ES2283168B1 - PROCEDURE AND DEVICE FOR MEASURING VOLUMETRIC, MASICAL, DENSITY, VISCOSITY AND REYNOLDS FLOW. - Google Patents

Abstract

Procedure and device for measuring volumetric flow, mass, density, viscosity and reynolds. The primary element for capturing the magnitudes (volumetric flow, density, mass flow, viscosity and Reynolds number) consists of a straight section of pipe with a cross section equal to that of the conduit, which contains a Pitot tube, a fluid based resistance in a bundle of capillary tubes that offer some resistance to flow and three pressure taps to capture two differential pressures and a densimeter. The densimeter is connected to two fluid outlets located upstream and downstream of the fluidic resistance (capillary tubular beam). The density is determined by the measurement of the load equivalent to the corrected weight of the float filled with the fluid to be measured.

Description

Procedure and flow measurement device volumetric, mass, density, viscosity and Reynolds.

Object of the invention

The object of the invention is the measurement of mass flow rate, volumetric density and viscosity and Reynolds number of liquid fluids by capturing three pressure values obtained in three different places and density. The three measures pressure form two gradients obtained respectively by Pitot effect and loss of load due to resistance to circulation, being used to calculate the mass flow. For Measuring density mechanical means are proposed.

Background of the invention

The elements are reviewed primary flow capture based on gradient measurement of pressure between two zones near a duct.

Primary flow sensors by differential pressure

Flow sensors based on the measurement of differential pressure, use the inherent property of all fluid moving within a conduit in the same direction, founded in which the velocity of the fluid is a function of the gradient of pressure between two points located on both sides of a constraint in the fluid path.

Pitot tube

Pitot tube is the primary element to measure the local velocity of a fluid within a conduit.

It consists of two types of windows pressure sensors and open to the fluid.

A group of static windows to capture the static pressure and unique dynamic window oriented transversely to the incidence of the fluidic vein.

If the pressure gradient between the two differential pressure windows Pd, the relationship that associates the differential pressure at the fluid velocity is given as,

Pd = P1 - P2 = \ rho \ frac {v2} {2}

where

Pd, differential pressure (Pa)

p, fluid density (kg / m 3)

v, fluid velocity (m / s)

Then, the speed associated with the gradient of pressure is given as,

one

For a compressible fluid it is verified that

2

where

k, ratio of specific heats (Cp / Cv) (dimensionless)

p1, static pressure (captured transversely to fluid vein) (Pa)

p2, total or dynamic pressure captured frontally to the fluid vein (Pa)

All gases are relevant fluids compressible and all liquid fluids can be considered with an acceptable error as incompressible fluids in terms of determination of flow in industrial environments.

Restrictor hole

The family of primary flow collectors based on the obstruction of the current or fluid vein by means of a restrictor, produce an output magnitude interpreted as differential pressure. Therefore, a pressure transducer differential provides the corresponding associated magnitude of flow. Although there are theoretical models to predict or estimate the flow rate depending on the pressure gradient, each fluid and type of  restrictor not only demands experimental knowledge of adjustment coefficients but, that the nonlinear function changes slightly parameters.

The obstructive or restrictive method of the vein fluidic consists of an orifice plate installed in a section of the conduit. The result of the restriction is the pressure difference between two points located immediately before and after the plate  restrictive

Although the relationship between the flow and the differential pressure is a complex nonlinear function, okay established (approximation with sufficient accuracy) by boards. Thus, the volumetric flow rate for an ideal fluid in phase liquid, which means an incompressible fluid without friction, is given as

3

where

Q, volumetric flow rate (m 3 / s)

Au, unrestricted section area (m 2)

Ad restricted section area (m 2)

pu, pressures before plaque or restriction (Pa)

Pd, pressures after plaque or restriction (Pa)

p, fluid density (kg / m 3)

On the basis that Au and Ad are constant, the pressure flow ratio is a quadratic function similar to model that describes the Pitot tube, resulting in an expression of the shape

4

There are different models of hole plate and different fluids in terms of characteristics. However such diversity, for almost everyone this type of sensor can be used primary with just setting one parameter, the meter constant, achieving an accuracy around 99%, that is an error around at 1%.

Element of linear resistance to flow

In many flow capture applications a restrictive medium based on obstruction is used for gases uniform of the total cross section of the duct. Like this method involves the introduction of cargo to the transport process of the fluid, is used primarily in the collection of the flow of low speed gases. For example breathing systems assisted employ such types of meter.

The construction characteristics of resistors Linear flow rates consist of a mesh filled package of stainless wire The characteristics of the wire (diameter and friction contact surface) make up the uniform resistance to the advance of the fluid vein.

In such systems you can approximate the resistance through a linear relationship in the range of interest, with what you have an expression based on Ohm's law according,

R = \ frac {\ Delta P} {Q}

It is evident that such a function implies a approach valid only within a narrow range of pressure gradients and at a certain temperature, for which it is really applied. The resistance depends on the viscosity and this of the temperature and the characteristics of the fluid. Hence the setting for a certain fluid and at a certain temperature It is problematic.

There is no knowledge of the existence of a volumetric and mass flow measurement system, density, viscosity and Reynolds number using a device that combines the measurement of differential pressures obtained by the principles Pitot tube and fluid displacement resistance within a conduit associated with density measurement.

Description of the figures

To start the description that is being performing and in order to help a better understanding of the characteristics of the invention, is accompanied herein descriptive, as an integral part of it, a set of figures in which, with an illustrative and non-limiting nature, represents next:

Figure 1 shows primary capture element pressure by Pitot effect

one.

Taking of static pressure.

2.

Taking of Pitot pressure.

Figure 2 shows the pressure function at duct length obstructed by hole plate or restrictor plate.

eleven.

Pressure gradient between intakes 1 and 2.

9.

Taking pressure before the restrictor plate.

10.

Taking pressure after the restrictor plate.

Figure 3 shows the reel equipped with hole plate for primary flow collection by differential pressure effect

9.

Taking pressure before the restrictor plate.

10.

Taking pressure after the restrictor plate.

Four.

License plate restrictor

Figure 4 shows the installation of a linear resistance based on a bundle of capillary tubes.

5.

Fluidic resistance (tube bundle capillaries)

one.

Taking pressure before resistance (upstream).

3.

Taking pressure after resistance (downstream).

Figure 5 shows the primary element of volumetric flow rate capture

one.

Taking of pressure P1 in the fluid line before resistance (water above).

2.

Taking P2 pressure inside the Pitot tube located downstream of the resistance.

3.

Taking P3 pressure downstream of the resistance.

Four.

Tube Pitot.

5.

Fluid resistance based on a beam tubular capillary

Figure 6 shows the preferred embodiment of the volumetric flow sensor and based on two sensors differential pressure

6.

Differential pressure sensor

7.

Flow Calculator

18.

Densimeter.

Figure 7. Preferred embodiment of the sensor volumetric flow rate with a single differential pressure sensor equipped with three-way valve and two positions for selection Alternative differential pressure capture.

6.

Differential pressure sensor

7.

Flow Calculator

8.

Three-way two-way valve positions.

18.

Densimeter.

Figure 8. Liquid density meter with cell from load to compression.

12.

Deposit.

13.

Compression load cell.

14.

Flexible fluid connections with the float.

Figure 9. Liquid density meter with cell from load to extension.

12.

Deposit.

13.

Extension load cell.

14.

Flexible fluid connections with the float.

Figure 10. Liquid density meter with cell load to compression

17.

Float.

13.

Compression load cell.

fifteen.

Bellows to isolate the load cell of the float enclosure by means of a transmitter rod of force.

Figure 11. Liquid density meter with pressure transmitter

17.

Float.

fifteen.

Hermetic fluid filled bellows Pressure transmitter to the pressure sensor.

16.

Pressure Sensor / Transmitter for density measurement.

Figure 12. Scheme of an embodiment preferred with two differential pressure sensors and the densimeter.

Description of the invention

The primary element for collecting the aforementioned quantities (volumetric flow, density, mass flow, viscosity and Reynolds number) consists of a straight section of pipe with a cross section equal to that of the conduit according to Figure 5, which contains a Pitot tube, a fluidic resistance based on a bundle of capillary tubes that offer some resistance to flow and three pressure taps for capturing two differential pressures at
ber:

\ blacklozenge

Pressure capture differential by the Pitot tube method. It is carried out by the measurement of pressures in sockets 2 and 3 of figure 5. We call this pressure gradient ΔP_ {p} = P2 - P_ {3}.

\ blacklozenge

Pressure capture differential by the resistance method. It is carried out by the measurement of pressures in sockets 1 and 3 of figure 5. We call this pressure gradient ΔP_ {R} = P_ {1} - P_ {3}.

The densimeter (18) figures 6 and 7, is connected to two fluid outlets located upstream and downstream of the fluid resistance (tubular capillary beam) also indicated in the embodiment shown in figure 12.

Density is determined by the measure of the load equivalent to the corrected weight of the float filled with the fluid to measure. Figures 8, 9, 10 and 11 show various Density measurement procedures. Figure 8 shows the preferred densimeter in the application, which consists of a tank that when filled with the fluid to be measured, changes weight. He total weight (fluid weight plus tank weight) corrected by the tank weight and captured in terms of compression load, provides a value proportional to density. The connections (14) Figure 8 must be flexible and not disturb or exert force some on the tank (12), so that the load cell (13) capture only the total weight due to the fluid and the Deposit.

Figure 9 shows a densimeter that operates on the same principle (measure the weight of the tank plus the liquid contained therein) only that the load cell operates by extension. This densimeter is hung by the load cell and the connections to it should not exert any disturbing force about it.

Figure 10 measures the density by a load cell, which captures the force or load by means of a push rod that transmits a force and an articulated lever to a float. The mission of the bellows (15) is to isolate the body where the float (17) of the load cell operates.

Figure 11 measures the density by a pressure transmitter, which receives the pressure signal through of a bellows (15) interposed between the float (15) and the sensor pressure (16).

Mode and determination of magnitudes

With the values of the two pressures described differential or pressure gradients and density \ rho, using the calculator 7 of Figures 7, 8 and 12, determine the following quantities:

- the volumetric flow rate given by Q_ {v} = A \ cdot \ sqrt {\ frac {2 \ cdot \ Delta P_ {P}} {\ rho}} = A \ cdot \ sqrt {\ frac {2 \ cdot (P_ {2} - P_ {3})} {\ rho}}

- the density \ rho.

- the mass flow rate Q_ {M}, which is given by Q_ {M} = \ rho \ cdot Q_ {v}

- viscosity, given by \ mu = \ frac {\ pi \ cdot R 4 \ cdot (P_ {1} - P_ {3}) \ Nd {T}} {8 \ cdot L \ cdot Q_ {v}} where L is the length of the fluidic resistance (tubular beam of capillaries), R is the radius of the resistance capillaries fluidic (tubular beam) and N_ {T} is the total number of tubes tubular beam capillaries.

- Reynolds number whose definition is given as R_ {e} = \ frac {\ rho \ cdot V \ cdot D} {\ mu} where V is the fluid velocity given as V = \ frac {Q_ {v}} {A} = \ sqrt {\ frac {2 \ cdot \ Delta P_ {P}} {\ rho}} = \ sqrt {\ frac {2 \ cdot (P_ {2} - P_ {3})} {\ rho}} and D is the diameter of the section duct transversal A.

For the conduction calculations to determine the aforementioned magnitudes two are proposed procedures:

\ blacklozenge

The use of two sensors differential pressure as shown in figure 6.

\ blacklozenge

The use of a single sensor differential pressure as shown in figure 7. In this case it is necessary to sequentially capture the pressures of the Pitot and the pressure upstream of the resistance making the change by a three-way, two-position remote control valve.

Description of a preferred embodiment

A preferred embodiment of the primary element Multivariable capture is illustrated with Figure 7. It consists of the following parts:

- a densimeter (18)

- a single differential pressure sensor (6) for capture two differential pressures alternately through the three-way, two-way valve (8).

The connections of the single pressure sensor differential come from:

\ blacklozenge

Pressure taking static (1) of figure 5 upstream of the resistor linear.

\ blacklozenge

Pressure sensor socket differential from a three-way two-way valve (8) positions according to figure 7.

One of the valve positions (8) captures the upstream pressure of the resistance and the other position of the valve (8) or alternative position captures the pressure of the Pitot tube. With both pressure values and static pressure captured waters below the resistance and the density value, the volumetric flow rate, mass flow rate viscosity and number of Reynolds according to the following expressions

- Q_ {v} = A \ cdot \ sqrt {\ frac {2 \ cdot (P_ {2} - P_ {3})} {\ rho}}, where A the cross-sectional area of the section duct

- Q_ {M} = Q_ {v} \ cdot \ rho

- \ mu = \ frac {\ pi \ cdot R 4 \ cdot (P_ {1} - P_ {3}) \ cdot N_ {T}} {8 \ cdot L \ cdot Q_ {v}}

- R_ {e} = \ frac {\ rho \ cdot V \ cdot D} {\ mu}

Figure 12 illustrates a configuration multivariable sensor alternative under one embodiment Preferred with two differential pressure sensors. The signals (6) of the differential pressure sensors and (13) of the densimeter enter the calculator (7) to determine the volumetric flow rate, density, mass flow rate, viscosity and Reynolds number.

Claims (5)

1. Procedure for measuring flow, density, viscosity and Reynolds number in a conduit characterized in that it comprises the steps of:

-

Introduction of a pipe reel endowed with a fluidic resistance based on a tube bundle capillaries, a Pitot tube and three pressure taps called: static pressure P1 upstream of the resistance, pressure of the Pitot P2 tube located downstream of resistance and pressure static P3 downstream of the resistor.

-

Measure of the density δ.

-

Measure of pressure at the three points of the measuring reel.

-

Obtaining volumetric flow rate Q_ {v} based on the application of the algorithm Q_ {v} = A \ cdot \ sqrt {\ frac {2 \ cdot (P_ {2} - P_ {3})} {\ rho}}, where A is the section area cross section.

-

Obtaining mass flow by application of Q_ {M} = Q_ {v} \ cdot \ rho.

-

Obtaining viscosity µ applying \ mu = \ frac {\ pi \ cdot R 4 \ cdot (P_ {1} - P_ {3}) \ cdot N_ {T}} {8 \ cdot L \ cdot Q_ {v}}.

-

Obtaining the Reynolds R_ {e} number applying the expression determined in the description according R_ {e} = \ frac {\ rho \ cdot V \ cdot D} {\ mu} = \ frac {\ rho \ cdot \ frac {Q_ {v}} {A} D} {\ mu} = \ frac {\ rho \ cdot Q_ {v} \ cdot D} {A \ cdot \ mu} = \ frac {\ sqrt {2 \ rho (P_ {2} - P_ {3})} \ cdot D} {\ mu}.

2. Multivariable primary sensor for application of the method mentioned in claim 1, which understands: a) A tubular reel that houses:

-

Fluid resistance based on the beam tubular capillaries.

-

Tube Pitot located downstream of the fluidic resistance.

-

Three pressure taps at the following points of the section: P1 upstream of the resistance, P2 in the Pitot tube located downstream of the resistance and P3 downstream of the resistance.

-

Densimeter connected to reel.

b) Means of calculation for the measurement of volumetric flow rates, mass, density, viscosity and Reynolds comprising:

-

Measure of the density δ.

-

Measure of pressure at the three points of the measuring reel.

-

Obtaining volumetric flow rate Q_ {v} based on the application of the algorithm Q_ {v} = A \ cdot \ sqrt {\ frac {2 \ cdot (P_ {2} - P_ {3})} {\ rho}}, where A is the section area cross section.

-

Obtaining mass flow by application of Q_ {M} = Q_ {v} \ cdot \ rho.

-

Obtaining viscosity µ applying \ mu = \ frac {\ pi \ cdot R 4 \ cdot (P_ {1} - P_ {3}) \ cdot N_ {T}} {8 \ cdot L \ cdot Q_ {v}}.

-

Obtaining the Reynolds R_ {e} number applying the expression determined in the description according R_ {e} = \ frac {\ rho \ cdot V \ cdot D} {\ mu} = \ frac {\ rho \ cdot \ frac {Q_ {v}} {A} D} {\ mu} = \ frac {\ rho \ cdot Q_ {v} \ cdot D} {A \ cdot \ mu} = \ frac {\ sqrt {2 \ rho (P_ {2} - P_ {3})} \ cdot D} {\ mu}.

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3. Multivariable primary sensor according to claim 2 wherein the means of determining the magnitudes cited in section (b) of claim 2, they consist of two differential pressure sensors that measure ΔP_ {P} = P2-P3 and ΔP_ {R} = P1-P3 and a calculator to compute the variables cited in section (b) of claim 2 4. Multivariable primary sensor according to claim 2 wherein the means of determining the variables consist of a differential pressure sensor, a valve three-way, a valve controller, and a calculator. 5. Multivariable primary sensor according to claim 2 wherein the proposed density meter adopts Four alternative configurations:

-

Densimeter consisting of a reservoir refillable with the fluid to be measured and whose weight is measured by a load cell that operates by compression.

-

Densimeter consisting of a reservoir refillable with the fluid to be measured and whose weight is measured by a load cell that operates by extension.

-

Float Densimeter that transmits the force of the flotation thrust by mechanical means to a cell of compression operating load.

-

Float Densimeter that transmits the buoyant thrust force to an intermediate bellows transforming it into pressure, and it transmits the pressure to a sensor of pressure.