| China is the world’s largest producer and consumer of coal,with the increase in the level of coal mining mechanization and mining intensity,the amount of dust produced has increased exponentially.The dust suppression and control measures in coal mines,mainly wet dust reduction,cannot achieve the desired effect,and the dust concentration in coal mines far exceeds the national standard,resulting in the number of new cases,cumulative cases and deaths of occupational diseases,mainly coal workers’ pneumoconiosis in China,becomes the highest in the world.In order to be protected from the hazards of coal mine dust,respiratory protection equipment becomes the last line of defense against pneumoconiosis for coal mine workers.Due to the high concentration dust environment in coal mines,self-inhalation filter type dust masks have problems such as poor comfort,small dust holding capacity,high breathing resistance and short effective protection time.Although powered air-purifying respirators can solve problems of poor comfort and breathing,but there are still drawbacks such as low air volume utilization,small dust loading capacity of the filter,too fast growth of filter resistance and short effective protection time.In order to solve the above problems,this paper uses a combination of theoretical analysis,experimental research and numerical simulation to study the air supply and dust filtration properties of the breath-following powered air-purifying respirator in high concentration dust environment.The main conclusions of the dissertation are list as below:(1)A theoretical model for air supply regulation at different labor intensities is constructed.The breathing flow characteristics under different labor intensities were studied,and the respirator air supply regulation system was designed according to the principle of breath-following respirator air supply regulation.The relationship between the duty cycle of the pulse signal and the rotational speed of the fan was obtained through experiments,and the variation law of the half mask outlet velocity,with the air supply flow was revealed.According to the variation law between air flow of the fan and the rotational speed of the fan,the air supply adjustment model which can be dynamically adjusted according to human breathing flow is built to realize the dynamic adjustment of air supply flow,and the experimental platform of breath-following air supply is built independently.(2)The variation law of fan speed and half mask outlet air velocity with the mean inspiratory flow and filtration resistance was explored.According to the breathingfollowing air supply experiment,it is found that the rotational speed of the inverter centrifugal fan and half mask outlet air velocity periodically change with the breathing flow.The average speed of the fan increases with the increase of the mean inspiratory flow and the filter resistance;the fluctuation of the fan speed increases with increasing the mean inspiratory flow,but is not affected by filtration resistance.The fluctuation of the half mask outlet air velocity increases with increasing the mean inspiratory flow,while the filtration resistance has no effect on the half mask outlet air velocity.The research established that the minimum value of the half mask outlet air velocity for the breathing-following respirator to meet the demand of respiratory protection is 3.41 m/s.(3)The effects of the duty cycle variation coefficient and the standard value of air velocity on the fan speed,the half mask outlet air velocity,and the breath-following delay time were found.The research results show that the standard value of air velocity and duty cycle variation coefficient will have a large impact on the air delivery flow,and the duty cycle variation coefficient will also lead to the fluctuation of fan speed and half mask outlet air velocity.The increase of duty cycle variation coefficient results in the increase of fan speed fluctuation,therefore,the air supply adjustment of the breathfollowing respirator can be achieved by adjusting the duty cycle variation coefficient.In addition,increasing the duty cycle increase coefficient is beneficial to speed up the fan response speed and reduce the breath-following delay time,but it also increases the average fan speed,which is not conducive to reducing the air supply flow.The study determined that when the value of air velocity is 12.1 m/s,the duty cycle increase coefficient is 1.5,and the duty cycle decrease coefficient is 1,the breath-following respirator can meet the demand of respiratory protection while minimizing the air supply flow.(4)The law of the influence of pleat structure on the dust filtration properties of the respirator was obtained.During dust loading process,the pressure drop of the smaller pleat ratio filter increases linearly with the mass of dust deposition per unit area,and the pressure drop of U-shaped filter is smaller than that of V-shaped under the same conditions,which is due to the relatively small loss of effective filtration area of the Ushaped filters.When the pleat ratio is relatively large,the pressure drop increases at an accelerated rate with the increase of the mass of dust deposition per unit area,and there is a situation that the pressure drop of U-shaped filter is larger than that of V-shaped under the same conditions,which is due to the fact that the channels between the pleats may be blocked when the pleat ratio is larger.It is found that the critical value of mass of dust deposition per unit area for pleated channel blockage gradually decreases with the increase of pleat ratio,and the critical value of U-shaped filter is smaller than that of V-shaped when the pleat ratio is the same.This is due to the fact that U-shaped filter with the same pleat ratio have a smaller pleat spacing than V-shaped,resulting in Ushaped filter is more likely to be blocked.The study determined that the U-shaped filter with PP10 media and a pleat ratio of 3.57 is used in the breath-following respirator,which has the characteristics of high efficiency and low resistance,large dust holding capacity and less likely to be clogged between pleat channels.(5)Experiments were conducted to confirm the applicability of the breathfollowing respirator in high concentration dust environment.The protection factor of the developed breath-following respirator exceeds 100,and the respiratory protection performance meets the national standard.Experimental verification of the breathfollowing respirator in high concentration dust environment,compared with the constant air supply respirator,the breath-following respirator can reduce the air supply flow by about 15%,and no blockage of the pleated channel of the filter was observed,achieving the purpose of reducing the filtration resistance and energy consumption and extending the respirator’s continuous working time.The paper contains 81 figures,17 tables,and 193 references. |
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