bluuebunny/crossref_metadata_2025 huggingface dataset:
Mortality risk factors among HIV‐exposed infants in rural and urban Cameroon
Authors: Boerma Ragna S. , Wit Ferdinand W. N. M. , Orock Sammy Oben , Schonenberg‐Meinema Dieneke , Hartdorff Caroline M. , Bakia Affuenti , van Hensbroek Michael Boele
Published: October 2014

Objectives

HIV‐exposed infants, including those who do not become infected, have higher morbidity and mortality rates than HIV unexposed infants. The underlying mechanisms of this difference are largely unknown. The objective of this study was to identify the risk factors for mortality among HIV‐exposed (infected as well as uninfected) infants in a prevention of mother‐to‐child transmission (PMTCT) programme in Cameroon.

Methods

We analysed the data from 319 mother‐infant pairs included in a PMTCT programme at a rural and an urban hospital between 2004 and 2012. The programme offered free formula feeding, monthly follow‐up visits and antiretroviral therapy (ART) according to national PMTCT guidelines. Mother‐infant pairs were divided in three study groups, based on year of recruitment and study site: (I) rural hospital, 2004–07; (II) rural hospital, 2008–12; (III) urban hospital, 2008–12.

Results

Two hundred and eighty‐five medical records were included in the final analysis. Infant mortality rates were 23.9%, 20.0% and 5.3% in group I, II and III, respectively (P = 0.02). Hazard ratios of infant mortality were 6.4 (P < 0.001) for prematurity, 4.6 (P = 0.04) for no maternal use of ARTs, 5.6 (P = 0.025) for mixed feeding, 2.7 for home deliveries (P = 0.087) and 0.4 (P = 0.138) for urban study group.

Conclusions

In this programme, prematurity, no ART use, and the practice of mixed feeding were independent predictors of infant mortality. Mixed feeding and not using ART increased the hazard of death, probably through its increased risk of HIV infection. Although mortality rates were significantly higher in the rural area, rural setting was not a risk factor for infant mortality. These findings may contribute to the development of tailor‐made programmes to reduce infant mortality rates among HIV‐exposed infants.
Targeted encouragement of sexually active drug‐ and alcohol‐dependent women to use long‐acting reversible contraception is legitimate
Authors: Eyo Mary , Chenoy Rashna
Published: October 2014

Key content

Harm and property rights of a fetus and a child.

Encouragement versus coercion in reproductive health.

The best interests of sexually active dependent drug users.

Learning objectives

To understand how to protect best interests for those who cannot consent and provide access to health care to those who cannot consent to it.

To understand how one can encourage the use of a treatment without coercion.

To understand how to protect the best interests of sexually active drug‐dependent users, who may have reduced (or, occasionally, no) capacity to consent to treatment.

Ethical issues

Is it possible for a fetus/unborn child to be ‘harmed’?

If foreseeable harm could arise in a child born to a female drug addict, is it wrong not to encourage the mother to prevent this in some way?
Short‐term adaptation and chronic cardiac remodelling to high altitude in lowlander natives and Himalayan Sherpa
Authors: Stembridge Mike , Ainslie Philip N. , Shave Rob
Published: October 2014

New Findings

What is the topic of this review?

At high altitude, the cardiovascular system must adapt in order to meet the metabolic demand for oxygen. This review summarizes recent findings relating to short‐term and life‐long cardiac adaptation to high altitude in the context of exercise capacity.

What advances does it highlight?

Both Sherpa and lowlanders exhibit smaller left ventricular volumes at high altitude; however, myocardial relaxation, as evidenced by diastolic untwist, is reduced only in Sherpa, indicating that short‐term hypoxia does not impair diastolic relaxation. Potential remodelling of systolic function, as evidenced by lower left ventricular systolic twist in Sherpa, may facilitate the requisite sea‐level mechanical reserve required during exercise, although this remains to be confirmed.

Both short‐term and life‐long high‐altitude exposure challenge the cardiovascular system to meet the metabolic demand for O2 in a hypoxic environment. As the demand for O2 delivery increases during exercise, the circulatory component of oxygen transport is placed under additional stress. Acute adaptation and chronic remodelling of cardiac structure and function may occur to facilitate O2 delivery in lowlanders during sojourn to high altitude and in permanent highland residents. However, our understanding of cardiac structural and functional adaption in Sherpa remains confined to a higher maximal heart rate, lower pulmonary vascular resistance and no differences in resting cardiac output. Ventricular form and function are intrinsically linked through the left ventricular (LV) mechanics that facilitate efficient ejection, minimize myofibre stress during contraction and aid diastolic recoil. Recent examination of LV mechanics has allowed detailed insight into fundamental cardiac adaptation in high‐altitude Sherpa. In this symposium report, we review recent advances in our understanding of LV function in both lowlanders and Sherpa at rest and discuss the potential consequences for exercise capacity. Collectively, data indicate chronic structural ventricular adaptation, with adult Sherpa having smaller absolute and relative LV size. Consistent with structural remodelling, cardiac mechanics also differ in Sherpa when compared with lowlanders at high altitude. These differences are characterized by a reduction in resting systolic deformation and slower diastolic untwisting, a surrogate of relaxation. These changes may reflect a functional cardiac adaptation that affords Sherpa the same mechanical reserve seen in lowlanders at sea level, which is absent when they ascend to high altitude.
Consideration of Geometric Imperfections in Three-Dimensional Finite Element Model Analysis of Stiffened Steel Liners Subjected to External Pressure
Authors: Valdeolivas J. L. G. , Mosquera J. C.
Published: October 2014

The availability of tools for safety evaluation of a pressure liner is a relevant issue in both structural and hydraulic engineering. A suitable design of a steel liner may involve a significant reduction in the investment cost of a hydropower plant and may also ensure its future integrity, avoiding prolonged stoppages in the operation stage. First, a review of the design methods for steel pressure liners is outlined and certain key aspects for the critical buckling load assessment are pointed out. Second, a numerical modeling and analysis procedure of a steel pressure liner is presented. The methodology is based on 3D nonlinear finite element modeling procedures, involving both liner constraining and the effect of stiffeners. In addition, both large displacements and a surrounding elastic medium are assumed in the model. Besides, some types of geometric imperfections such as weld-induced ones, initial gap, ovality, and wall-thickness loss due to corrosion are taken into account in this work. Finally, some conclusions are drawn regarding the role of imperfections in the calculated critical pressure of a steel liner.
An Approach for a Statistical Evaluation of Uncertainty in Assessing Fatigue Usage Including Environmental Effects
Authors: Garud Yogendra S. , Steininger David A. , Wolfe Ken
Published: October 2014

The assessment for adequacy in managing the effects of fatigue in the ASME Code Class-1 (pressure boundary) components is based on a calculated measure of the projected fatigue damage. This measure is the highest cumulative usage factor (CUF) in a given component under a specified set of cyclic loadings and their expected number of repetitions. The Code based calculation of CUF and its adjustments for potential environmentally assisted fatigue (EAF) damage accumulation utilize a multitude of inputs, and conservative assumptions and applied margins. To support the extended service life beyond the original design, or longer life of new designs, changes in inputs and/or conservative assumptions used in these deterministically calculated CUFs are often made to meet a deterministic performance criterion. This makes the impact of uncertainty in the inputs and/or changes in the conservative adjustments difficult to assess. This paper presents a generic, engineering approach for estimation of the uncertainty distribution of CUF based on the expected statistical characteristics of input variables used in the calculation of EAF-based CUF. The approach does not involve Monte Carlo sampling. The proposed statistical approach analytically combines variances of the inputs leading to an acceptable estimation of the total variance of the CUF. The approach does not require specification of full probability distribution(s) for the input variables, nor is the dependence between variables a critical issue from the analytical point of view. Feasibility and limitations of the approach are discussed in relation to the NB-3200 and NB-3600 procedures of the ASME Code and the current Fen-based augmentation for environmental effects. This approach is further examined in the framework of stress–strength interference methodology to account for the uncertainty in the fatigue performance criterion which can lead to a rational deterministic safety factor interpretation and its relation to a quantifiable measure of the probability of exceeding the fatigue performance criterion.
Possibilities of the Generation of Hardened Steel Parts With Defined Topographic Characteristics of the Machined Surfaces
Authors: Grzesik Wit , Żak Krzysztof
Published: October 2014

The main objective of the comparison of precision hard cutting and abrasive processes in terms of the surface texture is to facilitate the decision whether to possibly replace grinding operations by hard turning with low feed rates. In this study, hard turning operations with Cubic Boron Nitride (CBN) cutting tools and grinding operations using electrocorundum Al2O3 and CBN wheels were performed in order to generate surfaces with the Sa roughness parameter of about 0.2 μm. 3D roughness parameters and the frequency, fractal and motif characteristics were analyzed.
Formation of Nano-Adsorption Layer and Its Effects on Nanofluid Spray Heat Transfer Performance
Authors: Chang Tong-Bou
Published: October 2014

For spray cooling using nanofluid as the working fluid, a nano-adsorption layer is formed on the heated surface and affects the heat transfer performance of the cooling system. This study performs an experimental investigation into the formation of this nano-adsorption layer and its subsequent effects on the spray heat transfer performance of a cooling system using Al2O3–water nanofluid as the working fluid. The experiments consider four different nanoparticle volume fractions (i.e., 0 vol. %, 0.001 vol. %, 0.025 vol. %, and 0.05 vol. %) and two different surface roughnesses (i.e., 0.1 μm and 1.0 μm). The experimental results show that the 0.001 vol. % nanofluid yields the optimal heat transfer performance since most of the nanoparticles rebound from the heated surface directly on impact or are washed away by subsequently arriving droplets. The surface compositions of the spray-cooled specimens are examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). The results reveal that for all of the nanofluids, a nano-adsorption layer is formed on the surface of the spray-cooled test pieces. Moreover, the layer thickness increases with an increasing nanoparticle concentration. A greater nano-adsorption layer thickness not only results in a higher thermal resistance but also reduces the effect of the surface roughness in enhancing the heat transfer performance. In addition, the nano-adsorption layer absorbs the nanofluid droplets under the effects of capillary forces, and therefore reduces the contact angle, which induces a hydrophilic surface property.
Heat Transfer in Rotating Serpentine Coolant Passage With Ribbed Walls at Low Mach Numbers
Authors: Yang Shang-Feng , Han Je-Chin , Azad Salam , Lee Ching-Pang
Published: October 2014

This paper experimentally investigates the effect of rotation on heat transfer in typical turbine blade serpentine coolant passage with ribbed walls at low Mach numbers. To achieve the low Mach number (around 0.01) condition, pressurized Freon R-134a vapor is utilized as the working fluid. The flow in the first passage is radial outward, after the 180 deg tip turn the flow is radial inward to the second passage, and after the 180 deg hub turn the flow is radial outward to the third passage. The effects of rotation on the heat transfer coefficients were investigated at rotation numbers up to 0.6 and Reynolds numbers from 30,000 to 70,000. Heat transfer coefficients were measured using the thermocouples-copper-plate-heater regional average method. Heat transfer results are obtained over a wide range of Reynolds numbers and rotation numbers. An increase in heat transfer rates due to rotation is observed in radially outward passes; a reduction in heat transfer rate is observed in the radially inward pass. Regional heat transfer coefficients are correlated with Reynolds numbers for nonrotation and with rotation numbers for rotating condition, respectively. The results can be useful for understanding real rotor blade coolant passage heat transfer under low Mach number, medium–high Reynolds number, and high rotation number conditions.
Comparisons of Horizontal-Axis Wind Turbine Wake Interaction Models
Authors: Wilson Jordan M. , Davis Cole J. , Venayagamoorthy Subhas K. , Heyliger Paul R.
Published: October 2014

In this study, Reynolds-averaged Navier–Stokes (RANS) simulations are performed using the k-ε and k-ω shear stress transport (SST) turbulence closure schemes to investigate the interactions of horizontal-axis wind turbine (HAWT) models in the neutrally stratified atmospheric boundary layer (ABL). A comparative study of actuator disk, actuator line, and full rotor models of the National Renewable Energy Laboratory (NREL) 5 MW reference turbine is presented. The open-source computational fluid dynamics (CFD) code openfoam 2.1.0 and the commercial software ansysfluent 13.0 are used for simulations. Single turbine models are analyzed for turbulent structures and wake resolution in the downstream region. To investigate the influence of the incident wind field on very large turbine blades, a high-resolution full rotor simulation is carried out for a single turbine to determine blade pressure distributions. Finally, simulations are performed for two inline turbines spaced 5 diameters (5D) apart. The research presented in this study provides an intercomparison of three dominant HAWT models operating at rated conditions in a neutral ABL using an RANS framework. Furthermore, the pressure distributions of the highly resolved full rotor model (FRM) will be useful for future aeroelastic structural analysis of anisotropic composite blade materials.
Full State Feedback Control of Steam Temperature in a Once-Through Direct Steam Generation Receiver Powered by a Paraboloidal Dish
Authors: Zapata José I.
Published: October 2014

Once-through direct steam generation (DSG) plants convert water into superheated steam suitable for a steam turbine with a single pass of the fluid through the receiver. The control problem in such a plant is to set a feed-water mass flow that maintains a desired steam condition (e.g., temperature) while rejecting the disturbance effect of variable direct normal irradiance (DNI). A mass flow control strategy preserves the simplicity of the plant, but is challenging to implement from a control perspective, as the disturbance effect is nonlinear and difficult to measure, due to the complex physical nature of two-phase flow and the receiver geometry. A model of the receiver behavior can be incorporated into the controller design in the form of a state observer, to estimate the internal behavior of the receiver during operation. This paper presents the design, testing an experimental implementation of full state linear feedback controller for the steam temperature for a once-through DSG system. The system consists of a 500 m2 paraboloidal dish concentrator and a monotube cavity receiver at the Australian National University. The controller manipulates the feed-water mass flow at the receiver inlet to maintain a predetermined specific enthalpy at the receiver outlet, compensating for variations in DNI and other ambient conditions. The controller features three separate regulation mechanisms: a feedforward (FF) law to anticipate changes in DNI; a full state feedback (FSF) loop with a state observer for the receiver; and an additional integrator loop for robustness. Experiments on the Australian National University (ANU) system show that the linear controller maintains steam temperatures to within 3% of a set reference of 500 °C during clear sky conditions, subject to adequate controller tuning. These results show that it is possible to control the ANU system with an FSF loop and state estimator, opening the possibility to test more advanced state based controllers.
NiAl Matrix Self-Lubricating Composite at a Wide Temperature Range
Authors: Zhu Shengyu , Kong Lingqian , Li Fei , Yang Jun , Ma Jiqiang , Cheng Jun , Zhen Jinming , Qiao Zhuhui
Published: October 2014

Self-lubricating composite NiAl–Cr–Mo–CaF2–Ag was fabricated by powder metallurgy technique. The NiAl matrix composite with 10 wt.% Ag provides self-lubricating properties at a broad temperature range between room temperature and 1000 °C. Especially at 800 °C, the composite offers excellent friction reduction about 0.2 and wear resistance about 0.7 × 10−4 mm3 N−1 m−1. The lubricous behavior at a wide temperature range could be attributed to the synergistic effect of Ag, CaF2, CaCrO4, and CaMoO4.
Incorporating Reliability and Failure Models Into Energy System Analysis
Authors: Piana Umberto , Kowalski Gregory J. , Zenouzi Mansour
Published: October 2014

Estimation of the mean lifetime and reliability of sophisticated systems such as cogeneration power plant (CHP) is a challenging problem in energy-engineering applications. A simulation model that predicts failure and repair times is described and used to calculate operating time availability and costs to operate the system. The new concept of estimated repair time with a Weibull probability density function is the key to the study of the down time. This probability distribution was defined for each component to estimate the time necessary to repair and the associated costs in economic and sustainability terms. The described simulation model provides a tool that demonstrates the competitive advantage or disadvantage of the CHP system for an application and enables more informed decisions as to their designs.
Modeling Building HVAC Energy Consumption During an Extreme Heat Event in a Dense Urban Environment
Authors: Tibana Yehisson , Gutierrez Estatio , Marte Sashary , Gonzalez J. E.
Published: October 2014

Dense urban environments are exposed to the combined effects of rising global temperatures and urban heat islands, a thermal gradient between the urban centers and the less urbanized surroundings suburbs. This combination is resulting in increasing trends of energy consumption in cities, associated mostly to air conditioning to maintain indoor human comfort conditions. The energy demand is further magnified during extreme heat events to a point where the electrical grid may be at risk. Given the anticipated increased frequency of extreme heat events for the future, it is imperative to develop methodologies to quantify energy demands from buildings during extreme heat events.

The purpose of this study is to precisely quantify thermal loads of buildings located in the very dense urban environment of New York City under an extreme heat event that took place in the summer of 2010 (July 4–8). Two approaches were used to quantify thermal loads of buildings for these conditions; a single building energy model (SBEM), such as the US Department of Energy eQUEST and EnergyPlus™, and an urbanized weather forecasting model (uWRF) coupled to a building energy model. The SBEM was driven by Typical Meteorological Year (TMY) weather file and by a customized weather file built from uWRF’s weather data for the specific days of the heat wave. A series of simulations were conducted with both SBEM software to model building energy consumption data due to air conditioning for two locations in Uptown and Midtown Manhattan, NY, which represented a low density and a high density building area within the city. Assumptions were made regarding the building’s floor plans and operation schedule to simplify the model and provide a close comparison to uWRF.

Results of the ensemble of SBEM indicate there was an increase in energy consumption during the July 2010 heat-wave when compared with the central park TMY case. The uptown location consumed 137% more energy during the heat wave event, while the midtown location showed an increased in energy consumption of 125% when compared to a typical July three day period, reaching total loads of close to 9812 kWh for a 20 m height building. Comparison of the results directly from uWRF for the energy consumption for same locations, indicate that for the midtown location both SBEMs underestimated the total energy consumption within a factor of three. This may be due to the fact that uWRF energy model takes into account urban microclimate parameters such as anthropogenic sources and waste heat interactions between surrounding buildings.
Combustion Characteristics of Butanol-Soybean Oil Blended Droplets
Authors: Schoo Reilly , Hoxie Alison , Braden Joel
Published: October 2014

The combustion characteristics of single fuel droplets of soybean oil (SBO) and butanol binary blends simply mixed by volume were experimentally examined. The droplets were supported at an intersection of microfibers in a 100°C combustion chamber at atmospheric pressure in normal gravity. Ignition was achieved via a hot wire igniter. Ignition characteristics and burning behaviors including burning to completion, burning with microexplosion and incomplete combustion were analyzed for initial concentrations ranging from 25–75% butanol. Droplet size and temperature measurements were analyzed throughout the droplet lifetimes. Relative concentrations prior and during combustion were estimated. Temperature measurements at ignition and above the burning droplet were analyzed. The addition of butanol significantly lowered the droplet ignition temperature. All mixtures studied ignited similarly to pure butanol droplets. The results showed consistency with closed-cup flashpoint temperatures of butanol-soybean oil blends. A three-staged burn including a microexplosion was observed for all mixed droplets, which burned completely. The disruptive burning proved to be a result of a diffusion limited gasification mechanism that has been previously linked to bi-component droplets with high volatility differentials. Microexplosions occur as a result of homogeneous nucleation due to superheating of the more volatile component trapped within the droplet at flame shrinkage. Results show that more butanol is burned in the first stage for Bu75 droplets resulting in microexplosions occurring late in the combustion process. For droplets of near equal initial concentrations, the microexplosions occur earlier resulting in less fuel burned in the first stage of combustion and therefore higher concentrations of butanol trapped within the droplet at flame shrinkage. Consequently these mixtures experience more microexplosions and at a greater intensity. The reduced tendency for Bu75 droplets to experience microexplosions suggest that the maximum droplet surface temperature may be depressed compared to droplets of near equal concentrations reducing the possibility for superheating of the droplet interior. Blends of near equal concentrations by volume proved to exhibit the most favorable combustion characteristics. Bu40 exhibited the most violent microexplosions of all mixtures studied.
Magnesium Hydride Slurry — A Better Answer to Hydrogen Storage
Authors: McClaine Andrew W. , Brown Kenneth , Bowen David D. G.
Published: October 2014

Hydrogen has many properties that make it an attractive energy storage medium for a sustainable future. But hydrogen is also difficult to store safely and cheaply. By storing hydrogen in an oil-based slurry with powdered magnesium hydride, cheap and safe hydrogen storage can be realized. This paper describes the characteristics and benefits of cycling hydrogen in and out of magnesium hydride slurry.

Based on our experience with magnesium hydride slurry, we have performed a study to evaluate the cost effectiveness of applying bulk hydrogen storage, using magnesium hydride slurry, in a baseload wind power system that we will also discuss. This study concludes that a 150 MW baseload wind power system would produce an Internal Rate of Return (IRR) of 10% with an electric price of $0.088/kWh. The costs and performance characteristics of this power plant are described.
Simulation Study of the Heat and Mass Recovery on the Performance of Adsorption Cooling Systems
Authors: Chan K. C. , Tso C. Y. , Chao Christopher Y. H.
Published: October 2014

In this study, simulation was conducted to investigate the effect of mass recovery, heat recovery, pre-heating and pre-cooling time on the system performance of a double-bed adsorption cooling system. Pressures of different system components were considered in the simulation. The adsorbent-adsorbate pair used was silica-gel and water. The heating and cooling temperatures were selected to be 85°C and 27°C respectively. Both the adsorption and desorption phase times were set at 15 minutes. The coefficient of performance (COP) and specific cooling power (SCP) were used to quantify the performance of the system. From the simulation, the basic cycle provided COP and SCP of 0.20 and 40.9W/kg respectively. By conducting heat recovery for 120 seconds, the system COP was largely increased by 99% to 0.40 compared to the basic cycle. The SCP was also increased to 42.3W/kg. Mass recovery, however, did not have too much effect on the system performance. The COP and SCP only increased by 4.5% and 3.9% respectively when conducting mass recovery for 4.7 seconds. For conducting heat and mass recovery, the COP and SCP were increased to 0.36 and 44.68W/kg, respectively. Pre-heating and pre-cooling can also be beneficial in improving both COP and SCP. The COP and SCP were increased by 14.5% and 10.1% respectively, to 0.23 and 45.0W/kg by conducting pre-heating and pre-cooling for 50.3 seconds. The combinations of these processes were also studied. It is suggested heat and mass recovery then pre-heating and pre-cooling should be conducted to improve COP and SCP. The improvements showed 31.2% for COP, increasing to 0.27, and 11.9% for SCP, increasing to 45.7W/kg.
Properties of Brassica Carinata and Camelina Sativa Meals and Fast Pyrolysis Derived Bio-Oils
Authors: Harris John , Lawburgh James , Lawburgh Brian , Michna Gregory J. , Gent Stephen P.
Published: October 2014

Fast pyrolysis is one method of creating bio-oil from various sources of biomass. In this research, fast pyrolysis of Brassica carinata and Camelina sativa meals were performed using a fluidized bed reactor. Chemical and physical properties of each oil sample were analyzed to determine the initial characteristics of the samples produced. Karl Fischer method was used to determine the water content and a total acid test was used to determine the total number of strong acids in each oil sample. A bomb calorimeter was used to determine the energy content of each bio-oil sample. Calorimetry and particle sizing were also done on the meals, on “dried” samples and “as received” samples. Particle size distributions of ground and unground samples of the feedstocks were determined. The results from this study can be used to assess the possibilities of using Brassica carinata and Camelina sativa meals as viable biomass sources for producing bio-oil. This could add value to these meals by turning a by-product of the oil extraction process into a resource for production of bio-oil.
A Thermodynamic and Cost Analysis of Solar Syngas From the Zinc/Zinc-Oxide Cycle
Authors: Nicodemus Julia Haltiwanger , McGuinness Morgan , Maharjan Rijan
Published: October 2014

We present a thermodynamic and cost analysis of synthesis gas (syngas) production by the Zn/ZnO solar thermochemical fuel production cycle. A mass, energy and entropy balance over each step of the Zn/ZnO syngas production cycle is presented. The production of CO and H2 is considered simultaneously across the range of possible stoichiometric combinations and the effects of irreversibilities due to both recombination in the quenching process following dissociation of ZnO and incomplete conversion in the fuel production step are explored. In the cost analysis, continuous functions for each cost component are presented, allowing estimated costs of syngas fuel produced at plants between 50 and 500MWth. For a solar concentration ratio of 10000, a dissociation temperature of 2300K, and a CO fraction in the syngas of 1/3, the maximum cycle efficiency is 39% for an ideal case in which there is no recombination in the quencher, complete conversion in the oxidizer, and maximum heat recovery. In a 100MWth plant, the cost to produce syngas would be $0.025/MJ for this ideal case. The effect of heat recuperation, recombination in the quencher, and incomplete conversion on efficiency and cost are explored. The effect of plant size and feedstock costs on the cost of solar syngas are also explored. The results underscore the importance improving quencher and oxidizer processes to reduce costs. However, even assuming the ideal case, the predicted cost of solar syngas is 5.5 times more expensive than natural gas on an energy basis. The process will therefore require incentive policies that support early implementation in order to become economically competitive.
Granular Flow and Heat Transfer Study in a Near-Blackbody Enclosed Particle Receiver
Authors: Martinek Janna , Ma Zhiwen
Published: October 2014

Concentrating solar power (CSP) is an effective means of converting solar energy into electricity with an energy-storage capability for continuous, dispatchable, renewable power generation. However, challenges with current CSP systems include high initial capital cost and electricity price. The U.S. Department of Energy’s (DOE) SunShot program aims to reduce cost and improve performance of CSP technology. To this end, NREL is developing a solid-particle based CSP system projected to have significant cost and performance advantages over current nitrate-based molten salt systems. The design uses gas/solid, two-phase flow as the heat transfer fluid and separated solid particles as the storage medium. A critical component in the system is a novel near-blackbody (NBB) enclosed particle receiver with high-temperature capability developed with the goal of meeting DOE’s SunShot targets for receiver cost and performance. Development of the NBB enclosed particle receiver necessitates detailed study of the dimensions of the receiver, particle flow conditions, and heat transfer coefficients. The receiver utilizes an array of absorber tubes with a granular medium flowing downward through channels between tubes. The current study focuses on simulation and analysis of granular flow patterns and the resulting convective and conductive heat transfer to the particulate phase. This paper introduces modeling methods for the granular flow through the receiver module and compares the results with an in-situ particle flow test.
Computational Fluid Dynamics (CFD) Analysis of Building Integrated Photovoltaic Thermal (BIPV/T) Systems
Authors: Hailu Getu , Yang TingTing , Athienitis Andreas K. , Fung Alan S.
Published: October 2014

This paper presents CFD study of a BIPV/T system with forced convection. Air was circulated behind PV arrays and used as a coolant with various air flow rates (air velocities) to recover the thermal energy that could be used for space and/or domestic water heating. Turbulent flows were considered with Reynolds number ranging from 5199 to 9392. COMSOL Multiphysics finite element analysis (FEA) software was used to develop CFD models for the BIPV/T system using: (a) measured temperature profile at different flow rates, and (b) measured solar radiation as boundary condition. Predictions of the air temperature profiles inside the air flow channel and the backside of the PV were obtained and compared to experimentally obtained temperature profiles using both boundary conditions. In general, better agreement with the experimentally measured temperature profiles was obtained when the measured solar radiation was used as a boundary condition. The results of the study can be used to establish relationships between the average/local convective heat transfer coefficients and air flow velocity. The relationships obtained will also be useful for developing correlations and simple mathematical models that facilitate the design and optimization of different parts of the BIPV/T system, such as inlet regions.
A Comparison Between the Monte Carlo Ray Trace and the FLUENT Discrete Ordinates Methods for Treating Solar Input to a Particle Receiver
Authors: Mecit Ahmet Murat , Miller Fletcher
Published: October 2014

A new type of high temperature solar receiver for Brayton Cycle power towers is being designed and built in the Combustion and Solar Energy Laboratory at San Diego State University under a DOE Sunshot Award. The Small Particle Solar Receiver is a pressurized vessel with a window to admit concentrated solar radiation that utilizes a gas-particle suspension for absorption and heat transfer. As the particles absorb the radiation that enters the receiver through the window, the carrier fluid (air in this case) heats which oxidizes the particles and the flow leaves the receiver as a clear gas stream. After passing through an in-line combustor if needed, this hot gas is used to power a turbine to generate electricity.

The numerical modelling of the receiver is broken into three main pieces: Monte Carlo Ray Trace (MCRT) method (written in FORTRAN), ANSYS Fluent (CFD), and the User Defined function (written in C code) for oxidation. Each piece has its advantages, disadvantages, and limitations and the three pieces are coupled to finalize the calculation. While we have successfully demonstrated this approach to obtaining the velocity and temperature fields, one big challenge to this method is that the definition of the geometry is a time consuming programming task when using MCRT. On the other hand, arbitrary geometries can be easily modelled by Computational Fluid Dynamics (CFD) codes such as FLUENT.

The goal of this study is to limit the use of MCRT method to determining the appropriate input boundary condition on the outside of the window of the receiver and to use the built-in Discrete Ordinates (DO) method for all the radiation internal to the receiver and leaving the receiver due to emission. To reach the goal, this paper focuses on the DO method implemented within FLUENT. An earlier study on this subject is based and advanced. Appropriate radiation input for the DO method is extensively discussed. MIRVAL is used to simulate the heliostat field and VEGAS is used to simulate a lab-scale solar simulator; both of these codes utilize the MCRT method and provide intensity information on a surface. Output from these codes is discretized into DO parameters allowing the solution to proceed in FLUENT. Suitable benchmarks in FLUENT are used in a cylindrical geometry representing the receiver for the comparison and validation. This method will allow FLUENT to be used for a variety of problems involving concentrated solar energy.
High Temperature Flash Pyrolysis of Wood in a Lab-Scale Solar Reactor
Authors: Zeng Kuo , Gauthier Daniel , Flamant Gilles
Published: October 2014

Pyrolysis of biomass (wood) was studied at the focus of a 1.5 kW vertical axis solar furnace. The sweeping gas feeding system was designed based on the CFD simulation results. The effects of temperature on the product yields and compositions of gas were investigated by experiments performed at heating rate of 50°C/s up to 600, 800, 1000, and 1200°C. The role of heating rates influencing the product yields and gas composition was studied by experiments carried out at different heating rates of 5, 100, 25 °C/s to 1200°C. The results show that the increase of gas product from 27.7% to 47.8% with increasing temperature and heating rate comes from the tar decomposition. In the solar reactor, heating rate plays a more important role for the product yields than temperature does, which is different with respect to conventional reactors.
Feasibility and Economic Evaluation of Applying Two Alternative Energy (R.D.F. and T.D.F) in Cement Industries in Iran
Authors: Nejati Vahid , Roknizadeh Jalil
Published: October 2014

In 2012, approximately 3700 million tons of cement is produced all around the world. Iran by producing 65 million tons cement in 2012 is ranked in fifth. Production process of the cement requires a huge amount of energy and it is approximated that 25% to 35% (based on efficiency of factories) of total costs in cement industries belong to required heat energy in production process. To produce 65 million tons of cement in Iran, about 56×1012 kcal of heat energy is consumed. Thus applying the new and cheep sources of energy could play an important role in reducing energy costs. On the other hand one of the important environmental problems is the absolutely huge amount of used tire of vehicles and the Municipal Solid Waste (MSW) and they should be appropriately destroyed. As a result they can easily change to Tire-Derived Fuel (TDF) and Refuse-Derived Fuel (RDF) to provide the required heat energy in cement industries.

In this study the available amount of RDF and TDF for cement industry are estimated. The evaluation results show that in Iran TDF can only provide about 1.77 percent of this need. Also using RDF, whose production has large potential in Iran, can cover about 27.96 percent. It is concluded that reduction of 29.73 percent of fossil fuel consumption in cement industries stem from applying both of these fuels simultaneously, leading to gas saving about two billion cubic meters per year. It is determined that the export value of such volume of gas is equal to one billion and ten million dollars with current gas price. However there is no tendency for using the alternative energy by cement factories because of low price of oil and natural gas inside Iran than global rate. In fact at the moment applying RDF and TDF doesn’t have any benefit for cement factories.

The purpose of this paper is to evaluate the effects of using alternative fuels in the cement industry in Iran and to show that for persuading and encouraging the cement factories to apply RDF and TDF, instead of increasing the energy prices, the revenue from fuel savings in global rate should be paid directly to cement industries.
Thermal Stratification in Spherical Tanks
Authors: Khan Fahad , Savilonis Brian J.
Published: October 2014

Spherical tanks have the potential for cost reduction in sensible thermal energy storage (TES) systems, by using less tank building material and insulation.

The current CFD study compares the Thermal Efficiency (TE) of a thermocline storage system in a spherical tank to a cylindrical tank of the same volume. A parametric study is then performed on a spherical tank during the discharge process to determine the flow parameters that govern the thermocline formation and entrainment. The following parameters are used: tank diameter to inlet diameter ratio D/d = 10, inlet velocity (0.02–0.1 m/s), and ΔT (10–70° C), leading to an inlet Froude number (0.4–3), inlet Reynolds number (500–7500), and tank Richardson number (2–100).

The results show a significant correlation between the inlet Reynolds and inlet Froude numbers, and the tank TE, in addition to a weak correlation between the tank Richardson number, based on the tank diameter, and the tank TE. The parametric study also shows a maximum tank TE at a Froude number equal to 0.5, and a proportional decrease of TE as the Reynolds number increases.
Estimating the Biogas Potential From Colleges and Universities
Authors: Ebner Jacqueline , Win Shwe Sin , Hegde Swati , Vadney Scott , Williamson Anahita , Trabold Thomas
Published: October 2014

Academic institutions present a unique opportunity for anaerobic digestion (AD) projects in that they have a concentrated population that generates waste, utilizes heat and electrical power, and often are motivated to implement sustainability initiatives. However, implementation of AD on college campuses in the U.S. is only beginning to emerge and data required to size and operate digesters are limited. This paper provides formulae to estimate food waste generated at college and university campuses base upon data collected at the Rochester Institute of Technology. Bottom-up and top-down estimates are presented and results are compared to an extensive review of publicly available data from other colleges and universities. The bottom-up methodology resulted in a lower estimate (18 kg food waste/enrolled student) than the top-down estimate (29 kg/enrolled student). Both were significantly lower than the estimate previously reported in the literature (64 kg/enrolled student). Bench-scale co-digestion experiments of the food waste with dairy manure resulted in a methane yield of 437 ml CH4/g VS. Applying this methodology to only 4-year colleges in New York State has the potential to generate 27 million GJ of energy from food waste.
Transition to Sustainability With Natural Gas From Fracking
Authors: Wu Kangqian , Kreith Frank
Published: October 2014

This paper is an analysis of the energy and money needed to construct a renewable energy system with the excess energy available from natural gas obtained by hydraulic fracturing or “fracking”. Using data from the Energy Information Administration regarding the future availability of natural gas obtained by fracking and the energy required to build a sustainable system consisting of wind power, photo-voltaic energy generation and hydraulic storage, a scenario for the construction of a sustainable system is generated. Finally, a preliminary financial analysis of the cost of the renewable system is made. The analysis demonstrates that it is possible to build a sustainable system from the excess natural gas obtained by fracking in less than 30 years. After that time the energy produced from the renewable system is sufficient to replace those parts of the system that have reached their expected life and construct new sustainable generation technology as required by population growth.
Experimental Performance Analysis of External Compound Parabolic Concentrators With Low Concentration Ratios for Medium Temperature Applications
Authors: Xu Donghao , Qu Ming
Published: October 2014

Due to the mounting concerns about climate changes and depletion of fossil fuels, solar energy, as one type of renewable energy, has attracted a lot of interests from academia, industries, and government in the past few decades. Currently, solar thermal technologies have been applied to the applications at the low operating temperature below 100°C by using flat-plate solar collectors and at the high operating temperature above 250°C by using solar tracking concentrators. For the medium operating temperatures between 100°C and 250°C, flat-plate solar collectors can hardly reach 100°C and solar tracking concentrators are too expensive. In this context, the use of external compound parabolic concentrators (XCPC) for applications operated at medium temperature draws quite attentions because of its higher efficiency than flat plate solar collectors and better cost effectiveness than solar tracking concentrators. However, currently only a few experimental data is available on the actual performance of XCPCs from literatures, especially for the recently new XCPCs with a low concentration ratio. In order to contribute to the knowledge, a series of experiments have been conducted on the new XCPCs recently installed at Bowen Lab, Purdue University, West Lafayette, Indiana. The experiments showed that the XCPCs raised the temperature to 170°C, which is 140°C higher than the ambient temperatures, with a thermal efficiency of 29%. Based on the data collected from the experiments, the optical and thermal efficiencies of XCPCs are determined for different solar irradiations, operating temperatures, and incident angles. A new regression model is proposed and fitted accordingly. The experimental data and analysis demonstrated the feasibility and potentials of using XCPCs for applications in medium temperature range such as solar absorption cooling and heating systems, seawater desalination, solar disinfection, post-combustion carbon capture systems and other industrial process heating.
Design and Evaluation of an On-Sun Prototype Falling-Particle Cavity Receiver
Authors: Christian Joshua , Ho Clifford , Kolb William , Kelton John , Ray Daniel
Published: October 2014

Cavity receivers have been an integral part of Concentrated Solar Power (CSP) plants for many years. However, falling solid particle receivers (SPR) which employ a cavity design are only in the beginning stages of on-sun testing and evaluation. A prototype SPR has been developed which will be fully integrated into a complete system to demonstrate the effectiveness of this technology in the CSP sector. The receiver is a rectangular cavity with an aperture on the north side, open bottom (for particle collection), and a slot in the top (particle curtain injection). The solid particles fall from the top of the cavity through the solar flux and are collected after leaving the receiver. There are inherent design challenges with this type of receiver including particle curtain opacity, high wall fluxes, high wall temperatures, and high heat losses. CFD calculations using ANSYS FLUENT were performed to evaluate the effectiveness of the current receiver design. The particle curtain mass flow rate needed to be carefully regulated such that the curtain opacity is high (to intercept as much solar radiation as possible), but also low enough to increase the average particle temperature by 200°C. Wall temperatures were shown to be less than 1200°C when the particle curtain mass flow rate is 2.7 kg/s/m which is critical for the receiver insulation. The size of the cavity was shown to decrease the incident flux on the cavity walls and also reduced the wall temperatures. A thermal efficiency of 92% was achieved, but was obtained with a higher particle mass flow rate resulting in a lower average particle temperature rise. A final prototype receiver design has been completed utilizing the computational evaluation and past CSP project experiences.
Performance Evaluation of an Air Source Heat Pump Coupled With a Building Integrated Photovoltaic/Thermal (BIPV/T) System
Authors: Hailu Getu , Dash Peter , Fung Alan S.
Published: October 2014

A theoretical investigation of a variable capacity air-to-air air source heat pump (VC-ASHP) coupled with a building integrated photovoltaic/thermal (BIPV/T) system is presented in this paper. The BIPV/T system was integrated into the roof and the wall. Air was circulated behind the photovoltaic arrays to recover the thermal energy. The warm air recovered was supplied to the VC-ASHP. The thermal performance of the VC-ASHP was investigated for three scenarios when the heat pump is running in heating mode. The three scenarios are: (A) by feeding the ambient air to the ASHP; (B) by coupling the ASHP to the wall integrated BIPV/T only; and (C) by coupling the ASHP to the roof integrated BIPV/T only. The coefficient of performance (COP) of the VC-ASHP was evaluated for these three separate scenarios and compared. A typical winter day result suggests that the COP of the ASHP can be improved by coupling the VC-ASHP to either of the BIPV/T systems, i.e., either to the roof integrated BIPV/T system or to the wall integrated BIPV/T system.