Electrohydrodynamic Drying of Plant-Based Foods and Food Model Systems
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Electrohydrodynamic Drying of Plant-Based Foods and Food Model Systems Ivanna Bashkir 1 & Thijs Defraeye 1,2 & Tadeusz Kudra 1 & Alex Martynenko 1 Received: 28 November 2019 / Accepted: 22 May 2020 # Springer Science+Business Media, LLC, part of Springer Nature 2020
Abstract Electrohydrodynamic (EHD) drying is a novel technology, which appears to be beneficial for drying of heat-sensitive biomaterials with high moisture contents. Although numerous publications on EHD drying of fruits, vegetables, and other plant-based foods report high energy efficiency and superior product quality, the technology is still not commercialized. One of the reasons is incomplete information in published studies on the design of EHD dryers, including electrode geometry, dried materials, and experimental conditions, which hinder the comparison of experimental findings. Another reason is the gap in the knowledge about the actual mechanisms behind the EHD drying, including convective moisture removal by airflow and diffusive moisture transport inside the food. In this review, key findings in published reports on plant-based foods and food model systems have been critically analyzed and generalized using the same uniform metrics. The limiting factors, most favorable conditions, and future perspectives of EHD drying for plant-based foods are discussed. Keywords Electrohydrodynamics . Current . Voltage . Ionic wind . Corona discharge . Drying flux
Abbreviations AC alternating current DC direct current DR drying rate EHD electrohydrodynamic FC forced convection NC natural (free) convection RH relative humidity Nomenclature A Area, m2 E Electric field strength, kV/cm b Ion mobility, m2/(V·s) c Water vapor concentration, g/m3 D Water vapor diffusivity, m2/s δ Characteristic thickness of boundary layer, m d Gap between discharge and collecting electrodes, cm I Current, A * Alex Martynenko [email protected] 1
Department of Engineering, Faculty of Agriculture, Dalhousie University, Box 550, Truro, PO, Canada
2
Laboratory for Biomimetic Membranes and Textiles, Empa, Swiss Federal Laboratories for Materials Science and Technology, Lerchenfeldstrasse 5, 9014 St. Gallen, Switzerland
j hm L l ˙ m ρ r rtip V v
Current density, A/m2 Convective mass transfer coefficient, m/s Spacing between needles/wires, cm Sample thickness, mm Drying rate, g/s Air density, kg/m3 Needle/wire body radius, mm Needle tip radius, mm Applied voltage, kV Kinematic viscosity of air, m2/s
Introduction Among different methods for food preservation, drying is one of the most commonly used technologies to reduce the moisture content of fruits, vegetables, spices, fish, meat, and other products. Dried foods have many benefits compared to raw products, including an extended shelf life as well as reduced packaging, storage, handling, and transportation costs. However, the process of drying is energy intensive, accounting roughly for 12–20% of the energy consumed in the manufacturing industry [65]. Over 85% of the industrial dryers are of the convective type, which requires
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