How does an orifice plate flow meter work?

An orifice plate creates a constriction in the pipe. The fluid speeds up through the orifice, causing a pressure drop (ΔP). Flow rate is proportional to √(ΔP), calculated using Q=C×ε×A/√(1−β⁴)×√(2ΔP/ρ) per ISO 5167.

What is the beta ratio?

Beta (β) = d/D, the ratio of orifice bore diameter to pipe internal diameter. Typical range: 0.2 to 0.75. Higher beta = less pressure loss but lower accuracy.

What is the discharge coefficient C?

The discharge coefficient accounts for real fluid effects (vena contracta, friction). For ISO 5167 corner taps, C is calculated from the Reader-Harris/Gallagher equation and is typically 0.59–0.62 for β = 0.3–0.7.

What is the expansibility factor ε?

ε (epsilon) accounts for gas compressibility. For liquids, ε = 1. For gases, ε < 1 and depends on the pressure ratio and the isentropic exponent (κ). ε ≈ 1 for small ΔP/P ratios.

What are the ISO 5167 requirements for straight pipe?

ISO 5167 requires minimum straight pipe upstream (typically 10–44 D depending on fitting type and β) and 4–8 D downstream. Flow conditioners can reduce upstream requirements.

免費工程工具 — #152

孔板流量計算器 — ISO 5167

根據 ISO 5167 計算孔板流量。輸入孔板與管徑、差壓及流體密度。

ISO 5167Q = C·ε·A/√(1−β⁴)·√(2ΔP/ρ)液體與氣體

結果

體積流量

—

質量流量

—

Beta 比值 (β = d/D)

—

流量係數 C

—

孔板流速

—

管道流速

—

ISO 5167 孔板流量方程式

C — 流量係數（Reader-Harris/Gallagher 方程式）
ε — 膨脹係數（不可壓縮液體為 1.0）
β — 直徑比 d/D
ΔP — 孔板差壓
ρ — 上游流體密度

簡化流量係數

對於角接取壓，C ≈ 0.5959 + 0.0312β^2.1 − 0.184β⁸（簡化 Reader-Harris）。對於法蘭取壓，需增加管道直徑的修正項。

⚠️ 注意： 此計算器使用簡化的 C 估算。對於貿易交接計量，請使用符合 ISO 5167-2 的完整 Reader-Harris/Gallagher 方程式並進行雷諾數修正。

孔板流量計算器 ISO 5167 | 免費線上工具

結果

ISO 5167 孔板流量方程式

簡化流量係數

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