System and method for detection and characterization of cavitating flow patterns

Abstract

The present disclosure proposes a system (100) comprising one or more flow lines (1) extending along respective flow directions (FD) The flow line (1) comprises two or more pressure sensors (11) that are distributed in different respective locations along the flow line (1), arranged for obtaining pressure data (PD) from the respective locations on the flow line (1). The flow line (1) further comprises one or more acoustic sensors (12) for obtaining acoustic data (AD) from the flow line (1). The present disclosure proposes a method for determination of loci and characteristics of an onset, an inception and a shifting of HC such system (100). The method comprises acquisition of pressure data (PD) from the two or more pressure sensors (11) and acoustic data (AD) from the one or more acoustic sensors (12), and correlating the acquired pressure data (PD) and the acoustic data (AD) with one or more flow conditions and one or more flow characteristics.

Description

[0001] SYSTEM AND METHOD FOR DETECTION AND CHARACTERIZATION OF CAVITATING FLOW PATTERNS

[0002] Technical Field

[0003] The present application relates to systems prone to cavitating flow patterns. The present application particularly relates to a system and method for detection and characterization of cavitating flow patterns.

[0004] Background

[0005] Hydrodynamic cavitation (abbreviated as HC) can be defined as formation of vapor cavities which can also be referred to as HC bubbles, when a fluid undergoes a sudden pressure drop. The pressure drop arises from an increase in an extent of fluid flow through flow restrictive elements which decrease the pressure and trigger an inception of the HC. Formation of the HC bubbles occurs when the pressure is below the saturation pressure of the liquid at a constant temperature. Consequently, HC bubbles grow and suddenly collapse (that is, implode) at relatively high-pressure regions.

[0006] When HC bubbles implode, local microjets and shock waves occur, which generate noise and vibrations that distort the shape close to the exposed surfaces. Moreover, implosion of HC bubbles leads to the formation of hot spots, pressure fluctuations, and highly reactive free radicals. Concerning these destructive consequences of HC, this phenomenon should be controlled in hydraulic machinery such as propellers, pipes, and pumps, owing to erosion and malfunction concerns.

[0007] On the other hand, the phenomenon of HC could be utilized in a variety of engineering applications if a better understanding of its physics and control can be achieved. Moreover, the advances in microfabrication and microfluidic technologies during the last decades have paved the way for HC studies in microdomains. WO 2021 / 141547 Al and WO 2022 / 025836 Al disclose microfluidic systems in which HC is desired. The advantages of micro-scale cavitating flows include a high surface-to-volume ratio, reduced fluid consumption, and improved control over cavitation parameters. In this regard, this trend has also made it possible to use HC in engineering applications where tiny volumes of liquid are required such as in biomedical applications. Promising results could also be found in a number of applications, including heat transfer, energy harvesting, 2D material exfoliation, wastewater treatment, and heat transfer. While these show the variety of HC applications, especially in microscale, the physics behind HC and the associated measuring methods are not well assessed (POINT-1).

[0008] HC phenomenon can be characterized using a variety of imaging methods including X-ray computed tomography, laser-induced fluorescence (LIF), particle image velocimetry (PIV), and high-speed imaging. With the use of these methods, scientists may monitor and examine the features of cavitating flows and the behavior of cavitation bubbles. The aforementioned methods can be used to record flow patterns using mean or instantaneous velocity measurements and to collect data on macro-scale parameters. Nevertheless, these methods are not able to lead to consistent findings in the interaction of multiple phases in chaotic areas. Moreover, limitations on transparency flow in cavitating zones is considered one of the key issues caused by the numerous scattering and reflection effects of visible light. Thus, during recent years other techniques based on X-ray imaging have been developed. However, the inability to obtain a detailed understanding of HC using current X-ray techniques is attributed to the low spatial and temporal scales of the activities occurring inside the chaotic region and the low resolution of the tools developed for cavitation bubble interactions. Significantly, these methods have several drawbacks regarding accessibility, transparency, and cost; and they require specialized optical apparatus and experienced staff members, especially for microscale HC research. Additionally, a typical microscale cavitation device has transparency on one or more sides, enabling flow visualization. Yet, manufacturing transparent, high-pressure-resistant microfluidic HC devices is a big challenge, which delimits their use in various applications and makes a simple fabrication process flow impossible for these devices.

[0009] Pressure measurements are usually performed upstream and downstream of the device in microscale HC studies. Since the first studies in this field, these pressure measurements have been used parametrically for cavitation diagnosis, characterization, and indication of its severity. For example, a prior art study performed pressure measurements upstream and downstream of a microchannel in order to characterize the onset of HC and flow patterns in flow restrictive elements such as micro-orifices, and compare them with conventional scale HC. In said study, cavitating flows are monitored with a high-speed camera and explained the flow patterns with pressure differences. Although such method can be used to characterize cavitation in microdomains, it monitors the evolution of cavitation within the device. HC is affected by microchannel surface properties, impurities contained in respective flowing fluid, and unsteady pressure fields along the microchannel. Hence, inception and HC evolution can be independent from the upstream and downstream pressures in many cases (POINT-2).

[0010] Acoustic noise has been used for the detection, evaluation, and intensity of HC, and surroundings. Such method was employed mostly in conventional scale HC studies. For example, Ardiansyah et. al. placed an acoustic sensor in vicinity of a cavitating conventional scale venturi, and shown that in the case of HC, the noise varies between 600Hz to 20480Hz and as cavitation intensity, the frequencies change from higher frequency to lower frequency (T. Ardiansyah, M. Takahashi, Y. Yoshizawa, M. Nakagawa, K. Miura, M. Asaba, The Onset of Cavitation and the Acoustic Noise Characteristics of Sodium Flow in a Venturi, J. Power Energy Syst. 5 (2011) 33-44. https: / / doi.Org / 10.1299 / jpes.5.33). These noise measurements in HC studies were capable of giving insights into the detection of the cavitation inception, stabilization, and total intensity of the cavitation. However, this monitoring technique alone is insufficient to precisely monitor the cavitation development in microscale HC. Noise data is not captured locally, and total events are only captured (POINT- 3). CN113758675A discloses an auxiliary measurement method based on hydrophone and liquid pressure measurement in addition to high-speed camera measurements for large-scale cavitation devices (POINT-4).

[0011] Moreover, there are some HC cavitation detection methods based on only acoustic detection or pressure measurements in conventional-scale hydraulic machinery. For example, US5353627A proposes a passive acoustic method to detect multiphase flow in pipe systems. W02009016355A2 discloses an ultrasonic acoustic measurement system that detects cavitation in fluid machines such as pumps.

[0012] EP2853683B1 discloses a cavitation detection system, in which, in-line pressure transducers are applied into conventional pipe systems (POINT-5).

[0013] Summary

[0014] In various embodiments, the present disclosure relates to a system and method that overcome the shortcomings in the prior art.

[0015] A further object of the present application is to propose a system and method for detecting, locating and characterizing the onset, development and conclusion of hydrodynamic cavitation in a microfluidic system, without necessitating the acquisition of any optical data or information.

[0016] An even further object of the present application is to propose a simple, robust, low-cost and durable system and a corresponding method for detecting, locating and characterizing the onset, development and conclusion of hydrodynamic cavitation in a microfluidic system.

[0017] These objects are achieved by the set of features that constitute the appended independent claims.

[0018] The present disclosure proposes a microfluidic system that comprises a flow line. The flow line extends along a flow direction between an inlet port and outlet port. The system is arranged for being provided with two or more pressure sensors in hydraulic communication with the flow line at different respective distances from the inlet port along the flow direction. The system is further provided with one or more acoustic sensors in acoustic communication with the flow line.

[0019] The system can comprise two or more pressure communication lines arranged to provide hydraulic communication between the flow line and respective pressure sensors. This measure provides distance between the pressure sensors and the flow line that can be considered to include zones at which cavitation bubble implosions potentially occur. Thus, the pressure sensors can be protected from mechanical damage, in order to provide an increased service life.

[0020] The two or more pressure communication lines can be arranged to extend transverse to the flow direction. In other words, the pressure communication lines can be arranged to extend radially with regard to the flow direction. The system can be provided with a single acoustic sensor, thereby having an enhanced simplicity along with a reduced cost.

[0021] The pressure sensors can be selected from piezoelectric sensors and pressure gauges.

[0022] In a possible embodiment of the system, a number of the pressure sensors is three or more, or even four or more. In other words, the system can be arranged to comprise three or more, or even four or more of the pressure sensors.

[0023] Accordingly, the present disclosure proposes a method for detecting, locating and characterizing a hydrodynamic cavitation in a microfluidic system that comprises a flow line extending along a flow direction between an inlet port and outlet port. The method comprises acquisition of pressure data from two or more locations at respective two or more different flow advancement distances from the inlet port along the flow direction, simultaneous with acquisition of acoustic data from the flow line. The method further comprises use of the pressure data from the two or more locations in combination with simultaneous acoustic data in detecting, locating and characterizing the hydrodynamic cavitation in the flow line.

[0024] The acoustic data can be taken into account in terms of acoustic power spectra and acoustic frequencies detected at one or more point in times.

[0025] In a possible implementation, the method can comprise the acquisition of pressure data from the two or more locations through respective two or more pressure sensors that are in hydraulic communication with the flow line through respective two or more pressure communication lines.

[0026] The pressure data can be acquired from three or more locations at respective three or more different flow advancement distances from the inlet port along the flow direction. In a possible implementation of the method, the pressure data can be acquired from four or more locations at respective four or more different flow advancement distances from the inlet port along the flow direction.

[0027] Brief Description of the Drawings

[0028] Fig.l shows a footprint of an exemplary embodiment of the microfluidic system according to the present disclosure.

[0029] Fig.2 is a diagram in which the ordinates show pressure values in kilopascals from three pressure sensors distributed along a flow line, and abscissa shows time in seconds, during an implementation of the method according to the present disclosure.

[0030] Fig.3 shows, in relation with Fig.2, microscopic view of the flow line in an exemplary system on which the method is implemented, at a first point in time. Fig.4 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a second point in time.

[0031] Fig.5 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a third point in time. Fig.6 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a fourth point in time.

[0032] Fig.7 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a fifth point in time.

[0033] Fig.8 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a sixth point in time.

[0034] Fig.9 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at a seventh point in time.

[0035] Fig.10 shows, in relation with Fig.2, microscopic view of the flow line in the exemplary system shown in Fig.3, at an eighth point in time. Fig.11, in relation with Fig.3 to Fig.6, shows acoustic data taken at the first, second, third and fourth points in time.

[0036] Fig.12, in relation with Fig.7 to Fig.10, shows acoustic data taken at the fifth, sixth, seventh and eighth points in time.

[0037] Reference

[0038] I flow line

[0039] II pressure sensor

[0040] 12 acoustic sensor

[0041] 13 inlet port

[0042] 14 outlet port

[0043] 50 processor

[0044] 100 system

[0045] 110 pressure communication line

[0046] AD acoustic data

[0047] FD flow direction

[0048] L length

[0049] PD pressure data xl first flow advancement distance x2 second flow advancement distance x3 third flow advancement distance tl first point in time t2 second point in time t3 third point in time t4 fourth point in time t5 fifth point in time t6 sixth point in time t7 seventh point in time t8 eighth point in time

[0050] Detailed Description

[0051] With reference to the appended drawings, the present disclosure proposes a method for determination of loci and characteristics of an onset, an inception and a shifting of HC in a microfluidic system (100) that comprises one or more flow lines (1) extending along respective flow directions (FD), the flow line (1) being provided with two or more pressure sensors (11) that are distributed in different respective locations along the flow line (1), and the flow line (1) being further provided with one or more acoustic sensors (12) for obtaining acoustic data (AD) from the flow line (1).

[0052] The method comprises acquisition of pressure data (PD) from the two or more pressure sensors (11) and acoustic data (AD) from the one or more acoustic sensors (12), and correlating the acquired pressure data (PD) and the acoustic data (AD) with one or more flow conditions and one or more flow characteristics. The acoustic data (AD) can be considered to involve frequency and power in decibels (dB).

[0053] The method enables HC-related control in terms of occurrence or avoidance, locus and severity of HC in the system (100).

[0054] In accordance with the proposed method, the present application further discloses a system (100) comprising one or more flow lines (1) extending along respective flow directions (FD). Fig.l shows a schematic plan view of an exemplary embodiment of the system (100) according to the present disclosure.

[0055] The system (100) can be also referred to as microfluidic system or microfluidic device, and can be considered to have a hydraulic diameter (abbreviated as Dh) of 1000 micrometres or smaller across the flow direction (FD) at the flow line (1). The flow line (1) can be also referred to as channel and can be considered as a flow restrictive element that extends between an inlet port (13) and outlet port (14) which can have respective hydraulic diameters (Dh) greater than that of the flow line (1). The flow line (1) can have a length (L) of several thousands of micrometres (e.g., 1000 to 10000 micrometres; for instance, 2000 to 5000 micrometres) along the flow direction (FD).

[0056] The flow line (1) is arranged for being brought into hydraulic communication with two or more pressure sensors (11) at different and respective locations that are distributed along the flow line (1). Thus, the system is arranged for obtaining pressure data (PD) from the respective locations that are distributed along the flow line (1). The pressure sensors (11) can be also considered as pressure gauges or transmitters arranged for provision of real-time pressure data (PD).

[0057] In a relevant aspect within the present context, the system (100) can be considered to be provided (or, arranged for provision) with the two or more pressure sensors (11) in hydraulic communication with the flow line (1) at respective locations distributed along the flow line (1). In a possible embodiment, the system (100) includes two or more pressure communication lines (110) arranged to provide hydraulic communication between the flow line (1) and each of the respective pressure sensors (11). The pressure communication lines (110) provide distance between the flow line (1) and respective pressure sensors (11), thereby protecting the pressure sensors (11) from mechanical damage related to implosion of HC bubbles in the flow line (1).

[0058] The flow line (1) further comprises one or more acoustic sensors (12) for obtaining acoustic data (AD) from the flow line (1). The system (100) is arranged for combining acoustic data (AD) with pressure data (PD) in order to determine the loci and characteristics of an onset, an inception and a shifting of cavitation; including flow conditions / characteristics related thereto.

[0059] In a possible embodiment, the flow line (1) comprises one acoustic sensor (12). Considering that the system (100) is micro-fluidic, the acoustic data (AD) can be correctly collected using a single acoustic sensor (12) without necessitating the employment of further acoustic sensors (12). Thus, this embodiment of the system (100) has reduced complexity, possibility of failures, production costs and labour costs related to difficulty in maintenance.

[0060] The system (100) and method proposed herein serve for the detection and evaluation of HC in microdomains; facilitates the control, monitoring, and characterization of the HC phenomenon. The proposed technology involves real-time local pressure data (PD) measurements during cavitation at different locations (two or more locations; for example, three or more locations, preferably four or more locations) along the flow line (1) and acoustic data (AD) measurements from acoustic sensor (12) in acoustic communication with the flowline (1) (e.g., adjacent to, placed on or within the flow line (1)). Hence, local pressure data (PD) and overall acoustic data (AD) are combined to obtain both local and global flow characteristics.

[0061] In an aspect, pressure data (PD) measurements can be made at positions (that is, flow advancement distances) that are a function of the channel's hydraulic diameter (Dh). The acoustic sensor (12), which can be positioned in vicinity of the flow line (1) where HC can take place, captures and detects cavitation- induced noise. Acoustic data (AD) and pressure data (PD) can be simultaneously collected and / or synchronized with each other.

[0062] HC is initiated by a sudden pressure drop due to the micro flow restrictive elements such as micro-orifices and channels (here, flow line (1)), chaotic multi-phase flows including the formation and collapse of HC bubble, cause to local pressure variation and fluctuations along the restriction elements or cavitation zones (here, inside or after the flow line (1)). In addition, HC bubble collapse and multiphase flow interactions with solid surfaces such as inner walls of the flow line (1), liquid and vapor phases lead to generation of noise with different frequencies and intensities. Therefore, combination of measurements of local wall pressure fluctuations (that is, pressure data (PD) distributed along the flow direction (FD)) and cavitation-induced noise (that is, acoustic data (AD)) enables monitoring and control of the HC phenomenon in terms of cavitation inception (for both prevention and initiation), intensity (related to void fraction, cavitating flow length), stability of the cavitation phenomenon, and evolution of a cavitating flow. Controlling and monitoring these parameters will open new lines for futuristic applications and devices involving HC.

[0063] Features of the proposed system (100) and method enables detection and control of microscale cavitation phenomenon via syncretized or combined real-time local pressure data (PD) and acoustic data (AD) (in other words, noise) measurements without necessitating visualization-based methods, thereby eliminating the necessity of expensive and cumbersome optical instruments such as high-speed cameras and / or microscopes, and resolves challenges related to transparent and durable cavitation-on-a-chip device fabrication. Regarding the elimination of the need for optical instruments, low-durability transparent building materials and enablement of a non-invasive analysis, the combination of pressure data (PD) and acoustic data (AD) provides a synergistic advantage to the subject-matter of the present disclosure.

[0064] The proposed system (100) which can be considered as a microfluidic cavitation-on-a-chip device allows syncretized-combined-real-time pressure and acoustic measurements in microscale. The system (100) can be considered to provide the following features:

[0065] - microfluidic device design and local pressure measurement locations;

[0066] - acoustic sensor (12) implementation for overall flow characteristics;

[0067] - data analysis and interpretation;

[0068] - development and use of a software that is suitable for collection and analysis of the acoustic data (AD) in combination with simultaneous pressure data (PD) from multiple loci along the flow line (1).

[0069] EXAMPLE-1:

[0070] Referring again to Fig.l, a quantity of the two or more pressure sensors (11) is herein exemplified as four. Each pressure sensor (11) is in hydraulic communication with the flow line (1), through respective pressure communication lines (110).

[0071] Considering that Fig.l shows a schematic plan view showing an exemplary layout that is on a x-y plane defined by +x / -x and +y / -y orientations; an exemplary positioning of the acoustic sensor (12) is shown using a dashed line, indicating that the acoustic sensor can be disposed out-of-plane with regard to the x-y plane. That is, considering a case in which the system (100) is laid out on the x-y plane, the acoustic sensor (12) can be disposed on or beneath the plane. The acoustic sensor (12) can be considered in mechanical or vibrational communication with the flow line (1), in order to receive acoustic information from the flow line (1). Here:

[0072] - fluid communication between the flow line (1) and a first pressure sensor (11) corresponds to a locus at a first flow advancement distance (xl) from the inlet port (13) along the flow direction (FD);

[0073] - fluid communication between the flow line (1) and a second pressure sensor (11) corresponds to a locus at a second flow advancement distance (x2) from the inlet port (13) along the flow direction (FD);

[0074] - fluid communication between the flow line (1) and a third pressure sensor (11) corresponds to a locus at a third flow advancement distance (x3) from the inlet port (13) along the flow direction (FD);

[0075] - fluid communication between the flow line (1) and a fourth pressure sensor (11) corresponds to a locus at a fourth flow advancement distance (x4) from the inlet port (13) along the flow direction (FD).

[0076] When the system (100) is in operation, pressure data (PD) from the pressure sensors that are in communication with the flow line (1) at respective flow advancement distances (e.g., xl, x2, x3 and x4) can have different values at a point in time. Pressure data (PD) from each of the two or more pressure sensors (11) and acoustic data (AD) from the acoustic sensor (12) can be transmitted to a processor (50), in order to be processed for detection and characterization of onset, evolution (or, development) and implosion of HC. Differences in terms of magnitude, changes and other possible relevant characteristics between pressure data (PD) of pressure sensors (11) at different flow advancement distances from the inlet port (13) can be used in locating the onset, development and implosion of HC in the flow line (1). The pressure data (PD) is supported by acoustic data (AD), thereby providing an advanced characterization of the HC phenomenon.

[0077] Hence, by combining acoustic data (AD) from the flow line (1) with pressure data (PD) from the plurality of pressure sensors (11) distributed in the flow line (1) at different flow advancement distances (xl, x2; and if applicable, x3, x4 and so on) along the flow direction (FD); the proposed method enables the characterization of HC phenomenon, without necessitating transparent structure, optical devices such as high-speed camera and microscope, and without being invasive.

[0078] For a flow line with a geometry in an envisaged microfluidic device, a system (100) according to the present disclosure with a comparable or identical geometry can be used for acquisition of pressure data (PD) and acoustic data (AD); in order to have location-based information on the onset, development and implosion of HC in the envisaged microfluidic device. It can be considered that the operating conditions such as temperature and a model fluid (that is, liquid) that mimics the fluid to be run through the microfluidic device can be employed in the system (100); thereby a comparable or equivalent viscosity and specific volume (thus, linear velocity) can be achieved through the experiment. Within the present context, the term 'geometry' is considered to involve, e.g., hydraulic diameter (Dh) and length (L) in a planned flow direction (FD) of a flow line (1). It can be also considered that the proposed system (100) and method enable a non- invasive trial-and-error test, by which conditions relevant to avoidance or absence, and incurrence, extent, onset location, development location and implosion location of HC can be determined. Hence, - in the case where HC is desired to take place in a preferred locus (e.g., at a flow advancement distance relative to a respective inlet port (13)), required flow conditions in view of fluids dynamics (e.g., linear velocity, mass flow rate, pressure drop at a unit length along the flow direction (FD)) can be determined; and / or

[0079] - in the case where HC is not desired, limitations regarding the flow conditions in order to avoid occurrence of HC can be determined (e.g., a maximum allowable value of linear velocity, mass flow rate, and / or pressure drop at a unit length along the flow direction (FD)).

[0080] EXAMPLE-2:

[0081] The fluid enters the flow line (1) through the inlet port (13) and exits through the outlet port (14) while HC can occur in the flow line (1). Local pressure data (PD) measurements are made at pre-determined locations on the walls of the microchannel (flow line (1)) that respectively correspond to first flow advancement distance (xl), second flow advancement distance (x2), third flow advancement distance (x3) and fourth flow advancement distance (x4). The loci of these measurement locations can be considered as a function of the hydrodynamic diameter (Dh) and the length (L) of the flow line (1) along the flow direction (FD). For example, loci of hydrodynamic communication of the plurality of pressure sensors (11) can be positioned at respective flow advancement distances that correspond to 4Dh, 6Dh, lODh, and 15Dh. (that is, four, six, ten and fifteen folds of hydrodynamic diameter (Dh), respectively), as in the exemplary system (100) shown in Fig.3 to Fig.10.

[0082] In the present EXAMPLE-2, with reference to Fig.2 to Fig.12, particularly with reference to Fig.3 to Fig.10, the proposed method was experimented using an exemplary system (100) provided with three pressure sensors (11) for which the first flow advancement distance (xl), second flow advancement distance (x2) and third flow advancement distance (x3) were arranged as 4Dh, 13Dh and 18Dh, respectively. Referring to Fig.2, pressure data (PD) (in kilopascals, kPa) acquired from pressure sensors (11) that are in hydraulic communication with the flow line (1) at the first flow advancement distance (xl), second flow advancement distance (x2) and third flow advancement distance (x3) are shown in ordinate axis versus time (in seconds, s) in abscissa. Referring to Fig.2, the selected and indicated points in time correspond to: a first point in time (tl) which is 19.20 s (that is, seconds), a second point in time (t2) which is 29.99 s, a third point in time (t3) which is 44.80 s, a fourth point in time (t4) which is 80.96 s, a fifth point in time (t5) which is 99.99 s, a sixth point in time (t6) which is 103.63 s, a seventh point in time (t7) which is 159.85 s and an eighth point in time (t8) which is 290.47 s. For interpretation of Fig.2, at the first flow advancement distance (xl), t2 can be considered as a point in time in which an onset of HC occurs, and a progress of HC take place between t2 and t5. It can be further considered that a respective implosion of HC bubble(s) takes place in the interval between the point in times t5 and t6.

[0083] In line with Fig.2, high-speed photographs of an exemplary system (100) are shown in Fig.3 to Fig.10 captured at the first point in time (tl), second point in time (t2), third point in time (t3), fourth point in time (t4), fifth point in time (t5), sixth point in time (t6), seventh point in time (t7) and eighth point in time (t8), respectively.

[0084] For informative reasons, several features including the exemplary flow advancement distances (xl to x3) and respective pressure communication lines (110), inlet port (13), and flow line (1) are only shown in Fig.3, and the layout of the system (100) in Fig. 4 to Fig.10 remains identical with that shown in Fig.3. To avoid blocking visual presentation of the HC-related phenomena, these features are intentionally not indicated in Fig.4 to Fig.10. It should be considered the features indicated in Fig.3 with reference signs equally apply to Fig.4 to Fig.10.

[0085] Distributed pressure data (PD) measurement locations (that is, flow advancement distances (xl to x3) at which respective pressure sensors (11) are in hydrodynamic communication with the flow line (1)) can be considered as openings of respective pressure communication lines (110) dedicated to each of the pressure sensors (11), where real-time local pressure data (PD) measurements can be performed without disturbing the fluid flow through the flow line (1). It can be considered that cavitation can be observed only in a liquid; therefore, the term 'fluid' in the present disclosure corresponds to a liquid. Since liquids are practically non- compressible and the pressure communication lines (110) provide hydrodynamic communication between the flow line (1) and respective pressure sensors (11); fluctuations in local pressure at a flow advancement distance (xl, x2 or x3) simultaneously apply to pressure data (PD) that are acquired by a respective pressure sensor (11).

[0086] The pressure sensors (11) can be of any suitable type, including piezoelectric sensors and pressure gauges.

[0087] To record and analyze acoustic data (AD) simultaneously with local pressure data (PD) measurements, the acoustic sensor (12) is arranged in acoustic communication with the flow line (1) in order to collect global flow information.

[0088] Fig.11 represents HC-induced acoustic power spectra as acoustic data (AD) acquired via the acoustic sensor (12), in terms of acoustic power spectra at ordinates (in deciBells, dB) for each of the first to fourth points in time (tl to t4), versus frequencies in Hertz (abbreviated as Hz) at abscissa. Likewise, Fig.12 represents the same for each of the fifth to eighth points in time (t5 to t8). So, using the method according to the present disclosure, the system (100) can be first set using an optical device such as a high-speed camera as in the present example; using also acoustic data (AD) along with pressure data (PD) acquired via the plurality of pressure sensors (11). So, a location-based correlation between the onset, development and implosion of HC bubbles can be arranged on connection with pressure data (PD) and simultaneous acoustic data (AD). Such knowledge (that is, correlation) obtained from the system (100) can be used in controlled induction or avoidance of HC in a microfluidic device having a flow restrictive element with a geometry (e.g., hydrodynamic diameter (Dh) and length (L)) which is equivalent to that of the flow line (1) of the system (100). To this end, fluid that runs in the system (100) during this test is preferred to be also equivalent to a fluid to be conducted through the microfluidic device. As a result, controlled arrangement of flow parameters in use of such microfluidic device can be achieved without necessitating any optical device and optically transparent structure.

[0089] The acoustic sensor (12) can be considered to be placed in a vicinity of the cavitation zone, that is, flow line (1). For instance, the acoustic sensor (12) can be implemented on a front side, upper side, back side or lower side of the system (100), when in use. An optimal positioning of the acoustic sensor (12) relative to the flow line (1) can be considered contingent upon a type and properties of the acoustic sensor (12) and, such as whether the acoustic sensor (12) operates in a contact or contactless mode. When properly equipped, a suitably sensitive acoustic sensor (12) enables a real-time recording of acoustic data (AD) (that is, cavitation- induced noise). The acoustic data (AD) can be analyzed using any suitable signal analysis method, together with the local pressure data (PD) measurements that are obtained simultaneously, and used for cavitating flow monitoring and control in the system (100), as well as in a microfluidic device with comparable or equivalent geometry and operating conditions or parameters. The recorded audio raw data as acoustic data (AD) can be considered to be converted into frequency domain for spectrum analysis. In this way, cavitating flow monitoring can be performed upon frequency power changes in frequency ranges over time.

[0090] Our preliminary findings demonstrate that acoustic data (AD) measurements provide global information about the onset and evolution of HC across a broad frequency spectrum. Moreover, inception and the progression of HC along the flow line (1) can be tracked using pressure sensors (13) arranged in hydraulic communication with the flow line (1) in a distributed fashion along the flow direction (FD). For instance, in line with the visual demonstrations shown in Fig.3 to Fig.10 in respective combinations with Fig.2, Fig.11 and Fig.12, inception of HC can be accurately diagnosed using real-time local pressure data (PD) measurements that capture localized pressure drops and increases in the cavitation-induced noise power spectrum related to the acoustic data (AD):

[0091] - The sudden pressure drop in the pressure value at the first flow advancement distance (XI) at point in time t2 is due to the onset of a HC on the wall opposite to the respective pressure communication line (110). - The continuous decrease between point in times t2 to t5 shows the progress of the same HC. Referring to Fig.11 and Fig.12, the noise power spectrum values in the time interval between the first and fifth points in time (tl to t5) demonstrate that there is a dramatic extent of increase in the frequencies between 9kHz and 15kHz at the second point in time (t2) and, for the first time, in the frequencies after 20 kHz, and towards point at the fifth point in time (t5), the increase in these frequency values accelerate and the increases begin to shift towards higher frequencies.

[0092] - After the fifth point in time (t5), pressure data (PD) that corresponds to the first flow advancement distance (xl) is stable after the sudden drop, while pressure data (PD) that corresponds to the second flow advancement distance (x2) starts to decline at the sixth point in time (t6), which shows that the HC at said opposite wall reaches a distance of 13Dh and develops in the flow line (1) with the drop in pressure data (PD) values at the second flow advancement distance (x2).

[0093] - At the seventh point in time (t7), the developed sheet cavity in the wall opposite to the pressure communication line (110) at the first flow advancement distance (xl) disappears and forms on the wall which hosts the pressure communication line (110) at the first flow advancement distance (xl); and this dynamic sudden change is detected by pressure sensors (11). This shows that the distributed local pressure measurements can monitor dynamic changes in the progression of HC. This can be explained by the decrease at the second flow advancement distance (x2) suddenly becoming almost stationary and the sudden decrease at the third flow advancement distance (x3). Throughout these points in time, it is seen in the noise power spectrum that, in general, cavitation-induced noise spreads to the 6-17 kHz range in wider bandwidth, the frequency power increases after 20 kHz continues and at these frequencies, the power changes in accordance with the intensity of HC. While the pressure data (PD) values in the local pressure sensors (11) begin to become stable after the seventh point in time (t7), the HC becomes semi-stable in the flow line (1). This can also be seen with a slight decrease in the frequency powers indicated in the noise spectrum. Hence, by implementing simultaneous acquisition of acoustic data (AD) and multiple-location pressure data (PD) and creating synergy between pressure sensors (11) and acoustic sensor (12), the physics of cavitating flows in micro domains, such as the onset of HC, its intensity, and its progression within the flow line (1), can be monitored and controlled precisely without the need for flow visualization.

[0094] It can be contemplated that the present disclosure proposes a pioneering method and system (100) for monitoring cavitating flows in micro domains without necessitating any visualization. The proposed method relies on combined local real-time pressure and acoustic measurements that enable cost-effective monitoring and control of cavitation phenomenon in micro domains. This technology will find practical applications in various fields including diagnostic devices, microelectronic cooling systems, cavitation-based chemical reactors, and micro-mixers, where visualization can be considered disadvantageous because of introducing complexities and durability issues to microfluidic devices. For example, the proposed innovation enables detection of impurities in liquids, such as biological analytes and cells, by characterization of their impacts on inception and intensity of HC. The proposed technology will open new lines for compact HC-on- a-chip devices to be used in different applications thanks to enabling on-chip control and characterization technologies offered herein. Energy saving, micro heat exchangers and thermal fluid system can be considered as immediate and future fields in which the proposed technology find use. The present development is also useful for microelectronic companies and energy companies.

[0095] Regarding POINT-1 above: The measurement system (100) and method of the present disclosure enables progress in technical fields relevant to microfluidic devices, acquiring and producing comprehensive physical knowledge on microscale HC, thereby exploring the vast potential of HC.

[0096] Regarding POINT-2 above: The present disclosure can be considered as focused on utilizing in-channel local pressure measurements and noise of HC in microdomains. In the proposed system (100), pressure fluctuations and acoustic noise enable real-time monitoring of HC inception and evolution of cavitating flows through micro-scale pressure measurements and synchronized acoustic noise. The present disclosure proposes a more precise system and method that rely on in-channel local pressure and acoustic measurements.

[0097] Regarding POINT-3 above: The combination of acoustic measurements with in-channel local pressure measurements in the present disclosure offers detailed monitoring for both local and macro parameters and characteristics of microscale HC without any need for flow visualization.

[0098] Regarding POINT-4 above: The present disclosure proposes a non-invasive context that is suitable for microscale cavitation devices and does not rely merely on visualization, and local pressure data (PD) measurements are made in a distributed fashion along the microchannel, that is, the flow line (1).

[0099] Regarding POINT-5 above: The present disclosure enables a method for use in the microscale cavitation system (100), combining acoustic data (AD) and intra-canal local pressure data (PD) in the flow line (1).

Claims

AMENDED CLAIMS received by the International Bureau on 01 November 2025 (01.11 .2025)1. A microfluidic system (100) comprising a flow line (1) that extends along a flow direction (FD) between an inlet port (13) and outlet port (14); wherein the system (100) is arranged for being provided with two or more pressure sensors (11) in hydraulic communication with the flow line (1) at different respective distances from the inlet port (13) along the flow direction (FD); the system (100) is further provided with one or more acoustic sensors (12) in acoustic communication with the flow line (1).

2. The system according to claim 1; comprising two or more pressure communication lines (110) arranged to provide hydraulic communication between the flow line (1) and respective pressure sensors (11).

3. The system according to claim 2; wherein the two or more pressure communication lines (110) extend transverse to the flow direction (FD).

4. The system according to any of claims 1 to 3, provided with a single acoustic sensor (12).

5. The system according to any of claims 1 to 4, wherein the two or more pressure sensors (11) are selected from piezoelectric sensors and pressure gauges.

6. The system according to any of claims 1 to 5; wherein a number of the pressure sensors (11) is three or more.

7. The system according to claim 6; wherein the number of the pressure sensors (11) is four or more.

8. A method for detecting, locating and characterizing a hydrodynamic cavitation in a microfluidic system(100) comprising a flow line (1) that extends along a flow direction (FD) between an inlet port (13) and outlet port (14); the method comprising acquisition of pressure data (RD) from two or more locations at respective two or more different flow advancement distances from the inlet port (13) along the flow direction (FD), simultaneous with acquisition of acoustic data (AD) from the flow line (1); use of the pressure data (RD) from the two or more locations in combination with simultaneous acoustic data (AD) in detecting, locating and characterizing the hydrodynamic cavitation in the flow line (1).

9. (AMENDED) The method according to claim-6 _8, wherein the acoustic data (AD) is taken into account in terms of acoustic power spectra and acoustic frequencies detected at one or more point in times.

10. (AMENDED) The method according to any of claims 6 or 7 8 or 9, comprising the acquisition of pressure data (RD) from the two or more locations through respective two or more pressure sensors(11) that are in hydraulic communication with the flow line (1) through respective two or more pressure communication lines (110).

11. The method according to any of claims 8 to 10; wherein the pressure data (RD) is acquired from three or more locations at respective three or more different flow advancement distances from the inlet port(13) along the flow direction (FD).

12. The method according to claim 11; wherein the pressure data (RD) is acquired from four or more locations at respective four or more different flow advancement distances from the inlet port (13) along the flow direction (FD).

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