Heat Transfer to Fluid Foods

HEAT TRANSFER TO FLUID FOODS Thermorheological Models 

In order to understand or study heat transfer phenomenon, the rheological behavior of a fluid food must be known as a function of both temperature and shear rate. For convenience in computations, the effect of shear and temperature may be combined in to a single thermorheological (TR) model. A TR model may be defined as one that has been derived from rheological data obtained as a function of both shear rate and temperature. Such models can be used to calculate the apparent viscosity at different shear rates and temperatures in computer simulation and food engineering applications. For a simple Newtonian fluid, because the viscosity, r), is independent of shear rate, one may consider only the influence of temperature on the viscosity. For many foods, the Arrhenius equation (Equation 2.42) is suitable for describing the effect of temperature on t]  

As stated previously, for non-Newtonian foods, the simple power law model (Equation 2.3) can be used to describe shear rate (y) versus shear stress (cr) data at a fixed temperature  

The second equation commonly encountered in the food engineering literature and that has been used in several studies (Harper and El-Sahrigi, 1965 Rao et al., 1981  

In both Equations 8.36 and 8.37, h is the average value of the flow behavior index for data at all the studied temperatures. Vitali and Rao (1984a, 1984b) showed that the activation energy terms in Equations 3 and 4 are related according to  

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