Laser and plasma air decontamination

Mine, Takashi (2010) Laser and plasma air decontamination. PhD thesis, University of Glasgow.

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This research investigated novel decontamination methods of airborne microorganisms in enclosed public spaces. There are many ways the pathogenic micro-organisms can be transmitted from one body to another, which includes for example, physical contact between the contaminated surface to another, transfer of infected blood from a donor to another medium, or respiratory infections where the large droplets containing micro-organisms caused by talking, sneezing or coughing can infect another whether by direct or close contact, and airborne transmission where the tiny aerosol droplets containing the micro-organisms remain in the air for a long period of time thus spreading to wider areas, making this mode of transmission the most effective and thus dangerous.

There are many technique and systems in the market today in the field of air cleaning, and many more under development, these include: ozone, plasma, UV, IR, microwave irradiation, passive solar exposure, pulsed light, electrostatic precipitation, photo-catalytic oxidation etc. However air decontamination using a laser is an unexplored approach.

In general two different mechanisms are studied in detail in this research. The possibility of using radiation from the laser and also using plasma and its bi-products were investigated. Many variations and techniques were evaluated for both mechanisms to optimise each decontamination effect.

Two types of lasers were used to investigate the concept of using lasers to decontaminate air: a CO2 laser producing a beam at 10.6 μm in the IR region and a KrF excimer laser producing a beam at 248 nm in the UV region. This research was to investigate and make use of the power that is available in the laser in a certain way to decontaminate the air. The effect of laser beam absorption in the presence of microorganisms was modelled in Matlab and this could be used to analyse any wavelength.

Two variations of creating a plasma were investigated, one method used a Chang profiled, uniform field electrode and the other used an increased size flat electrode. The plasma produced from these systems emitted radiation around 200 nm to 900 nm.

The Chang profiled electrode, which was manufactured in house, was originally designed to be used as a Nitrogen air laser. However, experiments with a purchased Nitrogen laser (detailed in Chapter 3) did not show any significant bacterial killing so the system was modified to be used as a plasma air decontamination device. The electrode was sized 60 mm x 10 mm, and the discharge volume was varied by altering the discharge gap. The effects of various parameters were investigated including: the discharge voltage, type of pre-ionisers to optimise the discharge and air flow shaping through the discharge region. Microbiological experiments conducted using air seeded with microorganisms was used to test the system’s decontamination efficiency.

The second plasma system used larger 200 mm x 30 mm aluminium electrodes. Again various parameters were investigated to maximise the discharge stability which included, type of dielectric medium, type of power source, electrical circuit setup, use of laser marked electrodes, air flow shaping and using multiple electrode pairs running off the same power supply. Again, microbiological experiments conducted using air seeded with microorganisms was used to test the system’s decontamination efficiency.

Two further systems were built using the results obtained from testing the 200 mm x 30 mm aluminium electrodes, an Industrial Based Air Decontamination Unit and a Ozone Shock Plasma System. Both systems were comprised with multiple pairs of laser marked electrodes with dielectric media and possible addition of flow shaping. The two systems were tested as before with good effect. The developed prototypes can be applied to most applications where air cleanliness is required.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Laser, plasma, air decontamination, clean air, bactericidal, bacillus globigii, escherichia coli, lactobacillus acidophilus
Subjects: T Technology > TD Environmental technology. Sanitary engineering
Q Science > QR Microbiology
T Technology > TJ Mechanical engineering and machinery
Colleges/Schools: College of Science and Engineering > School of Engineering
Supervisor's Name: Watson, Dr. Ian A.
Date of Award: 2010
Embargo Date: 30 November 2014
Depositing User: Dr Takashi Mine
Unique ID: glathesis:2010-2276
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 01 Dec 2010
Last Modified: 15 Oct 2014 10:10

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