CN85204529U - Uniform speed tube flowmeter working at a large differential pressure - Google Patents

Abstract

The utility model discloses a uniform speed tube flowmeter working at a large differential pressure. The middle part of a detecting tube is embedded with an incident flow venturi tube exactly positioned in the center of a tube. The pressure is taken vertically on the sidewall of the throat of the venturi tube, and the low pressure much lower than the still pressure is obtained, forming a large differential pressure with the average total pressure coming from the total pressure hole of the detecting tube. After the total pressure hole is embedded with a flow guiding horn mouth, when the flow direction has a deflection angle of (+/-) 20 DEG, the measurement is still stable and accurate. The utility model is particularly applicable for the flow measurement with the large diameter and the low flow speed.

Description

Big differential pressure mean velocity tube flowmeter

The present invention is a flowmeter, is used for obtaining to have the differential pressure of determining relation with flow velocity in the pipeline of even velocity of flow, and this differential pressure can be through differential pressure gauge or differential pressure transmitter conversion, in the hope of flow.The present invention is specially adapted to the flow measurement of low velocity fluid in the large diameter pipeline.

Can with the invention (US3,803,921) of the known technology of the present invention contrast from P.D.Dieterich.This invention has two detecting devices that are made of hollow tube, can be described as upstream detector and downstream detector, and the perforate that is positioned at the detected pressures of pipeline all is in the fluid center.The upstream detector place be with one leave fluid mixing cavity extend to the sleeve pipe of pipeline to the closed at both ends of wall, sleeve pipe upper side wall one side is being left the paired pitot hole of meeting stream on the allocation really, fluid enters the sleeve pipe cavity through pitot hole to be mixed, and its average stagnation pressure is by the upstream detector introduction pipe.The position of opening of downstream detector is positioned at the downstream position outside the sleeve pipe, and its perforate direction towards downstream.When fluid flowed, the pressure of downstream detector output was lower than the average stagnation pressure of upstream detector output always, and the two constitutes differential pressure, and the relation of this differential pressure and flow velocity is confirmable, thereby can determine flow.

For many years, for determining of the position of pitot hole, proposed many theories once, representational is the homalographic distribution, etc. the flow distribution method, and linear-logarithmic distribution, Chebyshev approximate integration, Gaussian approximation integral method etc.These existing known localization methods are intended to make pitot hole rationally distributed, make upstream detector can obtain real as far as possible average stagnation pressure.The another improvement of above-mentioned same inventor P.D.Dieterich is to transform the pitot hole on the sleeve pipe into a length, the slit And of pipe diameter is with the downstream detector sleeve pipe of also packing into no better than, but the perforate of downstream detector still is in downstream position ， And and penetrates sleeve pipe opening (referring to FR2284884) towards downstream.

The common disadvantage of above-mentioned flowmeter is that the differential pressure that obtains is too little, when being used in heavy caliber low velocity gas stream, usually can only obtain the differential pressure less than the 10mm water column.Take into account the existing commodity selling of differential pressure transmitter though elementary errors is pressed, because of original differential pressure is low excessively, work is extremely unsettled, and the accuracy of measurement can't guarantee that therefore, the measurement of large diameter pipeline low velocity fluid metering fails to satisfactorily resolve so far.

Task of the present invention provides a kind of new mean velocity tube flowmeter, under identical flow velocity, therefore its low pressure output can obtain the differential pressure more much higher than prior art well below the low pressure of downstream detector output of the prior art, constitutes big differential pressure mean velocity tube flowmeter.

Solution is to adopt the detector tube (3) of a hollow, and two independently outlet connections are equipped with by sprue (11) sealing in its top on the tail end sprue (12), and one of them is high-pressure outlet joint (5), and another is low tension outlet joint (6).Side at this detector tube sidewall is opened some paired pitot holes (1) along vertical arrangement of segment of a cylinder, and pitot hole (1) tube cavity after testing directly communicates with high-pressure outlet joint (5).Give the position that will place pipeline center surely at the detector tube middle part, vertical importer of insert is to the Venturi tube (2) consistent with pitot hole (1).The length of this Venturi tube is slightly larger than the external diameter of detector tube and traverses detector tube, detector tube (3) is divided into up and down two partly, but the length of Venturi tube should make the unlikely detector tube that influences of the part that protrudes in detector tube (3) from socket joint (8) pipeline (7) of freely coming in and going out.The external diameter of Venturi tube designs less than the detector tube internal diameter, make to leave space (18) between Venturi tube outer wall and the detector tube inwall, hole (18) can make detector tube up and down two partly pitot holes (1) be able to communicate in detector tube inside.There is pipe (4) in a detector tube (3) inside, and interior Guan Yiduan locates vertical communicating with Venturi tube after a while in throat, forms the vertical pressure of Venturi tube throat's low pressure point sidewall; The other end of interior pipe communicates with low tension outlet joint (6), forms the unique path of Venturi tube low pressure output.The always paired De And in the position of pitot hole (1) is symmetrical in the axle center of pipeline (7), promptly is symmetrical in the axial line B-B of Venturi tube, and the layout of pitot hole can adopt the 3rd section described any localization method of this instructions.The length of detector tube is always traversed pipeline greater than pipeline bore And along the radial line of cross-section of pipeline, when inserting pipeline, detector tube should correctly locate, making the axial line B-B of Venturi tube (2) be in the position ， And of pipeline center makes pitot hole (1) and Venturi tube import towards the fluid upstream.When fluid is static, the pressure that high-pressure outlet joint (5) equates with low tension outlet joint (6) output, differential pressure is zero.As long as fluid flows, fluid will enter detector tube (3) inner chamber from the pitot hole (1) of meeting stream to be mixed, and its average stagnation pressure will be exported by high-pressure outlet joint (5).Meanwhile, fluid will enter Venturi tube, and (2) And produce a low pressure in its throat, this low pressure guides to low tension outlet joint (6) output through vertical interior pipe (4), the differential pressure that forms between two outlet joints, can determine flow rate of fluid through differential pressure gauge or differential pressure transmitter conversion, thereby determine flow.

Venturi tube has a hydraucone that sharply shrinks, and to the throat section minimum, enlarges gradually again thereafter.Enter and meet the fluid that flows to mouthful when flowing through the much smaller throat in cross section, must quicken.Because energy conservation, quickening must step-down, so the wall pressure of throat will be more much lower than the static pressure that fluid enters before the Venturi tube.In fact the low pressure point of minimum pressure is positioned at throat's the most further along point at thin place.Pipe (4) perforate is in the Venturi tube sidewall in of the present invention, communicate with Venturi tube is vertical, lead to the hole site is driveed just in throat, constitute this technical characterictic of the vertical pressure of Venturi tube throat's low pressure point sidewall, its advantage is that the low pressure of the existing mean velocity tube flowmeter gained of the low-pressure ratio that is obtained is much lower, thereby differential pressure is increased, overcome the too little shortcoming of original flowmeter gained differential pressure.When being used in the measurement of heavy caliber low velocity fluid, the particular significant effect of this big differential pressure mean velocity tube flowmeter.

Further improvement of the present invention is to go up insert diversion bell mouth (17) at pitot hole (1).This improvement is more meaningful to large diameter pipeline.Usually the large diameter pipeline system does not possess the sufficiently long straight length that can make fluid reach abundant development turbulent flow, so it is irregular that the fluid in the large diameter pipeline flows, the flow direction also not necessarily is parallel to conduit axis, and this will cause average stagnation pressure instability, and deviation is bigger.When behind diversion bell mouth (17) on the last insert of pitot hole (1), situation is improved greatly, and the average stagnation pressure of output is stable.Another beyond thought benefit is and since insert diversion bell mouth (please noting that Venturi tube itself also has tapered inlet), flowmeter of the present invention is when installing and locating, the drift angle can keep operate as normal to ± 20 ° greatly unexpectedly.The installing and locating of the mean velocity tube flowmeter that uses of tradition is but very harsh by contrast, has the deflection (drift angle is promptly arranged slightly) just can't steady operation slightly.

Improve as of the present invention another, also pitot hole can be made two slits (21) that extend along the detector tube segment of a cylinder respectively, open the both sides at Venturi tube symmetrically, opening direction and Venturi tube importer are to consistent, towards the fluid updrift side.Seam end near Venturi tube is slightly little from the distance of Venturi tube, and big slightly from the tube wall distance near the seam end of duct wall, the latter is about about 10% of pipeline (7) bore.

When using slit shape pitot hole (21), but the also flaring lip of insert (22) is used for water conservancy diversion, to improve stability and to be convenient to installing and locating.

Accompanying drawing 1 is the structure cut-open view of big differential pressure mean velocity tube flowmeter.

Accompanying drawing 2 is the A-A sectional views at flowmeter pitot hole place.

Accompanying drawing 3 is B-B sectional views of flowmeter Venturi tube.

Accompanying drawing 4 is synoptic diagram of the slit shape pitot hole of expression flowmeter.

Accompanying drawing 5 is E-E sectional views of slit shape pitot hole.

One embodiment of the present of invention such as Fig. 1, Fig. 2, shown in Figure 3.The Chebyshev approximate integration is adopted in the location of four pitot holes (1).The inlet diameter of Venturi tube (2) is 2:1 with the ratio of throat diameter.The external diameter of interior pipe (4) is 6mm, wall thickness 1mm, and the center of perforate is positioned at about 1mm behind the thinnest place of throat, and the detector tube external diameter is 30mm, wall thickness 5mm.Being positioned at ducted length is 300mm, and coupling pipeline (7) is φ 300mm.Flowmeter among Fig. 1 adopts two end localization methods, and the top is inserted in the locator sub (9), and insertion depth can limit with bolt.Locator sub (9) is welded on the pipeline with socket joint (8).Rubber-like O-ring seal (14) one ends are subjected to the restriction of packing ring (15), and the extruding the when other end is screwed in by socket bolt (13) just can seal well.Once this flowmeter was tried out in the high temperature low speed flow piping system of a φ 500mm bore.Experiment shows that traditional mean velocity tube flowmeter can only obtain 6～8mm water column pressure reduction, and extremely unstable.The straight tube of weldering the preceding paragraph φ 300mm in φ 500mm pipeline, attempt exchanges big differential pressure for to dwindle internal diameter, though can increase to nearly 35mm water column, because of the straight pipeline before the measurement cross section has only 3m, so job insecurity.After inserting the described big differential pressure mean velocity tube flowmeter of present embodiment, obtain the above differential pressure of 70mm water column, and working stability.

Claims (4)

1, big differential pressure mean velocity tube flowmeter, be used for obtaining to have the differential pressure of determining relation with flow velocity at the Guan Liuzhong of average rate, this differential pressure can be tried to achieve flow velocity after differential pressure gauge or differential pressure transmitter conversion, flow, be specially adapted to the mensuration of the flow velocity and the flow of large diameter pipeline low velocity fluid, detector tube (3) with hollow of traversing pipeline of length and pipeline (7) bore coupling, open some paired pitot holes with definite position (1) along the detector tube segment of a cylinder in detector tube tube wall one side, appropriate location made the symcenter of pitot hole just in time be in the center of pipeline (7) when detector tube inserted pipeline along the cross-section of pipeline radial line; And makes pitot hole towards the fluid upstream, the top of detector tube is sealed by sprue (11), two independently outlet connections are housed on the tail end sprue (12), wherein high-pressure outlet joint (5) communicates in detector tube with pitot hole (1), it is characterized in that: give the position that will be in pipeline (7) center surely at detector tube (3) middle part, there be the Venturi tube (2) of an import vertically to be installed in detector tube Shang And and traverse detector tube towards the fluid upstream, detector tube is divided into two parts up and down, the external diameter of Venturi tube makes up and down, and the pitot hole of two parts is able to communicate in detector tube inside less than the detector tube internal diameter, pipe (4) in one is arranged in detector tube inside simultaneously, one end is located vertical communicating with Venturi tube after a while in throat, the interior pipe other end communicates with low tension outlet joint (6), constitutes the unique path of the vertical pressure of Venturi tube throat's low pressure point sidewall.

2, by the described flowmeter of claim 1, it is characterized in that: pitot hole (1) studs with diversion bell mouth (17).

3, by the described flowmeter of claim 1, it is characterized in that: pitot hole can make two slits (21) that extend along the detector tube segment of a cylinder, is symmetrically distributed in the both sides of Venturi tube (2), and slit is towards the fluid upstream.

4, by claim 1 and 3 described flowmeters, it is characterized in that: slit shape pitot hole (21) studs with the tubaeform lip (22) of water conservancy diversion.

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