Radial Temperature Distribution Research Articles

Approximating Gas Turbine Combustor Exit Temperature Distribution Factors Using Spatially Under-Sampled Measurements

Abstract In gas turbine engines, the temperature field at the exit plane of the combustor is highly unsteady and complex, with large radial and circumferential variations. The circumferential temperature variations (hot-streaks) are caused by the discrete nature of fuel and dilution air jets, and combustor lining coolant flow results in a strong radial temperature gradient. Two widely adopted parameters include the radial temperature distribution factor (RTDF) and the overall temperature distribution factor (OTDF) to quantify combustor exit temperature nonuniformity. The state-of-the-art approach to characterizing the combustor exit temperature nonuniformity is to carry out an extensive traverse along the circumferential direction at a spatial resolution of two to three degrees. With hundreds of measurements in place, the combustor OTDF and RTDF can be obtained. Though the approach is practical, this involves the design of complex traverse mechanisms and can be costly. To address this challenge, this paper presents a novel method for predicting combustor exit TDFs using much sparser measurements. The approach's effectiveness was examined using three engine representative combustor exit temperature measurements covering a single-burner, double-burner, and entire annulus. In all cases, the hot-streaks-related features are well resolved in the reconstructed temperature field, and the multiwavelet approximation method yields almost identical RTDF to experiment with majority variations of less than 1.0% using sparse measurements. In addition, the method's robustness was examined, and considerations for the implementation of the method were provided.

Optimal design of heat dissipation on low power PCB

ABSRACT With the application of higher and higher power density IC in power driver circuits, an efficient modeling method of thermal design and heat dissipation is desired. In this paper, the printed circuit board (PCB) heat dissipation without heat-sink is discussed. Firstly, the thermal resistance of PCB thermal via array is analytically modeled. Then, the optimal via diameter and number are found in a limited area for minimum thermal resistance. Secondly, the radial temperature distribution is analyzed and a method of designing a proper copper pad for heat dissipation under the design power is posed. Finally, computational fluid dynamics (CFD) simulations are developed to verify the posed model and method.

Steam Methane Reforming with Chemical-Looping Combustion: Scaling of Fluidized-Bed-Heated Reformer Tubes

The combination of chemical-looping combustion (CLC) and steam methane reforming (SMR) bears the potential for quantitative and energy-efficient CO2 capture along with hydrogen production from natural gas. A 2-dimensional axisymmetric model of a SMR tube was used to estimate the possibility to adapt the tube dimensions to better fit into fluidized-bed heat exchangers. A constant surrounding fluidized-bed temperature was set as the boundary condition. There are two phenomena that affect the reactor performance: the effective heat-transfer rate from the fluidized bed to and through the tube wall and onward to and into the catalyst bed on the one hand and the effective reaction rates of the governing chemical reactions on the other hand. Literature models were used for the heat-transfer description assuming a state-of-the-art reforming catalyst and classical SMR kinetics were formulated. The simulation results show a temperature decrease toward the tube center in steady state operation. The gas phase composition at the tube outlet reflects the radial temperature distribution as the chemical equilibrium is approached well. Simulations with smaller tube diameters indicate that the necessary tube length for equivalent gas conversion is significantly reduced. In a 1/2-scale setting with 63 mm inner diameter (ID) of the tube instead of 126 mm ID in full scale, the necessary tube length is only 6.0 m instead of 12.5 m, and in a 1/4-scale setting with 31.5 mm ID, the necessary tube length is only 3.3 m. A temperature increase of the fluidized bed from 900 to 950 and 1000 °C may reduce the necessary tube length in the 1/4 scale from 3.3 to 2.6 and 2.2 m, respectively. These indications are promising with respect to the possibilities for fluidized-bed immersed reformer tube dimensioning and arrangement. More detailed reactor design studies will be necessary to judge the industrial feasibility of the CLC-SMR combination.

Computational Study of Gas‐Flow and Temperature Dynamics at Blast Furnace Charging

The burden in the blast furnace is charged to form separate layers of ore and coke, which makes it possible to control the conditions in the shaft because the materials have different gas permeabilities and therefore affect the gas distribution in the shaft. Since ore and coke are of fundamentally different densities, the burden mass flux at different radial locations will vary, which influences the heating of the burden upon its descent. To gain an understanding of the effect of charging on the thermal and flow conditions in the upper shaft, the system is analyzed by computational fluid dynamics combined with the discrete element method. A model of the counter‐current flow of gas and solids and the temperature of the two phases in a simplified setup is developed. It simulates the intermittent charging and continuous descent of burden and the simultaneous ascent of gas through the particle bed. The model captures the complex interaction between the solid and gas flows, which affects the radial temperature distribution due to heat transfer and gas redistribution. The dynamics of the system are illustrated and analyzed using a simple charging cycle, and some implications of the findings are discussed.

CO Line Emission Surfaces and Vertical Structure in Midinclination Protoplanetary Disks

High spatial resolution CO observations of midinclination (≈30°–75°) protoplanetary disks offer an opportunity to study the vertical distribution of CO emission and temperature. The asymmetry of line emission relative to the disk major axis allows for a direct mapping of the emission height above the midplane, and for optically thick, spatially resolved emission in LTE, the intensity is a measure of the local gas temperature. Our analysis of Atacama Large Millimeter/submillimeter Array archival data yields CO emission surfaces, dynamically constrained stellar host masses, and disk atmosphere gas temperatures for the disks around the following: HD 142666, MY Lup, V4046 Sgr, HD 100546, GW Lup, WaOph 6, DoAr 25, Sz 91, CI Tau, and DM Tau. These sources span a wide range in stellar masses (0.50–2.10 M ⊙), ages (∼0.3–23 Myr), and CO gas radial emission extents (≈200–1000 au). This sample nearly triples the number of disks with mapped emission surfaces and confirms the wide diversity in line emitting heights (z/r ≈ 0.1 to ≳0.5) hinted at in previous studies. We compute the radial and vertical CO gas temperature distributions for each disk. A few disks show local temperature dips or enhancements, some of which correspond to dust substructures or the proposed locations of embedded planets. Several emission surfaces also show vertical substructures, which all align with rings and gaps in the millimeter dust. Combining our sample with literature sources, we find that CO line emitting heights weakly decline with stellar mass and gas temperature, which, despite large scatter, is consistent with simple scaling relations. We also observe a correlation between CO emission height and disk size, which is due to the flared structure of disks. Overall, CO emission surfaces trace ≈2–5× gas pressure scale heights (Hg) and could potentially be calibrated as empirical tracers of Hg.

Comparison between 1D and 2D numerical models of a multi-tubular packed-bed reactor for methanol steam reforming

The hydrogen-rich gas produced in-situ by methanol steam reforming (MSR) reactions significantly affects the performance and endurance of the high-temperature polymer electrolyte membrane (HT-PEM) fuel cell stack. A numerical study of MSR reactions over a commercial CuO/ZnO/Al2O3 catalyst coupling with the heat and mass transfer phenomena in a co-current packed-bed reactor is conducted. The simulation results of a 1D and a 2D pseudo-homogeneous reactor model are compared, which indicates the importance of radial gradients in the catalyst bed. The effects of geometry and operating parameters on the steady-state performance of the reactor are investigated. The simulation results show that the increases in the inlet temperature of burner gas and the tube diameter significantly increase the non-uniformity of radial temperature distributions in reformer tubes. Hot spots are formed near the tube wall in the entrance region. The hot-spot temperature in the catalyst bed rises with the increase in the inlet temperature of burner gas. Moreover, the difference in simulation results between the 1D and 2D models is shown to be primarily influenced by the tube diameter. With a methanol conversion approaching 100% or a relatively small tube diameter, the simplified 1D model can be used instead of the 2D model to estimate the reactor performance.

Thermofluid characterization of nanofluids in spray cooling

The current study addresses a parametric characterization of nanofluid sprays as a way to improve the thermal performance of spray cooling systems. The nanofluids are prepared using as base solution of distilled water with 0.05% (m/m) cetyltrimethylammonium bromide – CTAB in which nanoparticles of alumina and silver are mixed at different concentrations, namely 0.5%, 1% and 2% (m/m). The effect of the shape of the nanoparticles is also considered. These nanofluids are sprayed using a pressure-swirl atomizer and impact, vertically at two different heights, onto an AISI 304 stainless steel foil. This foil is heated by Joule effect, with two imposed currents, delivering 915 and 2100 W/m2. Infrared thermography is used to measure the thermal footprint from which the dissipated heat flux is calculated. Results show that, in steady state operation, the lowest surface temperature is obtained with the 0.5% (m/m) alumina nanofluid, while increasing alumina nanoparticles, concentration increases the radial temperature distributions on the surface. Results also show a mild effect of the shape of the nanoparticles. Hence, lowest surface foil temperatures are achieved with the silver nanofluid with spherical particles, when compared with the same nanofluid with triangular particles. Heat transfer coefficients decreased with increasing thermal conductivity and dynamic viscosity of the nanofluids. On the other hand, a positive correlation is found between the specific heat capacity of the nanofluids and the spray cooling capacity. For the range of experimental conditions covered in this work, nanofluids have proven to increase the thermal performance of the spray.

Effect of Swirl on Temperature Decay Function in Straight Blade Liquid Fuel Swirl Burner

The need to shield the surroundings from fire or combustion generated pollutants has led to substantial demand for perk up burner design with better performance. In this study, the geometry of a liquid fuel burner has been modified by introduction of straight edge blade swirler and thereafter, measurement using chromium-zinc thermocouple of radial and axial temperature distributions. The straight blade swirl generator consists of 6 number of blades at angles 20°, 30°, 40°, 50° and 60°, respectively was fired by conventional diesel in an experimental model liquid fuel swirl burner. The highest axial temperature of combustion without and with swirler was 930℃ and 1121℃, respectively, while the highest radial temperature without and with swirler was 942℃ and 1130℃, respectively. The achieved 21% performance improvement suggests that burners with swirl have varied higher flame temperature and combustion intensity than their counterpart without swirl. The outcome of this study has revealed that higher agitation of the swirl significantly affected the thermal profile and this subsequently led to high combustion intensity. The changes can be attributed to turbulence being provoked at selected angles of swirl blade. The effect is enhanced as the angle of swirl blade increases, howbeit, until a threshold is reached.

Temperature measurements of long sparks in air using time-resolved moiré deflectometry

This paper presents an original investigation into time-resolved moiré deflectometry (MD) for gas temperature measurements of long sparks in air. In order to perform a rigorous comparative investigation with the widely used quantitative schlieren (QS) method, we set up an orthogonal optical measurement system. The impacts of spatial resolution and exposure time on the measurement accuracy are investigated by comparing the measured radial distribution of the gas temperature and its time evolution during the same spark discharge event. It is found that the time-resolved MD with an exposure time of 1.0 μs can accurately measure the gas temperature evolution during the isobaric heating and relaxation process of long sparks. The measured results of the expansion rate of cross-section and average temperature T g confirms that the energy loss is dominated by thermal conduction during the isobaric heating and relaxation process after the extinction of discharge current. The MD can achieve a finer spatial resolution than the QS method, which is beneficial to the reconstruction of steep radial temperature distribution and the suppression of measured temperature fluctuation. Moreover, the MD can obtain a sub-microsecond exposure time by increasing the power of continuous-wave laser source, which shows its potential to capture the rapid changes in gas temperature during the fast-heating process.

Simulation of a Hydrogen-Air Diffusion Flame under Consideration of Component-Specific Diffusivities

This work deals with the numerical investigation of a three-dimensional, laminar hydrogen-air diffusion flame in which a cylindrical fuel jet is surrounded by in-flowing air. To calculate the distribution of gas molecules, the model solves the species conservation equation for N-1 components, using infinity fast chemistry and irreversible chemical reaction. The consideration of the component-specific diffusion has a strong influence on the position of the high-temperature zone as well as on the concentration distribution of the individual gas molecules. The calculations of the developed model predict the radial and axial species and temperature distribution in the combustion chamber comparable to those from previous publications. Deviations due to a changed burner geometry and air supply narrow the flame structure by up to 50% and the high-temperature zones merge toward the central axis. Due to the reduced inflow velocity of the hydrogen, the high-temperature zones develop closer to the nozzle inlet of the combustion chamber. As the power increases, the length of the cold hydrogen jet increases. Furthermore, the results show that the axial profiles of temperature and mass fractions scale quantitatively with the power input by the fuel.

A continuum model for heat and mass transfer in moving-bed reactors for thermochemical energy storage

In this work, a continuum heat and mass transfer model coupling transport phenomena and high-temperature thermochemical reactions is developed for stationary packed-bed and counter-flow moving-bed reactors. After presenting the general modeling framework, we focus on the 2D axisymmetric version of the model for which validation is conducted with experimental results for a packed-bed reactor in the literature for manganese-iron oxide reduction/oxidation and an in-house counter-flow moving-bed reactor for magnesium-manganese oxide reduction up to 1450 °C. Transient simulation results including the local distributions of gas/solid temperatures, oxygen concentration and the extent of reaction, as well as the various energy flow components and energy conversion efficiencies are reported. The results based on the 2D axisymmetric model are also compared with those obtained from a previous 1D model. The comparison shows that capturing the radial variation is critical in reactor modeling and the 2D results demonstrate improved agreement with experiments. Specifically, large temperature variations along the radial direction are observed especially in the reaction zone; this non-uniform radial temperature distribution has a significant effect on the chemical reaction extent due to its strong dependence on temperature; and the overall oxygen concentration at the reactor exit and the predicted system efficiency are slightly lower in the 2D model compared to the 1D model. The present heat and mass transfer model can provide valuable insights into reactor design, scale-up, and operating conditions selection to maximize system energy storage efficiency.

Grid-shape electrical circuit assembled with resistance temperature detectors for multipoint temperature measurement of solid oxide fuel cells

A multipoint temperature measurement technique using a grid-shape sensor array constructed with resistance temperature detectors (RTDs) is proposed to reduce the number of cables for measurement compared with the conventional approaches such as thermocouples. DC voltage is applied between a set of nodes in the circuit, and the voltage of the other selected nodes at the outer perimeter and the response current are measured as outputs. Theoretical expressions to correlate these outputs with the resistance of the RTDs are derived to obtain the temperature of the RTDs. The feasibility of the proposed method is examined by applying the method to temperature measurement of a flat plate under uniform, linear, and radial temperature distributions near room temperature. The accuracy estimated by comparing the results obtained by this proposed method with those obtained by conventional thermocouple measurement is confirmed within 0.51 K in the temperature range tested. Moreover, the proposed circuit was established to profile the temperature of a practical-size solid oxide fuel cell (SOFC) at its operating temperatures of 920–1000 K with and without power generation. Through the experiments conducted, the proposed technique is proven to be feasible for multipoint temperature measurement of operating SOFCs.

Coupling MCNP6/ANSYS codes to calculate axial temperature and power distribution in a VVER-1000 fuel assembly

Abstract The precise simulation of the reactor core either in steady state or during transients is very important for the safety assessment of nuclear power plants. This requires accurate determination of the parameters that influence the reactor operation. Coupling neutronic and thermal hydraulic schemes are developed to calculate these parameters. In the present paper, a coupling scheme between MCNP6 and ANSYS-FLUENT17.2 codes is proposed to obtain accurate radial and axial temperature distribution and hence pin power distribution for VVER-1000 fuel assembly. The Performance of the developed coupling scheme is investigated in steady state calculations. An iterative process is associated with the exchange of data between codes to meet the convergence criteria. The results obtained demonstrate that the proposed coupling scheme is able to simulate the VVER-1000 fuel assembly accurately. It gives information about thermal and neutronic behavior of the assembly and allows the feedback effects to be accurately modeled. This work is a step forward to establish a consistent methodology to be used in transient calculations.

Combustion and emission characteristics of premixed biogas mixtures: An experimental study

In this study, effects of fuel composition, swirl number and hydrogen addition on combustion and emission characteristics of various biogas mixtures were experimentally investigated. To this end, a laboratory scale combustor and a swirl stabilized premixed burner were designed and manufactured. Later on, this combusting apparatus was equipped with flow, control, safety and measurement tools, hence entire test system was constituted. Combustion and emission characteristics of tested biogas mixtures were determined by measuring temperature and species (CO 2 , CO, O 2 and NO) distributions throughout the combustion chamber. Additionally, flame structures of tested biogas mixtures were evaluated by examining flame luminosity, visible flame length and flame thickness from instantaneous flame images. Results of this study showed that both radial and axial temperature distribution variations of tested biogas mixtures differently alter with hydrogen addition based on the gas composition. Although flame temperature increases with swirl number at burner outlet, it presents a non-monotonous dependence on swirl number outside the flame region because of the modified flow characteristics. This is also the case for emissions of CO 2 . • Premixed combustion characteristics of various biogas mixtures were investigated. • Gas composition, swirl number and hydrogen addition effects were examined. • Hydrogen addition differently altered temperature distribution based on the gas composition. • Flame temperature presented a non-monotonous dependence on swirl number.

Measurement of Heat Transfer and Flow Structures in a Closed Rotating Cavity

Abstract Buoyancy-induced flow occurs inside the rotating compressor cavities of gas turbines. These cavities are usually open at the inner radius, but in some industrial gas turbines, they are effectively closed. This paper presents measurements of the disk heat transfer and rotating flow structures in a closed cavity over a wide range of engine relevant conditions. These experimentally derived distributions of disk temperature and heat flux are the first of their kind to be published. The radial distribution of the nondimensional disk temperature virtually collapsed onto a single curve over the full experimental range. There was a small, monotonic departure from this common curve with increasing Reynolds number; this was attributed to compressibility effects where the core temperature increases as the rotational speed increases. These results imply that, if compressibility effects are negligible, all rotating closed cavities should have a disk temperature distribution uniquely related to the geometry and disk material; this is of important practical use to the engine designer. Unsteady pressure sensors detected either three or four vortex pairs across the experimental range. The number of pairs changed with Grashof number, and the structures slipped relative to the rotating disks by less than 1% of the disk speed.

Supplementing fuel behaviour analyses via coupled Monte Carlo neutronics and fission product solution

The accuracy of power distribution solution and burnup algorithms in standalone fuel behaviour codes is limited. For improved accuracy, fuel behaviour codes can be coupled with external reactor physics solvers. A coupled calculation system between the Monte Carlo neutronics and burnup calculation solver Serpent and the fuel behaviour solver TRANSURANUS was developed in an earlier work. The data exchanged between the solvers included fuel pin axial and radial power and temperature distributions, the axial fast flux distribution in the cladding and the changes in the pin radii. In this work the coupling was further improved by developing the capability to transfer and utilize Serpent calculated nuclide compositions in TRANSURANUS within the coupled calculations. Additionally, support for corrector type burnup algorithms in the coupled solution was now implemented for increased accuracy of the nuclide solution. The new capabilities were demonstrated with a coupled single rod burnup calculation utilizing power and coolant history data from the Loviisa nuclear power plant. The focus at this stage was on fission product nuclides as their accumulation adversely affects the fuel performance, making their accurate solution important to ensure safe yet economical use of fuel. The demonstration showed small but visible differences when compared to simulations that were run without using fission products calculated by Serpent. The developed capabilities will now facilitate import of further fission product nuclides to be taken into account in TRANSURANUS.

Ice thickness estimation method of overhead line based on distributed optical fiber temperature sensing

In order to monitor icing condition of overhead line based on distributed optical fiber temperature sensing, the transient temperature field models of radial and axial heat transfer for iced overhead line are constructed. The finite element method is used to solve the model to obtain the axial and radial temperature distribution inside the overhead line. Based on the two models, the change of the optical fiber temperature with time when the ambient temperature changes at a certain rate is investigated. At the same time, the change of optical fiber temperature with time in the iced and uniced sections under different ice thicknesses is also investigated. On this basis, the change of temperature difference with time is investigated. The formula of ice thickness estimation according to the temperature difference between iced and uniced sections’ optical fibers is obtained. This work lays a foundation for the evaluation of ice condition of overhead line based on distributed optical fiber temperature sensing.

Three‐dimensional thermal modeling and dimensioning design in the nuclear waste repository

AbstractA mathematical model is established by using the cylindrical heat source to simulate the temperature field in the nuclear waste repository. By means of the integral transformation method, the partial differential equations of heat conduction were transformed into ordinary differential equations to obtain the semi‐analytical solutions to temperature change. The radial temperature distribution around the nuclear waste canister was analyzed and compared with other analytical models. The built model was applied to determine the canister spacing with variable tunnel spacing for different type canister panel. Then, the quantitative effects of decay heat power at initial installation and of other parameters on the canister spacing were specified. The results show that the built model can predict the near‐field and far‐field temperature around the waste canister at the same time. The decay heat power at the initial installation and thermal properties of buffer layer and surrounding rock have strong effects on the canister spacing.

Measurement of electron density and temperature in an annular magnetically confined cold-cathode plasma of helium by optical emission spectroscopy

Magnetically confined cold-cathode plasmas in monatomic gases like helium can be used in a variety of devices and applications. In this paper, the radial distribution of electron temperature and electron density in cold-cathode helium plasmas constrained by an annular magnetic field were studied by optical emission spectroscopy. Helium plasma was generated under different pressures (7.5, 10, and 20 Pa) and values of current (23.5 and 33 mA). The spectral lines of He I 667.8 and He I 501.6 nm were studied and the Stark broadening method was applied to obtain the radial distributions of electron temperature and electron density. The results indicate that higher radial gradients or peak values of both electron density and electron temperature could be achieved with increasing operating pressures and discharge currents. It was found that the electrons were mainly concentrated in the area of the localized cusp magnetic field near the cathode surface and the electron density decreased rapidly as with the decrease in the magnetic field.

Numerical simulation of high-current pulsed arc discharge in air

A computational model of high-current pulsed arc discharge in air is proposed. This is, in general, a 2D model which takes into account the gas dynamics of the discharge channel, real air thermodynamics in a wide range of pressures and temperatures, the electrodynamics of the discharge including the pinch effect, and radiation. The 1D version of the model is tested and verified on several numerical and experimental works reported recently. It is concluded that low and moderate current discharges are satisfactorily described with the model. The model was then applied to simulate the electric discharge in air for the currents 1–250 kA and characteristic rise times in 13–25 µs, and the results of the calculations were compared with experimental ones. It was concluded that most characteristics of the discharge are predicted well. Namely, the arc column radius and shock wave position agree well with experimental data for all the current amplitudes and rise times considered. Radial distributions of temperature and electron density also satisfactorily agree with experimental data. It was found that the pinch effect should be considered for currents higher than 100 kA.