Measuring device, its use, system and procedure for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of a fluid

Abstract

The invention relates to a measuring device (1) for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of a fluid (100) using Raman spectroscopy with, The device (1) comprises at least one analysis chamber (2) for the fluid (100), which has at least one optical input (3) and at least one optical output (4), wherein the measuring device (1) includes an excitation source (5) whose radiation (51) excites the fluid (100) in the at least one analysis chamber (2), and Raman scatter radiation (52) from the fluid (100) is supplied to a spectral analysis unit (7) via an optical system (6) that guides the Raman scatter radiation (52). According to the invention, the optical system (6) comprises an optical fiber (8) which guides the radiation (51) from the excitation source (5) and is configured to couple out at least 90% of the radiation energy of the excitation source (5) introduced into the analysis chamber (2) through the at least one optical output (4). Furthermore, the invention relates to the use of the measuring device and a measuring method as well as a refrigeration and air conditioning system with a measuring device according to the invention.

Description

[0001] The invention relates to a measuring device, a system and a method for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of a fluid using Raman spectroscopy, as well as to the use of the measuring device.

[0002] In technical applications, Raman probes are already used effectively in many technological fields for the analysis of substances and mixtures. This method is also used in industry for quality control. Raman spectroscopy can be used, for example, to investigate the composition of liquids and gases, plastics, minerals, or even biological samples such as cells and tissues.

[0003] Raman spectroscopy is a technique in molecular spectroscopy that uses the interaction of radiation, often in the visible spectral range (i.e., light), with matter to obtain information about the structure or properties of a material. The information obtained in Raman spectroscopy originates from inelastic scattering by an excitation source, such as laser radiation. The underlying Raman effect produces a wavelength spectrum shifted relative to the wavelength of the excitation source. This spectrum is characteristic of the specific vibrations of a molecule and contributes to the identification of a substance.

[0004] German patent application DE 10 2009 026 744 A1 discloses a previously described method and a device for leak testing of components. A component with an internal, sealed volume is used, in which a pressure difference is first created between the sealed volume and a volume surrounding the component, such that a first pressure exists in the sealed volume and a second pressure in the surrounding volume. The number of gas molecules is typically determined in the volume where the lower pressure prevails. After a predetermined time interval, the number of molecules is measured using Raman spectroscopy in the volume where the lower pressure existed. The measured number of molecules is then compared with the number of molecules determined before the time interval. This comparison serves to verify any potential leakage in the component.Such a leak test can be used to check the functionality of the component after its manufacture.

[0005] Furthermore, publication WO 2022 / 199 928 A1 proposes an online or in-situ measuring device for the concentration measurement and quantitative evaluation of a gas or gas mixture using Raman spectroscopy. This device comprises at least one gas measurement chamber for the gas or gas mixture, and includes one or more optical inputs and one or more optical outputs. The measuring device includes a high-power laser that illuminates the gas or gas mixture in at least one measurement chamber with focused light in the visible spectral range. The Raman scatter radiation from the focused illumination of the gas or gas mixture is fed to a spectral analysis unit via an optical system with filters and apertures that amplifies the Raman intensity of the scatter radiation.This enables concentration measurements, particularly of nitrogen and other gases, to be performed in-situ using a compact and mobile measurement or sensor system based on Raman spectroscopy. The proposed online or in-situ measurement device or method for measuring the concentration of gases or gas mixtures can be used, for example, as a calibration system for fuel cells, fuel cell systems, gas sensors, or similar devices.

[0006] Other areas of interest in this field include condensers, which are essential components in numerous technical systems, including refrigeration and air conditioning technology. Optimizing condensation processes, such as reducing the amount of refrigerant required, can be significantly enhanced through analysis and control systems. This optimization is particularly relevant for environmental considerations related to greenhouse gas emissions and local safety concerns when using alternative refrigerants such as hydrocarbons like propane (R290), n-butane (R600), or ammonia (R717), which have a low global warming potential but are highly flammable or toxic.

[0007] The invention is based on the objective of further developing a measuring device, its use and a method for measuring the composition and / or quantitatively evaluating the composition of the components of a fluid.

[0008] The invention is described by the respective features of claim 1 relating to a measuring device, claim 7 relating to a method, claim 10 relating to a system, and claim 11 relating to a use. The further referenced claims relate to advantageous embodiments and further developments of the invention.

[0009] The invention includes a measuring device for measuring the composition and / or concentration and / or quantitatively evaluating the composition and / or concentration of the components of a fluid using Raman spectroscopy, comprising at least one analysis chamber for the fluid, which has at least one optical input and at least one optical output. The measuring device includes an excitation source whose radiation excites the fluid in the at least one analysis chamber and feeds Raman scattered radiation from the fluid to a spectral analysis unit via an optical system that guides the Raman scattered radiation. According to the invention, the optical system comprises an optical fiber that guides the radiation from the excitation source and is configured to extract at least 90% of the radiation energy of the excitation source introduced into the analysis chamber through the at least one optical output.

[0010] Studies have shown that heat transfer during condensation in heat exchanger tubes, such as those commonly used in shell-and-tube heat exchangers, can be significantly improved by using tubes with advanced surface structures compared to smooth tubes. However, in these systems, mixtures play a crucial role alongside pure substances; these mixtures are either unintentionally introduced as non-condensable gases or intentionally used to achieve specific properties.

[0011] According to the invention, the fluids examined with the measuring device can be both pure substances and mixtures of selected components, which are in liquid or gaseous form.

[0012] Results of scientific studies on the inventive measuring device in connection with heat exchanger tubes have shown that the vapor composition of an exemplary fluid mixture has a significant influence on the heat transfer coefficient of the heat exchanger tubes. To determine and monitor the vapor composition during the measurements, Raman spectroscopy was used at the optical inlet of the Raman cell as the analysis chamber. Continuous-wave laser light, for example with a wavelength of 532 nm, was guided from the excitation source to the optical inlet via an optical fiber. The laser beam exiting the optical fiber was collimated and directed into the Raman cell, where it interacts with the fluid flowing perpendicular to it. The Raman scattered radiation emerges from a detection window, which is, for example, arranged at a favorable angle to the incident window, and is collimated.

[0013] The Raman scattered radiation was subsequently coupled back into an optical fiber waveguide and directed to a CCD spectrometer, which recorded the spectrum of the incident radiation. The spectral information was stored on a measurement computer and evaluated in real time using suitable software to monitor changes in concentration.

[0014] It is advantageous if the spectral information of the Raman scattering radiation from a CCD spectrometer is evaluated for monitoring concentration changes either integrally over the entire spectral range or, in particular, only at a wavelength that characterizes the respective fluid. In other words, a monochromatic analysis and relationship of the respective intensities of the Raman scattering radiation to the characteristic peak maxima of a fluid is just as suitable for monitoring concentration changes as the integral acquisition and evaluation of the entire spectrum of a Raman signal.

[0015] A particular advantage of the invention is that the radiation from the excitation source is coupled into the optical fiber of the optical system, thus concentrating all the radiation energy there. This ensures that at least 90%, and preferably at least 95%, of the radiation energy introduced into the analysis chamber by the excitation source is coupled back out via the designated optical output. In the case of flammable or explosive fluids, this eliminates the risk of fire or explosion caused by an uncontrolled energy input from the excitation source's radiation and the associated temperature increase.

[0016] Furthermore, if the radiation energy introduced into the analysis chamber by the excitation source is lower than expected at the optical output, it is advantageous to shut down critical parts of a system or the entire system by means of a safety shutdown and thus eliminate the hazardous situation.

[0017] In a preferred embodiment of the invention, the spectral analysis unit can be arranged in extension to the optical axis of the optical fiber.

[0018] In the design of a measuring device, it is advantageous to perform a measurement both in the 180° direction to the primary wave propagation as backscattering or in the forward direction in transmission.

[0019] Alternatively, the spectral analysis unit can advantageously be arranged at an angle of approximately 90° to the optical axis of the optical fiber. However, the preferred angle of 90° can also deviate by a few degrees, for example by 5°, in either direction during the design process.

[0020] The Raman scattering radiation emerges from a detection window positioned at a 90° angle to the optical input. The scattered radiation is collimated in the direction of propagation after the detection window and coupled into another optical fiber. In this way, the radiation from the excitation source can be transmitted to the optical output, and the inelastically scattered Raman radiation can be directed more or less directly to a spectral analysis unit positioned at a 90° angle.

[0021] In contrast, it is also possible that the measuring device includes at least one further analysis chamber in addition to the analysis chamber, which contains a fluid with a known composition.

[0022] Since Raman spectroscopy is a relative measurement technique, the determination of vapor composition cannot be achieved solely by recording a single spectrum. Using an additional analysis chamber, a prior calibration of the Raman signal from the analysis chamber can be performed to correlate the intensity of specific characteristic peaks with the composition. This calibration can be carried out, for example, in a separate Raman cell as part of the spectral analysis unit designed for the precise determination of a fluid's vapor composition. Advantageously, several Raman spectra can be recorded at different compositions and temperatures for calibration purposes.

[0023] In an advantageous embodiment of the invention, a sensor device for measuring the intensity of the radiation from the excitation source can be arranged after the optical output.

[0024] This sensor device can determine the radiant energy present at the optical output. This can be compared with the radiant energy of the excitation source introduced into the analysis chamber to ensure that at least 90% of the radiant energy is extracted. If deviations below 90% are detected, the systems equipped with the measuring device can be switched to a safe operating mode or shut down completely, if necessary.

[0025] In a further advantageous embodiment of the invention, at least one radiation absorber can be arranged which absorbs the radiation from the excitation source from the analysis room and / or the further analysis room.

[0026] In the beam path, the Raman scattering radiation can, for example, pass through a long-pass filter or other spectral filters, which block the laser radiation and allow the Raman scattering radiation to pass through.

[0027] A further aspect of the invention includes a method for measuring the composition and / or concentration and / or for evaluating the quantitative composition and / or concentration of the components of a fluid using Raman spectroscopy and a measuring device according to the invention. The method comprises at least the following process steps: a) Illumination of the fluid in an analysis chamber using radiation from an excitation source, b) Diverting the radiation from the excitation source from the analysis room and / or a further analysis room into at least one radiation absorber, whereby at least 90% of the radiation energy of the excitation source is coupled out, and c) Receiving Raman scattered radiation from the illuminated analysis room with an optical system and feeding the Raman scattered radiation to a spectral analysis unit.

[0028] The invention is based on the premise that, for example, the vapor composition of a fluid can be continuously measured using Raman spectroscopy. One application is the determination of the mixture concentration of a multi-component fluid or its composition at a heat exchanger in a refrigeration and air conditioning system. Investigations have shown that the heat transfer coefficient for the condensation of zeotropic mixtures as fluids is significantly lower than that for pure substances.

[0029] This is due to the formation of a diffusion layer on the outer surfaces of heat exchanger tubes, caused by the preferential condensation of the respective high-boiling mixture component. Fundamentally, the mixture composition has a strong influence on the condensation heat transfer coefficient, as it affects the formation of the diffusion layer.

[0030] However, studies with tube bundles show that the impacting droplets from the upper rows of tubes appear to partially break up this diffusion layer, resulting in a significant increase in the heat transfer coefficient.

[0031] For example, short-chain hydrocarbon compounds, especially propane, butane and pentane, can be preferably used as fluids in refrigeration and air conditioning systems.

[0032] In an advantageous embodiment of the invention, the intensity of the radiation from the excitation source can be determined according to process step b).

[0033] The radiation energy present at the optical output can be determined by measuring the intensity. A comparison with the radiation energy introduced into the analysis chamber from the excitation source shows what proportion of the radiation energy is coupled back out. If deviations are below 90%, the systems equipped with the measuring device can be switched to a safe operating mode or shut down completely, if necessary.

[0034] In a particularly preferred embodiment, prior to process step b) the radiation (51) coupled out of the analysis chamber of the excitation source (5) can be coupled into a further analysis chamber in which a fluid with a known concentration is contained.

[0035] Using the additional analysis chamber, a prior calibration of the Raman signal from the analysis chamber can be performed to correlate the intensity of specific characteristic peaks with the composition and / or concentration. For calibration, it can be advantageous to record several Raman spectra at different compositions and temperatures.

[0036] Another aspect of the invention includes a refrigeration and air conditioning system comprising a measuring device according to the invention and / or a method according to the invention for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of fluids.

[0037] In such systems, smooth, finned, or high-performance condensing tubes can be used as heat exchanger tubes. Besides pure copper, heat exchanger tubes made of a copper-nickel alloy are also suitable materials.

[0038] Another aspect of the invention includes the use of the measuring device and / or the method according to the invention for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of fluids in refrigeration and air conditioning systems or process and / or plant engineering systems.

[0039] Condensation heat transfer in such systems is preferably carried out for zeotropic mixtures of hydrocarbon compounds, such as n-butane and propane, in conjunction with single tubes or tube bundles.

[0040] The Raman signal remains approximately linear to the molecular concentration, especially in mixtures of butane and propane, and allows for quantitative reproducibility of the measurement signal with minimal fluctuations across the entire molecular concentration range.

[0041] In a preferred embodiment, the measuring device according to the invention can be used in refrigeration and air conditioning systems or process and / or plant engineering systems which are operated with flammable or explosive fluids.

[0042] This enables online monitoring of the steam composition combined with safety aspects of process control using Raman spectroscopy.

[0043] Flammable or explosive fluids can be binary zeotropic mixtures consisting of propane and n-butane, which are used, for example, on horizontal single tubes and in tube bundles in refrigeration and air conditioning systems.

[0044] Exemplary embodiments of the invention are explained in more detail with reference to the schematic drawing.

[0045] It shows: Fig. 1 A schematic representation of a measuring device for use in refrigeration and air conditioning systems.

[0046] Corresponding parts are marked with the same reference symbols in all figures.

[0047] Fig. Figure 1 shows a schematic representation of a measuring device 1 for use in refrigeration and air conditioning systems.

[0048] In these systems, 100 mixtures play a crucial role as fluids, some of which are introduced unintentionally as non-condensable gases or are deliberately used to achieve certain properties.

[0049] Zeotropic mixtures, such as those of propane (R290) and n-butane (R600), exhibit more complex phase change behavior and can differ significantly from the pure substances. Existing models used to predict heat transfer during the condensation of mixtures are subject to large uncertainties and do not account for the influence of finned tubes or additional condensate from other rows within a tube bundle.

[0050] In zeotropic mixtures, the boiling point and dew point curves follow different paths, which are associated with preferential condensation of the higher-boiling component and preferential evaporation of the lower-boiling component. Phase diagrams for zeotropic mixtures of propane and n-butane are known from the prior art.

[0051] The mechanisms influencing condensation heat transfer in zeotropic mixtures have already been described in the scientific literature. At moderate temperature differences between the vapor and the cold boundary layer, the preferential condensation of the high-boiling component increases the concentration of the low-boiling component at the phase boundary. This behavior can significantly affect heat transfer.

[0052] The measuring device 1 according to the invention serves for measuring the composition or for quantitatively evaluating the composition of the components of a fluid 100 by means of Raman spectroscopy. The measuring device 1 has an analysis chamber 2 for a fluid 100. The analysis chamber 2 has an optical input 3 and an optical output 4. The measuring device 1 comprises a high-power laser as an excitation source 5, the coherent radiation 51 of which excites the fluid 100 in the analysis chamber 2.

[0053] In an advantageous embodiment of the invention according to Fig. In 1, the analysis chamber 2 is the interior of a heat exchanger tube 20, which is equipped with an optical inlet 3 and an optical outlet 4. The Raman scattered radiation 52 excited by the fluid 100 is fed to a spectral analysis unit 7 via an optical system 6 that guides the Raman scattered radiation 52. The optical system 6 comprises an optical fiber 8, which guides the radiation 51 from the excitation source 5. The optical system 6 is configured to couple out at least 90% of the radiant energy from the excitation source 5 introduced into the analysis chamber 2 via the optical outlet 4.

[0054] The optical system 6 is equipped with a first coupling device 61 upstream of or at the optical input 3. This coupling device extracts the radiation 51 from the excitation source 5 from the optical fiber 8 and directs it, in a focused beam, through the optical input 3 into the analysis chamber 2. The radiation 51 from the excitation source 5 exits the analysis chamber 2 via the optical output 4 and is guided further along the optical fiber 8 by a second coupling device 62.

[0055] The Raman scatter radiation 52 excited in the analysis chamber 2 is measured at an angle of 90° to the optical axis A of the optical fiber 8. A detection window 63 is integrated into the heat exchanger tube 20 for the exit of the Raman scatter radiation 52 from the analysis chamber 2. The diverging Raman scatter radiation 52 passing through this window is focused by lenses 64, 65 into a third coupling device 63 and guided via a waveguide 71 to the spectral analysis unit 7. A CCD camera, for example, can be used in the spectral analysis unit 7.

[0056] As in Fig.As shown in Figure 1, the radiation 51 from the excitation source 5 is guided via a second coupling device 62 in a waveguide 91 to a further analysis chamber 9 for reference measurement. This further analysis chamber 9 is used to calibrate the Raman signal from the analysis chamber in order to correlate the intensity of specific characteristic peaks with the composition.

[0057] Further along its path, the beam passes through the Raman cell for reference measurement and enters a sensor unit 10 to measure the intensity of the radiation 51 from the laser as excitation source 5. This sensor unit determines the remaining radiation energy. This energy is then compared by an evaluation and control unit 12 with the radiation energy introduced into the analysis chamber from the excitation source to ensure that at least 90% of the radiation energy is extracted. If deviations below 90% are detected, the system equipped with the measuring device is switched to a safe operating state or shut down completely.

[0058] In other words, to comply with explosion protection guidelines, the residual radiation from the excitation source 51 is collected and guided out of the danger zone using additional optical fibers 8 as waveguides. Outside the danger zone, the laser intensities of the incident and outgoing beams are compared to ensure that no laser radiation is absorbed within the experimental setup that could potentially act as an ignition source.

[0059] The radiation 51 remaining from the excitation source 5 is then completely absorbed by a radiation absorber 11, either integrated into or subsequently by the sensor device 10. Reference symbol list 1 measuring device 2 Analysis Room 20 heat exchanger tubes 3 Optical input 4 Optical output 5. Excitation source, high-power laser 51 Radiation from the excitation source 52 Raman scatter radiation 6 Optical System 61 first coupling device 62 second coupling device 63 detection windows 64 lens 65 lens 66 third coupling device 7 Spectral Analysis Unit 71 Waveguide Analysis Unit 8 Optical fiber 9 Further analysis space 91 Waveguide Reference 10 Sensor setup 11 radiation absorbers 12 Evaluation and control unit 100 Fluid 101 Fluid with known composition A optical axis QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 10 2009 026 744 A1

[0004]

Claims

[1] Measuring device (1) for a composition and / or concentration measurement and / or a quantitative composition and / or concentration evaluation of the components of a fluid (100) using Raman spectroscopy with, at least one analysis chamber (2) for the fluid (100) which has at least one optical input (3) and at least one optical output (4), wherein the measuring device (1) includes an excitation source (5) whose radiation (51) excites the fluid (100) in the at least one analysis chamber (2), and feeds Raman scattered radiation (52) from the fluid (100) to a spectral analysis unit (7) via an optical system (6) guiding the Raman scattered radiation (52), characterized by , that the optical system (6) comprises an optical fiber (8) which carries the radiation (51) of the excitation source (5) and is configured to couple out at least 90% of the radiation energy of the excitation source (5) introduced into the analysis space (2) through the at least one optical output (4). [2] Measuring device (1) according to claim 1, characterized by , that the spectral analysis unit (7) is arranged in extension to the optical axis (A) of the optical fiber (8). [3] Measuring device (1) according to claim 1, characterized by , that the spectral analysis unit (7) is arranged at an angle of approximately 90° to the optical axis (A) of the optical fiber (8). [4] Measuring device (1) according to any one of claims 1 to 3, characterized by , that in addition to the analysis chamber (2) it includes at least one further analysis chamber (9) which contains a fluid with a known composition (101). [5] Measuring device (1) according to any one of claims 1 to 4, characterized by , that a sensor device (100) for measuring the intensity of the radiation (51) of the excitation source (5) is arranged after the optical output (4). [6] Measuring device (1) according to any one of claims 1 to 5, characterized by , that at least one radiation absorber (11) is arranged which absorbs the radiation (51) of the excitation source (5) from the analysis room (2) and / or the further analysis room (9) in a radiation absorber (11). [7] Method for measuring a composition and / or concentration and / or for evaluating a quantitative composition and / or concentration of the components of a fluid (100) using Raman spectroscopy and a measuring device (1) according to one of the preceding claims comprising at least the following method steps: a) Illumination of the fluid (100) in an analysis chamber (2) by means of radiation (51) from an excitation source (5), b) Directing the radiation (51) from the excitation source (5) out of the analysis room (2) and / or a further analysis room (9) into at least one radiation absorber (11), whereby at least 90% of the radiation energy of the excitation source (5) is coupled out, and c) Receiving Raman scattered radiation (52) with an optical system (6) from the illuminated analysis room (2) and feeding the Raman scattered radiation (52) to a spectral analysis unit (7). [8] Method according to claim 7, characterized by , that after procedure step b) an intensity determination of the radiation (51) of the excitation source (5) is carried out. [9] Method according to claim 7 or 8, characterized by , that before process step b) the radiation (51) coupled out of the analysis chamber (2) of the excitation source (5) is coupled into a further analysis chamber (9) in which a fluid with known concentration (101) is contained. [10] Refrigeration and air conditioning system comprising a measuring device (1) according to claims 1 to 6 and / or a method according to claims 7 to 9 for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of fluids (100, 101). [11] Use of the measuring device (1) according to claims 1 to 6 and / or the method according to claims 7 to 9 for measuring the composition and / or concentration and / or for quantitatively evaluating the composition and / or concentration of the components of fluids (100, 101) in refrigeration and air conditioning systems or process and / or plant engineering systems. [12] Use of the measuring device (1) according to claim 11 in refrigeration and air conditioning systems or process and / or plant engineering systems which are operated with flammable or explosive fluids.

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