| Formaldehyde is one of the major indoor pollutants, which has adverse effects on human health and could last a longer time in indoor environments. Consequently, it is worthwhile to develop an innovative measure for effectively removing indoor formaldehyde. Photocatalysis has been one of the most popular techniques for indoor air purification for the past two decades. However, due to low concentration of indoor formaldehyde, the mass transfer resistance between the air and the surface of photocatalyst is significant, which make the mass transfer rate of formaldehyde become relatively low. Besdieds, the film-coated photocatalytic reactors commonly applied in previous investigations can't utilize the ultraviolet (UV) light sufficiently. These two reasons lead to lower formaldehyde conversion for the photocatalysis. In order to enhance the formaldehyde conversion, an innovative photocatalytic reactor has to be developed to achieve high performance of indoor air purifier.Packed-bed reactor was selected as the photocatalytic reactor for this study since it has the highest conversion among all the photocatalytic reactors. The packed-bed photocatalytic reactor was used to investigate the removal conversion and reaction rate of indoor formaldehyde. Moreover, the effects of operating parameters on the formaldehyde conversion were also investigated. The operating parameters investigated included influent formaldehyde concentration, reaction temperature, humidity, residence time, and oxygen content. An innovative air purifier was further designed to investigate its performance of indoor formaldehyde removal in a testing room. Furthermore, computational simulation was conducted for the velocity profile of the packed-bed photocatalytic reactor and the air purifier as well as the variation of formaldehyde concentration in then testing room.Black-light lamp was selected as the UV source for the photocatalytic reaction. The lamp was situated at the center of the reactor. Glass beads coated with TiO2 were filled inside the photocatalytic reactor as the photocatalysts. The simulated air velocity profile of the photocatalytic reactor showed that the velocity in the radial was not uniform. The velocity decreased from the center to the wall of the reactor, which could result in the insufficient utilization of the photocatalyst. Therefore, the photocatalytic reactor was modified and an innovative packed air purifier was designed. Air entered from the lateral surface of the air purifier. The width of the slots decreased from the top to the bottom of the lateral surfaces of the single purification device within the air purifier. The results measured with an anemoscope showed that the air uniformly entered the air purifier in a flow rate of 0.05 m/s. The simulation results of the air pattern in the single device showed that the air velocity was relatively uniform, which suggested that the photocatalyst can be utilized effectively.The decomposition of formaldehyde with packed-bed photocatalytic reactor was investigated for the formaldehyde concentration close to indoor level. The results showed that the decomposition of formaldehyde was apparently affected by influent formaldehyde concentration. Reaction temperature and humidity has limited effect on the decomposition of formaldehyde. The reaction rate for influent formaldehyde concentration of 5~20 mg/m3 can be accounted for by using the rate expression of L-H model. The reaction rate constant and adsorption equilibrium for the L-H model was 4.666~9.470 mg/g-hr and 0.0098~0.0128 mg-1 separately. However, Power-rate model was feasible for describing the photocatalytic oxidation for influent formaldehyde concentration of 0.6~1.2 mg/m3. The constant k and n for the Power-rate law was 0.317~0.452 and 1.082~1.370 separately. The constant k for the L-H model and the Power-rate law model decreased with the reaction temperature. The correlation between the constant k for these two models and the reaction temperature agrees with the Arrhenius equation.The experimental results of the innovative air purifier indicated that the formaldehyde removal efficiency was 84.7%~92.0% for initial concentration of 0.727~1.815 mg/m3. None new kind of organic pollutant was detected in the testing room during the operation of the air purifier. The formaldehyde reaction rate equation of the air purifier was developed. Based on mass balance, a mathematical model to simulate the variation of formaldehyde concentration in the testing room was constructed, in which there was continuous formaldehyde emission source and the air purifier was operated. The simulated results were proved by the experimental data. The relation expression of particle board amount and formaldehyde concentration in the room was used to approximately calculate the formaldehyde release rate. The variation of indoor formaldehyde concentration in actual room with using the air purifier was then simulated. The simulated results showed that the periodic operation of air purifier could keep the indoor formaldehyde concentration less than 0.1 mg/m3. The operation procedure of the air purifier was mainly determined by the release rate and amount of the release sources in the room.The decomposition of formaldehyde in the packed-bed photocatalytic reactor was investigated in this study. An innovative air purifier was designed based on the results obtained from the investigation of the packed-bed photocatalytic reactor. The application of the air purifier was further simulated to verify its performance on indoor formaldehyde removal. The outcome of this study provides the basic criteria for designing an innovative air purifier device. The operation procedure of the air purifier was also recommended in the study. Therefore, the results obtained from this study would be valuable for improving indoor air quality.
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