Static Temperature Measurements Research Articles

Laser-induced schliere anemometry in a Mach 6 flow with collinear light entry.

In this work, we demonstrate velocity, Mach number, and static temperature measurements in a Mach 6 flow using the recently developed laser-induced schliere anemometry (LISA) technique. To our best knowledge, this represents the first application of LISA for characterizing flow in the hypersonic Mach number regime, and a comparison with known tunnel values is provided. The laser-induced schliere in this work are written from a distance of roughly 76 cm away from the final lens, much further than in previous work. Furthermore, the schliere are created from a laser beam introduced parallel to the collimated schlieren light, which is a new arrangement that could be useful for facilities with limited optical access. A discussion of setup limitations is provided. The mean core flow velocity determined from LISA is within 1% of the expected value from isentropic theory, while the mean Mach number measurements are within 1.6% of the M=5.85 value used in literature for the facility. Furthermore, the determined mean static temperature of the core flow is within 2.5% of the value measured simultaneously in the facility.

10 kHz laser-induced schliere anemometry for velocity, Mach number, and static temperature measurements in supersonic flows.

A new, to the best of our knowledge, technique for measuring velocity and Mach number in freestream flow is discussed and demonstrated. The technique, laser-induced schliere anemometry, uses a laser to write a laser-induced schliere in the flow, which can then be imaged using high-speed schlieren imaging. Here, we use a laser-induced plasma from the focusing of nanosecond-duration laser pulses from a pulse burst laser to write the disturbance. The resulting localized index of refraction gradient left from the plasma is tracked well beyond the plasma emission lifetime using schlieren imaging, and velocity is found from tracking or through a simple correlation analysis. The blast wave is also used to independently determine the Mach number via the Mach cone effect, which provides information about the mean static temperature. This technique shows great potential for use in characterizing freestream flow in supersonic facilities and is demonstrated here in a Mach 2 blowdown facility and a Mach 4 Ludwieg tube.

Frequency sweep extension using the Kerr effect for static temperature measurement range enhancement in Chirped Pulse φ-OTDR.

In Chirped Pulse φ-OTDR systems used for sensing temperature or strain along an optical fiber, the largest disturbance between two single-shot measurements that can reliably be detected depends on the range of frequencies swept by the chirped pulse. If electrical modulation is used to generate the laser frequency sweep, the achievable sweeping range is limited by the electrical components, leading to a narrow measurement range for static measurements. In this work, we demonstrate the extension of the frequency range of a chirped laser pulse by all-optical means using evenly spaced frequency sidebands generated via the Kerr effect to improve the Chirped Pulse φ-OTDR measurement range. We report chirp extensions by factors up to 13 and apply the effect to achieve a sixfold increase in the measurement range of a Chirped Pulse φ-OTDR system measuring the temperature of a random fiber grating array. The method described in this paper can be applied to other optical systems utilizing chirped laser pulses and allow for variable extension of their chirping range.

Improving magnetic nanothermometry accuracy through mixing-frequency excitation.

This study proposes a temperature model for the relaxation of magnetic nanoparticles and a phase measurement method under a mixing-frequency excitation field, which can improve the accuracy of temperature measurements in magnetic nanothermometry. According to the Debye-based magnetization model for magnetic nanoparticles, phases at mixing frequencies are used to solve the problem of a delay in the relaxation phase of the magnetic field at a high frequency. This method can improve the signal-to-noise ratio of the response of the magnetic nanoparticles and weaken the phase shift of the detection coils caused by the changes in temperature. The results of experiments show that the proposed method can achieve static temperature measurement error less than 0.1 K and dynamic temperature measurement error less than 0.2 K.

Long-distance BOTDA sensing systems using video-BM3D denoising for both static and slowly varying environment.

In this paper, video block-matching and 3D filtering (VBM3D) denoising has been proposed and experimentally demonstrated for the first time in 100.8 km long-distance Brillouin optical time domain analyzer (BOTDA) sensing system with 2 m spatial resolution. Both experiments under static and slowly varying temperature environment are carried out. A temperature uncertainty of 0.43°C has been achieved with denoising by VBM3D in static temperature measurement. To our knowledge, this is one of the best temperature uncertainty reported for a sensing distance beyond 100 km. The slowly varying temperature at the end of 100.8 km fiber has also been accurately measured. VBM3D exploits both the spatial and temporal correlations of the data for denoising, thus it can significantly reduce the temperature fluctuations and keep the measured values close to the real temperature even if the temperature is temporally changing. We believe it would be useful for the long-distance sensing where the measurand may have temporal evolution in the slowly varying environment.

Simulation of Thin Film Thermocouple for High Temperature Measurement Applicable to Missiles

<p>Thermocouples have been extensively used for the measurement of temperature since the advent of seebeck effect. Numerous sensors have been developed for temperature measurement, yet measurement of high temperature flowing fluid has been a challenging task. For the measurement of static temperature the measuring device should travel with the fluid at the same speed without disturbing the flow, which is quite unrealistic. So indirect determination of static temperature of flowing fluid is done by using thermocouple exposed into the flowing fluid. Other sensors available for high temperature measurement may lead to problems like resistance in the flow path of fluid which changes the structural dynamics. Thin film thermocouple (TFTC) based on W-W26Re for super high temperature measurement has been investigated which can be used in missiles for surface temperature measurement of nozzle and rocket interior surface. TFTC does not cause disruption in the flow path with maintaining structural integrity. The W-W26Re thermocouple offers advantage of higher seebeck coefficient at high temperature i.e. above 750 K, and usability in vacuum, inert and hydrogen atmosphere. Zirconia Fiber has been proposed as insulation protection material over thermocouple. Modelling and simulation of the TFTC for the temperature range 300 K - 2900 K has been presented. FEA model using PDE has been presented to implement heat equation, current balance quation, Gauss theorem and Neumann boundary condition. The expected voltage production on exposed temperature gradient has been studied.</p>

On the Use of Static Temperature Measurements as Process Variation Observable

In this paper we present the use of static temperature measurements as process variation observable. Contrary to previously published thermal testing methods, the proposed methodology does not need an excitation signal, thus reducing test cost and improving built-in capabilities of thermal monitoring. The feasibility of the technique and a complete test methodology is presented using a narrowband LNA as example. Finally, a complete electro-thermal co-simulation test bench between the LNA and a differential temperature sensor embedded in the same silicon die is presented in order to validate the results. Results prove that RF figures of merit can be extracted from DC temperature measurements done without loading or exciting the RF circuit under test.

Isothermal phase equilibria and structural phase transition in the carbon dioxide + cyclopropane mixed-gas hydrate system

The isothermal phase equilibria of the carbon dioxide + cyclopropane mixed-gas hydrate system were investigated by means of static temperature measurement and Raman spectroscopic analysis. Raman spectra indicated that the crystal structure of the carbon dioxide + cyclopropane mixed-gas hydrate changes from structure-I to structure-II and back to structure-I with an increase of the equilibrium carbon dioxide composition at 279.15 K, while each simple gas hydrate belongs to structure-I at the temperature. Whereas, unlike 279.15 K, no structural phase transition occurs along the isothermal stability boundary at 284.15 K.

Temperature measurements by CARS and intrusive probe in an air–hydrogen supersonic combustion

Static and stagnation temperature measurements are performed by CARS and by an intrusive probe in a Mach 2 cylindrical jet of hydrogen, injected into a Mach 2 coflow of air. The single-shot CARS static temperature measurements are based on nitrogen. A stagnation temperature probe has been developed and tested. This method consists in identifying the transient regime of a thermocouple probe with a numerical prediction modeling the high speed effects on the probe recovery factor. The paper presents and discusses the comparison between the temperature measurements performed by the intrusive probe and the CARS non-intrusive techniques (1) at the inlet of the combustion chamber; (2) in the ignition zone of the hydrogen jet; (3) in the burnt gases.

A comparative computational/experimental investigation of Mach 2 flow over a rearward-facing step

A numerical study of the Mach 2 flow over a rearward-facing step was performed using the SPARK Navier-Stokes code as a companion to a comprehensive experimental investigation conducted at the University of Virginia using Laser-Induced Iodine Fluorescence (LIIF) and Laser Doppler Anemometry (LDA) techniques. Turbulence was modeled with the Baldwin-Lomax turbulence model. First, calculations of the Mach 2 nozzle were performed and excellent agreement was obtained between the calculated and measured velocity profiles one step height upstream of the step. Secondly, comparisons were made between the calculations and measurements obtained with both planar and pointwise fluorescence techniques for the rearward-facing step flow field. This study represents the first comparison between in-stream static temperature measurements and CFD calculations for supersonic flow over a rearward-facing step. Agreement between the planar measurements and the calculations was observed regarding the position of the prominent flow features: the expansion fan, the shear layer, and the reattachment shock. Significantly lower temperature measurements were observed in low-momentum regions of the flow field. Comparisons between the pointwise measurements and the calculations exhibited very good quantitative agreement. The calculated and measured pressures, temperatures and velocities agreed within 5% at approx. 85% of the experimental locations.

Dynamic thermographic imaging method for quantifying dermal perfusion: potential and limitations.

A new method of quantifying dermal perfusion on a regional basis using a dynamic thermographic technique is investigated. The technique is based on the relationship between dermal perfusion and the rate of skin surface reheating following the application of a transient cold challenge predicted by a theoretical model. Measurements were made using images from a Philips thermographic camera under rigorously controlled conditions. Experimentation on undisturbed volar forearm skin of normal subjects showed that measurements could be repeated with good accuracy but that differences in normalised reheat temperatures between subjects were highly dependent on subcutaneous fat thickness. Comparisons between normal and occluded forearms indicated that reheat temperatures were not sensitive to changes in low levels of dermal perfusion. Conversely, stimulation of dermal blood flow with prostaglandin E2 did produce significant differences from control conditions, but quantifying the extent of this hyperaemia was limited by the effects of intersubject variations in fat thickness. Quantifying skin blood flow from skin temperature reheat rates is shown to be limited by a lack of sensitivity and a dependence on subcutaneous fat thickness, although dynamic thermography is able to provide useful information on regional variations in skin perfusion which could not be reliably obtained from static temperature measurements alone.

A tissue heat transfer model for relating dynamic skin temperature changes to physiological parameters

A physical and mathematical model of the superficial tissues of the body is presented which takes into account tissue physiology, structure and blood supply. The model relates transient temperature changes at the skin surface to underlying physiological parameters. The analysis is based on a one-dimensional finite difference version of the bioheat equation applied to a multi-layered model of the superficial 10 mm of body tissue. Application of the model to the volar forearm predicts that under steady-state conditions skin surface temperature is maintained primarily by heat transfer from tissues below 10 mm, to a lesser extent by perfusion and to a small extent by superficial tissue metabolism. Model predictions of the reheat curve following a 15 s cold challenge to the skin agree closely with preliminary experimental data provided by thermography. The model also provides a physical explanation for the shape of the skin temperature reheat curve. Calculations further suggest that transient skin surface temperature measurements can provide a better indication of dermal perfusion than static temperature measurements as the effects of variations in environmental conditions, deep tissue temperature and tissue metabolism can be reduced.

Thin-film temperature sensors for biological measurements.

Dynamic as well as static temperature measurements are now possible in biological tissue using thin-film Cu-Ni microthermocouples. These probes which use a quartz substrate exhibit response times of less than a millisecond with thermal properties similar to tissue. Their thermoelectric EMF of 21 , ?m V/°C is linearly dependent on temperature over the range normally encountered in biological measurements. Probe-tip diameters as small as 10 ?m are being fabricated.

Static Temperature Measurements in a Flowing Gas

A method has been developed to measure vibrational and rotational static temperatures at any point in nonradiating low-density flows of nitrogen. An electron beam is used to excite emission in the first negative system of nitrogen. The relative intensities in the rotational and vibrational structure of the emission spectra are predicted theoretically. The theoretical predictions are used to obtain rotational and vibrational temperatures of the nitrogen through which the beam passes.