the flow patterns) influences transport of cleaning liquid containing detergent (chemistry) and heat (mass and heat transfer). Flow parallel to a surface generates a force (a wall shear stress) on the surface (or the soil on the surface). In a closed process the sole practical method of applying a force is through flowing fluid. The mechanical force is directly connected to the flow by the wall shear stress. The action of fluid flow is importantĬonsidering cleaning of closed processing equipment, fluid flow has an influence on all four components in Sinners circle, either directly or indirectly. On the contrary, if the concentration of chemicals, the temperature of the liquid or the mechanical force is too low, the cleaning time must be increased in order to remove the same amount of soil from the surface (Figure 1b). The longer the contact time between soil, chemicals and heat the weaker the attachment and, as a consequence, the lower the forces needed to remove the soil from the surface. During the application of cleaning chemicals and heat, bonds between soil and surface are loosened, while mechanical forces remove soil from the surface. The energy necessary to remove soil from a surface can be divided into four different contributions (see Figure 1a – based on Sinner, 1960) one from detergents (chemistry), one from temperature (heat), one from cleaning time (contact time between soil and liquid at different concentrations or temperatures) and one from mechanical forces (shear stress). Cleaning can be looked upon as the energy needed to remove soil from a surface. However, qualitative studies can be performed with less detailed knowledge. Fluid flow and cleaningĪpplying CFD for quantitative prediction of cleaning efficiency is only possible when the influences of flow on cleaning of surfaces are known in advance. This paper presents an example of applying CFD for validation of cleanability seen in relation to the EHEDG cleaning test (Anon, 2000). project at BioCentrum-DTU applied numerical models for prediction of flow (Computational Fluid Dynamics (CFD)) to predict areas difficult to clean in closed processing systems (Jensen, 2004).

Hence, alternative methods for validation, or at least prediction, of the efficiency of cleaning procedures are desired. The focus of this article is on equipment in closed process systems where validation of cleaning procedures is difficult (e.g. One area of potential development is the influence of flow patterns on cleaning efficiency in closed equipment (Friis et al., 2002). Hence, tools for evaluating the effect of local phenomena on cleaning characteristics in order to yield in-depth knowledge of why guidelines read as they do, will be beneficial. However, detailed information on good hygienic design in problem areas may be needed to increase the level of hygienic design still further. Generally, such guidelines provide excellent basic rules for the design and construction of equipment and process lines intended for producing safe and high quality products. A prerequisite for easy and effective cleaning is to use processes and equipment designed with respect to optimal cleaning characteristics.Ī good hygienic state of a production line can be achieved by designing and constructing in accordance with guidelines from, for example, the European Hygienic Engineering and Design Group (EHEDG). The ever increasing public awareness of microbial contamination of food also actualises overall optimisation of the hygienic state along the entire production chain. Additionally, the efficiency of cleaning has economical aspects due to reduced cleaning time, reduced consumption of cleaning agents and effluent reduction. Proper cleaning and good hygienic maintenance of processing equipment is a prerequisite for production of safe and high quality products in such diverse areas as: food processing, biotechnology, pharmaceutical processing, paper production, cosmetic production, etc. Finally, some commonly encountered questions on flow conditions during cleaning are discussed based on CFD results. Computational Fluid Dynamics (CFD) is applied for prediction of areas inside closed process equipment, which are potentially difficult to clean. This article discusses the importance of fluid flow as an aspect of the cleaning processes. Thorough understanding of the physical action of fluid flow during cleaning allows for redesign of equipment and design of CIP procedures with respect to optimal cleaning characteristics. the motion of detergent and rinsing water). The efficiency of Cleaning-In-Place (CIP) procedures greatly depends on fluid flow (i.e.

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