| With the rapid development of highway transportation infrastructure construction in China,the number of long and large tunnels is increasing.The drilling and blasting method often used in tunnel construction in our country will produce a lot of dust.If the dust can not be quickly removed,it will not only affect the construction progress,but also endanger the health of the constructors.Our research group applied negative ion system to the field of air purification of tunnels during construction period,but there are many problems and shortcomings in the dust removal efficiency of negative ion system and its influencing factors in previous studies(see 1.4.1 for details).In view of the problems and shortcomings existing in the previous research,the formula of dust removal efficiency of negative ion system and the influence of various factors on dust removal efficiency are obtained through theoretical analysis.The results of theoretical analysis are verified by laboratory and field tests,and compared with previous studies.The main conclusions are as follows:(1)The viewpoint that dust deposits on tunnel inner wall and ground under the action of negative ion system is put forward.The force and movement characteristics of dust in tunnel are analyzed,and the formulas of dust removal efficiency of the negative ion system in the whole section area and the breathing area are deduced respectively.The influence of various factors on the dust removal efficiency of the negative ion system is analyzed.It is concluded that the dust removal efficiency of negative ion system increases with the lower wind speed,the larger dust particle size,the higher working voltage and the longer installation length.(2)Laboratory tests show : the efficiency of respirable dust removal by negative ion system in 30 minutes is 35.46% higher than that by natural settlement in 30 minutes.After using the negative ion system,dust deposits occur on the walls around the room and roofs,which preliminarily verifies the viewpoint that "dust deposits on the(tunnel)wall and ground under the action of the negative ion system".The dust removal efficiency of negative ion system increases with the increase of working voltage.(3)Field tests show : the dust removal efficiency of using negative ion system(installation length is 300 m and working voltage is 60kV)is 35.56% higher than that of using mechanical ventilation only.The dust removal efficiency of negative ion system increases with the increase of dust particle size and installation length.By classifying the particle size of tunnel dust,the calculated values of dust removal efficiency of the negative ion system with installation length of 200 m and 300 m are 58.13% and 70.44% respectively.The measured values are 45.42% and 58.31% respectively.The errors between the calculated value and the measured value are 12.71% and 12.13%,respectively.Considering the influence of large space and complex environment of tunnel,it can be considered that the calculation value of dust removal efficiency formula in this paper are in line with the actual situation.After using the negative ion system,it is found that there are obvious dust deposition phenomena on the side wall and top of the tunnel,which further verifies the viewpoint that "dust deposits on the tunnel wall and ground under the action of the negative ion system".The dust removal efficiency under the two working conditions is calculated by using the formulas in preliminary study and in this paper respectively,and the calculated values are compared with the measured ones.The results show that the calculated values of the dust removal efficiency formula in preliminary study are quite different from the measured values.The calculated values of the dust removal efficiency formula in this paper agrees well with the measured values.The reasons for the great difference between the calculated value of dust removal efficiency formula in preliminary study and the measured value are analyzed. |
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