bluuebunny/crossref_metadata_2025 huggingface dataset:
Bioethanol Production From Canola Straw Using a Continuous Flow Immobilized Cell System
Authors: Mathew Anil , Crook Mitch , Chaney Keith , Humphries Andrea
Published: July 2013

Global cultivation of canola increased by approximately 22% between 2000 and 2009, due to increased demand for canola oil for biodiesel production and as an edible oil. In 2009 over 290,000 km2 of canola was cultivated globally. In contrast to oilseed, the commercial market for canola straw is minimal and it is generally ploughed back into the field. The high carbohydrate content (greater than 50 % by dry weight) of canola straw suggests it would be a good feedstock for second-generation bioethanol production. There are four major steps involved in bioethanol production from lignocellulosic materials: (i) pretreatment, (ii) hydrolysis, (iii) fermentation, and (iv) further purification to fuel grade bioethanol through distillation and dehydration. Previous research demonstrated a glucose yield of (440.6 ± 14.9) g kg−1 when canola straw was treated using alkaline pretreatment followed by enzymatic hydrolysis. Whilst bioethanol can be produced using cells free in solution, cell immobilization provides the opportunity to reduce bioethanol production costs by minimizing the extent to which down-stream processing is required, and increasing cellular stability against shear forces. Furthermore, the immobilization process can reduce substrate and product inhibition, which enhances the yield and volumetric productivity of bioethanol production during fermentation, improves operational stability and increases cell viability ensuring cells can be used for several cycles of operation. Previous research used cells of Saccharomyces cerevisiae immobilized in Lentikat® discs to convert glucose extracted from canola straw to bioethanol. In batch mode a yield of (165.1 ± 0.1) g bioethanol kg−1 canola straw was achieved.

Continuous fermentation is advantageous in comparison to batch fermentation. The amount of unproductive time (e.g. due to filling, emptying and cleaning) is reduced leading to increased volumetric productivity. The higher volumetric productivity of continuous fermentation means that smaller reactor vessels can be used to produce the same amount of product. This reduces the capital costs associated with a fermentation plant. Research demonstrated a higher bioethanol yield was attained (224.7 g bioethanol kg−1 canola straw) when glucose was converted to bioethanol using immobilized cells in packed-bed continuous flow columns. On an energy generation basis, conversion of 1 kg of canola straw to bioethanol resulted in an energy generation of 6 MJ, representing approximately 35% energy recovery from canola straw. The amount of energy recovered from canola straw could be improved by increasing the amount of energy recovered as bioethanol and by utilising the process by-products in a biorefinery concept.
Geometric and Material Optimization of Vortex-Induced Vibration Micro Energy Harvesters for Localized Wind Environments
Authors: French Jesse J. , Sheets Colton T.
Published: July 2013

Wind energy capture in today’s environment is often focused on producing large amounts of power through massive turbines operating at high wind speeds. The device presented by the authors performs on the extreme opposite scale of these large wind turbines. Utilizing vortex induced vibration combined with developed and demonstrated piezoelectric energy harvesting techniques, the device produces power consistent with peer technologies in the rapidly growing field of micro-energy harvesting. Vortex-induced vibrations in the Karman vortex street are the catalyst for energy production of the device. To optimize power output, resonant frequency of the harvester is matched to vortex shedding frequency at a given wind speed, producing a lock-on effect that results in the greatest amplitude of oscillation. The frequency of oscillation is varied by altering the effective spring constant of the device, thereby allowing for “tuning” of the device to specific wind environments. While localized wind conditions are never able to be predicted with absolute certainty, patterns can be established through thorough data collection. Sampling of local wind conditions led to the design and testing of harvesters operating within a range of wind velocities between approximately 4 mph and 25 mph. For the extremities of this range, devices were constructed with resonant frequencies of approximately 17 and 163 Hz. Frequency variation was achieved through altering the material composition and geometry of the energy harvester. Experimentation was performed on harvesters to determine power output at optimized fluid velocity, as well as above and below. Analysis was also conducted on shedding characteristics of the device over the tested range of wind velocities. Computational modeling of the device is performed and compared to experimentally produced data.
Rapid Production of Hydrogen and Carbon Monoxide via the Heterogeneous Oxidation of Zn(g)
Authors: Venstrom Luke J. , Davidson Jane H.
Published: July 2013

The heterogeneous oxidation of Zn(g) is considered as an improved approach to the production of H2 and CO in the two-step Zn/ZnO solar thermochemical cycle. The rate of Zn(g) oxidation by H2O and CO2 is measured gravimetrically in a quartz tubular flow reactor for temperatures between 800 and 1150 K, Zn(g) concentrations up to 36 mol%, and H2O/CO2 concentrations up to 45 mol%. The rate of the heterogeneous oxidation of Zn(g) by both H2O and CO2 is on the order of 10−8–10−5 mol cm−2 s−1. For similar oxidizing conditions, H2O oxidizes Zn(g) three times as fast as CO2, indicative of a lower heterogeneous oxidation activation energy in the H2O system. Less than one second is required to convert more than 85% of Zn to ZnO for all temperatures in both the H2O and CO2 reacting systems.
3D Experimental and Numerical Analysis of Natural Ventilation of Domed-Roof Buildings During Economizer Mode
Authors: Rahmatmand A. , Yaghoubi M. , Rad E. Goshtasbi
Published: July 2013

This paper present experimental measurements of velocity distribution at different sections around a reduced scale model of a real domed-roof building with several openings. Measurements are made in an open loop wind tunnel with atmospheric boundary layer. A new modified Counihan scheme which is a combination of the two systems is developed for the purpose of part-depth atmospheric boundary layer (ABL). The measured quantities are wind velocity profile, turbulence intensity, and air flow pattern around the building. For experiments a 1:54 scale model of a domed-roof building with six windows and an aperture on the roof is made. In addition, by using a numerical solution, turbulent air flow around such scale model in the wind tunnel is simulated and flow field inside the model and also the discharge coefficient are computed during the economizer mode.
Numerical Analysis of Convection Heat Transfer From an Array of Circular Perforated Fins due to Variable Perforation Size
Authors: Dastbelaraki A. H. , Yaghoubi M.
Published: July 2013

Among rapid advances of electrical systems electronic circuit boards have become more compact and heat production rate from their components increased considerably. Such developments raised more attention and tendency in tackling their cooling problems. A wide variety of cooling systems are developed such as various fins for decreasing the circuit board temperature. Extended surfaces or fins are good heat transfer equipments that are used for various industrial applications. The wide industrial applications of fins to enhance heat transfer rate highlighted the need for further research of optimization of fins to increase their thermal performances. Among various fin types, rectangular fins are commonly used due to their simplicity of manufacturing. Fin configurations affect the cooling rate significantly, hence a comprehensive parametric study on the fin geometries may be improve their performance. Rectangular fins show a good performance of increasing heat removal rate, while reducing the manufacturing cost. Moreover the inspiration of putting holes along the flow through the fins may be very helpful in increasing the heat removal and reduction of the needed material.

The present study investigates a numerical analysis of three dimensional, turbulent convection heat transfer from an array of rectangular perforated fins with increasing the perforation size from bottom to top. The perforations considered are like circular channels along the length of fins and the number of perforations is 3. For investigation, incompressible air as working fluid is modeled using Navier–Stokes equations. RNG based k-ε turbulent model is used to predict turbulent flow parameters. Temperature field inside the fins is obtained by solving Fourier’s conduction equation. The conjugate differential equations for both solid and gas phase are solved simultaneously by finite volume procedure using SIMPLE algorithm. Flow and heat transfer characteristics are presented for Reynolds numbers from 2 × 104 to 4 × 104 based on the fin length and Prandtl number of Pr = 0.71. Numerical model is first validated with previous experimental studies and good agreements were observed. Based on the valid simulation model, numerical solution is made to find flow field and temperature distribution for various perforation size. Results show that for a specific type of perforated fins the fin effectiveness is higher than other types and drag coefficient decreases with increasing the perforation size.
Maximum Power From Fluid Flow: Results From the First and Second Laws of Thermodynamics
Authors: Diaz German Amador , Santos John Turizo , Hernandez Elkin , Padilla Ricardo Vasquez , Corredor Lesme
Published: July 2013

The heat transfer principle of power maximization in power plants with heat transfer irreversibilities was cleverly extended by Bejan [1] to fluid flow, by obtaining that the energy conversion efficiency at maximum power is ηmax = 1/2(1 − P2/P1). This result is analog to the efficiency at maximum power for power plants, ηmax = 1 − (T2/T1)1/2 which was deduced by Curzon and Ahlborn [2]. In this paper, the analysis to obtain maximum power output delivered from a piston between two pressure reservoir across linear flow resistance is generalized by considering the piston cylinder friction, by obtaining relations of maximum power output and optimal speed of the piston in terms of first law efficiency. Expressions to relate the power output, cross sectional area of the chamber and first law efficiency, were deduced in order to evaluate the influence of the overall size constraints and fluid regime in the performance of the piston cylinder system. Flow in circular ducts and developed laminar flow between parallel plates, are considered to demonstrate that when two pressure reservoirs oriented in counterflow, with different and arbitrary cross sectional area, must have the same area in order to maximize the power output of the system. These results introduce some modifications to the results obtained by Bejan [1] and Chen [3]. This paper extends the Bejan and Chen’s work by estimating under turbulent regime the lost available work rate associated with the degree of irreversibilities caused by the flow resistances of the system. This analysis is equivalent to evaluate the irreversibilities in an endoirreversible Carnot heat engine model caused by the heat resistance loss between the engine and its surrounding heat reservoirs. This paper concludes with an application to illustrate the practical applications by estimating the lost available work of an actual steady-flow turbine and the layout pipes upstream and downstream of the same device.
Benefits of Monitoring Energy Use and Production Using Enhanced Smart Meters for California Houses
Authors: Vargas Sergio Escobar , Gonzalez Jorge E. , Aschheim Mark
Published: July 2013

Methodologies have been developed to allow real-time determination of energy production and use as well as sizing of HVAC equipment based on thermal loads at the residential level. The data obtained reflect actual properties of the thermal envelope and appliance efficiencies, as well as actual renewable power production. The use of properly sized HVAC equipment introduces further energy savings. Recovery of energy savings expressed in terms of carbon offsets provides an incentive to improve the occupant’s energy footprint. When monetized, the energy cost savings and carbon offsets have financial benefits. These benefits are evaluated for model homes in various climatic zones within the state of California.
Geothermal Energy for Small-Scale Power Generation Using an Organic Rankine Cycle
Authors: Hessami Mir Akbar
Published: July 2013

Geothermal power generation is achieved by feeding the harnessed geothermal heat into the boiler of an ORC (Organic Rankine Cycle) based engine which uses an organic working fluid characterised by its low boiling temperature. For the purpose of this study, such a system was designed, built and operated to verify the concept of small-scale power generation using heat from a low temperature source. This experimental facility used hot water as the source of heat, brazed plate heat exchangers as the boiler and the condenser, an automotive inline fuel pump for circulation and a Scroll compressor operated in reverse to act as the expander. The working fluid was R245fa with a boiling point of 80°C at a pressure of 790kPa (or 40°C at 250kPa). A Prony Brake was fitted on the shaft of the expander to determine its power output. Experimental investigations found that ∼600W of power could be produced under optimum conditions at a rotational speed of ∼2000RPM. The details of the experimental facility as well as the results of the experiments are provided in this paper.
A Quasi Steady State Model for Adsorption Cooling Systems: Automotive Applications
Authors: Sharafianardakani Amirhossein , Bahrami Majid
Published: July 2013

In this study, an analytical quasi-steady state thermodynamic cycle of an adsorption cooling system (ACS) for automotive applications is presented which allows evaluating impact of different parameters on the ACS performance as well as effects of various working pairs: zeolite 13X/water, zeolite 4A/water and activated carbon-35/methanol. A comprehensive parametric study has been performed to investigate effects of temperature variation of the evaporator and condenser as well as the ICE exhaust gas temperature on the COP, cooling load produced by the evaporator and entropy generation of ACS with (or without) the heat recovery cycle (HRC). The results show that using the heat recovery cycle in the ACS can increase the COP of system up to 41% for zeolite 13X/water pair at the base-line condition. In addition, the parametric study shows that increasing regeneration and evaporation temperature increase the COP and entropy generation of ACS while increasing condensation temperature has negative effect on the COP and entropy generation. Finally, based on our modeling results, the ACS with the heat recovery cycle (HRC) and zeolite 13X/water pair are proposed for the automotive A/C applications.
Trough Type Concentrating Solar Power Plant Cost Assessment With Component Scaling
Authors: Luo Jun , Schuller Michael , Lalk Thomas
Published: July 2013

A detailed numerical and empirical systems analysis tool was developed which incorporated component scaling cost equations. It was benchmarked against the known data from the Andasol-1 plant in Spain, and then used to evaluate the effect of changes in the size of the solar field, the thermal energy storage system, and the power block on the levelized cost of electricity (LCOE) for the plant. The simulation result indicates that when the power plant capacity increases from 50 MW to 400 MW, the LCOE decreases by 32%. Also, the model’s results indicate that an oversized field and thermal energy storage tanks help to lower the LCOE.
Societal Costs of Transportation Fuels: Enabling a True Comparison of Alternatives to Conventional Fuels
Authors: Law Karen H. , Chan Michael J. , Jackson Michael D.
Published: July 2013

Petroleum-based conventional fuels dominate the transportation sector due to simple economics. Per unit of energy, few fuels can rival gasoline and diesel in terms of total cost of ownership to the consumer. While some fuels, such as natural gas and electricity, offer lower fuel costs and/or higher vehicle efficiencies than conventional fuels, the fuel price differentials may not be sufficient to offset the higher initial costs of the vehicles, especially if petroleum prices are low. Even when total costs of ownership are similar or slightly lower for alternative fuels than conventional fuels, differences in attributes, such as vehicle range, fueling time, cargo space, vehicle availability, and fuel availability, and consumer loss aversion suggest that more substantial differences in costs are required before consumers are willing to adopt the alternatives.

In order for the transportation sector to achieve greater energy sustainability, the traditional economic paradigm for the vehicle purchase decision must expand to incorporate the true benefits of alternatives to conventional fuels, namely the societal benefits of increased energy security, lower criteria pollutant emissions, and lower greenhouse gas emissions. These benefits are not purely economic and yet are crucial to the future of transportation. To capture these benefits in the economic scheme, the societal costs of transportation fuels to the U.S. have been monetized according to measurable impacts. For energy security, the costs are tied to decreased economic output, loss of national gross product, economic strain and volatility, oil supply shocks and price spikes, supply disruption, and import costs. For criteria pollutant and greenhouse gas emissions, the costs are tied to human health impacts, property damage, loss of agricultural productivity, and destruction of terrestrial and aquatic ecosystems. These societal costs then applied to the use of specific fuels in two representative market segments, representing distinct applications, duty cycles, fuel consumption, and vehicle lifetime. Incorporating the monetized societal costs of transportation fuels in the total costs of ownership enables a fair comparison that reflects the benefits of alternatives to conventional fuels. As a result, these societal costs provide a justifiable framework for a real discussion on incentives and the direction of energy policy, beyond the mere objective of low fuel prices that has pervaded policy discussions to date.
Performance of Working Fluids for Power Generation in a Supercritical Organic Rankine Cycle
Authors: Vidhi Rachana , Kuravi Sarada , Besarati Saeb , Stefanakos E. K. , Goswami D. Yogi , Sabau Adrian S.
Published: July 2013

This paper reports on the performance of various organic refrigerants and their mixtures as working fluids for power generation in a supercritical Rankine cycle (SRC) from geothermal sources. Organic fluids that have zero or very low ozone depletion potential and are environmentally safe are selected for this study. Geothermal source temperature is varied from 125–200°C, and the cooling water temperature is changed from 10–20°C. The effect of varying operating conditions on the performance of the thermodynamic cycle has been analyzed. Operating pressure of the cycle has been optimized for thermal efficiency for each fluid at each source temperature. The condensation pressure is determined by the cooling condition and is kept fixed for each condensation temperature. Energy and exergy efficiencies of the cycle have been obtained for the pure fluids as a function of heat source temperature. Mixtures of organic fluids have been analyzed and effect of composition on performance of the thermodynamic cycle has been studied. It is observed that thermal efficiency over 20% can be achieved for 200°C heat source temperature and the lowest cooling temperature. When mixtures are considered as working fluids, the thermal efficiency of the cycle is observed to remain between the thermal efficiencies of the constituent fluids.
Comparison of Inviscid Flow Methods for Lift and Drag Calculations Over Thin-Sail Geometries
Authors: Spall Robert E. , Phillips Warren F. , Pincock Brian B.
Published: July 2013

Solutions obtained from lifting-line, vortex-lattice, and the Euler equations are presented for a series of rigid, thin wing and sail geometries. Initial calculations were performed for an untwisted, rectangular wing. For this case, lifting line theory, vortex lattice, and Euler solutions were all in reasonable agreement. However, the lifting-line theory was the only method to predict a constant ratio of induced drag coefficient to lift coefficient squared. Similar results were found for a forward-swept, tapered wing. Additional results are presented in terms of lift and drag coefficients for an isolated mainsail, and mainsail/jib combinations with sails representative of both a standard and tall rig Catalina 27. Although experimental data is lacking, overall conclusions are that the accuracy realized from lifting-line solutions is as good as or better than that obtained from vortex-lattice solutions and inviscid CFD solutions, but at a fraction of the computational cost. The linear lifting-line results compared quite well with the nonlinear lifting-line results, with the exception of the downstream mainsail when considering jib/mainsail combinations.
Study of the Transitional Flow and Particle Separation With a Fishhook Effect in a Mini-Hydrocyclone
Authors: Zhu Guofeng , Liow Jong-Leng , Neely Andrew
Published: July 2013

The mini-hydrocyclone is being proposed as a micro-separator in complex micro-devices for in-line fine particle separation as it has a concise geometry and no moving parts,. In this work, we present a numerical study combined by experiments on a 5 mm minihydrocyclone to investigate the transitional flow and particle separation with the presence of a fishhook effect. The results showed that the simulation from the LES model gave good agreement with that from DNS at an inlet velocity of 0.4 m/s. The LES model was then used to study the higher inlet velocity cases of 1.0 and 1.8 m/s. The particle separation was predicted by a Lagrangian model with an added user defined function (UDF) in the Fluent code to account for the particle interaction. The modeling results for the three inlet velocities studied showed that small particle Reynolds number, ReP, resulted in a poorly developed wake behind the large particles, which did not entrain fine particles leading to a barely noticeable fishhook effect for the 0.4 m/s inlet velocity. In contrast, a large ReP gives rise to larger wakes, which are capable of entraining fine particles more efficiently causing the pronounced fishhook effect at higher inlet velocities. The results show the particle separation with the fishhook effect could be modeled based on the particle entrainment model, whereas the accurate simulation of the fishhook effect in future should include a correction coefficient that varies with Rep to improve the separation efficiency predictions.
State-of-the-Art Review on Flow Patterns, Superficial Void Fraction and Flow-Induced Vibration During Two-Phase Flows Across Tube Bundles
Authors: Kanizawa Fabio Toshio , de Oliveira Leopoldo P. R. , Ribatski Gherhardt
Published: July 2013

This paper presents a comprehensive review on the open literature concerning two-phase flow across horizontal tube bundles. Initially, experimental studies available in the literature are described in an organized manner. This detailed description includes bundle configurations and the experimental techniques used for evaluating flow patterns, void fraction and flow-induced vibration. Most of studies were performed having air-water as working fluids. Several excitation mechanisms can be reproduced such as flow periodicity, fluid-elasticity and turbulence. Flow patterns are discussed and their predictive methods are compared. Void fraction predictive methods are also discussed and comparisons among them are presented. It was found that the predictive methods worked reasonably well when compared against the databases used during their development. Generally, the studies have obtained bundle average measurements which are not representative of the local conditions and, therefore, are not recommendable to be used as accurate designing tools. Most studies concerning fluid-induced vibration have addressed this problem through simplified bench structures, usually consisting of a single rigid tube over a flexible suspension.
Flows Through Reconstructed Porous Media Using Immersed Boundary Methods
Authors: Nagendra Krishnamurthy , Tafti Danesh K.
Published: July 2013

Understanding of the flows through real porous media is of considerable importance given their usage in a wide range of applications. Direct numerical simulations of such flows could be vastly informational but are rarely available in literature owing to the difficulty in simulating flows around complex surface contours that generally constitute porous media. In an effort to better the understanding of such flows, an immersed boundary method (IBM) framework capable of simulating flows through arbitrary surface contours is developed. For simulation of realistic porous media, a stochastic reconstruction procedure based on simulated annealing is utilized. Detailed studies to validate the results are undertaken. Further, numerous calculations are performed on flows through two-dimensional porous channels. The obtained results are compared with the analytical results from Darcy-Forchheimer equation. A study of the effect of varying sizes of the porous structures in such flows shows the increasing deviation from Darcy-Forchheimer equation as the size becomes significant in comparison to the channel height highlighting the need for such a framework and more such DNS studies.
On Reduced Order Modeling of Transient Flows Using the Proper Orthogonal Decomposition
Authors: Behzad Fariduddin , Helenbrook Brian T. , Ahmadi Goodarz
Published: July 2013

Reduced-order modeling (ROM) of transient fluid flows using the proper orthogonal decomposition (POD) was studied. Particular attention was given to incompressible, unsteady flow over a two-dimensional NACA0015 airfoil in the laminar regime. When the airfoil sheds vortices, a transient blowing through a jet placed at the 10% chord location was imposed. POD modes were derived from the numerical solution of the flow obtained using an hp-finite element method. The ROM was obtained by a streamwise-upwind-Petrov-Galerkin (SUPG) projection of the incompressible Navier–Stokes equations onto the space spanned by the POD modes.

The extraction of accurate POD-based reduced order model of this flow was explored using three different POD mode generation methods. The first approach was the split method, which superposes modes derived from simulations of the blowing jet with no flow and simulations of the baseline flow with no jet. The second method combined POD modes derived from simulations having both the jet and flow with modes obtained from simulation of only the flow. These modes were generated after the simulations reached the periodic state. The third and newly proposed approach was to generate a set of modes called “Generalized POD basis functions.” These modes were derived from simulations where the jet’s flow amplitude is varied slowly. For each method, the results were compared with detailed Finite Element solutions and the accuracy and efficiency of different methods were evaluated. The newly proposed “Generalized POD basis functions” approach predicted the transient response of the system most accurately.
Vortex Shedding From Low Aspect Ratio Dual Step Cylinders
Authors: Morton Chris , Yarusevych Serhiy
Published: July 2013

A low aspect ratio dual-step cylinder is comprised of two cylinders of different diameters (D and d). The large diameter cylinder (D) with low aspect ratio (L/D) is attached to the mid-span of a small diameter cylinder (d). This geometry is relevant to many engineering applications, e.g., finned-tube heat exchangers, underwater cables, and cylindrical support structures. The present study investigates the effect of Reynolds number (ReD) and L/D on dual step cylinder wake development for 1050 ≤ ReD ≤ 2100, D/d = 2, and 0.2 < L/D ≤ 3. Experiments have been performed in a water flume facility utilizing flow visualization, Laser Doppler Velocimetry (LDV), and Particle Image Velocimetry (PIV). The results show that vortex shedding occurs from the large and small diameter cylinders at distinct frequencies for L/D ≥ 1 & ReD = 2100 and L/D ≥ 2& ReD = 1050. At these higher aspect ratios investigated, large cylinder vortices predominantly form closed vortex loops in the wake and small cylinder vortices form half-loop vortex connections. In contrast, at lower aspect ratios, vortex shedding from the large cylinder ceases, with the dominant frequency centred-activity in the large cylinder wake attributed to the passage of vortex filaments connecting small cylinder vortices. The presence of the large cylinder distorts the vortex filaments causing cyclic vortex dislocations accompanied by the formation of half-loop vortex connections. Increasing L/D decreases the frequency of occurrence of vortex dislocations and increases the dominant frequency in the large cylinder wake. The results also show that the Reynolds number has a substantial effect on wake vortex shedding frequency, which is more profound than that expected for a uniform cylinder.
Experimental Study of Aerodynamic Noise From a Double Shaft Fan
Authors: Madadnia Jafar , Alshehri Faisal , Tilwa Kaushik
Published: July 2013

Noise pollution from wind turbines and blowers operating in the vicinity of residential buildings has in recent years been the focus of intensive research. This paper reports on the outcome of an experimental investigation to reduce the noise pollution through design, build and testing of a counter-rotating-double-row-fan with variable spacing. A single-row fan was selected as the benchmark fan. The mechanical noise and the background ambient noise were measured using the system operating with no-blades. The aerodynamic noise from the fan was then focused and air velocity, shaft-revolution, input-electric-power to fan, amplitude (dB) and Center Frequency (CF) in Hz of noise were measured using frequency-weighting of both “A” and “Linear”. Coefficients of performance (COP), dB, CF, Tip speed ratio (TSR) were plotted for a range of spacing between two-blade-rows.

It was noticed that double-shaft-fan relative to the benchmark single shaft fan has operated:

a) At a lower TSR due to division of the motor power between two shafts.

b) At a higher COP of up to 18% due to a higher air velocity generated at the same motor power.

c) Quieter at a lower dB (of up to 10 dB).

d) At the minimum noise levels (80 dB) at the spacing of 15mm-to-25mm, using the “Lin”-weighting.

e) At the minimum noise levels (20 dB) at the spacing of 12mm-to 50 mm when measured at the “A”-weighting.

f) With no significant change in frequency of noise when operate at the same TSR.
Experimental and Numerical Investigation of the DrivAer Model
Authors: Heft Angelina I. , Indinger Thomas , Adams Nikolaus A.
Published: July 2013

Automotive aerodynamic research often focuses on strongly simplified car models, such as the Ahmed body and the SAE model. Due to their high degree of abstraction, however, interference effects are often neglected which leads to an unrealistic representation of the flow field. Consequently, these results cannot be directly used for the aerodynamic optimization of production vehicles. On the other hand, aerodynamic investigations of real production vehicles are often limited due to the restricted availability of the geometric data. Therefore, a new realistic generic car model for aerodynamic research — the DrivAer body — is proposed. This paper focuses on the development of the model, summarizes first experimental results of the different configurations of the fastback geometry and compares them to numerical simulations performed using the open source software OpenFOAM®.
High Speed PIV Measurement of Impinging Flow on a Horizontal Axis Wind Turbine
Authors: Hu J. Stephen , Sheng Jian , Guala Michele , Chamorro Leonardo
Published: July 2013

The focus of this paper is to characterize the upstream wake of a three bladed Horizontal Axis Wind Turbine (HAWT) and its interaction with the native structures within a turbulent boundary layer (TBL). The overarching question is the most prevailing length and time scales of coherent structures that would interact with a HAWT and how they would be affected. The implications include wall flow and structure interaction and flow induced noise generation in large scale turbo machineries. The experiments are performed on a turbine that has a 0.128 m rotor diameter, a hub height of 0.104 m and a tip speed ratio of 4. The HAWT model is placed in a large scale wind tunnel in a boundary layer with a thickness δ of ∼0.6 m. The boundary layer is generated by a 60 mm picket fence trip and developed over a smooth wall under thermally neutral conditions. Measurements are performed under ReD of 4 × 105 and 6 × 105. Both turbine geometries and flow conditions are scaled from operating conditions in the field. High speed Particle Image Velocimetry (PIV), turbine voltage output, and angular velocity measurements are conducted simultaneously, by which one could relate the upwind flow structures with the power output of the turbine. High speed PIV offer details in spatial and temporal characteristics of the impinging flow structures, whilst the voltage anemometer and tachometer provide instantaneous measurement of angular velocity of the turbine. PIV measurements are taken at a rate of 1500 image pairs per second with a 100 μs delay between laser pulses. Each sample area is 0.15 × 0.15 cm. Two locations up to two rotor diameters upwind are measured. Instantaneous voltage is taken at a sampling rate of 30 kHz and a sampling time of 60s to ensure sufficient temporal resolution and coverage. Ongoing analysis using conditional averaging based on extreme power output events will provide insights in assessing a HAWT performance in unsteady flow conditions.
Relative Performance of Body-Fitted and Fictitious Domain Simulations of Flow Through Porous Media
Authors: Finn Justin R. , Apte Sourabh V.
Published: July 2013

The relative performance of (i) a body-fitted unstructured grid Navier-Stokes solver [Moin and Apte, AIAA J. 2006], and (ii) a fictitious domain based finite-volume approach [Apte et al. JCP 2009] is examined for simulating flow through packed beds of spheres at moderate flow rates, 50 ≲ Re ≲ 1300. The latter employs non-body conforming Cartesian grids and enforces the no-slip conditions on the pore boundaries implicitly through a rigidity constraint force. At these flow rates, fluid inertia can result in complex steady and unsteady pore scale flow features that influence macro-scale properties. We examine the requirements on both methods to properly capture these features in both simple and complex arrangements of spheres. First, two prototypical test cases of flow through packed beds are studied thoroughly at a range of Reynolds numbers in the inertial flow regime. Next flow through a random packing of 51 spheres at Re = 1322 is simulated using both methods. The suitability of both approaches to the complex configurations observed in large randomly packed beds is discussed.
Population Balance Modeling for Non-Homogeneous Bubble Column: Effect of Fluid Rheology on Gas Dispersion
Authors: Niazi Erfan , Shams Mehrzad , Ahmadi Goodarz
Published: July 2013

This work describes the development of a two-dimensional CFD model for gas-liquid flows in a bubble column. Population balance dynamic equation is solved for babbles including bubbles coalescence and break up in the column. Prince and Blanch model for bubbles coalescence extended to non-Newtonian rheology and used in the analysis. Luo and Svendsen model is used for bubbles breakup modeling and the k-e model equations are solved for analysis of primary fluid turbulence. Solutions of carboxy methyl cellulose in water with different concentrations are used as a non-Newtonian pesudoplastic liquid. Raise velocity of bubbles, which play an important role in population balance modeling, is discusses in details for non-Newtonian fluid. As a first step the results for Newtonian bubble column are presented and verified by comparison with the previous studies. Then the effect of changing fluid rheology is discussed in terms of gas volume fraction and continuous liquid velocity.
Experimental Study on Aero-Acoustic Characteristics of a Centrifugal Compressor and an Optimal Design for Noise Reduction
Authors: Ha Kyoung Ku , Jeong Tae Bin , Kang Shin Hyoung
Published: July 2013

A centrifugal compressor for fuel-cell vehicles, which makes compressed air and sends it to the fuel-cell stack, is investigated in this paper. It is the only part of revolution in the system, and it consumes most of the system power. Therefore, it is important to achieve low noise level as well as high efficiency. The operating line of this compressor is determined along the highest efficiency points and during the design-point operation the blade tone noise is the main contributor. It is widely known that the blade passing frequency (BPF) noise components is due to the circumferential flow fluctuations of the impeller. So the noise spectrum of this compressor needs to be examined closely. So, an experimental study is designed to investigate the aero-acoustic characteristics of a centrifugal compressor in detail. The existing system is modified to allow pressure measurements at the inlet and outlet of the impeller. Four microphone probes are also installed to determine the noise level in an isolated room. Tests are carried out to investigate the phenomena governing the tonal noise and the dominant noise source of the centrifugal compressor. With such information on noise, a design optimization process is carried out to determine a superior design point which will guarantee good performance and low noise level at the design point. The optimization is performed using the surrogate management framework with the simulated results obtained at sampled points. The final optimal design point and the comparison between the optimal designed compressor and the existing centrifugal compressor are described in the last section of this paper.
Development of a Hybrid Empirical-Analytical Method to Predict Adiabatic Flow Properties in Capillary Tubes
Authors: Abbasi Bahman , Kempiak Michael , Junge Brent
Published: July 2013

Capillary tubes have been used in household refrigerators and other cooling systems for several decades. Complicated geometry, inevitable manufacturing variations, and complex two-phase phenomena have been major prohibitory factors in the development of reliable and efficient modeling tools to analyze the flow properties inside capillary tubes. Friction factor correlations as are available in the open literature (as examined by the authors) unanimously fail to give accurate analysis of the refrigerant flow. The delicate operation of a capillary tube makes experimentation cumbersome, time and cost intensive, and prone to errors. The present study introduces a method to utilize the data from a standard Nitrogen flow test for a given capillary tube to develop a model specific to that tube which can predict the refrigerant flow properties through the tube at any desired spatial resolution, inlet state, and flow rate. Thereby, exploratory studies and capillary tube modifications for the purpose of system optimization can be greatly simplified.
New Approaches to Improve the Uniformity of the Radial Solids Concentration Distribution in CFB Risers
Authors: Peng B. , Zhang C. , Zhu J.
Published: July 2013

The so-called core-annulus structure, that is, lower solids concentration in the center region and higher solids concentration in the near wall region along the circulating fluidized beds (CFB) riser, usually has a negative effect on the performance of CFB risers since it may greatly decrease the reactor efficiency and controllability. In order to improve the performance of industrial CFB risers, two potential approaches are proposed in this study: (1) the use of the center-sparse side-dense air jets arrangement for the gas distributor and the side-covered arrangement for the solids distributor and (2) the use of the air jet from the riser circumference. The results show that the patterns of the inlet gas distributor and solids distributor have significant effect on the flow structure in both the entrance region and the fully-developed region in the riser. The gas distributor with center-sparse side-dense air jet arrangement improves the uniformity of the radial solids distribution, while the center-dense side-sparse air jet arrangement steepens the non-uniformity of the solids radial profile. The core-annulus structure can also be greatly flattened by applying a side-covered solids distributor, while it can be heavily steepened by employing the center-covered solids distributor. The results also show that by employing the circumferential air jet approach under appropriate jet velocities, the maximum solids concentration in the near wall region can be greatly reduced, the entrance region can be shortened, and the uniformity of the flow structure can be greatly improved.
Forecasting Reactant Ignition in Solid Oxide Fuel Cell Systems
Authors: Ardis Paul A. , Nenadic Nenad G. , Walluk Mark R. , Smith Daniel F.
Published: July 2013

Solid oxide fuel cell electrochemical stacks require high quality reformate for performance and durability. Insufficiently mixed reactants, carbon deposits, or improper chemical ratios thereof can result in reactant ignition during mixing prior to catalysis. Reactant ignition can warp and plug downstream components; therefore, it is desirable to predict and mitigate reactant ignition. Leading machine learning techniques were applied to the task of predicting ignition events in prototype (diesel-fueled) solid oxide fuel cells at a 30-second event horizon, using both current signal state and up to 30 seconds of signal history to make predictions. Based upon our analysis, first-order particle filtering using Fisher discriminant meta-reasoning provided the best cross-system performance when compared to other meta-reasoning methods (e.g., logistic regression, kernel support vector machine) as well as traditional vector quantization. In this paper, we demonstrate particle filter construction using data from eleven sensors, analyze predictive performance on real-world data, and discuss modifications to handle further system design changes.
Recent Advances in High Temperature Electrolysis at Idaho National Laboratory: Stack Tests
Authors: Zhang Xiaoyu , O’Brien James E. , O’Brien Robert C. , Hartvigsen Joseph J. , Tao Greg , Petigny Nathalie
Published: July 2013

High temperature steam electrolysis is a promising technology for efficiently sustainable large-scale hydrogen production. Solid oxide electrolysis cells (SOECs) are able to utilize high temperature heat and electric power from advanced high-temperature nuclear reactors or renewable sources to generate carbon-free hydrogen at large scale. However, long term durability of SOECs needs to be improved significantly before commercialization of this technology. A degradation rate of 1%/khr or lower is proposed as a threshold value for commercialization of this technology. Solid oxide electrolysis stack tests have been conducted at Idaho National Laboratory to demonstrate recent improvements in long-term durability of SOECs. Electrolyte-supported and electrode-supported SOEC stacks were provided by Ceramatec Inc., Materials and Systems Research Inc. (MSRI), and Saint Gobain Advanced Materials (St. Gobain), respectively for these tests. Long-term durability tests were generally operated for a duration of 1000 hours or more. Stack tests based on technologies developed at Ceramatec and MSRI have shown significant improvement in durability in the electrolysis mode. Long-term degradation rates of 3.2%/khr and 4.6%/khr were observed for MSRI and Ceramatec stacks, respectively. One recent Ceramatec stack even showed negative degradation (performance improvement) over 1900 hours of operation. A three-cell short stack provided by St. Gobain, however, showed rapid degradation in the electrolysis mode. Optimizations of electrode materials, interconnect coatings, and electrolyte-electrode interface microstructures contribute to better durability of SOEC stacks.
Temperature Sensitivity Analysis of Electrochemical Impedance Spectroscopy Results in PEM Fuel Cells
Authors: Rezaei Niya Seyed Mohammad , Hoorfar Mina
Published: July 2013

The proton exchange membrane fuel cell (PEMFC) is a promising substitute for classic energy converter machines. However, there are still concerns regarding reliability and durability of PEMFCs, and hence, various modeling methods have been employed. One of the effective methods used for analysis and diagnosis of the fuel cell and other electrochemistry systems is Electrochemical Impedance Spectroscopy (EIS) which has been well established due to its high speed and precision. In this paper, the temperature sensitivity of the EIS results at different current densities obtained for a high temperature PEMFC are studied using electrochemical impedances reported in the literature. The magnitude of different elements in the proposed equivalent circuit for different temperatures and current densities, and root mean squares of deviation of various measurements are extracted. Then, the significance of the variations for different temperatures is examined via t-test. Finally, the minimum temperature change at different currents that can be captured by EIS is determined considering the root mean squares of measured values.
A Solid Oxide Fuel Cell Radiation Model for the Mitigation of Temperature Gradients Using a Novel Geometric Design
Authors: Ong Katherine M. , Tibavinsky Ivan A. , Wepfer William J. , Haynes Comas L.
Published: July 2013

Solid oxide fuel cell (SOFC) systems possess the capability for highly-efficient power production at a low level of emissions. However, these fragile, high-temperature cells are prone to thermal failure, which shortens their life-span and hinders their marketability. Thermal radiation has proven itself effective at mitigating temperature gradients, and preventing thermal failure, in tubular SOFC stacks. However, the conventional planar SOFC design does not allow for sufficient radiation exchange inside the gas channels to have a significant impact on temperature gradients. For the purpose of investigating unconventional planar SOFC designs that would optimize radiation exchange, a 1-D radiation model was developed. This model focuses on the radiation exchange within the flow channels of an SOFC, and resolves a radiation profile based on the current temperature profile of the cell. This radiation model was integrated into a 1-D, planar SOFC Matlab-Simulink™ model developed for the HyPer fuel cell/gas turbine facility at NETL in Morgantown, WV. This paper describes the development of this radiation model, and verifies the model outputs against those of another SOFC radiation model. The model presented is designed to characterize SOFC operation over a broad range of geometric settings and operating parameters in order to determine the optimal conditions for radiation exchange. The capability of this model to characterize SOFC operation, for conventional and unconventional geometric designs, is presented and analyzed.