On chip planar capacitance tommography for two-phase fluid flow imaging

Abstract

This thesis presents the development of an on-chip planar electrical capacitance tomography (ECT) for two-phase fluid flow imaging. This miniaturized planar ECT device was developed based on Lab-on-chip (LOC) or microfluidic device concept. Microfluidic device is a portable device that integrates different laboratory activities within a small platform that handles micro-scale fluid and is normally used for small sample preparation, mixing and detection. To visualize the condition within the reaction chamber, an external optical instrument such as microscope is used, causing the device to be less portable. Furthermore, a camera that is attached to the optical sensor requires large memory for data storing; and intensive image processing is needed to analyze the data since it is recorded as video. Therefore, this research proposes another option to provide visual images via planar electrode array where the electrical data obtained can be stored directly to a computer. This research integrates tomography techniques utilizing capacitance measurement within the microfluidic device platform for fluid flow microanalysis purposes. To reconstruct images, ECT sensors measured variations in the permittivity of samples within the sensing area. Eight planar electrodes were fabricated on printed circuit board with dimension of 5.00 mm × 2.08 mm (length × width), distributed equally around 16 mm diameter of the sensing area. Simulation study was conducted using COMSOL Multiphysics to determine the design parameter of micro channel; and polydimethylsiloxane (PDMS) micro channel was fabricated using casting method. The integration of planar electrode sensors to the PDMS micro channel formed the micro device which allows two-phase fluid sample to flow in and out of the sensing chamber. Fan beam projection technique was used for data collection method. A software module was built using Microsoft Visual Basic and Linear Back Projection algorithm is implemented for the image reconstruction process. A portable data acquisition (DAQ) system comprising of signal conditioning unit and Arduino Mega microcontroller was developed for online measurement. Two-phase liquid-air and liquid-liquid sample were studied. The samples were flowed into the sensing chamber at a constant flow rate. The reconstructed images were compared to the real images captured by the camera and the feasibility of the system for two-phase fluid flow imaging was studied. At a flow rate of 12.03 ml/min, the accuracy of the developed system in reconstructing water sample in water-air flow measurement was nearly 97.9%, while the accuracy to reconstruct oil sample in water-oil flow measurement was nearly 94.3%. The study showed that the liquid concentration affects image reconstruction as the permittivity value varies with the liquid concentration. The reconstructed cross-sectional images showed good resemblance with the cross section of the camera captured images. This research showed that the miniaturized planar ECT system is feasible to capture images of dynamic flow substance within a sensing chamber.