In order to design and to adapt equipments for food processing, it is essential to know thermophysical properties. Once temperature and composition affects these properties, models based in such factors are important for further calculation. In this work, density and dynamic viscosity of bovine milk, probably the most processed food fluid in the world, were determined within large ranges of temperature and major constituents (moisture, fat, lactose, protein and minerals), based on typical processing values. Density varied from (962.01 to 1100.45) kg/m3 and dynamic viscosity varied from (0.60 to 63.70) mPa∙s. Temperature and moisture content negatively affected both properties, while lactose, protein and minerals contents positively affected them. An increase in fat content reduced density and increased dynamic viscosity. Experimental density data were fitted to the simplest multiple linear model and dynamic viscosity data were fitted to a multiple type Arrehnius’ model, obtaining good agreement.
Liquid–liquid
equilibrium data of aqueous two phase systems
(ATPS) composed of polyethylene glycol (PEG) 1500 g·mol–1 + sodium sulfate + water at T = (293.15, 303.15
and 313.15) K and p = 0.1 MPa were determined. The
density of the top and bottom phases of tie-lines (TL) was determined.
The universal functional activity coefficient (UNIFAC) model was correlated
to the experimental tie-line data, and the root-mean-square deviations
(RMSD) between experimental and calculated data were considered in
the calculation. The salting-out effect was evaluated using the model
of the effective volume (EEV). The temperature had no influence on
the binodal curves and TL, this effect can be attributed to a small
enthalpic contribution in the phase separation process. Increases
in the ATPS constituents concentrations resulting in an increase in
the density of the phases. The increase in temperature resulted in
an increase in the salting-out effect. The highest estimated value
of EEV was obtained for a system at 293.15 K. Calculated RMSD between
the experimental and predicted LLE compositions for the PEG 1500 +
sodium sulfate systems was 1.71%. The results of the UNIFAC model
agree with the experimental tie-line values. The use of this thermodynamic
model allowed the acquisition of reliable data for the system, being
able to reduce the number of experiments performed.
The influence of temperature and water content on thermophysical properties (density, thermal diffusivity, thermal conductivity and specific heat) of genipap (Genipa americana, L) pulp at medium maturity were studied. The thermophysical properties were determined at concentrations between 6.0% m/m and 24.0% m/m of water content and temperatures range of 5 to 80 • C. The density decreased with increase in temperature and water content, while the thermal diffusivity and conductivity increased as temperature and water content increased. The specific heat decreased with the moisture content. Empirical models were fitted to the experimental data for each property and the accuracy of those models was checked.
Liquid–liquid equilibrium data of aqueous two-phase
systems
(ATPS) composed of polyethylene glycol (PEG) 8000 + sodium sulfate
+ water, PEG 8000 + ammonium sulfate + water, and PEG 8000 + magnesium
sulfate + water at T = 298.15, 308.15, and 318.15
K and pH 2.0 were determined. The universal function activity coefficient
(UNIFAC) model was correlated to the experimental tie-line data, and
the root-mean-square deviations (RMSDs) between experimental and calculated
data were considered in the calculation. The effects of temperature
and cation type on the spinodal curves were evaluated. The salting-out
effect was studied by the determination of the effective excluded
volume (EEV). Rising temperature resulted in an increase in the biphasic
region and tie-lines. Regarding the cation type, the phase-separation
abilities followed the order Mg2+ > Na+ >
(NH4)+. Increases in the overall composition
of the
systems resulted in increased tie-line lengths. The tie-line slope
absolute values also tended to rise with increasing temperature. Increasing
the ATPS constituent concentrations resulted in an increase in the
phase densities. The increase in temperature resulted in an increase
in the salting-out effect. The exclusion volume values increased in
the following order: (NH4)+ < Na+ < Mg2+. The overall mean deviation between the experimental
and correlated LLE compositions for the PEG 8000 + ammonium sulfate
+ water, PEG 8000 + magnesium sulfate + water, and PEG 8000 g mol–1 + sodium sulfate + water was 3.901%. The results
of the UNIFAC model agree with the experimental tie-line values. This
allows the use of this model to obtain reliable data for this system,
thus reducing the number of experiments to be performed for a processing
design.
The sizing of equipment used in food processing, particularly heat exchangers and other equipment that require pumping of products, requires accurate data of thermophysical properties. Milk is one of the most processed liquid food fluids in the world and currently data on its thermophysical properties are limited. In a previous paper (Alcântara et al., 2010) density and dynamic viscosity data of bovine milk were presented and how these properties are affected by temperature and composition, in ranges commonly encountered in food processing. Here the thermal diffusivity and specific heat data for milk are presented, evaluating the effect of composition (moisture, fat, lactose, protein and minerals contents) and temperature (only for thermal diffusivity). Linear regression was used and the best models were selected based on the determination coefficient (R²), lack of fit, significance parameters and root mean square error (RMSE) values. Predictive ability of fitted models was compared with Choi and Okos (1986) correlations. Thermal diffusivity ranged from (1.00 to 9.03) × 10-7 m2s-1 and specific heat from (3.078 to 4.121) kJkg-1K-1. Thermal diffusivity presented a polynomial quadratic behavior affected by temperature and composition, except for lactose concentration which showed no significant effect (p0.05). For specific heat, increase in the moisture content led to an increase in the specific heat while elevations in fat, protein, lactose and mineral contents promoted a decrease of this property. In both cases the fitted models showed satisfactory R² values, nonsignificant lack of fit (p0.05) and significant parameters (p0.05), with RMSE values lower than Choi and Okos (1986) correlations. From the properties presented here and in the earlier paper, accurate calculations can be made for correct sizing and adaptation of equipment, as well as provide information of other thermophysical properties such as thermal conductivity and thermal expansion coefficient.
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