Study on Flow Field Characteristics of the 90° Rectangular Elbow in the Exhaust Hood of a Uniform Push–Pull Ventilation Device

Abstract

A uniform push–pull ventilation device can effectively improve indoor air quality (IAQ). The 90° rectangular elbow is an important part of the push–pull ventilation device. This paper analyzes the flow field characteristics of the 90° rectangular elbows under different working conditions. This was done by using computational fluid dynamics (CFD) simulation (Fluent). The flow lines, velocity and pressure distribution patterns of the elbow flow field are revealed in detail. The wind velocity non-uniformity and wind pressure non-uniformity of the 90° rectangular elbows with different coefficients of radius curvature R and rectangular section height h are also compared. The results show that when R ≥ 2.5 h, the wind flow traces inside the elbow are basically parallel lines. At the same time, the average wind velocity and the average wind pressure are stable. Also, the wind velocity non-uniformity and wind pressure non-uniformity decrease with the increase of R. Therefore, considering the space and material loss caused by an increase in radius of curvature, the elbow with R = 2.5 h can be used as the best design structure for the 90° rectangular elbow, which is of great significance for improving the control effect of dust and toxic pollutants in a uniform push–pull ventilation device.

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

“…Due to limitations of the working space and operations, the contaminants captured by the exhaust hood can only be exhausted from one side outlet of the lower exhaust workbench, which means the velocity at its farthest point is 0 m/s, as shown in Refs. [ 18 , 19 ]. When the size of the hood face is large, it is difficult to achieve uniform airflow distribution on the hood face so the structures shown in Figure 2 can be used to improve airflow distribution [ 20 ]:…”

“…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.…”

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

“…The mathematical model of gas motion was the same as that employed in previous studies [ 16 , 17 , 18 ]. It was assumed that the air in the flow field is an incompressible Newtonian fluid.…”

“…The center-line velocity change regime for a parallel-flow exhaust hood is helpful to the study of velocity change regime in a parallel-flow push–pull ventilation system, and can further improve the ability of controlling dust and poisonous pollutants for the exhaust hood since its strong anti-interference air flow ability [ 4 , 5 ]. It has a positive effect on reducing the dust and poison in the operating environment and ensuring the occupational health of workers [ 14 , 16 , 17 ]. Therefore, this study aimed to establish the velocity change regime for a parallel-flow square exhaust hood used in a push–pull ventilation system without a parallel-flow push hood, and the results can provide a theoretical basis for improving the ability of controlling dust and poisonous pollutants for the exhaust hood.…”

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

“…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 ].…”