New measurements of the sticky behavior of skim milk powder

The drying of sugar-rich foodstuffs is often complicated by depositions on the walls of spray dryers, due to the stickiness of the products. This mate rial property has been found to depend on both product temperature and mois ture content and undergoes a rapid change from non-sticky behaviour to stic ky behaviour with only a small change in these parameters. In this investig ation, this so-called sticky point is measured for skim milk powder by meas uring the cohesive force between stirred particles in a heated flask. The l ine separating the sticky and the non-sticky regions is given as a function of bulk temperature and moisture content. For the temperature range from 2 5 to 95 degreesC investigated here, the line shows good agreement with the predicted glass transition temperature for lactose, shifted up by 23.3 K. T his information can then be used in CFD simulations carried out to model th e build-up of wall depositions inside spray drying chambers. As a first ord er approximation to estimate the behaviour of a particle impacting oil a wa ll, sticky particles can be assumed to adhere to the wall, whereas non-stic ky particles can be considered to bounce off it.