Assessment of the Electrohydrodynamic Drying Process

Abstract

Industries using energy-intensive processes are being forced to explore ways for reducing their energy consumption. In the food industry, air drying is one of the more energy-consuming processes. To reduce the energy consumption during this operation, alternative processes should be investigated. One promising alternative consists in the electrohydrodynamic (EHD) enhancement of heat and mass transfer. This paper analyses the literature and describes the great potential of this innovative process based on the generation of an electric wind by a corona discharge. The main aspects of this technique are discussed and special emphasis is given on its benefit for food processes. The main part of this paper concerns experimental investigations carried out to assess the EHD enhancement on the drying process. An experimental setup was designed to measure the weight losses on a food product submitted to an electrostatic field and to a cross air flow. Present results confirm that, for a low cross air velocity, the ionic wind leads to an enhancement of the drying rate. The best results are obtained for the smaller distance between the food surface and the corona electrode. Nevertheless, the process is less efficient for a high air velocity. The last part deals with a numerical model that was developed to evaluate the electric parameters and the flow field in turbulent regime. This model provides useful information on the coupled phenomena and permits to explain the experimental observations and to help in designing EHD drying processes. Nomenclature a surface (m 2 ) b ionic mobility (m 2 V −1 s −1 ) d food surface-electrode gap (m) e edge of the wind tunnel (m) E electric field (V m −1 ) F e electric body force (C m −2 s −1 ) g gravity (m s −2 ) I electric current (A) J current density (A m −2 ) k turbulent kinetic energy (m 2 s −2 ) L length of the wind tunnel (m) p pressure (Pa) U velocity vector (m s −1 ) v i ionic wind velocity (m s −1 ) V voltage (V) x distance along surface (m) y height above surface (m) φ diameter (m) ɛ turbulent dissipation rate (m 2 s −3 ) ɛ 0 permittivity of free space (C m −1 V −1 ) Ρ density of air (kg m −3 ) ρ c space charge density (C m −3 ) μ dynamic viscosity of air (Pa s −1 ) μ t turbulent viscosity (Pa s −1 )

Quantifying Enhancement in Heat Transfer Due to Natural Convection During Canned Food Thermal Sterilization in a Still Retort

“…Computational fluid dynamic methods have become useful in the food industry to simulate and analyze different processes such as drying, refrigeration, and sterilization (Norton and Sun 2006). Combined heat transfer and fluid flow encountered in industrial ovens (Mirade et al 2004), ventilated packaging systems (Zou et al 2006), electrohydrodynamic dryers (Ahmedou et al 2009), and high hydrostatic pressure food processors (Khurana and Karwe 2009) have been simulated using CFD.…”

Multiphysics simulation of corona discharge induced ionic wind

“…This model will be hereon denoted SCCC, as in "space charge controlled current". Using (10) to determine the coefficients of the general expression (8) …”

“…For example, Adamiak and others [2,3,4,5] studied the DC and pulsed corona discharge between a needle and a plate collector, using different numerical methods (FEM, BEM, FCT etc.) for the approximation of each equation in the PDE system; Ahmedou and Havet [6,7,8] used a commercial FEM software to investigate the effect of EHD on turbulent flows; Moreau and Touchard, [9] Huang and others, [10] and Kim and others [11] experimentally studied different EHD devices designed for cooling or air pumping purpose; Chang, Tsubone and others [12,13,14] made extensive experimental study of the forced airflow and the corona discharge in a converging duct; Jewell-Larsen and others [15,16,17,18,19,20,21] and Go and others [22,23,24,25,26] conducted both experimental and numerical studies aimed at designing and applying ionic wind cooling devices to thermal management of electronic devices.…”

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

“…Along their path, these ions collide with neutral air molecules and transfer their momentum to the neutral air molecules. The resulting flow of ions from the discharge electrode to the grounded electrode is called corona wind (Ould Ahmedou et al, 2009). The net effect of corona wind is destabilization of boundary layer, thus leading to a substantial increase in moisture removal rate (Ramachandran and Lai, 2010) due to the enhancement of heat and mass transfer coefficients (Lai and Wong, 2003).…”