Study On Flow Field Characteristics And Contaminant Capture Effect Of Vortex Side Suction Exhaust Hood

Local exhaust ventilation plays an important role in capturing indoor pollutants and maintaining indoor environment of industrial buildings.However,due to the fast attenuation of the axial air velocity and the limited control range,the traditional local exhaust hood is difficult to effectively control the non-organized diffusion of pollutants.The column vortex,such as tornado,has a strong entrainment effect,and the principle of which can be applied to the local exhaust hood.The column vortex has strong negative pressure gradient,high axial velocity and long conveying distance,which makes the pollutants near the bottom be quickly collected and transported to the outlet,thereby greatly improving the exhaust efficiency of the local exhaust hood.Most of the existing vortex ventilation systems use the canopy hood,however,in many industrial production processes,the location where the pollutants are emitted needs to be operated and observed,which makes the hood cannot be placed at the top of the pollutant source.Therefore,it is necessary to develop a kind of vortex side suction hood.Based on the principle of column vortex,this paper proposes a new type of vortex side suction hood,which uses the supply jet and the baffle to generate angular momentum airflow,and finally a curved column vortex is formed under the exhaust airflow from the outlet to control the pollutants.In this paper,the basic structural characteristics of the column vortex are firstly studied by theoretical derivation,and the formation conditions of the column vortex are analyzed.The column vortex is divided into three regions according to its flow characteristics,which provides a theoretical basis for application of the column vortex to the the local exhaust hood.Then,a preliminary study on the new vortex side suction hood is carried out by experimental method.Firstly,the flow field visualization method can be used to observethat the airflow forms a curved column vortex along the baffle.By comparing the traditional side suction hoods with the vortex side suction hood,it can be observed that the vortex flow field can exhaust pollutants more quickly and efficiently than the traditional one.Then changing the air supply volume and the position of the outlet,and measuring the velocity and pressure field of the bottom plane,it can be found that larger air supply volume can provide more angular momentum to the bottom plane airflow,which leads to an increase in the intensity of the vortices,and the optimal outlet position is located on the side line of the battle.Finally,the vortex side suction hood was further studied by numerical simulation method.Firstly,the structure of the curved columnar air vortex generated in the flow field is analyzed.Then,the influence of the configuration of the air supply port,the exhaust vent and the baffle on the vortex flow field in the vortex side suction hood is studied,and the optimal setting form of the vortex side suction hood is preliminarily obtained.Finally,the influence of the air supply volume and the exhaust air volume on the vortex side suction hood capture efficiency is studied.The main conlusions are as follows:1)The optimum length of the air supply port is 1/2 of the radius of the baffle arc.When the length of the air supply port is small,the air jet does not provide enough angle Momentum to the bottom plane airflow,resulting in a lower intensity of the vortices.When the length of the air supply port is large,the air supply jet will squeeze the vortex formed at the bottom to deform it,resulting in a decrease in the strength of the vortex.2)The width of the baffle affects the strength of the vortex.In order to reduce the entrainment of clean air outside the suction hood and energy consumption,the vortex should be generated inside the baffle.This paper determines the minimum baffle width is 0.3m,which is 3/10 of the radius of the baffle arc.The wider the baffle is,the stronger the vortex is.In application,the baffle with larger width should be adopted according to the actual industrial environment.3)The optimal position of the exhaust outlet is that the center of the exhaust outlet is facing the edge of the baffle,and the distance between the exhaust outlet and the edge of the baffle is 3/10 of the radius of the baffle arc.The position of the exhaust outlet mainly affects the trajectory of the vortex near the exhaust outlet.When the vortex is vertically sucked into the exhaust outlet in the shape of a relatively regular cylinder,the vortex shape is not distorted,and the intensity of the vortex is the highest.4)The capture efficiency of the new exhaust hood under the coupling effect of different air supply speed and exhaust speed is studied by using DPM model,and the optimal ratio of air supply than exhaust volume was determined to be0.3,which provides a design basis for the practical application of the new type of vortex side suction hood.