bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbine Cooling Systems Design: Past, Present and Future
Authors: Downs James P. , Landis Kenneth K.
Published: February 2010

Over a half a century ago, the power and performance of the first gas turbine engines were constrained by material limits on operating temperature. In these machines, the combustor exit temperature could not exceed the capability of the materials used to construct the turbine. Eventually, cooling was introduced into turbine components to enable turbine power and efficiency to be increased. That revolutionary step enabled gas turbines to become competitive with other heat engines for business, particularly in the rapidly expanding aviation and electrical power generation sectors. Although the first cooled turbine components may be considered crude by present standards, the underlying foundation of internal convection cooling remains the backbone for cooled turbine components today. Since its introduction, many improvements and additions to the fundamental basis of turbine component cooling have been developed. The introduction of film cooling is a prominent example. With this past research and development, turbine cooling system designs have progressed to the point where they represent the norm, rather than the exception in today’s gas turbines. Further, the confidence and robustness of these systems has been elevated to the point where the working fluid temperatures can exceed the maximum temperature of the structural materials by wide margins. In this paper, from an engineering perspective, we explore some of the significant accomplishments that have led to the current state-of-the-art in turbine cooling systems design. These systems employ a delicate balance of structural material capabilities with advanced internal and film cooling and the use of thermal barrier coatings to satisfy the goals and objectives of specific applications. At the same time, it is widely recognized that the use of cooling flows in the turbine results in parasitic losses that reduce performance. To that end, we also consider some of the specific challenges that face cooling system designers to reduce cooling flows today. Based on the research and development that has been performed to date, we consider the current status of cooling technology relative to a theoretical peak. Finally, we explore some of the hurdles that must be overcome to effectively raise the bar and realize future advancement of the state-of-the-art. The goal is to measure and separate new technologies that are merely different from those that are superior to past designs. Clearly, the identification of risk and risk reduction will play an important role in the development of future turbine cooling systems.
Capturing the Shape Variance in Gas Turbine Compressor Maps
Authors: Drummond Chris , Davison Craig R.
Published: February 2010

The production of accurate compressor maps is an essential, but time consuming, step in gas turbine engine modeling. Insight into how the shape of a map depends on the compressor type, and design point characteristics, should accelerate this exercise. It should also serve as the basis of a more accurate scaling procedure than is currently available. In this paper, we extract information empirically from a collection of maps for different types of compressor. A technique, used in computer vision, generates smooth transformations between maps, producing intermediate ones of the right form. Not only can the total shape change between maps be determined, but also the principal dimensions of that change. We present figures that capture both typical maps of various types and the most significant dimensions of variation between types. We discuss how these are tied to physical processes within the compressors. We then show how this information can be used to accurately scale maps.
CFD Investigation of Temperature Rise in a Combustor Test Rig Exhaust System
Authors: Boulanger Joan , Han Yinghua , Jiang Leiyong , Manipurath Shaji
Published: February 2010

This paper presents a study of temperature rise in the exhaust system of a combustor test rig, Test Cell #1, at the Gas Turbine Laboratory, Institute for Aerospace Research, the National Research Council of Canada. As the flow regime is supersonic with a mixture of hot air & water vapour, condensation of water vapour in the system is suggested to explain the temperature rise observed along the exhaust pipe. The method of Computational Flow Dynamics is used to carry out the first investigation on this hypothesis. The exhaust system is reproduced by CAD, meshed and modelled by the ANSYS-FLUENT CFD package. Simulations of a two-phase complex mixture are performed. The numerical results indicate that the pressure control devices in the exhaust flow towards the stack create phenomena similar to nozzles and yield condensed water into the system. The simulations of liquid phase content and temperature fields are qualitatively consistent with experimental observations and support the hypothesis that condensation is occurring and may therefore threaten the structural integrity of the system through thermal effects.
Flame Transfer Functions and Their Applications to Combustion Analysis and Control
Authors: Yi Tongxun , Santavicca Domenic A.
Published: February 2010

Heat release rate responses to inlet fuel modulations, i.e. the flame transfer function (FTF), are measured for a turbulent, liquid-fueled, swirl-stabilized, LDI combustor. Fuel modulations are achieved using a motor-driven rotary fuel valve designed specially for this purpose, which is capable of fuel modulations up to 1 kHz. Small-amplitude fuel modulations, typically below 2.0% of the mean fuel, are applied in this study. There is almost no change in FTFs at different fuel modulation amplitude, implying that the derived FTFs are linear and that the induced heat release rate oscillations mainly respond to variations in the instantaneous fuel flow rate rather than in the droplet size and distribution. The gain and phases of the FTFs at different air flow rates and preheat temperature are examined. The instantaneous fuel flow rate is determined from pressure measurements upstream of a fuel nozzle. Applications of the FTF to modeling and control of combustion instability and lean blowout are discussed. Near-LBO stability enhancement using small-amplitude fuel modulation based on the output of a LQG controller is numerically demonstrated.
Experimental Study of Reaction and Vortex Breakdown in a Swirl-Stabilized Combustor
Authors: Umeh Chukwueloka O. U. , Rusak Zvi , Gutmark Ephraim J.
Published: February 2010

Non-reacting and lean reacting flow experiments are conducted in a swirl-stabilized combustor with several configurations of a Triple Annular Research Swirler (TARS) fuel injector. The test chamber is composed of the TARS swirler at the inlet of a straight cylindrical fuel pre-mixing section, followed by a sudden expansion and a finite-length concentric pipe. The combustor chamber exit is open to the atmosphere, hence pressure is ambient for all test cases. Non-reacting flow tests are conducted with air at 300K and 600K. The reacting flow tests use premixed air (preheated to 600K) and commercial grade gaseous propane fuel (injected at ambient temperature) at low equivalence ratios. Particle imaging velocimetry (PIV) is used to measure the distribution of axial, radial and circumferential velocity fields from which the swirl ratio at a cross section near the expansion plane and the position and size of the vortex breakdown zone are determined for a certain swirler configuration with non-reacting cold and pre-heated flows and with reacting flows at various equivalence ratios. Simultaneous OH chemiluminescence is taken and used to identify the location of the reaction zones and hence the flame anchoring point for each reacting-flow case. Results show the complex dynamical interaction between the flame and the breakdown zone, and the appearance of oscillations in the position of both. In the non-reacting cold flow case, the breakdown zone appears near the expansion plane. In the non-reacting pre-heated flow case on the other hand, it is pushed downstream of the dump plane. For reacting flows with low equivalence ratios (near the lean blow out point) the breakdown zone is anchored to the dump plane and expansion corners and is relatively stable, while the flame oscillates inside it. On the other hand, at higher equivalence ratios, the flame is anchored to the dump plane and expansion corners while the breakdown zone oscillates behind it. The swirl numbers measured near the expansion plane exhibits nice correlation with the position of the vortex breakdown and satisfies the necessary theoretical conditions for the first appearance of breakdown in a premixed reacting swirling flow.
Low-Pressure System Component Advancements and Its Influence on Future Turbofan Engine Emissions
Authors: Gro¨nstedt Tomas , Au Dax , Kyprianidis Konstantinos , Ogaji Stephen
Published: February 2010

Within the European research project EnVIronmenTALly Friendly Aero Engines, VITAL, a number of low pressure system component technologies are being investigated. The emerging progress will allow the design of new power plants providing a step change in engine fuel burn and noise. As part of the VITAL project a Technoeconomic and Environmental Risk Assessment tool, the TERA2020, is being developed. Within this tool, means to assess the impact of component technology progress on the engine/aircraft system level has been implemented. Sensitivities relating parameters traditionally used to describe component performance, such as allowable shaft torque, low pressure turbine stage loading, fan blade weight and system level parameters have been established. This allows a direct assessment of the impact of component research progress on the VITAL power plant CO2 and noise emissions.
A Detailed and Reduced Reaction Mechanism of Biomass-Based Syngas Fuels
Authors: Braun-Unkhoff Marina , Slavinskaya Nadezhda , Aigner Manfred
Published: February 2010

In the present work, the elaboration of a reduced kinetic reaction mechanism is described which predicts reliably fundamental characteristic combustion properties of two biogenic gas mixtures consisting mainly of hydrogen, methane, and carbon monoxide, with small amounts of higher hydrocarbons (ethane and propane), in different proportions. From the in-house detailed chemical kinetic reaction mechanism with about 55 species and 460 reactions, a reduced kinetic reaction mechanism was constructed consisting of 27 species and 130 reactions. Their predictive capability concerning laminar flame speed (measured at T0 = 323 K, 373 K and 453 K, at p = 1 bar, 3 bar, and 6 bar for equivalence ratios φ between 0.6 and 2.2) and auto ignition data (measured in a shock tube between 1035 and 1365 K at pressures around 16 bar for φ = 0.5 and 1.0) are discussed in detail. Good agreement was found between experimental and calculated values within the investigated parameter range.
A Model-Based Mission Planning and Decision Support Tool
Authors: Jessop Simon M. , Cook Thomas C.
Published: February 2010

Impact Technologies developed a model-based decision support Framework that facilitates the use and development of decision support tools in a CBM environment. The Framework leverages existing CBM and PHM data to provide enhanced automated strategic analysis. Its modular structure promotes reusability of components to expedite development of new decision capabilities, making it extensible to many different operational environments. The Framework also embraces open architecture and standardized data interfaces for increased supportability and upgradeability. An advanced probability-based mission readiness forecasting and assessment tool developed by Impact Technologies for the U.S. Navy was used to illustrate how the proposed Framework facilitates the assembly of independent decision support tools to provide a high fidelity knowledge product. In this application the Framework combined three separate functional areas — a mission profile modeling tool, a system relational model, and a maintenance optimization module. The mission profile modeling tool provided the ability to create functional representations of multi-layered complex systems for any mode of operation, accounting for different machinery line-ups, redundancy, system-to-system interactions, and component and sub-system criticalities. The system relational model provided the overall system probability of failure calculated based on the current and projected system configuration and usage. The maintenance optimization module determined the safest and most cost-effective time to perform required and opportunistic maintenance. The resulting software product enables the comparison of multiple what-if scenarios where the scheduling of maintenance and logistics support activities can be optimized based on resource availability and the propagation effects of those actions can be measured in terms of readiness at any level within the system hierarchy. A visual assessment of the ship’s probability of completing the prescribed mission of any combination of ship operations (e.g., anti-surface warfare, non-combat operations, or mine warfare) can be generated so corrective actions in the form of maintenance or changes to mission operations can be evaluated. The tool incorporates several novel approaches including fusion of multiple independent low-level indicators to predict overall system readiness, methodologies to account for the interactive effects of interconnected subsystems, and a risk-based optimization to select and schedule the optimal maintenance schedule. This paper summarizes the features of the model-based decision support tool Framework and the mission readiness software application developed using this architecture.
Turbo Gas Power Plants Performance Evaluation for Putting Into Commercial Operation
Authors: Rosado Tamariz Erik , Pe´rez Rodri´guez Norberto , Garci´a Illescas Rafael
Published: February 2010

In order to evaluate the performance of new turbo gas power plants for putting in commercial operation, it was necessary to supervise, test and, if so the case, to approve the works of commissioning, operational and acceptance of all equipments and systems that constitute the power plant. All this was done with the aim of guaranteeing the satisfactory operation of these elements to accomplish the function for which they were developed. These activities were conducted at the request of the customer to confirm and observe that the evidence of the tests was carried out according to the specifications and international regulations. The putting into commercial operation activities were done in collaboration with the supplier and manufacturer of equipment, the client and the institution responsible for certification and approval of the plant. All this in a logical and chronological order for the sequence of commissioning tests, operation and acceptance. Commissioning tests were carried out on-site at normal operating conditions, according to the design and operation needs of each power plant of a group of 14. Once the commissioning tests were completely executed and in a satisfactory manner, operational tests of the plants were developed. This was done by considering that they must operate reliable, stable, safe and automatically, satisfying at least, one hundred hours of continuous operation at full load. After evaluating the operational capacity of the machine, it was necessary to determinate the quality of the plant by carrying out a performance test. Finally, it was verified if every unit fulfills the technical requirements established in terms of heat capacity of the machine, noise levels and emissions. As a result of this process, it is guaranteed to the customer that the turbo gas power plants, their systems and equipments, satisfy the requirements, specifications and conditions in agreement with the supplier and manufacturers referring to the putting into commercial operation of the plant.
Experimental Simulation of a Film Cooled Turbine Blade Leading Edge Including Thermal Barrier Coating Effects
Authors: Maikell Jonathan , Bogard David , Piggush Justin , Kohli Atul
Published: February 2010

For this study a simulated film cooled turbine blade leading edge, constructed of a special high conductivity material, was used to determine the normalized “metal temperature” representative of actual engine conditions. The Biot number for the model was matched to that for operational engine conditions ensuring that the normalized wall temperature, i.e. the overall effectiveness, was matched to that for the engine. Measurements of overall effectiveness were made for models with and without TBC (thermal barrier coating) at various operating conditions. This was the first study to experimentally simulate TBC and the effects on overall effectiveness. Two models were used, one with a single row of holes along the stagnation line, and the second with three rows of holes straddling the stagnation line. Film cooling was operated using a density ratio of 1.5 and for range of blowing ratios from M = 0.5 to M = 3.0. Both models were tested using a range of angles of attack from 0.0 to ± 5.0 degrees. As expected, the TBC coated models had significantly higher external surface temperatures, but lower “metal temperatures.” These experimental results provide a unique database for evaluating numerical simulations of the effects of TBC on leading edge film cooling performance.
Experimental Study of the Effects of an Oscillating Approach Flow on Overall Cooling Performance of a Simulated Turbine Blade Leading Edge
Authors: Johnson Ross , Maikell Jonathan , Bogard David , Piggush Justin , Kohli Atul , Blair Michael
Published: February 2010

When a turbine blade passes through wakes from upstream vanes it is subjected to an oscillation of the direction of the approach flow resulting in the oscillation of the position of the stagnation line on the leading edge of the blade. In this study an experimental facility was developed that induced a similar oscillation of the stagnation line position on a simulated turbine blade leading edge. The overall effectiveness was evaluated at various blowing ratios and stagnation line oscillation frequencies. The location of the stagnation line on the leading edge was oscillated to simulate a change in angle of attack between α = ± 5° at a range of frequencies from 2 to 20 Hz. These frequencies were chosen based on matching a range of Strouhal numbers typically seen in an engine due to oscillations caused by passing wakes. The blowing ratio was varied between M = 1, M = 2, and M = 3. These experiments were carried out at a density ratio of DR = 1.5 and mainstream turbulence levels of Tu ≈ 6%. The leading edge model was made of high conductivity epoxy in order to match the Biot number of an actual engine airfoil. Results of these tests showed that the film cooling performance with an oscillating stagnation line was degraded by as much as 25% compared to the performance of a steady flow with the stagnation line aligned with the row of holes at the leading edge.
Green’s Function Approach to Nonlinear Conduction and Surface Radiation Problems
Authors: Jones Matthew R. , Solovjov Vladimir P.
Published: February 2010

An analytical approach for solving both transient and steady state conduction and surface radiation problems is presented. The method is based on the use of a Green’s function, and the temperature field is obtained by solving an integral equation. This is in contrast to the approach presented in radiative heat transfer texts in which temperature profiles are obtained from the simultaneous solution of coupled integral and differential equations. The analysis presented in this paper provides insight into the solution of this important class of problems. The method is illustrated by solving two representative problems. The first problem considered is the steady state analysis of radiating fins, which are frequently incorporated in the design of spacecraft. The second problem considered is the transient analysis of a radiating target, which is used to determine the temporal response of radiation thermometers.
Hotwire Measurements Downstream of a Delta Winglet Pair at Two Angles of Attack
Authors: Hernon Domhnaill , Patten Norah
Published: February 2010

Hotwire measurements were obtained downstream of a delta winglet pair placed on an unheated flat surface. Time-averaged mean velocity, RMS, fast Fourier transform and instantaneous velocity statistics are examined to gain insight into the effect that a delta winglet pair has on manipulating an otherwise steady baseline flow. Typically, results presented in the literature are in time-averaged form and this implies that the majority of information that relates to enhanced heat transfer, i.e. unsteady flow phenomena, is lost. It is for this reason that the current investigation examines the flow downstream of the vortex generator (VG) with hotwire anemometry so as to achieve good temporal and spatial measurement resolution. The mean velocity and RMS profiles presented at two different Angles of Attack (AoA) provide valuable information on the extent to which the VG manipulates the flow. In the centreline the boundary layer is significantly thinned in comparison to other spanwise locations indicating the presence of the downwash region. The shape of the mean velocity and RMS profiles also indicate the extent to which the vortex structures grow in the spanwise direction with downstream distance from the VG. The peak RMS values are shown to increase with downstream distance in some spanwise planes and decrease with downstream distance for other spanwise planes thereby illustrating complex fluid flow interactions. Examining the instantaneous flow features reveals the true nature of the unsteadiness and also elucidates some of the more complex flow phenomena, such as positive spikes found in the near-wall region, that may lead to enhanced heat transfer. It is also observed from the instantaneous velocity traces that large negative spikes are observed in the freestream region close to the boundary layer edge. These structures help to explain the interaction between the near wall and freestream flow field thereby resulting in significantly enhanced mixing.
An Efficient Sparse Finite Element Solver for the Radiative Transfer Equation
Authors: Widmer Gisela
Published: February 2010

The stationary monochromatic radiative transfer equation (RTE) is posed in five dimensions, with the intensity depending on both a position in a three-dimensional domain as well as a direction. For non-scattering radiative transfer, sparse finite elements [1, 2] have been shown to be an efficient discretization strategy if the intensity function is sufficiently smooth. Compared to the discrete ordinates method, they make it possible to significantly reduce the number of degrees of freedom N in the discretization with almost no loss of accuracy. However, using a direct solver to solve the resulting linear system requires O(N3) operations. In this paper, an efficient solver based on the conjugate gradient method (CG) with a subspace correction preconditioner is presented. Numerical experiments show that the linear system can be solved at computational costs that are nearly proportional to the number of degrees of freedom N in the discretization.
Effectiveness of Counter Flow Microchannel Heat Exchangers Subjected to External Heat Transfer and Internal Heat Generation
Authors: Mathew B. , John T. J. , Hegab H.
Published: February 2010

The effect of external heat transfer and internal heat generation on the thermal performance of a balanced counter flow microchannel heat exchanger is theoretically analyzed in this paper. External heat transfer occurs due to the thermal interaction between ambient and the fluids. Internal heat generation takes into account the heat generated inside the channels due to the conversion of pumping power into heat. One-dimensional governing equations for both fluids were developed and solved to obtain the axial temperatures. The governing equations were solved using a 2nd order finite difference scheme. The effectiveness of the fluids is dependent on NTU, the ambient temperature, the thermal resistance between the individual fluids and the ambient and the pumping power. With increase in ambient temperature the effectiveness of the hot and cold fluid decreased and improved, respectively. On the other hand, reductions in the ambient temperature always lead to the improvement and degradation of the hot and cold fluid effectiveness, respectively. Depending on the ambient temperature, the thermal resistance between the individual fluids and the ambient increased or decreased the effectiveness of the fluids. Internal heat generation always reduced and improved the hot and cold fluid effectiveness, respectively. The combined effect of external heat transfer and internal heat generation on the effectiveness of the fluids depends on the net amount of heat gained/lost by the individual fluids. The effectiveness of a microchannel counter flow heat exchanger is found to be better than of a parallel flow heat exchanger subjected to the same set of external conditions. The model developed in this paper has been verified using existing models that consider each of these effects individually.
A Simple Model for Transient Thermal Behavior of Integrated Circuit Package Systems for Use in Determining a Thermal Design Power
Authors: Huang Julia C. , Pise Niyati , Ganapathy Deepak , Prabhu Shushanth , Warner Ethan J.
Published: February 2010

The ever increasing power dissipation requirements of electronic components and the need to provide reliable, cost-effective thermal solutions requires the thermal engineer to accurately understand the component’s thermal design power (TDP). The TDP is impacted not only by the power-performance characteristics of the component architecture, but also by the inherent thermal characteristics of the cooling solution. A suitable TDP definition thus requires a clear understanding of the transient thermal response (resistance and capacitance) of the cooling solution. In this paper, a simple electrical analogy impedance network model that resembles the component with cooling solution is developed. Correlation models to predict the resistance and capacitance for this impedance network are built based on easily available parameters such as heat sink mass, surface area, specific heat etc. The accuracies of these models are validated experimentally with data collected on a PCB with several different thermal solutions. Development of these correlation models eliminates the need for complex time consuming transient experiments to characterize the system thermal characteristics like capacitance, which allows faster, more realistic TDP definitions and ability to analyze multiple thermal designs quickly and accurately.
Thermal Models for Determining Thermal Conductivity and Thermal Boundary Conductance Using Pump-Probe Thermoreflectance Techniques
Authors: Hopkins Patrick E. , Serrano Justin R. , Phinney Leslie M.
Published: February 2010

Pump-probe transient thermoreflectance (TTR) techniques are powerful tools for measuring thermophysical properties of thin films, such as thermal conductivity, Λ, or thermal boundary conductance, G. TTR experimental setups rely on lock-in techniques to detect the response of the probe signal relative to the pump heating event. The temporal decays of the lock-in signal are then compared to thermal models to deduce the Λ and G in and across various materials. There are currently two thermal models that are used to relate the measured signals from the lock-in to the Λ and G in the sample of interest. In this work, the thermal models, their assumptions, and their ranges of applicability are compared. The advantages and disadvantages of each technique are elucidated from the results of the thermophysical property measurements.
An Experimental Investigation of Microchannel Size Effects on Flow Boiling With De-Ionized Water
Authors: Holcomb Bradley T. , Harirchian Tannaz , Garimella Suresh V.
Published: February 2010

The heat transfer characteristics during flow boiling of deionized water in parallel microchannels are investigated. The silicon heat sinks contain an array of integrated heaters and diodes for localized heat-flux control and temperature measurement. The channel widths for the three different test pieces range from 250 μm to 2200 μm, with a nominal depth for all channels of 400 μm. The present study investigates the effects of the channel width and mass flux on the boiling performance. This study follows a previous study using a wetting dielectric liquid, and aims to understand the role of wetting since water is relatively non-wetting. From the results of the present study, a weak dependence of the boiling curve and heat transfer coefficient on mass flux was observed. Varying the channel width also does not have a strong effect on either the boiling curve or the heat transfer coefficient. The experimental results are compared to those obtained previously for a dielectric liquid. They are also compared with predictions from several correlations from the literature.
Thermal Conductivity of α-Tetragonal Boron Nanoribbons
Authors: Waltermire Scott W. , Yang Juekuan , Li Deyu , Xu Terry T.
Published: February 2010

Elemental boron has many interesting properties, such as high melting point, low density, high hardness, high Young’s modulus, good oxidation resistance, resulting from its complex crystalline structure from its electron-deficient nature. Boron forms complex crystalline structures according to the various arrangements of B12 icosahedra in the lattice, such as α (B12)- and β (B105)-rhombohedral and α (B50)- and β (B196)-tetragonal boron polymorphs, among others. Even though considerable materials research has been conducted over the past half century on boron and boron-based compounds, investigating their unique structures and corresponding properties, our understanding of this complex class of materials is still poor, compared to some other well-studied materials with much simpler structures such as silicon. Thermal transport studies through bulk boron have been performed mainly on β-rhombohedral and amorphous boron, because of the difficulty to grow high quality bulk α-rhombohedral boron samples [1–3]. Some efforts have been made to measure B12As2, B12P2, AlB12 samples that have an α-rhombohedral form [2,3]. There is almost no information available on α-tetragonal boron. However, Slack predicted the thermal conductivity of α-boron should be ∼200 W/m-K at room temperature, which is 1/2 that of copper. Large phonon mean free path has been predicted for α-boron (from ∼200 nm at room temperature to 6 nm at the Debye temperature), which could lead to interesting thermal transport properties for low dimensional boron structures.
A Parametric Case Study in Radiative Heat Transfer Using the Reverse Monte-Carlo Ray-Tracing With Full-Spectrum k-Distribution Method
Authors: Sun Xiaojing , Smith Philip J.
Published: February 2010

A combined method of Reverse Monte-Carlo Ray-tracing (RMCRT) with Full-Spectrum k-distribution (FSK) for computing the radiative heat transfer is applied to an extreme non-homogeneous case (both temperature and gas mixture composition vary with positions) with absorbing, emitting media. Parameter Studies of the scaled FSK (FSSK) and correlated FSK (FSCK) methods for the case, such as g point resolution, mesh resolution, reference states and integration quadratures, are carried out. The results from the FSSK and FSCK are only affected by the chosen reference states, and are not sensitive to other parameters.
Experimental Investigation of Closed Loop Pulsating Heat Pipe With Nanofluids
Authors: Jamshidi Hamed , Arabnejad Sajad , Shafii Mohammad Behshad , Saboohi Yadollah , Rasoulian Ramin
Published: February 2010

In this paper, the effect of several different parameters on the thermal resistance of a Closed Loop Pulsating Heat Pipe (CLPHP) has been investigated. These parameters include the working fluid, the inclination angle, the filling ratio and the heat influx. Also, the impact of using nanofluids with different nano-particle concentrations has been analyzed. It was observed that a CLPHP can increase the heat transfer up to 11.5 times compared to an empty pipe. Optimum performance for a system with the water-silver nanofluid was achieved at conditions of 50% filling ratio and 0.9 K/W of thermal resistance, and for the water-titanium oxide system, these optimal conditions were found to be 40% filling ratio and 0.8 K/W of thermal resistance. In addition, the optimum performance for pure water occurs at a filling ratio of 40% and a thermal resistance of 1.15 K/W. The nanofluid reduces the thermal resistance by 30%. With a decrease in the concentration of nano-particles in the base fluid, the performance of the system decreases as well and the total thermal resistance increases. In low powers (under 20 W), the two-phase flow pattern inside the pipes was slug-plug, but in higher powers (over 30 W), this changed to an annular flow. The performance of the system was better in the annular mode, but there was a probability of dry out and sudden increase of condenser temperature.
Numerical Simulation of Heat Sink Performance With Interrupted and Staggered Fins
Authors: Gururatana Suabsakul , Li Xianchang
Published: February 2010

Extended surfaces (fins) have been used to enhance heat transfer in many applications. In electronics cooling, fin-based heat sinks are commonly designed so that coolants (gas or liquid) are forced to pass through the narrow straight channel. To improve the overall heat sink performance, this study investigated numerically the details of heat sinks with interrupted and staggered fins cooled by forced convection. Long and narrow flow passages or channels are widely seen in heat sinks. Based on the fundamental theory of heat transfer, however, a new boundary layer can be created periodically with interrupted fins, and the entrance region can produce a very high heat transfer coefficient. The staggered fins can take advantage of the lower temperature flow from the upstream. The tradeoff is the higher pressure loss. A major challenge for heat sink design is to reduce the pressure loss while keeping the heat transfer rate high. The effect of fin shapes on the heat sink performance was also examined. Two different shapes under study are rectangular and elliptic with various gaps between the interrupted fins in the flow direction. In addition, studies were also conducted on the parametric effects of Reynolds number and gap length. It is observed that heat transfer increases with the Reynolds number due to the feature of developing boundary layer. If the same pressure drop is considered, the heat transfer rate of elliptic fins is higher than that of rectangular fins.
Spectral Module for Photon Monte Carlo Calculations in Hypersonic Nonequilibrium Radiation
Authors: Ozawa Takashi , Modest Michael F. , Levin Deborah A.
Published: February 2010

In this paper, efficient spectral modules and random number databases are developed for atomic and diatomic species for use in photon Monte Carlo (PMC) modeling of hypersonic nonequilibrium flow radiation. To model nonequilibrium flow conditions, the quasi steady state (QSS) assumption was used to generate electronic state populations of atomic and diatomic gas species in the databases. For atomic species (N and O), both bound-bound transitions and continuum radiation were included, and were separately databased as a function of electron temperature and number density as well as the ratio of atomic ion to neutral number density. For the radiating diatomic species of N2+, N2, O2, and NO, databases were generated for each electronic molecular electronic system. In each molecular electronic system, the ro-vibrational transition lines were separately databased for each electronic upper state population forming the electronic system. The spectral module for the PMC method was optimized toward computational efficiency for emission calculations, wavelength selections of photon bundles and absorption coefficient calculations in the ray tracing scheme.
A Conceptual Design of I-125 Generator at the HANARO
Authors: Kim Heonil , Park Jonghark , Lee Byungchul , Chae Heetaek , Kim Youngki
Published: February 2010

A simple I-125 generating device at the research reactor, HANARO, is developed. Xenon-124 gas circulates continuously in the generator producing I-125 by neutron capture and the I-125 is adsorbed at the upper part of the generator, which is to be chemically recovered in a hot-cell. The continuous xenon circulation technology is devised by the design of the generator structure with the consideration of thermal hydraulics and neutron physics involved. A computational fluid dynamics technique is used for the conceptual design of the generator.
The Influence of Chrome in the Oxidation Process of Steels in Flowing LBE
Authors: Tan Taide , Chen Yitung
Published: February 2010

The role of the alloying element has been analyzed during the oxidation process of stainless steels in the flowing lead bismuth eutectic (LBE) environment. The growth of the protective oxide film of steels has been studied at a mesoscopic scale. The influence of chrome has been studied using the developed stochastic cellular automaton mesoscopic oxidation model, considering the formation of the chrome oxide and magnetite. During the oxidation process, the scale removal effect has been taken into account as well.
Risk-Informed Approach for the Regulation of Decommissioning of Nuclear Facilities
Authors: Iguchi Yukihiro , Kato Masami
Published: February 2010

During decommissioning of nuclear facilities, it is generally thought that the risk is relatively low after high activity inventory such as the spent fuel is removed. However, dismantlement works may be carried out with non-multiple barriers with a non-regular process depending mainly on human activities. Moreover, fire or gas incidents caused by conventional industry methods may lead to accidents with radioactivity release. This means more attention is necessary for safer dismantlement especially for nuclear reactors with high activity. Therefore, utilization of risk information based on risk assessment of the decommissioning was proposed. A method of risk assessment for decommissioning was developed and applied for the dismantlement of typical reactor facilities and nuclear fuel facilities (a uranium enrichment plant and a reprocessing plant). The results show that the consequences of such troubles are low, but their occurrences are still not negligible. This fact is supported by past trouble cases. Taking into account of the risk assessment results, a methodology to secure the safety of decommissioning was proposed. It consists of four steps i.e. 1) risk-informed approach, 2) graded approach, 3) phased approach and 4) layered approach and the results can be reflected to the management and regulation. The regulation means are for example, review of the decommissioning plan or the fitness-for-safety, the periodic safety inspections and usual monitoring. The methodology can evaluate the risk level of decommissioning more objectively and enable reasonable regulation based on the risk level. This leads to the appropriate distribution of resources with safety enhancement.
Actual Problems of VVER SG Tubing Service Life Management
Authors: Trunov N. B. , Popadchuk V. S. , Davidenko S. E. , Zhukov R. Ju.
Published: February 2010

Reliable operation of steam generator heat exchanging tubes is the major problem for NPPs of different types. The paper deals with current approaches to horizontal steam generator tubes inspection and plugging and the actual problems of service life management. The causes and laws of tubing corrosion degradation are considered using the information - analytical system. The results of SG prototype corrosion tests are presented. A possibility of corrosion degradation process management is demonstrated. The experimental verification was made to prove the possibility of flaws initiation under standby modes. The methodology of the plugging criteria choosing and the proposals on their optimization are given. The studies are provided for pressure loading of the tubes with real flaws. The recommendations are given for improving of SG operation.
The Influence Irradiation-Induced Microstructure on the Hardening of RPV Steels
Authors: Lambrecht Marlies , Almazouzi Abderrahim
Published: February 2010

The hardening and embrittlement of reactor pressure vessel steels has been investigated for many years. Nowadays, a consensus is reached assuming a two-component hardening model of copper-enriched clusters and matrix damage. Nevertheless, despite being the subject of significant research efforts, it is still a debatable question, whether a linear or quadratic superposition law is appropriate. The inaccuracy of either choice might be the effect of the existence of different populations of defects, such as loops, decorated interstitial and vacancy clusters, as every defect contributes to the hardening in a particular way. In this work, a correlation on model alloys is attempted between experimental results on microstructure found by different complementary techniques and a theoretical prediction of the hardening, where each defect is defined by a specific pinning strength. It is found that loops are very strong defects, but due to their low concentration, they only play a minor role in the hardening itself. For the precipitates, the contrary is found, although they are quite soft (due to their very low sizes), they still play the dominant role in the hardening due to their high density. Vacancy clusters are important for the formation of the former two defects, but they will play almost no role in the hardening by themselves.
Safety and Design Principles for Use in a Risk-Informed, Technology-Neutral Design and Licensing Framework for New Nuclear Plants
Authors: Chapman Jim , Hess Stephen M.
Published: February 2010

The regulatory framework for the current generation of operating plants and advanced light water reactors (ALWRs) planned for near term construction has evolved over several decades to permit effective regulation of the light water reactor (LWR) designs. To address other reactor types, development of a framework that possesses the attributes of being technology neutral, risk-informed and performance-based is ongoing by several U.S. and international organizations. To support development of a revised framework, the Electric Power Research Institute (EPRI) conducted research to identify and assess specific elements of the proposed possible frameworks; to develop a preliminary integrated framework based on the results of this review and evaluation; and to provide recommendations in areas where additional development and testing would appear to be most beneficial. This research identified Fundamental Safety Principles (FSPs) and Fundamental Design Principles (FDPs) to be the cornerstones that provide the underlying basis for the proposed integrated framework. FSPs provide the safety objectives which are to be achieved. Associated with each FSP is a corresponding FDP that provides mechanisms by which achievement of the FSP can be demonstrated. In this paper we describe the 11 FSPs and associated FDPs that were developed. We note that these FSPs / FDPs are for the most part consistent with comparable criteria provided in the frameworks which were reviewed. The results of this research have been and are being used to support ongoing industry efforts to develop applicable standards and guidance for licensing of advanced plants (Generation 3 Plus and 4) that address safety characteristics which differ from the current generation of plants and advanced LWRs.
Numerical and Modeling Issues in Application of CFD to Flow in a Simplified Plenum Relevant to a Prismatic VHTR
Authors: Celik Ismail , Karaismail Ertan
Published: February 2010

CFD (computational fluid dynamics) calculations have been performed for turbulent flow inside a plenum model that resembles a section of the lower plenum in a typical prismatic VHTR (Very High Temperature Reactor). Different RANS (Reynolds Averaged Navier-Stokes) based turbulence models are employed to investigate the capability in capturing unsteady large scale coherent structures due to vortex shedding at two different Reynolds numbers. A grid convergence study is conducted with those models which were able to capture unsteady vortex shedding. The non-linear interaction of mesh quality, turbulence model and numerical scheme lead to flow regime changes with significantly different unsteady behavior. This makes it difficult to assess numerical and modeling uncertainty using the procedure that is recommended for Journal of Fluids Engineering (JFE). Some remedies to overcome this difficulty are recommended. The numerical uncertainty in the local values of velocity components at selected locations inside the plenum, as well the uncertainty associated with derived quantities such as wall shear stress at critical locations are calculated and reported. Since there are no experiments corresponding to the present cases simulated, the current analysis can be considered as a blind application of the proposed uncertainty estimation procedure.
Molten Pool Models Validation and Cross-Verification: CFD and SOCRAT Code
Authors: Filippov Alexander , Strizhov Valery , Tarasov Oleg
Published: February 2010

The objectives of the paper are, first, to advance SOCRAT/HEFEST code in the area of molten pool simulation, and, second, to perform the cross-verification of the code. The set of verification data includes the known experiments and CFD calculations. Fluent 6.3 is used as supporting CFD code. The results of the verification are presented concerning the behavior of homogeneous/stratified molten pool and the melting propagation as well. These results shows the applicability of simplified models of SOCRAT/HEFEST to simulation of heat transfer in the stratified molten pool. The possibilities of CFD simulation with k-ε model have been demonstrated for a large range of the inner Rayleigh number up to 1017.
Development and Validation of a Multifield Model of Churn-Turbulent Gas/Liquid Flows
Authors: Tselishcheva Elena A. , Antal Steven P. , Podowski Michael Z. , Guillen Donna Post , Beyer Matthias , Lucas Dirk
Published: February 2010

The accuracy of numerical predictions for gas/liquid two-phase flows using Computational Multiphase Fluid Dynamics (CMFD) methods strongly depends on the formulation of models governing the interaction between the continuous liquid field and bubbles of different sizes. The purpose of this paper is to develop, test and validate a multifield model of adiabatic gas/liquid flows at intermediate gas concentrations (e.g., churn-turbulent flow regime), in which multiple-size bubbles are divided into a specified number of groups, each representing a prescribed range of sizes. The proposed modeling concept uses transport equations for the continuous liquid field and for each bubble field. The overall model has been implemented in the NPHASE-CMFD computer code. The results of NPHASE-CMFD simulations have been validated against the experimental data from the TOPFLOW test facility. Also, a parametric analysis on the effect of various modeling assumptions has been performed.