Viscous dissipation and apparent wall slip in capillary rheometry of ice cream

We have analysed sets of capillary rheometry data (0.3 s-1 ≤ γapp ≤ 360 s-1) for a commercial ice cream as it flowed from a freezer on an industrial flow line. Pressure drop measurements were used and particular attention was paid to viscous dissipation effects. A semi-analytical model presented by Bird in 1955 indicated that over one third of the data points were subject to local wall heating, which was consistent with available temperature measurements. The filtered data were used to construct a viscosity function which, when implemented in a detailed CFD simulation of the flow, predicted the observed flow curve behaviour. The results demonstrate that viscous dissipation can be significant in ice cream and that interpretation of this behaviour in terms of wall slip is erroneous. © 2008 The Institution of Chemical Engineers.