Numerical Study Of The Dispersion And Dilution Ventilation Of Indoor Ultrafine Particle

As a pollutant in indoor environment, particulate matter may have great impact on human health. Meanwhile, ventilation technology is a common method for excluding harmful gas and particulate matter in the building. So it is worth discussing how to establish a health and comfortable indoor environment by controlling or decreasing the harm of indoor particle by combining ventilation technology with particle dispersion law, which is obtained by simulating particle dispersion characteristic and analyzing its influencing factors.Ultrafine particle can transport toxic chemicals into the human respiratory system and damage macrophage phagocytosis more than micron particles do, implying a greater threat to human health. In this paper, the dispersion characteristic of ultrafine particle and its dilution by ventilation are studied numerically. Research results have provided important reference for mastering particle dispersion law, making accurate prediction of particle concentration distribution, along with studying the effective ventilation method for controlling indoor particle concentration. The specific contents include the following work:(1) The dispersion characteristic of indoor ultrafine particle is simulated numerically. By the particle concentration in respiration region as evaluation indicator, the effects of air-condition ventilation types, air supply temperature differences, particle source positions, obstacles and indoor heat sources on the dispersion and distribution of particle are analyzed. The results illustrate that global airflow pattern has strong effects on the global concentration distribution of particle. All the factors have different effects on the concentration distribution of ultrafine particle. It is found that the concentration distribution and maximum value of particle on the breathing plane are obviously different due to the relative source positions in the airflow path. An increase of the distance between particle source and exhaust leads to an increase of the particle dispersion region in the breathing plane.(2) The ultrafine particle distribution under eight different air exchange rates in a mixing ventilation room is analyzed by numerical simulation method. Meanwhile, the effectiveness of particle removal and relative infection risk for ventilation system are evaluated by personal exposure index. In addition, the diffusion process of ultrafine particle indoor in the unsteady case is simulated. The results show that ventilation rate has a significant effect on the distribution of ultrafine particle indoor in mixing ventilation room. It is also found that the higher air exchange rate, the more particles are removed out, but the removal quality of particle is not in direct proportion to air exchange rate. However, the personal exposure index is fluctuating with the increment of air exchange rate and it can be seen that when the air changes per hour is eleven the minimum personal exposure index is obtained, implying that the effectiveness of particle removal by ventilation is best.