Utilização de metodologia em estado transiente como ferramenta para a determinação da difusividade e condutividade térmica de polpa de goiaba em baixas temperaturas

Abstract

The demand for concentrate juice and frozen products is increasing, making knowledge of their thermophysical properties more meaningful. In this study, we determined conductivity and thermal diffusivity of red guava pulp at low temperatures and the data obtained experimentally were compared with values estimated by structural models in the literature. The thermal diffusivity was measured indirectly through the conductivity and values obtained from models to calculate the density and specific heat. The conductivity varied from 0,64 Wm-1K-1 to 1,66 Wm-1K-1 at temperatures of 0 to -30 °C, respectively, and diffusivity was between 5,01x10-7 m2 s -1 to 1,03x10-6 m2 s -1 at temperatures of -5 °C to -30 °C, respectively. Linear heating probe method was used for which was calibrated with 10% sucrose solution at temperatures of analysis. The freezing point also was measured, ice fractions were calculated using different equations and used in Series, Parallel and Maxwell-Eucken models. The data obtained experimentally for thermal conductivity and indirectly diffusivity were submitted to regression analysis for fitting functions that allow direct calculation of those properties using only the knowledge of the history of temperatures during heat processing.