An example is given below showing the quality of the predictions of
cleanabilityin an upstand geometry testedby the EHEDG test method.This
shows that prediction is indeed possible.
11.4.2 Example 1: Predictionof different zonesof cleanability± short
upstandgeometry
Closed processing lines veryoftencontain a number of so-calledupstand
geometries,e.g. for mountingpressuretransducers, thermocouples,sampling
equipmentor a T-branchfor a bypassing pipe. Upstands are knownto present a
hygiene problemas recirculation zonesare presentin the dead-ends.Guidelines
(Anon,1993)and legislation(Anon,1997) statesthatdead-endsshould be
avoidedand, if unavoidable, the upstand should be as short as possible.
CampdenChorleywood publishedthe results of an EHEDGcleaningtrail on a
shortupstand (Richardsonet al., 2001)showing that the dead-end itselfwas
uncleanedand, surprisingly, also the pipe surfacelocated just downstreamof the
dead-end on the side of the mainpipewherethe upstand was fastenedto the
mainpipewas uncleaned.
Fromthe CFD simulationsof the flow in thatparticularupstandduring
cleaning,areasof different categories of cleaninglevelcan be identified when
comparingwallshearstressand fluidexchange.Figure11.3showsthe areas
exposed to the differentcleaningconditiontypes:
∑ Cleaning conditiontype1. Areasexposed to high wallshearstressand very
goodfluidexchange (goodcleaning conditions) in the entireupstream-
undisturbedpart of the geometryand in the downstreampart located on the
opposite side of the pipeas the upstand.
∑ Cleaning conditiontype2. Areas exposed to highwall shearstress and
intermediate fluidexchange (cleaning conditionsnot so good)in the down-
streamregionof the upstandon the sameside of the pipeas the upstand, but
onlyon the non-horizontal part of the surface.
∑ Cleaning conditiontype3. Areasexposed to intermediatewallshearstress
and poorfluidexchange (badconditionsfor cleaning) in the downstream
regionof the upstandin a bandrunningfromthe upstandand downstreamon
the horizontalpart of the surface.
∑ Cleaning condition type4. Areasexposed to low wallshearstressand very
poorfluidexchange (verybad for cleaning)in the upstanditself.
Predictionof cleanability in the upstand wouldbe as follows.Cleaningis
possible in areas with cleaning conditiontype 1, areasof cleaningconditionstype
2 wouldbe expected to be eithercleanedor uncleaned, areas of cleaning
conditionstypes 3 and 4 would be expected to be uncleaned. It is difficult to state
whether types2 and 3 are cleanedor not, as informationis lackingto evaluate the
levels of fluid exchange± here a critical value is needed. However, the
categorisation of cleaning levelwas performedbasedon experiencefromsimilar
investigations on a spherical valvehouse(Jensen,2003).Comparing the cleaning
202 Handbookof hygiene controlin the foodindustry