Non-intrusive Temperature Measurement Research Articles

Simultaneous measurement of liquid water film thickness and vapor temperature using near-infrared tunable diode laser spectroscopy

A fiber-based multiplexed tunable diode-laser absorption sensor with three near-infrared distributed-feedback diode lasers at ∼1.4 μm is used for simultaneous nonintrusive measurements of liquid water film thickness and vapor-phase temperature. Water film thicknesses are derived from broad-band absorption determined at two fixed wavelengths while gas-phase temperature above the film is obtained via two-line thermometry using the fast wavelength tuning with line-integrating absorption. Probing the liquid film at two wavelengths with significantly different liquid-phase absorption cross sections allows discriminating against additional signal losses due to surface fowling, reflection, and beam steering. The technique is demonstrated for liquid layers of defined thicknesses and in time-resolved measurements of evaporating films.

E143 炎色反応による燃焼火炎の非接触温度計測(OS-12:次世代の燃焼技術(IV))

E143 炎色反応による燃焼火炎の非接触温度計測(OS-12:次世代の燃焼技術(IV))

Non-intrusive temperature measurement using microscale visualization techniques

μPIV is a widely accepted tool for making accurate measurements in microscale flows. The particles that are used to seed the flow, due to their small size, undergo Brownian motion which adds a random noise component to the measurements. Brownian motion introduces an undesirable error in the velocity measurements, but also contains valuable temperature information. A PIV algorithm which detects both the location and broadening of the correlation peak can measure velocity as well as temperature simultaneously using the same set of images. The approach presented in this work eliminates the use of the calibration constant used in the literature (Hohreiter et al. in Meas Sci Technol 13(7):1072–1078, 2002), making the method system-independent, and reducing the uncertainty involved in the technique. The temperature in a stationary fluid was experimentally measured using this technique and compared to that obtained using the particle tracking thermometry method and a novel method, low image density PIV. The method of cross-correlation PIV was modified to measure the temperature of a moving fluid. A standard epi-fluorescence μPIV system was used for all the measurements. The experiments were conducted using spherical fluorescent polystyrene-latex particles suspended in water. Temperatures ranging from 20 to 80°C were measured. This method allows simultaneous non-intrusive temperature and velocity measurements in integrated cooling systems and lab-on-a-chip devices.

Microscale Thermal Transport and Electromechanical Microfluidic Actuation

This paper summarizes recent advances in fundamental research on microscale thermal transport in phase-change processes and developments in novel microfluidic actuation methods using electromechanical effects. The research topics covered include thin-film transport, pool boiling heat transfer enhancement, convective flow boiling in microchannels, microscale ionic winds, micropumping using electrohydrodynamic effects including ion induction and dielectrophoresis, and electrowetting-based control of liquid droplet motion. Progress in microscale flow characterization and non-intrusive temperature measurement is also discussed.

Film thickness effects on calibrations of a narrowband thermochromic liquid crystal

Thermochromic liquid crystals (TLCs) have been widely employed by researchers in heat transfer and fluid flow communities as a reliable and non-intrusive temperature measurement tool due to their unique optical properties such as birefringence, optical activity, circular dichroism and selective reflection of colours in the visible spectrum as function of temperature. The use of narrowband TLCs are attractive for temperature and heat transfer measurements due to their higher precision in temperature measurements and due to the fact that narrowband TLCs are less affected by variations in illumination-viewing angles and illumination disturbances. Narrowband TLCs have been used with full intensity-matching methods to provide robust image processing for measurements of thermal parameters in transient heat transfer tests. Calibration of narrowband TLCs is necessary in order to obtain the intensity-temperature relationship of the TLCs. Film thickness is one of the factors which affects calibrations of TLCs. In this research, film thicknesses of 10, 20, 30, 40 and 50 μm were investigated on green intensity-based calibrations of R35C1W TLC during heating and cooling. Results showed an increase in magnitude of peak green intensity with increasing film thickness, with a percentage increase of nearly 18% when film thickness increased from 10 to 50 μm. Results also showed an inconsistent shift in temperature at which peak green intensity occurs, with a maximum shift of 0.40 °C, suggesting that film thickness effects may be insignificant for narrowband TLCs compared with wideband TLCs. A theoretical method for estimating the volume of TLC coating required to achieve a desired film thickness has also been described in this paper, based on the surface area and dry solids content of the TLC. The method is easily implemented and applicable for sprayable TLC coatings.

Comparison between multiwavelength infrared and visible pyrometry: Application to metals

A device for non-intrusive temperature measurements of metallic materials has been developed. Moreover, as the emissive properties of the metal cannot be known a priori, multiwavelength pyrometry was used to address this issue in the following way:– Simultaneous measurement of thermal emission at N wavelengths.– Use technique of parameter identification including a physical or an empirical model for the emissivity to determine temperature and spectral emissivity.This method was applied to a temperature range between 500K and the melting/solidification point of the metallic materials. The results obtained in visible and infrared spectral range were compared. Various metallic samples were studied (steels, titanium), and for each sample, the relative deviation between identified and experimental (thermocouple) temperatures is lower than 2%, using the more suitable models. For some groups of materials (austenitic stainless steels, and carbon steels), one or several models giving suitable results for similar samples were selected.

Real time, non-intrusive measurement of particle emissivity and gas temperature in coal-fired power plants

We present a novel, remote technique for measuring in situ and in real time (every 2 s) the spectral emissivity of particles at λ = 3.95 µm, in optically thick combustion environments. The novelty lies in the use of spectral information in the mid-IR (the blackbody emission profile of the 4.3 µm CO2 band and the gray emission profile of particles between 3.8 and 4.1 µm) to determine the physical and brightness temperatures of the gas–particle medium, from which particle emissivity can be calculated. The retrieved particle emissivity at 3.95 µm is a reasonable average of total particle emissivity between 1 and 15 µm. Thus, CFD researchers who work with radiation sub-models may use this technique to obtain in situ emissivities at different locations, with a portable, rugged and inexpensive device. A small prototype was built with off-the-shelf components: standard light collection optics, a grating spectrometer and a linear-array pyroelectric detector. The particle emissivity is calculated from the asymptotic solution of the radiative transfer equation for optically thick media with isotropic scatterers. Results from a proof-of-concept test at a full-scale, coal-fired boiler 10 m above the top row of burners showed an average particle emissivity of 0.41 and an average gas temperature of 1533 K. Intrinsic and prototype error as well as the impact of temperature gradients in the line of sight of the instrument are discussed.

Experimental tests of dropwise cooling on infrared-transparent media

The present work is aimed at analyzing the cooling of hot solid surfaces induced by liquid droplets. In particular, the study is focused on the non-intrusive measurement of the transient contact temperature between impinging droplets and hot solid surfaces. An experimental apparatus was built and set up in order to approach the non-trivial problem of the measurement of a solid–liquid interface temperature after droplet impingement. The solid–liquid interface temperature was monitored from below through a transparent-to-infrared material. That material had been coated with a very thin layer of high-emissivity, opaque paint on its upper side, so that it could effectively respond to the infrared camera located below. The paper reports the main results that have been collected to date, with particular regard to the approaches used to coat the transparent solid. Some considerations are also expressed about the effectiveness of the proposed method and about the improvements that are currently being implemented to get new and more accurate interface temperature measurements.

Spatially resolved optical measurements of water partial pressure and temperature in a PEM fuel cell under dynamic operating conditions

In situ non-intrusive measurements of water vapor partial pressure and temperature were performed simultaneously along two gas channels on the cathode side of a PEM fuel cell using tunable diode laser absorption spectroscopy. This measurement technique developed by us was utilized earlier to make measurements in a single bipolar plate channel of a prototype PEM fuel cell. The current study examines the variation of water partial pressure and temperature near the flow inlet and outlet during operation under both steady state and time-varying load conditions. For steady-state operation, an increase in the water vapor partial pressure was observed with increasing current density due to electrochemical production of water. As expected, the measurement channel near the inlet of the flow path showed a lower water vapor partial pressure than the outlet under identical load conditions; however, the quantitative distribution of water content across the cell is important to understanding operational behavior of a PEM fuel cell. These quantitative water concentration differences between two measurement channels are reported with variations in cell load and temperature. Temperature in the gas phase remained constant due to thermal equilibrium of the fuel cell. For time varying operation, no phase lag was observed between the load and the water vapor partial pressure. The outlet measurement channel showed higher partial pressure than the inlet with larger differences for increasing cell load. The transient data matched the steady-state measurements at the same conditions. A temperature rise from the controlled value was observed at high current densities for the unsteady operation; thus, the temperature did not equilibrate on the same time scale as the water partial pressure.

Surface temperature monitoring of convex molten polymer using interferometric tomography with direct cylindrical reconstruction

Temperature monitoring and control of a convex molten polymer sheet and surrounding cooling air flows are demanded in order to improve both the productivity and the quality of the polymer sheet products. The accurate measurement of temperature is desired when molten polymer changes its phases. An intrusive thermometer such as a thermocouple has difficulty because a molten polymer blown out from a ring die is extremely thin. Also temperature measurement with an infrared camera is not applicable since the polymer film is lightly transparent for the infrared radiation and the intensity of infrared radiation from the polymer film is too weak. In this research, we proposed a novel method for non-intrusive temperature measurement with the quantitative interferometer in conjunction with direct cylindrical computer tomography, and discussed its feasibility for measuring the temperature distribution on a convex surface.

Development of a fast temperature sensor for combustion gases using a single tunable diode laser

The 12 best NIR water transition line pairs for temperature measurements with a single DFB laser in flames are determined by systematic analysis of the HITRAN simulation of the water spectra in the 1–2 μm spectral region. A specific line pair near 1.4 μm was targeted for non-intrusive measurements of gas temperature in combustion systems using a scanned-wavelength technique with wavelength modulation and 2f detection. This sensor uses a single diode laser (distributed-feedback), operating near 1.4 μm and is wavelength scanned over a pair of H2O absorption transitions (7154.354 cm-1 & 7153.748 cm-1) at a 2 kHz repetition rate. The wavelength is modulated (f=500 kHz) with modulation amplitude a=0.056 cm-1. Gas temperature is inferred from the ratio of the second harmonic signals of the two selected H2O transitions. The fiber-coupled-single-laser design makes the system compact, rugged, low cost and simple to assemble. As part of the sensor development effort, design rules were applied to optimize the line selection, and fundamental spectroscopic parameters of the selected transitions were determined via laboratory measurements including the temperature-dependent line strength, self-broadening coefficients, and air-broadening coefficients. The new sensor design includes considerations of hardware and software to enable fast data acquisition and analysis; a temperature readout rate of 2 kHz was demonstrated for measurements in a laboratory flame at atmospheric pressure. The combination of scanned-wavelength and wavelength-modulation minimizes interference from emission and beam steering, resulting in a robust temperature sensor that is promising for combustion control applications.

Submicrosecond temperature measurement in liquid water with laser-induced thermal acoustics

Using laser-induced thermal acoustics, we demonstrate nonintrusive and remote sound-speed and temperature measurements in liquid water. Unsteady thermal gradients in the water sample produce fast, random laser beam misalignments, which are the primary source of uncertainty in these measurements. For water temperatures over the range 10 degrees C to 45 degrees C, the precision of a single 300-ns-duration measurement varies from +/-1 to +/-16.5 m/s for sound speed and from +/-0.3 degrees C to +/-9.5 degrees C for temperature. Averaging over 10 s (100 laser pulses) yields accuracies of +/-0.64 m/s and +/-0.45 degrees C for sound speed and temperature, respectively.

B306 LIFによる非定常表面温度計測に関する基礎的研究

A temperature sensitive particle, which can be utilized for the three-dimensional non-intrusive simultaneous measurement of velocity and temperature of water flow, had been developed by one of the author of this study. Presently, non-intrusive measurement of surface temperature has been carried out by developing a temperature sensitive paint and its thermo-optical characteristics are quantified. Even though the temperature sensitive particle can be formed by introducing a fluorescent substance into polystyrene, it cannot be used as a paint which elastically covers many kind of surface. Presently, several polymers have been investigated for the base material for the paint and the polyvinylbuthyral (PVB) is found to fit the condition very well. The thermo-optical characteristics of the temperature sensitive paint made from PVB has been intensively investigated. The optimal concentration of the fluorescent dye and the solvent has been quantified. The effect of the thickness of a paint and its unsteady response are also investigated.

Simultaneous characterization of flow velocity and temperature fields in a gas jet by use of electrostrictive laser-induced gratings

Time-resolved light diffraction of cw read-out laser radiation by electrostrictive laser-induced gratings (LIGs) is demonstrated to be applicable, under a special experimental arrangement, for non-intrusive, local, and remote simultaneous measurements of velocity and temperature in gas flows. The experimental set-up and the model developed for adequate description of the experimental results are described. The method for treating the data and estimating the experimental parameters is reported.

A Duhamel Integral Based Solution for the Sideways Heat Equation Applied to the Non-intrusive Temperature Measurement

In the present study, an inverse heat conduction problem is considered, the Sideways Heat Equation, which is a model of a problem, where one wants to determine the temperature on both sides of a thick wall, but where one side is inaccessible to measurements. Considering the problem of an intrinsic thermocouple attached to a slab, and no thermal contact, a transfer function is proposed. It is based on Duhamel Integral and the measured response is approximated by a quasi-periodical function. The derived transfer function is the product of two transfer functions, for the slab and for the intrinsic thermocouple respectively. To validate the present model, a comparison with actual measurements is carried out. It was found that the present model can predict the inner temperatures more accurately than the previous model, which did not take into account the effect of the thermocouple.

Non-intrusive temperature measurements using three-color laser-induced fluorescence

This paper presents a new temperature measurement technique in a liquid, based on laser-induced fluorescence of rhodamine B. The fluorescence intensity is detected on three spectral bands, where the ratios between the emission of each band determine the temperature while correcting for the effects of fluorescent re-absorption. In addition, the influence of parameters such as probe volume size, dye concentration, and Beer’s absorption is removed. The principles of the technique are described in this paper, and the technique is demonstrated on a heated liquid jet studied under a constant and a spatially variable dye concentration.

Aerospace applications of luminescent paint

AbstractLuminescent paints allow non-intrusive measurement of pressure and temperature at high spatial resolution without prior knowledge of the flow-field. Experiments have demonstrated that a ‘standard’ luminescent paint technique, developed by BAE Systems, can simultaneously measure steady pressure and temperature. This is achieved through knowledge of the paint phosphorescence lifetime rather than the absolute intensity, which increases the measurement accuracy. In addition, a new ‘fast’ paint has been calibrated at the University of Bath for the measurement of unsteady pressure using a variable frequency pulsing air jet. Pressure measurements were made with both paints in the wake of various excrescences, sized to produce vortex shedding in the frequency range 500–4,200Hz, in a transonic tunnel. The extent of the wakes was determined from a flow visualisation technique. Time-averaged measurements, using both luminescent paints, and transient measurements of the unsteady pressure field, made with the fast paint, were compared with transducer data. For all cases the luminescent paint data compared well with the conventional measurements and the Strouhal number agreed well with data from the literature. The use of luminescent paint for the simultaneous measurement of pressure and temperature over a NACA 0012 aerofoil, as well as the quantification of convective heat transfer is examined in Part 2.

Digital recording and numerical reconstruction of holograms: an optical diagnostic for combustion.

Holographic interferometry (HI) has proved to be a useful tool for nonintrusive temperature measurements in flames (and thereafter for inference of the local composition based on the state relationship approach) with high spatial and temporal resolution. Digital holographic interferometry (DHI) is a relatively new imaging and measurement technique that electronically records a hologram (e.g., on a CCD) and reconstructs it by a numerical method. Cumbersome chemical processing of the hologram is avoided in DHI, which thereby provides greater flexibility, speed, and the potential for real-time processing. In conventional holography, fringes that are neither bright nor dark on a hologram cannot be accurately resolved. The DHI technique has not yet to our knowledge been used for combustion applications. Herein we evaluate its efficacy for making temperature measurements in flames and assess its applicability through a simulation. Each part of a double exposure associated with the holographic technique is considered to be recorded by a hypothetical CCD sensor at a separate time from the other part. We applied the principles of Fourier optics to develop two numerical methods for hologram reconstruction, and we show that both methods provide an accurate reconstruction of the phase image associated with a flame. Because of the periodic nature of the wave function, the reconstructed phase values are limited to the interval [-pi/2, pi/2]. Thus an unwrapping algorithm is provided that produces a continuous phase distribution based on the condition that the reconstructed phase is jumped by a value of -pi or pi. We have also developed an iterative calculation method to adjust the value of the digital reference wave parameters that determines the phase imaging reconstruction in DHI.

Applications of Fiber Bragg Grating Sensors in the Composite Industry

AbstractOptical-fiber sensors based on fiber Bragg gratings (FBGs) provide accurate, nonintrusive, and reliable remote measurements of temperature, strain, and pressure, and they are immune to electromagnetic interference. FBGs are extensively used in telecommunications, and their manufacture is now cost-effective. As sensors, FBGs find many industrial applications in composite structures used in the civil engineering, aeronautics, train transportation, space, and naval sectors. Tiny FBG sensors embedded in a composite material can provide in situ information about polymer curing (strain, temperature, refractive index) in an elegant and nonintrusive way. Great improvements in composite manufacturing processes such as resin transfer molding (RTM) and resin film infusion (RFI) have been obtained through the use of these sensors. They can also be used in monitoring the “health” of a composite structure and in impact detection to evaluate, for example, the airworthiness of aircraft. Finally, FBGs may be used in instrumentation as composite extensometers or strain rosettes, primarily in civil engineering applications.

The Lock-in Heating-Cooling Method for the Measurement of the Thermal Diffusivity of Solid Materials

A new test method is presented for the on-field nondestructive measurement of the thermal diffusivity of solid materials. A periodic thermal disturbance is supplied to the inspected material by a thermoelectric source based on the Peltier effect. This can alternate heating and cooling stages and provide, if properly controlled, a harmonic disturbance with null net heat flux. A steady-periodic temperature field can thus be induced within the specimen. The diffusivity of the material is then estimated by monitoring the propagation of the temperature cycles along the optically accessible surface of the specimen, adjacent to the thermal input surface area. A camera for infrared thermography is used for nonintrusive surface temperature measurement. At the current stage of development, the focus is on the accurate reproduction of the theoretical model on which the method is based. Ease of operation and portability of the test equipment are also pursued. However, tests on thin specimens of materials with known properties give measurements in encouraging agreement with the nominal values.