WO1990002939A1

WO1990002939A1 - Apparatus for measuring parameters in a moving fluid

Info

Publication number: WO1990002939A1
Application number: PCT/SE1989/000454
Authority: WO
Inventors: Ivan Aladjoff
Original assignee: BETA SENSOR AB
Current assignee: BETA SENSOR AB
Priority date: 1988-09-01
Filing date: 1989-08-31
Publication date: 1990-03-22
Anticipated expiration: 1991-03-01
Also published as: SE8803054D0; SE8803054L

Abstract

An apparatus for measuring parameters in a moving fluid, said apparatus comprising a hollow body (2, 6, 11) with an inner measuring chamber (12) through which the fluid moves, and a measuring cell (3) disposed in said body and having an active surface (4). To reduce the volume of the measuring chamber (12) and to obtain therein a fluid flow distribution ensuring accurate measuring results, the apparatus (1) is provided with a flow distributing means (8) having a through passage (15) into which the fluid moves via an inlet (9). In the measuring chamber (12) which is defined by the surface (4), the upper end surface (13) of the means (8), and a sealing ring (14) arranged therebetween, the fluid flow is, via the upper outlet of the passage (15), first directed axially against the active surface (4) and is then radially and uniformly distributed along said surface. Subsequently, the fluid flows in the opposite direction into an annular gap (20) and, finally, out of the apparatus (1),via an outlet (23, 10). Thus, the outlet of the passage (15) in the flow distributing means (8) forms the inlet of the measuring member (12), whereas the annular gap (20) of the means (8) constitutes the outlet of the measuring chamber (12). The fluid thus moves in a closed system, and a radial flow is obtained in the measuring chamber.

Description

APPARATUS FOR MEASURING PARAMETERS IN A MOVING FLUID

The present invention relates to an apparatus for measuring parameters in a moving fluid, said apparatus comprising a hollow body with an inner measuring chamber through which the fluid moves, and a transducer disposed in said body and having an active part or active surface constituting a boundary wall of the measuring chamber.

When measuring different parameters in a fluid flow, one often wishes to make electrochemical analyses, to determine e.g. the content of oxygen in a moving gas or liquid solution by means of a measuring electrode. In this type of measuring in small-scale flow systems, e.g. in liquid chromatography, two requirements must be fulfilled if sufficiently accurate measurement results are to be obtainable. Firstly, the measurement chamber through which the fluid moves should usually be as small as possible, depending on the demands made upon the measuring, and secondly the flow should be uniformly distributed at the active part of the measuring electrode. One prior art electrochemical measuring electrode which, for instance, may serve to measure the partial pressure of oxygen in a fluid, is described in US-A-4,017,374. When measuring is to take place, the lower end of the electrode is placed in a corresponding recess having a measuring chamber to which the fluid is supplied via an inlet conduit and from which it is discharged via an outlet conduit. The measuring chamber is situated opposite to the free end of the electrode. However, no steps have been taken to make the measuring chamber as small as possible, or to obtain a uniform distribution of the fluid flow at the end of the electrode. Thus, this known apparatus does not fulfil the above-mentioned requirements.

One object of the present invention is to provide an apparatus for measuring parameters in a moving fluid, said apparatus having a small measuring chamber through which the fluid moves in such a manner that it is uniformly distributed with a large fluid turnover at the active part of the measuring means.

Another object of the invention is to make it possible, by changing the measuring means, to use the apparatus for measuring different parameters.

A further object of the invention is to give the apparatus only a few component parts which are easily assembled and disassembled for maintenance.

These and other objects that will become apparent from the following description have been achieved by means of an apparatus according to the invention, which is of the type described above and which is characterised by a flow distributing means disposed in said body and having a central through passage with a fluid inlet and a fluid outlet which forms the inlet of the measuring chamber, and an end surface which faces the active surface and is situated a short distance therefrom, the outlet of said passage being disposed in the end surface and essentially axially directed towards the centre of the active surface, said end surface constituting an opposite boundary wall of the measuring chamber and having a circumferential outlet substantially opposite to or radially outside the periphery of the active surface, thus producing a radial flow in the measuring chamber.

Preferred embodiments of the apparatus according to the invention are stated in the appended subclaims. The invention will be described in more detail below, reference being had to the accompanying drawings showing embodiments of the invention.

Fig. 1 is a view of an apparatus according to the invention, with some of its parts disassembled and in section.

Fig. 2 shows an apparatus of a somewhat modified design in the assembled state and cut open where the measuring takes place.

Fig. 3 is an enlarged view of a flow distributing means incorporated in the apparatus. Fig. 4 is a top plan view of the flow distributing means.

In Fig. 1, the general reference numeral 1 denotes an apparatus according to the invention for measuring parameters in a fluid which moves in a small-scale flow system and which, in this embodiment, is an oxygen-con¬ taining liquid. A measuring means or transducer disposed in a sleeve 2 is here in the form of an exchangeable measuring cell 3 for measuring the partial pressure of the oxygen in the liquid. The measuring cell 3 is of a type known per se, e.g. the one described in the above- mentioned US-A-4,017,374, and comprises an active part or active surface 4 which is in contact with the liquid flow when measuring takes place. An oxygen-pervious membrane (not shown) is stretched in known manner across the active surface 4; cf. the above-mentioned US patent.

The measuring cell 3 contains an anode, a cathode, and an electrolyte (not shown) in whichelectrically measurable changes occur when oxygen pervades the membrane stretched across the active surface 4. These changes generate signals which are sent to a measuring equipment (not shown) via conductors (not shown) enclosed in a cable 5.

The apparatus 1 also comprises a lower holder 6 having a bore 7 in which a flow distributing means 8 is disposed, said means being described in more detail below. The holder 6 has an inlet connection 9 and an outlet connection 10, by means of which the apparatus 1 is connected to flow lines (not shown) in the flow system where measuring is to take place.

The sleeve 2 and the holder 6 are assembled by means of a socket 11 which is mounted therebetween. The socket 11 preferably has an internal thread (not shown) which is screwed onto an external thread (not shown) on the holder 6, a construction that greatly simplifies dismantling of the apparatus 1 for cleaning. A particular advantage is that the flow distributing means 8 can be removed for cleaning, and said means is moreover exchangeable, which makes it possible to obtain different flow distributions by using different means. The sleeve 2 and the holder 6 may also be assembled in another manner by other coupling means (not shown). Fig. 2 shows an apparatus 1 according to the invention in a somewhat modified design and in the assembled state. A measuring chamber 12 through which the fluid moves, is defined between the surface 4 of the measuring cell 3 and the opposing end surface 13 of the means 8, situated a short distance from the surface 4. A sealing ring, 4 is arranged between the measuring cell 3 and the means 8. Thus, the measuring chamber 12 is defined by the surfaces 4 and 13, and the sealing ring 14.

The liquid flows through the inlet 9 and via a through passage 15 in the means 8 into the measuring chamber 12 where the flow is first directed axially against the active surface 4 and then is radially and uniformly distributed along said surface. There¬ after, the liquid flows in the opposite direction down through the means 8 and out through the outlet 10, as will be described in more detail below.

In Figs 3 and 4, the flow distributing means 8 is shown in detail. The means 8 comprises an elongated cylindrical column 16, through which the central through passage 15 extends. The column 16 is surrounded by a cylindrical tubular member 17 which, in this embodi¬ ment, is somewhat longer than the column 16, although this is not necessary. Preferably, however, the column 16 and the tubular member 17 are given approximately the same length. At its lower end, the column 16 has a thickened portion 18 sealingly connected to the inside of the tubular member 17, and an upper cylindrical thickened portion 19 defining, together with the inside of the tubular member 17, an annular gap 20 (see Fig. 4). The mid-portion 21 of the column 16 has a diameter considerably smaller than the inside diameter of the tubular members 17 and the outside diameters of the two thickened portions 18, 19, thus promoting the downward flow in the means 8. An annular elongated flow chamber 22 is thus defined 'between the mid-portion 21 of the column 16 and the inside of the tubular member 17, the liquid moving downwards in said chamber in a direction opposite to that of the flow in the through passage 15, and finally flowing out through an outlet 23 formed in the tubular member 17 and communicating with the outlet connection 10.

The passage 15 extending through the column 16 has an inlet 24 disposed centrally in the end surface of the lower thickened portion 18, and an outlet 25 dis¬ posed centrally in the end surface 13 of the upper thickened portion 19. The outlet 25 of the means 8 thus forms an inlet of the measuring chamber 12 (see Fig. 2), whereas the annular gap 20 forms the outlet of the measuring chamber 12, said outlet being situated essen¬ tially opposite to the periphery of the active surface 4 of the measuring cell 3. In an embodiment not shown, the gap 20 is situated radially outside the periphery of the active surface 4, in relation to the longitudinal axis of the measuring cell 3 and the apparatus 1 in its entirety.

Thus, the flow is first directed axially into the measuring chamber 12 against the active surface 4, subsequently radially outwards with respect to the passage 15, and then downwards in the gap 20 and into the flow chamber 22, to be finally discharged via the outlets 23 and 10. This means that the liquid is always circulating in a closed system. In order to promote the downward flow in the means 8, the flow chamber 22, as indicated above, has a far larger volume than the gap 20. The cross-sectional area of the gap 20 should be considerably larger than the cross-sectional area of the outlet 25 of the passage 15. The liquid flow at or inside the flow distributing means 8 is indicated by arrows.

In this manner, the dimensions of the measuring chamber 12 can be kept small. Depending on the axial extent of the sealing ring 14, the measuring chamber 12 can have different volumes, e.g. in the order of a few μl. Owing to the above-mentioned radial flow along the end surface 13 of the flow distributing means 8, an excellent flow distribution and flow turnover is obtained in the measuring chamber 12 before the active surface 4 of the measuring cell 3. It should here be pointed out that the surface 4 of the measuring cell 3 is advantageously flat and parallel to the end surface 13 of the means 8, said surface 13 preferably being mainly flat as well. Furthermore, these two surfaces 4, 13 advantageously have approximately equal areas.

In an embodiment not shown in detail, the flow distributing means 8 forms a part of the holder 6, in which case the tubular member 17 can be dispensed with, its functioning being taken over by the inside of the bore 7.

Finally, it should be observed that the exchangeable transducer by no means must be a cell for measuring oxygen; it may also consist of an ion-selective measuring cell, a pH electrode, a conductivity cell, or other means for measuring other parameters. Under certain conditions, it should also be possible to use the trans¬ ducer outside a flow system. For example, a pH electrode may, if constructed for this purpose, be applied directly to a surface, e.g. the human skin, for measuring para¬ meters. It should preferably be possible to use the same pH electrode in an apparatus according to the invention.

Finally, it should be pointed out that the invention is not restricted to the embodiment described above, and that a number of modifications are conceivable within the scope of the appended claims.

Claims

1. Apparatus for measuring parameters in a moving fluid, comprising a hollow body (2, 6, 11) with an inner measuring chamber (12) through which the fluid moves, and a transducer (3) disposed in said body and having an active member or active surface (4) constitut¬ ing a boundary wall of the measuring chamber, c h a r ¬ a c t e r i s e d by a flow distributing means (8) disposed in the body and having a central through passage (15) with a fluid inlet (24) and a fluid outlet (25) which forms the inlet of the measuring chamber (12), and an end surface (13) which faces the active surface (4) and is situated a short distance therefrom, the outlet (25) of said passage (15) being disposed in the end surface and essentially axially directed towards the centre of the active surface (4), said end surface constituting an opposite boundary wall of the measuring member (12) and having a circumferential outlet (20) substantially opposite to or radially outside the periphery of the active surface (4), thus producing a radial flow in the measuring chamber.

2. Apparatus as claimed in claim 1, c h a r ¬ a c t e r i s e d in that the outlet (20) of the measuring member (12) has a cross-sectional area which is considerably larger than the cross-sectional area of the outlet (25) of the passage (15).

3. Apparatus as claimed in claim 1 or 2, c h a r ¬ a c t e r i s e d in that the flow distributing means (8) comprises an elongated cylindrical column (16) through which the through passage (15) extends and which is surrounded by a cylindrical tubular member (17) of essentially the same length as the column (16) which at its inlet end has a first cylindrical thickened portion (18) sealingly connected to the inside of the tubular member (17) and, at its outlet end, a second cylindrical thickened portion (19), the diameter of which is smaller than that of the first cylindrical thickened portion (18) and which, together with the inside of the tubular member (17), defines an annular gap (20) forming said outlet of the measuring chamber (12), the portion (21) of the column (16) situated between said thickened portions having a diameter which is considerably smaller than the inside diameter of the tubular member (17) and forming an elongated annular flow chamber (22), in which the fluid moves in a direction opposite to that of the flow in the passage (15) and which, at the first thickened portion (18), has an outlet through the tubular member (17).

4. Apparatus as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the opposing surfaces (4, 13) of the transducer (3) and the flow distributing means (8) are flat and essentially parallel to each other, and mainly have equally large areas.

5. Apparatus as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that a seal (14) is arranged between the transducer (3) and the flow distributing means (8).

6. Apparatus as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that the volume of the measuring chamber (12) is in the order of a few μl.

7. Apparatus as claimed in any one of the preceding claims, c h a r a c t e r i s e d in that it comprises three mounting means, i.e. a sleeve (2) in which the transducer (3) is disposed, a hollow holder (6) in which the flow distributing means (8) is arranged, and a socket (11) for clamping the sleeve to the holder, while forming the measuring chamber (12) between the transducer (3) and the flow distributing means (8).