There are three kinds of electrohydrodynamics (EHD) pumping based on Coulomb
force: induction pumping, ion-drag pumping, and pure conduction pumping. EHD
induction pumping relies on the generation of induced charges. This charge
induction in the presence of an electric field takes place due to a
non-uniformity in the electrical conductivity of the fluid which can be caused
by a non-uniform temperature distribution and/or an inhomogeneity of the fluid
(e.g. a two-phase fluid). Therefore, induction pumping cannot be utilized in an
isothermal homogeneous liquid. In order to generate Coulomb force, a space
charge must be generated. There are two main mechanisms for generating a space
charge in an isothermal liquid. The first one is associated with the ion
injection at a metal/liquid interface and the related pumping is referred to as
ion-drag pumping. Ion-drag pumping is not desirable because it can deteriorate
the electrical properties of the working fluid. The second space charge
generation mechanism is associated with the heterocharge layers of finite
thickness in the vicinity of the electrodes. Heterocharge layers result from
dissociation of the neutral electrolytic species and recombination of the
generated ions. This type of pumping is referred to as pure conduction pumping.
This project investigates the EHD pumping through pure conduction phenomenon.
Very limited work has been conducted in this field and the majority of the
published papers in this area have mistakenly assumed that the electrostriction
force was responsible for the net flow generated in an isothermal liquid. The
main motivation behind this study is to investigate an EHD conduction pump for a
two-phase loop to be operated in the microgravity environment. The pump is
installed in the liquid return passage (isothermal liquid) from the condenser
section to the evaporator section. Unique high voltage and ground electrodes
have been designed that generate sufficient pressure heads with very low
electric power requirements making the EHD conduction
pumping attractive to applications such as two-phase systems (e.g. capillary
pumped loops and heat pipes). Currently, the EHD conduction pump performance is
being tested on a two-phase loop under various operating conditions in the
laboratory environment. The simple nonmechanical and lightweight design of the
EHD pump combined with the rapid control of performance by varying the applied
electric field, low power consumption, and reliability offer significant
advantages over other pumping mechanisms; particularly in reduced gravity
applications.
Seyed-Yagoobi, J., Didion, J. Ochterbeck,J.M., Allen, J., Thermal Control and Enhancement of Heat Transport Capacity of Two-Phase Loops with Electrohydrodynamic Conduction Pumping, Fifth Microgravity Fluid Physics and Transport Phenomena Conference, NASA Glenn Research Center, Cleveland, OH, CP-2000-210470, pp. 542-565, August 9, 2000.