Removal of ultrafine particles from indoor environment: Experimental and computational studies of possibilities, limitations and applications

Siamak Rahimi Ardkapan

    Publikation: Bog/antologi/afhandling/rapportPh.d.-afhandling

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    Abstrakt

    In Denmark, people spend most of their time indoors. Therefore, indoor air quality is an important public health issue as people are exposed to pollutants indoors. Pollutants including gases and particles come from outdoors to the inside of a building. They may also be generated indoors by cooking, candle burning, emission from building material, etc. Particles are divided into coarse, fine and ultrafine particles (UFP) depending on their size. Research has indicated that UFPs with diameters less than 100 nanometer (nm) may be harmful to the human body.
    Increased ventilation is commonly discussed by researchers as a solution for reducing the particle concentration in the indoor air. Recirculation of air through portable air cleaners has also been discussed.
    The scope of this study is to investigate possibilities, applications and limitations of using recirculated air in combination with new air cleaning technologies in order to improve indoor air quality. The objective of this study is to determine the effectiveness of portable air cleaners and to investigate the approaches of using these devices aiming at reducing the concentration of UFPs in the indoor environment.
    Experimental investigations and computational fluid dynamics (CFD) simulations were performed parallel in order to investigate the possibilities, limitations and possible applications to reach this aim.
    The Danish market was searched for portable air cleaners to be evaluated in the experiments. Five technologies were selected: Non Thermal Plasma, Corona Discharge Ionizer, Portable Air Purifier, Electrostatic Fibrous Filter (EFF) and Three Dimensional Filter. In the experimental investigations, the effectiveness and the generation of by-products of the air cleaners were evaluated, based on measurements performed in a duct, in a clean room and in an unoccupied office building, respectively.
    According to the results from the experiments in the clean room, the effectiveness for Non Thermal Plasma, Corona Discharge Ionizer, Portable Air Purifier, EFF and Three Dimensional Filter was 0.2, 0.4, 0.2, 0.7 and 0.5 respectively. The EFF had the highest removal effectiveness. The filter was investigated and it was selected to be combined with a chilled beam. The improvement in UFP removal effectiveness of the combined chilled beam was evaluated.
    The simulations were performed using a commercial software STAR-CCM+. Two cases were studied, first the influence of the location of an air cleaner in a room on its UFP removal effectiveness and second, the influence of the height of a heat source and the height of a particle source on the UFP dispersion. The simulated room was based on the dimensions of a laboratory room. Experiments were performed in the laboratory room to validate the predictions by the simulation. According to the experiments performed, comparing the decay rate of UFPs and the decay rate of tracer gas in a room, particles having a diameter smaller than 73 nm had a faster decay rate than the tracer gas. Therefore, if particles are considered as a gas in a CFD simulation or if particles are considered of one single size, a deviation from reality may occur.
    It was concluded that an ozone generating air cleaning technology may increase the level of ozone to a level that exceeds the allowed level of 120 μgm-3 according to Air Quality Guidelines for Europe provided by World Health Organization. It was also concluded that the maximum ozone concentration in the room and the particle generation rate of reactions between ozone and volatile organic compounds depend mainly on air change rate, the age of the building material and the size of the room.
    In addition, it was concluded that the removal efficiency of an electrostatic fibrous filter is directly correlated with UFP concentrations. The reason for this seems to be the formation of chain-like dendrites with electrostatically charged UFPs.
    The CFD simulations showed that the location of an air cleaner has a minimal effect on the removal effectiveness in a room with a displacement airflow pattern. According to the simulation study of particle dispersion in a room, it was concluded that the location of a particle source has impact on the UFP concentration profile in the room.
    OriginalsprogEngelsk
    ForlagSBI forlag
    Antal sider93
    StatusUdgivet - 2013

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