DD201198A1 - ARRANGEMENT FOR MEASURING THE VOLUME OF A STROEMENDING MEDIUM - Google Patents

Abstract

The invention relates to an arrangement for measuring the quantity of a flowing medium in a pipeline or duct system. The aim of the invention is to maintain the advantages of the known quantity measurement by means of Kruemmer (low construction costs, no additional pressure losses) and to eliminate the disadvantage (low differential pressure difference). According to the invention, this objective is achieved by arranging a total pressure probe at the outer radius or near the outer radius of the armature and by removing the pressure taken by the total pressure probe and the static pressure tap against each other via a differential pressure measuring instrument or measuring transducer. figure

Description

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Arrangement for measuring the quantity of a flowing medium

Field of application of the invention

The invention relates to an arrangement for measuring the volume of a flowing medium in a pipeline or duct system, wherein pressure measuring probes are arranged in a manifold «

Characteristic of the known technical solutions

In piping and sewer systems, the task is to measure the flow of Plüssigkeits- or gas quantities by measurement and appropriate measuring devices that determine the mass flow (kg / h) or flow rate (m3 / h) to install.

Known measuring devices for this purpose are, for. As screens, nozzles, Venturi nozzles. Also elbows are used for measurement purposes.

Assuming a linear velocity distribution, over the flow cross-section of a bend in the radial direction (which is often approximately true in practice when the manifold is flowed evenly) of Art

p · r - (1)

R = mean radius of curvature of the bend r = current coordinate of the radius in the direction of R W = flow velocity

mean »is formed between the inner and outer radius of the manifold a difference of the static pressures

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I ² (2) off

/ = Density

W _m s mean velocity D = pipe diameter C a constant (£ <1.05) ρ. = stat. Pressure outside

^{= sta1;} · Pressure inside

mean. '

This means that the static pressure difference between the inner and outer radii of the manifold is approximately proportional to the square of the mean flow rate and thus also approximately proportional to the square of the flow. By relationship (2), flows through a manifold only provide sufficient pressure differences for technical purposes .

1. if the ratio D / R is sufficiently large,

2. if the speed W _{m is} not too small,

3. if the density of the medium is sufficiently high,

These conditions are often not given, as with high ratio D / R and high speed. W _m for a given density P the remaining losses in the pipeline or canal system are too large. On the other hand, the flow measurement by means of an elbow the advantage that no additional constructional for flow measurement (such as orifice plates, nozzles ,. Venturi nozzle with appropriate ^A nlaufstrecke) is required and that also no additional permanent pressure loss as in the above-mentioned measuring results.

Object of the invention

The aim of the invention is to maintain the advantages of the manifold measurement (low construction costs, no additional pressure losses, attaching the measuring point during operation) and to eliminate the disadvantage (low differential pressure).

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Explanation of the essence of the invention ν

The invention has for its object to increase the achievable difference in the effective pressures between the inner and outer radius of a bend so that even with a smaller ratio D / R and lower speeds W _ffl for a given density f a sufficient for metrological purposes difference _{value is} achieved ·

According to the invention, the object is achieved in that a total pressure probe is arranged by means of a pitot tube at the outer radius or in the vicinity of the outer radius of the manifold and that taken by the total pressure probe and the static pressure tap at the inner radius or in the vicinity of the inner radius pressure via a differential pressure gauge or transmitter are switched against each other ·.

embodiment

In one embodiment, the invention is explained in more detail. The drawing shows the arrangement of the total pressure probe in the manifold.

The manifold 3 with the pipe diameter D, the mean radius of curvature R ,. the inner radius R ^ = R - D / 2 and the outer radius R _a = R + D / 2, the total pressure probe in the vicinity of the outer radius of the manifold 3 outside the boundary layer of the flow on.

The dynamic pressure at the outer radius is calculated from (1) / to .: '',

dyx, = { "OW = I W ² ()

§ w- ² (ι>'Sr) ² O)

with R _a = H + §,

where p _Q dyn = dyn. Pressure outside

CL

P _a ges = mean total external pressure.

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^{With p} a sat ^p a stat ^{+ p} a dyn

and relations (2); (3) you get:

^ a ges or

^p a ges " ^p is" ^ 2

Substituting relationships (5a); (5b) to relationship (2) in proportion so does one obtain?

(6a)

^p a ges - ^p is 2D , D \ - ⁺ W ^p or - ^p is - ^p is ^ 1 + d | ₂ ^p ast - ^p is   + M 2D "ff" 2D R

(6b)

Relationships (6a) and (6b) represent the enlargement ratio ¹ * of the differential pressure measurement according to the invention for manifolds according to the invention The enlargement ratio occurs when there is uniform inflow to the manifold in both cases Increase or decrease the type of unevenness β The ratio D / R amounts to 1/2

 Thus, relationship (6a) or (6b) becomes

^p a ges " ^p is ^ 2,56 ^p ast '" ^p

The "enlargement ratio ¹¹ is therefore> 2.5 in this case. Thus, with the device according to the invention, a significant increase in the pressure difference has occurred compared to the known manifold measurement.

The total pressure probe 1 consists of an angled, open-front pipe, z. B. a pitot tube, wherein the tube faces with its open end of the incoming flow.

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Through a bore 2 at the inner radius of the manifold 3, the static pressure is tapped in a conventional manner · The arrangement of the total pressure probe and the static pressure removal is the following

 1. The incoming flow facing the front open tube of the total pressure probe forms the associated tangent of the manifold at the point of passage of the total pressure probe in the manifold at an angle not equal to zero degrees.

2. The angle at the manifold, where the static pressure extraction takes place, does not correspond to half the elbow angle.

3. The angle at the manifold, where the total Druckentnahine takes place, not equal to half the elbow angle.

4. The angles at the manifold, where on the one hand the static pressure on the other hand, the total pressure is taken, are not equal.

5. The pressure-taking probes are traversed by the bubbling process of a liquid or gaseous medium which flows at the measuring openings in the flow *

Claims (6)

232 32 8 .6 Claim for invention 1 · Arrangement for quantitative measurement of flowing media by means of static pressure tap at the inner radius or in the vicinity of the inner radius of a bend, characterized in that the outer radius or in the vicinity of the outer radius of the manifold, a total pressure probe is arranged and that by the total pressure probe and the static Druckanzapfun removed pressure via a differential pressure gauge or transmitter are connected against each other. 2. Arrangement according to item 1, characterized in that the incoming flow facing, open front pipe of the total pressure probe to the associated tangent of the manifold ¹ at the point of the passage of the total pressure probe in the manifold forms an angle not equal to zero degrees. Arrangement according to item 1 and / or item 2, characterized in that the angle at the manifold, in which the static pressure is removed, does not correspond to half the elbow angle. ' 4. Arrangement according to item 1 and optionally according to item 2 and / or 31 characterized in that the angle at the manifold, in which the total pressure is removed, does not correspond to half the elbow angle. 5 · Arrangement according to item 1 and / or items 2, 3 »4-» characterized by the fact that the angles at the manifold, where on the one hand the static pressure extraction on the other hand the total pressure extraction takes place, are not the same. 6 · Arrangement according to item 1 and 2 to 5, characterized in that the pressure sampling probes are traversed by the Einperlverfahren of a liquid or gaseous medium which flows at the measuring openings in the flow · "β, ^ Β, β ,, Β, ^ ---