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    Drop impact of non-Newtonian dairy-based solutions

    Year: 2021

    Journal: Colloid Surf. A-Physicochem. Eng. Asp., Volume 625, SEP 20

    Authors: Balzan, Miguel; Abdollahi, Ayoub; Wells, Frederick S.; Willmott, Geoff R.

    Organizations: New Zealand's Ministry for Business, Innovation and Employment [UOAX1718]

    Keywords: Drop impact; Dairy products; Non-Newtonian fluids; High-speed photography

    Vertical drop impacts of dairy-based solutions on to smooth stainless steel surfaces have been experimentally studied using high-speed photography. Seven test fluids were prepared using infant formula, whole milk, and whey protein powders, reconstituted at 10-45% total solids content in water. Their shear-thinning rheology yielded Herschel-Bulkley consistency indices up to 385 (mPa s)n with a flow index of n = 0.67. Impacts covered ranges of drop diameters (1.75-3.15 mm) and impact velocities (0.90-3.50 m s-1) producing Weber numbers between 35 and 605. Observed outcomes for different fluids were dominated by differences in rheology, and shear-thinning was evident when comparing maximum spread of the two most viscous solutions. To describe the normalised maximum spreading diameter (beta max), a model which interpolates between capillary and viscous regimes, and which was developed for Newtonian fluids, was successfully adapted for shear-thinning drops. The time taken to reach maximum spread (ts) was best described using power-law models in which the dimensional time is proportional to either the Reynolds or Ohnesorge number raised by an exponent. This research should assist with understanding spray-drying of milk, and will be more broadly applicable to processes involving spraying and impact of shear-thinning droplets.
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