88C-14 |
Temperature and concentration dependence of heat capacity of model aqueous solutions |
R. D. BARBOSA, M. O. Balaban, and A. A. Teixeira. Food Science & Human Nutrition Dept., Univ. of Florida, PO Box 110370, Gainesville, FL 32611 Heat capacity plays an important role in thermal processes and refrigeration. Heat loads and processing times, and equipment size are influenced by the product’s heat capacity. Heat capacity is affected by temperature and composition. The objective of this study was to investigate the temperature and concentration dependence of heat capacity of model liquid solutions and to fit experimental data into predictive equations. The aqueous solutions investigated were binary solutions and combinations of sucrose, glucose, fructose, citric acid, malic acid, pectin, and inorganic salts. Heat capacity was measured with a differential scanning calorimeter in the temperature range from 5°to 65°C, and heating rate of 7°C-min-1. Sapphire was used as the reference standard. Solutions were prepared with analytical grade reagents using double-distilled water at varying concentrations from 1% to 65% (w/v) for sugar solutions, from 0.1% to 10% (w/v) for acid solutions, 0.025% to 2.5% (w/v) for pectin solutions, 0.05% to 5% (w/v) for inorganic salt solutions. Other combinations were tested for component interaction and predictive analysis. Heat capacity increased with increasing water content and increasing temperature. At low concentrations, heat capacity tends towards that of pure water, with less pronounced effect of temperature, and the similar abnormal behavior of pure water with a minimum around 30°-35°C. For low concentrations, a correction factor has been proposed in order to accommodate for the effect of water that evaporates into the headspace of the sample holder due to exponential increase of water vapor pressure with temperature. Coefficients of mathematical equations were determined by fitting the experimental data. These models can be used for prediction purposes of heat capacity of liquid food systems based on the composition and temperature. Special interest would be for numerical-computer based applications where full advantage can only be realized if product properties are known or can be accurately predicted.
Session 88C, Food Engineering: Physical and Chemical Properties
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