11.4 Applicationsof computationalfluiddynamicsin
improvedhygienicdesign
Taking advantage of the possibilities that lie withinCFDsimulations performed
using modelsand a set-upthat is applicablefor industrial purposes(reasonable
simulationtime, timefor modelset-upand timefor meshing) for improving the
hygienic designof foodequipment is a relativelynovelidea.Towardsthe end of
the last centuryand the beginning of this one,workperformedat Campden
Chorleywood (Tucker and Hall, 1998; Hall,1999;Richardsonet al., 2001),
CycloneFluidDynamics(Hauser and Kru»s, 2000)and the Technical University
of Denmark (Jensenet al., 2000,2001)indicates, basedon bothexperimental
dataand generally acceptedmechanisms of cleaning, that dataregardingthe
flow conditionsobtained using CFDcould in fact be usedfor explainingwhy
certain areas of differenttypes of equipmentweredifficultto cleanand others
werenot. The workof the authorsof this chapter(Friisand Jensen, 2002;Jensen,
2003;Jensen and Friis, 2005 ; Jensenet al., 2005)supportstheseconclusions; it
is possible, withincertainlimits, to predictthe outcome of the well-known
EHEDG (EuropeanHygienicEngineeringand DesignGroup)cleanability test
for assessing the In-placecleanability of food-processingequipment (Anon,
1992).
In this section, the processproposed by Jensen (2003)and Jensen and Friis
(2004c) for identifying areasof different levels of cleanability is briefly
explainedto showhowCFDcan helpin improving hygienic design.Thisis
followedby examples on howCFD has beenapplied to provideincreased
understanding of whycertain designsare goodfor cleaning and others are not.
These examples cover:
∑ predicting the outcomeof a an EHEDGcleaning test;
∑ flowin expansions;
∑ cleaning of a spherical-shaped valvehouse.
11.4.1 Virtualcleaningtest
The outcome of the EHEDG cleaning tests can be predicted from CFD
simulationsvisualisingwall shearstressand fluid exchange. The stepsneeded to
make a prediction of the areaswithdifferentdegrees of cleanability are:
- a critical wallshearstressundercontrolled flowconditions is needed for the
cleaning test method; - wallshearstress and fluidexchange is predictedusinga CFDmodel of the
piece of equipment; - areas exposed to differentlevels of wallshearstressin relation to the critical
value are identified± a roughestimationof cleanability is possible; - areas exposed to differentlevelsof fluidexchange relativelyto the fluid
exchange in the undisturbedpart of the floware identified; - grouping the differentareasof wall shearstressand fluidexchange makes the
prediction of areas of different cleanability possible.
200 Handbookof hygiene controlin the foodindustry