Methods

Technical Field

The present invention relates to a device (in other words, an instrument or probe) for measuring viscosity and/or temperature, and to related apparatus. The present invention also relates to corresponding methods of measuring viscosity and/or temperature. More particularly, the present invention relates to said measuring viscosity and/or temperature using ultrasound.

Background

Viscosity is a key fluid property that is of importance in many industrial and engineering applications. Viscosity can be measured in many ways. Prominent examples include falling ball viscometers, viscosity cups, transit time in-glass capillaries, tuning fork resonance-based methods and rotation and torque-based measurement methods. While many of these examples are cheap and easily implemented, they don’t lend themselves to industrial applications where fast, online measurement (i.e., non-disruptive or non-intrusive measurement, for example a measurement carried out in ‘real time’ in a production line, without the need for perturbing or stopping the production line, without specific preparations other than the predisposition of an appropriate measuring instrument) on small volumes of fluid is required.

In industrial applications, ultrasonic viscosity measurement methods can be of advantage as they can be performed in time periods that only span a few microseconds. Further, they can be carried out on small volumes of fluid, without causing pressure drops in the flow medium and without the need for moving parts. While there are many different ultrasonic methods that measure material properties such as viscosity, not all of them are suitable for online measurement in harsh environments. For example, reflection-based methods that measure viscosity on the basis of ultrasonic reflection from an interface between a solid and a fluid, or from a thin layer of fluid, have been described in scientific literature. However, these methods require a transducer to be in contact with a solid, which can break the transducer if the measurement is carried out in a harsh environment. Further, these methods only probe said interface, or a small volume of the fluid. These methods may thus not be suited to the requirements of at least certain industrial applications. There are also surface acoustic wave- type devices, which again need to be in close contact with the fluid and therefore can easily break and malfunction in harsh environments.

The present invention provides one or more improvements in relation to ultrasonic measurement of viscosity and/or temperature in fluids, which improvements may be advantageously used to satisfy the requirements of at least certain specific, industrial applications.

The present invention aims to overcome at least one drawback associated with the prior art.

Overview of the Invention

This overview introduces concepts that are described in more detail in the detailed description. It should not be used to identify essential features of the claimed subject matter, nor to limit the scope of the claimed subject matter.

The present disclosure relates to the construction of a novel, practical ultrasonic viscosity and/or temperature probe (or, in other words, an ultrasonic viscosity and/or temperature measurement instrument or ultrasonic viscosity and/or temperature measurement device) for fixation to a fluid- containing structure or recipient, and for insertion into a measurement medium, or fluid, such as pressurised fuel in fuel delivery lines for marine propulsion systems.

The measurement device comprises an ultrasonic waveguide for measuring viscosity and/or temperature, and an attachment for mechanical fixation and sealing of the waveguide to a fluid- containing recipient. A seal is formed which seals, and may optionally locate, at least a portion of the waveguide in the attachment. The attachment may comprise a protective tube, and the waveguide may be sealingly received within the protective tube.

The device may further comprise a compression fitting that may be used to easily install the measurement device with a measurement length of the waveguide immersed at the right depth and orientation into the measurement medium, for example by connection to a standard pipe, such as to a piping T-piece or boss.

It is desirable to isolate a measurement length of the waveguide, that is the portion of the waveguide immersed in the fluid, from a relatively fragile wave-generating transducer in scenarios where high temperature and/or high-pressure liquids are used. The measurement device may thus function, for example, at temperatures around 150°C, and/or pressures around 30bar. However, higher or lower temperatures and pressure are also possible.

The measurement device may be used to measure temperature of the measurement medium based on transit time of ultrasonic waves between two reference reflectors (one of which may be at the end of the waveguide). The underlying viscosity measurement principle relies, instead, on attenuation of the ultrasonic waves between said reference reflectors.

Since viscosity is temperature-dependent, the measured viscosity will also depend on the transit time of the ultrasonic waves. Accordingly, a novel (and optionally iterative) method of simultaneously measuring viscosity and temperature is also disclosed herein.

Several physical and engineering principles are combined into a single measurement device that can be easily integrated into high pressure and high temperature lines, that seals adequately onto the waveguide without excessive attenuation of the ultrasonic wave by the seal and protects a wave-generating transducer in, for example, a rugged steel tube that can be easily fitted into standard and industrial fuel piping systems via standard compression fittings, such as double ferruled compression fittings.

Furthermore, the waveguide may comprise a relatively thin cross section which ensures that flow resistance is minimised, and that liquid can flow through the measurement device with minimal pressure drop.

According to an aspect of the present disclosure, there is provided a device for measuring viscosity and/or temperature of a fluid, the device comprising: a transducer for generating and receiving ultrasonic waves; a waveguide for guiding the ultrasonic waves away from and back to the transducer, the waveguide having a total length along a longitudinal axis thereof; and, an attachment for attaching the device to a structure containing the fluid, the attachment being constructed and arranged to provide mechanical fixation of the device to the fluid- containing structure such that, in use, a measurement length of the waveguide is sealingly immersed in the fluid, the measurement length being a portion of said total length of the waveguide. The attachment may comprise a sheathing structure, wherein at least a portion of the waveguide is disposed within said sheathing structure.

Optionally, the measurement length of the waveguide is disposed within said sheathing structure.

Optionally, the total length of the waveguide is disposed within said sheathing structure.

Optionally, the sheathing structure is tubular, and the tubular sheathing may have a generally circular cross section.

Optionally, the sheathing structure is made of a metal, such as steel.

The attachment may comprise a sealing structure constructed and arranged to form a fluidic seal between the sealing structure and the waveguide.

Optionally, the fluidic seal is disposed around an entry section of the waveguide, wherein the ultrasonic waves enter into said measurement length of the waveguide at said entry section of the waveguide.

Optionally, wherein the sealing structure comprises a resiliently deformable material, such as a polymeric material

Optionally, the sealing structure comprises at least two compression members for compressing the resiliently deformable material therebetween.

Optionally, each of the compression members and the resiliently deformable material comprise an opening for receiving the waveguide therethrough.

Optionally, said resiliently deformable material has a Shore Hardness of 20 to 100.

Accordingly, the transducer is adapted to excite ultrasonic waves (of notional wavelength lambda) in the waveguide. The waves may travel through the sealing structure and will ultimately reach the measurement length of the waveguide. The waves will partially reflect, at least once, from each of an entry section to the measurement length and an (immersed) end section of the waveguide. The waves will travel back to the transducer for reception and analysis. The measurement length of the waveguide presents an impedance mismatch to the travelling waves, caused by the partial immersion of the waveguide, and, if present, by the seal. It is this impedance mismatch that results in the first, partial wave reflection back to the transducer at the entry section of the waveguide.

The waveguide may have an elongated shape.

Optionally, the waveguide has a uniform cross section.

Optionally, the waveguide comprises an elongated strip of a material such as an inert metal.

Optionally, said strip has a first dimension or side that is at least 20 times larger than a second dimension or side.

Optionally, the second dimension or side is 0.25, 0.5 or 1mm;

Optionally, said strip is made of Aluminium.

The measurement length of the waveguide may comprise a notch.

Optionally, the notch has a depth which is 10 to 50% of the thickness of the measurement length.

Optionally, the notch has a width which is less than 25% of a wavelength associated with the ultrasonic waves.

The measurement length of the waveguide may comprise two symmetrically oriented notches penetrating 5 to 35% into the cross section of the waveguide from either side of the second, smaller dimension or side of the cross section.

Optionally, each notch has a width which is less than 25% of a wavelength associated with the ultrasonic waves.

The device may be arranged such that 5 to 95% of the energy in the ultrasonic waves generated by the transducer is transmitted to the measurement length of the waveguide.

The transducer may be attached to a proximal end of the waveguide. Optionally, the transducer is attached to a proximal edge of the waveguide.

Optionally, the attachment is mechanically connected to the proximal end or edge of the waveguide, for example via and/or to the transducer.

The mechanical connection to the proximal end or edge of the transducer may be constructed and arranged to provide strain relief of cables attached to the transducer, and/or to provide a pathway arranged to thermally conduct heat from the transducer to the attachment.

The attachment may comprise a heat sink constructed and arranged to dissipate heat and cool the transducer.

The attachment may comprise markings that enable orientation of the waveguide with respect to a flow of the fluid within said fluid containing structure and/or control of a depth of immersion of the measurement length of the waveguide.

Optionally, the fluid-containing structure is a conduit or pipe containing the fluid.

Optionally, the fluid is pressurized, and/or the fluid is a streaming fluid through said conduit or pipe.

The ultrasonic transducer may be adapted to generate shear waves at a centre frequency in the range 2-10MHz.

Optionally, the centre frequency is around 2MHz, 5MHz or 10MHz.

The attachment may comprise an industrial standard compression fitting for fitting the device to an opening provided on said fluid-containing structure.

Optionally, the industrial standard compression fitting comprises a double ferruled compression fitting,

According to a further aspect of the present disclosure, there is provided apparatus for measuring viscosity and/or temperature of a fluid, the apparatus comprising a device as described herein. Optionally, the apparatus comprises a computer operably connected to said transducer for generating the ultrasonic waves and for receiving signals representative of reflected ultrasonic waves.

According to another aspect of the present disclosure, there is provided a method of measuring a viscosity of a fluid contained in a structure using a device as described herein, or an apparatus as described herein, the method comprising: using the attachment, mechanically fixing the device to the structure; using the transducer, generating ultrasonic waves and receiving reflected ultrasonic waves; analysing signals representative of the reflected ultrasonic waves to evaluate amplitude changes in the reflected ultrasonic waves occurred in the measurement length of the waveguide; calculating the viscosity of the fluid based upon said amplitude changes.

Calculating the viscosity may be carried out based on equation: wherein h is the fluid viscosity, p _f and p _s are the fluid and waveguide material densities respectively, G is the shear modulus of the waveguide material, a is the measured signal attenuation, h is the thickness of the waveguide and w is the angular frequency of operation and Co is the shear velocity of sound.

According to another aspect of the present disclosure, there is provided a method of measuring a temperature of a fluid contained in a structure using a device as described herein, or an apparatus as described herein, the method comprising: using the attachment, mechanically fixing the device to the structure; using the transducer, generating ultrasonic waves and receiving reflected ultrasonic waves; analysing signals representative of the reflected ultrasonic waves to evaluate time of travel changes in the reflected ultrasonic waves occurred in the measurement length of the waveguide; calculating the temperature of the fluid based upon said time of travel changes. Calculating the temperature may comprise looking up the temperature on a predetermined reference dataset that expresses changes in ultrasonic waves travel time in the measurement length of the waveguide as a function of the temperature.

According to another aspect of the present disclosure, there is provided a method of measuring a viscosity and a temperature of a fluid contained in a structure using a device as described herein, or an apparatus as described herein, the method comprising a method of measuring the viscosity as described herein and a method of measuring the temperature as described herein.

Optionally, the two methods are carried out based on the same ultrasonic waves and reflected ultrasonic waves.

Calculating the viscosity may be carried out based on equation

_ 2 p _s Gh ² a ² _ 2 p _s ² c ₀ ² h ² a ² R/w R/ ^w ’ wherein h is the fluid viscosity, p _f and p _s are the fluid and waveguide material densities respectively, G is the shear modulus of the waveguide material, a is the measured signal attenuation, h is the thickness of the waveguide and w is the angular frequency of operation and Co is the shear velocity of sound; wherein G, c ₀ , P _f and p _s are calculated based upon the temperature measured by the method of measuring a temperature of a fluid as described herein.

Calculating said viscosity and temperature may be performed iteratively taking account of a mass loading effect of the viscosity on the speed of sound in the waveguide.

The iterative calculation may comprise a first iteration wherein a first temperature is estimated from the ultrasonic travel time, then a first viscosity is estimated based on the measurement of the ultrasonic attenuation; the first estimated viscosity is then used to assess the additional mass loading effect on the travel time and a second, corrected temperature is estimated, and the second, corrected temperature is then used to obtain a second, corrected viscosity estimate.

The iterative calculation may comprise one or more further iterations wherein one or more further temperature and viscosity estimates are obtained until the estimated temperatures and viscosities converge based on criteria of predefined variability in relative change of the estimates. According to another aspect of the present disclosure, there is provided a computer storage medium comprising computer-readable instructions for causing an apparatus as described herein to perform at least one of the methods described herein.

Drawings

Illustrative implementations of the present concepts will now be described, by way of example only, with reference to the drawings. In the drawings:

Figure 1 is a schematic representation of an ultrasonic viscosity measurement device installed in a conduit;

Figure 2a) [left] is a perspective view of the ultrasonic viscosity measurement device showing a waveguide, a measurement section (i.e., a measurement length), a protective tube, a seal, an ultrasonic transducer and a cable;

Figure 2b) [right] is an illustration of the waveguide only showing the transducer, an excited ultrasonic wave and travel direction, the measurement section and reverberation of the ultrasonic wave in the measurement section;

Figure 3 schematically shows the effect of increased temperature and change in viscosity in liquid surrounding the measurement section on the measurement device of Figures 1 and 2: the schematic illustrations on the left show the waveguide with the transducer at the top and measurement section at the bottom, in a reference state and in the measurement state, respectively; the graphs on the right show the corresponding changes in the measured signals, i.e., travel time (also known as “time of flight” or 'ToF”) in the case of temperature (Figure 3a), and attenuation in the case of viscosity (Figure 3b);

Figure 4 shows shear wave velocity of ultrasound measured in the measurement section of a 0.5mm-thick aluminium waveguide as a function of temperature, with the solid line representing a best linear fit;

Figure 5a) shows measured attenuation of the wave in the measurement section of the 0.5mm-thick aluminium waveguide referenced in connection with Figure 4, immersed in a Paragon N350 viscosity standard medium at different temperatures; Figure 5b) shows the viscosity estimated based on the attenuation in Figure 5a) as a function of temperature and a comparison to viscosity data provided by the supplier of the viscosity standard medium;

Figure 6 shows ultrasonic shear velocity vs temperature measurements in the 0.5mm-thick aluminium waveguide referenced in connection with Figures 4 and 5, immersed in an inviscid liquid (top data set), a low viscosity liquid (middle data set) and in a high viscosity liquid (bottom data set), wherein the dots represent individual measurements and the lines the respective best-fit;

Figure 7 shows drawings of an assembly in side and front views, the assembly comprising an ultrasonic viscosity measurement device of the type shown in Figures 1 to 6; an industrial T- piece pipe and a compression fitting;

Figure 8 shows a perspective view and an exploded view of the ultrasonic viscosity measurement device of Figure 7;

Figure 9 shows drawings of a variant of the waveguide of Figures 7 and 8;

Figure 10a) shows a schematic representation of different, possible waveguide thicknesses;

Figure 10b) shows a schematic representation of different, possible waveguide lengths: the choice of thicknesses and lengths makes the transducer (which works as a sensor, in addition to providing ultrasonic excitation) more or less sensitive to the viscosity of a fluid that is surrounding the waveguide (as far as thickness is concerned) or to better isolate the transducer from high temperatures (as far as length is concerned);

Figure 11 is a perspective view of a seal (also visible in Figure 8) that seals the waveguide into a protective tube and mechanically fixes the waveguide within the tube;

Figure 12a) shows a protective tube with one cut out in correspondence of the measurement section of the waveguide;

Figure 12b) shows an alternative protective tube with several cut outs; Figure 13 illustrates typical signals acquired from an ultrasonic viscosity measurement device as described herein.

Throughout the description and the drawings, like reference numerals are used to refer to like features.

Description

The focus of the present disclosure is on ultrasonic guided wave-type measurements. These measurements have the advantage of providing a degree of isolation between a transducer and a measurement area and hence enable measurements in harsh environments.

It has been shown that temperature can be measured using guided waves and that viscosity can also be measured with guided waves, especially with guided waves travelling along waveguides of cylindrical cross-section. However, it is difficult to transduce torsional waves of the type that propagate in cylindrical waveguides at high frequencies, and therefore these arrangements (which are usually based on magneto-strictive transducers) may exhibit limited sensitivity to fluids of low viscosity.

There has also been research work at higher frequencies that has shown measurements using waveguides of different geometries, such as plates and rectangular cross section waveguides. However, in this prior art the waveguides were only immersed into a measurement fluid in laboratory conditions. The prior art has never shown arrangements with waveguide attachments that would be suitable for industrial applications, let alone arrangements wherein a workable attachment is used to support the waveguide in configurations that prevent the measurement fluid from escaping the measurement area, thus enabling online temperature and/or viscosity measurements, for example in a processing plant such as a refinery, or in marine fuel delivery systems, such as onboard ships or other water-going vessels.

Previous academic work carried out by one of the present inventors, Cegla, shows that in rectangular section waveguides most of the energy tends to propagate along the centre of the waveguide and that, therefore, it would be possible to support guided-wave viscosity and/or temperature probes, laterally, by attachment or connection to the elongated sides of the waveguide. However, Cegla has also shown that supporting the waveguide substantially transversally, that is across a central section of the waveguide, part-way along its length would significantly distort the propagating wave (and, accordingly, any resulting measurements). This limitation has been investigated and overcome in the experimental work that has led to the present disclosure. The arrangements described herein have been tested to overcome such a limitation, and the inventors have reported that it is instead possible to support the waveguides part-way, along their longitudinal extension, in such a way that the waveguides can be only partially inserted into the measurement medium (such as a pressurised fluid in a conduit, for example at 30bar and 150°C), without losing ultrasonic signal fidelity. Accordingly, the novel arrangements described herein are extremely practical and convenient, since they allow the transducer to be disposed at a suitable distance from a potentially harsh environment, thus enabling fast and reliable online viscosity and/or temperature measurements suited to most industrial applications.

Additionally, a novel iterative method to estimate the temperature and viscosity simultaneously, that is from the same ultrasonic measurements, is proposed to produce better temperature and viscosity measurements.

Figure 1 shows an overall assembly of an ultrasonic viscosity measurement device or probe 10 (hereinafter also referred to as “viscometer”) in use in an industrial fluid conduit 20, such as a marine fuel supply line of the kind that may be found onboard ships or other seagoing vessels. The conduit 20 contains a viscous fluid 30 whose viscosity is to be measured. A standard industrial piping T-section 40 is inserted into the conduit 30 and the viscometer 10 is inserted into the flow of viscous fluid 30 through a central port 41 of the T-section 40. The viscometer 10 is fixed in place by means of a standard industrial compression fitting 5 (a double ferruled compression fitting is envisaged). This is a fast and effective method to seal against pressures for example exceeding 30bars.

Markings 11 on an outside sheathing element 2 of the viscometer 10 (here in the form of a tube) help with positioning a waveguide 1 that runs inside the tube 2 at the correct depth and orientation with respect to the flow of the fluid 30, so that pressure drop, and flow resistance, are minimised. The tube 2, and the internal waveguide 1 , exhibit a natural temperature gradient along a longitudinal axis a - as shown in Figure 1 - from a distal end 12 of the waveguide 1 that is inserted in the (potentially hot) fluid 30 towards a proximal end 13 of the waveguide 1 that is freely protruding into the ambient atmosphere. Only a measurement length (or measurement section) 100 of the waveguide 1 is this immersed in the fluid 30. While the temperature gradient is usually large enough so that an ultrasonic transducer 15 (shown in Figure 2) coupled to the waveguide 1 at the protruding end 13 is not exposed to excessive temperature, an additional heat sink 16 can be added onto the tube 2 to cool the protruding end 13 that contains the transducer 15. A strain relief element 17 helps relieve strain in a cable 16 connected to the transducer 15.

Figure 2a) shows a more detailed view of the viscometer 10 of Figure 1 including the waveguide 1 and measurement section 100, ultrasonic transducer 15 and protective tube 2, wherein a seal is formed between the waveguide 1 and a sealing structure 3 provided in the tube 2 for this purpose, and for simultaneously supporting the waveguide 1 in the protective tube 2. The strain relief element 17 can be seen in Figure 2a) as being provided, in this device 1 , as a cable gland 4 that can be coupled to the tube 2 at one end.

Figure 2b) shows the waveguide 1 , the transducer 15 at one end 13 that sends the ultrasonic waves along the waveguide 1 into the measurement section 100, that is the portion of the waveguide 1 which, in use, is immersed in the measurement medium 30. There is an impedance mismatch between the remainder of the waveguide and the measurement section 100, so that at the entrance in the measurement section 100 the waves are partially reflected. The ultrasonic waves travel further, to reach the end of the measurement section 100 where they are substantially fully reflected. On the way back to the transducer 15, the waves are again partially reflected by the impedance mismatch between the measurement section 100 and the remainder of the waveguide 1 so that a train of echoes (reverberations of the signal) from the measurement section 100 is received at the transducer 15.

Figures 3a) and 3b) illustrate the measurement principles used by the device 10, and how a change in temperature in the measurement section 100 or a change in viscosity of the fluid 30 that surrounds the measurement section 100 results in a change of key parameters in the reverberant signals, i.e. the time of flight (ToF) of the reverberant signals in the measurement section 100, or the attenuation of the signals in that region. Based on the length of the measurement sectionlOO, and the relation of speed of (ultra )sound with temperature in the material of the measurement section 100, the average temperature of the measurement section 100 can be estimated.

Figure 4 shows a typical relation between temperature and speed of (ultra)sound in an aluminium waveguide 1. The shear velocity of (ultra)sound (co) can also be expressed as a function of the shear modulus G and density p of the material of which the waveguide 1 is made, both being temperature dependent, as shown in Equation 1 :

Equation 1

Furthermore, for an ultrasonic shear wave that travels in the waveguide 1 in the measurement section 100, the presence of a viscous fluid 30 will strongly affect the attenuation of the wave and by measuring the change in attenuation compared to a reference state in an inviscid liquid and using the formula in Equation 1 , the viscosity of the liquid 30 can be estimated. To use Equation 1 , it is also necessary to know the fluid density, however for many industrial processes - such as those involving the delivery of marine fuels - the density of the fluid 30 does not change considerably, and it can therefore be assumed to be constant:

Equation 2 wherein h is the fluid viscosity, p _f and p _s are the fluid and waveguide material densities respectively, G is the shear modulus of the waveguide material, a is the measured signal attenuation, h is the thickness of the waveguide and w is the angular frequency of operation of the ultrasound.

Figure 5 shows the attenuation measurements of the waves in the measurement section 100 of a 0.5mm thick aluminium waveguide 1 over a range of temperatures when the measurement section 100 of the device 10 is immersed in a Paragon N350 viscosity standard fluid. The measurements clearly show the reduction in attenuation (Figure 5a)) and viscosity (Figure 5b)) with temperature. There is a very good agreement between the measured viscosity and the viscosity data that are provided by the supplier of the viscosity standard fluid.

The two previous examples (referring to the setups shown in Figure 3) have shown measurements of temperature and viscosity in isolation. The physical effect of viscosity on the waveguide 1 is such that a small amount of fluid mass (the viscous skin depth or viscous boundary layer) is attached to the surface of the waveguide 1. This additional mass adds inertia to the waveguide material and slows down the wave propagation. There is therefore an additional effect of the viscosity on the wave propagation and therefore the time of flight change as a function of temperature if a fluid 30 of higher viscosity surrounds the waveguide 1. The additional effect of added mass can be corrected for if the viscosity and ultrasonic velocity temperature relation of the unloaded waveguide is known. The effect of viscosity on velocity of (ultra)sound is shown in Figure 6.

Equation 3 can be used to predict the velocity of the viscous fluid-loaded waveguide based on the original wave velocity:

Equation 3 wherein Co is the shear wave velocity in the waveguide 1 without viscous loading, p _f and p _s are the fluid and waveguide material densities, respectively, h is the waveguide thickness and d is the viscous skin depth.

Equation 4

The viscous skin depth can be determined according to Equation 4 above, wherein h is the dynamic viscosity and w is the angular frequency.

Figure 6 shows that for large viscosities considerable temperature measurement errors would result if the shear wave velocity only were used as a temperature measurement. These errors can be removed by iterating, i.e. first estimating the temperature using the measured velocity assuming an inviscid fluid, then estimating the viscosity from the attenuation method, using the viscosity measurement the viscous loaded shear wave velocity can be predicted and an updated temperature measurement can be obtained.

The updated temperature measurement can be used for a better viscosity estimate and this is repeated until the estimate converges, or a satisfactory precision is reached. In real life, acceptable results are achieved after 1 or 2 iterations.

Example

Figure 7 shows a fully assembled viscometer 10 (or, “viscosity sensor” hereinafter) that is inserted into a standard industrial T-piece 40. This T-piece 40 can be inserted into the piping system by means of welding or a flanged connection. The T-piece 40 is made of the same material as the piping system, in the described case this is stainless still.

The viscosity sensor 10 is secured and sealed into the T-piece 40 by means of a compression fitting 5. The flow and depth markings 11 on the outside of the protective tube 2 of the viscosity sensor 10 enable insertion into the appropriate depths within the T-piece 40 and the correct orientation of the measurement section 100 within the flow that will pass through the T-piece 40.

Figure 8 shows the main elements that are assembled to form the viscosity sensor 10 of Figure 7. The waveguide 1 is sealed against and mechanically located inside the protective tube 2 by means of a sealing structure 3 (visible in more detail in Figure 11). The protective tube 2 is made out of the same material as the piping system, in the described case stainless steel. The proximal end 13 of the tube 2 is sealed with a cable gland 4 that enables cable strain relief and the conduction of an electric wire or cable 16 from the transducer 15 on the waveguide 1 to external apparatus 50 (comprising a computer, amplifier, digital-to-analogue converters, analogue-to-digital converters, as the case may be, and as necessary) that sends and receives the electrical signals to the transducer 15. At the end 12 opposite to where the cable gland 4 is installed, the protective tube 2 includes one or several cut-outs 7 that minimise flow resistance and expose the measurement section 100 of the waveguide to the fluid 30 that is flowing along the T-piece conduit 40.

Figure 9 shows a typical waveguide 1 . The waveguide 1 can be made of any robust material, however in the illustrated example it is made out of aluminium. The waveguide 1 can have different thicknesses, in the illustrated example it is 0.5mm thick. At the transducer end 13, the waveguide 1 has a spanner shaped section that allows the attachment of a piezo electric transducer 15 to its cross section. Other transducer types could in principle be used. Also, other manners of attachment of the transducer 15 are possible. The piezo electric crystal is used to excite an ultrasonic shear wave that travels along a waveguide main section 99 into the measurement region 100. Other wave types could however equally successfully be used, depending on the application and/or available transducer types. Epoxy is used to encapsulate the piezo electric crystal so that it is damped and that any wires that are soldered onto the electrodes are strain relieved.

At the other (distal) end 12 of the waveguide 1 the measurement section 100 can be identified. The measurement section 100 is, in this particular waveguide 1 , delimited by an additional impedance mismatch between the main portion 99 of the waveguide and the measurement section 100 (or measurement length) of the waveguide 1. In the illustrated arrangement, this additional impedance mismatch is achieved by cutting a 0.1mm deep notch 6 into the thickness of the waveguide 1 from both sides (as shown in Figure 9). The notch 6 creates an additional impedance mismatch, which better reflects the wave partially before it is fully reflected from the end of the waveguide 1. The notch 6 depth of 0.1mm depth results in the first two ultrasonic echoes having roughly the same amplitude. The notch depth can be adjusted if necessary.

There are also other ways that can in principle be used to provide the above added impedance mismatch, and these comprise: a step up or down in thickness of the waveguide; and, the addition of a protrusion of material of the same or a different type of material compared to the material that makes up the main section of the waveguide. It is possible to employ different thicknesses and lengths of waveguides 1 as is shown in Figures 10a) and 10b).

Figure 10a) shows waveguides 1 of different thicknesses. It may be desirable to use measurement sections 100 of different thickness because the thickness governs the sensitivity of wave attenuation to the viscosity of the surrounding fluid 30 as can be deduced from Equation 2. Figure 10b) also shows that different length variants of waveguides 1 can be employed. The dimensions of the protective tube 2 will change accordingly so that the measurement section 100 of the waveguide is aligned with the cut-outs 7 in the protective tube 2 at one end 12 and the cable gland 4 can be fitted at the other end 13 to seal the waveguide 1 within the protective tube 2.

It is desirable to use different length variants so that the temperature difference between the measurement section 100 that may be immersed in a hot fluid 30 and the temperature of the waveguide end 13 where the transducer 15 is located can be increased by simple natural convection cooling. This means that the device 10 can be immersed in hotter liquids while the temperature at the transducer end 13 remains low (below e.g. the glass transition temperature of the epoxy that is used for bonding). This ensures that the measured amplitude values are stable and not influenced by the temperature at the measurement section 100.

Figure 11 shows an example of sealing structure 3. It consists of a soft gasket material 8 that is inserted in between two metal plates 9. In the described arrangement, the metal plates 9 are made out of stainless steel. The metal plates 9 and the gasket 8 have cut-outs 14 for six fasteners and the waveguide and the diameter of all components is slightly (e.g. -0.01- 0.05mm) smaller than the internal diameter of the protective tube. Once the waveguide 1 is inserted into a central slot 16, the six fasteners (or bolts) can be tightened so that the separation between the metal plates 9 is reduced. The force that the two metal plates exert on the gasket material 8, deforms the gasket material 8 so that it is pressed against the waveguide 1 and the inner surface of the protective tube 2. This forms a tight seal interface, which separates out the measurement length 100 of the waveguide 1 from the remainder 99 of the waveguide 1. In the described arrangement, Viton is used as the gasket material 8, however nitrile or silicone materials might can also be suitable. Any material that is malleable (shore Hardness on the A scale between 20-100) and will expand laterally when compressed between two plates 9 can be used to make the seal.

Figure 12 shows drawings of two protective tube variants 2 with different cut-outs 7 to enable protection of the measurement section 100 from external mechanical contact while also minimising flow resistance once the measurement device 10 is inserted in the T-piece 40. The described protective tube 2 is made of stainless steel; however, any other strong metal alloy is also suitable. The length of the tube 2 (190mm dimension) can be adjusted according to the different waveguide length variants that it needs to protect.

Measurement process and signal analysis

To perform a measurement the following steps are performed:

An electric signal is sent to the ultrasonic transducer 15 on the waveguide 1. Suitable signals are 5 or 10 cycle Hann-windowed tone bursts of centre frequency 2, 2.5 or 3MHz.

The resulting ultrasonic waves travel along the waveguide 1 and interact with the fluid 30 in the measurement section 100. The returning ultrasonic waves are recorded by the transducer 15 in the form of corresponding signals, appropriately amplified and then digitised. The first reflections from the beginning and end of the measurement section 100 are then used to estimate the temperature and viscosity of the fluid 30 that is in contact with the measurement section 100. Typical signals are shown in Figure 13, separated out by a time “Time lag” and having a difference in amplitudes A1 minus A2.

To determine the temperature of the measurement medium, the first two echoes are cross correlated and the time lag between them is extracted. Since the length of the measurement section 100 is precisely known, the ultrasonic velocity in the waveguide can be determined by dividing the length of the path that the wave has travelled in the measurement section 100 by the time lag between echoes.

The ultrasonic velocity estimate is then compared to a calibration curve that describes the variation of ultrasonic velocity in the measurement section 100 as a function of temperature and the corresponding temperature is determined.

To determine the viscosity of the fluid that the waveguide 1 is immersed in, the maximum amplitude of the second reflection A2 (wave that has travelled through the measurement section 100) is compared to the maximum amplitude of the first reflection A1 (wave that hasn’t travelled through the measurement section 100). This ratio is then compared to a reference measurement that was previously performed with the waveguide 1 is immersed in an inviscid liquid. The increase in attenuation will be determined and the excess attenuation is the attenuation due to the presence of the viscous liquid near the measurement section 100. The measured attenuation together with the waveguide properties are input into Equation 2 to estimate the viscosity.

For highly viscous fluids, the time lag will also be influenced by the attenuation induced by the viscosity and therefore the temperature estimate will be influenced. In that case the estimate in Figure 4 can now be used to correct the original temperature measurement in Figure 3 using Equation 3.

The above detailed description describes a variety of exemplary arrangements and methods of using an ultrasonic viscosity measurement device. However, the described arrangements and methods are merely exemplary, and it will be appreciated by a person skilled in the art that various modifications can be made without departing from the scope of the appended claims. Some of these modifications will now be briefly described, however this list of modifications is not to be considered as exhaustive, and other modifications will be apparent to a person skilled in the art.

The first reflector has been described in the above description as comprising one or more notches 6 which generate an impedance mismatch between external and internal (i.e., immersed) portions of the waveguide 1 . While it will be appreciated that said notches 6 may have a variety of shapes or profiles, alternatives encompass protrusion of ridges which increase rather than diminish the waveguide cross section at the discontinuities. However, the sealing structure 3 may itself provide such discontinuity, with part of the ultrasonic energy reflecting back from the sealing interface between the sealing structure 3 and the waveguide 1.

While various specific combinations of components and method steps have been described, these are merely examples. Components and method steps may be combined in any suitable arrangement or combination. Components and method steps may also be omitted to leave any suitable combination of components or method steps.

The described methods may be implemented using computer executable instructions. A computer program product or computer readable medium may comprise or store the computer executable instructions. The computer program product or computer readable medium may comprise a hard disk drive, a flash memory, a read-only memory (ROM), a CD, a DVD, a cache, a random-access memory (RAM) and/or any other storage media in which information is stored for any duration (e.g., for extended time periods, permanently, brief instances, for temporarily buffering, and/or for caching of the information). A computer program may comprise the computer executable instructions. The computer readable medium may be a tangible or non-transitory computer readable medium. The term “computer readable” encompasses “machine readable”.

The singular terms “a” and “an” should not be taken to mean “one and only one”. Rather, they should be taken to mean “at least one” or “one or more” unless stated otherwise.

The word “comprising” and its derivatives including “comprises” and “comprise” include each of the stated features but does not exclude the inclusion of one or more further features.

The above implementations have been described by way of example only, and the described implementations are to be considered in all respects only as illustrative and not restrictive. It will be appreciated that variations of the described implementations may be made without departing from the scope of the disclosure.

It will also be apparent that there are many variations that have not been described, but that fall within the scope of the appended claims.