An ultrasonic measuring device for online measurement of the degree of homogenization of a fluid product in a dispersion unit

Abstract

A measuring apparatus (1) for online measuring the degree of homogenization of a fluid product in a dispersion unit (100), the measuring apparatus (1) comprising: - a tubular device (2) disposed at an outlet (100b) of the dispersion unit (100), the tubular device (2) having an internal cavity (3) for the passage of the fluid product received from the dispersion unit (100); - a plurality of ultrasonic sensors (4) mounted on the tubular device (2), characterized in that the internal cavity (3) has a variable diameter along the length of the tubular device (2), the internal cavity (3) having at least a first conduit (31) with a conical development from an inlet (2a) of the tubular device (2) to an outlet (2b) of the tubular device (2).

Description

An ultrasonic measuring device for online measurement of the degree of homogenization of a fluid product in a dispersion unit Technical field The present invention relates to a measuring device for online measurement of the degree of homogenization of a fluid product in a dispersion unit. The invention proposed herein is used in the food industry, particularly in the dairy sector, or in the chemical, pharmaceutical, or cosmetic industries. The invention can also be used in manufacturing areas where homogenization is a step in the production process. Let us consider, for example, the production of carbon-based nanostructured materials, such as graphene and carbon nanotubes, or the cellular breakdown of yeast, algae, or microorganisms for the production of intracellular material. Background of the technique Although in various embodiments currently known, a homogenizing apparatus comprises a high-pressure pump and a homogenizing valve that acts on fluid products in order to: - crush the fluid particles to uniformize their dimensions, reducing the average size and the variance of the distribution in order to stabilize the product and increase its shelf life in the case of emulsions; - break cell membranes to facilitate the extraction of active ingredients in the case of pharmaceutical applications; - modify the structure of the particles in the case of chemical applications and cellulose or unicellular organisms. For most products, the main parameters that define the level of homogenization are the average particle size and the standard deviation. In known solutions, the pressure of the homogenizing apparatus is adjusted as described below in this case. First, the optimum average particle size and standard deviation for a given fluid product are experimentally determined. Then, the necessary pressure is applied to obtain particles with the calculated parameters. Pressure maintenance is achieved using one of the following methods: - by periodically adjusting the pressure value through manual interventions; - using a feedback system that receives as input the pressure level detected in the fluid product and forces the output to follow a set point. Both methods act directly on the homogenization pressure. However, homogenization pressure cannot be considered a reliable real-time indicator of the actual level of homogenization. In fact, even with the same pressure and fluid product, different levels of homogenization can be achieved, for example, due to changes in the new product being introduced into the apparatus and / or due to component wear. Known methods cannot detect differences in the fluid product introduced into the homogenization apparatus. Furthermore, known methods do not take into account the changes caused in the fluid product by non-ideal components. These situations are usually addressed by designing a homogenization device capable of guaranteeing a level of homogenization higher than a pre-established threshold, which corresponds to the most adverse conditions. Having an oversized homogenizing device increases the risk of mechanical stress on some components, which can reduce their lifespan. Furthermore, applying higher pressures than required results in increased energy consumption. Finally, applying higher pressures than required does not guarantee the desired level of homogenization, as it causes a temperature increase that can damage the fluid product. Some of the product may even have to be discarded due to thermal damage. EP 1121973 A1 describes a system for monitoring a dispersion produced in a dispersion unit, in particular its degree of homogenization, in which it is proposed to couple at least one measuring sensor to the dispersion unit to achieve an online measurement of the degree of homogenization of the dispersion. The sensor used in this document may be an ultrasonic sensor immersed in or in contact with the fluid product. Therefore, the sensor becomes easily contaminated and unreliable. Furthermore, it is more susceptible to damage from the high temperature of the fluid product. US patent 2009 / 0272190 A1 describes a non-invasive method for measuring parameters in a fluid flowing through a conduit, wherein the method consists of transmitting ultrasonic signals through the fluid. US patent 2004 / 0112121 A1 describes a method and device for monitoring and controlling critical parameters, such as particles, biomolecules, and viscosity, in pharmaceutical, food, and chemical industrial processes, again based on the transmission of ultrasonic signals. DE patent 33 19 922 A1 describes a method for controlling processes involving a dispersed phase. Specific designs of ultrasonic transducers are described in documents CN 103323064 A and CN 111189500 A. In the online publication entitled "Design of piezoelectric transducers", which can be accessed via the Internet at Document CN 108414039 A describes a method for detecting water temperature and a water flow sensor for a water heater. Description of the invention In this context, the objective of the present invention is to propose a measuring device for online measuring the degree of homogenization of a fluid product in a dispersion unit, which overcomes the problems of the prior art cited above. In particular, the objective of the present invention is to propose a measuring device for online measuring the degree of homogenization of a fluid product in a dispersion unit, achieving greater measurement reliability than known solutions. Another objective of the present invention is to provide a measuring device for online measuring the degree of homogenization of a fluid product in a dispersion unit, without affecting the fluid product. Another objective of the present invention is to propose a measuring device for measuring online the degree of homogenization of a fluid product in a dispersion unit, which is robust, less prone to wear over time and easy to clean. Another objective of the present invention is to propose a measuring device for measuring online the degree of homogenization of a fluid product in a dispersion unit, in which preventive maintenance operations can be scheduled more efficiently. The technical task set and the specified objectives are achieved by means of a measuring apparatus according to claim 1. In one embodiment of the invention, the ultrasonic sensors are attached to the first tube. Preferably, the first tube is made of plastic and the second tube of metal. More preferably, the first tube is made of PEEK or PTFE. The second tube is made of stainless steel. Brief description of the drawings Other features and advantages of the present invention will become clearer from the non-restrictive description of a preferred, though not exclusive, embodiment of a measuring device for online measuring the degree of homogenization of a fluid product in a dispersion unit, as illustrated in the accompanying drawings, in which: - Figures 1 and 2 illustrate two different embodiments of a measuring device for online measuring the degree of homogenization of a fluid product, according to the present invention; - Figure 3 shows the waveforms of the measured signals received by four sensors in an experimental test conducted to choose the best material for the first tube of the measuring apparatus; - Figure 4 illustrates a block diagram of the measuring apparatus of Figures 1 and 2 at the output of a dispersion unit. Detailed description of the preferred embodiments of the invention With reference to the figures, the number 100 denotes a dispersion unit. Dispersion unit 100 has an input 100a and an output 101b for a fluid product. For example, the dispersion unit 100 is a high-pressure homogenizer comprising a volumetric piston pump and a homogenizing valve arranged downstream of the volumetric piston pump. In particular, the 100 high-pressure homogenizer operates at a pressure of up to 4000 bar. The number 1 indicates a measuring device for measuring online the degree of homogenization of a fluid product in the dispersion unit 100. The measuring apparatus 1 comprises a tubular device 2 arranged at the outlet 100b of the dispersion unit 100. The tubular device 2 has an inlet 2a that receives the homogenized fluid product from the dispersion unit 100, and an outlet 2b. The tubular device 2 has an internal cavity 3 for the passage of the fluid product received from the dispersion unit 100. The internal cavity 3 extends from the inlet 2a to the outlet 2b of the tubular device 2. The diameter of the internal cavity 3 at the inlet 2a and outlet 2b of the tubular device 2 is essentially the same. Initially, the internal cavity 3 has a variable diameter along the tubular device 2. Specifically, the internal cavity 3 has at least a first section 31 with a conical development from the inlet 2a to the outlet 2b of the tubular device 2. In other words, the first section 31 has a convergent shape from the inlet 2a to the outlet 2b of the tubular device 2. Preferably, the first section 31 of the internal cavity 3 is made up of several essentially cylindrical parts 310 that are joined by truncated conical parts 311. The cylindrical sections 310 have corresponding diameters that decrease from the inlet 2a to the outlet 2b of the tubular device 2. In the illustrated embodiment, the first section 31 comprises five cylindrical sections 310 joined by four truncated conical sections 311. The internal cavity 3 preferably has a second section 32 that originates from the first section 31 and ends at the outlet 2b of the tubular device 2. The second section 32 has a conical development from the outlet 2b of the tubular device 2 towards the first section 31. In other words, the second section 32 has a convergent shape from the outlet 2b of the tubular device 2 towards the first section 31. Specifically, the second section 32 consists of a truncated conical part 321 that connects the first section 31 with the outlet 2b of the tubular device 2. Specifically, the last cylindrical section 310 of the first section 31 connects to the truncated conical section 321 of the second section 32. The measuring apparatus 1 further comprises several ultrasonic sensors 4 mounted on the tubular device 2 and configured to detect ultrasonic waves. According to the illustrated embodiment, the tubular device 2 comprises a first tube 5 and a second tube 6. The first tube 5 is coaxial with the second tube 6 and is located inside it. The first tube 5 delimits the internal cavity 3. In particular, the internal cavity 3 is delimited by an internal surface 5a of the first tube 5. Specifically, the internal surface 5a of the first tube 5 has a partial conical development from the inlet 2a to the outlet 2b of the tubular device 2, so that it delimits the corresponding conical development of the first section 31 of the internal cavity 3. According to the invention, the ultrasonic sensors 4 are arranged between the first tube 5 and the second tube 6. Preferably, the ultrasonic sensors 4 are distributed along the tubular device 2. According to the embodiments illustrated in this document, the first tube 5 has several housings 7 to accommodate the ultrasonic sensors 4. Preferably, the housings 7 are obtained as recesses into an external surface 5b of the first tube 5. According to one embodiment of the invention, the ultrasonic sensors 4 are attached to the first tube 5. In particular, they are placed inside the housings 7 and attached to the outer surface 5b of the first tube 5. For example, the ultrasonic sensors 4 are screwed externally to the second tube 6 so that they are close to the first tube 5. Preferably, in this embodiment, an ultrasonic gel is placed between the ultrasonic sensors 4 and the first tube 5 to ensure signal transmission. Preferably, the measuring device 1 has an electrical connector mounted on the second tube 6. The electrical connector serves for the connections of the ultrasonic sensors 4. According to one embodiment of the invention, illustrated in Figure 1, each cylindrical part 310 is coupled to an ultrasonic sensor 4. Said ultrasonic sensor 4 is arranged inside a housing 7 obtained in a section of the first tube 5 surrounding the corresponding cylindrical part 310. In this embodiment, called "Pulse Echo", the 4 ultrasonic sensors are configured to generate and detect ultrasonic waves. In other words, the 4 ultrasonic sensors act as both emitters and receivers. The waves generated by the ultrasonic sensors 4 pass through the fluid product circulating through the internal cavity 3 and are reflected by the second tube 6, which is made of metal. Alternatively, reflectors can be mounted on one side opposite the housings 7 with respect to the internal cavity 3, in order to increase the reflection of the ultrasound waves. According to another embodiment of the invention, illustrated in Figure 2, each cylindrical part 310 is coupled to one of the aforementioned ultrasonic sensors 4 (hereinafter referred to as the "receiver"), and to another ultrasonic sensor 14 configured to generate ultrasonic waves (hereinafter referred to as the "emitter"). The receivers 4 and emitters 14 are arranged, respectively, in two housings 7 located opposite each other with respect to the internal cavity 3. The two housings 7 are formed in a section of the first tube 5 surrounding the corresponding cylindrical part 310, but are located on opposite sides with respect to the flow of the fluid product. In this embodiment, called "direct transmission", the waves generated by the emitters 14 pass through the fluid product circulating through the internal cavity 3 and are detected by the receivers 4. According to one aspect of the invention, the first tube 5 is made of a plastic material. Therefore, the ultrasonic waves can pass through the first tube 5. In a preferred embodiment, the first tube 5 is made of PEEK. Alternatively, the first tube 5 is made of PTFE. An experimental test was carried out to select the best material for the first tube 5. The test consisted of creating four different sample tubular sections, each made from a different material to simulate the first tube 5. Each sample section has its own ultrasonic sensor, which is a piezoelectric ceramic sensor with a resonant frequency of 5 MHz. The ultrasonic sensor is screwed onto the corresponding sample section. These are the four sample tubular sections created for the test: - 1st sample section: tube made of AISI 316L, with a thickness of 2 mm (from the internal cavity to the corresponding screwed sensor); - 2nd sample section: tube made of PTFE, with a thickness of 10 mm (from the internal cavity to the corresponding screwed sensor); - 3rd sample section: PEEK tube, with a thickness of 10 mm (from the internal cavity to the corresponding screwed sensor); - 4th sample section: AISI 316L tube, with a thickness of 4 mm (from the internal cavity to the corresponding threaded sensor). In practice, the sample sections are simplified versions of the tubular device 2 (with only the first tube 5), with a Pulse echo configuration, in which the ultrasonic sensors act as both emitters and receivers. The thicknesses of the first three samples are different. They were chosen to obtain a suitable mechanical strength value to withstand an internal pressure of 40 bar inside the tube. The fluid in the cavity is tap water at room temperature. The 3rd sample (PEEK) turned out to be the best option, as the signal after the first reflection is clearly distinguishable from the noise. PEEK is the best option, as it combines high mechanical strength with chemical inertness, suitability for food and pharmaceutical grade substances, resistance to high sterilization temperatures, and transparency to ultrasonic waves. In addition, a fourth sample was included to compare how the signal is transmitted in AISI 316L, which is twice as thick as the first sample. In the fourth sample, the greater thickness of the AISI 316L significantly attenuates the transmission of the ultrasound signal, and the first reflection of the signal is affected by noise. The measured signals received by the four sensors are shown in Figure 3 to facilitate comparison, where: - S1 refers to the first sample section; - S2 refers to the second sample section; - S3 refers to the third sample section; - S4 refers to the fourth sample section. The second tube 6 is made of a metallic material. For example, the second tube 6 is made of stainless steel. Therefore, the ultrasonic waves are reflected by the second tube 6 and contained within the tubular device 2. According to the invention, the tubular device 2 comprises a heat exchanger 8 for cooling the ultrasonic sensors 4. Preferably, heat exchanger 8 is a conduit for the passage of a refrigerant fluid. Preferably, the conduit 8 passes through the tubular device 2 along its entire length and has a main section parallel to the longitudinal axis AA of the tubular device 2. According to one embodiment of the invention, the conduit 8 has an inlet made in the second tube 6, corresponding to the housing 7 located closer to the inlet 2a of the tubular device 2, and an outlet made in the second tube 6, corresponding to the housing 7 located closer to the outlet 2b of the tubular device 2. Alternatively, the inlet of duct 8 is located closer to the outlet 2b of the tubular device 2, and the outlet of section 8 is located closer to the inlet 2a of the tubular device 2. In particular, duct 8 is supplied with air at a temperature between 5 °C and 40 °C. The air circulating through duct 8 serves to keep the temperature of the ultrasonic sensors 4 under control, regardless of the temperature of the fluid product circulating through the internal cavity 3. This has advantages both during normal operation of the dispersion unit 100 and during sterilization cycles, in which the tubular device 2 can reach high temperatures (e.g., 130 °C) that could affect the reliability of the ultrasonic sensors 4 or even damage them. Furthermore, in the embodiment where the ultrasonic sensors 4 are attached to the first tube 5, a high temperature could detach the sensors 4 from the first tube 5, and an air layer could form between the sensors 4 and the first tube 5, thereby interrupting the transmission of signals. The 4 ultrasonic sensors are configured to receive ultrasonic waves with a frequency between 2 MHz and 20 MHz. Preferably, the 4 ultrasonic sensors are chosen to operate at different frequencies, in order to detect ultrasonic waves passing through fluid products with different acoustic impedances. The signal detected by the ultrasonic sensors 4 can be used to control the pressure of the fluid product in the dispersion unit 100. The characteristics of the measuring apparatus for online measurement of the degree of homogenization of a fluid product in a dispersion unit, according to the present invention, are clearly evident from the above description, as are its advantages. Since the ultrasonic waves are distributed along the entire length of the tubular device, detection is performed simultaneously at multiple points along the flow of the fluid product. Therefore, this detection is more reliable than that performed at a single point or on a single sample of the fluid product. This redundancy also offers advantages in the event of damage to one or more sensors. Furthermore, the placement of the ultrasonic sensors on the outer surface of the first tube prevents direct contact with the fluid circulating through the inner cavity. This results in a beneficial hygienic design of the tubular device. Furthermore, in the embodiment where the ultrasonic sensors are bonded to the first tube, there is virtually no air in the sensor housings. This ensures good signal quality, as air would attenuate the ultrasonic waves. Furthermore, in the embodiment where the ultrasonic sensors are bonded to the first tube, they essentially remain in position during assembly and disassembly of the tubular device. This is ensured by their placement within recesses on the outer surface of the first tube. This arrangement also protects the ultrasonic sensors from potential damage. In this embodiment, the ultrasonic sensors are not mechanically coupled to the second tube, which is made of stainless steel. Therefore, there is no risk of particle accumulation (i.e., dust) between the second tube and the ultrasonic sensors. Moreover, the second tube is almost smooth, with a single electrical connector. The outer surface of the second tube is thus easy to clean.

Claims

1. A measuring device (1) for online measuring the degree of homogenization of a fluid product in a dispersion unit (100), said measuring device comprising: - a tubular device (2) that can be arranged at an outlet (100b) of the dispersion unit (100), said tubular device (2) having an internal cavity (3) for the passage of the fluid product received from the dispersion unit (100), said tubular device (2) comprising a first tube (5) and a second tube (6), the first tube (5) being coaxial with and disposed inside the second tube (6), and said internal cavity (3) being delimited by an internal surface (5a) of the first tube (5), said tubular device (2) further comprising a heat exchanger which is a section (8) for the passage of a cooling fluid,traversing said conduit (8) the tubular device (2) along its entire length and having a main section parallel to a longitudinal axis (AA) of the tubular device (2), several ultrasonic sensors (4) distributed along the tubular device (2) and arranged between the first tube (5) and the second tube (6), said first tube (5) having several housings (7) to accommodate said ultrasonic sensors (4), said housings (7) being obtained as recesses into an external surface (5b) of the first tube (5), and said several ultrasonic sensors being cooled by the heat exchanger, wherein said internal cavity (3) has a variable diameter along the tubular device (2), the internal cavity (3) having at least a first section (31) that has a convergent shape from an inlet (2a) of the tubular device (2) to an outlet (2b) of the tubular device (2),said internal cavity (3) also having a second section (32) originating from the first section (31) and terminating at the outlet (2b) of the tubular device (2), said second section (32) having a conical development from the outlet (2b) of the tubular device (2) towards said first section (31), said second section (32) being formed by a truncated conical part (320) connecting the first section (31) with the outlet (2b) of the tubular device (2), wherein the first section (31) of the internal cavity (3) is formed by several essentially cylindrical parts (310) joined by truncated conical parts (311), said cylindrical parts (310) having corresponding diameters that decrease from the inlet (2a) towards the outlet (2b) of the tubular device (2),each cylindrical section (310) being: - coupled to one of said ultrasonic sensors (4) acting as both an ultrasonic wave emitter and receiver and arranged inside one of said housings (7) formed in a section of the first tube (5) surrounding said corresponding cylindrical section (310), or - coupled to one of said ultrasonic sensors (4) acting as an ultrasonic wave receiver and another of said ultrasonic sensors (14) acting as an ultrasonic wave emitter, said emitter and said receiver being arranged, respectively, in two housings (7) of said housings (7) located opposite each other with respect to the internal cavity (3) and formed in a section of the first tube (5) surrounding the corresponding cylindrical part (310), but on opposite sides with respect to the flow of the fluid product.

2. The measuring apparatus (1) according to claim 1,wherein the ultrasonic sensors (4) are attached to the first tube (5).

3. The measuring apparatus (1) according to claim 1, wherein the first tube (5) is made of a plastic material and the second tube (6) is made of a metallic material.

4. The measuring apparatus (1) according to claim 3, wherein the first tube (5) is made of PEEK or PTFE.

5. The measuring apparatus (1) according to claim 3 or 4, wherein the second tube (6) is made of stainless steel.

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