## Flowable Concentrated Suspensions

### Dr Caroline Bird

#### Unilever, Colworth

Ice cream is a four phase system comprising ice, fat, air and an aqueous
phase. We would like to determine under what conditions ice cream will flow at
low temperatures, approximately -5°C to -25°C.

For a given ice cream formulation and temperature we can establish the
viscosity of the continuous phase and the phase volume of solid dispersed phase.
(Note that for a given formulation, changes in temperature will change the
concentration of the continuous phase and the phase volume of ice.) From the
above, we wish to calculate the bulk ice cream viscosity, which may contain a
given phase volume or air. This system is then held in some sort of container
for a given time. A pressure is applied (possible by only gravity and the weight
of the system) and the ice cream is extruded through an orifice. We want to know
what the flow rate is through the orifice.

In other words, we would like to model the flow rate of the material from the
orifice as a function of viscosity of continuous phase, phase volume of solid
phase, ratio of these two, phase volume of air, applied pressure and orifice
size. Due to the complexity of this problem, achieving a full mathematical
description may not be realistic. An understanding of the relative importance of
the factors would be a useful first step.