In this study, the authors experimentally investigated the changes of the mean velocity component profiles, half-widths （b12）, turbulence intensities, Reynolds shear stress and intermittency of turbulence of a trans...In this study, the authors experimentally investigated the changes of the mean velocity component profiles, half-widths （b12）, turbulence intensities, Reynolds shear stress and intermittency of turbulence of a transient plane turbulent jet developing from a jet exit into a hood opening. The values of maximum mean-velocity and half-widths of the axial velocity profile along the center-line of the jet are greater than those for a fully developed two-dimensional jet. Turbulence intensity in the axial direction is not affected by the flow rate ratio. At the same time, turbulence intensity in the lateral direction becomes greater as the hood is approached and the flow rate ratio Q3/Q1 becomes larger （QI is jet flow rate from nozzle and Q3 is suction flow rate produced by the hood）. These experimental results are in accord with the distributions of production terms in the axial and lateral directions. Reynolds shear stress becomes smaller as the flow rate ratio becomes larger near the hood. Dimensionless distance y1/br2, from the center axis of the flow to the point where intermittency factor y becomes a constant value, narrows as the flow rate ratio becomes larger near the hood.展开更多
Push-pull ventilation systems provide excellent control of contaminants and harmful gases.However,since both a push inlet and a pull outlet are used in the push-pull ventilation system,the flow rate required by the sy...Push-pull ventilation systems provide excellent control of contaminants and harmful gases.However,since both a push inlet and a pull outlet are used in the push-pull ventilation system,the flow rate required by the system is large.In that case,the energy consumption of the system is large.The purpose of this paper is to study the flow field and economic characteristics of a parallel push-pull ventilation system by reducing the flow rate of the exhaust outlet,which will be achieved by reducing the size of the exhaust hood.The three commonly used push-pull ventilation systems were analyzed:a high velocity push-pull system with high air supply velocity,a low velocity push-pull system with wide airflow and small velocity,and a parallel push-pull system with wide airflow and uniform air supply velocity.Results showed that the parallel push-pull ventilation system was the only one in which the flow rate of the exhaust outlet could be reduced,reducing the overall energy consumption.Under conditions of the parallel air supply jet,the diffusion range of contaminants in the push-pull flow field was the smallest and reducing the exhaust air flow rate did not affect the capture efficiency of pollutants.These results may be useful in guiding the design of push-pull ventilation system and optimize economic constraints.展开更多
This paper proposes a push-pull airflow combined with a top draft hood to conduct local exhaust in a rubber workshop.Field measurements are carried out to investigate the characteristics of the emission source,while n...This paper proposes a push-pull airflow combined with a top draft hood to conduct local exhaust in a rubber workshop.Field measurements are carried out to investigate the characteristics of the emission source,while numerical simulation is performed based on the measurement to test the capture efficiency and to further optimize various parameters including push velocity,hood height and exhaust air rate.Compared with the high-hanging hood,the low-hanging hood can effectively capture the pollutant generated by tyre with lower exhaust air rate.The capture efficiency of the low-hanging hood reaches 98.18%with exhaust air rate of 6000 m^(3)/h and push air velocity of 5m/s.The results indicates that the new ventilation appliance can effectively collect the pollutant at a relatively low exhaust rate.展开更多
文摘In this study, the authors experimentally investigated the changes of the mean velocity component profiles, half-widths （b12）, turbulence intensities, Reynolds shear stress and intermittency of turbulence of a transient plane turbulent jet developing from a jet exit into a hood opening. The values of maximum mean-velocity and half-widths of the axial velocity profile along the center-line of the jet are greater than those for a fully developed two-dimensional jet. Turbulence intensity in the axial direction is not affected by the flow rate ratio. At the same time, turbulence intensity in the lateral direction becomes greater as the hood is approached and the flow rate ratio Q3/Q1 becomes larger （QI is jet flow rate from nozzle and Q3 is suction flow rate produced by the hood）. These experimental results are in accord with the distributions of production terms in the axial and lateral directions. Reynolds shear stress becomes smaller as the flow rate ratio becomes larger near the hood. Dimensionless distance y1/br2, from the center axis of the flow to the point where intermittency factor y becomes a constant value, narrows as the flow rate ratio becomes larger near the hood.
文摘Push-pull ventilation systems provide excellent control of contaminants and harmful gases.However,since both a push inlet and a pull outlet are used in the push-pull ventilation system,the flow rate required by the system is large.In that case,the energy consumption of the system is large.The purpose of this paper is to study the flow field and economic characteristics of a parallel push-pull ventilation system by reducing the flow rate of the exhaust outlet,which will be achieved by reducing the size of the exhaust hood.The three commonly used push-pull ventilation systems were analyzed:a high velocity push-pull system with high air supply velocity,a low velocity push-pull system with wide airflow and small velocity,and a parallel push-pull system with wide airflow and uniform air supply velocity.Results showed that the parallel push-pull ventilation system was the only one in which the flow rate of the exhaust outlet could be reduced,reducing the overall energy consumption.Under conditions of the parallel air supply jet,the diffusion range of contaminants in the push-pull flow field was the smallest and reducing the exhaust air flow rate did not affect the capture efficiency of pollutants.These results may be useful in guiding the design of push-pull ventilation system and optimize economic constraints.
文摘This paper proposes a push-pull airflow combined with a top draft hood to conduct local exhaust in a rubber workshop.Field measurements are carried out to investigate the characteristics of the emission source,while numerical simulation is performed based on the measurement to test the capture efficiency and to further optimize various parameters including push velocity,hood height and exhaust air rate.Compared with the high-hanging hood,the low-hanging hood can effectively capture the pollutant generated by tyre with lower exhaust air rate.The capture efficiency of the low-hanging hood reaches 98.18%with exhaust air rate of 6000 m^(3)/h and push air velocity of 5m/s.The results indicates that the new ventilation appliance can effectively collect the pollutant at a relatively low exhaust rate.
