Research on the axial velocity change rule of desktop slot exhaust hood

Abstract

The desktop slot exhaust hood has been widely used, but it is calculated by empirical formula. Axial velocity change rule of desktop slot exhaust hood can effectively provide the basis of the wind speed needed in order to control the poison. According to gas motion mathematical model, the geometry model and boundary conditions of desktop slot exhaust hood was established, and the influence of the hood sizes to axial velocity were analyzed by Fluent simulation. The changes of relationship between the axial velocity (V) and the distance from the hood mouth (L), the short edge of the hood mouth (a), the long edge of the hood mouth (b), the equivalent diameter of the hood mouth (d) and the square root of the hood mouth area (A) were comparative analyzed by dimensionless processing. The result is the V/V0 with L/d have better change rule. The axial velocity change rule of different axial velocity were also analyzed using V/V0 with L/d change rule, and the change rule of V/V0 with L/d of desktop slot exhaust hood was obtained, which was verified by experiment.

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

“…The center-line velocity decreased rapidly with an increasing distance from the hood face, because the velocity decreased to approximately zero at a distance of 1.5 m from the hood face for all hood face velocities. When the hood face velocity was different, the variation law of the center-line velocity was different, which is consistent with conclusions in previous research [ 14 , 15 ]. Therefore, we used the same dimensionless method as used in previous literature [ 14 , 15 ] to study the velocity change regime and explore whether the similar variation law can be obtained.…”

“…Both the parallel-flow exhaust hood studied in this paper and the desk-top slot hood studied in Wu et al [ 15 ] are exhaust hoods, but their center-line velocity change regimes are different because of the different hood type. Both the parallel-flow exhaust hood studied in this paper and the parallel-flow supply hood studied in Chen et al [ 14 ] were uniform flow, but their center-line velocity change regimes were quite different.…”

“…Whether it was a parallel-flow square exhaust hood studied in this paper, a parallel-flow square supply hood studied Chen et al [ 14 ], or a desktop slot exhaust hood without flange studied in Wu et al [ 15 ], V/V 0 had a good change law with L/d ; d is the equivalent diameter, which is the length of square hood side ( a ). It shows that the center-line velocity change regime can be obtained by dimensionless method, and it can eliminate the influence of hood face velocity and the hood size on the velocity change regime outside the exhaust hood; however the relationship between V/V 0 with L/d was different for different type hoods.…”

“…When the velocity decreased to 10% of the hood face velocity, L/d ( d is equal to a in a square hood) of a parallel-flow exhaust hood was 1.2, but L/d of a desktop slot exhaust hood without flange was about 1.5 [ 15 ], which shows that the control distance of the hood rest on the table is larger than that of the open hood, because the table can be considered a flange. Therefore, if a parallel-flow exhaust has a flange, it may also enhance the exhaust effect.…”

“…The velocity change regime for a parallel-flow square supply hood [ 14 ] and a desktop slot exhaust hood without flange [ 15 ] via dimensionless numerical simulation were studied. However, it is not clear whether the center-line velocity of a parallel-flow square exhaust hood has a similar change regime as a parallel-flow supply hood or a desktop slot exhaust hood without flange.…”