Publication Date

12-2012

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Civil Engineering

Department

Civil Engineering

Supervisory Committee Chair

Arvin Farid, P.E., Ph. D.

Abstract

Air sparging is a popular soil and groundwater remediation technique, which enables the removal of volatile organic compounds (VOCs) through diffusing contaminant-free air into saturated zones of soil. However, the VOC removal process is slow due to the soils' low permeability, and might take months to years depending on the type of the soil and contaminant. The goal of this thesis is to study the effect of electromagnetic (EM) waves —with minimal heat generation— on transport mechanisms such as diffusion, in order to improve airflow and expedite the cleanup process using air sparging or similar technologies. Because water dipole molecules oscillate under alternating electric fields, EM waves can enhance transport mechanisms such as diffusion in saturated media. This effect is studied through an experimental setup that examines the diffusion of a nonreactive dye into water.

Prior experimental work is analyzed and simulated by the author to find the potential correlation between the electric field magnitude/power and the flow characteristics of the dye. The experiment is simulated using the finite element software, COMSOL Multiphysics, to obtain a full vector representation of the EM field. In addition, the results from the digital analysis of the prior work are manipulated to study the concentration of the dye as well as the flow rate at different locations and times for all tests. The study, however, proved the necessity of a modified experimental setup for finding the correlation between the electric field pattern and the flow of the dye. For this reason, a modified experimental setup was developed. The new setup was tested at a range of frequencies 50-200 MHz. Measurement of the electric field component of EM waves is taken to map the electric field. In addition, the electric fields are simulated in COMSOL Multiphysics for better 3D visualization and analysis. A dielectrophoretic study is performed on the simulation data. The result of this study is in agreement with the experimental result of the dye flow.

Recording the temperature change of the medium for different frequencies shows the same trend of the temperature change (less than 1°C) for all tests. However, only at the specific frequency of 65 MHz did the dye flow occur. Therefore, this observation suggest that thermal effects are not controlling the movement of the dye in the water. Since the flow of the dye is in the direction of the dielectrophoretic forces, it is believed that the governing mechanism for the dye transport is mainly dielectrophoresis.

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