bluuebunny/crossref_metadata_2025_split huggingface dataset:
Using High Resolution Solar Measurement in PV Variability Studies
Authors: Sengupta Manajit 
Published: July 2013

Clouds, aerosols, water vapor and other atmospheric constituents influence solar energy reaching the earth’s surface. Each of these atmospheric constituents has it’s own inherent scale of temporal and spatial variability and they in turn influence the variability in the amount of solar radiation reaching the earth’s surface. This combined influence of the atmospheric constituents and their separate variability characteristics makes solar variability modeling a complicated task.
Output from photovoltaic (PV) power plants is dependent on the amount of solar energy reaching the surface. Therefore variability in solar radiation results in variability in PV plant output. The issue of variability in PV plant output has become important in the last couple of years as utility scale PV plants go online and increase in size. Understanding variability in PV plant output requires an understanding of (a) the spatial and temporal variability of solar radiation; (b) the influence of this solar variability on PV plant output.
The goal of this paper is to understand what temporal and spatial scales of variability in Global Horizontal Radiation (GHI) are important to a PV plants and what measurements are needed to be able to characterize them. As solar radiation measuring instruments are point receivers it is important to understand how those measurements translate to energy received over a larger spatial extent. Also of importance is the temporal nature of variability characterized not at a single point on the ground but over large spatial areas.
In this research we use high temporal and spatial resolution measurements from multiple time synchronized solar radiation sensors to create solar radiation fields at various spatial and temporal scales using a wide range of interpolation techniques. These solar fields are then used to create plant power output for various size PV plants. As various interpolation schemes can produce different distributions we investigate the impact of interpolation schemes on GHI and power output distribution. While power output from PV plants is an important quantity the temporal variability of power is a matter of concern to utilities. In this paper we show how PV plant output varies across different time scales.
Heat and Mass Transfer Characteristics of a Zeolite 13X/CaCl2 Composite Adsorbent in Adsorption Cooling Systems
Authors: Chan K. C. , Chao Christopher Y. H. , Bahrami M. 
Published: July 2013

The performance of the adsorption cooling system using the zeolite 13X/CaCl2 composite adsorbent was studied using a numerical simulation. The novel zeolite 13X/CaCl2 composite adsorbent with superior adsorption properties was developed in previous studies [11]. It has high equilibrium water uptake of 0.404 g/g between 25°C and 100°C under 870Pa. The system specific cooling power (SCP) and coefficient of performance (COP) were successfully predicted for different operation parameters. The simulated COP with the composite adsorbent is 0.76, which is 81% higher than a system using pure zeolite 13X under desorption temperature of 75°C. The SCP is also increased by 34% to 18.4 W/kg. The actual COP can be up to 0.56 compared to 0.2 for zeolite 13X-water systems, an increase of 180%. It is predicted that an adsorption cooling system using the composite adsorbent could be powered by a low grade thermal energy source, like solar energy or waste heat, using the temperature range of 75°C to 100°C.
The performance of the adsorber with different design parameters was also studied in the present numerical simulation. Adsorbents with smaller porosity can have higher thermal conductivity and may result in better system performance. The zeolite bed thickness should be limited to 10mm to reduce the thermal response time of the adsorber. Addition of high thermal conductivity materials, for example carbon nanotube, can also improve the performance of the adsorber. Multi-adsorber tube connected in parallel can be employed to provide large heat transfer surface and maintain a large SCP and COP. The desorption temperature also showed a large effect on the system performance.
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.
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.
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.
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.
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.
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.