Energy consumption and mathematical modeling of microwave drying of potato slices

In this research, drying characteristics and energy requirements for microwave drying of potato slices were reported at four microwave power densities, 5, 10, 15 and 20W/g. During the experiments, potato slices were dried to the final moisture content of 0.08 from 2.294(kgH2O/kgdry matter).  The experimental data were fitted to six drying models: Linear, Lewis, Henderson and Pabis, Wang and Singh, Page, and Midilli et al. models. The models were compared using the coefficient of determination, root mean square error and reduced chi-square. The Midilli et al. model best described the drying curve of potato slices. The effective moisture diffusivity was determined by using Fick’s second law and was observed to lie between 0.025×10−8 and 3.05×10−8 m2/s for the potato samples. The minimum and the maximum energy requirements for drying of potato slices were also determined as 4.22 MJ/kgH2O and 10.56 MJ/kgH2O for 15 and 5 W/g, respectively.Keywords: potato, drying, mathematical model, effective diffusivity, energy consumptio

Ohmic processing of liquid whole egg, white egg and yolk

The Ohmic heating rate of a food is highly influenced by its electrical conductivity. In this study, electricalconductivities, colour changes and system performance of liquid whole egg, white egg and yolk were determined on alaboratory scale static Ohmic heater by applying 30 V/cm voltage gradient. The samples were heated from room temperaturethrough to pasteurization temperature (19 – 60℃). In all cases, the linear temperature dependent electrical conductivityrelations were obtained. Conductivity measurements of liquid egg indicated that white egg is highly conductive compared toyolk and whole egg. The system performance coefficients for liquid egg samples were in the range of 0.814 to 0.857. Ohmicheating revealed better colour values from the values of heated samples for convectional heating.Keywords: egg, Ohmic heating, electrical conductivity, colou

Ohmic heating of pomegranate juice: Electrical conductivity and pH change

Ohmic heating is an alternative fast heating method for food products. In this study, the effect of ohmic heating technique on electrical conductivity, heating rate, system performance and pH of pomegranate juice was investigated. Ohmic heating rate, electrical conductivity, and pH are dependent on the voltage gradient used (30–55 V/cm). As the voltage gradient increased, time, system performance and pH decreased. The electrical conductivity of the sample increased with temperature rise (20–85 °C). The range of electrical conductivity during ohmic heating was 0.209–1.013 (S/m). Among the two models tested to fit the electrical conductivity of pomegranate juice, the linear model gave the best fit for all the data points. Bubbling was observed above 81 °C especially at high voltage gradients. The system performance coefficients for pomegranate juice samples were in the range of 0.764–0.939

Effects of fluidized bed drying on the quality of soybean kernels

AbstractThe effects of air temperature and velocity on the drying qualities (cracking, bulk density, shrinkage and rehydration) of soybean kernels in fluidized bed dryer were investigated. Drying was carried out at 80, 100, 120 and 140°C and air velocity of 1.8, 3.1 and 4.5m/s. Soybean kernels were dehydrated from the initial moisture content of 25% (w.b) to a final moisture content of 10%. The drying evaluation showed that high drying temperature and air velocity resulted in high cracking and low rehydration ratios (P<0.05). However, air velocity had no significant effect on bulk density and shrinkage of soybeans. By increasing the temperature and air velocity over their full ranges, drying time decreased from 380 to 50min. Cracking, bulk density, degree of shrinkage and rehydration ratio varied from 31.80% to 58.22%, 1101.31 to 1186.39kg/m3, 0.730 to 0.787, and 0.583 to 0.873, respectively. Regression equations were established which can be used for the estimation of the quality parameters as a function of the drying variables

Drying characteristics of sardine fish dried with microwave heating

Fresh fish contains up to 80% of water. It is a highly perishable material and having a short storage life. Therefore, the study of the drying kinetics of fish is necessary. In this study, the effect of microwave drying on drying rate, effective diffusivity, and energy consumption of sardine fish was examined at four different microwave powers (200, 300, 400 and 500 W). It was found that the moisture content was reduced from 2.76 to 0.01 (dry basis) and drying time of the samples was significantly reduced from 9.5 to 4.25 min as the power input increased. Five thin layer drying models were fitted to drying data. The Midilli model was selected as the best according to R2, χ2 and RMSE. The drying of fish samples took place in the falling rate period and was governed by moisture diffusion. The effective diffusivity varied from 7.158 × 10−8 to 3.408 × 10−7 m2/s over the microwave power range. No significant differences were observed between the specific energy consumption of microwave-dried sardine fish (α = 0.05). However, minimum specific energy consumption (3.78 MJ/kg water) was obtained at 500 W microwave levels

Energy analyses and drying kinetics of chamomile leaves in microwave-convective dryer

Drying characteristics and energy aspects as well as mathematical modeling of thin layer drying kinetics of chamomile in a microwave-convective dryer are reported in this article. Drying experiments were carried out at 8 microwave power levels (200–900 W), air temperature of 50 °C, and air velocity of 0.5 m/s. Increasing the microwave output power from 200 to 900 W, decreased the drying time from 40 to 10 min. The drying process took place in the falling rate period. The Midilli et al. model showed the best fit to the experimental drying data. Moisture diffusivity values increase with decreasing moisture content down to 1.70 (kg water kg−1 dry matter) but decrease with a further decrease in moisture content from 1.72 to 0.96 (kg water kg−1 dry matter). The average values of Deff increased with microwave power from 5.46 to 39.63 × 10−8 (m2 s−1). Energy consumption increased and energy efficiency decreased with moisture content of chamomile samples. Average specific energy consumption, energy efficiency and energy loss varied in the range 18.93–28.15 MJ kg−1 water, 8.25–13.07% and 16.79–26.01 MJ kg−1 water, respectively, while the best energy results were obtained at 400 W, 50 °C and 0.5 m s−1

Study of the drying kinetics of pepper

The present study investigated the influence of microwave power on the drying kinetics, energy consumption and drying efficiency of green pepper during microwave drying at 180, 240, 300, 360, 420, 480 and 540 W. Seven mathematical models for describing the thin-layer drying behaviour of pepper samples were investigated. The models were compared based on their R2, RMSE and χ2 values between experimental and predicted moisture ratios. By increasing the microwave output powers (180–540 W), the drying time decreased from 9 to 2.5 min. The drying process took place in the falling rate period. The results show that the Midilli model is the most appropriate model for drying behaviour of thin layer pepper samples. A third order polynomial relationship was found to correlate the effective moisture diffusivity with moisture content. The effective moisture diffusivity increased with decrease in moisture content of pepper samples. The average effective diffusivity varied from 8.315 × 10−8 to 2.363 × 10−7 m2/s, over the microwave power range studied, with an energy activation of 14.19 W/g. Energy efficiency increased with increase in microwave power and moisture content. The least specific energy consumption (4.99 MJ/kg water) was at the microwave power of 240 W and the highest (6.80 MJ/kg water) was at 180 W