Study On The Flow Characteristics And Controlled Effect Of Large Specific Gravity Gas In Fume Cabinet

Cabinet type exhaust hood(exhaust cabinet)is an important local ventilation equipment for pollutant emission in special process.The position of the exhaust vent of the fume cupboard is generally determined according to whether there is a heat source in the process operation.The cold process without a heat source generally uses the lower exhaust vent,and the thermal process with a heat source usually adopts the upper exhaust vent or the form of simultaneous exhaust air at the top and bottom.The determination of the air volume is often based on the different toxicity control of the harmful substances emitted by the pollution source.A certain wind speed of the working face is selected for design calculations,and the specific gravity effect of the pollutants is rarely considered.When the process emits high-concentration gas with high specific gravity,it often causes pollutants to overflow.Blindly increasing the exhaust air volume,the pollutant removal effect is not clear,and it will cause a lot of waste of energy.Therefore,to find out the influence of the specific gravity effect of pollutants on the flow field in the fume cupboard,reveal the relationship between the specific gravity effect of the pollutants and the characteristic parameters of the fume cupboard,and achieve the goal of energy saving and safety,has important theoretical value and practical significance.Aiming at the above-mentioned problems,this paper has carried out a study on the flow characteristics and controlled effects of large specific gravity gas in the fume cupboard.The factors that affect the effect of the fume cupboard mainly include internal factors and external factors.The internal factors mainly include the emission characteristics of the pollution source in the fume cupboard,the form and structure of the fume cupboard and the exhaust air volume;the external factors are mainly the influence of the boundary conditions of the space where the fume cupboard is located.Based on the comparison of different types of fume hoods,this paper selects the lower exhaust fume hoods,and uses computational fluid dynamics(CFD)technology to study the flow field characteristics and pollutant removal effects under the conditions of typical internal and external influencing factors.The main contents of the paper are as follows:On the basis of the existing exhaust cabinet,the model of the exhaust cabinet is established.and uses Fluent simulation software to establish different exhaust volumes,different pollution sources,different pollutant release rates and different pressures.The simulated data were compared with the experimental data in the literature,and a certain number of measurement points were selected from the simulation results to analyze the relevant content.Paper main research content is as follows:(1)Based on the verification of the numerical model,taking the common heavy-weight gas sulfur hexafluoride as an example,the method of controlling the wind speed of the working face is used to determine the exhaust air volume,and the upper exhaust air volume under the same exhaust air volume and pollutant release concentration conditions is compared.The airflow distribution characteristics in the three types of exhaust cabinets: wind,bottom exhaust,and simultaneous exhaust at the top and bottom.It is found that the bottom row type fume hood is more suitable for the removal of large specific gravity gas without significant spillage;while the upper row type and the upper and lower exhaust type simultaneously have the risk of overflow at the bottom of the working face.Therefore,the lower row type is selected as the main object for in-depth research.(2)Aiming at the internal factors that affect the control effect of the fume cupboard on the large specific gravity gas,such as different exhaust air volume,different types of pollution sources,different pollutant release rates and different pressures on the working surface,the airflow distribution in the fume cupboard.The calculation and correction method of the exhaust air volume of the bottom row fume hood when the pollutants with a large specific gravity are removed is also given.(3)Aiming at the external factors that affect the control effect of the fume cupboard on the large specific gravity gas,consider the adjustment and change of the flow heat transfer boundary of the room where the fume cupboard is located,such as the influence of air supply and wall heat transfer on the airflow distribution in the fume cupboard.Further verify the calculation and correction method of exhaust air volume given in(2).