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1. What is the influence of the diameter of the Venturi tube throat on the measurement accuracy and measurement range of the Venturi flowmeter? (Specifically...
According to the Venturi tube mass flow formula: M=[C/(1- β ^ 4) ^ (1/2)] ·ε · (π/4) · d ^ 2 · (2 ·Δ P ·ρ) ^ (1/2), where M - mass flow rate C - outflow coefficient C=[M (1- β ^ 4) ^ (1/2)]/[(π/4) · d ^ 2 · (2 ·Δ P ·ρ) ^ (1/2)] C depends on the Reynolds number, which depends on the mass flow rate M and must be obtained iteratively. β - throat diameter d/pipe diameter D ε - pipeline expansion coefficient ε=[M (1- β ^ 4) ^ (1/2)]/[(π/4) · d ^ 2 · C · (2 ·Δ P ·ρ) ^ (1/2)] d - throat diameter Δ P - differential pressure ρ - medium density under working conditions. It can be seen that changing the throat diameter can change the differential pressure range, and your problem can actually be attributed to the influence of differential pressure range on measurement; The design of throttling components must ensure that the outflow coefficient C is constant, that is, the Reynolds number remains unchanged within the required accuracy range (throttling flow meters can only ensure the accuracy of a commonly used section within the measurement range). And the Reynolds number is also related to the throat diameter (which affects the flow velocity and the flow velocity at maximum and minimum flow rates). Due to the iterative method required to obtain the outflow coefficient C, it is necessary to first give a differential pressure, calculate the throat diameter, and then verify whether it meets the requirements. If it does not meet the requirements, the throat diameter should be recalculated. If it still does not meet the requirements after multiple repetitions, the cal
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2. Venturi tube flow calculation
The Venturi tube flow calculation adopts the standard formula derived from Bernoulli equation and continuity equation, and the core parameters are upstream and downstream pressure difference, throat cross-sectional area, and fluid density.
. 1. The core calculation formula for the volumetric flow rate (Q) of a Venturi tube is: Q=C_d × A ₂ × √ {[2 × (P ₁ - P ₂)]/[ρ× (1- (A ₂/A ₁) ²)]}, where: • C_d: Discharge Coefficient, which needs to be obtained through real flow calibration. Ideally, it is about 0.98, and the actual value depends on the specific geometry and Reynolds number of the pipeline. • A ₁: Upstream pipeline cross-sectional area (m ²) • A ₂: Throat cross-sectional area (m ²) • P ₁: Static pressure measured at the upstream pressure tap (Pa) • P ₂: Static pressure measured at the throat pressure tap (Pa) • ρ: Fluid density (kg/m ³) 2. Key calculation steps 2.1 Measuring pressure difference: Accurately measure the static pressure difference between the upstream and throat using a high-precision differential pressure transmitter or U-tube differential pressure gauge Δ P=P ₁ - P ₂2.2 Determine geometric parameters to accurately measure the inner diameter of the upstream pipeline (D ₁) and the inner diameter of the throat (D ₂), and Calculate the correspondi