Modeling multiscale transport mechanisms, phase changes and thermomechanics during frying

Simultaneous fluid flow (water, oil, and gas) along with heat transfer during frying affects the quality of food product. Hybrid mixture theory (HMT) based two-scale equations were solved using the finite element method to simulate transport processes during frying of rice crackers. The model was used to predict moisture and oil content, pore pressures, evaporation rates, elasticity coefficient and temperature distribution as a function of frying time and spatial coordinates inside a rice cracker. The average absolute differences between the experimental and predicted values of average moisture and oil content were 2.5% and 14%, respectively. Simulations showed that about 99% of the initial average moisture was lost in the first 40s when fried at 200°C. Oil absorption took place throughout the frying process and the final average fat content after 140s of frying at 200°C was 0.30 (g oil/g solids). Presence of negative gage pore pressure gradients at the center of the rice cracker geometry in the early stages of frying appeared to be the driving force for initiation of oil uptake. The range of gage pore pressure in the rice cracker during the frying process was between -20 and +15kPa. Overall temperature of the rice cracker rose to that of frying temperature in 60s. The maximum coefficient of elasticity of the order of 10⁷Pa was obtained at 40s of frying. HMT based model was suitable for simulating the heat and mass transfer mechanisms during frying.