Drying of Mushroom Slices Using Hot Air Combined with an Electrohydrodynamic (EHD) Drying System

In this study, hot air combined with EHD drying is examined as an improved method for drying mushroom slices. The effects of three levels of voltage (17, 19, and 21 kV) and electrode gap (5, 6, and 7 cm) on the drying kinetics, time, effective water diffusion coefficient, and energy consumption of the EHD, pure hot air (provided within a chamber), and hot air combined with EHD drying systems were investigated. ANOVA showed that there were significant differences between EHD treatments and control (pure hot-air-drying treatment) for all of the investigated responses. Voltage and electrode gap factors had significant effects on all investigated responses. The results confirmed that the combination of EHD and hot air can significantly reduce the drying period, resulting in a greater effective water diffusion coefficient and drying rate and reduced energy consumption. As such, this technique offers a promising solution to the considerable energy consumption of the drying industry.     

ELECTROHYDRODYNAMIC (EHD) DRYING OF APPLE SLICES

Conventional dryings at high temperatures often produce undesirable changes in the physical-chemical properties of materials. This paper describes the relatively novel technique of electrohydrodynamic (EHD) drying of apple slices, which did not cause any observable product degradation and extensive color changes. Multiple point-to-plate electrodes with AC high voltages, accelerated the initial drying rates to almost 4.5 times over the ambient air drying control. The size of the point electrode, electric field strength, electrode gap, and interelectrode separation were the determinant factors in EHD drying which could be maximized by optimizing these variables. A theoretical consideration showed the principal driving force behind EHD drying to be due to the generation of an electric wind which produced turbulence and thereby enhanced the drying rate of the slices. EHD drying is basically non-thermal and convective, and hence could provide an advantage to industries involved in manufacturing heat-sensitive materials     

ELECTROHYDRODYNAMIC (EHD) DRYING OF APPLE SLICES

ABSTRACT

Conventional dryings at high temperatures often produce undesirable changes in the physical-chemical properties of materials. This paper describes the relatively novel technique of electrohydrodynamic (EHD) drying of apple slices, which did not cause any observable product degradation and extensive color changes. Multiple point-to-plate electrodes with AC high voltages, accelerated the initial drying rates to almost 4.5 times over the ambient air drying control. The size of the point electrode, electric field strength, electrode gap, and interelectrode separation were the determinant factors in EHD drying which could be maximized by optimizing these variables. A theoretical consideration showed the principal driving force behind EHD drying to be due to the generation of an electric wind which produced turbulence and thereby enhanced the drying rate of the slices. EHD drying is basically non-thermal and convective, and hence could provide an advantage to industries involved in manufacturing heat-sensitive materials     

Sensitivity analysis pertaining to effective parameters on electrohydrodynamic drying of porous shrinkable materials

Abstract

A phenomenological computational fluid dynamics model was developed to simulate drying process of a porous body using electric field corona discharge. The set of coupled nonlinear partial differential equations were solved simultaneously and compared with the experimental findings in the literature. The relative error of the corona wind velocity compared to the experiments was less than 1%. The main gradients of the EHD volume force and corona wind were close to the discharge electrode. Moreover, for no inlet air, the corona wind velocity and field distribution indicated the existence of vortices as the main factor for enhancing mass transfer during the drying process. At a constant air velocity, increase in the voltage caused increasing the corona velocity. In addition, by increasing the air velocity to some extent, the corona velocity first increased and then started to drop. As a result, for any voltage and electrode distance from the surface, an optimum air velocity could be determined. Due to the sweep impact of the primary air flow and moving the ionized molecules to the outside, the drying rates at air velocity of 1?m s^?1 were higher than those for air velocity of 1.5?m s^?1. Applying an intake air flow also altered the optimal electrode velocity from the surface due to the occurred change in the corona discharge. Therefore, is concluded that the severity of mass humidity changes is affected by the applied voltage, electrode distances from the surface, temperature, and the intake air velocity.     

Ultrasound-assisted fluidized bed drying of paddy: Energy consumption and rice quality aspects

Several studies have been conducted on equipping conventional fluidized bed with some technologies to increase drying efficiency and its performance. The objective of this study was to investigate the influence of high-power ultrasound (HPU) on fluidized bed drying of paddy in terms of drying kinetics, grain quality (percentage of cracked kernels and bending strength of grain kernels), and specific energy consumption (SEC). To decrease the initial moisture content of paddy from 26.5?±?0.5% (kg/kg, d.b) to the final moisture content of 13?±?0.5% (kg/kg, d.b), the experiments were conducted in a factorial design at three levels of ultrasound power densities (11.1, 14.6, and 18.7?kW/m³), four levels of frequencies (20, 25, 28, and 30?kHz), and three levels of drying air temperatures (30, 40, and 50°C). Application of HPU in conjunction with conventional fluidized bed drying led in 23% decrease in drying time as well as improvement in grain quality, in terms of percentage of cracked kernels and bending strengths. In addition, SEC reduced approximately by 22%, as HPU applied at selected drying condition.     

Multipin EHD dryer: Effect of electrode geometry on charge and mass transfer

Electrohydrodynamic (EHD) drying is considered as energy-efficient nonthermal technology suitable for dewatering of heat-sensitive materials. This technology relies on the ionic discharge from the vertical pin or fine horizontal wire, impinging wet material deposited on the plate electrode of opposite polarity. The critical issue for the scaling of EHD dryer is the geometry of a multipin/wire discharge and collecting electrodes, in particular the spacing between pins/wires and the gap between discharge electrode and material surface. This paper presents the results of experimental study and mathematical simulation of multipin discharge current to maximize total charge and mass transfer at the material surface. A mathematical model for discharge current based on Poisson’s and Warburg fundamental equations was developed and validated in experiments with multipin electrodes of different spacing (1, 2, 3, 4, and 6?cm) and gaps from 2 to 4?cm. It was demonstrated that linear relationship between total electric current and drying rate is valid for any spacing and any gap with the range from 2 to 4?cm. It was experimentally documented that the judiciously selected geometry of the multipin discharge electrode could mitigate adverse effect of interference between neighboring ionic jets and bring the concept of EHD dryer to industrial practice.     

Electrohydrodynamic Drying—A Concise Overview

Electrohydrodynamic (EHD) drying is a novel method of non-thermal processing. The drying can be carried out using either AC or DC high voltages. The thermodynamic considerations regarding the lowering of temperature under EHD drying include rapid rates of evaporation and exothermic interaction of the electric field with a dielectric material. Multi-point and plate electrode systems are efficient in accelerating drying of agricultural materials. Compared to hot air (convective) drying systems, EHD drying systems offer lower food production costs along with superior quality in terms of physiochemical properties such as color, shrinkage, flavor, and nutrient content. Compared to convective and freeze-drying, EHD drying systems, given their simpler design and lesser energy consumption, show great potential for bulk and industrial drying applications.     

Electrohydrodynamic Drying—A Concise Overview

Electrohydrodynamic (EHD) drying is a novel method of non-thermal processing. The drying can be carried out using either AC or DC high voltages. The thermodynamic considerations regarding the lowering of temperature under EHD drying include rapid rates of evaporation and exothermic interaction of the electric field with a dielectric material. Multi-point and plate electrode systems are efficient in accelerating drying of agricultural materials. Compared to hot air (convective) drying systems, EHD drying systems offer lower food production costs along with superior quality in terms of physiochemical properties such as color, shrinkage, flavor, and nutrient content. Compared to convective and freeze-drying, EHD drying systems, given their simpler design and lesser energy consumption, show great potential for bulk and industrial drying applications.     

Numerical investigation of the multi-pin electrohydrodynamic dryer: Effect of cross-flow air stream

Abstract

This article presents the results of numerical simulation and experimental study of a multi-pin electrohydrodynamic (EHD) dryer. Combined effect of EHD flow and the external air cross-flow on drying performance was investigated with 3-D numerical model, which accounts for electric field, electric charge transport, external air cross-flow and material-gas moisture transport. Effect of cross-flow air stream on drying was positive in the range of low velocities, changing to negative at high velocities due to counteracting with EHD flow. Numerical simulation predicted previously unknown effect of EHD flow on the cross-flow air stream, which was quantified as an increase of airway resistance. This prediction was fully validated by experiments. Both numerical simulation and experiment proved that for given intensity of EHD flow there is an optimum value of the cross-flow, resulting in maximum drying performance. The numerical model can be applied to determine the optimal operating parameters for multi-pin EHD dryer.     

Energy and Quality Attributes of Combined Hot-Air/Infrared Drying of Paddy

The kinetics of combined hot-air/infrared thin-layer drying of paddy was studied. The mechanical quality aspects of paddy kernels dried at different drying conditions were evaluated in terms of percentage of cracked kernels and also required failure force obtained from bending tests. The well-known Artificial Neural Network (ANN) modeling technique was applied to predict the drying time, variations in paddy moisture content, the percentages of cracked kernels, and the values of required failure force of paddy at different drying conditions. The best ANN topologies, transfer functions, and training algorithms were determined for prediction of the mentioned parameters. In addition to the product quality aspects, the specific energy consumption (SEC) was estimated for all drying conditions. The results indicated that application of a low-intensity IR radiation (2000 W/m²), together with lower values of inlet air temperature (30°C) and moderate values of inlet air velocity (0.15 m/s), can effectively improve the final quality of paddy (as a heat-sensitive product) with a reasonable SEC.     

EHD-Enhanced Drying with Needle Electrode

Abstract

The enhancement of drying rate by corona discharge from a needle electrode has been experimentally evaluated in this study. The electrode produces corona wind, which resembles a round jet, impinges and removes moisture from the surface. Corona discharges with positive and negative polarities have been considered. The samples used are 3 and 6 mm glass beads saturated with water. Two sets of experiments have been conducted (one with the cross-flow of air and the other one without), at 1 kV increment from the corona threshold voltage until the occurrence of sparkover. For each case, a companion experiment was carried out simultaneously under the same ambient conditions but without the application of electric field. The result of which is used as a reference in the evaluation of drying enhancement using electric field. Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. The results are compared with those obtained with a wire electrode to determine the optimal configuration to be used in an EHD drying system.     

EHD-Enhanced Drying with Needle Electrode

The enhancement of drying rate by corona discharge from a needle electrode has been experimentally evaluated in this study. The electrode produces corona wind, which resembles a round jet, impinges and removes moisture from the surface. Corona discharges with positive and negative polarities have been considered. The samples used are 3 and 6 mm glass beads saturated with water. Two sets of experiments have been conducted (one with the cross-flow of air and the other one without), at 1 kV increment from the corona threshold voltage until the occurrence of sparkover. For each case, a companion experiment was carried out simultaneously under the same ambient conditions but without the application of electric field. The result of which is used as a reference in the evaluation of drying enhancement using electric field. Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. The results are compared with those obtained with a wire electrode to determine the optimal configuration to be used in an EHD drying system.     

EHD-ENHANCED DRYING WITH WIRE ELECTRODE

The enhancement of drying rate by electrostatic field (corona wind) has been experimentally evaluated in this study. The samples used are 3 mm and 6 mm glass beads saturated with water. Two sets of experiments were conducted, with and without cross-flow, at 1 kV increment from the corona threshold voltage until the occurrence of sparkover. For each case a companion experiment was carried out simultaneously under the same ambient conditions but without the application of electric field. The result of which is used as a basis in the evaluation of drying enhancement using electric field (with or without cross-flow). Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. For EHD drying without cross-flow, the enhancement in drying rate increases with the applied voltage. With the presence of cross-flow, the enhancement in drying rate is nearly independent of the applied voltage and is close to the result obtained by drying with cross-flow alone.     

Combined Electrohydrodynamic (EHD) and Vacuum Freeze Drying of Sea Cucumber

A combination of electrohydrodynamic drying (EHD) and vacuum freeze drying (FD) is examined as an improved method for dehydrating sea cucumbers. The energy consumption, shrinkage and rehydration ratio, protein content, and sensory properties, such as the color and trimness, of the dried product in the EHD–FD method are measured. Compared with FD, the combined process consumes less drying time and has lower energy consumption than EHD drying alone. Also, the product processed by combined drying displays lower shrinkage, higher rehydration rate and higher protein content, along with better sensory qualities.     

Simplification and Energy Saving of Drying Process Based on Self-Heat Recuperation Technology

A simplified drying process based on self-heat recuperation (SHR), which can further reduce energy consumption compared to previous SHR drying processes, is proposed. The specific energy consumption (SEC) of the SHR drying process was evaluated at various air flow rates and compared with a mechanical vapor recompression (MVR) drying process with superheated steam. The results show that the SEC of SHR can be reduced from 474 to 147 kJ (kg-H₂O evaporated)^?1 by removing heat exchangers for preheating. The SEC of the simplified SHR process was only 1/16 of a conventional drying process with heat recovery and 3/5 of an MVR process. Exergy transfer of the process was also analyzed and summarized as exergy flow diagrams.     

Influence of the electrohydrodynamic process on the properties of dried button mushroom slices: A differential scanning calorimetry (DSC) study

In this paper, drying of button mushroom (Agaricus bisporus) slices with an innovative drying technique of hot air combined with Electrohydrodynamic (EHD) drying process was investigated at three electrode gaps (5, 6, and 7 cm) and voltage levels (17, 19, and 21 kV). The effects of different hot air combined with EHD drying treatments on the temperature of the mushroom slices, drying time, final color and protein denaturation features including enthalpy (ΔH), onset temperature (T_o), peak transition temperature (T_p), conclusion temperature (T_c), and temperature range (T_c–T_o) of endothermic peaks were systematically evaluated. In addition, water state changes in DSC cooling thermograms of dried mushroom slices were investigated. The results obtained by differential scanning calorimetry showed that the ΔH values in the DSC traces of the EHD-dried mushroom slices were reduced with a decrease in the electrode gap and an increase in the voltage. Specifically, among voltages of 21, 17, and 19 kV, a voltage of 21 kV resulted in the lowest ΔH and T_c–T_o values and the highest T_p and T_o values. This result indicated that voltage had a significant effect on these responses. Similarly, the DSC results showed a considerable effect of high electric field intensity on ΔH, T_c–T_o and T_p responses related to protein denaturation in comparison to low electric field intensity.     

错流降膜液体干燥剂除湿/再生传热传质数学模型及分析

分析了错流降膜液体干燥剂除湿及再生传热传质过程 ,建立了基于实际除湿系统的描述再生和除湿过程的数学模型 ,考虑到除湿过程中产生的热效应 ,以氯化钙溶液为除湿剂时 ,对气侧和液侧的传热传质系数进行了理论和数值求解 .计算结果表明 ,传热传质系数与气流流动状态、除湿剂的热物理性质等因素有关     

EHD-ENHANCED DRYING WITH WIRE ELECTRODE

ABSTRACT

The enhancement of drying rate by electrostatic field (corona wind) has been experimentally evaluated in this study. The samples used are 3 mm and 6 mm glass beads saturated with water. Two sets of experiments were conducted, with and without cross-flow, at 1 kV increment from the corona threshold voltage until the occurrence of sparkover. For each case a companion experiment was carried out simultaneously under the same ambient conditions but without the application of electric field. The result of which is used as a basis in the evaluation of drying enhancement using electric field (with or without cross-flow). Each experiment lasted for at least 5 h. The weight loss of water as well as the ambient temperature and humidity were measured. For EHD drying without cross-flow, the enhancement in drying rate increases with the applied voltage. With the presence of cross-flow, the enhancement in drying rate is nearly independent of the applied voltage and is close to the result obtained by drying with cross-flow alone.     

电极极性影响EHD强化沸腾传热的机理

The effects of electrode polarities on EHD enhancement boiling heat transfer were investigated theoretically and experimentally based on the analysis of electric field distribution affected by superheat boundary layer and charge injection. The results showed that electric field distribution was changed by the charge induced by temperature gradients in the superheat boundary layer, but the change was independent of electrode polarities. However, when electric charge injection occurred, the electrode applied positive high voltage might generate different characteristics of charge injection from that generated by applied negative high voltage. If the electric field on the surface of heat transfer increased due to charge injection, the augmentation effects would increase. The experiments demonstrated that positive high voltage gave larger enhancement factors than negative high voltage. The experimental phenomena could be interpreted well on the basis of charge injection characteristics.     

THIN LAYER AND DEEP BED DRYING OF LONG GRAIN ROUGH RICE

ABSTRACT

The paper presents new data for thin-layer drying characteristics of Thai long grain rough rice measured under various conditions of drying air temperature (35 to 60?°C), drying air relative humidity (30 to 70 % ) and the initial moisture content of rough rice (20 to 40 % dry basis). Empirical equations were developed using the instantaneous weight, the weight loss and drying time, with temperature, relative humidity and initial moisture content of rough rice as the independent variables. A computer program was developed to simulate the deep-bed drying process. The thin-layer drying equation developed before was used in the computer simulation. Experimental data from the fixed bed dryer were compared with the results from the calculation.