Study On The Parameters Of Compensating Vent Of The Air Curtain Fume Hood Based On Sash Attachment Jet

The laboratory is an important place for researchers to conduct experiments.The occupational exposure in the laboratory has a great impact on the health of the laboratory staff.Therefore,most of people have been paid more and more attention to the laboratory environment.Fume hood is used to remove contaminants in the laboratory.It needs to be effectively improved to ensure the safety of laboratory staff.Traditional fume hood mainly relies on the confluence of exhaust air on the operation surface to control pollutants.This design has its inherent shortcomings:large eddy current will be formed in the chest of the operator in front of the fume hood,eddy current and backflow will occur at the door handle and threshold of the fume hood.Moreover,the anti-interference of traditional fume hood is not enough,and it is easy to be affected by external disturbance.In this paper,an innovative air curtain fume hood based on sash attachment jet is proposed.The structure is achieved by installing a jet inlet in the fume hood,forming a high-speed air curtain at the operation surface of the fume hood.It can realize the air isolation inside and outside the cabinet,enhance the anti-interference and improve the air distribution in the cabinet.In this paper,through theoretical research,experimental measurement and CFD simulation,the performance and key design parameters of the air curtain fume hood based on sash attachment jet are studied.First of all,through the method of theoretical analysis,combined with the theoretical formula of attached jet,free jet and confluence.The formula of jet axis trajectory of air curtain fume hood based on sash attachment jet is derived.Three parameters of compensating vent affecting the air flow of air curtain fume hood based on sash attachment jet are obtained:supply air velocity of compensating vent（u₀）,width of compensating vent（b₀）and the distance between the compensating vent and the sash（s）.Secondly,the flow type of the air curtain fume hood based on sash attachment jet in this paper is the coupling of the wall attached jet,free jet and the confluence formed by the exhaust of the fume hood at the operating surface.Therefore,the face velocity of the traditional fume hood and the air velocity of jet area of the attached jet ventilation room were measured in the air distribution laboratory.Two experiment results were used to verify the CFD simulation of the confluence effect of the fume hood and the sash attachment jet.In addition,the experimental data in the literature were used to verify the simulation of pollutant leakage in the laboratory.The experimental data are close to the CFD simulation results.The results show that CFD simulation can be used to accurately predict the air distribution and performance of the air curtain fume hood based on sash attachment jet.Using numerical simulations validated through the experiments,the influence of parameters of compensating vent on the air distribution the performance of air curtain fume hood based on the sash attachment jet were analyzed.The results are as follows:1)The influence of supply air velocity（u₀）of compensating vent on the leakage concentration of fume hood is not monotonous.When the supply air velocity is 2m/s,eddy current will be generated at the operation surface of fume hood.And the pollutant leakage concentration is as high as 2.3ppm,which does not meet the EN14175 standard.When the supply air velocity is increased to about 5m/s,the performance of fume hood is better.The pollutant leakage concentration is lower than 0.01ppm,which meets the EN14175 standard.When the supply air velocity rises to about 7 m/s,eddy current appears at the operation surface of the fume hood.The concentration of pollutant leakage will increase and the performance of the fume hood will deteriorate.2)The wider the width of the compensating vent（b₀）is,the larger the air volume of the air jet is.The effect of blocking the leakage of pollutants in the fume hood will better.But it will increase the energy consumption of the fume hood.Therefore,the appropriate width of the compensating vent should be selected on the premise of ensuring that the leakage value of pollutant concentration meets the specification requirements.3)The influence of the distance between the compensating vent and the sash（s）on the performance of the air curtain fume hood based on the sash attachment jet is related to the"distance limit".When the distance is less than 6cm,a stable attached jet can be formed to ensure the performance of the fume hood.When the distance exceeds the"distance limit",the conada effect gradually fails and the performance of the fume hood deteriorates.Thirdly,the difference of air distribution of traditional fume hood and the air curtain fume hood based on sash attachment jet is compared.It is found that the air curtain fume hood based on sash attachment jet obviously weakens the eddy current at the"threshold".However,the eddy current behind the sash is more obvious than that of the traditional fume hood.In order to ensure the performance of the air curtain fume hood based on sash attachment jet,it is necessary to optimize the parameters of the compensating vent to determine the optimal air supply parameters and design parameters.Finally,the orthogonal design method is adopted in this paper.The evaluation index of the performance of the air curtain fume hood in this study is the leakage concentration of SF₆on the operation surface specified in EN14175.Through extreme analysis,the influencing factors of the air curtain fume hood based on sash attachment jet were analyzed.The results are as follows:the order of the three factors is u₀>b₀>s.The optimal parameters are as follows:the velocity of the compensating vent is 5m/s,the width of compensating vent is 3cm,and the distance between compensating vent and sash is 5cm.Under the optimal design parameters,the pollutant leakage concentration of the air curtain fume hood is 0.003ppm,less than 0.01ppm,which meets the requirements of EN14175standard.The research results of this paper provide a theoretical basis and design guidance for the air curtain fume hood based on sash attachment jet.It can contribute to effectively improve the performance of the fume hood,realize the air pollution control in the chemical laboratory,and protect the health of the chemical laboratory staff.