Planar imaging thermometry in gaseous flows using upconversion excitation of thermographic phosphors

Temperature measurement in gaseous flows is of significant practical importance for determining convection coefficients for heat transfer calculations, validating computation fluid dynamic simulations, and understanding the fundamentals of turbulent mixing and transport in flows. Here, we report on a new diagnostic technique for measuring temperature in gaseous flows which relies upon upconversion luminescence from inorganic phosphors. The phosphor used for the study consists of erbium (Er³⁺) and ytterbium (Yb³⁺) ions doped into a yttrium oxysulfide host material. The theoretical background behind the upconversion diagnostic is presented and spectral emission data taken using upconversion excitation are used to design a temperature diagnostic which is quite sensitive for temperatures ranging from approximately 300–600 K. Demonstration temperature measurements were performed in an air jet heated to temperatures ranging from 295–523 K. Single-shot images of temperature were obtained with a temperature precision of approximately ±5 K (1 standard deviation basis). This is the first known application of upconversion excitation to imaging temperatures in gaseous flows.     

Investigation of potential laser-induced heating effects when using thermographic phosphors for gas-phase thermometry

The spectral emission from thermographic phosphors in free flow and its dependence of laser energy per cross section area (laser fluence [J/cm²]) has been investigated. Temperature measurements in gaseous flows using thermographic phosphors require higher laser energy than measurements performed on surfaces, due to lower particle density. A troublesome systematic error associated with high fluences would be introduced if the excitation laser heats the particles. In the presented work, three different types of the thermographic phosphor BaMg₂Al₁₀O₁₇:Eu (BAM) are investigated. Spectra of the phosphorescence are achieved for a range of laser fluences. The results show no indications of the laser heating the particles, making further development of phosphor thermography in free-flow applications feasible.     

Surface thermometry in combustion diagnostics by sputtered thin films of thermographic phosphors

The accuracy and robustness of the thermographic phosphors (TP) technique relies in the use of coatings with low thickness, high-intensity luminescent emission and high adhesion to the surfaces. Sputter deposition has been evaluated as an alternative for coating preparation of TPs for surface thermometry in combustion diagnostics. Thin films of \(\hbox {Gd}_{3}\hbox {Ga}_{5}\hbox {O}_{12}{:}\hbox {Cr}^{3+}\) have been deposited on fused silica and stainless steel substrates by radio frequency magnetron sputtering. Physical, chemical, and temperature-dependent luminescence properties of the phosphor films have been evaluated using X-ray diffraction, X-ray photoelectron spectroscopy and laser-induced luminescence, respectively. The results showed that the luminescence features of the thin films must be activated by heat treatment after sputter deposition. The \(\hbox {Gd}_{3}\hbox {Ga}_{5}\hbox {O}_{12}{:}\hbox {Cr}^{3+}\) films exhibited appropriate temperature sensitivity with adequate precision of the temperature determination, proving to be suitable for pointwise (0D) surface thermometry. An evaluation of the spatial homogeneity of the luminescence properties, which has not been yet addressed in the literature for thin films of TPs, revealed that thin \(\hbox {Gd}_3\hbox {Ga}_5\hbox {O}_{12}{:}\hbox {Cr}^{3+}\) films deposited on fused silica can be used for spatially resolved surface thermometry while those deposited on stainless steel require improvements to overcome spatial inhomogeneities of the luminescence lifetimes.     

High-speed planar thermometry and velocimetry using thermographic phosphor particles

Simultaneous gas-phase temperature and velocity imaging using micrometer-size thermographic phosphor particles seeded into the flow is demonstrated at a 3 kHz repetition rate. The velocity field is measured using a standard particle image velocimetry approach, while the temperature is determined from the temperature sensitive phosphorescence emission of the particles following excitation at 355 nm. Since the particles are very small, they rapidly assume the temperature and velocity of the surrounding gas. A single shot temperature precision of better than 5 % was achieved at 500 K. Time-resolved measurements in the wake of a heated cylinder are presented, demonstrating the utility of these imaging diagnostics to observe transient, coupled heat and mass transfer phenomena.     

2D-temperature imaging of single droplets and sprays using thermographic phosphors

A novel 2D-technique for temperature visualization of single droplets and sprays is presented. Laser induced emission from thermographic phosphor seeded to the investigated liquid was detected by a fast framing camera. The subsequent phosphorescence images measured by seven consecutively gated CCD detectors allowed pixel-to-pixel lifetime evaluation of the phosphorescence emission. The temperature at each pixel position was evaluated using a calibration procedure of temperature against lifetime. These measurements were applied first to a free falling water based droplet, then to a suspended droplet in an ultrasonic levitator. Finally, the technique was applied to spray. PACS 07.20.Dt; 46.65.Fi; 32.50.+d; 43.25.Uv; 34.50.Gb     

Simultaneous 2D flow velocity and gas temperature measurements using thermographic phosphors

In this paper a new approach for simultaneous 2D velocity and temperature measurements using phosphoric particles is presented. The phosphoric particles respond to the temperature changes in the flow while acting as tracers for velocity mapping. The temperature sensitive particles were seeded into a heated flow and were excited by a pulsed UV laser. The subsequent red shifted emission was detected and analyzed to infer temperature using calibration procedures for lifetime and emission spectra against temperature. The diameter of the temperature sensitive particles, usually in the range of 1–10 μm, makes them useful for velocity measurements using particle image velocimetry (PIV). As such, simultaneous measurement of temperature and flow velocity of a gaseous flow were performed and presented. PACS  42.62.-b; 47.80.Cb; 47.80.Fg     

Determination of surface normal temperature gradients using thermographic phosphors and filtered Rayleigh scattering

Wall temperature as well as the temperature distribution within or close-by the boundary layer of an electrically heated axisymmetric jet impinging on a flat plate were monitored to deduce wall-normal temperature gradients. The radial surface temperature profile of the plate was determined by coating it with thermographic phosphors (TPs), materials whose phosphorescence decay time is dependent on their temperature. The TP was excited electronically by a frequency-tripled Nd:YAG laser (355 nm) and the temporal decay of the phosphorescence intensity was measured zero-dimensionally by a photomultiplier tube. In this case the 659-nm emission line of Mg₃F₂GeO₄:Mn was monitored. The non-intrusive measurement of gas temperatures near the surface was performed two-dimensionally by filtered Rayleigh scattering (FRS). A tunable frequency-tripled single-longitudinal-mode alexandrite laser beam at 254 nm was formed into a light sheet pointing parallel to the surface. The scattered light was imaged through a very narrow linewidth atomic mercury filter onto an intensified charged coupled device (ICCD). The elastic stray light from surfaces was strongly suppressed, whereas Doppler-broadened light was detected. Thermographic phosphors proved to be reliable for the measurement of surface temperatures. Dependent on the specific experimental conditions, problems appeared with signals interfering with the FRS radiation close-by the surface. Results and challenges of this approach are discussed. PACS 07.20.Dt; 32.50.+d; 44.20.+b; 42.65.Es; 33.20.Fb     

A novel strategy to improve the sensitivity of aerosol phosphor thermometry using co-doped phosphors

A novel strategy is presented to improve the temperature sensitivity and potentially extend the temperature range of aerosol phosphor thermometry (APT) by co-doping host materials with two rare-earth ions. The ratio of the emission bands from each ion are measured and calibrated versus temperature to utilize the high sensitivity of thermographic phosphor absolute signal levels. The potential of the technique is illustrated using trivalent cerium (Ce³⁺) and praseodymium (Pr³⁺) co-doped into yttrium aluminum garnet (Ce,Pr:YAG). The measured fractional sensitivity of this phosphor from 300–450 K was 0.004–0.006 K⁻¹, a factor of 1.5–2 better than previously observed for Eu:BAM. Additionally, the single-shot precision (1σ) was between 9 and 25 K over the range of temperatures measured, illustrating the utility of this co-doping strategy. The level of temperature sensitivity and single-shot precision observed here should be achievable over different temperature ranges by doping Ce³⁺ and Pr³⁺ into different hosts. This new strategy should provide a pathway to ultimately extend the high-temperature single-shot measurement limit for APT to temperatures greater than 1000 K and push forward the state-of-the-art for planar temperature diagnostics in combustion applications.     

A research bibliography on the temperature dependencies of thermographic phosphors

We have prepared a comprehensive research bibliography on the fundamental physics and engineering applications of thermographic phosphors. It is available upon request.     

Two-dimensional cycle-resolved exhaust valve temperature measurements in an optically accessible internal combustion engine using thermographic phosphors

Phosphor thermometry was employed to measure the temperature distribution of the exhaust valves in an optically accessible direct injection internal combustion engine. A CMOS high-speed camera was used to two-dimensionally resolve the temperature dependent luminescence decay of the phosphor Gd₃Ga₅O₁₂:Cr. Measurements were performed under motored and fired conditions for several degrees crank angle to determine the temperature distributions within cycles. Additionally, several binders have been tested in terms of survivability and signal strength to guarantee ideal phosphor coating.     

Progress towards absolute intensity measurements of emissions from high temperature thermographic phosphors

Phosphor thermometry has been successfully used in a number of applications ranging from turbo-machinery, pyrolysis, supersonic and hypersonic studies in the past few decades. There are a number of issues related to high temperature, which include faster decays, decreasing emission intensity and increasing blackbody radiation. Although absolute lifetime decay values are readily available, there has been no known work presenting absolute intensity measurements throughout the phosphors operating temperature range. This additional information could help design engineers facilitate phosphor and instrument selection, optimise system setup, and help estimate the performance of the technique at higher temperatures, for any given optical setup. A number of well known high temperature thermographic phosphors were investigated including YAG:Tm, YAG:Tb and Y₂O₃:Eu from 20 °C in an excess of 1000 °C. Both 355 and 266 nm excitation wavelengths from a Q-switched Nd:YAG laser were used. The subsequent emissions were passed through a narrowband interference filter to isolate the peak emission wavelengths, and were collected using PMT. The methodology for an absolute measurement, which requires a sound understanding of the PMT, including solid angle, collection efficiency, dynode gain, calibration and electronic temporal response for intensity measurements is presented and discussed. The results clearly indicate a variation in phosphor intensity with an increasing temperature, which is considerably different amongst different phosphors under different excitation wavelengths. The combined standard uncertainty of measurement was estimated to be approximately ±10.7%. The existing system was able to monitor intensity values up to 900 °C for Mg₃F₂GeO₄:Mn phosphors, 1100 °C for Y2O3:Eu, 1150 °C for YAG:Tb and up to 1400 °C for YAG:Tm thermographic phosphors. Y₂O₃:Eu using 266 nm excitation was found to exhibit the highest peak intensity per mJ of laser excitation from all the phosphors investigated at 20 °C. However, at high temperatures (900 °C+) YAG:Tm using 355 nm excitation was found to exhibit the highest peak intensity per mJ of an excitation energy.     

Two-dimensional gas-phase temperature measurements using phosphor thermometry

A new technique based on phosphor thermometry for measurements of two-dimensional gas-phase temperature, was examined as a new laser diagnostic. Calibration of Dy:YAG phosphor was carried out on the surface of a solid. The data were applicable for gas thermometry since the validation of the line intensity ratios method, showed good agreement with both the lifetime method and thermocouple data in a steady gas flow. Single-shot phosphor thermometry was examined in turbulent combustion in an engine. A reasonable temperature deviation and agreement with calculated data to within 5% precision was achieved in the ignition process of a compression ignition engine. Influencing factors such as chemical luminescence and intrusion into the combustion have also been discussed. PACS 07.20.Dt; 33.50.Dq; 42.62.-b     

Co-doped Y2O3:Tb3+/Tm3+ multicolor emitting phosphors for thermometry

In this study, the new temperature-dependent phosphor, Y2O3:Tb3+/Tm3+, was investigated for high-temperature thermometry. The photoluminescence intensity at 456?nm emitted from Tm3+ was strong at temperatures higher than 1100?K, whereas the peak intensities emitted from Tb3+ decreased due to the thermal quenching effect. Thus, the intensity ratio between those emissions showed an appropriate variation for thermometry over a wide temperature range. In addition, the phosphors showed a distinct change of visible emission colors from green to blue with increasing temperature. These findings suggest the applicability of these phosphors in visual thermo-sensors.     

Fast thermometry for trapped atoms using recoil-induced resonance

We have employed recoil-induced resonance(RIR) with linewidth on the order of 10 k Hz to demonstrate the fast thermometry for ultracold atoms. We theoretically calculate the absorption spectrum of RIR which agrees well with the experimental results. The temperature of the ultracold sample derived from the RIR spectrum is T = 84 ± 4.5 μK, which is close to 85 μK that measured by the method of time-of-flight absorption imaging. To exhibit the fast measurement advantage in applying RIR to the ultracold atom thermometry, we study the dependence of ultracold sample temperature on the trapping beam frequency detuning. This method can be applied to determine the translational temperature of molecules in photoassociation dynamics.     

Temperature measurement using infrared thermometry within semi-transparent media

ABSTRACT

Infrared thermometry is a widely used technique for contactless temperature measurement, which is often conducted through semi-transparent media. In the present work, influences on the measurement results stemming from semi-transparent media and from the optical characteristics of the measurement setup are discussed. Results of two experimental setups, containing low, medium, and high transmission media are presented and compared to calculated data using a one-dimensional analytical approach and a three-dimensional ray-tracing algorithm. It is shown through modeling and experiments that the surroundings and, in particular, the (semi)transparent materials within the optical path are critical for accurate temperature measurements.     

Assessing concrete density using infrared thermographic (IRT) images

This paper presents the results of a study conducted to evaluate the possibility of utilizing infrared thermography to assess the quality of concrete. Concrete specimens were prepared with varying water to cement (w/c) ratio, cement content and consolidation effort. The concrete specimens were heated and the IRT images were recorded as they cooled down. The IR thermographs indicated a good variation in the surface temperature with varying concrete composition and consolidation effort. Concrete with similar composition exhibited a greater variation in surface temperature as the consolidation effort was decreased; indicating the presence of less dense structure in the specimens prepared with low consolidation effort. An increase in the water–cement ratio also increases the temperature variation indicating a decrease in the concrete denseness. The variation in cement content also influenced the denseness of concrete as indicated by the enhanced variation in the surface temperature. Concrete specimens with cement content of 300 kg/m³ (less dense) exhibited a greater temperature variation compared to those prepared with cement content of 400 kg/m³ (more dense).     

Induction motor inter turn fault detection using infrared thermographic analysis

Induction motors are the most commonly used prime movers in industries. These are subjected to various environmental, thermal and load stresses that ultimately reduces the motor efficiency and later leads to failure. Inter turn fault is the second most commonly observed faults in the motors and is considered the most severe. It can lead to the failure of complete phase and can even cause accidents, if left undetected or untreated. This paper proposes an online and non invasive technique that uses infrared thermography, in order to detect the presence of inter turn fault in induction motor drive. Two methods have been proposed that detect the fault and estimate its severity. One method uses transient thermal monitoring during the start of motor and other applies pseudo coloring technique on infrared image of the motor, after it reaches a thermal steady state. The designed template for pseudo-coloring is in acquiescence with the InterNational Electrical Testing Association (NETA) thermographic standard. An index is proposed to assess the severity of the fault present in the motor.     

One-dimensional single-shot thermometry in flames using femtosecond-CARS line imaging

We report single-laser-shot one-dimensional thermometry in flames using femtosecond coherent anti-Stokes Raman scattering (fs-CARS) line imaging. Fs-CARS enables high-repetition-rate (1-10?kHz), nearly collision-free measurement of temperature and species concentration in reacting flows. Two high-power 800?nm beams are used as the pump and probe beams and a 983?nm beam is used as the Stokes beam for CARS signal generation from the N2Q-branch transitions at ～2330?cm(-1). The probe beam is frequency-chirped for single-laser-shot imaging. All three laser beams are formed into sheets and crossed in a line which forms the probe region. The resulting 1D line-CARS signal at ～675?nm is spatially and spectrally resolved and recorded as a two-dimensional (2D) image. Single-shot temperature measurements are demonstrated in flat-field flames up to temperatures exceeding 2000?K, demonstrating the potential of fs-CARS line imaging for high-repetition-rate thermometry in turbulent flames. Such measurements can provide valuable data to validate complex turbulent-combustion models as well as increase the understanding of the spatio-temporal instabilities in practical combustion devices such as modern gas-turbine combustors and augmentors.