GB2250594A

GB2250594A - A method of temperature measurement and apparatus therefor

Info

Publication number: GB2250594A
Application number: GB9124670A
Authority: GB
Inventors: Philip John Thomas; Leslie Melbourne Barrett; James Alan Mcknight
Original assignee: UK Atomic Energy Authority
Current assignee: UK Atomic Energy Authority
Priority date: 1990-11-20
Filing date: 1991-11-20
Publication date: 1992-06-10
Also published as: GB9124670D0; GB9025194D0

Abstract

The temperature of a liquid in a gas/vapour/liquid contacting column 10 is determined by applying an ultrasonic signal directed by a waveguide 22 external to the column, and processing the reflected or transmitted signal to determine the velocity of the signal in the liquid. The signal may be reflected by a tray in the column and may be in the form of pulses. <IMAGE>

Description

A Method of Temperature Measurement and Apparatus Theretor This invention relates to a method of measuring the temperature of a liquid by means of ultrasound.

It is known that the velocity of sound in a medium, particularly a liquid is a function of the temperature of the liquid. Hence a measurement of the velocity of sound in the liquid can be used to derive the temperature of the liquid (Krautkramer et al - Ultrasound Testing of Materials, 2nd Ed. 1977 PS8S-6). GB Patent 2 129 130 describes an application of this principle.In the arrangement described, pulses of ultrasound are passed through a pipeline which carries alternately fluids at different temperatures and the change-over from one fluid to the other is detected according as to whether pulses of ultrasound are detected or not by a receiving transducer which is gated to be operative at a time interval after a given input pulse corresponding to the velocity of sound in the fluid at the selected temperature, but not that at the other temperature, thereby to detect the presence or absence of the selected fluid.

The present invention is concerned with the application of this principle for measuring the temperature of a liquid contained within a gas/vapour/liquid contacting column of the tray type such as a chemical distillation column.

According to the present invention there is provided a method of measuring the temperature of a liquid in a gas/vapour/liquid contacting column having contacting trays therein, the method comprising applying an ultrasonic signal to a waveguide located at the outside of the column and integral therewith directing the signal through a liquid in the column, receiving the signal, and processing the signal to determine the velocity of the ultrasonic signal in the column and thereby the temperature of the liquid medium therein.

The ultrasonic signal may be arranged to intersect a portion of a said tray and be reflected therefrom to a receiver for the ultrasonic signal. Alternatively, a receiver may be located at the other side of the column opposite the waveguide.

Advantageously, there may be a plurality of receivers ~~dispërsed along and around the -column, The invention in another aspect provides a gas/vapour/liquid contacting column having contacting trays therein, wherein there is provided at least one ultrasonic waveguide arranged to direct signals generated by an ultrasonic transducer into a liquid medium in the column, means for receiving ultrasonic signals after they have traversed the liquid medium and means for processing the received ultrasonic signals to determine the velocity of the ultrasound in the liquid medium and hence its temperature.

The invention will now be further described with reference to the single Figure of the accompanying drawing which shows a diagrammatic sectional representation of part of a chemical distillation column.

Referring now to the Figure, part of a chemical distillation column 10 is shown having a tubular metal wall 12 and a number (only three are shown) of conventional transverse trays 14 axially displaced inside the column 10 at a number of stages. The trays 14 extend from one side of the wall 12, and have a side wall 15 that defines a respective gap 16 with the other side of the wall 12. The trays 14 are in off-set relationship so that alternate trays 14 extend from opposite sides of the wall 12. Each tray 14 has a number of conventional one-way valves or bubble-caps 18 upstanding therefrom.

A waveguide in the form of a metal rod 22 is welded to the outside of the wall 12 opposite one of the bubble-caps 18 of a tray 14. An ultrasonic transducer 24 is bonded to the end 26 of the rod 22 and is connected by a mineral insulated cable 28 to an electric power supply (not shown).

In operation, gas/vapour passes upward through the column 10 and liquid 29 passes downward, some liquid 29 being retained in each tray 14. The gas/vapour passes through the respective bubble-caps 18 into the liquid 29 in each tray 14 forming bubbles 30 in the liquid 29, surplus liquid 29 overflowing from the trays 14. An ultrasonic signal is transmitted from the transducer 24 through the waveguide 22 and the wall 12 into the liquid 29 along path 1D1 shown in the Figure where it is reflected from the respective bubble-cap back to the transducer 24.

Analysis of the returned ultrasonic signal enables the velocity of sound in the liquid to be determined given the distance between the transducer 24 and the bubble-cap 18.

One method of doing this is to pulse the ultrasonic transducer 24 and measure the time taken for the echo to be returned. Another method is to emit continuous or long pulses of ultrasound, and to modulate the frequency or phase of the ultrasound in a controlled manner, a simultaneous comparison between the transmitted and received signals enabling the sonic velocity to be deduced.

Given the velocity of sound, and a calibration for the liquid involved, the temperature of the liquid can be calculated.

The transducer 24 is of a special construction known as a "Solid Coupled Probe" (hereinafter referred to as ("SCP"). The SCP consists of an integral assembly of a sensitive piezo-electric or electro-strictive element bonded to the end of the rod 22. The element is usually housed (not shown) and the housing is integral with the mineral insulated cable 28. One special feature of the SCP is that it is possible to weld the entire assembly onto the outside of the column 10 in one operation.

Although the ultrasonic signal transmission path 'D' is chosen to minimise interference from bubbles 30 in the liquid, it is inevitable that some will be present. The presence of bubbles 30 in the liquid may be dealt with in two ways. Firstly, the frequency of the ultrasound is chosen so as to be high enough not to excite the resonance of any of the bubbles 30. Frequencies in the range 1-5 MHz are generally satisfactory. At this high frequency, the bubbles 30 will not affect the velocity of sound, but may interrupt the ultrasonic beam and scatter its energy.

However, the motion of the bubbles 30 is statistical, and there will be occasions when the ultrasonic beam is not interrupted. With a typical pulse repetition rate, for example, of 400 per sec, it would only be necessary for 0.25% of the pulses to be successful to achieve a measurement every second. A digital signal processing apparatus can then handle the received signals and distinguish the successful reflections against spurious echoes from the bubbles 30.

Although the invention has been described in relation to using the same transducer to transmit and receive the ultrasonic signal, the signal may be received by another transducer.

Instead of using one SCP and relying on reflection of the ultrasonic signal, two SCP's 32, 34 respectively may be welded to the outside of the wall 12 in diametral relationship to define a path between them through the liquid 29 and the respective tray 14. Ultrasonic signals can then be timed in both directions. Data from such an arrangement can be processed to yield independently the flow velocity vector of the liquid 29 in the direction of the sonic path, as well as the temperature of the liquid 29.

Several SCP's may be welded along and around the wall 12, the positions thereof being chosen so that an ultrasonic signal pulse from one transducer can be detected by all the other transducers. Processing of the received pulses by tomography provides a temperature distribution plot in the plane of the transducers.

It will be understood that the invention also includes apparatus for performing the method of the invention, the apparatus comprising at least one transducer means weldable to a metal wall of a gas/vapour/liquid contacting column having contacting trays therein, the transducer means being arranged to transmit ultrasonic signals into the column, and means for processing signals received by the transducer means.

Claims

1. a method of measuring the temperature of a liquid in a gas/vapour/liquid contacting column having contacting trays therein, the method comprising applying an ultrasonic signal to a waveguide located at the outside of the column and integral therewith directing the signal through a liquid in the column, receiving the signal, and processing the signal to determine the velocity of the ultrasonic signal in the column and thereby the temperature of the liquid medium therein.

2. A method according to Claim 1 wherein the ultrasonic signal travelling through the fluid is arranged to intersect a portion of a tray and be reflected therefrom to a receiver for the ultrasonic signal.

3. A method according to Claim 1 wherein the ultrasonic signal is arranged to travel through the fluid to a receiver for the ultrasonic signal positioned opposite the waveguide.

4. A method according to Claim 1, Claim 2 or Claim 3 wherein the ultrasonic signal is in the form of pulses.

5. A method according to any of Claims 1 to 3 wherein the ultrasonic signals are generated continuously or quasi-continuously, a parameter of the ultrasonic signal is varied continuously and the values of that parameter in the transmitted and received signals are compared simultaneously to determine the time which has elapsed since any particular part of the received signal was generated thereby to determine the velocity of the ultrasound in the fluid.

6. A method according to any preceding claim wherein the frequency of the ultrasonic signal is such that resonance is not excited in any bubbles which may be present in the liquid.

7. A method according to Claim 6 wherein the frequency of the ultrasonic signal is in the range 1-5 MHz.

8. A method according to Claim 4 wherein the pulse repetition rate is 400 per second.

9. A method according to any preceding claim wherein there is included the operation of measuring the velocity of liquid flowing in the column.

10. A gas/vapour/liquid contacting column having contacting trays therein, wherein there is provided at least one ultrasonic waveguide arranged to direct signals generated by an ultrasonic transducer into a liquid medium in the column, means for receiving ultrasonic signals after they have traversed the liquid medium and means for processing the received ultrasonic signals to determine the velocity of the ultrasound in the liquid medium and hence its temperature.

11. A column according to Claim 10 wherein the arrangement is such that the ultrasound is reflected from a portion of one of the trays to a receiving transducer.

12. A column according to Claim 11 wherein the arrangement is such that the transducer for generating ultrasonic signals also operates as the receiving transducer.

13. A column according to claim 10 wherein there is provided means for measuring the temperature of the liquid medium at a plurality of positions in the column.

14. A method of measuring the temperature of a liquid medium in a gas/vapour/liquid contacting column having contacting trays therein substantially as hereinbefore described and with reference to the accompanying drawing.

15. A gas/vapour/liquid contacting column having contacting trays therein including means for measuring the temperature of a liquid medium therein substantially as hereinbefore described and with reference to the accompanying drawing.