What Is a Venturi Tube?
- Chinese name
- Venturi tube
- Foreign name
- Venturi tube
- Function
- Pipe gauge measurement
- Features
- Wide measuring range and easy installation
- Range
- Petroleum, chemical, metallurgy, power
Venturi principle
- A device for measuring the pressure difference of a fluid was invented by the Italian physicist GB Venturi, hence the name. Venturi is a tube that shrinks and then expands. The pressure difference between the inlet cross section and the minimum cross section is measured, and the flow rate can be obtained by using Bernoulli's theorem.
- Venturi tube
- Venturi tube consists of the following parts: entrance section: a short cylindrical section with a diameter of D ; contraction section: a cone-shaped tube with a cone angle of about 21 ° ± 2 °; A short straight pipe section with a diameter of about 1/3 to 1/4 D and a length equal to the pipe diameter; diffusion section: a tapered pipe with a cone angle of 8 ° to 15 °. There is a pressure measuring ring at a distance of 0.25 to 0.75 D from the end of the inlet section, and there are at least 4 pressure measuring holes on it, and the pressure ring leads to the pressure gauge. In addition, in the center of the larynx, there is also a porous pressure gauge ring leading to the pressure gauge. The pressure difference between the cross section of the inlet and the smallest cross section (that is, the cross section of the throat) can be measured through the scale of the pressure gauge or the automatic recorder.
- Let the average speed, average pressure, and cross-sectional area at the inlet section and throat be v 1 , p 1 , S 1 , and v 2 , p 2 , S 2, respectively ; the fluid density is . Applying Bernoulli's theorem and the continuity equation and noting that the streamlines of the mean motion are of equal height, we can get:
- From this, the formula for calculating the flow Q can be obtained:
- After knowing , S 1 and S 2 and measuring p 1 - p 2 , the flow rate Q can be obtained according to the above formula.
- The main advantage of the venturi is the simple device. Secondly, because its diffusion section slows down the fluid gradually and reduces the degree of turbulence (see turbulence), the head loss is small, not exceeding 10 to 20 between the pressure difference between the inlet and the throat %.
Venturi tube use
- Venturi tubes are divided into built-in Venturi tubes and plug-in Venturi tubes according to their structure. Good results have been obtained in the measurement of combustion air, cold air, and gas measurement (blast furnace gas, coke oven gas, and converter gas) of hot blast stoves in iron and steel plants, as well as in the measurement of primary air, secondary air large pipe diameter, and low flow rate pipe meters in boilers of thermal power plants. Solve the accurate measurement of various types of gas flow in current industrial enterprises with low pressure, large pipe diameter and low flow rate. Fluid measuring device with wide measuring range and convenient installation. The unique structure design and data processing method have strict hydrodynamic basis, and the actual flow calibration is carried out in the national key wind tunnel laboratory.
- It can be widely used in the control and measurement of large-diameter fluids in petroleum, chemical, metallurgical, and power industries.
- Features
- (1) The resistance to the fluid is small, about 150Pa, so the energy consumption is low.
- (2) Large differential pressure, high accuracy and wide measuring range.
- (3) Good stability and smooth pressure difference.
- (4) Wide range of use. General gas, flue gas, blast furnace gas with a lot of impurities, etc., will not cause blockage for long-term use.
- (5) Easy installation and long-term maintenance.
- (6) The front and rear straight pipe sections are shorter than the standard throttling device, about 1.5D before and 1D after.
- (7) It has an integrated structure of online temperature and pressure self-correction.
Venturi reference
- 1. terms of: Wang Wu a "Encyclopedia of China", 74 (second edition) physics entries: Fluid Mechanics: Encyclopedia of China Publishing House, 2009-07: 380.