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A special issue of Sensors (ISSN 1424-8220). This special issue belongs to the section "Optical Sensors".

Deadline for manuscript submissions: closed (20 July 2022) | Viewed by 27120

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Special Issue Editors

Prof. Dr. Yasuhiro Egami

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Guest Editor

Department of Mechanical Engineering, Aichi Institute of Technology,1247 Yachigusa, Yakusa-Cho, Toyota 470-0392, Aichi-Prefecture, Japan
Interests: pressure-sensitive paint; temperature-sensitive paint; optical measurement
Special Issues, Collections and Topics in MDPI journals

Prof. Dr. Hiroki Nagai

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Guest Editor

Institute of Fluid Science, Tohoku University, Sendai 982-8577, Japan
Interests: mars airplane; pressure and temperature-sensitive paint; low reynolds number; hypersonic flow; thermofluid dynamics; spacecraft thermal control
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Dr. Yu Matsuda

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Guest Editor

Department of Modern Mechanical Engineering, Waseda University, 3-4-1 Ookubo, Shinjuku-ku, Tokyo 169-8555, Japan
Interests: pressure- and temperature-sensitive paint (PSP, TSP); pressure-sensitive molecular film (PSMP); single-molecule tracking (SMT)
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The purpose of this Special Issue is to contribute to the state-of-the-art by introducing the latest developments in optical pressure (oxygen) and temperature imaging sensors based on the photochemical reaction and their applications. This Special Issue welcomes submissions of original research, novel developments, and experimental studies on optical sensors and their application in optical sensing of thermofluid dynamics.

In recent years, the development of optical pressure (oxygen) and temperature sensors has been remarkable. A pressure sensor based on oxygen quenching has significantly improved the time response. With the improvement of high-speed cameras and the development of measurement methods and post-measurement image processing, the time and pressure resolutions of the pressure imaging measurements are greatly extended. Optical pressure sensors are also applied to measurement on deformed and free-flight objects. Temperature sensors are used not only to measure temperature distribution, but also for a wide range of applications such as to measure heat flux and shear stress, and visualize boundary layer transitions. With the development of sensors, hardware, metrology, and post-image processing, we will be able to apply them to a wider range of measurements. We contribute to the development of new sensing technologies by featuring the latest research cases.

Pressure-sensitive paint (PSP);
Temperature-sensitive paint (TSP);
Pressure (oxygen) sensor;
Thermal sensor;
Luminescence;
Photochemical sensor;
Thermofluid dynamics;
Unsteady measurement;
High-speed imaging.

Optical pressure and temperature sensors, known as pressure- and temperature-sensitive paints, are photochemical sensors based on oxygen quenching and temperature quenching, respectively. These sensors are receiving more and more attention in recent years and are being used by a wider range of researchers and engineers. Therefore, it is of great significance to feature these sensors in Sensors.

Dr. Yasuhiro Egami
Prof. Hiroki Nagai
Dr. Yu Matsuda
Guest Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Sensors is an international peer-reviewed open access semimonthly journal published by MDPI.

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Published Papers (14 papers)

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Research

15 pages, 4239 KiB

Open AccessArticle

Investigation of Formulations on Pyrene-Based Anodized-Aluminum Pressure-Sensitive Paints for Supersonic Phenomena

by Kazuma Yomo, Tsubasa Ikami, Koji Fujita and Hiroki Nagai

Sensors 2022, 22(12), 4430; https://0-doi-org.brum.beds.ac.uk/10.3390/s22124430 - 11 Jun 2022

Cited by 2 | Viewed by 1489

Abstract

Pressure-sensitive paint (PSP) is an optical sensor that can measure global pressure distribution by using the oxygen quenching of dye molecules. In particular, anodized aluminum pressure-sensitive paint (AA-PSP) exhibits a fast time response. AA-PSP has been used in unsteady measurements at supersonic and transonic speeds, such as on the surface of a transonic free-flying sphere or the wall of a shock tube when the shock wave passes. To capture such ultrafast phenomena, the frame rate of the camera must be sufficiently fast, and the exposure time must be sufficiently short. Therefore, it is desirable that the AA-PSP exhibits bright luminescence, high-pressure sensitivity, and fast response time. This study focused on pyrene-based AA-PSPs and investigated their characteristics, such as luminescence intensity and pressure sensitivity, at different anodization times, dipping solvents, and dipping concentrations. Furthermore, a time-response test using a shock tube was conducted on the brightest AA-PSP. Consequently, the time for a 90% rise in pressure was 2.2 μs. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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13 pages, 3775 KiB

Open AccessArticle

Temperature Measurement of Hot Airflow Using Ultra-Fine Thermo-Sensitive Fluorescent Wires

by Shumpei Funatani, Yusaku Tsukamoto and Koji Toriyama

Sensors 2022, 22(9), 3175; https://0-doi-org.brum.beds.ac.uk/10.3390/s22093175 - 21 Apr 2022

Cited by 1 | Viewed by 1257

Abstract

In this paper, we propose a temperature measurement method that uses ultrafine fluorescent wires to reduce the wire diameter to a much lesser extent than a thermocouple. This is possible because its structure is simple and any material can be used for the wire. Hence, ultrafine wires with a Reynolds number of less than 1.0 can be selected. Ultra-fine wires less than 50 µm in diameter were set in the test volume. The wire surfaces were coated with fluorescent paint. The test volume was illuminated using an ultraviolet light-emitting diode. The paint emits very tiny, orange-colored fluorescent light with an intensity that changes with the temperature of the atmosphere. The experimental results showed that the heating/cooling layers were well visualized and the temperature field was well analyzed. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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14 pages, 3304 KiB

Open AccessArticle

Influence of Formulations on Characteristics of Ruthenium-Based Temperature-Sensitive Paints

by Tsubasa Ikami, Koji Fujita and Hiroki Nagai

Sensors 2022, 22(3), 901; https://0-doi-org.brum.beds.ac.uk/10.3390/s22030901 - 25 Jan 2022

Cited by 4 | Viewed by 1817

Abstract

Temperature-sensitive paint (TSP) can optically measure a global temperature distribution using a thermal quenching of dye molecules. The TSP measurement is often used in wind tunnel tests to measure the temperature and flow fields in the aerodynamic field. The measurement accuracy is affected by the characteristics of TSP, such as temperature sensitivity, pressure dependency, luminescent intensity, photostability, and surface condition. The characteristics depend on the formulation of TSP. This study investigates the characteristics of the TSP using dichlorotris (1,10-phenanthroline) ruthenium(II) hydrate (Ru-phen). We compare the characteristics of TSPs using different polymers, solvents, and dye concentrations. The TSPs using polyacrylic acid as a polymer shows linear calibration curves, high luminescent intensity, high photostability, and smooth surface. On the other hand, the TSPs using polymethyl methacrylate have nonlinear calibration curves, low luminescent intensity, strong photodegradation, and a rough surface. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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15 pages, 8969 KiB

Open AccessArticle

An Ultra-Fast TSP on a CNT Heating Layer for Unsteady Temperature and Heat Flux Measurements in Subsonic Flows

by Martin Bitter, Michael Hilfer, Tobias Schubert, Christian Klein and Reinhard Niehuis

Sensors 2022, 22(2), 657; https://0-doi-org.brum.beds.ac.uk/10.3390/s22020657 - 15 Jan 2022

Cited by 5 | Viewed by 1497

Abstract

In this paper, the authors demonstrate the application of a modified Ru(phen)-based temperature-sensitive paint which was originally developed for the evaluation of unsteady aero-thermodynamic phenomena in high Mach number but short duration experiments. In the present work, the modified TSP with a temperature sensitivity of up to −5.6%/K was applied in a low Mach number long-duration test case in a low-pressure environment. For the demonstration of the paint’s performance, a flat plate with a mounted cylinder was set up in the High-Speed Cascade Wind Tunnel (HGK). The test case was designed to generate vortex shedding frequencies up to 4300 Hz which were sampled using a high-speed camera at 40 kHz frame rate to resolve unsteady surface temperature fields for potential heat-transfer estimations. The experiments were carried out at reduced ambient pressure of

p_{\infty}

= 13.8 kPa for three inflow Mach numbers being

M a_{\infty} = [0.3; 0.5; 0.7]

. In order to enable the resolution of very low temperature fluctuations down to the noise floor of

10^{- 5}

K with high spatial and temporal resolution, the flat plate model was equipped with a sprayable carbon nanotube (CNT) heating layer. This constellation, together with the thermal sensors incorporated in the model, allowed for the calculation of a quasi-heat-transfer coefficient from the surface temperature fields. Besides the results of the experiments, the paper highlights the properties of the modified TSP as well as the methodology. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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10 pages, 1672 KiB

Open AccessCommunication

Markerless Image Alignment Method for Pressure-Sensitive Paint Image

by Kyosuke Suzuki, Tomoki Inoue, Takayuki Nagata, Miku Kasai, Taku Nonomura and Yu Matsuda

Sensors 2022, 22(2), 453; https://0-doi-org.brum.beds.ac.uk/10.3390/s22020453 - 07 Jan 2022

Cited by 2 | Viewed by 1824

Abstract

We propose a markerless image alignment method for pressure-sensitive paint measurement data replacing the time-consuming conventional alignment method in which the black markers are placed on the model and are detected manually. In the proposed method, feature points are detected by a boundary detection method, in which the PSP boundary is detected using the Moore-Neighbor tracing algorithm. The performance of the proposed method is compared with the conventional method based on black markers, the difference of Gaussian (DoG) detector, and the Hessian corner detector. The results by the proposed method and the DoG detector are equivalent to each other. On the other hand, the performances of the image alignment using the black marker and the Hessian corner detector are slightly worse compared with the DoG and the proposed method. The computational cost of the proposed method is half of that of the DoG method. The proposed method is a promising for the image alignment in the PSP application in the viewpoint of the alignment precision and computational cost. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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18 pages, 3493 KiB

Open AccessArticle

Characterization and Improvement of Heat Resistance of a Polymer-Ceramic Pressure-Sensitive Paint at High Temperatures

by Takenori Furuya, Takumi Nakai, Masato Imai and Masaharu Kameda

Sensors 2021, 21(24), 8177; https://0-doi-org.brum.beds.ac.uk/10.3390/s21248177 - 07 Dec 2021

Cited by 3 | Viewed by 2436

Abstract

Degradation of fast response pressure-sensitive paints (PSP) above room temperature is a serious problem for PSP measurements in high-temperature environments. A standard polymer-ceramic PSP (PC-PSP) composed of platinum(II)-5,10,15,20-tetrakis-(2,3,4,5,6-pentafluorphenyl)-porphyrin (PtTFPP), titania particles and poly(isobutyl methacrylate) (polyIBM) was characterized to elucidate the degradation mechanism. Applying a two-gate lifetime-based method, the PC-PSP has sufficient pressure and temperature sensitivities even at 100 °C, while the luminescence intensity significantly decreases during the test. Subsequent measurements on thermal and photostability as well as luminescence spectra reveal that the main cause of the degradation is the photodegradation of PtTFPP due to direct exposure of the dye molecules to the atmosphere. In order to suppress such degradation, a small amount of urethane resin is added to the dye solution as a simple additional step in the preparation of PC-PSP. The addition of the urethane resin significantly reduces the degradation of the PSP, although its time response is slightly slower than that of the standard PC-PSP. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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11 pages, 6992 KiB

Open AccessCommunication

Signal Enhancement of Pressure-Sensitive Film Based on Localized Surface Plasmon Resonance

by Bei Zhou, Feng Gu, Yingzheng Liu and Di Peng

Sensors 2021, 21(22), 7627; https://0-doi-org.brum.beds.ac.uk/10.3390/s21227627 - 17 Nov 2021

Cited by 1 | Viewed by 1580

Abstract

Pressure-sensitive films have been used for measurement in micro flow, but thin films have very limited intensity, resulting in poor signal-noise ratio (SNR). This paper presents a pressure-sensitive film whose emission signal is enhanced by silver nanoparticles (AgNPs) based on localized surface plasmon resonance (LSPR). Electronic beam evaporator and annealing furnace are used to fabricate silver nanotexture surface. PtTFPP and polystyrene are dissolved in toluene and then spin-coated on the silver nanotexture surface to prepare the pressure-sensitive films. Signal enhancement of film with AgNPs due to LSPR is analyzed and enhancement effect of samples with different particle sizes and spacer thickness are compared. Pressure and temperature calibrations are performed to assess the sensing performance of pressure-sensitive films. Pressure-sensitive films with AgNPs demonstrate signal enhancement due to LSPR and show promise for measurement in micro flow. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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9 pages, 1533 KiB

Open AccessCommunication

Pressure-Sensitive Nano-Sheet for Optical Pressure Measurement

by Yu Matsuda, Riki Orimo, Yusaku Abe, Yuri Hiraiwa, Yosuke Okamura and Yuta Sunami

Sensors 2021, 21(21), 7168; https://0-doi-org.brum.beds.ac.uk/10.3390/s21217168 - 28 Oct 2021

Cited by 2 | Viewed by 2026

Abstract

Pressure-Sensitive Paint (PSP) is a powerful measurement technique to obtain pressure distribution on a model of interest by measuring the emission intensity of the PSP coating with a camera. Since a PSP coating is prepared by applying a solution containing an organic solvent, generally, by sprayer, the properties such as the pressure- and the temperature-sensitivity depends on the skill of the person applying it. This fabrication process is one of the barriers to use of the PSP technique because of the legal restrictions on the use of organic solvents. Thus, a sticker-like PSP coating is useful because it does not require the use of organic solvent and the applying skill. In this study, we have fabricated freestanding Pressure-Sensitive Nano-Sheet (PSNS) by a sacrificial layer process using a spin-coating method. We employed Pt(II) meso-tetra(pentafluorophenyl)porphine (PtTFPP) as a pressure-sensitive dye and poly(1-trimethylsilyl-propyne) (PTMSP) and poly(L-lactic acid) (PLLA) as a polymer binder; thus, the PSNS samples based on PTMSP and PLLA were prepared. The pressure- and the temperature-sensitivity, the lifetime of the luminescence, and the quantum yield of the fabricated PSNS have been investigated. The pressure-sensitivity of PTMSP-based PSNS is higher than that of PLLA-based PSNS. Conversely, the quantum yield of PLLA-based PSNS is higher than that of PTMSP-based PSNS. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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13 pages, 1164 KiB

Open AccessArticle

FBG-Based Sensor for the Assessment of Heat Transfer Rate of Liquids in a Forced Convective Environment

by Renan Lazaro, Anselmo Frizera-Neto, Carlos Marques, Carlos Eduardo Schmidt Castellani and Arnaldo Leal-Junior

Sensors 2021, 21(20), 6922; https://0-doi-org.brum.beds.ac.uk/10.3390/s21206922 - 19 Oct 2021

Cited by 6 | Viewed by 1768

Abstract

The assessment of heat transfer is a complex task, especially for operations in the oil and gas industry, due to the harsh and flammable workspace. In light of the limitations of conventional sensors in harsh environments, this paper presents a fiber Bragg grating (FBG)-based sensor for the assessment of the heat transfer rate (HTR) in different liquids. To better understand the phenomenon of heat distribution, a preliminary analysis is performed by constructing two similar scenarios: those with and without the thermal insulation of a styrofoam box. The results indicate the need for a minimum of thermal power to balance the generated heat with the thermal losses of the setup. In this minimum heat, the behavior of the thermal distribution changes from quadratic to linear. To assess such features, the estimation of the specific heat capacity and the thermal conductivity of water are performed from 3 W to 12 W, in 3 W steps, resulting in a specific heat of 1.144 cal/g °C and thermal conductivity of 0.5682 W/m °C. The calibration and validation of the HTR sensor is performed in a thermostatic bath. The method, based on the temperature slope relative to the time curve, allowed for the measurement of HTR in water and Kryo 51 oil, for different heat insertion configurations. For water, the HTR estimation was 308.782 W, which means an uncertainty of 2.8% with the reference value of the cooling power (300 W). In Kryo 51 oil, the estimated heat absorbed by the oil was 4.38 kW in heating and 718.14 kW in cooling. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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15 pages, 10968 KiB

Open AccessArticle

Investigation of Factors Causing Nonuniformity in Luminescence Lifetime of Fast-Responding Pressure-Sensitive Paints

by Yasuhiro Egami, Yuya Yamazaki, Naoto Hori, Yosuke Sugioka and Kazuyuki Nakakita

Sensors 2021, 21(18), 6076; https://0-doi-org.brum.beds.ac.uk/10.3390/s21186076 - 10 Sep 2021

Cited by 7 | Viewed by 1500

Abstract

Factors that cause nonuniformity in the luminescence lifetime of pressure-sensitive paints (PSPs) were investigated. The lifetime imaging method of PSP does not theoretically require wind-off reference images. Therefore, it can improve measurement accuracy because it can eliminate errors caused by the deformation or movement of the model during the measurement. However, it is reported that the luminescence lifetime of PSP is not uniform on the model, even under uniform conditions of pressure and temperature. Therefore, reference images are used to compensate for the nonuniformity of the luminescence lifetime, which significantly diminishes the advantages of the lifetime imaging method. In particular, fast-responding PSPs show considerable variation in luminescence lifetime compared to conventional polymer-based PSPs. Therefore, this study investigated and discussed the factors causing the nonuniformity of the luminescence lifetime, such as the luminophore solvent, luminophore concentrations, binder thickness, and spraying conditions. The results obtained suggest that the nonuniformity of the luminophore distribution in the binder caused by the various factors mentioned above during the coating process is closely related to the nonuniformity of the luminescence lifetime. For example, when the thickness of the binder became thinner than 8 μm, the fast-responding PSPs showed a tendency to vary significantly in the luminescence lifetime. In addition, it was found that the luminescence lifetime of fast-responding PSP could be changed in the depth direction of the binder depending on the coating conditions. Therefore, it is important to distribute the luminophore uniformly in the binder layer to create PSPs with a more uniform luminescence lifetime distribution. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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11 pages, 1310 KiB

Open AccessCommunication

Predicting Pressure Sensitivity to Luminophore Content and Paint Thickness of Pressure-Sensitive Paint Using Artificial Neural Network

by Mitsugu Hasegawa, Daiki Kurihara, Yasuhiro Egami, Hirotaka Sakaue and Aleksandar Jemcov

Sensors 2021, 21(15), 5188; https://0-doi-org.brum.beds.ac.uk/10.3390/s21155188 - 30 Jul 2021

Viewed by 1726

Abstract

An artificial neural network (ANN) was constructed and trained for predicting pressure sensitivity using an experimental dataset consisting of luminophore content and paint thickness as chemical and physical inputs. A data augmentation technique was used to increase the number of data points based on the limited experimental observations. The prediction accuracy of the trained ANN was evaluated by using a metric, mean absolute percentage error. The ANN predicted pressure sensitivity to luminophore content and to paint thickness, within confidence intervals based on experimental errors. The present approach of applying ANN and the data augmentation has the potential to predict pressure-sensitive paint (PSP) characterizations that improve the performance of PSP for global surface pressure measurements. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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34 pages, 7470 KiB

Open AccessArticle

Skin-Friction-Based Identification of the Critical Lines in a Transonic, High Reynolds Number Flow via Temperature-Sensitive Paint

by Marco Costantini, Ulrich Henne, Christian Klein and Massimo Miozzi

Sensors 2021, 21(15), 5106; https://0-doi-org.brum.beds.ac.uk/10.3390/s21155106 - 28 Jul 2021

Cited by 4 | Viewed by 2067

Abstract

In this contribution, three methodologies based on temperature-sensitive paint (TSP) data were further developed and applied for the optical determination of the critical locations of flow separation and reattachment in compressible, high Reynolds number flows. The methodologies rely on skin-friction extraction approaches developed for low-speed flows, which were adapted in this work to study flow separation and reattachment in the presence of shock-wave/boundary-layer interaction. In a first approach, skin-friction topological maps were obtained from time-averaged surface temperature distributions, thus enabling the identification of the critical lines as converging and diverging skin-friction lines. In the other two approaches, the critical lines were identified from the maps of the propagation celerity of temperature perturbations, which were determined from time-resolved TSP data. The experiments were conducted at a freestream Mach number of 0.72 and a chord Reynolds number of 9.7 million in the Transonic Wind Tunnel Göttingen on a VA-2 supercritical airfoil model, which was equipped with two exchangeable TSP modules specifically designed for transonic, high Reynolds number tests. The separation and reattachment lines identified via the three different TSP-based approaches were shown to be in mutual agreement, and were also found to be in agreement with reference experimental and numerical data. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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20 pages, 1944 KiB

Open AccessArticle

Frequency Response of Pressure-Sensitive Paints under Low-Pressure Conditions

by Miku Kasai, Daisuke Sasaki, Takayuki Nagata, Taku Nonomura and Keisuke Asai

Sensors 2021, 21(9), 3187; https://0-doi-org.brum.beds.ac.uk/10.3390/s21093187 - 04 May 2021

Cited by 19 | Viewed by 2690

Abstract

The characteristics of fast-response pressure-sensitive paints (PSPs) in low-pressure conditions were evaluated. Three representative porous binders were investigated: polymer-ceramic PSP (PC-PSP), anodized-aluminum PSP (AA-PSP), and thin-layer chromatography PSP (TLC-PSP). For each PSP, two types of luminophores, Pt(II) meso-tetra (pentafluorophenyl) porphine (PtTFPP) and tris(bathophenanthroline) [...] Read more.

_{3}

), were used as sensor molecules. Pressure sensitivities, temperature sensitivities, and photodegradation rates were measured and evaluated using a pressure chamber. The effect of ambient pressure on the frequency response was investigated using an acoustic resonance tube. The diffusivity coefficients of PSPs were estimated from the measured frequency response and luminescent lifetime, and the governing factor of the frequency response under low-pressure conditions was identified. The results of static calibration show that PC-PSP/PtTFPP, AA-PSP/Ru(dpp)

_{3}

, and TLC-PSP/PtTFPP have high pressure sensitivities that exceed 4%/kPa under low-pressure conditions and that temperature sensitivity and photodegradation rates become lower as the ambient pressure decreases. Dynamic calibration results show that the dynamic characteristics of PSPs with PtTFPP are dependent on the ambient pressure, whereas those of PSPs with Ru(dpp)

_{3}

are not influenced by the ambient pressure. This observation indicates that the governing factor in the frequency response under low-pressure conditions is the lifetime for PC-PSP and TLC-PSP, whereas the governing factor for AA-PSP is diffusion. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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15 pages, 1542 KiB

Open AccessArticle

Effect of Oxygen Mole Fraction on Static Properties of Pressure-Sensitive Paint

by Tomohiro Okudera, Takayuki Nagata, Miku Kasai, Yuji Saito, Taku Nonomura and Keisuke Asai

Sensors 2021, 21(4), 1062; https://0-doi-org.brum.beds.ac.uk/10.3390/s21041062 - 04 Feb 2021

Cited by 11 | Viewed by 1961

Abstract

The effects of the oxygen mole fraction on the static properties of pressure-sensitive paint (PSP) were investigated. Sample coupon tests using a calibration chamber were conducted for poly(hexafluoroisopropyl methacrylate)-based PSP (PHFIPM-PSP), polymer/ceramic PSP (PC-PSP), and anodized aluminum PSP (AA-PSP). The oxygen mole fraction [...] Read more.

P_{ref}

) was set to 0.5–140 kPa. Localized Stern–Volmer coefficient

B_{local}

increased and then decreased with increasing oxygen mole fraction. Although

B_{local}

depends on both ambient pressure and the oxygen mole fraction, its effect can be characterized as a function of the partial pressure of oxygen. For AA-PSP and PHFIPM-PSP, which are low-pressure- and relatively low-pressure-type PSPs, respectively,

B_{local}

peaks at

P_{O_{2} ref} < 12

kPa. In contrast, for PC-PSP, which is an atmospheric-pressure-type PSP in the investigated range,

B_{local}

does not have a peak.

B_{local}

has a peak at a relatively high partial pressure of oxygen due to the oxygen permeability of the polymer used in the binder. The peak of

S_{PR}

, which is the emission intensity change with respect to normalized pressure fluctuation, appears at a lower partial pressure of oxygen than that of

B_{local}

. This is because the intensity of PSP becomes quite low at a high partial pressure of oxygen even if

B_{local}

is high. Hence, the optimal oxygen mole fraction depends on the type of PSP and the ambient pressure range of the experiment. This optimal value can be found on the basis of the partial pressure of oxygen. Full article

(This article belongs to the Special Issue Optical Sensors for Flow Diagnostics)

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