Characterization of fouled flat sheet membrane by Infrared thermography (IRT) in continuous thermal excitation mode

Kennethrex Obianika Ndukaife, Purdue University

Abstract

In this thesis, a low-cost Infrared thermography (IRT) technique for continuous characterization of fouling progression from feed to retentate side without mutilation of the membrane has been developed. The emitted spectral power from the fouled membrane is a function of emissivity and surface morphology. In this work, a FLIR A320 IR camera was used to measure surface temperature and emissivity of known locations on the membrane surface. This was made possible by employing the active thermography scheme whereby heat was supplied to membrane surface using a hotplate set at 60°C so as to cause the heated surface to give off thermal radiations captured by the IR camera. The temperature at which the heat source was set was considered optimum for the experiment for two distinct reasons. Firstly, to ensure feasibility of the active thermography scheme, it is crucial to establish a thermal contrast between the fouled and unfouled region and the temperature of the surface under investigation must be at least 20°C greater than the room temperature [66]. Secondly, 60°C was just an optimum temperature for which the membrane under study was not compromised due to excessive heating. Different fouling experiments were performed using different concentrations of synthetic wastewater made from aluminum microparticle, aluminum oxide nanoparticle and clay respectively so as to investigate the effect of feed concentration on the degree of fouling and thus its effect on the emissivity values measured on the membrane surfaces. Surface plots in 3D's are obtained for the measured emissivity values and thickness of the fouling deposit on the membrane surface. Results indicate that the IRT technique is sensitive to changes that occur on the membrane surface due to deposition of contaminants on the membrane surface and that emissivity is a function of temperature, surface roughness and thickness of the specimen under investigation. Some of the key findings in this work are that the deposition of the contaminants on the membrane surface as fouling progressed led to roughness of the membrane surface and this caused the emissivity to increase. Secondly, temperature difference in the range 0.7≤T≤7 °C as seen by the IR camera was sufficient enough to cause variations in emissivity across the length of the membrane surface. It was observed that the central section of the membrane experienced the highest deposition of fouling. This was attributed to the high pressure experienced on the feed side which causes contaminants to move to the mid-section of the membrane. Most importantly, this work provides an opportunity for continuous fouling monitoring from feed to retentate side without having to cut the membrane into smaller pieces. The losses experienced when the camera was focused over water as against in free space (air) limits the techniques application for insitu fouling monitoring in water environment during filtration.

Degree

M.S.E.

Advisors

Nnanna, Purdue University.

Subject Area

Mechanical engineering|Water Resources Management

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