to lower production costs. Cleaning models based on CFD can be a tool, which enable to identify locations in a plant difficult to clean and enhance the cleaning efficiency by appropriate fluid dynamics, i.e. the application of transient flows. The objective of this work is to enhance the local cleaning efficiency using pulsed flow. It was shown that this aim can be achieved through the application of transient flows [Bode 2007]. The present research project concentrates on gaining an in-depth knowledge of parameters influencing the cleaning process while utilizing pulsed flow. The efficiency and the effective reach of the pulsation are of special interest. In this work, a CFD cleaning model was generated which is based on the assumption of a diffusion controlled cleaning process. The physical basis of the model is the analogy between heat and mass transfer. Several steps of validation with experimental data were carried out. A fluid dynamic validation resulted in the best turbulence model and the appropriate mesh discretization for the expected fluid flow regime. This was followed by a complex validation of the cleaning mechanism, using experimental data of local cleaning times in several complex geometries with varied static and transient flow velocities. A modified waxy maize starch with phosphorescent tracers is used as model food soil. The cleaning model is suitable for the calculation of the qualitative cleaning progress for all fouling systems, where the cleaning mechanism is diffusion controlled. The received results show a good agreement between the measured and simulated cleaning times for complex geometries and transient flow regime. It is now possible to visualize the effect of complex pipe geometries or inappropriate hygienic design on the overall cleaning time. Especially in locations difficult to reach with steady flow, the application of pulsed flow shows a shorter cleaning time. Based on the presented new CFD model the cleaning efficiency using pulsed flow can be predicted.