Dual-pump coherent anti-Stokes Raman scattering measurements of nitrogen and oxygen in a laminar jet diffusion flame

Dual-pump coherent anti-Stokes Raman scattering (CARS) has been demonstrated for the simultaneous measurement of gas-phase temperature and concentrations of molecular nitrogen and oxygen. A polarization technique was used to vary the relative intensities of the two CARS signals and expand the dynamic range of the relative concentration measurements. Detailed temperature and oxygen mole fraction measurements were performed in the stabilization region of a hydrogen-nitrogen jet diffusion flame. These results indicate that there is a region below the nozzle exit where significant amounts of oxygen are found on the fuel side of the peak flame temperature profile.     

The Limits of a Rayleigh-Scattering Primary Thermometer

Progress in the development of an apparatus to compare the thermodynamic temperature of a gas with the temperature as determined by the International Temperature Scale of 1990 (ITS-90) is reported. The apparatus uses the Rayleigh scattering of light from a gas to provide an intensive measure of gas density, thus avoiding the need for corrections for dead volumes or wall adsorption required by conventional gas thermometry. A laser beam is shone through gas in two cells that are at the same pressure but different temperatures, and the measured ratio of the Rayleigh scattering signals from the two cells can be related to the ratio of the gas density in the cells. From the density ratio, the thermodynamic temperature of one cell can be inferred if the other cell is held close to the triple point of water. However, the Rayleigh scattering is weak and signals are small, making measurements with sufficiently small uncertainty extremely challenging. Since previous reports, the apparatus has been significantly modified, and these changes are described along with indicative results. In this paper, results of measurements in the range from 211 K to 292 K using both argon and xenon are reported. The results suffer from large systematic errors due to contamination in one of the measurement cells. Although the results do not provide reliable estimates of T  − T ₉₀, they indicate that measurements with uncertainties below 1 mK are feasible.     

Temperature and velocity measurement fields of fluids using a schlieren system

This paper proposes a combined method for two-dimensional temperature and velocity measurements in liquid and gas flow using a schlieren system. Temperature measurements are made by relating the intensity level of each pixel in a schlieren image to the corresponding knife-edge position measured at the exit focal plane of the schlieren system. The same schlieren images were also used to measure the velocity of the fluid flow. The measurement is made by using particle image velocimetry (PIV). The PIV software used in this work analyzes motion between consecutive schlieren frames to obtain velocity fields. The proposed technique was applied to measure the temperature and velocity fields in the natural convection of water provoked by a heated rectangular plate.     

Practical ultrasonic spectrometric measurement of solution concentrations by a tracking technique

A practical technique for solution concentration measurement, based on a resonator with enclosed piezoceramics, which can operate at a resonant frequency mode around 500 kHz is designed and evaluated. The resonance can be tracked automatically by means of a phase-locked loop. Measurements made on water-methanol mixtures showing that concentration can be expressed as a function of temperature and resonance frequency, where a multiple regression technique is used to relate them, are reported. It was possible to evaluate the concentration with a repeatability of about 0.06%, which depends essentially on the temperature measurement. Various milk mixtures have also been tested to check if the evaluation of both butterfat and protein concentrations could be achieved from measurements at two different temperatures. It was found that calculations based on two measurements cannot be used when the composition varies too widely.     

甲烷气体多点光纤传感系统的研究

基于气体在其特征吸收波长下光的吸收随浓度变化的机理和空分复用技术,复用多个气体吸收型光纤传感器,并通过谐波检测技术对微弱信号进行处理,设计了一套甲烷气体多点光纤传感系统。研究表明,该传感器的精确度为 5ppm,精确度和稳定性均可满足实际要求,仪器可在多场合进行多点在线测量。     

Effect of heat conduction through the fins of a microchannel serpentine gas cooler of transcritical CO2 system

This paper presents results of an experimental study to investigate the effect of conduction through the fins on the capacity of a serpentine gas cooler. The gas cooler was a part of a transcritical CO₂ system which was operated in A/C mode. The capacity of the gas cooler was carefully measured in the chamber which simulated the outdoor condition with the original heat exchanger. In order to experimentally validate the conduction effect on the capacity, some sections of the fins, where the conduction was most significant, were cut by EDM (Electrical Discharge Machining). The capacity of the heat exchanger, after cutting fins, was measured in the same chamber at nearly identical test conditions as before cutting. Gas cooler capacity was improved up to 3.9% by cutting the fins, and temperature difference between refrigerant exit and air inlet for the gas cooler was reduced by 0.9–1.5 °C. The maximum uncertainty in the capacity measurements was 2.5% and the accuracy of temperature measurements was 0.1 °C. It was shown by system simulation that system COP could be improved by 5% by eliminating this severe conduction effect, as was done in this experiment. The tube surface temperature at some points of the gas cooler was measured and infrared images were taken to show the conduction effect before and after cutting fins.     

Practical Acoustic Thermometry with Acoustic Waveguides

Acoustic thermometry is capable of phenomenal accuracy, but is a difficult technique to apply in many practical situations. Here, we describe a modification of the technique, which permits robust temperature measurements to be made, potentially with millikelvin resolution, over a temperature range extending from cryogenic temperatures to over 1000 °C. The technique uses measurements of the time of flight of acoustic pulses in tubes, usually filled with an inert gas such as argon. The tubes—typically made of stainless steel with an outer diameter of 6mm—act as acoustic waveguides and can be several meters long and bent into complex shapes. The time of flight is determined by the average temperature along the entire length of the tube. Local temperature information can be inferred in several ways. Typically a second shorter tube is used and the difference in time of flight reflects the temperature in the region at the end of the first tube. If the measurement length is sufficiently long—typically 1m of tube—then a measurement resolution of less than 1mK is achievable. The technique is well suited to measurements in harsh environments in which conventional sensors degrade. Results from early tests are shown, which highlight the strengths and weaknesses of the technique.     

Characteristics of plasma produced by MHD technology and its application to propulsion systems

This paper analyzes plasma characteristics for the newly proposed concept of a closed-loop MHD power generation combined cycle system, which is used as a pulse-driven MHD accelerator to accelerate plasma to high velocity, with a nuclear plant. In this paper, since the final goal is for the space propulsion system applications, the performance of a MHD acceleration system is also analyzed by the Q1D analysis program. Results reveal that the radial velocity with the MHD effect is accelerated rapidly at the channel exit, with a calculated maximum velocity of about 4700 m/s. Consequently, specific impulse approximately 480 s and thrust of about 6550 N are estimated. The static gas temperature is evaluated at less than 600 K, while the value of about 1800 K is calculated for the stagnation gas temperature in the MHD channel.     

Gas phase temperature measurements in the liquid and particle regime of a flame spray pyrolysis process using O₂-based pure rotational coherent anti-Stokes Raman scattering

For the production of oxide nanoparticles at a commercial scale, flame spray processes are frequently used where mostly oxygen is fed to the flame if high combustion temperatures and thus small primary particle sizes are desired. To improve the understanding of these complex processes in situ, noninvasive optical measurement techniques were applied to characterize the extremely turbulent and unsteady combustion field at those positions where the particles are formed from precursor containing organic solvent droplets. This particle-forming regime was identified by laser-induced breakdown detection. The gas phase temperatures in the surrounding of droplets and particles were measured with O₂-based pure rotational coherent anti-Stokes Raman scattering (CARS). Pure rotational CARS measurements benefit from a polarization filtering technique that is essential in particle and droplet environments for acquiring CARS spectra suitable for temperature fitting. Due to different signal disturbing processes only the minority of the collected signals could be used for temperature evaluation. The selection of these suitable signals is one of the major problems to be solved for a reliable evaluation process. Applying these filtering and signal selection steps temperature measurements have successfully been conducted. Time-resolved, single-pulse measurements exhibit temperatures between near-room and combustion temperatures due to the strongly fluctuating and flickering behavior of the particle-generating flame. The mean flame temperatures determined from the single-pulse data are decreasing with increasing particle concentrations. They indicate the dissipation of large amounts of energy from the surrounding gas phase in the presence of particles.     

应用气体吸附—量热联用技术研究储氚材料性能

基于Sivert’s原理的体积法高压气体吸附分析技术已被证明为评估材料针对某种气体吸附性能的最有力工具，相比于其他技术Sivert’s气体吸附分析技术具有更多优势，首先实验温度及压力更为宽广，可满足绝大数应用领域要求，同时得益于该技术中样品容器的尺寸及外形设计极其灵活，不受任何因素的限制，因此为体积法吸附分析技术与其他各种物理、化学性能评估手段同步联用提供了可能性，本文中即包含了体积法吸附分析技术与量热技术及元素分析技术之间的联用介绍。     

In-process rheometry as a PAT tool for hot melt extrusion

Real time measurement of melt rheology has been investigated as a Process Analytical Technology (PAT) to monitor hot melt extrusion of an Active Pharmaceutical Ingredient (API) in a polymer matrix. A developmental API was melt mixed with a commercial copolymer using a heated twin screw extruder at different API loadings and set temperatures. The extruder was equipped with an instrumented rheological slit die which incorporated three pressure transducers flush mounted to the die surface. Pressure drop measurements within the die at a range of extrusion throughputs were used to calculate rheological parameters, such as shear viscosity and exit pressure, related to shear and elastic melt flow properties, respectively. Results showed that the melt exhibited shear thinning behavior whereby viscosity decreased with increasing flow rate. Increase in drug loading and set extrusion temperature resulted in a reduction in melt viscosity. Shear viscosity and exit pressure measurements were found to be sensitive to API loading. These findings suggest that this technique could be used as a simple tool to measure material attributes in-line, to build better overall process understanding for hot melt extrusion.     

Analysis of laser-induced-fluorescence carbon monoxide measurements in turbulent nonpremixed flames

The influence of fluctuating concentrations and temperature on the laser-induced-fluorescence (LIF) measurement of CO in turbulent flames is described, under conditions in which the fluorescence and the temperature are measured independently. The analysis shows that correlations between CO concentration and temperature can bias the averaged mole fraction extracted from LIF measurements. The magnitude of the bias can exceed the order of the average CO mole fraction. Further, LIF measurements of CO concentrations in a turbulent, nonpremixed, natural gas flame are described. The averaged CO mole fractions are derived from the fluorescence measurements by the use of flame temperatures independently measured by coherent anti-Stokes Raman spectroscopy. Analysis of the fluctuations in measured temperature and fluorescence indicates that temperature and CO concentrations in flame regions with intensive mixing are indeed correlated. In the flame regions where burnout of CO has ceased, the LIF measurements of the CO mole fraction correspond to the probe measurements in exhaust.     

High-resolution acoustic measurements in fluids and gases by a path length modulation technique

An acoustic technique has been developed that permits high-resolution velocity measurements to be performed in liquids and gases under circumstances where the acoustic attenuation may become very large. This cavity resonance method has been demonstrated in cavities with lengths as small as 150 µm at acoustic frequencies up to 151 MHz. The acoustic path length is continuously adjusted by a piezoelectric bimorph controlled by feedback from a sensitive acoustic impedance spectrometer. The measurement of velocity then simply reduces to measurement of position of the bimorph, and this can be performed with high accuracy using a capacitance bridge. Absolute measurements of the attenuation of sound can also be performed with this arrangement. It is suggested that this approach will be useful for the study of collective excitations in quantum fluids.     

Flame synthesis of carbon nano-onions enhanced by acoustic modulation

Ethylene jet diffusion flames modulated by acoustic excitation in an atmospheric environment were used to synthesize carbon nano-onions (CNOs) on a catalytic nickel substrate. The formation of CNOs was significantly enhanced by acoustic excitation at frequencies near either the natural flickering frequency or the acoustically resonant frequency. The rate of yield of CNOs was high at 10 and 20 Hz (near the natural flickering frequency) for a sampling position z = 5 mm above the burner exit where the gas temperature was about 450-520?°C, or at 10, 20 and 30 Hz for z = 10 mm with the gas temperature ranging from 420 to 500?°C. Additionally, for both z = 5 and 10 mm, a quantity of CNOs can be obtained at 60-70 Hz, near the acoustically resonant frequency, where the gas temperature was between 620 and 720?°C. Almost no CNOs were produced for the other frequencies due to low temperature or lack of carbon sources. CNOs synthesized at low frequencies had a greater diameter and a higher degree of graphitization than those at high frequencies.     

Laser heterodyne method for high-resolution gas-density measurements

A new method for noncontact, high-resolution measurement of gas density is described. The method uses a two-frequency Zeeman-split He-Ne laser and cumulative phase-measuring electronics. The measurement is resolved in two dimensions and provides density that is averaged only along the length of the laser beam that passes through the test section. The technique is based on highly accurate measurement of the optical path-length change of the laser beam as it passes through a test cell (in principle, to within 0.001lambda, where lambda is the wavelength of the laser). The technique also provides a very large dynamic range (again, in principle, up to 10(10)), which makes the method additionally attractive. Although the optical path length through the test section is directly related to the index of refraction, and hence to the density of the gas, the method can also be used to measure temperature (if the gas pressure is known) or pressure (if the temperature is known).     

Large deformation mechanical testing of biological membranes using speckle interferometry in transmission. II: Finite element modeling

In holography and speckle interferometry the measurement range is generally limited by the greatest number of fringes that can be resolved in a single image. As a result these techniques have been generally confined to small displacement measurement applications. In the case of out-of-plane measurements one can overcome this limitation by simply adding incremental measurements at individual detector pixels. In the case of in-plane measurements, however, summing incremental measurements is not a straightforward procedure since the interference pattern moves laterally across the detector as the material deforms. We describe a modeling technique based on finite elements which solves this problem. In combination with a full field method such as holography or speckle interferometry, it provides a very sensitive measurement technique with dense spatial sampling and large dynamic range. Experimental results of speckle interferometry operating in transmission to measure in-plane displacements of biological membranes are presented, where total material displacements are of the order of millimeters. The results also demonstrate how the finite strain tensor is calculated analytically from the data at any point on the material.     

Investigation of the performance of an optimised MicroCAT, a GEM and their combination by simulations and current measurements

A Micro compteur à Trous (MicroCAT) structure which is used for avalanche charge multiplication in gas filled radiation detectors has been optimised with respect to maximum electron transparency and minimum ion feedback. We report on the charge transfer behaviour and the achievable gas gain of this device. A three-dimensional electron and ion transfer simulation is compared to results derived from electric current measurements. Similarly, we present studies of the charge transfer behaviour of a Gas Electron Multiplier (GEM) by current measurements and simulations. Finally, we investigate the combination of the MicroCAT and the GEM by measurements with respect to the performance at different voltage settings, gas mixtures and gas pressures.     

Speckle interferometry for analysing anisotropic thermal expansion—application to specimens and components

This paper describes a non-destructive optical technique, digital speckle pattern interferometry (DSPI), that has been developed particularly for strain analysis and has proved well suited for thermal deformation measurement. Fibre-reinforced composites with both metal and polymer matrices have been analysed by DSPI to determine their thermal expansion behaviour as a function of direction and temperature. Complete series of measurements can be performed quickly and without any restriction on the specimen shape. Engineering components including composite structures have been the subject of investigation. Besides quantitative results, real-time observation provides basic information for materials understanding.     

Domain-adaptive finite difference methods for collapsing annular liquid jets

A domain-adaptive technique which maps a time-dependent, curvilinear geometry into a unit square is used to determine the steady state mass absorption rate and the collapse of annular liquid jets. A method of lines is used to solve the one-dimensional fluid dynamics equations written in weak conservation-law form, and upwind differences are employed to evaluate the axial convective fluxes. The unknown, time-dependent, axial location of the downstream boundary is determined from the solution of an ordinary differential equation which is nonlinearly coupled to the fluid dynamics and gas concentration equations. The equation for the gas concentration in the annular liquid jet is written in strong conservation-law form and solved by means of a method of lines at high Peclet numbers and a line Gauss-Seidel method at low Peclet numbers. The effects of the number of grid points along and across the annular jet, time step, and discretization of the radial convective fluxes on both the steady state mass absorption rate and the jet's collapse rate have been analyzed on staggered and non-staggered grids. The steady state mass absorption rate and the collapse of annular liquid jets are determined as a function of the Froude, Peclet and Weber numbers, annular jet's thickness-to-radius ratio at the nozzle exit, initial pressure difference across the annular jet, nozzle exit angle, temperature of the gas enclosed by the annular jet, pressure of the gas surrounding the jet, solubilities at the inner and outer interfaces of the annular jet, and gas concentration at the nozzle exit. It is shown that the steady state mass absorption rate is proportional to the inverse square root of the Peclet number except for low values of this parameter, and that the possible mathematical incompatibilities in the concentration field at the nozzle exit exert a great influence on the steady state mass absorption rate and on the jet collapse. It is also shown that the steady state mass absorption rate increases as the Weber number, nozzle exit angle, gas concentration at the nozzle exit, and temperature of the gases enclosed by the annular liquid jet are increased, but it decreases as the Froude and Peclet numbers, and annular liquid jet's thickness-to-radius ratio at the nozzle exit are increased. It is also shown that the annular liquid jet's collapse rate increases as the Weber number, nozzle exit angle, temperature of the gases enclosed by the annular liquid jet, and pressure of the gases which surround the jet are increased, but decreases as the Froude and Peclet numbers, and annular liquid jet's thickness-toradius ratio at the nozzle exit are increased. It is also shown that both the ratio of the initial pressure of the gas enclosed by the jet to the pressure of the gas surrounding the jet and the ratio of solubilities at the annular liquid jet's inner and outer interfaces play an important role on both the steady state mass absorption rate and the jet collapse. If the product of these ratios is greater or less than one, both the pressure and the mass of the gas enclosed by the annular liquid jet decrease or increase, respectively, with time. It is also shown that the numerical results obtained with the conservative, domain-adaptive method of lines technique presented in this paper are in excellent agreement with those of a domain-adaptive, iterative, non-conservative, block-bidiagonal, finite difference method which uncouples the solution of the fluid dynamics equations from that of the convergence length.     

Three-dimensional rainbow schlieren tomography of a temperature field in gas flows

We present quantitative rainbow schlieren deflectometry with tomography for measurements of temperature in three-dimensional gas flows. The schlieren apparatus with a continuously graded spectral filter of known transmissivity was used to create color schlieren images of the test media. These images at multiple viewing angles were used to infer beam deflection angles by the medium. The deflection data were used with a tomographic technique to reconstruct the refractive index and thus the temperature field. The temperature distributions obtained by the rainbow schlieren tomography agreed with those measured by a thermocouple probe. This research demonstrates that tomography can be used with full-field schlieren deflectometry to measure quantitatively temperature in asymmetric gas flows. The technique could be used to obtain related properties such as pressure, density, and gas composition.