High-temperature Gas Stream Research Articles

Au nanoparticle–incorporated plasmonic nanocomposite films for high-temperature sensing

Functional sensing materials with desirable responses to a particular quantity of interest can be an enabling technology for successful development of sensors that can be deployed in a wide variety of applications. Au nanoparticle–incorporated metal oxide–based sensing layers have recently shown significant promise as optical sensing layers for high temperatures and harsh environments relevant for fossil- and nuclear-based power generation, aviation/aerospace applications and industrial manufacturing processes. Recent results are presented and discussed for Au nanoparticle–incorporated TiO2 thin films. It is demonstrated that simultaneous temperature and gas sensing using a single sensing element is possible for this class of materials through multiple wavelength–monitoring schemes. The presented results clearly illustrate that Au nanoparticle–incorporated metal oxide films and other plasmonic nanocomposites show significant promise for monitoring both the composition and temperature of high-temperature gas streams with a single sensing element.

A Fiber-Optic Sensor for Monitoring Trace Ammonia in High-Temperature Gas Samples With a ${\hbox{CuCl}}_{2}$-Doped Porous Silica Optical Fiber as a Transducer

An optical fiber chemical sensor for detecting/monitoring trace ammonia in high-temperature gas streams has been developed. This sensor uses a CuCl2-doped porous silica optical fiber, prepared via a previously reported sol-gel process, as a transducer. Trace ammonia in a gas sample diffuses into the porous fiber to react with the doped agent to form a Cu2+-ammonia complex. The concentration of the Cu2+ -ammonia complex inside the porous silica optical fiber is proportional to ammonia concentration in the gas sample, to which the sensing porous silica fiber is exposed. Therefore, ammonia concentration in the gas sample can be detected through detecting the optical absorption signal of the formed Cu2+-ammonia complex inside the fiber by using a fiber-optic UV/V is absorption spectrometric method. This sensor can be used to reversibly monitor trace ammonia in a gas sample at an elevated temperature up to 450degC in the tested range. A detection limit of 0.24 ppmv ammonia in an air gas sample was achieved when the sensor was tested at a temperature of 450degC.

Hot gas granular moving bed filters for advanced power systems

In advanced coal-fire cycles it is important to remove the fine particles from high temperature and high pressure gas streams, to satisfy gas turbine fuel quality requirements. J Smid, S S Hsiau, C Y Peng and H T Lee assess granular moving bed hot gas particulate clean-up systems for advanced IGCC and PFBC, under development in the USA.

Resistance of Ceramics in the Si3N4– BN System to Long-Term Oxidation, Thermal Cycling, and High-Temperature Gas Stream

Composite ceramics in the Si3N4 – BN system (BN = 0 – 50%) are tested for resistance to long-term oxidation, thermal cycling, and high-temperature gas stream. The results of high-temperature tests suggest a potential of the developed material for application as the rotary seal in gas-turbine engines at 1000 – 1300°C. The composite material owing to its hardness and resistance to oxidation at lower temperatures can be used for fabrication of bearing cages.

Measurement of the temperature distribution within monodisperse combusting droplets in linear streams using two-color laser-induced fluorescence

Two-color laser-induced fluorescence can be use to perform space-averaged flying droplet temperature measurements. In this paper, the possibility to extend this technique to the measurement of the temperature distribution within a moving combusting droplet is considered and demonstrated. This technique may provide new experimental data related to the heat diffusion in liquid fuel droplets injected in high-temperature gas streams, for example, in combustion chambers. The main principles of the technique and the data reduction process are discussed, and a test on combusting a monodisperse ethanol droplets (200 μm in diameter) stream is presented.

Thermal optimization of polybenzimidazole meniscus membranes for the separation of hydrogen, methane, and carbon dioxide

Membranes of the glassy polymer polybenzimidazole (PBI) were formed and tested at temperatures above 300 °C. The membrane formation method provides a rapid screening technique for the evaluation of polymeric systems at elevated temperatures. The rigidity in the structure that limits appreciable gas transport at room temperature appears to be responsible for the retention of permselectivities in the material at temperatures above 100 °C. The notion that PBI is a poor room temperature gas separation polymer is supported by its extremely low flux for hydrogen and carbon dioxide at room temperature. The rigid structure of PBI appears to be more suited to the type of diffusivity-based selectivity at temperatures above 150 °C. This result opens a new tool for studying gas separation by polymeric membranes. By selecting the optimal temperature for a membrane suited for a specific objective, it will be possible to develop tools for separating high temperature gas streams at their processing temperature. This advantage could offer cost savings that may provide a new incentive for polymeric membranes.

99/03076 Granular filtration in a fluidized bed

Successful development of advanced coal-fired power conversion systems often require reliable and efficient cleanup devices which can remove particulate and gaseous pollutants from high-temperature high-pressure gas streams. A novel filtration concept for particulate cleanup has been developed at the Morgantown Energy Technology Center (METC) of the U.S. Department of Energy. The filtration system consists of a fine metal screen filter immersed in a fluidized bed of granular material. As the gas stream passes through the fluidized bed, a layer of the bed granular material is entrained and deposited at the screen surface. This material provides a natural granular filter to separate fine particles from the gas stream passing through the bed. Since the filtering media is the granular material supplied by the fluidized bed, the filter is not subjected to blinding like candle filters. Because only the inflowing gas, not fine particle cohesive forces, maintains the granular layer at the screen surface, once the thickness and permeability of the granular layer is stabilized, it remains unchanged as long as the in-flowing gas flow rate remains constant. The weight of the particles and the turbulent nature of the fluidized bed limits the thickness of the granular layer on the filter leading to a self-cleaning attribute of the filter. This paper presents work since then on a continuous filtration system. The continuous filtration testing system consisted of a filter, a two-dimensional fluidized-bed, a continuous powder feeder, a laser-based in-line particle counting, sizing, and velocimeter (PCSV), and a continuous solids feeding/bed material withdrawal system. The two-dimensional, transparent fluidized-bed allowed clear observation of the general fluidized state of the granular material and the conditions under which fines are captured by the granular layer.

Velocity measurements in a ceramic candle filter element undergoing pulse cleaning

Ceramic candle filters have been developed for cleaning high-temperature gas streams. They have demonstrated high collection efficiencies under normal operating conditions, but the brittle materials can fail suddenly with disastrous consequences. Reverse pulse cleaning has been shown to introduce severe thermal stressing of the material. Modelling of the flows to estimate the life of the element is difficult due to non-uniformities in the material. It is important to obtain experimental measurements of flows in the candle to provide input to stress models. In addition it is essential to ensure uniform cleaning of the filter and knowledge of the pulse cleaning flow processes are also important for this. This paper reports velocity measurements obtained using a hot-wire probe located at different positions along the length of a ceramic candle filter. The data have been analysed to estimate the outflow along the length of the candle filter to investigate the cleaning potential of different configurations and operating parameters. The effect of pulse length on cleaning performance was investigated for cases with and without a venturi educer. It was found that the maximum peak mean velocity was produced at a pulse duration of 0.2 s. Longer duration pulses did not have a significant influence on the maximum velocity levels inside the filter.

Thermal stability of ceramic gas turbine blade models

A procedure developed for studying heat resistance in a high-temperature gas stream has made it possible to determine the resistance of NKM-2 materials to thermal shock and fatigue. Damage mechanisms are determined for this type of ceramic depending on the thermoelastic state in which they are found. The ultimate permissible levels of thermal shock are established at which material NKM-2 resists thermal fatigue.

Evaporation Rate of Free Paraffin Hydro-carbon Droplets in a High-Temperature and High-Pressure Gas Stream.

A series of evaporation rate constants has been obtained for fine free droplets of paraffin hydrocarbons, n-heptane, iso-octane and n-undecane in the range of 623 to 1023K in temperature and 0.1 to 0.5 MPa in pressure as the ambient conditions. To obtain the time histories of droplet diameter a fine droplet stream generated by an electrically controlled piezoelectric element was synchronized with a flash light, and enlarged droplet images were taken on a still camera. The evaporation rate constant increases with ambient pressure and temperature and is expressed by empirical equations. A mixed-hydrocarbon droplet of n-heptane and n-undecane was also examined in terms of the evaporation rate constant, and the evaporation history, the so-called D2-t relation, displays a bending line with two separate straight lines of respective constituents.

Procedure and test unit for studying the operating capacity of gas turbine engine blades under the combined action of mechanical and thermal loads, and atmosphere in a gas-dynamic test bed

A procedure and a gas-dynamic test bed are described for testing gas turbine engine blades with programmed mechanical and thermal loading. The test bed provides fatigue and heat resistance tests for GTE blades under conditions of the corrosive action of a high-temperature gas stream including variable thermodynamic parameters as well as other corrosive components, for example sea water salts injected into the stream in order to simulate GTE marine operating conditions.

Destruction of refractories by a high-temperature gas stream

Destruction of refractories by a high-temperature gas stream

Transpiration Cooling Using Air as a Coolant.

Transpiration cooling is one of the most effective techniques for protecting a surface exposed to a high-temperature gas stream. In the present paper, the transpiration cooling effectiveness was measured under the steady state. Air as a coolant was transpired from the surface of a tested porous plate exposed to a hot gas stream, and the transpiration rate was varied in the range of 0.001∼0.006. The transpiration cooling effectiveness was evaluated by measuring the temperature of the upper surface of the tested plate. Also, a theoretical study was performed and it was clarified that the effectiveness increases with increasing transpiration rate and heat transfer coefficient on the back surface of the tested plate, and with decreasing heat transfer coefficient of the upper surface. Further, the effectiveness was expressed as a function of the blowing parameter only. The agreement between the experinental results and theoretical ones was satisfactory.

An experimental study on the evaporation of freely falling droplet under high temperature and high pressure gas stream

An experimental apparatuses and measuring system have been made to obtain characteristics connected with evaporation, ignition delay, combustion of a freely falling liquid fuel droplet in high temperature and high pressure gas stream. In this study some systematic experiments were performed to test the utility of the system. The newly devised apparatus was ensured reliability and utility from the tentative experimental results.

Solution of ablation equation with a low degree of asymmetry

The change of body shape (ablation) in a high-temperature gas stream has been the subject of numerous studies involving the consideration of two-dimensional and, to a lesser extent, three-dimensional problems (for a bibliography, see [11). In [1], the problem of three-dimensional ablation under the influence of convective or radiative heat transfer was posed in a simplified integrolocal form. In this paper, a semianalytic solution is proposed for similar, almost axisymmetric problems in the same formulation. By means of linearization (used only to substantiate the method, not in the computational algorithm), the general problem is reduced to a set of isolated two-dimensional problems for each harmonic of the Fourier series in the circumferential variable. Calculated examples indicate a perfectly finite region of applicability of the method with respect to the degree of asymmetry of the problem. The method can be used to provide an efficient means of calculating the complex problem of ablation and dynamics of a body moving in the atmosphere. For high-frequency oscillations, a simple solution of this (generally very awkward) problem is obtained within the framework of the corresponding asymptotic theories.

Three-dimensional theory of the equation of ablation of bodies in a high-temperature gas stream

An integrodifferential ablation equation is obtained within the framework of a local-integral model with allowance for three-dimensional effects in the convective heat transfer law. Owing to the dependence of the latter on the azimuthal derivatives of the surface shape, determined by the divergence of the inviscid streamlines at the surface, this equation is third-order in the space variables, and if the asymmetry of the problem is small, acquires the features of the wave equation. An attempt is made to classify such equations, and in particular their characteristic properties, and the regions of influence and dependence of the solutions, etc., are investigated. These results can be useful both for further analytic research and in developing numerical methods of solution.

Observations on the role of oxide scales in high-temperature erosion-corrosion of alloys

The results are presented of exposure to a controlled high-temperature erosive gas stream of a series of alloys, which were selected to represent the range of microstructures and mechanical properties available in commercial high-temperature alloys. Analysis of the kinetic and morphological data suggested that the high-temperature oxidation behavior of a given alloy plays a very important role in determining its erosion-corrosion behavior under the conditions studied. In terms of relative behavior, alloys which are weak but ductile at temperature, and which form tenacious oxide scales, exhibited the highest resistance to high-temperature erosion-corrosion. Simple models were developed to describe the expected interaction between high-temperature oxidation and erosion.

Measurement of particle velocity in a high-temperature gas stream

Measurement of particle velocity in a high-temperature gas stream

Stress state in the vicinity of a drillhole cut by flame

The authors consider the thermoelastic component of stresses in the vicinity of a drillhole cut by flame; they use the model of a homogeneous, isotropic half-space around which a high-temperature gas stream flow, in which the temperature distribution has a domed shape. Here the boundary conditions of thermal conductivity of the third type hold, corresponding to the convective heat exchange which occurs during flame drilling.

Development of the Transpiration Air-Cooled Turbine for High-Temperature Dirty Gas Streams

Studies of combined cycle electic power plants have shown that increasing the firing temperature and pressure ratio of the gas turbine can substantially improve the specific power output of the gas turbine as well as the combined cycle plant efficiency. Clearly this is a direction in which we can proceed to conserve the world’s dwindling petroleum fuel supplies. Furthermore, tomorrow’s gas turbines must do more than operate at higher temperature; they will likely face an aggressive hot gas stream created by the combustion of heavier oils or coal-derived liquid or gaseous fuels. Extensive tests have been performed on two rotating turbine rigs, each with a transpiration air cooled turbine operating in the 2600 to 3000°F (1427 to 1649°C) temperature range at increasing levels of gas stream particulates and alkali metal salts to simulate operation on coal-derived fuel. Transpiration air cooling was shown to be effective in maintaining acceptable metal temperatures, and there was no evidence of corrosion, erosion, or deposition. The rate of transpiration skin cooling flow capacity exhibited a minor loss in the initial exposure to the particulate laden gas stream of less than 100 hours, but the flow reduction was commensurate with that produced by normal oxidation of the skin material at the operating temperatures of 1350°F (732°C). The data on skin permeability loss from both cascade and engine tests compared favorably with laboratory furnace oxidation skin specimens. To date, over 10,000 hr of furnace exposure has been conducted. Extrapolation of the data to 50,000 hr indicates the flow capacity loss would produce an acceptable 50°F (10°C) increase in skin operating temperature.