Moisture Diffusivity Coefficient and Convective Drying Modelling of Murta (Ugni molinae Turcz): Influence of Temperature and Vacuum on Drying Kinetics

In this study, murta (Ugni molinae Turcz) or murtilla berries were dried in single layer at air temperatures of 50, 60 and 70 °C under vacuum and atmospheric pressure conditions. The effect of drying air temperature and vacuum on the basic dehydration characteristics of murta was determined. For the kinetic modelling, ten mathematical expressions were fitted to the experimental data. Kinetic parameters and diffusion coefficients as evaluated by an Arrhenius-type equation, showed temperature dependency. Fick’s second law was used to calculate the effective moisture diffusivity that varied from 3.10 to 11.27?×?10^?10 m²/s and from 5.50 to 11.30?×?10^?10 m²/s with activation energy values of 59.27 and 34.30 kJ/mol for atmospheric pressure and vacuum drying, respectively. According to the statistical tests applied, the Midilli–Ku?uk model obtained the best-fit quality on experimental data, followed closely by the Weibull distribution model, the Page and the modified Page models.     

Modeling engineering characteristics of hazelnut kernel during infrared fluidized bed drying

In this study, a laboratory scale infrared fluidized bed dryer was used to dry the hazelnut kernels. The drying experiments were performed under the following drying conditions: air temperatures of 45, 65 and 85?°C, air velocities of 1.30, 3.09 and 4.87 m/s and infrared powers of 500, 1000 and 1500 W. Maximum and minimum values of effective moisture diffusivity for hazelnut kernels were obtained 1.87?×?10^?9 and 1.75?×?10^?10 m²/s, respectively. Activation energy was obtained between 33.02 and 50.22 kJ/mol. Specific energy consumption of hazelnut kernels was obtained between 1.72?×?10³ and 2.23?×?10⁴ MJ/kg. Six mathematical models were used to predict the drying behavior of hazelnut samples. Among these models, the Midilli model sufficiently fitted the experimental drying data. The shrinkage values were obtained within the range of 0.10 and 0.24. The results obtained showed that the \({{L}^{*}},\) \({{a}^{*}},\) \({{b}^{*}}\) and \(\Delta E\) color values of the kernels were significantly affected (P?<?0.05) by air temperature. The highest color changes were related to the air temperature of 85?°C at all air velocities and infrared powers. Maximum values of energy (103.57 N mm) and force (129.84 N) at initial rupture point was related to air temperatures of 85?°C and infrared powers of 1500 W. Minimum values of energy (16.47 N mm) and force (31.74 N) at initial rupture point was related to air temperatures of 45?°C and infrared powers of 500 W.     

Evaluation of Mathematical Models for Prediction of Thin-Layer Drying of Banana Slices

Drying characteristics of bananas were experimentally determined. The drying experiments were carried out in a hot air dryer at four inlet temperatures of 50, 60, 70 and 80°C, at a constant air velocity of 2.4 m/s and relative humidity of 4–25%. The experimental results were fitted to five thin-layer drying models and it was found that the Page and Logarithmic models gave better fit that the other models. Values of the effective diffusivity ranged from 7.374 × 10^?11 to 2.148 × 10^?10 m²/s. Activation energy for moisture diffusion of the banana slices was found to be 32.65 kJ/mol.     

Effects of infrared heating on drying kinetics,antioxidant activity,phenolic content,and color of jujube fruit

This study investigated the effects of different infrared power (IP) levels (62, 88, and 125 W) and a pretreatment (soaking in a solution of 5 % potassium carbonate and 0.5 % olive oil) on the drying kinetics and some quality parameters of jujube fruit. The drying characteristics of jujube were greatly influenced by the pretreatment and IP level. The models of Lewis, Logarithmic, Page, and Aghbashlo et al. were fitted to the obtained experimental data using nonlinear regression analysis. The Page model showed a better fit to the experimental drying data when compared to the other models. The effective moisture diffusivity, calculated using Fick’s second law, ranged from 4.75 × 10^?10 to 4.17 × 10^?9 m²/s. Significantly, higher total phenolic content (TPC) and antioxidant capacity values were obtained for the pretreated samples subjected to higher IP levels. The total color change (ΔE) of the dried samples significantly increased with increasing IP level. Jujube fruits should be pretreated and then dried at 88 W IP to reduce phenolic degradation and undesired color changes and to increase the quality of the dried product.     

Comparison of Freeze-Drying and Freeze-Drying Combined with Microwave Vacuum Drying Methods on Drying Kinetics and Rehydration Characteristics of Button Mushroom (Agaricus bisporus) Slices

Button mushroom slices were dried using freeze-drying (FD) and freeze-drying combined with microwave vacuum drying (FD?+?MVD) methods. Drying parameters including drying temperatures (20, 30, and 40 °C), chamber pressures (70, 100, and 130 Pa) and material layer thicknesses (single, double, and triple) during FD process, and microwave power densities (20, 40, and 60 W/g) and material layer thicknesses (single, double and triple) during MVD period of FD?+?MVD process, were investigated for their drying characteristics. The FD and FD?+?MVD products were then rehydrated at two temperatures (20 and 70 °C). Different mathematical models were tested with the drying and rehydration behaviors of button mushroom slices, and the effective diffusivities (D _eff) in the FD and FD?+?MVD processes were also calculated. The results indicated that based on the statistical tests, the Page model and logarithmic model provided the best fit for FD (in both FD and FD?+?MVD processes) and MVD (in FD?+?MVD process) curves, respectively. The regression equations obtained from selected models can accurately predict the relationships between moisture ratio (MR) and time (t). Furthermore, the D _eff values of the MVD period in FD?+?MVD process (2.318–5.565?×?10^?5 m²/s) were about ten times greater than those in FD process (1.291–3.389?×?10^?6 m²/s). In addition, the Peleg model gave a better fit for rehydration conditions applied in both FD and FD?+?MVD products. The values of equilibrium moisture content (W _e) of FD?+?MVD products were almost similar to those of FD products, which indicated that the rehydration capacities of the two dehydrated products were comparable.     

Modeling some thermal and physical characteristics of terebinth fruit under semi industrial continuous drying

In this research, the effect of different drying conditions on thermal and physical properties of terebinth fruit was studied. Experiments were conducted with a semi industrial continuous dryer in air temperature levels of 45, 60, 75 °C, air velocity levels of 1, 1.5 and 2 m/s and belt linear speeds of 2.5, 6.5, 10.5 mm/s. Results showed that the Midilli model had the best performance in predicting the moisture ratio. Effective moisture diffusivity of terebinth fruit during experiments was 6.48 × 10^?11–2.34 × 10^?10 m²/s achieved. Activation energy of the samples between 25.45 and 35.16 kJ/mol was obtained. The highest and lowest values of specific energy consumption 65.2 and 10.5 GJ/kg were calculated. Maximum value of shrinkage (16.70 %) was calculated at air temperatures of 75 °C and minimum value (12.34 %) was achieved at air temperature of 45 °C. After drying, total color difference was increased, and hue angle and chroma were decreased. Rupture force for dried terebinth between 80.15 and 112.68 N mm were calculated.     

Experimental study on drying of pear slices in a convective dryer

The experiments were conducted on pear slices with thickness of 5 mm at temperatures of 50, 57, 64 and 71 °C with an air velocity of 2.0 m s^?1. Prior to drying, pear slices were pretreated with citric acid solution (0.5% w/w, 1 min, 20 °C) or blanched in hot water (1 min, 85 °C). Also, the untreated samples were dried as control. The shortest drying time of pear slices was obtained with pretreatment with citric acid solution. It was observed that whole drying process of pear slices took place in a falling rate period. Four mathematical models were tested to fit drying data of pear slices. According to the statistical criteria (R², χ² and RMSE), the Midilli et al. model was found to be the best model to describe the drying behaviour of pear slices. The effective diffusivity of moisture transfer during drying process varied between 8.56 × 10^?11 and 2.25 × 10^?10 m² s^?1, while the activation energy of moisture diffusion in pear slices was found to be 34.95–41.00 kJ mol^?1.     

Drying of pomegranate seeds using infrared radiation

Effect of different infrared (IR) power levels on drying kinetics of pomegranate seeds was investigated. The pomegranate seeds were dried at 83, 104, 125, and 146 W IR power levels. It was observed that the power levels affected the drying rate and time. Drying time reduced from 150 to 60 min as the IR power level increased from 83 to 146 W. The experimental data obtained from drying study were fitted with 10 mathematical models to evaluate the drying kinetics of the pomegranate seeds. The Page, Midilli et al., and Weibull models are given better prediction than the other models and satisfactorily described drying kinetics of pomegranate seeds. Effective diffusivity varied from 1.96 to 6.29×10^?11 m²/s and was significantly influenced by IR power.     

Modelling of air drying of fresh and blanched sweet potato slices

Effects of blanching, drying temperatures (50–80 °C) and thickness (5, 10 and 15 mm) on drying characteristics of sweet potato slices were investigated. Lewis, Henderson and Pabis, Modified Page and Page models were tested with the drying patterns. Page and Modified Page models best described the drying curves. Moisture ratio vs. drying time profiles of the models showed high correlation coefficient (R² = 0.9864–0.9967), and low root mean squared error (RMSE = 0.0018–0.0130) and chi‐squared (χ² = 3.446 × 10^–6–1.03 × 10^–2). Drying of sweet potato was predominantly in the falling rate period. The temperature dependence of the diffusion coefficient (D_eff) was described by Arrhenius relationship. D_eff increased with increasing thickness and air temperature. D_eff of fresh and blanched sweet potato slices varied between 6.36 × 10^–11–1.78 × 10^–9 and 1.25 × 10^–10–9.75 × 10^–9 m² s^–1, respectively. Activation energy for moisture diffusion of the slices ranged between 11.1 and 30.4 kJ mol^–1.     

Experimental characterization and modelling of drying of pear slices

The effect of temperature on the drying kinetics of pear slices was investigated. The drying process was carried out at temperatures of 55, 65, and 75°C. Drying time decreased considerably with increased air temperature. Seven mathematical models available in the literature were tested with the drying patterns. The Wang and Singh, and Midilli et al. models were given the best results in describing drying of pear slices. Effective moisture diffusivity increased with increasing air temperature, and varied from 0.85 to 2.18×10^?10 m²/s over the temperature range investigated, with activation energy equal to 44.78 kJ/mol.     

Empirical and diffusion models to describe water transport into chickpea (Cicer arietinum L.)

To describe water transport in a porous media, a mathematical model is usually used. Among the models available in the literature, empirical and diffusive ones can be cited. In this paper, Page and diffusion models are used to describe drying and soaking of chickpea. In addition, new empirical equation is proposed to describe the mentioned processes. According to the results, the two empirical models well describe drying and soaking, but the proposed one gives the best statistical indicators. The use of the diffusion model to describe the drying process makes it possible to determine the effective diffusivities (7.13 × 10^?11, 10.39 × 10^?11 and 13.78 × 10^?11 m² s^?1 for the drying air at 40, 50 and 60 °C, respectively) and also the activation energy associated with the process (27.9 kJ mol^?1).     

Prediction of Drying Characteristics of Pomegranate Arils

The thin-layer drying characteristics of pomegranate arils were investigated at the temperature of 55, 65 and 75°C, and the thin-layer drying models were used to fit the drying data. The increase in drying air temperature resulted in a decrease in drying time. Five different thin-layer drying models were used to predict the drying characteristics. The Midilli et al. model showed a better fit to experimental drying data as compared to other models. Effective moisture diffusivities were calculated based on the diffusion equation for a spherical shape using Fick’s second law, and varied from 9.373 × 10⁻¹¹ to 3.429 × 10⁻¹⁰ m²/s over the temperature range. Moisture diffusivity values increased as air temperature was increased. The dependence of moisture diffusivity on temperature was described by an Arrhenius-type equation. The activation energies of control and pre-treated samples were determined to be 49.7 and 40.1 kJ/mol, respectively.     

Study on kinetics of flow characteristics in hot air drying of pineapple

The aim was to evaluate the kinetic parameters, total color differences (?E*) and browning index differences (?BI) of air flow pineapple drying. The experiments were performed on air temperatures at 60 and 70 °C, and air velocities at 1.5 and 2.0 m/s. The kinetic parameter (k) increased when air temperature was increased for all air velocity. The effective diffusivity coefficient (D_eff) increased as high as the temperature of the heating medium. The variation of D_eff of swirling flow was ranging from 6.72?×?10^?9 to 10.23?×?10^?9 m²/s, while the variation of D_eff of non-swirling flow was ranging from 6.40?×?10^?9 to 9.42?×?10^?9 m²/s. The drying time of swirling flow was shorter than non-swirling flow in each drying condition. Moreover, the ?E* and ?BI of pineapple in swirling flow were lower than that obtained from non-swirling flow. Therefore, the convective drying using swirling flow can be minimized for drying time and color deterioration.     

Intermittent and Continuous Microwave-Convective Air-Drying Characteristics of Sage (<Emphasis Type="Italic">Salvia officinalis</Emphasis>) Leaves

The effect of microwave-convective air-drying (continuous and intermittent) and convective air-drying of sage (Salvia officinalis) on color and essential oil content were studied. For microwave-convective air-drying, four pulse ratio levels (PR1, PR2, PR3, and PR4) at 25 °C drying air temperature were used and the average drying rates were 0.404, 0.158, 0.114, and 0.085 kg H₂O kg^?1 DM min^?1 for PR1, PR2, PR3, and PR4, respectively. For convective air-drying, two drying temperatures of 40 and 50 °C were examined and the average drying rates were 0.005 and 0.006 kg H₂O kg^?1 DM min^?1 for 40 and 50 °C, respectively. The experimental data were fitted to 11 different moisture ratio models to describe the drying kinetics under various drying conditions. Page model was found satisfactory to describe the drying curves of sage leaves. Comparing with the fresh sage, lightness (L*), greenness, and yellowness decreased for all drying applications. Lightness, greenness, and yellowness of the convective air-dried sage leaves were higher than those of microwave-convective air-dried sage leaves. The deviation from fresh product color (ΔE*) increased as the pulse ratio or the drying air temperature increased. The total quantity of essential oils of sage decreased considerably during microwave-convective air-drying whereas the loss of essential oils was limited during air-drying.     

Mass transfer characteristics during convective,microwave and combined microwave–convective drying of lemon slices

BACKGROUND: The investigation of drying kinetics and mass transfer phenomena is important for selecting optimum operating conditions, and obtaining a high quality dried product. Two analytical models, conventional solution of the diffusion equation and the Dincer and Dost model, were used to investigate mass transfer characteristics during combined microwave‐convective drying of lemon slices. Air temperatures of 50, 55 and 60 °C, and specific microwave powers of 0.97 and 2.04 W g^?1 were the process variables. RESULTS: Kinetics curves for drying indicated one constant rate period followed by one falling rate period in convective and microwave drying methods, and only one falling rate period with the exception of a very short accelerating period at the beginning of microwave‐convective treatments. Applying the conventional method, the effective moisture diffusivity varied from 2.4 × 10^?11 to 1.2 × 10^?9 m² s^?1. The Biot number, the moisture transfer coefficient, and the moisture diffusivity, respectively in the ranges of 0.2 to 3.0 (indicating simultaneous internal and external mass transfer control), 3.7 × 10^?8 to 4.3 × 10^?6 m s^?1, and 2.2 × 10^?10 to 4.2 × 10^?9 m² s^?1 were also determined using the Dincer and Dost model. CONCLUSIONS: The higher degree of prediction accuracy was achieved by using the Dincer and Dost model for all treatments. Therefore, this model could be applied as an effective tool for predicting mass transfer characteristics during the drying of lemon slices. © 2012 Society of Chemical Industry     

Thin-layer drying characteristics of kurut, a Turkish dried dairy by-product

Kurut, which is made in villages of Eastern part of Turkey, is a sun‐dried dairy product. Thin‐layer drying behaviour of kurut at a temperature range of 35–60 °C, with 5 °C increments, and constant thickness of 0.5 cm and drying air velocity of 1.5 m s^?1 was determined in a convective type dryer. The data of sample weight, dry and wet‐bulb temperatures were recorded continuously during each experiment and drying curves obtained. The drying process took place in the falling rate period. Drying curves were then fitted to eleven mathematical models available in the literature to estimate a suitable model for drying of kurut. Two‐term model gave better predictions than other models and satisfactorily described the thin‐layer characteristics of kurut. The effective diffusivity varied from 2.444 × 10^?9 to 3.597 × 10^?9 m² s^?1 over the temperature range. The temperature dependence of diffusivity coefficient was described by the Arrhenius‐type relationship. The activation energy for moisture diffusivity was found to be 19.88 kJ mol^?1.     

Effect of air temperature,slice thickness and pretreatment on drying and rehydration of tomato

The effect of air temperature, pretreatment with alkaline emulsion of ethyl oleate (AEEO) and slice thickness on drying and rehydration characteristics of tomato slices was studied. Drying time decreased with pretreatment, but it increased considerably with the increase in air temperature and slice thickness of tomato. Besides, pretreatment was found to improve the rehydration ratio of tomato slices. The experimental drying curves obtained show only falling rate period. To estimate and select the suitable form of drying curves, five different mathematical models were applied to the experimental data. Among the mathematical models investigated, the Midilli et al. and logarithmic models satisfactorily described the drying characteristics of tomato slices with highest R² and lowest χ² and root mean square error. The effective moisture diffusivity varied from 3.123 to 10.03 × 10^?11 m² s^?1 over the temperature range studied, and the activation energy values varied from 59.6 to 70.2 kJ mol^?1.     

Experimental study on drying characteristics of pomegranate peels

Drying kinetics of pomegranate peels has been experimentally investigated in a cabinet dryer. Drying experiments were performed at constant air velocity of 2.0 m/s and initial thickness of 2.8 cm for pomegranate peels, and 3 drying air temperatures of 50, 60, and 70°C. The drying time decreased with increase in drying air temperature. Experimental data were fitted to 10 mathematical models. The fit quality of models on experimental data were evaluated using 3 statistical tests, coefficient of determination, reduced chi-square, and root mean square error. The statistical analysis concluded that the best model in terms of fitting performance was the Midilli et al. model. The effective diffusivity varied from 4.02 to 5.31×10⁻⁹m²/s over temperature range. Temperature dependence of the diffusivity was well documented by Arrhenius-type relationship. The activation energy was found to be 12.72 kJ/mol for pomegranate peels.     

Evaluation of Drying Methods with Respect to Drying Kinetics,Mineral Content,and Color Characteristics of Savory Leaves

Sun, oven (50 °C), and microwave oven (700 W) drying of savory leaves (Satureja thymbra L.) were carried out to monitor the drying kinetics, changes in mineral content, and color degradation of the product. Oven and microwave oven drying shortened the drying time over than approximately 70% and 99% when compared to the sun and oven drying methods, respectively. Fresh and dried savory leaves had high amounts of K (8875.2–28468.0 mg/kg), Ca (3681.6–9852.03 mg/kg), Mg (1388.0–3102.0 mg/kg), and P (2313.2–5045.8 mg/kg) minerals. K, Ca, P, and Mg were the most abundant elements in savory samples. Mineral content of oven-dried savory were higher than the sun and microwave dried samples. Midilli and Küçük model was shown to give a good fit to the sun and oven drying. The Midilli and Küçük, modified page and page models exhibited high coefficient of determination (R ² ) values ranging between 0.9995 and 0.9997, to the experimental microwave oven drying data of savory. Microwave oven drying revealed optimum color values. Oven drying resulted in a considerable decrease in color quality of savory.     

Characterization of hot air drying and microwave vacuum drying of fingerroot (Boesenbergia pandurata)

Fingerroot (Boesenbergia pandurata) was subjected to hot air drying and microwave vacuum drying. Effective moisture diffusion coefficient during the hot air drying at 60 and 70 °C were 0.2073 × 10^?10 and 0.4106 × 10^?10 m² s^?1 respectively. By using the microwave vacuum drying (13.3 kPa) at the power of 2880 and 3360 W, the effective moisture diffusion coefficient were increased to 5.7910 × 10^?10 and 6.8767 × 10^?10 m² s^?1 respectively. Based on Lewis model, drying rate constants were 0.0002, 0.0004, 0.0061 and 0.0072 s^?1 for the hot air drying at 60 and 70 °C and the microwave vacuum drying at 2880 and 3360 W respectively. Compared with the hot air drying, the microwave vacuum drying decreased drying time by 90%. Rehydration ability of the microwave vacuum dried samples was also significantly improved (P ≤ 0.05), because of porous structure. In addition, the rehydrating water of the microwave vacuum dried samples contained higher b*‐value (yellowness) than that of the hot‐air‐dried samples (P ≤ 0.05).