Handbook of Hygiene Control in the Food Industry

In practicethe design processis morecomplexthanpurelyheat transfer and
thereare a numberof product and process factors that can havea significant
impacton the designof the exchanger(Tables12.2and 12.3).In additionthe
design of the heat exchangeris oftenonlya small,thoughimportant,part of the
completeline.Individual heatexchangersare also beingrequired to handlean
increasinglybroadrange of products, whichhave widelydiffering charac-
teristics,makingoptimisationdifficultas the heatexchangerwill haveto be
designedto handle the most challenging fluid.
Current food industry guidelines on heat exchanger design,particularly
hygiene-relatedissues, refer moreto the overallprocess within whichthe
equipmentis utilisedthanthe individualheatexchanger.The 3 As guidelines
havebeendevelopedwitha strongfocuson the dairyindustry, whereas the more
recent EHEDGguidelinesare focused on the principles involved.

Table12.2 Effectof productand processfactorson heatexchangerdesign

Impacton exchangerdesign

Productfactors
∑ Particles Heatexchangergeometry
∑ Specificheat Thermalloadon exchangerand heattransferarea
∑ Thermalconductivity Heattransferarea
∑ Fouling Heattransferarea
∑ Rheology/viscosity Heattransfer,pressuredrop,exchangergeometry

Processfactors
∑ Temperatureprofile Heatingrate,foulingof exchanger
∑ Pressuredrop Typeof exchanger
∑ Heatingmedium Heattransferarea,fouling
∑ Heatrecovery Heattransferarea,energycosts,exchangergeometry

Table12.3 Influenceof fluidviscosityon heattransferperformance

Servicefluid:Water

Flowregime:Turbulent

Productviscosity Heattransferperformance

(N S mˇ^2  10 ˇ^3 ) (%)

1 100

2 87

4 74

6 67

8 62

10 59

214 Handbookof hygiene controlin the foodindustry