Multi-jets Air Flow Optimization And Dust Control Mechanism Research Of Open-circuit Powered Air Purifying Respirator

Aerosol particles such as coal dust and viral droplets are extremely hazardous to human health and respiratory protection is an important means of preventing aerosol hazards.However,traditional self-priming filtered particulate respirators have a low protection factor and high inspiratory resistance,while power-fed respirators,which offer a higher level of protection,suffer from comfort problems such as dead space,compromised vision and protection failure due to excessive inhalation.In view of this,this thesis replaces the facepiece with a wind curtain and uses theoretical analysis,numerical simulation and simulation experiments to develop an open-circuit powered air purifying Respirator;comprehensively investigates the effects of air supply hole shape and arrangement,breathing interference and ambient wind speed on the flow field and aerosol filtration efficiency in the breathing zone;simulates the general industrial environment and the underground coal mine environment respectively through an independent respirator performance testing experimental system.By simulating the general industrial environment and the underground coal mine environment,the key performance indicators such as total particle size filtration efficiency,fractional particle size filtration efficiency and relative pressure were evaluated under different breathing flow rates(30 L/min,85 L/min)and air supply flow rates(170 L/min,220 L/min,280 L/min)of the two optimal parameter combinations.The main conclusions of this thesis are as follows:1)single/double orifice jet simulation found that the distance between two orifices is inversely proportional to the central velocity and cross-sectional flow rate of the mixed jet,which is consistent with the Coanda effect;comparing the velocity decay and pressure fluctuation of three orifice shapes,rectangular orifice was selected as the respirator orifice shape;comparing the filtration performance of the model under four air supply angles,a single row of 30° was selected as the respirator air supply angle;comparing the filtration after adding respiratory disturbance and ambient wind speed(1)Numerical simulations showed that the respirator model had an orifice diameter of3 mm and the number of orifices was 10;(2)the orifice diameter was 2.5 mm and the number of orifices was 16;2)Numerical simulation shows that the total particle size filtration efficiency of the respirator model is 85.5%,and the fractional particle size filtration efficiency is 80%(≤2.5μm)to 90.6%(≥7.5μm),and the total particle size filtration efficiency is70.80%～78.41%(coal mine underground environment)and 71.57%～90.02%(general industrial environment);the filtration efficiency of particles around 0.3μm drops to below 0%.(general industrial environment),and the filtration efficiency of PM2.5dropped to 55.2%～60.13%(underground coal mine environment);the average relative pressure inside and outside the respirator was 7.07 Pa～9.09 Pa(under medium labour intensity)and 8.45 Pa～11.22 Pa(under heavy labour intensity);3)The experimental results showed that the filtration efficiency increased with increasing air supply flow and the number of orifices,and decreased with increasing respiratory flow;the relative pressure increased with increasing air supply flow;the ANOVA and multiple linear regression analysis proved that air supply flow and orifice arrangement would have a significant positive effect on the filtration efficiency,and respiratory flow would have a significant negative effect on the filtration efficiency;the respiratory flow had a A significant positive effect on relative pressure;4)Considering the key performance and the influence of different environments and labour intensity on the performance,it is found that the filtration efficiency of the sixteen-hole model is the highest under the 280 L/min air supply flow rate(the total particle size filtration efficiency reaches 88.01%～90.02% in the general industrial environment and 77.36%～78.18% in the underground coal mine environment),and the filtration performance and labour intensity are less affected(the total particle size filtration efficiency fluctuates within 1%).The filtration performance and labour intensity are less affected(the total particle size filtration efficiency fluctuates within1%,and the average difference in the sub-particle size filtration efficiency is within 1%to 1.5%),indicating that the protection effect can be maintained at different labour intensities,which can be used as the design index for the selection of open air supply units in respirators.