『Calculation formula for Venturi flowmeter』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)
1. Experimental principle and calculation formula of Venturi flowmeter
Experimental principle and calculation formula of Venturi flowmeter: Venturi flowmeter is a flow measurement device designed based on the basic principles of Venturi effect and fluid mechanics. The Venturi effect refers to the increase in fluid velocity when a restricted flow passes through a reduced cross-section, and the velocity is inversely proportional to the cross-section. In a Venturi tube, when fluid flows through the throttling element (i.e. the throat), local contraction occurs, resulting in an increase in flow velocity and a decrease in static pressure, thereby creating a pressure difference before and after the throat. There is a direct relationship between this pressure difference and fluid flow rate, so fluid flow rate can be calculated by measuring the pressure difference. Specifically, the working principle of the Venturi flowmeter is based on the continuity equation and Bernoulli equation of fluid flow. The Bernoulli equation describes the relationship between pressure, flow velocity, density, gravitational acceleration, and height at a certain point in a fluid, that is, kinetic energy+gravitational potential energy+pressure potential energy=constant. When the flow velocity is high, the pressure is low, which is an important consequence of the Bernoulli equation. Calculation formula: Application of Bernoulli equation: In a Venturi tube, taking points 1 and 2 (located before and after the throat), applying Bernoulli equation, we can obtain: where p
1 and p2 are the pressure at points 1 and 2, v
1 and v2 are the flow velocity at points 1 and 2, ρ is the fluid density, g is the gravitational acceleration, and h
1 and h2 are the heights at points 1 and 2, respectively (which can be ignored in contour flow). Flow continuity equation: Due to the stable flow in the pipeline, the internal flow field does not change over time, and the fluid properties do not change over time. Therefore, the water quality inside the pipeline remains constant, meaning that the flow rate is equal at all points. It can be expressed as: where A
1 and A2 are the cross-sectional areas of the pipeline at points 1 and 2, respectively, and v
1 and v2 are the flow velocities at points 1 and 2, respectively. Calculation of flow velocity and pressure difference: By simplifying and deriving the Bernoulli equation, the relationship between flow velocity v1 and pressure difference Δ p can be obtained. The specific process is as follows: Divide both sides of the Bernoulli equation by ρ g and simplify to obtain the expression for the flow velocity v1. Using the flow continuity equation, represent v2 as a function of v1. Substitute the expression of v2 into the simplified Bernoulli equation and solve for the relationship between v1 and the pressure difference Δ p. The final expression for the flow rate Q is: or where Q represents the volumetric flow rate inside the tube, measured in m ^ 3/s; K is a constant; Δ h is the head difference of the cross-section, which is related to the pressure difference Δ p; D is the diameter inside the tube. Correction of flow coefficient: Due to factors such as resistance in actual flow, the actual flow Q may be lower than the theoretical value. Therefore, it is necessary to use the flow coefficient μ of the Venturi tube for correction. The flow coefficient μ can be calculated by experimentally measuring the actual flow ra
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