| Abstract | Air jet impingement combined with infrared drying (IMIRD) was developed as an alternative processing method to produce potato chips in place of conventional deep-fat frying. This study investigates the effects of IMIRD compared to air jet impingement drying alone (IMD) and conventional convective drying (CCVD) on potato being processed as potato chips in term of quality attributes (shrinkage, color, and hardness), drying characteristics, and specific energy consumption (SEC).
A laboratory-scale air jet impingement combined with infrared dryer was designed and constructed with the capability of conducting an analysis of heat and mass transfer. Thin layer-drying models were fitted to the experimental data of moisture ratio in order to find a suitable drying curve. Effective moisture diffusivity, analogy of heat and mass transfer coefficients (ht/hm), and simulation of potato dried under combined convective and infrared radiation were examined. Numerical simulation of coupled heat and mass transfer equation was solved using finite element method to simulate the drying process in a two dimension. Drying parameters such as moisture distribution and temperature profile were obtained. The predicted core temperature and average moisture content were validated with experimental data.
The experimental results of different drying parameters using different impingement air velocity (5, 10, 15 m/s), impingement air temperature (85, 100, 115 C), and infrared intensity (0.16, 0.27, and 0.33 W/cm2) were shown, indicating improvements in potato chips quality parameters, such as color, volume shrinkage, and texture. IMIRD, compared to IMD and CCVD, provided less shrinkage, lower hardness, and less color deterioration. Also, the results showed that increase in the impingement air velocity, impingement air temperature, and infrared intensity led to significantly increase in moisture removal rate. Drying by IMIRD at air velocity of 15 m/s, air temperature of 115 C, and infrared intensity of 0.33 W/cm2 reduced the drying time by 82.5% compared to CCVD at the same drying air temperature. Furthermore, increase in impingement air velocity and air temperature at each infrared intensity caused a decrease in the total SEC value.
For heat and mass transfer analysis, modified Page model was found to be the best model for drying behavior prediction in potato chips drying. Effective moisture diffusivities of potato chips were computed by applying the Fick’s second law of diffusion. Experimental results showed that effective moisture diffusivities were a function of moisture content and temperature. Empirical model relating effective moisture diffusivity with moisture content and temperature of drying air, infrared source, and sample was developed from the modification of Arrhenius equation. Calculated values of moisture diffusivities for different drying conditions were in the range of 1.52×10−10 and 8.39×10−9 m2/s. The ratio of total heat and mass transfer coefficient for potato chips dried under combined hot air impingement and infrared drying could not be predicted by using the classical model of heat-mass analogy. The modified correlations for predicting the ratio of ht/hm, heat transfer coefficient in term of Nusselt number and mass transfer coefficients were established which depend on the interaction between temperature distribution and the moisture ratio of potato chips. Finally, combination drying using impingement jet and infrared was simulated by coupling heat and mass transfer equation. Time-dependent governing equations were used to predict temperature and moisture distribution. Predicted average moisture content and core temperature were in good agreement with the experimental data. |