Tales Márcio de Oliveira Giarola

Thermal Conductivity Measurements and Predictive Models for Frozen Guava and Passion Fruit Pulps

The thermal conductivity of guava and passion fruit pulps was measured at temperatures between −30°C and their initial freezing temperature using the hot wire probe method. The results were compared with those calculated using the parallel, perpendicular, and Maxwell-Eucken models as a function of the ice fraction, and the discrepancies in the results are discussed. Exponential equations were then fit to the experimental data to determine the thermal conductivity of the pulps as a function of temperature. These equations produce mean relative errors of 8.1 and 4.0% in the values estimated for the guava and passion fruit pulp, respectively.

Thermal Conductivity of Mango Pulp (Mangifera indica L.) Cultivar “Ubari” in Freezing Temperatures

The aim of this study was the experimental determination of the thermal conductivity of mango pulp of cultivar “ubari” and its subsequent comparison with values estimated using different structural models, such as the serial, parallel, and Maxwell-Eucken models. A linear heating probe calibrated with a solution of 10% sucrose was utilized. Heat was applied to the probe, generating an increase in temperature, which was recorded through a signal conditioning system. The thermal conductivity of the pulp was calculated from the slope obtained by linear regression of the natural logarithm of the temperature versus time. The data was within the range of 0.465 to 1.595 W/m.K for temperatures of 0 and –30°C, respectively, showing an increase of conductivity with freezing. The initial freezing temperature and ice fraction were determined at every temperature of analysis for further use in the models. The best fit to the experimental data were obtained using the Maxwell-Eucken model, yielding minimum and maximum errors of 10.8 and 17.8%, respectively. An exponential model was fitted, which allowed for the direct calculation of the thermal conductivity of mango pulp using only the knowledge of the recorded temperature during thermal processing.