GB2201001A

GB2201001A - Fluid flow measurement

Info

Publication number: GB2201001A
Application number: GB08807839A
Authority: GB
Inventors: Gunther Weber
Original assignee: Individual
Current assignee: Individual
Priority date: 1984-05-25
Filing date: 1988-04-05
Publication date: 1988-08-17
Also published as: GB8513239D0; DE3419504A1; GB2216846A; GB2201001B; GB2159631A; GB8807838D0; GB8807839D0; GB2159631B

Description

1 M 1 FLOW MONITOR 2 0 10 0 1 The invention relates to a flow monitor

comprising a heat-conducting element of which a first portion is exposed to a flowing medium and a second portion, spatially separated from the first, has both a thermal element of predetermined heat capacity altering the temperature of the heat-conducting element so that it. differs from the temperature of the medium, and also a measuring element sensing its temperature.

In such flow monitors that end of the heat-conducting element which is nearer the flowing medium projects through a wall (e.g. the wall of a pipe) into the path of the f low. In many cases this can have an effect on the flow; eddies arise the path of the flow and these eddies may well upset the flow significantly. In particular with small cross-sections the flow may recover to a smooth state only relatively slowly following the disturbance..

Moreover the formation of eddies can cause errors of measurement since more heat is extracted by or from the element by a turbulent flow than by a smooth laminar flow, undisturbed by anything projecting into it. In addition the end which projects into the flow gives rise to a sealing problem in that it projects through, a wall which separates the flowing medium from the heat-conducting element and the meas'uring element and the end must be sealed to the wall in a m anner which is effective and lasting. This seal is a potential source of trouble and also adds Appreciably to the cost.

Accordingly it is the aim of the present invention to improve the flow monitor of the kind stated- in the introduct ion in such a way that it can be installed with an outlay which is as low as possible and gives the minimum of trouble.

c 1 2 According to first aspect of the invention a flow monitor - for measuring the flow of fluid through a pipe is provided comprising, (a) a thermal element of predetermined heat capacity secured at the outside surface of the pipe and capable of changing the temperature of a region of the, pipe within its thermal influence, (b) the region of the pipe itself that is within the thermal influence of the thermal element, and, (c) a measuring element capable_ of producing an electrical signal indicative of its temperature secured at the outside surf ace of the pipe in thermal contact with the pipe and within the region of thermal influence of the thermal element, at least the region of the pipe within the thermal influence of the thermal element being of ceramic material.

The flowing medium flows directly past one face of the wall of the pipe. Between the wall and the medium there is accordingly a very intimate contact. There is an exchange of heat between the medium and the wall almost regardless of the material of the wall. The measurement of the flow does not depend on the magnitude of the heat conduction but only on the change in the amount of heat conducted as a result of changing -flow relationships. This means, in fact, that one can use as the heat conducting element wall a material of relatively bad thermal conductivity, such as ceramic, for example. Furthermore the use of theawall itself as the heat conducting element has the important advantage that the wall does not have to be interrupted in order to mount a separate heat conducting element in contact with the flow. On the contrary both the thermal element and also the measuring element are mounted directly on that face of the wall which is away from the flow. Accordingly the above-mentioned sealing p:oblems are totally eliminated.

The costs involved in providing the opening in the wall can be saved as well as the cost of the seal itself.

a IS F4 1 I- 3 The thermal element and the measuring element are both secured on that surface of the wall which faces away from the medium. This can be done without damaging the wall, for example by 'the use of adhesive mounting means, such as adhesive strips, to secure both the thermal element and the measuring element to the. wall. All that is necessary is to take care that the spatial separation between the thermal element and the measuring element is relatively small. Preferably the measuring element is mounted downstream of the thermal element, looked at in the direction of flow of the medium.

Further details of the invention are revealed in the following detailed description and accompanying drawing's, in which a preferred embodiment-of the invention by way of example is illustrated.

In the drawings:

Figure 1 is a side view of a section of pipe with a measuring element arranged adjacent to a thermal element, Figure 2 is a side view of a section of pipe with an additional thermal element which is secured next to the measuring element, Figure 3 is a, side view of a section of pipe with a first and second measuring element and with a thermal element mounted in the neighbourhood of the first measuring element, Figure 4 shows an enlarged cross-section through a wall with a measuring. element secured to the wall and a thermal element mounted over the measuring element.

- 4r k, 4 The flow monitor. illustrated comprises substantially a thermal element 1 and -a measuring element 2, both secured to a wall 3. This wall 3 can be in the form of the wall of a pipe 4. A flowing medium 5 flows inside the pipe along one face 6 of the wall 3.

On a second face 7 of the wall 3, opposite the face 6., are mounted the thermal element 1 and the measuring element 2. The measuring element 2 is present in the immediate neighbourhood of the thermal element 1 so as to be within the zone of influence of the heating effect exerted by the element 1. Advantageously the measuring element 2 is placed downstream of the thermal element 1, looked at in the direction of flow of the medium 5. However it would also be possible to envisage mounting the measuring element 2 upstream of the thermal element 1, The thermal element 1 can be formed either as a heating element or as a cooling element.Where- it is a heating element it can act as a heat transfer medium to transmit indirectly to the wall 3 the heat which is supplied to it from another body in a known controlled manner. It is however also possible for the thermal element to be formed by an actual heating element, for example in the form of an electric heater. ' Thd electric heating element may be in the form of a wirewound heating resistor or thick film resistor-.

The measuring temperature-dependent thermo-electric element element 2 resistor could be a (thermistor), a or a temperature-dependent semiconductor. The essential feature of whatever measuring element is used is that it is able to respond elCctrically to the changes in temperature in the flowing medium 5 which arise when the thermal element 1 is switched on, - so that the change in temperature detected as an electrical signal.

In the embodiments of Figures I to 3 -the heat 5 produced by -the element I is transmitted directly to the wall 3. From the wall the heat flows into the flowing medium 5. The influence which the thermal element I exerts on the measuring element 2 when there is no f low is known. With the fluid stationary the transfer of heat from the thermal element I to the measuring element 2 is not influenced by the flowing medium. Then, when the medium 5 is set in motion, the flow causes a change in the amount of heat extracted by it from the wall 3. This causes the temperature of the wall to fall. This change in temperature is detected by the measuring element 2 and represents medium 5.

a measure of the amount of flow of the As the velocity of flow increases the temperature in the region of the measuring element 2 falls further, and it is possible to calibrate the monitor so f - that the magnitude of the electrical signal gives a measure of the rate of flow of the medium through the pipe.

Dependent on the magnitude of the velocity of flow a 25_ second thermal element may be attached to the wall 3 in addition, downstream of the measuring element 2, This second thermal element 8 likewise has a predetermined heat capacity or output, The provision of this second element 8 improves the ability of the measuring element 2 to pick up clear changes of temperature resulting from the changes in velocity of the flowing medium 5.

It is possible further to envisage mounting a second measuring element 9 on the wall 3 at a more or less substantial distance away from the element 2, this second measuring element being used simply. to measure the 6 temperature of the flowing medium 5. In this way one can detect any changes in the temperature of the flowing medium 5 which are occurring independently of the influence of the thermal element 1.. If it should change, a corresponding correction factor must be applie d to the results of the measurement by the element 2, so that the accuracy of the measurement of flow is independent of the absolute temperature of the medium.

The thermal element 1 could equally well be in the form of a cooling element. Decisive only is the fact that heat is either transmitted from the element 1 to the flowing medium 5 or extracted from the medium by the element 1. In the one case, therefore, the temperature of the thermal element 1, when it is in the form of a heating element, must lie above the temperature of the flowing medium 5, whereas when the element 1 is in the form of a cooling element the temperature of the flowing medium 5 must lie above the temperature of the cooling element.

Finally it is Possible to envisage mounting the measuring element 2 at the same point as the thermal element 1 in relation to the flow of the medium 5. With this aim in mind the measuring element 2 is pressed against the second face 7 of the wall 3 by a retainer 10. The thermal element 1 and its mounting 11 are then secured to that face of the retainer 10 which is away from the measuring element 2. This mounting 11 holds the thermal element 1 against the retainer 10. The measuring element 2 has electric terminals 12,13 projecting clear of the retainer PO.

i After the thermal element 1 has been switched on and everything has reached a steady state a predetermined steady flow of heat takes place through the retainer 10 and the measuring element 2 and on through the wall 3 IQ 11 t r 7 towards the f lowing medium 5. The surface temperature at the second f ace 7 under these conditions is measured by the element 2. Then the medium 5 is set in motion. Under the influence of this flow the temperature at the second face 7 changes. This change in temperature is measured by the element 2. It is a measure of the magnitude of the velocity of flow of the medium 5.

Instead of by the use of appropriate adhesive strips, the measuring element 2 and the thermal element 1 could also be secured to the second face 7 directly or in some other way. It is also possible to envisage using the thermal element 1 itself to secure the measuring element 2 to the second face 7. -In a modification the thermal element could be sandwiched between the measuring element and the face 7.

The wall 3 can be made of any material suitable for the formation of walls, for example of ceramic or metal.

Both the retainer 10 and the mounting 11 could be made of a good thermal conductor. Where the wall is that of a pipe the thermal element 1 and the measuring element 2 (and also the second heating element 8 and the second measuring element 9 where present) could be wound around the pipe 4. In this manner a. particularly simple manufacture of the flow monitor ispos'sibl6. The different elements, and any necessary electrically insulating layers (where, for example, the pipe is of metal) could be deposited by known printing, electro-deposition or thick film techniques.

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Claims

1.. A flow monitor for measuring the flow of fluid through a pipe comprising, (a) a thermal element of predetermined heat capacity secured at the outside surface of the pipe and capable of changing the-temperature of a region of the pipe within its thermal influence, (b) the region of the pipe itself that is within the thermal influence of the thermal element, and, (c) a measuring element capable of producing an electrical signal indicative of its temperature secured at the outside surface of the pipe in thermal contact with the pipe and within the region of thermal influence of the thermal element, at least the region of the pipe within the thermal influence of the thermal element being of ceramic material.

2. The flow monitor according to claim 1 wherein the thermal element and the measuring element are superposed, one overlying the other.

3. A flow monitor according to claim 2, in which the measuring element lies between the pipe and the thermal element.

4. A flow monitor _according to claim 1 or claim 3, in which the measuring element is secured to the pipe by a retainer.

5. A flow monitor according to claim 4 as dependent on claim 3 in which the thermal element is secured to the retainer.

6. A flow monitor according to claim 5 in which the thermal element is secured to the retainer by a mounting of good heat- conducting properties.

It 1 1 1 2 j v I,1 9

7. A flow monitor according to any one of claims 1 to 6, in which the thermal element is secured to the outside surface of the pipe by an adhesive mounting.

8. A f low monitor according to any one of claims 1 to 7 in which the measuring element is secured to the outside surface of the pipe by an adhesive retainer.

9. A flow monitor according to claim 1 in which there is 10 but a single measuring element.

10. A flow monitor according to claims 1, 4, 7, 8, in which the measuring element is arranged immediately downstream of the thermal element looked at in the direction of flow of the flowing medium.

11. A flow monitor apcording to any preceding claim in which a second measuring element, measuring the temperature of the flowing fluid itself, is.provided at the outer surface of the pipe.

12. A flow monitor according to claim 11, in which the second measuring element is outside the thermal influence of the thermal element.

13. A flow monitor according to any preceding claim in which the thermal element is in the form of a heating element.

14. A flow monitor according to any one of claims"l to 12 in which- the thermal element is in the form of a cooling element.

15. A flow monitor according to any preceding claim in which the- thermal element is wound around the pipe.

16. A f low monitor according to any preceding claim in which the measuring element-is wound around the pipe.

17. A f low monitor according to any preceding claim in which the thermal element is in the form of a heat transfer body of predetermined capacity secured to the pipe.

18. A flow monitor according to any one of claims 1 to 16, in which the thermal element is in the form of an electric heater.

19. A f low monitor according to claim 18, in which the electric heater is in the form of a wound heating resistor.

20. A flow monitor -nccording to claim 18, in which the electric heater is in the form of a thick film resistor.

21. A flow monitor according to any preceding claim in which the measuring element is in the form of a temperature-dependent resistor.

22. A flow monitor according to any one of claims 1 to 20, in which the measuring element is in the form of a thermo-electric element.

23. A flow monitor according to any one of claims 1 to 20, in which the measuring element is in the form of a temperature-dependent semiconductor.

24. A flow monitor according to any preceding claim in which a second thermal element is provided downstream of the measuring element, as viewed in the direction of flow of the flowing fluid.

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414, i 11 J

25.. - A flow monitor substantially as described with reference to Figure 1 of the accompanying drawings.

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26. A flow monitor substantially as described with reference to Figure 2 of the accompanying drawings.

27. A flow monitor substantially as described with reference to Figure 3 of the accompanying drawings.

28. A f low monitor substantially as described with reference to Figure 4 of the accompanying drawings.

is A pvollshed 1955 at The Patent Mce. STAt,- House. 66 71 Mgh Holborn. Lo"don WCIR 4TP, Further ooples mkv be ob=Ied frorn The Patent O:nce. Sales Branc!',. St Me-3, Cray. Orpington, Kent BR5 3RD Printed by Mjltjplex techniques ltd. St Mary Cray, Kent Con. 1187.

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