Electrohydrodynamic drying versus conventional drying methods: A comparison of key performance indicators

Preserving fruits and vegetables by drying is a traditional yet effective way of reducing food waste. Existing drying methods are either energy-intensive or lead to a significant reduction in product quality. Electrohydrodynamic (EHD) drying is an energy-efficient low-temperature drying method that presents an opportunity to comply with the current challenges of existing drying methods. However, despite its promising characteristics, EHD drying is yet to be accepted by industry and farmers. The adoption of EHD drying is hindered due to different reasons, such as uncertainties surrounding its scalability, quality of dried product, cost of operation, and sustainability compared to conventional drying methods. To address these concerns, this study quantifies and benchmarks the Key Performance Indicators (KPIs) of EHD drying compared to the standard conventional drying methods based on lab-scale experiments. These drying methods include hot-air, freeze, microwave, and solar drying. The results show that drying food using EHD is at least 1.6, 20, and 70 times more energy-efficient than the microwave, freeze, and hot-air, respectively. Similar results could be observed for exergy efficiency. EHD drying has superior product quality compared to other drying methods. For instance, it could retain 62% higher total phenolic content with 21% less color degradation than freeze-drying. Although microwave drying resulted in significantly higher drying kinetics than other techniques, EHD performed better than solar and freeze-drying but was comparable with hot-air drying. EHD drying also shows promising results in economic performance assessment. It is the cheapest drying method after solar drying and has the highest estimated net present value (NPV) after hot-air drying. Overall, compared to the currently used drying methods for small to medium-scale drying, EHD was found to be a more exergy and energy-efficient, cost-effective, and sustainable alternative that can provide higher-quality dried products. However, its drying kinetics should be improved for industrial applications

Electrohydrodynamics for dehydration of soft, heat-sensitive biological materials

Background and motivation: Reducing post-harvest losses is one of the major measures considered by food system experts to increase global food security. Fruits and vegetables have the highest share of post-harvest losses, with 37 to 50% loss. Preserving fruits and vegetables as dried materials is one of the oldest and most established techniques for increasing off-season availability. Nevertheless, drying is an energy-intensive process due to the high latent heat of evaporation required to evaporate water. In addition, the existing drying methods are energy-intensive and costly, hence adding a substantial cost for high-volume, low-value products such as fruits and vegetables. Therefore, researchers and industry are continuously looking for more sustainable alternative solutions. Electrohydrodynamic (EHD) drying is a promising yet not commercialized technology for drying different biomaterials, including fruits and vegetables. This drying technique has gained the attention of researchers due to its promising features, such as low energy consumption, operation at ambient temperature, and good preservation of the nutritional content and sensory appeal of dried fruits and vegetables. Despite all these promising characteristics, researchers and industry have not yet been able to implement EHD drying as an industrial-scale unit operation. Currently, we lack comprehensive knowledge about the physics behind the EHD drying process, its energy consumption and exergy situation, its impact on product quality, its scalability, and the associated costs and economics. These challenges hinder the initiation of the next steps that could finally lead to industrial implementation. Scope and approach: This thesis addresses these challenges by exploring the underlying physics of EHD drying, introducing an optimized and scalable EHD drying configuration, and benchmarking the performance of EHD drying against standard conventional drying methods. To this end, the three main tools of a scientific approach, namely theoretical development, modeling and simulation, and experimental verification, are employed. First, the main dehydration mechanisms in EHD drying are identified, modeled by theoretical formulation, and analyzed. Using these theoretical models, we quantified the relative contribution of each dehydration mechanism to the overall mass transfer and ranked them based on their contribution. Then, a physics-based model which couples EHD-generated airflow directly to the convective heat and mass transfer from the food was developed and solved using the finite element method. This validated model enabled us to design a scalable configuration in silico. Different arrangements of electrodes were tested in silico to improve the energy efficiency and drying kinetics of this scalable configuration. After selecting the configuration based on the simulation results, a lab-scale setup was developed to experimentally verify the scalability of this novel configuration. Moreover, the sustainability of the scalable EHD drying was evaluated by quantifying the Key Performance Indicators (KPIs). The performance indicators were selected based on the current concerns and interests of the food industry, namely, drying kinetics, energy consumption and environmental impact, product quality, and final product cost. By comparing the KPIs between EHD drying and conventional drying methods, this thesis provides a clear overview for industry, farmers, and other stakeholders about the advantages and disadvantages of using EHD drying as an alternative to their current technologies, such as hot-air, solar, and freeze-drying. Pre-treatment methods were also combined with EHD drying to improve the drying rate of the EHD drying process to satisfy the high throughput demand of the food processing industry. Key findings and conclusions: Theoretical modeling of the different EHD-driven dehydration mechanisms shows that convective dehydration by ionic wind is the dominant dehydration mechanism, with a contribution of about 93% to the overall water flux for a capillary-porous material. The contribution of all the other water transport mechanisms, such as transmembrane flow and electro-osmosis, is only 7%. These findings prove that EHD drying is a convective-based drying and convection should be the focus of any design and process optimization in the next steps. Our experiments and simulations showed that using a mesh collector instead of a plate collector and smart activation of wires in the mesh results in more energy-efficient and uniform dehydration than the conventional EHD drying configurations employed in previous studies. Using these insights, we introduced a new configuration for EHD drying. This novel design is independent of fruit loading density showing better scalability in terms of production capacity compared to the conventional EHD drying designs. In addition, it significantly improves the drying rate by more than 65% and energy consumption by more than 60% compared to the conventional configurations. We also observed a 50% decrease in drying time compared to control drying (i.e., natural convection) by operating EHD at only 1 W. Finally, this technology was benchmarked against other conventional drying methods by KPI evaluation. The results show that compared to the currently used drying methods for small to medium-scale drying, EHD was found to be a more exergy and energy-efficient, cost-effective, and sustainable alternative that can provide higher-quality dried products. Using pre-treatment methods is one of the options to increase the drying rate in EHD drying. Therefore, pulsed electric fields (PEF), ultrasound, and blanching pre-treatment methods were studied to explore their impacts on the drying rate. Results show that only PEF pre-treatment could significantly (by 39%, p<0.05) decrease the drying time. However, it resulted in a 26% higher browning index than the untreated EHD-dried apples, which is not appealing to consumers. Other quality attributes, such as antioxidant activity, total phenolics, and rehydration ratio, were not significantly affected by the applied pre-treatment methods. The obtained insights into the EHD drying process, and the significant improvements of the EHD dryer with our optimized and up-scalable design, together with the holistic evaluation of its performance, could provide the push needed to finally implement EHD drying as an industrial unit on a full scale

Electrohydrodynamic drying: Can we scale-up the technology to make dried fruits and vegetables more nutritious and appealing?

Electrohydrodynamic (EHD) drying is a promising technology to better preserve the nutritional content and sensory appeal of dried fruits and vegetables. To successfully scale up this technology, we need to rethink the current EHD dryer designs. There is also a significant potential to further enhance the nutritional content and sensory quality of the dried products by optimizing EHD process parameters. This study particularly highlights the current bottlenecks in scaling up the technology and improving nutrient retention and sensory appeal of the dried products. We discuss plausible future pathways to further develop the technology to produce highly nutritious dried products. Particular emphasis has been given to quantifying the residual nutritional and sensory properties of EHD dried products, and possible EHD dryer configurations for farmers and the industry. Concerning the nutritional content, EHD drying preserves vitamins, carotenes, and antioxidants significantly better than convective air drying. From the sensory perspective, EHD drying enhances the color of dried products, as well as their general appearance. With respect to scalability, placing the fruit on a grounded mesh electrode dries the fruit much faster and more uniformly than the grounded plate electrode. Future research should be directed toward simultaneous measurements of multiple food nutrients and sensory properties during EHD drying with a grounded mesh collector. Quantifying the impact of the food loading density on drying kinetics and energy consumption of the EHD drying process should also be a future research goal. Research comparing EHD drying with commercially available drying methods such as freeze-drying, microwave-drying, and infrared drying should also be carried out. This study gives promising insight toward developing a scalable novel thermal drying technology tailored to the requirements of the current and future society.ISSN:1541-433

Dehydration mechanisms in electrohydrodynamic drying of plant-based foods

Electrohydrodynamic drying (EHDD) is an energy-efficient and non-thermal technique for dehydrating heat-sensitive biological materials, like fruits, vegetables, or medicinal plants. Although this method has been studied for more than three decades, still little is known about the relative contribution of the different dehydration mechanisms in EHDD. An accurate understanding of the impact of the different EHD-driven mass transfer processes inside the food and its surrounding air is essential for a targeted future optimization and successful upscaling of EHDD technology. Examples of these dehydration mechanisms are convective moisture removal, electroporation of the cell membrane, or electro-osmotic flow in the fruit. In this modeling study, we first identify possible dehydration mechanisms for mass transfer during the EHDD process of plant-based food materials. Using available theoretical models, we then estimate the relative contribution of each dehydration mechanism to the overall mass transfer during the constant rate period and rank them based on their contribution. We show that convective dehydration by ionic wind is the dominant dehydration mechanism, with a contribution of about 93% to the overall water flux for a capillary-porous material. Cell-membrane electroporation is the second important driving force that increases the contribution of the transmembrane water flow to about 6.5% of the total mass flux in fruit tissue. The contribution of all the other water transport mechanisms is only 0.5%. These insights provide a stepping stone towards developing a full physics-based model of the dehydration process by EHD, including the falling rate period.ISSN:0960-3085ISSN:1744-357

Scaling-up electrohydrodynamic drying for energy-efficient food drying via physics-based simulations

Electrohydrodynamic (EHD) drying is a novel non-thermal drying method to dry heat-sensitive foods faster and with lower energy. Upscaling EHD drying to dry large amounts of food is the current challenge of this technology. In this regard, we quantify how successful a newly-proposed electrode configuration for EHD dryers is for drying commercial amounts of fruit for a wide range of operating conditions. To achieve this goal, we simulate an EHD dryer using physics-based modeling. The scalability was evaluated by quantifying the impact of fruit loading density in the dryer, applied voltage, and distance between electrodes on the drying time and energy consumption. Drying fruits in a commercial EHD dryer is more optimal when the dryer is densely loaded, compared to a low loading density. Loading the trays in the dryer to a capacity of 70% increased the drying time by 16%, compared to drying a few fruits widely spaced apart, but the energy consumption was 28% less. We identified the best strategy to dry a particular batch of fruit with EHD drying to achieve the fastest drying with the least energy possible. We found that it is most energy-efficient and quick to load the dryer close to its full capacity, instead of drying smaller batches in many different runs. By loading the trays in the dryer to 70% of their capacity, we could dry 7 times faster and with 11 times less energy in a single drying run instead of drying the same amount of fruit by many different runs. This study presents a key step towards upscaling EHD drying systems for the industry to dry large amounts of fruits in the shortest possible time and more energy-efficiently.ISSN:0959-652

An in-silico proof-of-concept of electrohydrodynamic air amplifier for low-energy airflow generation

Electrohydrodynamic (EHD) technology generates airflow without moving parts, making it a reliable solution for various low-energy applications. EHD-based airflow devices enhance airflow patterns, resulting in significant energy savings in air-moving systems. This airflow, also known as ionic wind, is created through Corona discharge, which accelerates electrically charged air molecules in a strong electric field. Currently, EHD's low electrical-to-mechanical energy conversion rate still limit its ability to generate large flow rates. The objective of this study is to enhance the flow rate of EHD-based devices, for applications where EHD can be used as an effective auxiliary technology with low pressure lift, to enhance airflow distribution and circulation. To this end, a novel bladeless air propulsion device is proposed that combines ionic wind with air amplification based on the Coanda phenomenon to amplify EHD-generated flow rates. We assess the performance of the bladeless air propulsion device to generate airflow by investigating fluid dynamics, electrostatics, and energy consumption. We demonstrate the proof-of-concept with an innovative fully-coupled simulation approach for corona discharge and EHD modeling. We explore different design parameters on the conceptual EHD air amplifier, such as the electric potential (10–30 kV) of the discharge electrode, the electrode spacing (5–25 mm), and the channel height (30–150 mm). The studies are performed on a 2D constrained channel flow and a 2D-axisymmetric open space design, respectively. In order to quantify the benefit of air amplification on EHD, the results are benchmarked to a regular EHD setup without amplifying vane as well as to a comparable commercial axial fan. We assess the performance in terms of flow rate per electric power input. Here, the EHD air amplifier in the constrained flow configuration increases the total flow rate by 59% compared to regular EHD and 48% compared to the axial fan for the same electrical energy input. Amplification factors of 16.5–19 are achieved for the constrained configuration and 5.5 to 6.4 for the open space configuration. The predicted energy consumption is 4–17.5 W for the open space configuration, resulting in flow rates up to 140 m3 h−1. These results show that EHD air amplification is a promising way to generate high flow rates with low pressure rise at a low electrical cost, by which it can provide a more sustainable alternative to conventional fans in specific applications.ISSN:0959-652

Electrohydrodynamic drying versus conventional drying methods: A comparison of key performance indicators

Preserving fruits and vegetables by drying is a traditional yet effective way of reducing food waste. Existing drying methods are either energy-intensive or lead to a significant reduction in product quality. Electrohydrodynamic (EHD) drying is an energy-efficient low-temperature drying method that presents an opportunity to comply with the current challenges of existing drying methods. However, despite its promising characteristics, EHD drying is yet to be accepted by industry and farmers. The adoption of EHD drying is hindered due to different reasons, such as uncertainties surrounding its scalability, quality of dried product, cost of operation, and sustainability compared to conventional drying methods. To address these concerns, this study quantifies and benchmarks the Key Performance Indicators (KPIs) of EHD drying compared to the standard conventional drying methods based on lab-scale experiments. These drying methods include hot-air, freeze, microwave, and solar drying. The results show that drying food using EHD is at least 1.6, 20, and 70 times more energy-efficient than the microwave, freeze, and hot-air, respectively. Similar results could be observed for exergy efficiency. EHD drying has superior product quality compared to other drying methods. For instance, it could retain 62% higher total phenolic content with 21% less color degradation than freeze-drying. Although microwave drying resulted in significantly higher drying kinetics than other techniques, EHD performed better than solar and freeze-drying but was comparable with hot-air drying. EHD drying also shows promising results in economic performance assessment. It is the cheapest drying method after solar drying and has the highest estimated net present value (NPV) after hot-air drying. Overall, compared to the currently used drying methods for small to medium-scale drying, EHD was found to be a more exergy and energy-efficient, cost-effective, and sustainable alternative that can provide higher-quality dried products. However, its drying kinetics should be improved for industrial applications.ISSN:0196-8904ISSN:1879-222

Impact of pre-treatment methods on the drying kinetics, product quality, and energy consumption of electrohydrodynamic drying of biological materials

Electrohydrodynamic (EHD) drying is an energy-efficient drying method. This novel drying technology operates at room temperature, which makes it particularly suitable for drying biomaterials that contain heat-sensitive compounds. It has a higher drying rate than other low-temperature methods, such as solar and freeze-drying. However, its drying rate is not high enough to compete with other conventional thermal methods, such as hot-air drying. For industrial applications requiring high product throughput, the drying rate of EHD drying should be improved. One way to do this is to combine EHD with pre-treatment methods. Therefore, this study evaluated the impact of different pre-treatment methods on drying kinetics, energy consumption, and product quality attributes of apple slices dried using EHD drying. Pulsed electric fields (PEF), ultrasound, and blanching are the studied pre-treatment methods. Results show that only PEF pre-treatment could significantly decrease the EHD drying time by 39%. However, it resulted in a 26% higher browning index than the untreated EHD-dried apples, which is not appealing to consumers. The applied pre-treatment methods did not significantly affect other quality attributes, such as antioxidant activity, total phenolics, and rehydration ratio. In conclusion, using the studied pre-treatments for EHD drying increases the complexity of the process, whereas it is arguable whether the added values outweigh the energetic and quality downsides or not.ISSN:1466-856

Time-Resolved Study on Self-Assembling Behavior of PEGylated Gold Nanoparticles in the Presence of Human Serum Albumin: A System for Nanomedical Applications

The combination of a microfluidic approach for synchrotron-based dynamic (early structural changes) with lab-based static small-angle X-ray scattering (SAXS) measurements (longer time scale) allows qualifying nanoparticle (NP) systems for their use in nanomedicine. Time-resolved in situ investigations are performed on self-assembly and colloidal behavior of 5 nm PEGylated (polyethylene glycol) gold NPs in different media. SAXS methods combined with a micromixing fluidic system are used to observe the early stage of NP interactions. Dynamic measurements cover a time range from 1 to 100 s after mixing thoroughly, while static measurements complete the study for up to 10 days after sample preparation. These NPs, after mixing with saline solution (0.9% NaCl solution), self-assemble in 3D ordered domains. The NPs also show this ordering in the presence of human serum albumin (HSA) molecules. It is shown that, although the presence of protein molecules slows down the NP self-assembling process, these molecules improve the long-term colloidal stability of the ordered domains probably via interpolymer complexation between PEG and HSA molecules

Energy-saving discharge needle shape for electrohydrodynamic airflow generation

Electrohydrodynamics (EHD) is a way to produce low energy-consuming airflow without moving components. The basis of airflow by EHD is corona discharge. A way to generate corona discharge is done, among others, via needle-type emitter electrodes whose shape and arrangement play a crucial role in the effectiveness of the discharge. Until now, the needle shape was chosen somewhat arbitrarily, although it impacts the energy consumption of the EHD process. We lack systematic studies on the impact of needle shape on the EHD discharge process and associated airflow to help engineers and scientists choose the best shape. This in-silico study screens the impact of the needle shape parameters on EHD performance in terms of electrical power consumption and airflow generation. The study aims to find the ideal EHD needle shape for unrestricted and confined flow. For this purpose, we test three different geometrical configurations. The first configuration is a free-flow single-needle configuration. The second configuration adds a dielectric nearby, which represents a needle enclosure. Lastly, a configuration including a dielectric and a converging nozzle is examined. All studies use a 2D-axisymmetric, fully automatized EHD physics-based model. The first set of parametric studies explores the inherent geometrical properties of the needle shape, like tip radii (10–250 μm), needle cone angle (10–70°), and needle diameters (0.5–2 mm). The second set of parametric studies investigates the operation conditions, such as the emitter-collector distance (10–40 mm), the nozzle contraction ratio (0.04–1), and the operating voltage (6–32 kV). The results of the free-flow configuration show qualitative agreement with experiments on existing needle products. The ideal energy-saving needle shape for free flow configuration features a short conical tip length (i.e., a large angle ≥30°), a diameter of 2 mm, and a needle rip radius of 100 μm. The situation changes when a dielectric is present, and a sharp angle of 10° is favorable to reduce energy consumption. Since a dielectric inverts the optimal needle shape, it makes sense to customize it for a particular application in EHD airflow generation. We provide performance maps that can be used as design charts. This study is a guideline to optimize EHD devices further to reduce energy consumption and increase airflow speed.ISSN:1873-5738ISSN:0304-388