Investigating the effect of starting mode on food fat gel layer formation on cold surfaces

In a previous study, Huang et al. (2012) employed a spinning disc apparatus to study deposition of fats on cooled stainless steel surfaces using model solutions of tripalmitin in non-crystallising paraffin. The apparatus was modified to give more accurate estimation of the test surface temperature, allowing the surface temperature and shear stress to be manipulated independently. The effect of different starting modes, simulating various situations which arise in pipelines, was studied. When fouling is induced by a step change in the test surface temperature, the presence of a subcooled surface promotes the rapid formation, initially, of a gel layer, followed by a period of linear fouling, and eventually falling rate fouling behaviour. When fouling is driven by a change in concentration the initial gel formation step is absent. The linear fouling regime was relatively insensitive to temperature, shear stress and starting mode for the conditions studied here. In the falling rate regime, the rate was determined by the deposit/solution interface temperature, following normal growth kinetics. At low tripalmitin concentrations, of 2.5 wt.%, sigmoidal growth behaviour was observed, which is attributed to the wall shear stress being initially high enough to disrupt the gel. As time proceeded, the gel increased in strength and was able to grow as before.