Drying, being the most crucial unit operation that is often utilized in food business and is normally deployed for use in the dehydration of food materials to preserve and extend shelf life. By using thermal processing methods, the moisture content of food materials is decreased, reducing microbial growth and chemical deterioration. High drying temperatures can harm food products’ nutritional and organoleptic qualities, (Dalvand et al., 2013a). To create dried food products of better quality, cutting-edge techniques including microwave, freeze drying, radio frequency, etc. can be used alone or in combination. Freeze-drying gives outstanding rehydration and sensory qualities, but the industrial use of the technique is very complex and expensive. The application of radio frequency and microwave has reduced drying periods and led to usage of less energy. However, concerns with scaling up have created significant implementation problems, (Singh et al., 2012). Hence, Food Industry has been compelled to look for alternative procedures because of rising consumption of energy across the globe and the use of more energy-intensive technologies.
Electrohydrodynamic drying (EHD) is a creative and promising alternative technique, (Singh et al., 2012). It is a novel non-thermal processing technique which uses high voltages that are either AC or DC to dry the material. EHD drying systems offer cheaper food production costs, while also providing greater quality, flavour, colour, shrinkage and nutritional content, (Paul & Martynenko, 2021). Owing to their simpler design and lower energy demand, EHD drying technique finds plenty of its applications for bulk and industrial purposes, (Bajgai et al., 2007).
EHD drying is not a very popular drying technique. Although, in order to enhance the transport of heat from vertical plates, fluid mechanics comprehensively studies and applies EHD concepts, (Jones, 1979). Although, the non-thermal action of EHD is crucial, the issue of bulk material drying has remained a barrier to the practical application of the approach. (Hashinaga et al., 2007)
Fig. 1 depicts the experimental setup to research the impact of EHD drying on goji berries, (Ni et al., 2020). A voltage controller, a high voltage power supply and a multi-needle to plate electrode system were its main components. The multi-needle electrode is connected to the high-voltage power source. A microampere metre was linked between the steel plate and the ground for measuring the current produced throughout the experiment and needle spacing between consecutive needles could be changed. When power is turned on, an electric field is generated between the electrodes also known as corona discharge, which is used to dry the food materials.
Corona discharge is the term used to describe the phenomena shown in Fig. 2, which occurs with the existence of a powerful electric field to ionize the dielectric close to a conductor, while being so intense to induce any problem. However, a regulated coronal ejection can be utilized to create ion flow and producing kinetic energy. This phenomenon is undesirable and harmful in high-voltage systems. EHD phenomena, which directly transform electrical energy into kinetic energy have a wide range of modern uses. (Fylladitakis et al., 2014)
Both the positive and the negative polarities of the applied voltage causes the corona current to rise linearly and compared to a positive corona discharge, but stronger corona current can be produced from a negative corona discharge (Singh et al., 2012). However, it was discovered that the EHD method required less specific energy than the latent heat of vapourization, suggesting that methods other than evaporation were used to remove water from the sample’s surface. Additionally, it was discovered that the specific energy consumption for both polarities rose with applied voltage, while remaining lower than that of more traditional drying methods like fluidized bed drying. The efficacy of the EHD process is significantly influenced by the electrode configuration; Wire and single-electrode setups did not work as well as multiple-needle electrode configurations. Quick evaporation rates and the electric field interaction with a dielectric material that produces heat are two thermodynamic factors that contribute to the temperature drop during EHD drying. Agribusiness materials can be dried more quickly using plate and multi-point electrode methods. EHD is a good substitute for processing biological materials that are thermally sensitive, because of the advantage of using it for food and bioprocessing due to its special features.
Additionally, typical drying methods that rely on radiation, conduction or other types of heat transfer are more widely known than electrostatic field drying, which is comparatively less popular, (Esehaghbeygi & Basiry, 2011). Heat-sensitive materials are a good candidate to be dried using the revolutionary non-thermal drying process known as Electrohydrodynamic Drying, (Ahmedou et al., 2009). To increase the drying rate, this method of drying employs a high electric field made up of a plate electrode and one or more-point electrodes (Li et al., 2006a). According to (Allen & Karayiannis, 1995), electrophoresis, dielectrophoretic forces and the flow of “corona wind” are the three main ways that EHD might improve single-phase convective heat transfer. Because of how the dipoles in the electric field are oriented, rapid evaporative cooling and less entropy contribute to the drop in temperature in the EHD process. EHD drying systems are less complex than convective and freeze-drying systems and use less energy, (Bajgai et al., 2007). Various organic as well as inorganic materials were tested with different DC voltage levels at room temperature and pressure and it was found that the evaporation rates increased several-fold as a result. (Barthakur & Al-Kanani, 1989)
Some important studies carried out by different researchers on EHD drying of food materials are listed in table 1.
The ability to speed up drying, improve product quality and use less energy than traditional drying techniques makes Electrohydrodynamic Drying (EHD) a viable technology for drying food materials. EHD works by using high voltage electric fields to produce electrostatic forces that speed up the removal of water. This technology has showed promise for a range of food items, including fruits, vegetables, cereals and meat. To optimize the EHD process for various food materials and to look at how EHD affects the nutritional and sensory qualities of dried foods, more research is required. The food drying business may undergo a revolution, owing to the ongoing developments in EHD technology since it will serve as a highly effective, sustainable and high-quality drying method.
References:
1. Ahmedou, S. A. O., Rouaud, O., & Havet, M. (2009). Assessment of the electrohydrodynamic drying process. Food and Bioprocess Technology, 2(3), 240–247. https://doi.org/10.1007/S11947-008-0078-6
2. Allen, P. H. G., & Karayiannis, T. G. (1995). Electrohydrodynamic enhancement of heat transfer and fluid flow. Heat Recovery Systems and CHP, 15(5), 389–423. https://doi.org/10.1016/0890-4332(95)90050-0
3. Bajgai, T. R., Raghavan, G. S. V., Hashinaga, F., & Ngadi, M. O. (2007). Electrohydrodynamic Drying—A Concise Overview. Http://Dx.Doi.Org/10.1080/07373930600734091, 24(7), 905–910. https://doi.org/10.1080/07373930600734091
4. Barthakur, N. N., & Al-Kanani, T. (1989). Impact of air ions of both polarity on evaporation of certain organic and inorganic liquids. International Journal of Biometeorology, 33(2), 136–141. https://doi.org/10.1007/BF01686291
5. Chen, Y., Barthakur, N. N., & Arnold, N. P. (1994). Electrohydrodynamic (EHD) drying of potato slabs. Journal of Food Engineering, 23(1), 107–119. https://doi.org/10.1016/0260-8774(94)90126-0
6. Dalvand, M. J., Mohtasebi, S. S., Rafiee, S., Dalvand, M. J., Mohtasebi, S. S., & Rafiee, S. (2013a). Effect of needle number on drying rate of kiwi fruit in EHD drying process. Agricultural Sciences, 4(1), 1–5. https://doi.org/10.4236/AS.2013.41001
7. Esehaghbeygi, A., & Basiry, M. (2011). Electrohydrodynamic (EHD) drying of tomato slices (Lycopersicon esculentum). Journal of Food Engineering, 104(4), 628–631. https://doi.org/10.1016/J.JFOODENG.2011.01.032
8. Fylladitakis, E. D., Theodoridis, M. P., & Moronis, A. X. (2014). Review on the history, research, and applications of electrohydrodynamics. IEEE Transactions on Plasma Science, 42(2), 358–375. https://doi.org/10.1109/TPS.2013.2297173
9. Hashinaga, F., Bajgai, T. R., Isobe, S., & Barthakur, N. N. (2007). ELECTROHYDRODYNAMIC (EHD) DRYING OF APPLE SLICES. Https://Doi.Org/10.1080/07373939908917547, 17(3), 479–495. https://doi.org/10.1080/07373939908917547
10. Jones, T. B. (1979). Electrohydrodynamically Enhanced Heat Transfer in Liquids—A Review. Advances in Heat Transfer, 14(C), 107–148. https://doi.org/10.1016/S0065-2717(08)70086-8
11. Li, F. de, Li, L. te, Sun, J. F., & Tatsumi, E. (2006a). Effect of electrohydrodynamic (EHD) technique on drying process and appearance of okara cake. Journal of Food Engineering, 77(2), 275–280. https://doi.org/10.1016/J.JFOODENG.2005.06.028
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13. Meng, Z., Cui, X., Zhang, H., Liu, Y., Wang, Z., & Zhang, F. (2023). Study on drying characteristics of yam slices under heat pump-electrohydrodynamics combined drying. Case Studies in Thermal Engineering, 41, 102601. https://doi.org/10.1016/J.CSITE.2022.102601
14. Ni, J., Ding, C., Zhang, Y., Cao, Z., Song, Z., Hu, X., & Hao, T. (2020). Infrared Spectrum Analysis of Goji Berry during Electrohydrodynamic Drying. Journal of Spectroscopy, 2020. https://doi.org/10.1155/2020/4395425
15. Paul, A., & Martynenko, A. (2021). Electrohydrodynamic drying: Effects on food quality. Https://Doi.Org/10.1080/07373937.2021.1906694, 39(11), 1745–1761. https://doi.org/10.1080/07373937.2021.1906694
16. Singh, A., Orsat, V., & Raghavan, V. (2012). A Comprehensive Review on Electrohydrodynamic Drying and High-Voltage Electric Field in the Context of Food and Bioprocessing. Https://Doi.Org/10.1080/07373937.2012.708912, 30(16), 1812–1820. https://doi.org/10.1080/07373937.2012.708912
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18. Taghian Dinani, S., Hamdami, N., Shahedi, M., Havet, M., & Queveau, D. (2015). Influence of the electrohydrodynamic process on the properties of dried button mushroom slices: A differential scanning calorimetry (DSC) study. Food and Bioproducts Processing, 95, 83–95. https://doi.org/10.1016/J.FBP.2015.04.001
19. Taghian Dinani, S., & Havet, M. (2015). The influence of voltage and air flow velocity of combined convective-electrohydrodynamic drying system on the kinetics and energy consumption of mushroom slices. Journal of Cleaner Production, 95, 203–211. https://doi.org/10.1016/J.JCLEPRO.2015.02.033
20. Taghian Dinani, S., Havet, M., Hamdami, N., & Shahedi, M. (2014). Drying of Mushroom Slices Using Hot Air Combined with an Electrohydrodynamic (EHD) Drying System. Drying Technology, 32(5), 597–605. https://doi.org/10.1080/07373937.2013.851086
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