| Due to the large area of pollution source,long control distance,strong interference with air flow and open operation,the poison concentration in places such as organic solvent preparation,plate washing and viscose seriously exceeds the standard,which is harmful to workers’ occupational health.Parallel push pull ventilation can effectively solve those problems,but the airflow characteristics and control technology of parallel push pull ventilation are not clear at present.Therefore,research on the parallel airflow movement mechanism and the airflow control technology of uniform air supply,uniform exhaust and parallel push pull ventilation are studied by the methods of numerical simulation,theoretical analysis,experimental test and practical application.The movement mechanism of supply airflow and exhaust airflow,as well as the movement characteristics of airflow and pollutant control mechanism in the parallel push pull ventilation are analyzed by the basic theoretical knowledge of fluid mechanics.The change law between the hood axial velocity and the short side,the long side and the equivalent diameter of the hood is analyzed by numerical simulation and non quantitative processing methods.It is found that both uniform air supply and uniform exhaust have the best correlation between the axial velocity ratios(v/v0)and the equivalent diameter distance ratios(L/d),which eliminates the influence of hood face velocity and hood face geometric size on the change law of hood axial velocity.The results show that the uniform air supply hood axial velocity basically remains unchanged in the range of 0≤L/d<2.5,and conforms to the change law of "v/v0=-0.0409(L/d)+1.0933" equation in the range of 2.5≤L/d≤25,but when L/d>25,it is basically 0;While the uniform exhaust hood axial velocity conforms to the change law of "v/v0=-0.02777(L/d)3+1.246(L/d)2-1.8773(L/d)+1.0176" equation in the range of L/d<2,but when L/d>2,it is basically 0.The airflow control technology of uniform side exhaust hood and uniform lower exhaust hood with uniform velocity distribution are studied by using the method of numerical simulation,and the airflow control technology of uniform exhaust hoods with specific size are proposed.The results show that when the size of the side exhaust hood is 0.7m long × 0.7m high × 0.25m thick,the uniformity of hood face velocity is the best when the following conditions are adopted.Two vertical baffles are arranged in the hood,and the baffle divides the area of the hood face into three equal parts in the height direction.An 8 cm high forward flow deflector is arranged 19 cm away from the hood face,between 19cm and 25cm is the top exhaust area,which is divided into three equal parts by two vertical baffles,and a porous plate is arranged above each area,and a front porous plate is arranged 12cm away from the hood.The results also show that when the size of the lower exhaust hood is 0.7m long × 0.7m high × 0.55m wide,the uniformity of hood face velocity is the best when the following conditions are adopted.Five slots are set in the worktable,the expansion angle of the baffles on both sides of the slot is 83°,the width of the slot opening from the exhaust outlet of the worktable to the right is 4cm,4.5cm,5cm,7cm and 9.5cm,the inclination angle of the bottom plate of the worktable is 5°,the height of the rectifier section at the top of the worktable is 5cm,and the surface of the worktable is provided with porous orifice plates with 2mm hole diameter and 60° staggered round holes.A 0.7m long × 0.7m high × 0.25m thick air supply hood is taken as the research object and the experimental research on the airflow control technology of uniform air supply is carried out.The research results show that when the air supply hood adopts the combination scheme of "3mm honeycomb+punching plate+punching plate+two fans",the airflow distribution uniformity at the hood face is the best,in which the 3mm honeycomb is a regular hexagon with the thickness of 1mm aluminum foil,the hole of 3mm aluminum honeycomb plate and the thickness of 20mm aluminum honeycomb plate;The punching plate is a stainless steel orifice plate with a hole diameter of 2mm,a hole spacing of 2mm,a staggered arrangement of 60 0 and a thickness of 1mm.The airflow control technology of parallel push pull ventilation is studied by using the method of numerical simulation.The research results show that although the parallel push pull ventilation system can effectively increase the control distance of pollutants,it is not suitable for use in the case of L/d≥6.In the range of 1.5≤L/d≤5.0,the flow ratio(k)is the key parameter for the airflow control of parallel push pull ventilation.When L/d remains unchanged and different K values are adopted,the airflow pattern in the push pull ventilation area can be divided into three States:"forced delivery","collaborative control" and "forced exhaust".When the push pull airflow is in the state of "forced supply",the push pull ventilation can not effectively control the pollutants,but it increases the diffusion of pollutants due to the effect of air supply;When the push pull airflow is in the"strong exhaust" state,the pollutant concentration can be effectively controlled,but the greater the k value,the higher the energy consumption of the exhaust system;Only by setting an appropriate k value can the collaborative control of push pull airflow be realized.It is revealed that the relationship between the optimal k value and L/d conforms to the change law of the equation "k=0.1675(L/d)3-1.318(L/d)2+3.6085(L/d)-1.5352" in the range of 1.5≤L/d≤5.0.The numerical simulation and theoretical derivation results are verified one by one by using the experimental test method.The results show that the numerical simulation and theoretical derivation results are credible.The workplace for vaccine purification using chloroform is taken as the application scene,and the main research results of this paper are applied in practice.The test results show that the research results of this paper are credible,feasible and scientific.After application,the concentration of chloroform decreased by 93.8%,which fully proved the pollutant protection effect of parallel push pull ventilation.The workplaces with the large area of pollution source,long control distance,strong interference with air flow and open operation exist in a large number of processes in many industries,and the research results of this paper can provide basic theory and key technology support for the prevention and control of pollutants in these workplaces.So it is expected to have wide market application prospects and good economic and social benefits. |
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