understanding of the interactionbetween flowcharacteristicsand soil attachedto
surfaces can aid validation of hygienic design. Such information can be
containedin fluiddynamics theoryand modelsor by rulesof thumb.Thistype
of information can be used to assist improvement the design of process
equipmentwithrespect to cleaning characteristicsand optimisationof cleaning
procedures.Predictionof cleaningefficiency in especiallycomplexpartsof
closed processplantsby use of computationalfluiddynamics (CFD)has an
excellent potentialfor desktop improvementsand computerpre-validation of the
hygienic performanceof processplants. Hence, the hygienic design of closed
equipmentrelated to the movementof detergent can be improved.
11.2 The importance of flowparametersin hygienicperformance
The importance of addressingfluid flowin relationto cleaningefficiencyin
closed processes has beenillustrated(e.g.Be¬ne¬zechet al., 1998; Lelie¡vreet al.,
2002,2003;Jensen,2003).In this section, differentaspectsof the influence of
flow on cleaningcharacteristics are discussed withreference to published
studies and newideason the subject. Guidelines and legislationon flowcon-
ditions in processing equipment to obtainsatisfactorycleaningcharacteristics
are discussed and new parameters for validating the cleaning effectof floware
presented.Finally, a brief discussionon methodsfor visualising flowfeatures is
given to underlinethe needfor CFDtoolsin hygienicdesign.
11.2.1 Importance of flowin cleaningof closedequipment
Froma simplistic pointof view,proper hygienic designof closed equipmentis
an exerciseof making detergent (temperature and chemicals) accessible to the
soil for a certainperiod(time)and exposingthe soil to a force(mechanical)that
is sufficientlylarge to remove the soil fromthe surface. Sinner(1960)suggests
thatfor cleaning to takeplace all fourcleaningparameters± temperature,
chemicals,timeand mechanicalaction(Fig.11.1a± Sinner'scircle)± should be
present. A changein one of the parameters in Sinner's circle must be compen-
sated for by changes in the threeother parameters.Additionally,detergentand
heat haveto be transported to the soil on the surfaceto be effective and the soil
must be removed from the surface and out of the equipment to avoid
reattachment. In this section,the importance of flowis illustratedbasedon
Sinner's circle and the effect of flowon the fourpartsof Sinner's circle is
introduced.
Anycleaningprocedurecan be consideredas a process of applyingthe
required energyneeded to removesoil froma surface. Sinner(1960)and Holah
(2003)dividethe energy into foursources: contacttime (time),detergent
temperature(temp.), detergent strength (chem.)and mechanical action (mech.).
The temperatureand chemicals weakenthe bondbetweensoil and surfaceas a
192 Handbookof hygiene controlin the foodindustry