Handbook of Hygiene Control in the Food Industry

35.3.2 Predefined processusingexisting sensors

The majority of fouling, cleaningand disinfectionprocesses are monitoredusing

fairly conventionalsensors suchas temperature, conductivity,pressure and flow

rate.Cleaning and disinfectionwill usuallyhavethe sensorsincorporated with

the cleaning-in-place (CIP) system rather than the process plant and will

therefore be monitoring the end of line conditions.The deliveryof the processes

is therefore defined by achieving a minimum set of conditions for a

predeterminedtime.Whilethis approachhas beenshown to be effective for

many foodapplications,the processdoes not easilylend itselfto optimisation,in

particular when processlinesare processinga far widerrangeof products than

theywereoriginallydesignedfor. It is unrealisticto expecta single cleaning

process to be optimalfor cleaninga line that might be processing20±30very

differentproducts.

35.3.3 Heattransfer
For heat exchangers, foulingis one of the majorproblems that limitsoperation
and requires regular cleaning. Foulingwill resultin a depositon the heat transfer
surface,which willact as an insulating layerand reducethe heat transfer
performanceof the exchanger.Typically the performance of a heat exchangeris
measuredby the overallheattransfercoefficientand the effectof foulingis to
reduce this. On-line measurement of heat transfercoefficient therefore provides
a simple meansof monitoringthe conditionof the surface during bothfouling
and cleaning.The heat transfercoefficientcan be calculatedfromthe following
equations.
Overall heattransferred to the product:
QàMcpÖToutˇTinÜ Ö 35 : 1 Ü

whereQis the overallheattransferred,W,Mis the mass flowrate of product

being heated,kg/s,cp is the specific heatof the product, J/kg K,Toutis the

temperatureof the productat the exit of the heatexchanger, ÎC, andTinis the

temperatureat the inletof the heatexchanger, ÎC.

In addition

QàUA
t Ö 35 : 2 Ü

whereUis the overall heattransfercoefficient,W/m^2 K,Ais the heattransfer

areaof the heatexchanger,m^2 ,
tis the log meantemperaturedifference,ÎC.

tà

ÖT 1 ˇToutܡÖT 2 ˇTinÜ

lnâÖT 1 ˇToutÜ=ÖT 2 ˇTinÜ

Ö 35 : 3 Ü

whereT 1 is the inlettemperature of the heatingfluidandT 2 is the outlet

temperatureof the heatingfluid.

If the temperatures,product flowrate,specificheat and heat transferarea of

the exchangerare known,the overall heat transfercoefficient can be calculated

from equations 35.1, 35.2 and 35.3.The build-up of fouling can thenbe

578 Handbookof hygiene controlin the foodindustry