Gas Sampling Probe Research Articles

Effects of Swirl and Skew Upon Supersonic Wall Jet in Crossflow

The results of an experimental investigation of the effects of swirl and skew on the mixing of a supersonic light gas jet injected from a e at wall into a supersonic airstream are presented. Tests were at nominally equal injectant masse owrate, totalpressure,andinjectornozzleexitstaticpressure. Data includesurveysofcross-sectionalplanes of the e ow for several different cases of swirl and skew using cone static pressure, pitot, stagnation temperature, and gas sampling probes (with gas analysis system ). The results are analyzed to determine mixing efe ciency and lateral motions of the center of the injectant plume. The effect of combined swirl and skew on injectant mixing is to slightly increase mixing in the near e eld of injection, but there is little effect of either swirl or skew on mixing far downstream. Both swirl and skew slightly reduce penetration.

00/03549 Influence of air-staging on the concentration profiles of NH 3 and HCN in the combustion chamber of a CFB boiler burning coal

The characterisation of the concentration profiles of NH3 and HCN are of great importance for increasing the knowledge of the formation and destruction pathways of NO and N2O in a fluidized bed boiler. Further improvements of the sampling methods for the determination of both NH3 and HCN in the combustion chamber in full-scale CFB boilers are also needed. A gas-sampling probe connected to a Fourier Transform Infra Red (FTIR) instrument and a gas-quenching (GQ) probe in which the sample is quenched directly in the probe tip by a circulating trapper solution were used. The FTIR technique is based on analysis of hot combustion gases, whereas the trapper solutions from the GQ probe were analysed by means of wet chemistry. The tests were performed during coal combustion in a 12 MW CFB boiler, which was operated at three air-staging cases with the addition of limestone for sulphur capture. The concentration profiles of NH3 and HCN in the combustion chamber showed a different pattern concerning the influence of air-staging. The highest levels of NH3 were observed during reducing conditions (severe air-staging), and the lowest were found under oxidising conditions (no air-staging). The levels of HCN were much lower than those measured for NH3. The highest levels of HCN were observed for reversed air-staging and severe air-staging showed almost no HCN. The potential reactions involving NH3 and HCN in the combustion chamber as well as the potential measurement errors in each sampling technique are discussed for the three air-staging cases.

Design, numerical simulation and experimental testing of a modified probe for measuring temperatures and humidities in two-phase flow

This paper describes the design of a modified gas sampling probe for measuring gas temperatures and humidities in a two-phase flow, based on the layout of Kieviet et al., [F.G. Kieviet, J. Van Raaij, P.J.A.M. Kerkhof, A device for measuring temperature and humidity in a spray drying chamber, Trans. Inst. Chem. Engrs, Part A, 75 (1997) 329–333]. This device separates small particles from the gas flow by means of the difference in inertia between the fluid and the particles. Two mechanisms of separation are employed successively, namely a swirling motion and a sharp change in direction of the flow. A small fraction of the clean flow is then directed to a thermocouple and subsequently to a dew-point hygrometer. The commercial computational fluid dynamics (CFD) package CFX4.2 has been used to assess the performance of the probe and to optimise the flow rates of the main and the clean air flow. Experimental testing confirms the prediction that this probe is able to measure temperatures and humidities in two-phase flows accurately down to particle diameters of 5 μm in droplet-laden flows. Due to deposition of wet solids on the swirl vanes, the separation performance for them decreases, so that only wet particles of more than 16 μm can be separated.

Modeling and measurement of sulfur dioxide absorption rate in a laminar falling film reactor

A kinetic study of sulfur dioxide absorption in a laminar falling film reactor is presented. A theoretical study is carried out taking into account mass transfer with chemical reaction in the liquid phase and parabolic velocity profiles in both phases. The transport equations are solved by a Runge–Kutta–Merson integration and a Newton–Raphson iteration method. The experimental study consists of measurements of sulfur dioxide concentration with respect to axial and radial position. Four different liquid phases are used: 0.5 M sulfuric acid solution (no reaction in liquid phase), 1.5 M sodium hydroxide solution (instantaneous surface reaction) and two organic solvents, N-Methyl-2-pyrrolidone and N-N′-Dimethylpropylene urea (equilibrium reaction in liquid phase). A good qualitative agreement is found between the experimental and theoretical profiles. Lack of reliable quantitative information is due to the gas sampling probes which induced perturbations in the gas phase. For the organic solvents the experimental absorption flux is about 80% of the maximum value, obtained with sodium hydroxide solution.

Analyses and Application of Gas Sampling to Scramjet Engine Testing

Gas sampling has been used in combustor studies and in scramjet engine testing. Because the gas sampling is based on the assumption that the gas composition is frozen in the sampling process, the critical Damkohler numbers necessary to quench reactions in the gas-sampling probes were evaluated using a reduced kinetic model. The phase plane analysis showed that reactions in probes can be extinguished if the probe Damkohler number is less than about 10. The analytical results were cone rmed by numerical calculations using full kinetics. The shock swallowing into sampling probes was examined using numerical simulations for the low-Reynolds-number e ow. These theoretical results were verie ed by experiments using four kinds of probes with various cone gurations in a Mach 2.5 supersonic combustor. Based on the results, e ne sampling probes with a tip diameter less than 0.3 mm are recommended for scramjet testing. Based on these calibration studies, gas sampling was successfully applied to scramjet engine testing under a e ight Mach number up to 8, to reveal interesting features in the internal e ow in swept-back engines.

An Experimental Study of the Formation of Perfluoroisobutene

This paper presents an experimental study that focuses on the formation of perfluoroisobutene (i-C4Fg). Experiments were carried out at atmospheric pressure in a quartz flow tube reactor over the temperature range of 823 to 1273K and an initial reactant feed concentration of 2% with the balance nitrogen. Reactants studied include chlorodifluoromethane (CHF2Cl), 1,1,1,2-tetrafluoro-2-chloroethane (CF3CHFCl), trifluoromethane (CHF3), perfluoropropene (C3F6), and mixtures of these species. Effluent gas concentrations were obtained using a water cooled gas sampling probe, and analysis of products was performed via on line gas chromatography with flame ionization detection and gas chromatography with mass selective detection. C3F6 pyrolysis produced more than 22% i-C.F, yield, while mixtures with CHF2Cl and CHF3 resulted in i-C4Fg yields of 14% and 28%, respectively. The pyrolysis of CF3CHFCI resulted in slightly greater than 6% i-C4Fg yield, and CHF2Cl decomposition produced up to 6% i-C4Fg yield, while CHF2Cl/CF3CHFC1 copyrolysis produced 8% yield of i-C4Fg. These results show that the addition of a difluoromethylene (iCF2) source increases i-C4Fg production. This suggests that a major pathway to i-C4Fg production may be C3F6 isomerization to singlet perfluorodimethylcarbene (l:C(CF3)2) and subsequent collisional stabilization to the triplet carbene (3:C(CF3)2) followed by either 1:CF2 addition or further reaction with C3F6. This work focuses on an experimental study. Detailed modeling work is ongoing.

98/01452 Measurement of the concentration of ammonia and ethene in the combustion chamber of a circulating fluidised-bed boiler: Åmand, L.-E. et al. J. Institute of Energy, March 1997, 70, 25–30

This paper presents the results of measuring the ammonia and ethene concentration profiles in the combustion chamber of a circulating fluidised-bed boiler. The boiler was operated in three air-staging conditions with peat as fuel, and with the addition of lime. Two sampling techniques were used for the analysis of ammonia: gas-sampling probe connected to a Fourier transformed infra-red (FTIR) instrument, and a gas-quenching (GQ) probe where the sample was quenched directly in the probe tip by a trapper solution. Both techniques are accurate enough to distinguish the influence on air staging of the level of ammonia in the combustion chamber. Comparison of the concentration profiles for ammonia measured by the two procedures shows similar results. The levels of ammonia and ethene measured by FTIR follow each other in the combustion chamber for all three staging conditions. The FTIR spectra were evaluated by three methods: spectral subtraction, differential absorbance and the multiple variable analysis method named 'partial least square' (PLS). Almost equal levels of concentration of ammonia and ethene were found, regardless of the method employed. The measurement error from reactions with ammonia at the GO probe tip was estimated in a simple model.

スクラムジェット用ガス採取管における反応凍結 （１） 理論解析

We conducted a sensitivity analysis of engine performance on measurements of gas sampling, pitot pressure and static pressure. It indicates that the heat loss in engine and the insufficient quenching of reactions in the gas sampling probes results in the mismatch in the mass flux through the engines. An analytical study of the reactive flow in probes showed that the introduction of a small heat of reaction with radical recombination to the energy equation yielded a saddle-type singularity in a phase plane for temperature and radical. The separatrix running from the initial point to the saddle point gave the criterion dividing the thermal runaway and the chemical quenching. A one-dimensional reaction code with a full-kinetics confirmed this analytical results.

Mach 2.5 experiments of reaction quenching in gas sampling for scramjet engines

In the measurement of combustion performance of scramjet engines using the gas-sampling method, quenching of reactions consuming reactants is a prerequisite. This requirement becomes difficult under conditions of hypersonic flight, because the air temperature ( T a ) greatly increases. To quantify the degree of quenching of reactions in the probes, we constructed four kinds of gas sampling probes, that is, freezing-oriented probes, in which the gas compositions were expected to be frozen in the sampling process, and reaction-oriented probes, in which unburned reactants might react as much as possible in the probes. We conducted sampling experiments using these probes and compared their combustion efficiencies using a supersonic combustor operating with a M2.5 airflow of T a up to 2200 K. Autoignition was observed in the reaction-oriented probes for T a >910 K. This “yes or no” behavior of the probes supported our theoretical probes yielded gas compositions consisting of partially burned H 2 and O 2 , even at T a =2190 K. The combustion efficiency calculated from the gas compositions increased from 0% to 100% in the freezing-oriented probes as T a increased. Pitot pressure is sensitive to the development of localized combustion in supersonic flow. The pitot pressure measurement indicated that the combustion actually took place in the supersonic combustor, not in the freezing-oriented probes. We concluded, by comparing with the static pressure-type probes, that the probes with a fine tip orifice of 0.3 mm indicated the correct combustion efficiency for the scramjet engine conditions.

スクラムジェット用ガス採取管における反応凍結 （２） 超音速燃焼器を用いた検証実験

Quenching of reactions in probes is the prerequirement in measurements of combustion performance of engines by the gas sampling. In order to quantify degrees of the quenching in the probes used for scramjet testing, we tested four kinds of gas-sampling probes, three freezing-oriented and a reaction-oriented probes using a supersonic combustor operating with an M 2.5 air flow of the temperature up to 2250K and compared the combustion efficiency (ηc) measured. The freezingoriented probes yielded gas compositions consisting of partially burned H2 and O2 even at an air temperature of 2200K. The pitot pressure indicated that the combustion took place in the supersonic combustor not in the probes. The freezing-oriented probes with the tip diameter of 0.3mm indicated the correct ηc in the scramjet combustor.

Analysis of intermittency and probe data in a supersonic flow with injection

Probe measurements were performed in the flow field produced by injection of helium or air into a supersonic airstream. The injectant was seeded with water and Rayleigh scattering was used to image the injectant plume. The region of the flow containing injectant–air mixture is seen to be highly unsteady, leading to the intermittent presence of injectant in certain regions. The intermittency is inferred. It is shown that bias errors can occur when the probe data is analyzed by techniques which assume steady flow. A technique for relatively bias-free analysis utilizing the intermittency measurements is presented and the bias errors are estimated. The gas-sampling probe is shown to measure the mass-weighted-mean mass fraction of helium, which is significantly less than the simple mean. A new measure of mixing efficiency obtained from the combined probe and intermittency measurements is discussed.

Field Test Results of a Dry Low NOx Combustion System for the MS3002J Regenerative Cycle Gas Turbine

A dry low NOx combustion system for the MS3002J regenerative cycle gas turbine has been developed and successfully installed at two pipeline compressor stations. Preparation for the DLN retrofits began with initial field testing of the conventional system intended to characterize some of the unique features of the two-shaft, regenerative cycle machine that might affect the proposed premixed combustor design. Combustor transition pieces were instrumented with gas sampling probes for CO2 analysis. Fuel flow to each combustor was measured and controlled. Consequently, the fuel/air ratio, exit temperature, and air flow for each combustor could be determined over the operating range. The dry low NOx combustion system for the MS3002J R/C is based on an existing system for the MS6001B gas turbine. A description of the hardware and system operation is given, Because of the relatively high inlet temperature of the MS3002J R/C (950°F), some portions of the liner required highly efficient effusion cooling. A new transition piece seal was developed to reduce leakage and ensure uniform air flow throughout the machine. A control strategy was developed to guide the machine through diffusion modes of operation at low load to premixed combustion at higher loads. Results showed acceptable component temperatures throughout. Emissions measurements were consistent with previous laboratory measurements and met design targets of 33 ppm NOx and 25ppm CO (at 15 percent O2) over the required range. The fuel split between the two premixed flame zones was controlled over the load range of the turbine to optimize CO, NOx, and liner temperatures. Because of the high inlet temperature and low overall temperature rise, dynamic pressure activity was low. Following a successful inspection after 6000 hours of operation, the hardware inspection interval has been set at 12,000 h.

Thermal Reactions of 2-Chloro-1, 1 1,2-Tetrafluoroethane

An experimental study of the pyrolytic behavior and thermal reactions of 2-Chloro-l,I,I,2tetrafluoroethane(HCFC-124) has been conducted overthe temperature range 923 to 1048K and atmospheric pressure. A tubular reactor was fed mixtures diluted to 2% HCFC-124 by volume with a helium or hydrogen balance. Results were obtained using a water-cooled gas sampling probe with on-line GC/MS and GC/FID analysis for stable product identification and reactant and stable product quantification. Products of the decomposition in helium include C3,F6 (major product), C2F4, CFCI2CF3, the cis and trans isomers of perfluoro-2-butene, and isoC4F8, Products observed in hydrogen include CH2FCF3, (major product), CH2F2, CHF3, CH3F, CF3CH3 and CHF2CHF2. The addition of hydrogen was observed to greatly increase reactant conversion and shift product selectivities away from perfluorinated olefins and chlorinated species. A QRRK analysis of reactant decomposition is presented and discussed. HCFC-124 appears to decompose primarily by α,α-HCl elimination to form singlet perfiuoromethylcarbene (I: CFCF3) with carbon-chlorine bond rupture competing at higher tempertures. Also presented is a QRRK analysis on the I: CFCF3→C2F4 1,2-F migration isomerization. This isomerization as a major pathway toward C3F6 formation in helium is consistent with experimental observations. C3F6/C2F4 product selectivity observed in helium is consistent with a high activation energy for the isomerization (36 kcal/mole) and a lowI: CF2, heat of formation ( - 44 kcal/mole).

On the plasma chemistry of the C/H system relevant to diamond deposition processes

The chemistry of hydrogen-rich hydrocarbon-hydrogen mixtures is of primary interest for the understanding of the low-pressure synthesis of diamond. We per formed experiments under well-defined conditions like temperature, pressure, initial gas composition, etc. The gas composition at the end of a flow reactor was analyzed by a calibrated mass spectrometer and compared to results obtained from the Chemkin computer code. Residence thne in the reactor as well as other process parameters were similar to those of diamond-growing PA CVD processes performed earlier with the same experimental set-rip. Modeling and experiment under isothermal conditions show quantitative agreement. We realized time-resolved mass .spectrometry by means of a helium-flushed gas sampling probe. There is evidence that the commonly used reaction kinetic data for the dissociation C2H6 (+ M) ⇔ 2CH,(+M) gives 2 too small C2H4 concentrations for hydrogen-rich conditions. This could be attributed to the poorly known third-body efficiencies of the H2 molecules compared to Ar or C2H6 from which kinetic data are commonly derived.

Quenching of reaction in gas-sampling probes to measure scramjet engine performance

The problem of chemical quenching in gas-sampling probes was studied as a reactive, Rayleigh, and Fanno flow. The typical lengths of friction, convective heat transfer, and reactions in the probes are evalnated under the testing conditions of ramjet and scramjet engines. A reduced chemical kinetic scheme was adopted, and the reaction times were evaluated from the ignition times derived by reflected shock wave experiments. Thereby, criteria for quenching in probes were obtained analytically. The critical Damköhler number ( Da ) for quenching in an H 2 -air reaction was found to be 23 (1500 K) to 10.5 (3000 K). A 2.6-fold greater Da was derived for CH 4 -air mixtures. Because reactions in CH 4 -air mixtures can be quenched even above 2200 K, combustion performance in a CH 4 -fueled ramjet combustor was measured from gas analysis. However, quenching of H 2 unburned gas in more difficult than quenching of CH 4 , Cooling with supersonic expansion is essential to freeze reactions in H 2 -air mixtures in scramjets tested under a total temperature higher than 2000 K. A constant Mach number expansion is recommended downstream of the sampling orifice. The contour of the expansion region and the decay of total pressure were determined taking into account friction and cooling effects. Reactions with unburned H 2 can be quenched if the sampling probe works as a supersonic diffuser operating in the supercritical mode.

NOxFormation in Large-Scale Oxy-Fuel Flames

The use of pure oxygen in the combustion of fossil-fuels is fuelled by the large potential for NO x reduction. This paper describes experiments conducted on a semi-industrial scale test furnace using a single oxy-natural gas burner. The burner was operated in two modes : the oxygen acting as the high velocity fluid, entraining the fuel gas into the flame, and vice versa. A steam-cooled gas-sampling probe was employed allowing gas samples to be taken from inside the furnace. Temperature and species concentration, including NO x were measured and were corroborated by numerical predictions. This study investigated two main areas, (a) the influence of mixing on the flame characteristics and the formation of nitric oxide in semi-industrial scale burners at high temperature combustion and (b) verification of the model used for high temperature combustion processes. The numerical analysis indicates that reasonable agreement can be obtained for the gas temperature and species concentration, using a 4-step reaction mechanism for the combustion process. The temperature predictions appear to be accurate within ± 50 K and computed NO emissions differ at most by 20% from measured NO x levels. This study shows that NO x emissions are influenced by the mixing of oxygen and fuel and injection angles. Also fast combustion produced a higher flame temperature and complete combustion but resulted in lower NO emissions.

A flow reactor system for catalytic reaction studies, allowing time- and space-resolved measurements of gas composition and temperature around the catalyst

A flow reactor system for catalytic reaction studies is described. The system is equipped with a movable gas sampling device and on-line mass spectrometry (MS), allowing time- and space-resolved measurements of gas composition and temperature. Results from H2 oxidation on Pt are used to illustrate the system performance. Spatial variations of H2, O2, and H2O concentrations can be measured, e.g., during mass transport limited conditions. Temporal variations in H2, O2, and H2O during chemical oscillations are well resolved close to the catalyst, but successively smeared away at increasing distance. The special design of the gas sampling probe allows quantible MS measurement even of H2O and other ‘‘difficult’’ gases, and of gas temperature variations.

Use of probes in combustion systems

ABSTRACT While use of optical techniques has become common in combustion research, physical probes have still many useful, and in some cases unique, applications. In industry particularly, optical techniques are often ill-suited to the situation and physical probes moreover offer compelling cost advantages. Effective exploitation of these probes, as with any sensor, requires a sound knowledge of response characteristics and of the principles of optimum design and use. The behaviour in respect to spatiotemporal resolution and effects of turbulence, for example, should be adequately recognised. The present paper covers simple pitot probes, differential pitot probes, static pressure probes, five-hole probes and gas sampling probes.

Mixing and combustion in a spinning combustor

The effect of spin on mixing and combustion in a circular diict with a primary air jet and secondary gas injection through the duct wail was studied using a spin rig, with spin rates up to 10,000 rpm. The spinning ducted flowfield was compared to stationary conditions. Spin enhanced the spreading rate of the pipe and orifice jets, resulting in a larger radial velocity component and an onset of a tangential component in the jet's core for the pipe jet and in the jet's shear layer for the orifice jet. The turbulence amplification rate was enhanced predominantly in the pipe jet. The tests showed that the duct-spin affects the flow even for a relatively short entrance duct. Measurement of the mixture ratio distribution using gas sampling probes in nonreacting tests were done with inert gas injection. Centrifugal forces affected the mixing depending on the weight of the gas relative to air. The mixing was enhanced for lighter-than-air gas and suppressed for heavier. Combustion tests included both ethylene as secondary gas and solid-fuel at the wall, In gaseous fuel combustion, the spin increased the combustion temperature due to improved mixing caused by low-molecular -weight products and reduced density. For solid-fuel combustion the spin had an adverse effect. Combustion temperatures were decreased due to reduced mixing caused by centrifugal forces acting on soot and heavy hydrocarbon products.

Measurement of alveolar gas mixing in mechanically ventilated patients.

To evaluate a computer-based, real-time, multibreath nitrogen washout technique in mechanically ventilated patients, incorporating an in-line flow measurement device to measure functional residual capacity and two indices of gas mixing, ventilatory efficiency, and alveolar mixing efficiency. ICU, Charing Cross Hospital, London. Within-patient reproducibility of a multibreath nitrogen washout technique. Seven intubated patients requiring mechanical ventilation. One patient completed two sets of readings. Patients were connected to a pneumatically driven ventilator fitted with a switching device to be operated either by an appropriate oxygen-nitrogen mixture or equivalently blended oxygen-argon mixture. An inspiratory-expiratory, two-way valve was attached to the delivery port of the ventilator, with a pneumotachograph for flow measurement and a gas sampling probe for gas concentration measurement in line with the patient's endotracheal tube. The analog signals were digitized and handled by a microcomputer. No significant differences were found for any index, with coefficients of variation of 1.5%, 2.9%, and 2.1% for functional residual capacity, ventilatory efficiency, and alveolar mixing efficiency, respectively. This method gives excellent reproducibility for biological measurements in a clinical setting and shows that these measurements can readily be made on mechanically ventilated patients.