bluuebunny/crossref_metadata_2025 huggingface dataset:
Developing the Small Particle Heat Exchange Receiver for a Prototype Test
Authors: Miller Fletcher J. , Hunt Arlon J.
Published: July 2013

The concept of absorbing concentrated solar radiation volumetrically, rather than on a surface, is being researched by several groups with differing designs for high temperature solar receivers. The Small Particle Heat Exchange Receiver (SPHER), one such design, is a gas-cooled central receiver capable of producing pressurized air in excess of 1100 C designed to be directly integrated into a Brayton-cycle power block to generate electricity from solar thermal power. The unique heat transfer fluid used in the SPHER is a low-density suspension of carbon nano-particles (diameter ∼ 200 nm) to absorb highly concentrated solar radiation directly in a gas stream, rather than on a fixed absorber like a tube or ceramic foam. The nano-particles are created on-demand by pyrolyzing a small flow of natural gas in an inert carrier gas just upstream of the receiver, and the particle stream is mixed with air prior to injection into the receiver. The receiver features a window (or multiple windows, depending on scale) on one end to allow concentrated sunlight into the receiver where it is absorbed by the gas-particle suspension prior to reaching the receiver walls. As they pass through the receiver the carbon nano-particles oxidize to CO2 resulting a clear gas stream ready to enter a downstream combustor or directly into the turbine. The amount of natural gas consumed or CO2 produced is miniscule (1–2%) compared to what would be produced if the natural gas were burned directly to power a gas turbine.

The idea of a SPHER, first proposed many years ago, has been tested on a kW scale by two different groups. In the new work, the engineering for a multi-MW SPHER is reported. An in-house Monte Carlo model of the radiation heat transfer in the gas-particle mixture has been developed and is coupled to FLUENT to perform the fluid dynamic calculations in the receiver. Particle properties (size distribution and complex index of refraction) are obtained experimentally from angular scattering and extinction measurements of natural gas pyrolysis in a lab-scale generator, and these are corroborated using image analysis of Scanning Electron Microscope (SEM) pictures of particles captured on a filter. A numerical model of the particle generator has been created to allow for scale-up for a large receiver. We have also designed a new window for the receiver that will allow pressurized operation up to 10 bar with a 2 m diameter window. Recent progress on overcoming the engineering challenges in developing this receiver for a prototype test is reported.
Micro- and Nano-Structured Catalytic Reactor for Biofuel Reforming in a Solar Collector
Authors: Hotz Nico
Published: July 2013

In this study, a novel flow-based method is presented to place catalytic nanoparticles into a reactor by solgelation of a porous ceramic consisting of copper-based nanoparticles, silica sand, ceramic binder, and a gelation agent. This method allows for the placement of a liquid precursor containing the catalyst into the final reactor geometry without the need of impregnating or coating of a substrate with the catalytic material. The so generated foam-like porous ceramic shows properties highly appropriate for use as catalytic reactor material, e.g., reasonable pressure drop due to its porosity, high thermal and catalytic stability, and excellent catalytic behavior.

The catalytic activity of micro-reactors containing this foam-like ceramic is tested in terms of their ability to convert alcoholic biofuel (e.g. methanol) to a hydrogen-rich gas mixture with low concentrations of carbon monoxide (up to 75% hydrogen content and less than 0.2% CO, for the case of methanol). This gas mixture is subsequently used in a low-temperature fuel cell, converting the hydrogen directly to electricity. A low concentration of CO is crucial to avoid poisoning of the fuel cell catalyst. Since conventional Polymer Electrolyte Membrane (PEM) fuel cells require CO concentrations far below 100 ppm and since most methods to reduce the mole fraction of CO (such as Preferential Oxidation or PROX) have CO conversions of up to 99%, the alcohol fuel reformer has to achieve initial CO mole fractions significantly below 1%. The catalyst and the porous ceramic reactor of the present study can successfully fulfill this requirement.

The results of the present study confirm that product gas mixtures with up to 75% hydrogen content and less than 0.2% CO content can be achieved, which is an excellent result. The reactor temperature can be kept as low as 220°C while obtaining a methanol conversion of up to 70%. The used PROX catalyst showed selective CO conversion rates above 99.5% for temperatures between 80 and 100°C in presence of large molar fractions of H2O and CO2.
Numerical Simulation of CSP Based on Nanorectenna Technology
Authors: de Risi Arturo , Milanese Marco , Lomascolo Mauro , Taurino Antonietta , Farella Isabella
Published: July 2013

Concentrated solar power (CSP) plants are one of several renewable energy technologies with significant potential to meet a part of our future energy demand. By now, CSP systems are used to supply photovoltaic or thermal power plant, but results on nanorectennas suggest the possibility to use this technology for direct energy conversion of solar radiation into electricity. A rectenna is a rectifying antenna that can be used to directly convert wave energy into DC electricity. Experiences in microwave applications have shown energy conversion efficiency in the order of 85%, and recently empirical tests have demonstrated that this technology can be used up to the infrared wavelength. The present paper, together with first preliminary results on the fabrication of the rectifier (the key element of a rectenna) and its electrical behavior, proposes the numerical simulation of a new CSP system where a receiver, heated by concentrated solar radiation, reemits infrared energy on the nanorectenna, which converts the incoming energy into electricity. In this way the receiver plays the role of a sunlight radiation converter to infrared energy.

The numerical simulation of the system consists of two steps. The first is a ray-tracing model to calculate the concentrator optical efficiency and the energy distribution on the focusing area of the parabolic mirror. The second step consists in the receiver temperature calculation as function of the incident solar radiation. The numerical procedure allows the calculation of the concentrator/receiver assembly performance which returns the energy incident on the nanorectenna as a function of external environmental conditions.
Simulation of Direct Steam Power Tower Concentrated Solar Plant
Authors: Neises Ty , Wagner Michael J.
Published: July 2013

Power tower concentrated solar plants have the potential to reach temperatures higher than those achievable by a parabolic trough plant. These higher temperatures allow for greater power cycle efficiencies and therefore make power towers an attractive option and a growing topic of research. One common design is to pump water through the tower such that it boils and returns to the power cycle as saturated or superheated vapor. One option to increase power cycle efficiency for a direct steam system is to send the steam exiting the high pressure turbine through a committed reheat receiver section and then through a low pressure turbine.

This paper details a new semi-empirical, first-principles thermal model of a direct steam receiver consisting of dedicated boiler, superheater, and reheater sections. This thermal model — integrated with a regression power cycle model and a heliostat field model in SAM — is used to simulate the performance of a direct steam power tower concentrated solar plant and the analysis results are presented.
Evaluation of Hybrid Distributed Generation Systems for Four Locations in Mexico
Authors: Almanza Huerta L. , Krarti Moncef , Hernandez Guerrero A.
Published: July 2013

The present work provides a feasibility analysis of a hybrid distributed generation system to meet the energy needs for residential communities in four locations in Mexico. Tuxtla Gutierrez (Oaxaca), Puerto Escondido (Oaxaca), Guaymas (Sonora) and Mexicali (Baja California Norte) were the four locations selected to assess the potential available energy resources in meeting cost-effectively and sustainably the electricity and thermal loads of small communities in Mexico. Electricity and thermal loads are obtained for the four locations by using calibrated building energy models for residential buildings in Mexico. Based on the feasibility analysis, it is found that while hybrid systems can reduce significantly CO2 emissions, they are not cost-effective to implement in all locations due to the relatively cheap electricity costs from the only federal utility company in Mexico.
Numerical Study of Supercritical CO2 Convective Heat Transfer for Advanced Brayton Cycles for Concentrated Solar Power
Authors: Flueckiger Scott M. , Garimella Suresh V. , Groll Eckhard A.
Published: July 2013

Advancement of supercritical carbon dioxide Brayton cycle technology in concentrated solar power plants requires an improved understanding of duct-flow convection in the supercritical region. Numerical simulation, based on a modified carbon dioxide hot gas bypass load stand with an external heat source, is conducted to determine carbon dioxide convective heat transfer coefficients at supercritical pressures and temperatures beyond the range for which results are available in the literature.

The simulation geometry is derived from the heated test section included in the physical load stand. Inlet pressure, temperature, and mass flux are varied to assess the influence on Nusselt number. Cases that achieve fully developed flow and temperature conditions inside the tube geometry agree with predictions from a Nusselt number correlation in the literature with a mean absolute error of 6.4 percent, less than the 6.8% average error reported for the correlation. This agreement includes pressure and temperature conditions outside the defined range of the correlation. Future experiments will provide additional validation of the model and correlation, enabling analysis farther into the supercritical region necessary for Brayton cycle operation.
Preparation and Experimental Study of Mixed Carbonates With High Maximum Using Temperature
Authors: Ren Nan , Wu Yu-ting , Ma Chong-fang
Published: July 2013

In order to meet the demands of future high-temperature solar thermal power generation, 37 kinds of mixed carbonate molten salts were prepared by mixing potassium carbonate, lithium carbonate, sodium carbonate in accordance with different proportions in this paper. Melting point of molten salt, as the most important basic character, is the primary parameter to select molten salt. Melting point and decomposition temperature are measured by Simultaneous Thermal Analyzer. The results show that melting points of major ternary carbonates are close at around 400°C and decomposition temperatures of most ternary carbonate are between 800 and 850°C. In accordance with energy variation, when the system is cooled from the molten state, precipitates of crystalline phases is orderly. Crystallization temperatures of some samples are much higher than their melting points. Therefore, through comparative experimental study of heating and cooling, 10 kinds of mixed carbonates with low melting point and crystallization temperature were selected primarily. Then, latent heat, density and thermal stability of these mixed salts were studied.
Numerical Analysis of Latent Thermal Energy Storage System With Embedded Thermosyphons
Authors: Nithyanandam Karthik , Pitchumani Ranga
Published: July 2013

Latent thermal energy storage (LTES) system offers high energy storage density and nearly isothermal operation for concentrating solar power generation. However, the low thermal conductivity possessed by the phase change material (PCM) used in LTES system limits the heat transfer rates. Utilizing thermosyphons to charge or discharge a LTES system offers a promising engineering solution to compensate for the low thermal conductivity of the PCM. The present work numerically investigates the enhancement in the thermal performance of charging and discharging process of LTES system by embedding thermosyphons. A transient, computational analysis of the LTES system with embedded thermosyphons is performed for both charging and discharging cycles. The influence of the design configuration of the system and the arrangement of the thermosyphons on the charge and discharge performance of the LTES installed in a concentrating solar power plant (CSP) is analyzed to identify configurations that lead to improved effectiveness.
Comparing Measured and Satellite-Derived Surface Irradiance
Authors: Habte Aron , Sengupta Manajit , Wilcox Stephen
Published: July 2013

The purpose of this study is two-fold: 1) To examine the performance of the Global Solar Insolation Project (GSIP) physics-based model in characterizing global horizontal solar radiation across the United States by comparing to the ground measured data, and 2) to examine improvements of the GSIP data to address temporal and spatial variations. The study enumerates and examines the spatial and temporal limitations of the GSIP model. Most comparisons demonstrate relatively good statistical agreement. However, the methodology used in the satellite model to distinguish microclimate conditions presents significant challenges, and the model requires refinement in addressing aerosol estimates, water vapor estimates, and clear sky optical properties. Satellite derived datasets are only available at half-hour intervals. Surface measurement can easily be made at temporal resolution in the order of seconds. Therefore intra-hour variability, an important quantity for understanding how power production in power plants will vary, cannot be directly derived from satellites. This paper illustrates how intra-hour variability in ground measurements cannot be captured by the satellite based datasets. We also discuss the potential for improved next-generation geostationary satellite data to improve the accuracy of surface radiation estimates.
Reduction in Spot Size via Off-Axis Static and Dynamic Heliostat Canting
Authors: Bonanos Aristides M. , Noone Corey J. , Mitsos Alexander
Published: July 2013

Heliostat canting is the alignment of facets on a common frame which provides focusing of sunlight on a prescribed target. Traditionally, this alignment has been parabolic, in which the focal point of the heliostat lies on its optical axis. Two alternative off-axis canting methods are compared in this article, (i) fixed facet (static) canting in which the facet alignment is optimized for a single design day and time and then rigidly mounted to the frame and (ii) dynamic canting in which the facets are actively controlled such that the center of each facet is always perfectly focusing. For both methods, two case studies are considered: (i) a power tower with planar heliostat field (heliostat dimensions and tower height modeled after the 11 MWe plant PS10) and (ii) a hillside heliostat field which directs light down to a ground-level salt pond. In both case studies, static heliostat canting provides a small improvement in focusing by reducing the average annual insolation-weighted spot size by roughly 1–2%. Dynamic canting, in contrast, provides a 20–25% reduction in spot size.
Energy Performance Analysis of a Combined Cooling Heating and Power System for a Data Center
Authors: Xu Donghao , Qu Ming
Published: July 2013

Data centers play an important role in modern business. They require a large amount of electricity and cooling energy simultaneously. In 2007, the percentage of total energy consumed by data centers in total US energy doubled over seven years and it is estimated to be double again by 2012. Currently data centers typically employ separate cooling, heating and power (SCHP) systems. The Combined Cooling Heating and Power (CCHP) system is an efficient, clean, and reliable approach to generating power and thermal energy from a single fuel source simultaneously on site. They could be suitable energy supply systems for data centers since demands from data centers match with the energy generation of the CCHP systems. This paper assesses the energy performance of a CCHP system for the Qualcomm data center in San Diego, California, by means of modeling and operational data analysis. The CCHP system mainly consists of four gas turbines, one exhaust fired absorption chiller, three hot water fired absorption chillers, three electrical chillers and seven cooling towers. System performance models have been developed and validated by experimental data in TRNSYS. The modeling result shows that the CCHP system is capable of meeting the electricity and cooling demands with an overall system efficiency of 46%. As a result, the CCHP system could approximately save 12.9GWh of energy per year compared with SCHP systems. Therefore, the CCHP system is a sustainable and green option for data centers.
Power Generation From Concentrated Solar-Heated Air Using Buoyancy-Induced Vortices
Authors: Simpson Mark W. , Pearlstein Arne J. , Glezer Ari
Published: July 2013

Thermally-stratified air layers overlying solar-heated ground are exploited for power generation by the deliberate formation of intense buoyancy-induced vertical columnar vortices, similar to naturally-occurring desert “dust devils.” In hot-climate regions, such buoyancy-driven columnar vortices occur spontaneously with core diameters of 1–50 m at the surface and heights up to one km, leading to flows with considerable angular and axial momentum. Unlike “dust devil” vortices, which are typically free to wander laterally and are therefore susceptible to crosswind, anchored columnar vortices are deliberately triggered and confined within a domain laterally bounded by an azimuthal array of stationary ground-mounted vertical vanes, and are sustained by continuous entrainment of heated air passing between these vanes. Hot air near the solar-heated ground plane sustains the anchored vortex, and electric power is generated by using the resulting rotational and vertical flow induced by an “anchored” vortex to drive a vertical-axis wind turbine coupled to an electric generator. This novel approach to the collection of solar energy provides a low-cost, scalable, and sustainable method for generation of electric power from vast amounts of solar-heated air in arid regions. Meter-scale laboratory experiments have demonstrated the nucleation and sustainment of strong, buoyancy-driven vortices above a thermally controlled ground plane. The present investigation focuses on fundamental mechanisms of columnar vortex formation, evolution, and dynamics using stereo particle image velocimetry (PIV), with particular emphasis on scaling and assessment of the available mechanical power. The strength and scaling of theses vortices can be significantly altered by adjustment of the vanes and the rate of sensible heat uptake by the air flow, related to the “buoyancy flux”. Recent outdoor tests of a meter-scale prototype coupled with a simple vertical-axis turbine placed on a surface directly heated by solar radiation, have demonstrated continuous rotation of the turbine with significant extraction of kinetic energy from the column vortex, in both the absence and presence of crosswind.
Thermal Characterization of High Temperature Inorganic Phase Change Materials for Thermal Energy Storage Applications
Authors: Trahan Jamie , Kuravi Sarada , Goswami D. Yogi , Rahman Muhammad , Stefanakos Elias
Published: July 2013

As the importance of latent heat thermal energy storage increases for utility scale concentrating solar power (CSP) plants, there lies a need to characterize the thermal properties and melting behavior of phase change materials (PCMs) that are low in cost and high in energy density. In this paper, the results of an investigation of the melting temperature and latent heat of two binary high temperature salt eutectics are presented. Melting point and latent heat are analyzed for a chloride eutectic and carbonate eutectic using simultaneous Differential Scanning Calorimetry (DSC) and Thermogravimetric Analsysis (TGA). High purity materials were used and the handling procedure was carefully controlled to accommodate the hygroscopic nature of the chloride eutectic. The DSC analysis gives the values of thermal properties of the eutectics, which are compared with the calculated (expected/published) values. The thermal stability of the eutectics is also examined by repeated thermal cycling in a DSC and is reported in the paper along with a cost analysis of the salt materials.
Generative Textiles for Non-Rotary Power Production From Wind
Authors: Lux Scott , Foster Christopher , Sellers Meredith , Friedl Andrew , Feickert Carl , Hesterberg Justin , Marsh Charles
Published: July 2013

The U.S. Army Engineer Research and Development Center, Construction Engineering Research Laboratory (ERDC-CERL) is developing a new class of flexible, generative textile as a novel means of sustainable wind energy generation. Flexible, generative carbon nanotube (CNT)-based textiles may have excellent potential for electrical capacitive storage and reuse in conjunction with small-scale energy-harvesting systems, both from wind for fixed applications and from human locomotion.

This paper describes the design and optimization of a three-layer generative textile composed of discrete layers for generation, distribution, and storage. Initial results suggest that improvement in the generation layer will provide the highest increase in overall performance. The output of the electromagnetic tests shows a power density of 0.17 mW/cm3. However, the efficiency can be significantly improved through increasing the voltage output of the generation layer from 20 mV to around 1V. In an analysis of the operational envelope, wind data collected locally at ERDC-CERL and at other sites around the world reveal close similarity in the probability distributions, which could allow for a practical engineering approach capable of harvesting the steady “ram” component in addition to a variable energy component of the wind. To further study the textile-wind interactions, a wind simulation environment is being developed and has been able to obtain reproducible wind speed data thus far.
Reactivity of Iron/Zirconia Powder in Fluidized Bed Thermochemical Hydrogen Production Reactors
Authors: Al-Raqom F. , Klausner J. F.
Published: July 2013

A fluidized bed reactor has been developed which uses a two-step thermochemical water splitting process with a peak hydrogen production rate of 47 Ncm3/min.gFe at an oxidation temperature of 850°C. Of particular interest, is that a mixture of iron and zirconia powder is fluidized during the oxidation reaction using a steam mass flux of 0.58 g/min-cm2, and the zirconia powder serves to virtually eliminate iron powder sintering while maintaining a high reaction rate. The iron/zirconia powder is mixed with a ratio of 1:2 by apparent volume, equivalent mass ratio, and both iron and zirconia particles are sieved to sizes ranging from 125–355 μm. Fluidized bed reactors are advantageous because they have high reactivity, strong thermal and chemical transport, and tend to be compact. There has been significant interest in developing fluidized bed reactors for solar thermochemical reactors, but sintering of the reactive powder has inhibited their development. The current powder mixture and reactor configuration shows great potential for achieving high hydrogen production rates for operation at high temperature.

The experimental investigations for utilizing zirconia as a sintering inhibitor was found to be dependent on the iron and zirconia particle size, particle size distribution and iron/zirconia apparent volume ratio.

For example at 650 °C the oxidation of iron powder with a mean particle size of 100 μm and a wide particle size distribution (40–250 μm) mixed with 44 μm zirconia powder with an iron/zirconia apparent volume ratio of 1:1 results in 75–90 % sintering. In all cases when iron is mixed with zirconia, the hydrogen production rate is not affected when compared with the pure iron case. When iron powder is mixed with zirconia, both with a narrow particle size distribution (125–355 μm) the first oxidation step results in 3–7% sintering when the reactions are carried out at temperatures ranging between 840–895 °C. The hydrogen fractional yield is high (94–97%). For subsequent redox reactions, the sintering is totally eliminated at 867 and 895 °C although the hydrogen fractional yield decreases to 27 and 33%, respectively. This study demonstrates that mixing iron with zirconia in an equivalent mass ratio and similar particle size can eliminate sintering in a fluidized bed reactor at elevated temperatures up to 895°C.
Experimental Study on the Performance of the Single Screw Expander Prototype by Optimizing Configuration
Authors: Wang Wei , Wu Yu-ting , Xia Guo-dong , Ma Chong-fang , Wang Jing-fu , Zhang Yong
Published: July 2013

Improving thermodynamic efficiency of prime movers is the key issue for efficient utilization of low temperature heat resources. Because of many good characteristics, the single screw expander is perhaps a good choice. Precisions in manufacture and assembly are very important factors to the performance of single screw expanders. In this paper, experimental results of the first single screw expander prototype made by ourselves was analyzed and reported for the first time. From the experimental data, the power output of the prototype was about 5kW, but the gas consumption rate was above 105kg/kWh, so the shaft efficiency was only 34% or so. The results indicated that internal leakage was very serious. Hence, the second single screw expander prototype was manufactured. The gap between gate rotor and shell of the new prototype was reduced. The gap is about 0.02mm. From the new experimental data, the mass flow rate was significantly decreased. However, the power output was only 1.4kW. So, the gas consumption rate was even more than the first prototype. The reason of bad experimental results may arise from the too large friction between screw, gate rotor and shell in the case of small gap. So, we manufactured the third single screw expander prototype, which is 0.04mm in gap. From the experimental data, the maximum power output was about 4.5kW, but the mass flow rate was decreased sharply. So the gas consumption rate was about 60kg/kWh, and the shaft efficiency was about 60%. The result indicated that the performance of the single screw expander was remarkable improved by optimizing its configuration.
Heat Transfer Enhancement of Launch Tube Using Free Convection: Parametric Design and Investigation
Authors: Jongpairojcosit Nadda , Pankaew Ekaratch , Ridluan Artit , Veeraklaew Tawiwat
Published: July 2013

To alleviate the damages on launch tube surface from high temperature the rocket exhaust gas during firing the missile, we thus propose the heat transfer enhancement mechanism for the tube wrapped with metal sheet providing the small space, so-called air gap. The idea of the augmentation is by creating the free convection flow pattern in the narrow gap making by wrapping the metal sheet around the launch tube.

In this present work, design of experiment is applied to parametrically design the launch tube with metal cover sheet configuration (cylindrical annulus with fins). The objective is to parametrically design and investigate the configuration of the metal-sheet-wrapped launcher. To predict the free convection in narrow cylindrical annulus heated from the below surface (launch tube) including the rotating effect, the CFD investigation of the time-variant axissymmetric flow is conducted. The influences of three design factors, diameter and position of exit channels and air gap thickness on the flow field and the heat transfer are investigated.
Effects of Buoyancy on the Turbulent Wake of a Horizontal Cylinder in Cross-Flow
Authors: Boirlaud Matthieu , Couton Dominique , Plourde Frédéric
Published: July 2013

While heat transfer around bluff-bodies have been extensively studied in natural and forced convection regime, the mixed convection regime has not still yet brought so much attention; however the latter has direct interest either in various engineering applications or for fundamental point of views. Direct Numerical Simulation was applied in this paper to study the buoyancy effects in the wake of a horizontal cylinder in cross-flow for Re∞ = 1000 and Ri = 2.77. In the framework of mixed convection regime, results mainly focus on the role of thermal field and buoyancy effects. The main visible impact in the thermal field introduction is the asymmetry in the cylinder wake. In addition, typical mushroom-like structures driven by thermal field develop along the wake. From an unsteady point of view, a thermal wave develops from the bottom of the cylinder and the latter follows the cylinder surface. As a consequence, the upper shear-layer that occurs in isotherm case is strongly disturbed because of the interaction with the thermal wave and the lower shear-layer is stretched in the flow direction. Comparisons with the isotherm case help us to better understand the role of the thermal field and the effects of buoyancy in the transition to turbulence.
Case Study of Tandem Impeller Rotating at Different Speeds
Authors: Tsugawa Takuji
Published: July 2013

In previous study, the optimum meridian profile of tandem impeller rotating at the same speed was obtained by means of calculation of efficiency and suction specific speed considering two diffusion factors of tandem impeller. The effect of theoretical head ratio between the first impeller and the second impeller was obtained. In this study, the optimum meridian profile and design parameters of tandem impeller rotating at two kinds of different speed was obtained. In the process of this study, a lot of design parameters were needed. Therefore, in the optimum calculation process the predominant design parameters of two impellers were selected and re-selected. The predominant design parameters were inlet relative flow angle, turning angle, meridian velocity ratio, inlet and outlet diameter ratio and so on. The impeller meridian velocity ratios of shape factors were defined as kc12(= Cm2/Cm1) and kcp2(= Cm2/Cmp), and the impeller diameter ratios were defined as kd12(= D1c/D2c) and kdp2(= Dpc/D2c). The subscripts 1,p and 2 means the first impeller inlet, the second impeller inlet and the second impeller outlet respectively. And theoretical head ratio between first impeller and second impeller was defined as kHth(= Htha/Hthb). The rotational ratio between the first impeller and the second impeller defined as Rna(= na/nb). The Optimum Rna(= na/nb) was effected by the other design parameter. As the result, the optimum meridian profile of tandem impeller rotating at different speeds was obtained. This method can be also used for the suitable rotative guidevane.
Study of Drag Reduction Devices for a Square Back Vehicle Configuration Using RANS CFD Simulations
Authors: Khalighi Bahram , Chen Kuo-Huey , Iaccarino Gianluca
Published: July 2013

The aerodynamic flow around a simplified road vehicle model with and without drag reduction devices is investigated. The simulations are carried out using the unsteady RANS in conjunction with the ν2-f turbulence model. The corresponding experiments are performed in a small wind tunnel which includes pressure and velocity fields measurements. The devices are add-on geometry parts (a box with a cavity and, boat-tail without a cavity) which are attached to the back of the square-back model to improve the pressure recovery and reduce the flow unsteadiness. The results show that the recirculation regions at the base are shortened and weakened and the base pressure is significantly increased by the devices which lead to lower drag coefficients (up to 30% reduction in drag). Also, the results indicate a reduction of the turbulence intensities in the wake as well as a rapid upward deflection of the underbody flow with the devices in place. A suppression or damping of the unsteadiness is the common element of the devices studied. The baseline configuration (square-back) exhibits strong three-dimensional flapping of the wake. The main shedding frequency captured agrees well with the available experimental data. Comparisons with the measurements show that the simulations agree reasonably well with the experiments in terms of drag and the flow structures.
Imbedded Dual-Number Automatic Differentiation to Support CFD Analysis
Authors: Spall Robert E. , Yu Wenbin
Published: July 2013

Dual number automatic differentiation was applied to two different computational fluid dynamics codes, one written specifically for this purpose and one larger “legacy” Fortran code. Results for the simple case of a fully developed laminar flow in a channel validated the accuracy of the approach in computing derivatives with respect to both a fluid property, and a geometric dimension. DNAD was also implemented into the JET Fortran program which is available with a popular turbulence modeling textbook as companion software. Mean centerline velocity derivatives for a self-similar round jet with respect to all applicable turbulence model closure coefficients for both k–ω and k–ε models were obtained. The method proved to be accurate and relatively simple to implement into both the new and legacy Fortran codes.
Adhesion of Wax Droplets to Porous Substrates
Authors: Dadvar Shima , Chandra Sanjeev , Ashgriz Nasser , Drappel Stephan
Published: July 2013

The adhesion of solid wax ink droplets to porous polyethylene and Teflon substrates was studied experimentally. Wax droplets with a diameter of 3 mm and an initial temperature of 110°C were dropped onto test surfaces from heights varying from 20–50 mm. The Teflon surfaces had holes drilled in them to create idealized porous surfaces while the porous polyethylene sheets had mean pore sizes of either 35 or 70 μm. The force required to remove the wax splats from the substrates was measured by a pull test. The detachment force increased with droplet impact velocity. A simple analytical model is proposed to predict the force attaching the wax splat to the surface: it has an adhesive component, calculated by multiplying the contact area between the splat and substrate by the strength of adhesion; and a cohesive component, calculated by multiplying the area of the pores into which wax penetrates by the ultimate tensile strength of wax. Predictions from the model agreed reasonably well with measurements.
Grid-Zone Particle Hydrodynamics and Solid Circulation in a Multiple Jet Fluidized Bed
Authors: Agarwal Gaurav , Lattimer Brian , Ekkad Srinath , Vandsburger Uri
Published: July 2013

Particle Image Velocimetry (PIV) and Digital Image Analysis (DIA) were used to investigate the evolution of multiple inlet gas jets located at the distributor base of a two-dimensional fluidized bed setup. Experiments were conducted with varying distributor orifice diameter, orifice pitch, particle density, particle diameter, and fluidization velocity to understand the motion of particles in the grid-zone region of a fluidized bed. Results were used to develop a phenomenological model that quantifies the conditions throughout the entire grid-zone. The results and the model were further analyzed to understand the effect of operating conditions on the solid circulation dynamics of a multiple jet system fluidized bed. It was determined that the solid circulation rate increased linearly with an increase in the fluidization velocity until the jet system transitioned from isolated to an interacting system. The solid circulation increased at a much lower rate in the interacting system of jets. This sudden change in the solid circulation rate has not been reported in the literature possibly due to the lack of multiple jet studies. For multiple jet systems, this phenomenon may indicate the presence of an optimum operating condition with high circulation rate and low air input in the bed.
Interactions Between High-Viscosity Droplets Deposited on a Surface: Experiments and Simulations
Authors: Esmaeelpanah J. , Dalili A. , Chandra S. , Mostaghimi J. , Fan H. C. , Kuo H.
Published: July 2013

A combined numerical and experimental investigation of coalescence of droplets of highly viscous liquids dropped on a surface has been carried out. Droplets of 87 wt% glycerin-in-water solutions with viscosity 110 centistokes were deposited sequentially in straight lines onto a flat, solid steel plate and droplet impact photographed. Impacting droplets spread on the surface until liquid surface tension and viscosity overcame inertial forces and the droplets recoiled, eventually reaching equilibrium. Droplet center-to-center distance was varied and droplet line length was measured from photographs. As droplet spacing was increased there was less interaction between the droplets. A three dimensional parallel code has been developed to simulate fluid flow and free surface interaction by solving the continuity, momentum and volume-of-fluid (VOF) equations. The two-step projection method was employed to solve the governing equations for the whole domain including both liquid and air phases. The continuum-surface-force (CSF) scheme was applied to model surface tension and the piecewise-linear-interface-construction (PLIC) technique used to reconstruct the free surface. Computer generated images of impacting droplets modeled droplet shape evolution correctly and compared well with photographs taken during experiments. Accurate predictions were obtained for droplet line length during spreading and at equilibrium.
Coupled Sliding Grids and Adaptive Grid Refinement for RANS Simulation of an Oscillating Car Model
Authors: Guilmineau Emmanuel , Queutey Patrick , Leroyer Alban , Wackers Jeroen
Published: July 2013

Ground vehicles travelling on the road are often subjected to unsteady flows. The yaw angle increases with stronger wind conditions such as gusty cross winds caused by unsteady atmospheric conditions, tunnels, bridges or trucks passing. Separations appear on the leeward side of the body, interact with the base flow and cause unsteady vehicle loading. These aerodynamic elements, added to dynamic properties of the suspension, springing and tires are finally the factors of its dynamic stability and of the safe manoeuvrability appreciated by the driver. With an unsteady separation, it is difficult to have a mesh adapted to the flow. For improved accuracy, automatic adaptive grid refinement is a technique for optimising the grid in the simulation of fluid flow, by adapting the grid to the flow. This is done by locally dividing cells into smaller cells, or if necessary, by merging small cells backs into larger cells in order to undo earlier refinement.

The present work aims to explore the flow physics in which the vehicle is exposed to steady wind, but with continuous changes in the yaw angle. For this purpose, the unsteady numerical technique with a sliding grid approach is used in the flow solver ISIS-CFD, developed by the Laboratory of research in Hydrodynamics, Energetics, and Atmospheric Environment, ex-Fluids Mechanics Laboratory of the Ecole Centrale de Nantes. The CFD simulation is carried out with the Explicit Algebraic Reynolds Stress Model (EARSM) turbulence model.

The numerical simulations are performed on the square-back Willy model. The Reynolds number is Re = 900,000 and the yaw motion of the model is close to a sinusoidal motion with an amplitude of oscillation Δβ = 10° and a frequency f = 2Hz.

The numerical solution is compared with numerical results obtained in static positions. The pressure on the model is also compared with experimental data.
Discrete Element Modeling and Validation of Fluidized Bed With Multiple Jets
Authors: Deb Surya , Tafti Danesh
Published: July 2013

Fluidized beds with multiple jets have widespread industrial applications. They are used to aid in proper mixing of coal or biomass in the bed, which in turn increases the combustion and heat transfer. The objective of this paper is to investigate the jet interactions and hydrodynamics of a fluidized bed with multiple jets. Discrete Element Modeling coupled with a CFD code GenIDLEST has been used to numerically simulate 9 jets. The results are compared with published experiments. Mono dispersed particles of size 550 microns are used with 1.4 times the minimum fluidization for the particles. Two dimensional computations have been performed. The solid fraction at different heights from the jetting bed is compared with the experiments along with the solid circulation at the grid zone or the jetting zone. Average solid fraction across the cross-section of the bed is plotted along the height and compared with the experiments to estimate the bed expansion due to fluidization. Comparison of time averaged jet heights with the experiments is also shown. Discrepancies between the experiments and simulations are discussed in the context of the dimensionality of the simulations. The time averaged solid fraction at different heights from the distributor plate match well with the experimental results except near the walls. A slight over prediction of solid fraction values is obtained near the walls from the simulations. The average solid fraction along the height of the bed is in good agreement with the experiments, showing similar trends in bed expansion for both the experiments and simulations. The results obtained from DEM computations serve as validation for the experiments and help us understand the complex jet interaction and solid circulation patterns in a multiple jet fluidized bed system.
3D Unsteady Simulation of a Planing Hull Propelled by a Waterjet Pump System
Authors: Forest Simon , Moreau Stéphane , Desrochers Alain
Published: July 2013

A comprehensive modeling of the physics and dynamics of a realistic planing boat has been simulated. This study considers a two degree-of-freedom (DOF) unsteady model to investigate the equilibrium of the boat at steady speed and mimic the system dynamics properly. The numerical model consists of a planing hull with a waterjet pump inlet duct and a mathematical representation of the main forces and mass flow to model the pump. Indeed, it includes the interaction of the hull and the waterjet propulsion system, which has never been done before. The mathematical model of the pump is based on a full 3D unsteady simulation of a reduced control volume of the propulsion system. The numerical robustness and accuracy have been confirmed after being compared to other studies and to a prototype boat. Finally, the results provide a novel 3D unsteady numerical model of the equilibrium of a planing hull at a steady speed, including the effect of the waterjet pump.
Development of a Log-Time Integration Method for Reactive Flows
Authors: Escobar Jose , Celik Ismail , Ferguson Donald
Published: July 2013

In reactive flow simulations integration of the stiff species transport equations consumes most of the computational time. Another important aspect of combustion simulation is the need to simulate at least tens of species in order to accurately predict emissions and the related combustion dynamics. Small time scales and systems with tens of species lead to very high computational costs. Classic integration methods such as Euler method are restricted by the smallest characteristic time scale, and explicit Runge-Kutta methods require intermediate predictor corrector steps which make the problem computationally expensive. On the other hand, implicit methods are also computationally expensive due the calculation of the Jacobian. This work presents a strategy to significantly reduce computational time for integration of species transport equations using a new explicit integration scheme called Log-Time Integration Method (LTIM). LTIM is fairly robust and can compete with methods such as the 5th order Runge-Kutta method. Results showed that LTIM applied to the solution of a zero dimensional reactive system which consists of 4 chemical species obtains the solution around 4 times faster than 5th order Runge-Kutta method. LTIM was also applied to the solution of a one dimensional methane-air flame. The chemical reactions were modeled using a reduced chemical mechanism ARM9 that consists of 9 chemical species and 5 global reactions. The solution was carried out for 9 species transport equations along with the energy equation. Governing equations were decoupled into flow and chemical parts and were solved separately using a split formulation. Thermodynamic properties were obtained using NASA format polynomials and transport properties using kinetic-theory formulation. It is shown that the new one dimensional flame code is able to calculate the adiabatic flame temperature of the system and corresponding flame speed for the methane-air flame thus validating its robustness and accuracy.
Multi-Parameters Pump Impeller Optimization
Authors: Siddiqi Mohammed A. , Boppa Praneetha , Strongin Mikhail P.
Published: July 2013

Rotodynamic pumps designed by traditional methods have persisted at their current levels of maturity, vis-à-vis performance and efficiency, for decades now. These historical statistics of performance have been formulated as industry standard charts of efficiency based on specific speed and flow-rate (Fig. 1). Through the last decade, research activity aimed at challenging and surpassing these historical performance levels, via the application of various optimization methods and tools, has been slowly but surely building up.

The work presented in this paper is one such effort to enhance the performance of a pump, with the impeller blade of a medium specific speed centrifugal pump chosen as its subject, the blade being the heart of any turbo-machine.

This study is somewhat unique in the respect that intuitive, high-level features were used to optimize the blade design rather than inanimate variables. A radical and proprietary blade development scheme allowed a 75% reduction in the number of parameters needed to fully describe the blade, compared to conventional blade layout and development schemes.

A software suite comprised of an intimate blend of proprietary and commercial tools, for design, performance simulation and optimization, constituted the engine for this study. A template was generated with all software linked in a seamless bi-directional communication loop for hands-off execution of the optimization study (Fig. 3).

A Design of Experiments (DoE) scheme is used to generate several hundred design points corresponding to different geometry and flow configurations. Computational Fluid Dynamics (CFD) software was used to simulate the performance and yield integrated output parameters, viz., head, power, and efficiency, for each design point at multiple flow-rates. Data from the simulated DoE table was then used to generate an n-dimensional Response Surface (RS), which established pre-validated relationships of the output to the input parameters.

Finally, a Multi Objective Genetic Algorithm (MOGA) technique was used to extract the most efficient designs satisfying other weighted goals or objectives. The weighting process forces some objectives to be sacrificed to a certain extent in favor of others, which is a good reflection of reality, since a trade-off between different objectives is an essential element of any design process. The predictions from the optimizer were then subjected to a final round of CFD simulations for validation.

Two discrete application examples were used as test cases for this study, using the optimization template described in the foregoing.

This multi objective optimization approach resulted in a performance improvement of 2 efficiency points over a mature baseline blade design, developed using an advanced proprietary design code. Traditional CFD-assisted design enhancements were found to provide less than 1 point of efficiency improvement over this baseline design.