Mathematical modelling of the performance of photocatalytic decomposition of defined gaseous pollutants

The photodegradation of formaldehyde by the photocatalyst titanium dioxide was studied using mathematical modelling and the physical application of photocatalytic oxidation (PCO) reactors in air conditioning systems. Two field PCO reactors (FM1 and FM2) were constructed that were suitable for the installation within common commercially available fan coil units within heating and cooling ventilation air conditioning (HVAC) systems. Due to the application within air conditioning systems the parameters chosen were between the temperatures 15-25°C and relative humidity 55% based upon traditional comfort levels common in Hong Kong. The further approximation of the Colebrook equation-specifically the Darcy-Weisbach equation, allowed for the calculation of the friction factor ƒ which led to evaluation of the turbulent pipe flow pressure loss in a straight duct. It was found that within the volumetric flow rate ranges (289-1876m3/h according to the commercial fan coil units used) and face velocity (which was less that 10m/s in low pressure duct work according to DW142) the pressure drop is less than 40 Pa which had an insignificant change on the air balance of the fan coil unit in the HVAC system. It was also appeared that the copper earthing mesh was required and placed five centre meters away from the PCO reactor which made it possible to prevent the static electricity build up on the titanium dioxide coating plate surface. It could be a potential safe guide device for limiting catalytic poison during the photo degrading process. The FM1 and FM2 PCO reactors could be used in common commercial fan coil unit in the existing HVAC system. The calibration and validation of the computing modelling were also used for the design optimisation, operation and control of the PCO system.;During the elimination of variables, it was found that the titanium dioxide coating on the aluminium supporting metal has no photocatalytic ability. It was also found that the UV light in PCO unit needs to be turn off for at least 30 min after 2 hours operation, then further photocatalysis can be obtained.