“…This relationship is in consistent with the consequence discovered by Lai and Wong (2003) and Lai et al (2004) who reported that in the absence of cross-flow, the mass transfer enhancement factor strengthened with the voltage increase. Heidarinejad and Babaei (2015) reported that when the cross-flow velocity was 1.1 m s −1 , it causes significant evaporation enhancement with the voltage increase, in other word the mass transfer enhancement factor (the evaporation enhancement factor) significantly enhanced with the increase of voltage.Fig. 2Variation of drying rate of Chinese wolfberry fruits.…”
Section: Resultsmentioning
confidence: 97%
“…The value of 28 kV multiple needles-to-plate electrode under AC electric field treatment to 28 kV multiple needles-to-plate electrode under DC electric field treatment was as high as 36.9 times. The enhanced corona wind velocity by electric field can be expressed as function of the corona current, when other conditions were fixed, the corona wind velocity enhance with the increase of corona current and the corona wind can enhanced water evaporation rate (Lai et al 2004; Heidarinejad and Babaei 2015). As can observed from Table 2, the mass transfer enhancement factor of 28 kV multiple needles-to-plate electrode under AC electric field treatment is very more bigger than that of 28 kV multiple needles-to-plate electrode under AC electric field treatment, so Fig.…”
The conventional methods of drying Chinese wolfberry fruits cause loss of active ingredients and the drying time is very long. In order to explore and investigate the new method of drying Chinese wolfberry fruits, electrohydrodynamic (EHD) drying system was used to drying for Chinese wolfberry fruits with a multiple needle-to-plate electrode on five levels alternating voltage at 0, 20, 24, 28 and 32 kV and a multiple needle-to-plate electrode on a level direct voltage at 28 kV. The drying rate, the moisture rate, shrinkage rate, rehydration ratio, and Vitamin C contents of Chinese wolfberry were measured. Ten different mathematical drying models were also determined and compared to simulate drying curves based on the root mean square error, reduced mean square of the deviation and the coefficient of correlation. Each drying treatment was carried out at (25 ± 2) °C, the drying relative humidity was (30 ± 5) % and all samples were dehydrated until they reached the final moisture content (17 ± 1)/100 g. The results showed that the drying rate of Chinese wolfberry was notably greater in the EHD system when compared to control, and improved by 1.8777, 2.0017, 2.3676 and 2.6608 times, respectively, at 20, 24, 28 and 32 kV, compared to that of the control in the 5 h. The drying rate with multiple needles-to-plate electrode under AC electric field is faster than that with a multiple needle-to-plate electrode under DC electric field and the mass transfer enhancement factor heightened with the increase of voltage. The EHD drying treatments have a significant effect on rehydration ratio, and Vitamin C contents of Chinese wolfberry, but no significant differences was observed in shrinkage rate of Chinese wolfberry. The specific energy consumption of EHD drying (kJ·kg−1 water) were significantly influenced by the alternating voltage, it heightened with the increase of voltage. The Parabolic model was best suited for describing the drying rate curve of Chinese wolfberry fruits. Therefore, this work presents a facile and effective clue for experimentally and theoretically determining the EHD drying properties of Chinese wolfberry.
“…This relationship is in consistent with the consequence discovered by Lai and Wong (2003) and Lai et al (2004) who reported that in the absence of cross-flow, the mass transfer enhancement factor strengthened with the voltage increase. Heidarinejad and Babaei (2015) reported that when the cross-flow velocity was 1.1 m s −1 , it causes significant evaporation enhancement with the voltage increase, in other word the mass transfer enhancement factor (the evaporation enhancement factor) significantly enhanced with the increase of voltage.Fig. 2Variation of drying rate of Chinese wolfberry fruits.…”
Section: Resultsmentioning
confidence: 97%
“…The value of 28 kV multiple needles-to-plate electrode under AC electric field treatment to 28 kV multiple needles-to-plate electrode under DC electric field treatment was as high as 36.9 times. The enhanced corona wind velocity by electric field can be expressed as function of the corona current, when other conditions were fixed, the corona wind velocity enhance with the increase of corona current and the corona wind can enhanced water evaporation rate (Lai et al 2004; Heidarinejad and Babaei 2015). As can observed from Table 2, the mass transfer enhancement factor of 28 kV multiple needles-to-plate electrode under AC electric field treatment is very more bigger than that of 28 kV multiple needles-to-plate electrode under AC electric field treatment, so Fig.…”
The conventional methods of drying Chinese wolfberry fruits cause loss of active ingredients and the drying time is very long. In order to explore and investigate the new method of drying Chinese wolfberry fruits, electrohydrodynamic (EHD) drying system was used to drying for Chinese wolfberry fruits with a multiple needle-to-plate electrode on five levels alternating voltage at 0, 20, 24, 28 and 32 kV and a multiple needle-to-plate electrode on a level direct voltage at 28 kV. The drying rate, the moisture rate, shrinkage rate, rehydration ratio, and Vitamin C contents of Chinese wolfberry were measured. Ten different mathematical drying models were also determined and compared to simulate drying curves based on the root mean square error, reduced mean square of the deviation and the coefficient of correlation. Each drying treatment was carried out at (25 ± 2) °C, the drying relative humidity was (30 ± 5) % and all samples were dehydrated until they reached the final moisture content (17 ± 1)/100 g. The results showed that the drying rate of Chinese wolfberry was notably greater in the EHD system when compared to control, and improved by 1.8777, 2.0017, 2.3676 and 2.6608 times, respectively, at 20, 24, 28 and 32 kV, compared to that of the control in the 5 h. The drying rate with multiple needles-to-plate electrode under AC electric field is faster than that with a multiple needle-to-plate electrode under DC electric field and the mass transfer enhancement factor heightened with the increase of voltage. The EHD drying treatments have a significant effect on rehydration ratio, and Vitamin C contents of Chinese wolfberry, but no significant differences was observed in shrinkage rate of Chinese wolfberry. The specific energy consumption of EHD drying (kJ·kg−1 water) were significantly influenced by the alternating voltage, it heightened with the increase of voltage. The Parabolic model was best suited for describing the drying rate curve of Chinese wolfberry fruits. Therefore, this work presents a facile and effective clue for experimentally and theoretically determining the EHD drying properties of Chinese wolfberry.
“…Some studies also included the dielectrophoretic force, caused by spatial variations in dielectric properties of the air, and the electro-restrictive force due to inhomogeneity in the electric field (Ayuttaya et al 2012;Singh, Orsat, and Raghavan 2012). For single phase, isothermal fluids, these two terms can be neglected (Dalvi-Isfahan et al, 2016;Heidarinejad and Babaei, 2015).…”
Electrohydrodynamic (EHD) drying is a non-thermal technology with promising perspectives to dehydrate heatsensitive materials such as foods. With EHD drying, corona discharge is used to generate airflow, which enhances convective drying of the food product. Further development and upscaling of this technology are hindered by a lack of insight both the airflow and the dehydration process inside the material during drying. This study is the first to develop a conjugate continuum model which couples EHD-generated airflow directly to the convective heat transfer and moisture removal from the food. For the wire-to-plate configuration with impinging flow, the impact of different geometrical and operational parameters (wire radius, distance to collector electrode, emitter voltage) on the EHDdriven airflow and resulting drying kinetics is quantified. The fruit drying time is found to increase linearly with increasing distance between electrodes or increasing emitter electrode radius, but decreases in a non-linear way with increasing voltage between the electrodes. For other emitter-collector configurations, where airflow passes around the fruit, such as wire-to-mesh, wire-to-plate, wire-to-wires and wire-to-parallel plates, significant differences in drying kinetics were quantified. Such configurations provide better perspectives towards upscaling to dry large amounts of products uniformly. Of all tested configurations, the wire-to-mesh configuration provided the highest drying rate. Placing the fruit on a mesh also showed to be advantageous since the fruit can be dried more uniformly. The developed conjugate approach has the distinct advantage that the impact of EHD process parameters and geometrical configurations on the drying rate can be quantified very swiftly. Such modeling approach is thereby a valuable tool for further optimization of EHD drying technology towards industrial implementation.
“…[23] Aside from purely experimental research on EHD drying of apples, carrot, potato, tomato, mushrooms, spinach, rapeseed, grapes blueberry, cranberry, etc., as well as model materials such as water, paper tissue, agar gel, wet sand and glass, theoretical studies on EHD drying are focused on determination of the ionic wind characteristics, such as space charge and corona current distributions [9,10] or numerical solution of the mathematical model with experimental validation through drying experiments. [11][12][13][14] Electrohydrodynamic (EHD) drying relies on the so-called corona (electric or ionic wind), originating from a sharp electroconductive needle or horizontal fine wire under high AC or DC voltage. [24] As a result, ions leaving discharge electrode impinge the surface of the drying material located on the metallic and electrically grounded plate-type electrode.…”
Following background to the phenomenon of electrohydrodynamics with concise review of basic features like shorter drying time, lower energy consumption and better product quality, the selected key factors affecting EHD drying are examined. These include the geometry of discharge electrodes, effects of air humidity on drying rate, depression of material temperature, and cooling effect of ionic wind. Examples are given for: (i) prototype EHD dryers of multi-belt types, and (ii) pilot-scale multi-belt EHD dryer in vertical arrangement that can be aggregated into one unit of higher capacity, and vertical cylindrical EHD dryer with vibrated shelves. Keywords: ionic wind; corona discharge; drying; energy; quality
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