(1992)reportedpaperson the cleaning of a numberof foods, suchas: chocolate
desserts (Bird,1992;Reneet al., 1988),coffeesolutions,cornsyrup, meat
products, soyaoil protein (Wilkinson,1982),starch(Maruyamaet al., 1991)and
tomatosoft solids(Cheowand Jackson, 1982a,b). The diverse natureof food
fluidsled to a number of components beingdepositedon heat transfer surfaces
(seeTable 29.2);the foulingmechanismis oftena combinationof chemical
reaction(for example,of proteins) and crystallisation (of mineral salts).
Table29.1 Summaryof the foulingmechanismsand the underlyingprocessinvolved
(Bott,1995).
Foulingmechanism Underlyingprocess
Crystallisationor
scaling
Formationof crystalson the surface.Depositsformedfrom
solutionsof dissolvedsubstanceson to heattransfersurface.
Cooledsurfacesare subjectto foulingfromnormallysoluble
saltsand fats and waxes.Inverselysolublesalts,e.g. calcium
carbonatedepositsontoheatedsurfaces.
Particulate Smallsuspendedparticlessuchas clay,silt or iron oxidedeposit
on heattransfersurfaces.Wheresettlingby gravityis the
determiningfactorthis is thencalledsedimentationfouling.
Chemicalreaction The depositformedon the surface(particularlyheattransfer
surfaces)is not the initialreactant(e.g.in petroleumrefining,
polymerproduction,dairyplants).
Corrosion The materialof the heattransfersurfaceis involvedin reactions
withcomponentsof the fluidto formcorrosionproductson the
surface,i.e. a specifictypeof chemicalreactionfouling.
Biological Microbialfouling± depositionand growthof organicfilms
consistingof microorganismsand theirproducts.
Macrobialfouling± attachmentand growthof macroorganisms,
suchas barnaclesor mussels.
Freezing Depositformedfroma frozenlayerof the processfluid.
Table29.2 The natureof fooddepositsdepositduringproduction,the effectof heating
and the solubilityof the deposit(Grasshoff,1997)
Component Solubility Easeof Changeuponheating
deposited removal
Sugar Watersoluble Easy Caramelisation:moredifficultto clean
Fat Waterand alkali Difficult Polymerisation:moredifficultto clean
soluble
Protein Waterinsoluble, Very Denaturation:denaturedprotein
alkalisoluble, difficult depositsare verydifficultto clean
slightlyacidsoluble
Mineral Watersolubility Easyto Interactionswithotherconstituents:
salts is variablebut most difficult generallyeasierto clean
are acidsoluble
Improvingthe cleaning of heatexchangers 469