Center-Line Velocity Change Regime in a Parallel-Flow Square Exhaust Hood

Abstract

A parallel-flow exhaust hood is an effective ventilation device to control dust and toxic pollutants and protect the occupational health of workers, whether it is used alone or combined with a uniform air supply hood in a push–pull ventilation system. Some scholars have studied the outside air flow characteristics of the conventional exhaust hood with non-uniform air speed at the hood face, but the law of velocity variation outside the parallel-flow exhaust hood is not clear at present. Therefore, this paper uses the dimensionless method to study the center-line velocity change regime in a parallel-flow square exhaust hood based on simulation and experimental data. The results show that the dimensionless center-line velocity has a good change law with the characteristic length of exhaust hood in a parallel-flow square exhaust hood, which can eliminate the influence of hood face velocity and the hood size on the velocity change regime; and the experimental data is basically consistent with the calculated data, which shows that the regression equation method is reliable.

Changing Patterns of the Flow Ratio with the Distance of Exhaust and Supply Hood in a Parallel Square Push-Pull Ventilation

“…According to Reference [ 16 ], if there is only uniform supply air, the supply velocity at this position is about 90% of the push hood face velocity. According to Reference [ 17 ], if there is only uniform exhaust air, the exhaust velocity at this position is about 10% of the pull hood face velocity. As can be seen from Figure 5 , the velocity at this position is about 0.5 m/s, which is basically the same as the push hood face velocity, but the toluene concentration is still high even with k = 10.…”

“…If there is only uniform supply air [ 16 ] for square hood, the center-line velocity and L off push hood / a have good change patterns, and if there is only uniform exhaust air [ 17 ] for square hood, the center-line velocity and L off pull hood / a also have good change patterns; however, the variation of wind speed with distance is different in the above two cases. Compared with other geometric parameters of exhaust hood, such as short side, long side and square root of area of exhaust hood, the center line with L off pull hood / d have the best change patterns for a desktop slot exhaust hood [ 1 ], where d is the equivalent diameter of hood face.…”

“…Wu X. et al studied the influence of a 90-degree elbow on the velocity uniformity of exhaust hoods in parallel push-pull ventilation [ 14 ]. Chen J. et al studied the internal structure of the static pressure chamber in a spray room in order to get the uniform air supply [ 15 ], and also studied the center-line velocity change regime in a parallel-flow exhaust hood [ 16 ] and supple hood [ 17 ]. Wang Y. discussed the effects of the pull-flow velocity on the capture efficiency in a high-velocity jet push-pull ventilation system [ 18 ] and found that the significant reduction in exhaust air flow ratio will not affect the dispersion of contaminants in parallel push-pull ventilation systems [ 19 ].…”

Simulation Experiment Research of Mine Roadway Simulating Test Device with Adjustable Wind Velocity and Temperature and Humidity

“…Therefore, the installation of the rectifier orifice plate was required to accomplish the equal distribution of wind velocity, temperature, and humidity. The regularity of air flow may be significantly improved using rectifier orifice plates, according to studies [18,19]. Ingeniously, this invention suggests combining a heating tube with a rectifier orifice plate to simultaneously heat and correct the air flow.…”

Influence of the Internal Structure Type of a Large-Area Lower Exhaust Workbench on Its Surface Air Distribution

“…The method of CFD simulation is widely used for this kind of application, and the 3D steady-state incompressible Navier–Stokes equations and the standard k-equation model are also used widely used when only momentum transfer is considered and heat transfer is ignored [ 12 , 13 , 14 , 15 , 16 , 17 , 18 , 19 ]. For example, the velocity change rules along the centerline outside the hood with a uniform airflow [ 12 , 13 , 14 ], the influence of the internal structure of the duct [ 15 , 16 , 17 ], the roof structure in a static pressure chamber [ 18 ] and the radius of the 90° rectangular elbow curvature in a lower exhaust hood [ 19 ] have each been studied in terms of airflow distribution using CFD simulations. Yet, the influence of the internal structure of a lower exhaust large-area workbench with an air outlet at the short side of the workbench has not been studied regarding surface airflow distribution.…”