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.
Highlights
A parallel-flow square exhaust hood can supply uniform exhaust air, which is different from the general exhaust hood
It was not clear whether the center-line velocity can be predicted by the dimensionless method for the uniform air flow push–pull ventilation system, and it should be researched in future studies
The center-line velocity change regime in a parallel-flow square exhaust hood can be described by Equation (1), which is y = −0.2778x3 + 1.246x2 − 1.8773x + 1.0176, where y is V/V 0, and x is length of exhaust hood (L/a)
Summary
A parallel-flow square exhaust hood can supply uniform exhaust air, which is different from the general exhaust hood. Because of the parallel-flow, it improves the exhaust hood performance during indoor ventilation, and it can be combined with a uniform supply hood to produce a parallel-flow push–pull ventilation system. Previous studies have analyzed the aerodynamic characteristics, design guidelines [7], performance [8], and field measurements [9] of push–pull ventilation systems, as well as the design of uniform air supply and exhaust [10], balanced ventilation principle and calculation [11], and non-adjustment of static pressure in a supply air duct [12]. The comparison for a parallel-flow square exhaust hood with large hood opening and uniform velocity, which can be used in a parallel-flow push–pull ventilation system, is not discussed.
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