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In this paper, the possibility of the flow rate measurement for a circular pipe flow by using a wo-ven screen with the property of straightening un-uniform flows is discussed. The resistance coefficient and the flow rate coefficient are estimated from the pressure difference caused by the woven screen under the experiment ranges of the wire Reynolds number, Red = 2.2 × 102-1.8 × 103, and of the open area ratio, β = 0.28-0.65. As a result, the resistance coefficient decreases and the flow rate coefficient increases as the wire Reynolds number Red or the open area ratio β increases. In addition, both coefficients are not affected by the difference between uniform and turbulent pipe flows approaching the woven screen. Therefore, the possibility of a flow-meter having the property to straighten the un-uniform flow is expected.

It is a significant assignment to measure the flow rate exactly in engineering fields using pipe line flows. A flow- meter generally requires a long runway approaching it and/or a straightening device, such as perforated plates, honeycombs or woven screens upstream of it. As for a woven screen, often used to straighten un-uniform flows such as a prejudice flow and a turbulent flow in many engineering fields [

Therefore, an idea of measuring the flow rate by using a woven screen is proposed in this paper, because it is expected that it could play both the role of straightening the flow as well as measuring the flow rate. The possibility as a flow-meter having the ability to straighten an un-uniform flow from the measurements of the flow rate coefficient and resistance coefficient of a woven screen for two different pipe flow fields is discussed.

_{d}, is defined in Equation (1) based on the wire diameter, the velocity averaged in the pipe’s cross section and the kinematic viscosity of the air was varied from 2.2 × 10^{2} to 1.8 × 10^{3}.

_{D} = 8.3 × 10^{3} − 8.7 × 10^{4}, before the woven screens is set. The velocity in the pipe is obtained from the pressure difference between total pressure measured by a small handmade total pressure tube and static pressure taken from a pressure hole in the position nearest to the tip of the total pressure tube.

It is understood that the velocity distributions obtained at the pipe’s cross section in the case of L = 1080 mm are almost consistent with the 1/6-power law as shown in

_{p} upstream and downstream of the woven screen. The wall pressure coefficient is defined as

d [mm] | M | β | Symbol |
---|---|---|---|

1.0 | 12 | 0.28 | ◆ |

1.0 | 8 | 0.47 | ■ |

1.0 | 6 | 0.58 | ▲ |

1.0 | 5 | 0.65 | ● |

where P is the wall pressure, P_{∞} is the atmospheric pressure and ρ_{air} is the density of the air. It is noted that the wall pressure varies linearly over the wide range of

_{d}. The resistance coefficient K is defined as

The resistance coefficient K decreases as the wire Reynolds number Re_{d} and the open area ratio β increase. Although the resistance coefficients K for each β is obtained under two different pipe flow approaching the woven screen, the turbulent flow and the uniform flow, they agree very well. Then, it is noted that the resistance coefficient is not affected by the difference of flow approaching the woven screen. This may be because two approaching-flows become similar to each other by the damming effect which occurs in front of the woven screen. Therefore, it is expected that the woven screen has a property which could straighten the turbulent pipe flow as well as the uniform pipe flow. The black-lines in _{d} and the open area ratio β. They approximate the resistance coefficient K very well.

_{d} and the open area ratio β. The flow rate coefficient α is derived from general formulas, _{o} is the open area of the woven screen. The flow rate coefficient α increases as the wire Reynolds number Re_{d} and the open area ratio β increases. In addition, it was noticed that the flow rate coefficient α obtained in two different pipe flows, the turbulent pipe flow and the uniform pipe flow, are close to each other. On the other hand, the flow rate coefficient α can be calculated from the wall pressure difference based on the following Equation (5), where A is the pipe cross-sectional area.

The black-lines in

Generally, in the case of the flow rate measurement using the pressure difference, the pressure difference

The resistance coefficient K and the flow rate coefficient α of the woven screen placed in the circular pipe were experimentally investigated. As a result, although the flow rate coefficient α varies depending on the wire Reynolds number Re_{d} and the open area ratio β increases, both coefficients is not affected by the difference between

a uniform and a turbulent pipe flows approaching the woven screen. Therefore, the possibility of a flow-meter having the ability of straightening an un-uniform flow can be expected. Furthermore, considering the pressure measurement points, the numbers of woven screens and/or combination with perforated plates and honeycombs, its ability as a straightening flow-meter will rise.