Editing Electrohydrodynamics (section)

{{Short description|Study of electrically conducting fluids in the presence of electric fields}}
{{Use American English|date = February 2019}}
'''Electrohydrodynamics''' ('''EHD'''), also known as '''electro-fluid-dynamics''' ('''EFD''') or '''electrokinetics''', is the study of the [[dynamics (mechanics)|dynamics]] of [[electrically charged]] fluids.<ref name="Castellanos">{{cite book | author=Castellanos, A. | title=Electrohydrodynamics | year=1998 | author-link=Antonio Castellanos Mata }}</ref><ref name=":0" /> Electrohydrodynamics (EHD) is a joint domain of electrodynamics and fluid dynamics mainly focused on the '''fluid motion induced by electric fields'''. EHD, in its simplest form, involves the application of an electric field to a fluid medium, resulting in fluid flow, form, or properties manipulation. These mechanisms arise from the interaction between the '''electric fields''' and '''charged particles''' or '''polarization effects''' within the fluid.<ref name=":0">{{Cite journal |last1=Iranshahi |first1=Kamran |last2=Defraeye |first2=Thijs |date=2024 |title=Electrohydrodynamics and its applications: Recent advances and future perspectives |journal=International Journal of Heat and Mass Transfer |volume=232 |doi=10.1016/j.ijheatmasstransfer.2024.125895|doi-access=free |bibcode=2024IJHMT.23225895I |hdl=20.500.11850/683872 |hdl-access=free }}</ref> The generation and movement of '''charge carriers (ions)''' in a fluid subjected to an electric field are the underlying physics of all EHD-based technologies.
[[File:EHD Wiki Iranshhai et al.tif|thumb|Electrohydrodynamics employed for drying applications (EHD Drying)<ref name=":0" />.|353x353px]]


The electric forces acting on particles consist of electrostatic (Coulomb) and electrophoresis force (first term in the following equation)., dielectrophoretic force (second term in the following equation), and electrostrictive force (third term in the following equation):

<math>F_e= \rho_e \overrightarrow{E} - {1 \over 2}\varepsilon_{0}\overrightarrow{E}^2\triangledown\varepsilon_r + {1 \over 2}\varepsilon_{0}\triangledown\Bigl(\overrightarrow{E}^2 \rho_{f}\left ( \frac{\partial \varepsilon_{r}}{\partial \rho_{f}} \right ) \Bigr)</math><ref name=":0" />

This electrical force is then inserted in [[Navier–Stokes equations|Navier-Stokes]] equation, as a body (volumetric) force.[[File:EHD Wiki 2 Iranshhai et al.tif|thumb|Electrohydrodynamics employed for [[Plasma actuator|Airflow control]] and [[Electrospinning]] applications.]]EHD covers the following types of particle and fluid transport mechanisms: [[electrophoresis]], [[Electrohydrodynamics#Electrokinesis|electrokinesis]], [[dielectrophoresis]], [[electro-osmosis]], and [[electrorotation]]. In general, the phenomena relate to the direct conversion of [[electrical energy]] into [[kinetic energy]], and ''vice versa''.

In the first instance, shaped [[electrostatic field]]s (ESF's) create [[hydrostatic pressure]] (HSP, or motion) in [[dielectric media]]. When such media are [[fluid]]s, a [[Fluid dynamics|flow]] is produced. If the dielectric is a [[vacuum]] or a [[solid]], no flow is produced. Such flow can be directed against the [[electrode]]s, generally to move the electrodes. In such case, the moving structure acts as an [[electric motor]]. Practical fields of interest of EHD are the common [[air ioniser]], [[electrohydrodynamic thruster]]s and EHD cooling systems.

In the second instance, the converse takes place. A powered flow of medium within a shaped electrostatic field adds energy to the system which is picked up as a [[potential difference]] by electrodes. In such case, the structure acts as an [[electrical generator]].