Conclusions•Buoyancy force dominated electric field in the vertical displacement of bubbles. However, horizontal displacement of bubble trajectories were observed when field was switched on.•Decrease in temperature was observed when electric field was turned on suggesting fluid flow at the heater–liquid interface

Further Research•A suspension of neutrally-buoyant particles in HFE-7100 and water may be used to mimic bubbles in terrestrial experiments and observe the effect of field on particle motion.•Investigations will be conducted in microgravity to determine the effect of electric field on the motion of vapor bubbles in the absence of buoyancy force.

Sponsors:National Aeronautics and Space Administration (NASA)NASA Goddard Space Flight Center (GSFC)NASA Goddard Institute for Space Studies (GISS)NASA New York City Research Initiative (NYCRI)New Jersey Institute of Technology (NJIT)

Contributors:Dr. Boris Khusid, Dr. John Tang, Dr. Ezinwa EleleDana Qasem Ian Peczak, High School StudentTiffany Boney, High School TeacherRai Munoz, Undergraduate Student

Introduction The objective of the project is to utilize a novel method of

EHD found in an ensemble of air bubbles driven by interplay of electric and hydrodynamics forces. The experiment contrasts to previous experiments studying EHD. Previous experiments utilized only the dielectrophoretic force, the force a non-uniform electric field exerts on a particle in a dielectric medium, to substitute for buoyancy effects. This force only manifests when the medium and the particle have different polarizabilities. If the polarizability of the particle is greater than the medium, a positive force towards the higher electric field gradient is observed. If the polarizability is lower, then a negative force in the direction of the lower field gradient is observed. In the case of bubbles, a negative force is experienced as bubbles have a lower polarizability than their dielectric medium. This provides an adequate substitute for the effects of gravity. The experiment employs oscillatory fluid flow along with the dielectrophoretic force, which, when exerted on bubbles, more heavily influence the displacement in microgravity. This enables an improvement of two-phase separation to be achieved in comparison to current techniques.

Figure 1: Schematic of the EHD device in ground-based tests: 1, fluid cell; 2, imaging system; 3, data acquisition system; 4, high voltage AC amplifier controlled by a programmable function generator; 5, grounded electrode; 6, two mini-heaters; 7, Bubbles; 8, Liquid; 9, Fluid cell (cuvettes); 10, energized electrode with insulated tip.

Works Cited•S.W. Ahmad, T.G. Karayiannis, D.B.R. Kenning, A. Luke, Compound effect of EHD and surface roughness in pool boiling and CHF with R-123 (2011) 1994-2003•D. A. Saville, ELECTROHYDRODYNAMICS: The Taylor-Melcher Leaky Dielectric Model (1997) 27-64•S. Siedel, S. Cioulachtjian, A.J. Robinson, J. Bonjour, Electric field effects during nucleate boiling from an artificial nucleation site (2011) 762-771•Y. Hristov, Zhao, D. B. R. Kenning, K. Sefiane, T. G. Karayiannis, A study of nucleate boiling and critical heat flux with EHD enhancement (2009) 999–1017•R. DeLombard, E. M. Kelly and K. Hrovat, E. S. Nelson, D. R. Pettit, Motion of Air Bubbles in Water Subjected to Microgravity Accelerations (2006) •Green, Nicolas G. "Dielectrophoresis and AC Electrokinetics".Electrokinetics and Electrohydrodynamics in Microsystems. CISM Courses and Lectures (2011) 61-84

Figure 2. Vapor bubbles are produced within water subjected to a voltage of 3kV and frequencies of 1 and 20 Hz.

Figure 4 (Below). When electric field was turned on, temperature decreased and reached a steady state profile with a uniform distribution of heat.

Figure 3 (Above). Electric field is switched on and off at 10 second intervals. Temperature decreased each time electric field was switched on.

Materials and Methodology The experimental setup consisted of two setups: Module 1 and Module 2. Module 1 was comprised of a programmable function generator placed on top of a high-voltage amplifier. Module 2 consisted of samples of water and HFE-7100 in two quartz cuvettes. A thermistor, powered by DC generators, was enclosed in a silicon-based PDMS insulating layer and placed at the bottom of each cuvette. Stainless-steel electrodes insulated in Teflon were inserted into each cuvette so as not to touch the PDMS layer. The cuvettes were monitored using video recording equipment, which consisted of an LED backlight illumination (placed behind the cuvettes), a camera with a lens and mount, and uc480 video software. Data was collected using a LabJack U6-Pro Data Logger. Both data and video footage were saved on the hard drive of a PC.

A square wave function was programmed into the function generator to produce an AC voltage electric field. The voltage (in kV) and frequency (in Hz) of the electric field were varied in order to observe their effects on heat transfer in HFE-7100 and water. Electric fields of 3kV and 4kV were tested, each at frequencies of 1Hz, 10Hz, and 20Hz. Samples of HFE-7100 and water were also tested without an electric field.

Abstract This report presents the validation of a novel electro-hydrodynamic (EHD) technology for two-phase separation in microgravity. In an environment with Earth gravity, gas-liquid phase separation readily occurs as a result of buoyancy forces. However, in a microgravity environment, bubbles do not rise out of a fluid due to the viscosity of the fluid and the absence of the buoyant force, leading to bubble coalescence, and the formation of gas pockets during transfers of bulk liquids. This presents a problem to life-sustaining systems and biomedical research as it can lead to failure in the storage, analysis and transportation of two-phase systems.

The main goal of the project is the study of bubble dynamics in fluids subjected to electric fields.

COLUMNHeating without field

COLUMNHeating with field

Temperature Data Calculations:The temperature of the heater, TH can be calculated from the circuit depicted right. This temperature is assumed to be the temperature of the liquid-boundary layer. V is the total circuit voltage, I is the current, VR the voltage across the resistor while R and RH are the resistances of the resistor and the heater, respectively.

The cycles of heating with and without an electric field were as follows:Field off

Field on

3827.0

25.100

0

HH

RH

R

HR

RT

I

VVR

R

VI

VVV

Figure 2: Video footage of the formation of bubble columns with and without an electric field, at 4kV/1Hz. The method of testing was 40 seconds of heating without a field, and 40 seconds of heating with field, followed by 40 seconds with both heater and field switched off.

Field off

Field on

Electrohydrodynamic Gas-Liquid Phase Separation in MicrogravityTiffany Boney, Dr. Boris Khusid, Rai Munoz, Ian Peczak, Dana Qasem

Otto H. York Department of Chemical, Biological, and Pharmaceutical Engineering New Jersey Institute of Technology, Newark, NJ 07102

Abstract

Introduction

Materials and Methodology

Conclusions

Further Research

Works Cited