GB2314161A

GB2314161A - Detecting liquid flow in a pipe subjected to freeze blocking or heating

Info

Publication number: GB2314161A
Application number: GB9612075A
Authority: GB
Inventors: Trevor Hallett
Original assignee: Freeze Master Ltd
Current assignee: Freeze Master Ltd
Priority date: 1996-06-10
Filing date: 1996-06-10
Publication date: 1997-12-17
Also published as: GB9612075D0

Abstract

A method of detecting liquid flow in a pipe 20 subjected to freeze blocking or heating comprises determining by means of temperature probes 10, 12 the temperature upstream and downstream of the section 22 of the pipe 20 at which heat is added to or removed from the liquid. The difference between the two temperatures indicates whether the liquid in the pipe is flowing and, if so, in which direction. The method may also be used to determine the strength of any liquid flow. If liquid is flowing slowly through the section 22 to be, for example, frozen, it will become cooled, such that the probe 12 downstream of the section 22 will record a lower temperature than the probe 10 which is positioned upstream. Therefore, an immediate indication of liquid flow and its direction can be obtained. The disclosed method is relatively cheap and simple, but highly effective for providing an indication of liquid flow and the direction of such flow, for pipe freezing or heating techniques.

Description

Pipe Freezing The present invention relates to pipe freezing apparatus, and in particular to a method for indicating the presence and direction of flow of liquid within a pipe, prior to freezing thereof.

EP-A-O 145114 describes a pipe freezing apparatus which is particularly suited to freezing water in pipes, to enable a pipe to be cut without draining the system. .A freezer head is attached to the pipe to each side of the region to be worked on, and plugs of frozen water are formed in the pipe, at the location of the freezer heads. The freezer heads constitute expansion chambers, liquid refrigerant being pumped (or drawn) into the chamber and evaporating in the chamber to cool the chamber walls. This arrangement is well known.

A pipe freezing apparatus such as that described above operates by extracting heat energy from a small section of water. However, flowing water continually carries a replacement source of energy to the point being frozen. It is therefore impractical to attempt to freeze a fully flowing pipeline.

Pipe freezer manufacturers usually specify the amount of time it takes to freeze the water in a section of a pipe. However, such freeze times are based upon water which is cold and stationary. Unfortunately, the plumber or heating engineer has no control over these conditions until arriving at the job. Even if the heating and water pump have been switched off for many hours, water may still be moving slowly around the system.

Furthermore, although the water may have cooled down substantially, it may still be hot with respect to the pipe freezer manufacturerls specifications, such that it will take substantially longer to freeze the water than the time specified by the pipe freezer manufacturer. For instance, water at a temperature of 40 OC will take twice as long to freeze as water at 20 "C. Furthermore, warm water within the system will rise and displace cooler water, since hot always travels to cold.

Finally, it will be recognised when freezing a pipe that if the water temperature is 20 "C and the freeze head is -40 "C, there is a 60 "C temperature difference. Such differences in temperature can cause a natural thermo-cycle such as that in a heating system.

Obviously, more energy is required to freeze a warm or hot pipe than is required to freeze a pipe which is already relatively cold. Furthermore, in a gas pipe freezing kit, the gas is contained in an insulating jacket, which may hold heat within the pipe such that freezing the water takes even longer. If the water is still moving, or a thermocycle motion has been set up, it may not be possible extract all of the cycling heat from the water before the gas runs out.

Even in the case of an electric pipe freezing arrangement, such as in EP-A - 0145114, which will continue to run until sufficient heat is extracted to freeze the water in the pipe, it would be desirable to know if the water is flowing and, if so, in which direction such that the specified freeze times can be adjusted accordingly.

There are several pipeline flow detectors or indicators currently available. Such detectors usually operate by means of ultrasonic or radar emitters or sensors.

Alternatively, some known detectors rely on bubbles in the liquid in order to detect movement. Known pipeline flow detectors may be used as an effective method of flow measurement, but such detectors are relatively expensive and can be complicated and time-consuming to use.

We have now devised a method which seeks to overcome the problems outlined above.

In accordance with the present invention, there is provided a method of detecting the presence and direction of liquid flow within a pipe to be subjected to freeze blocking or heating, the method comprising the steps of: detecting the temperature of the liquid in the pipe at a position upstream of the section of liquid to be frozen or heated; detecting the temperature of the liquid in the pipe at a position downstream of the section of liquid to be frozen or heated; and determining the presence and direction of liquid flow on the basis of the difference between the two detected temperatures.

The temperature at one position may be determined a predetermined time interval after the temperature at the other position has been determined. Alternatively, the temperature on both sides of the section of liquid to be frozen or heated can be detected substantially simultaneously. In either case, the temperature may be determined by means of for example digital temperature probes. Thus, the present invention provides a relatively cheap method of detecting liquid flow. More importantly, the present invention provides a relatively simple method of detecting the direction of any liquid flow. This is highly advantageous, particularly when performing work on a large or unknown installation.

The present invention is not intended to indicate the rate of liquid flow. It is merely intended to provide an indication that liquid in the pipe is flowing, and in which direction the liquid is flowing. The method of the present invention may also be arranged to indicate the strength of liquid flow. Thus, the present invention provides a relatively cheap and simple method which is highly suitable for use in pipe freezing or heating techniques.

The method may include the step of indicating the strength and direction of liquid flow on display means, consisting of, for example, a centre zero moving coil, and a needle for indicating the strength and direction of any liquid flow. Alternatively, the indicator means may include a series of light emitting diodes (LED's), each LED being arranged to operate in sequence. In this case, the display means may be arranged such that the speed at which the LED operation sequence occurs indicates the strength of liquid flow, while the direction of the sequence operation indicates the direction of flow.

Also in accordance with the present invention, there is provided an apparatus for detecting liquid flow in a pipe to be subjected to freeze blocking or heating, the apparatus comprising temperature detecting means for detecting the temperature of liquid in the pipe at a position upstream of the section of liquid to be frozen or heated, temperature detecting means for detecting the temperature of liquid in the pipe at a position downstream of the section of liquid to be frozen or heated, and means for determining the presence and direction of liquid flow on the basis of the difference between the two detected temperatures.

Embodiments of the present invention will now be described by way of example only and with reference to the accompanying drawings, in which: Figure 1 is schematic diagram illustrating the method and apparatus of the present invention; Figure 2 is a schematic diagram of a first embodiment of a display means for use in the method described with reference to Figure 1; and Figure 3 is a schematic diagram of an alternative display means for use in the method described with reference to Figure 1.

With reference to Figure 1 of the drawings, there is shown apparatus for detecting the presence and direction of liquid flow within a pipe to be subjected to freeze blocking comprising first and second digital temperature probes 10, 12. Each probe 10, 12 comprises a temperature detecting section 14 at one end, the opposite end being connected to an input of an indicator module 16.

In use, a freeze head 18 is attached to a section of a pipe 20 containing liquid, in order to freeze a section of the liquid. A temperature probe 10, 12 is placed on either side of the section 22 to be frozen, at substantially the same distance from that section.

The probes measure the temperature of the liquid at positions upstream and downstream respectively of the section 22 to be frozen, the measured temperature at both positions being input to the indicator module 16. If the liquid is moving slowly through the pipe, then as it passes through the section being frozen, it will be cooled.

Thus, the temperature probe which is situated downstream of the flow will measure a lower temperature than that upstream, and give an immediate indication of liquid flow and its direction.

The indicator module may include means for calculating the temperature difference first, in which case the presence and direction of liquid flow would be determined on the basis of the calculation. This information is displayed on display means 24.

Alternatively, the indicator module may include a comparator, the outputs of the temperature probes 10, 12 forming the inputs of the comparator. The output of the comparator would in this case be applied directly to the display means 24 which displays the size and direction of the temperature difference, thereby indicating the presence and direction of liquid flow.

With reference to Figure 2 of the drawings, the display means may comprise a centre zero moving coil 26 housed within the indicator module 16. Movement of a needle 27 indicates the strength and direction of liquid flow.

With reference to Figure 3 of the drawings, the display means may alternatively comprise a series of light emitting diodes (LED's) 28, each LED being arranged to operate in sequence. In this case, the display means is arranged such that the speed at which the LED operation sequence occurs indicates the strength of liquid flow, while the direction of the sequence operation indicates the direction of flow.

While the present invention has been described with reference to freeze blocking, it will be appreciated that the method and apparatus of the present invention can be used to determine the presence and direction of liquid flow in a pipe which is to be heated.

In the light of this disclosure, modifications of the described embodiments, as well as other embodiments, all within the scope of the present invention as defined by the appended claims, will now become apparent to persons skilled in the art.

Claims

CLAIMS:

1. A method of detecting liquid flow within a pipe to be subjected to freeze blocking or heating, the method comprising the steps of: detecting the temperature of the liquid in the pipe at a position upstream of the section of liquid to be frozen or heated; detecting the temperature of the liquid in the pipe at a position downstream of the section of liquid to be frozen or heated; and determining the presence and direction of liquid flow on the basis of the difference between the two detected temperatures.

2. A method according to claim 1, wherein the temperature at one of the positions is determined a predetermined period of time after the temperature at the other position has been determined.

3. A method according to claim 1, wherein the temperatures at both positions are determined substantially simultaneously.

4. A method according to any preceding claim wherein the temperature is determined by means of digital temperature probes.

5. A method according to any preceding claim, further comprising the step of indicating by means of indicator means the presence and direction of liquid flow.

6. A method according to claim 5, further comprising the step of indicating the strength of liquid flow.

7. A method of detecting liquid flow substantially as herein described with reference to the accompanying drawings.

8. Apparatus for detecting liquid flow in a pipe to be subjected to freeze blocking or heating, the apparatus comprising temperature detecting means for detecting the temperature of liquid in the pipe at a position upstream of the section of liquid to be frozen or heated, temperature detecting means for detecting the temperature of liquid in the pipe at a position downstream of the section of liquid to be frozen or heated, and means for determining the presence and direction of liquid flow on the basis of the difference between the two detected temperatures.

9. Apparatus according to claim 8, wherein said temperature detecting means comprise digital temperature probes.

10. Apparatus according to claims 8 or 9, further comprising indicating means for indicating the presence and direction of liquid flow.

11. Apparatus according to claim 10, wherein said indicating means are arranged to indicate the strength of liquid flow.

12. Apparatus according to claims 10 or 11, wherein the indicating means includes display means comprising a centre zero moving coil and a needle for indicating liquid flow.

13. Apparatus according to claims 10 or 11, wherein the indicating means includes display means comprising a series of light emitting diodes, the sequence of operation of which indicates characteristics of any liquid flow.

14. Apparatus for detecting liquid flow substantially as herein described with reference to the accompanying drawings.