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『Venturi flowmeter experiment』Related information(clamp on meter|electromagnetic meter|venturi meterrotameter|orifice meter|ultrasonic flow meter|mass flow meter|coriolis mass flow meter|coriolis flow meter|magnetic flow meter|magmeter flow meter|magflow flow meter|mag meter flow meter|electromagnetic flow meter|vortex flow meter|turbine flow meter|thermal mass flow meter|thermal flow meter|rotameter flow meter)
How to use a Venturi flowmeter?
The data obtained from the measurement of the U-shaped tube is more accurate, but the measurement range is small. However, the differential pressure transmitter has a larger error at low flow rates, and a smaller error at high flow rates.. First use an inverted U-tube differential pressure gauge, and when it exceeds the range, use a differential pressure transmitter. Note that the change in flow rate should ensure that the experimental points are evenly distributed on the λ - Re curve. Experimental objective
1. Find the relationship curve between the flow rate and pressure difference of the Venturi flowmeter.
2、 Measure the flow coefficient of the Venturi flowmeter. According to Bernoullis principle, the flow rate is related to the pressure difference before and after the Venturi flowmeter as follows: (4-14) in equation: - volume flow rate m3/s; - cross-sectional area of the throat neck of the Venturi tube, m2; Cv - flow coefficient of the Venturi flowmeter, dimensionless; R-reading of U-shaped differential pressure gauge, m; - indicated liquid density inside the differential pressure gauge, kg/m3. - fluid density. kg/m3。 However, the numerical value of the flow coefficient is often influenced by the structure and processing accuracy of the Venturi meter, as well as fluid properties, temperature, and pressure. Therefore, before using such quantity meters on site, it is often necessary to calibrate the flow meter by measuring the differential pressure readings at different flow rates, directly plotting them into curves, or obtaining the relationship curve between CV and Re (the flow coefficient CV varies with Re number when the ratio of throat diameter to pipe
2. Evaluation of calibration uncertainty of Venturi flowmeter
The core of uncertainty evaluation of Venturi flowmeter calibration is to systematically analyze the sources of errors in each link and achieve quantitative synthesis of errors through mathematical modeling.
. 1. Accurate construction of measurement model. The calculation model of the Venturi flowmeter is based on the Bernoulli equation, with the core formula being Q=C · A ₀·√ (2 Δ P/ρ). The accuracy of the flow coefficient C, throat cross-sectional area A ₀, pressure difference Δ P, and fluid density ρ directly determines the reliability of the final calculation result. When deriving the model, it is necessary to consider the compressibility and viscosity effects of the fluid. 2. Three dimensional perspective equipment error for error tracing: the accuracy error of differential pressure sensors, such as ± 0.1% range, will amplify the deviation of the grinding tool Δ P, and the accuracy error of calipers for throat diameter measurement will cause A ₀ square level amplification. The temperature compensation failure of the laboratory densitometer may cause a deviation of more than 0.3% from the true value of ρ. Environmental disturbance: Temperature fluctuations of 1 ℃ can cause a 0.05% shift in the density of low viscosity fluids, and the temperature drift characteristics of the pressure sensing module can cause a benchmark shift in Δ P. Dynamic parameter deviation: The fluctuation amplitude of the flow coefficient C can reach ± 0.5% when the Reynolds number exceeds 150000, which is due to the uneven distribution of flow velocity d