Abstract
Ice cream viscosity is one of the properties that most changes during crystallization in scraped surface heat exchangers (SSHE), and its online measurement is not easy. Its estimation is necessary through variables that are easy to measure. The temperature and power of the stirring motor of the SSHE turn out to be this type of variable and are closely related to the viscosity. Therefore, a mathematical model based on these variables proved to be feasible. The development of this mathematical relationship involved the rheological study of the ice cream base, as well as the application of a method for its in situ melting in the rheometer as a function of the temperature, and the application of a mathematical model correlating the SSHE stirring power and the ice cream viscosity. The result was a coupled model based on both the temperature and stirring power of the SSHE, which allowed for online viscosity estimation with errors below 10% for crystallized systems with a 30% ice fraction at the exit of the SSHE. The model obtained is a first step in the search for control strategies for crystallization in SSHE.
Highlights
In the ice cream crystallization process, viscosity is the most evolving property
The results show that the energy increase in the power consumed by the stirring motor and the ice fraction were similar in all the tests carried out at different agitation rates.of the SSHEThe is proportional thethe increase in increase the fraction of crystals formed, and must be related results showtothat energy in the power consumed by the stirring motor of the to the is increase in the to viscosity of theinice during its crystallization
The liquid mixture near the freezing point behaves as a shear-thinning pseudoplastic fluid, which of the mixture is dependent on the shear rate, this being a typical characteristic of a non-Newtonian has already been reported by other authors [2,31]
Summary
In the ice cream crystallization process, viscosity is the most evolving property. This is due to the liquid transforming into a semi-solid as a result of the occurrence of ice crystals. Clarke [1] described that ice cream mixture viscosity increases for two reasons: the liquid mixture temperature decreases and the volume fraction of solid particles (ice crystals) increase. Ice cream viscosity is determined by the non-frozen phase viscosity and the ice fraction generated during its freezing. For an ice cream liquid mixture, apparent viscosity values have been reported between 0.1 and 0.8 Pa·s, at a shear rate of 115 s−1 [2,3]. For already crystallized ice cream, there are not many references about viscosity values
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