bluuebunny/crossref_metadata_2025 huggingface dataset:
Performance Analysis of Photovoltaic Panels Using Tracking, Concentration and Cooling in Alabama Area
Authors: Najafi Hamidreza , Woodbury Keith
Published: July 2013

Using photovoltaic panels in the southeast Unites States has been judged less attractive than in other parts of the country owing to the humid climate and numerous cloudy days. Nowadays, use of lenses or mirrors to concentrate sunlight on PV cells can multiply the direct incident sunlight on the cells leading to higher power output and better conversion efficiency. In the present paper, the annual performance of a photovoltaic panel located in Alabama is investigated. A computer simulation via MATLAB is carried out by using typical meteorological data for Alabama in order to accurately model the behavior of the system. The effect of using fixed optimal tilt and single-or double-axis tracking methods on incident solar irradiation on the PV panel is presented. The power generated by the system under different levels of concentration during the year is discussed and the effect of cooling is also investigated. Comparison graphs are presented in order to demonstrate the effect of tracking, concentration and cooling on the output power and conversion efficiency of the PV panel. The result of this paper can be utilized to select the most appropriate system regarding the application and available funding of the project in Alabama area.
Long Term Performance of the SkyTrough Solar Concentrator
Authors: White David , Mason Alison , Clark Ryan
Published: July 2013

The SkyTrough is an advanced integrated parabolic trough concentrator designed for high performance and low cost to achieve economic objectives in the market for high grade heat for industrial processes and electrical generation. To achieve low cost, a comprehensive optimization process was carried out for every component based on the choice of low cost silvered polymer film as the reflector. To verify high performance, the optical efficiency of a single module was measured at the National Renewable Energy Lab (NREL), and a demonstration loop was constructed in December, 2009 at the SEGS-II solar power plant in Daggett, CA, USA. This paper compares operating data recorded over eighteen months for the commercial demonstration at the SEGS-II plant with model predictions based on the NREL efficiency measurement. The comparison demonstrates that the SkyTrough system will perform predictably over time. Additional data illustrating the good performance of the collector in wind, and the sustained reflectance of the mirror film, are presented.
Energy Impacts of Nonlinear Behavior of PCM When Applied Into Building Envelope
Authors: Tabares-Velasco Paulo Cesar
Published: July 2013

Research on phase change materials (PCM) as a potential technology to reduce peak loads and HVAC energy use in buildings has been conducted for several decades, resulting in a great deal of literature on PCM properties, temperature, and peak reduction potential. However, there are few building energy simulation programs that include PCM modeling features, and very few of these have been validated. Additionally, there is no previous research that indicates the level of accuracy when modeling PCMs from a building energy simulation perspective. This study analyzes the effects a nonlinear enthalpy profile has on thermal performance and expected energy benefits for PCM-enhanced insulation. The impact of accurately modeling realistic, nonlinear enthalpy profiles for PCMs versus simpler profiles is analyzed based on peak load reduction and energy savings using the Conduction Finite Difference (CondFD) algorithm in EnergyPlus. The PCM and CondFD models used in this study have been previously validated after intensive verification and validation done at the National Renewable Energy Laboratory. Overall, the results of this study show annual energy savings are not very sensitive to the linearization of enthalpy curve. However, hourly analysis shows that if simpler linear profiles are used, users should try to specify a melting range covering roughly 80% of the latent heat, otherwise, hourly results can differ by up to 20%.
Minimization of the Total Area of Heat Exchangers in Refrigeration Systems Based on the Entransy Theory
Authors: Chen Qun , Xu Yun-Chao
Published: July 2013

In order to reduce the consumption of energy and material, the optimization design of the refrigeration systems, especially the minimization for the total area of the heat exchangers, has been an attractive but tough issue in both research and engineering fields. Therefore, the entransy dissipation theory is introduced in this article to analyze the refrigeration systems. The systems are analyzed through the entransy dissipation analysis for the irreversible heat transfer processes in the heat exchangers and the thermodynamic analysis for the compressors and expanders, which are combined to deduce the mathematical relation between the known conditions, i.e. inlet temperatures of fluids, the heat absorbed from the cold end of the systems, and the design parameters, i.e. the heat conductances of heat exchangers and heat capacity rates of working fluids. Based on the relation, the optimization design for the refrigeration systems is converted to the conditional extremum problem that offers the optimization equations group. Solving the equations yields the optimal configuration of all the design parameters. Then a typical refrigeration system is numerically optimized to obtain the optimal configuration, optimal compression ratio and the minimum for the total area of heat exchangers, which is proved to be the least through the comparison with other configuration of the design parameters.
Dynamic Performance of Solar PCM Thermal Storage System
Authors: Aldoss Taha
Published: July 2013

The dynamic performance of a PCM thermal storage system is investigated. The most affecting parameters on the system performance are the type and properties of PCM material, and the heat transfer fluid (HTF) inlet temperature. The time variant solar collector discharge temperature and that from the heating/cooling coils due to space load variation results in time dependent HTF inlet temperature. This paper is to study the behavior of the PCM thermal storage system under such time dependent HTF inlet temperature operating condition. A simple one dimensional model were used and solved numerically using the finite difference technique. To assure stability of solution the right time step and element size were applied. A MATLAB Program is formulated and used to solve the result system of equations. Results are presented in terms of the storage tank fluid temperature profiles, effectiveness of PCM usage and capacity of the storage system. The above were calculated for the cases of constant and a time-dependent HTF inlet temperature conditions for comparison. The performance of the PCM storage system is found to be substantially different for the above two mode of operation.
Scale Adaptive Simulation of Flows Past an Airfoil After Stall
Authors: Du Lei , Ning Fangfei
Published: July 2013

The Scale Adaptive Simulation (SAS) models can keep standard RANS capabilities in stable flow regions but resolve turbulent structures in unsteady regions of flow field like LES. This RANS/LES property of SAS model relies on the v. Karman length-scale as a scale determining variable, which allows the model to automatically adapt to the appropriate length-scales in the simulated flows. Although SAS is young and still in developing, it has been proved to be very suitable for the predictions of massive separation flows. In the current study, the SST-SAS model is implemented in an in-house CFD code. First, the test case of decaying homogenous isotropic turbulence is selected for calibrating a constant associated with high wave number damping. Then, the simulation of flow past NACA 0021 airfoil at 60° attack angle is carried out for the validation of this turbulence model in our code. After that, the numerical results of NACA 0021 airfoil at a range of attack angles after stall are also presented for the comprehensive understanding of the SAS model.
Effect of Artificial Perturbation on Unsteady Wake Vortices in Jets in Cross-Flow
Authors: Milanovic Ivana , Zaman Khairul B. M. Q. , Bencic Timothy J.
Published: July 2013

The current experimental study investigated unsteady wake vortices of jets in cross-flow in order to explore the possibility of periodic perturbation of these vortices with the method of oscillating tabs. Two triangular tabs were placed at the 90° and 270° edges of the jet orifice relative to the direction of the cross-flow. An isolated circular jet passed through a nozzle and entered the cross-flow normal to the wall. Free stream velocities up to 4.1 m/s and jet-to-cross-flow velocity ratio range between 3 and 12 were covered. Strouhal number (fpD/Ucf) for excitation cases was about 0.19. The oscillation frequency was somewhat higher than the ‘preferred’ frequency of the wake vortices. The smoke flow visualizations did not indicate an organization of wake vortices. Artificial excitation simply tilted the jet cross section from side to side in sync with the tab oscillation.
Acoustic Field Effects on Minimum Fluidization Velocity in a 3D Fluidized Bed
Authors: Escudero David R. , Heindel Theodore J.
Published: July 2013

Fluidized beds are used in a variety of process industries because they provide uniform temperature distributions, low pressure drops, and high heat/mass rates. Minimum fluidization velocity is an important factor in understanding the hydrodynamic behavior of fluidized beds, and this characteristic may be modified through high frequency (sound) vibrations. The effects caused by sound wave frequency on the minimum fluidization velocity in a 3D fluidized bed are investigated in this study. Experiments are carried out in a 10.2 cm ID cold flow fluidized bed filled with glass beads with material density of 2600 kg/m3, and particles sizes ranging between 212–600 μm. In this study, four different bed height-to-diameter ratios are examined: H/D = 0.5, 1, 1.5, and 2. Moreover, the sound frequency of the loudspeaker used as the acoustic source ranges between 50–200 Hz, with a sound pressure level fixed at 110 dB. Results show that the minimum fluidization velocity is influenced by the frequency change. As the frequency increases, the minimum fluidization velocity decreases until a specific frequency is reached, beyond which the minimum fluidization velocity increases. Thus, acoustic fields provide an improvement in the ease of fluidization of these particles.
Numerical Simulation in Turbine Mode of Counter-Rotating Type Axial Flow Pump (Preparation of Pump-Turbine Unit in Cooperation With Wind Power Unit)
Authors: Murakami Tengen , Kanemoto Toshiaki , Takano Gohki , Kasahara Risa
Published: July 2013

Pumped storage system contributes to adjust the electric power unbalance between day and night, in general. The pumping operation, however, may be unstable in the rising portion of the head characteristics, and/or bring the cavitation at the low suction head. To simultaneously overcome both weak points, the authors have proposed a superior pumping unit that is composed of counter-rotating type impellers and a peculiar motor with double rotational armatures. This paper discusses the operation at the turbine mode of the above unit. It is concluded with the numerical simulations that this type unit can be also operated acceptably at the turbine mode, because the unit works so as to coincide the angular momentum change through the front runners/impellers with that thorough the rear runners/impellers, namely to take the axial flow at not only the inlet but also the outlet without the guide vanes.
Study of Transient Behavior in Centrifugal Pump During Startup Period
Authors: Zhang Yu-liang , Zhu Zu-chao , Cui Bao-ling , Li Yi
Published: July 2013

To explore the transient characteristic of a centrifugal pump with the specific speed of 90 during startup period, the internal three-dimensional unsteady flow was solved by using CFD. Wherein to overcome the difficulty in implement of boundary conditions in numerical simulation, a closed-loop pipe system that includes a centrifugal pump was built to accomplish self-coupling calculation. The results show that at the very beginning of startup, flow rate rises slowly and non-dimensional head coefficient is much higher than quasi-steady value, the quasi-assumption can not be competent for predicting transient effect well. Moreover, the insufficient of energy conversion makes the evolvement of transient flow field lags behind that of quasi-steady flow field, i.e., kinetic energy can’t convert pressure energy in time during acceleration flow period. Rotor-stator interaction makes flow rate present slight fluctuation characteristic under stable operating conditions.
Low Reynolds Number Open Channel Flows Over a Backward Facing Step
Authors: Ampadu-Mintah Afua A. , Tachie Mark F.
Published: July 2013

Low Reynolds number effects on turbulent flows over a backward facing step (BFS) in an open channel were investigated. The Reynolds numbers based on momentum thickness (θ) and step height (h) are in the range 590 ≤ Reθ ≤ 1950 and 950 ≤ Reh ≤ 2900, respectively. The Froude number based on the approach water depth and freestream velocity varied from 0.12 to 0.37. A particle image velocimetry technique was used to measure the velocity field. The flow patterns in the reattachment and redevelopment regions are qualitatively similar for all the three Reynolds numbers studied. The mean velocity profiles in outer coordinates do not exhibit significant Reynolds number effects downstream of the BFS. On the contrary, the turbulence intensities and Reynolds shear stress do not show Reynolds number similarity. As expected, similarity with the upstream profile improves with increasing streamwise distance from the reattachment point. Data obtained in this study were also compared with previous measurements made over backward facing step in a closed channel to study free surface effects. The results showed that deviation of flow over BFS in open channel from flow over BFS in a closed channel is more significant in the immediate vicinity of the step.
Mono-Disperse Spray Generation by a Flow Focusing Atomizer: A Numerical Study
Authors: Samareh Babak , Kashani Arash , Mostaghimi Javad
Published: July 2013

Pneumatic flow focusing technology is a relatively new atomizing process first introduced in 1998. A liquid microjet is formed by a high speed co-flowing gas stream when a pressure drop is applied across an orifice. The microjet eventually disintegrates into fine droplets by the perturbing gas downstream of the atomizer exit. Under certain controlled flow regimes the resulting spray demonstrates strong monodispersity. In the present study, the gas flow is numerically modeled by a compressible turbulent flow solver and the liquid jet evolution is captured using Volume of Fluid (VOF) interface tracking method. Jet breakup parameters and drop size distribution are studied for different liquids and flow rates. Results are in good agreement with experiments and theoretical models.
Pulsatile Non-Newtonian Flow in a Three-Stream Coaxial Airblast Injector
Authors: Strasser Wayne
Published: July 2013

Previously published efforts regarding the unsteady nature of a self-exciting air/water (AW) coaxial three-stream airblast injector considered first the effects of feed stream flow rate changes and then the effects of nozzle geometric permutations. Frequency domain analysis, automated video analysis, and spray profile assessments were used to draw conclusions about spray quality and character. The computational method was validated using an AW test stand (AWTS). Here, the focus of the work shifts to the use of slurry and a high-density gas (SH). Again, the effects of flow rate and nozzle geometry are considered. It was found that the nature of the SH flow changed dramatically in comparison with its AW counterpart. As a result, the video analysis technique had to be revamped, and therefore direct comparisons are limited. As with its AW counterpart, inner nozzle retraction and stream meeting angle proved to be the most influential geometry variables. A flushed nozzle showed a wider spray with a strongly trimodal character. Increasing the relative inner gas flow rate had a pronounced, but mixed, effect on the considered metrics. In general, the transient signatures of the pressure and video analysis metrics were similar enough to indicate that the unsteady driving mechanisms were consistent for each. Lastly, attempts to further stimulate the spray via modulating the inner gas proved futile for both sets of flowing materials for the measures considered.
DNS Studies of Turbulent Bubbly Flows in Vertical Channels
Authors: Tryggvason Gretar , Dabiri Sadegh , Lu Jiacai
Published: July 2013

Recent results from direct numerical simulations of deformable bubbles in turbulent flows in vertical channels are discussed. The results show that the lateral migration of the bubbles due to lift forces controls the flow. For upflow, nearly spherical bubbles form a dense bubbly wall-layer but more deformable bubbles stay away from the walls, resulting in very different flow structures and flow rates. The different flow regimes have a very simple structure, but to understand them it is necessary to examine the collective motion of many bubbles rather than individual ones. Here, the effect of bubble deformability and Reynolds number are discussed.
Coupling of 1-D and 2-D Hydrodynamic Models Using an Immersed-Boundary Method
Authors: Zhang Ning , Li Puxuan , He Anpeng
Published: July 2013

Numerical simulations of flooding events through rivers and channels require coupling between 1-D and 2-D hydrodynamic models. The rivers and channels are relatively narrow and the widths are smaller than the grid resolution of the 2-D model. The shapes of the rivers and channels are complex and do not necessarily coincide with the grid points. The coupling between the 1-D and 2-D models are challenging. In this paper, a novel Immersed-Boundary (IB) type coupling is implemented. Using this method, no linkpoint needs to be manually determined, nor does the discharge boundary conditions need to be specified on the linkpoints. The linkpoints will be dynamically determined by comparing the water levels in the 1-D channel and the surrounding dry cell elevations in the 2-D model. The linkpoint flow conditions thus can be dynamically calculated by the IB type of implementation. This coupling method enables more realistic simulations of water exchange between channels and dry lands during a flooding event comparing to the traditional coupling method.
Droplet Impact: A GPU Based Smoothed Particle Hydrodynamics (SPH) Approach
Authors: Farrokhpanah Amirsaman , Samareh Babak , Mostaghimi Javad
Published: July 2013

A parallel GPU compatible Lagrangian mesh free particle solver for multiphase fluid flow based on Smoothed Particle Hydrodynamics (SPH) scheme is developed and used to capture the interface evolution during droplet impact. To solve Navier-Stokes equations, the computational domain is discretized using fluid particles. Surface tension is modeled employing the multiphase scheme of Hu et al. In order to precisely simulate the wetting phenomena, a method based on the work of Šikalo et al. is used and compared to ensure accurate dynamic contact angle calculation. Using this method, accurate perditions were obtained for droplet contact angle during equilibrium and spreading. A simple analytical model is developed to predict maximum droplet spread diameter after impact. Solver predictions agreed well to analytical results. To improve stability and performance of the solver, a customized reduction algorithm is used on the shared memory of GPU. Speedup using a variety of different memory management algorithms on GPU-CPU is studied. The proposed algorithm is validated using the Rayleigh-Taylor instability test. Droplet impact simulations are compared side by side against a Volume of Fluid (VOF) solver to ensure accuracy and robustness. GPU speed ups of up to 120 times faster than a single processor CPU were obtained. Variations of droplet spread factor and recoil height during the impact are shown to be in good agreement with experimental results.
Optical Measurement of the Internal Geometry of a CFD Validation Experiment
Authors: Jones Kyle L. , Nani David , Smith Barton L.
Published: July 2013

Computational Fluid Dynamics (CFD) validation experiments require careful documentation of the boundary conditions. Many validation experiments contain complex geometries or facilities that are not accesible for meaurement using calipers. This paper describes a method for providing accurate optical measurement of physical geometries using an Nd:YAG laser, a CCD camera, and two 1-dimensional traverses. The facility used is a cylinder array test section. The laser sheet is aligned perpendicular to the cylinder span and the camera is aligned parallel to the cylinders.

After images were acquired, a code was written to analyze the images based on the Gaussian-like intensity profiles of the illuminated cylinder edges and walls in the facility. The peaks were extracted and a least squares fit applied to the peaks resulting in the center coordinates and diameter of the cross-sections. These were then reconstructed into a surface which can be imported into a CFD simulation package. This study shows that the cylinder diameters and x- and y-coordinates can be determined accurately.

The effects of various surface finishes are also compared. Three finishes were used: transparent, painted flat black, and a rhodamine painted surface with an appropriate band pass filter. The intensity profiles were compared using a single laser power setting.
Vertical Migration of the Small Organisms in a Stratified Fluid
Authors: Doostmohammadi Amin , Ardekani Arezoo M.
Published: July 2013

Significant progress has been made in analyzing low-Reynolds number locomotion in homogeneous fluids. Even though density interfaces due to temperature or salinity gradients (pycnoclines), ubiquitously occur in oceans and lakes, the effects of stratification on the hydrodynamics of swimming of small organisms, their interaction with each other and their migration are very poorly understood. In this article, we implement a direct numerical simulation of the migration of swimmers at pycnoclines and illustrate the role of the diffusivity of the stratified agent on the swimming of small organisms. We demonstrate that for an archetypal swimmer model, squirmer, the migration at density stratified fluid can be largely influenced by buoyancy effects. We also show that the effects of density stratification are increased as the diffusivitty of the stratified agent is reduced. The results demonstrate that the stratification suppresses the vertical migration and consequently affects the life of low Reynolds number swimmers across pycnoclines. Our recent computational results reveal the full nonlinear effects of stratification on the locomotion of small organisms.
Computational Fluid Dynamics Analysis of Vertical Mixing in Algae Biofuel Raceways Through the Addition of Delta Wings at Angle-of-Incidence
Authors: Godfrey Aaron H. , Spall Robert E. , Wood Byard D.
Published: July 2013

CFD calculations of experimental algae raceways under consideration for biofuel production studies were performed in an effort to assess the effectiveness of delta wing vortex formation as a means of enhancing vertical mixing. The impact of delta wings on the level of turbulence dissipation rate in these raceways was also investigated. All simulations were completed at a constant level of power input into the raceway. Velocity profiles as well as characteristic mixing times were used to analyze and quantify the vertical mixing both with and without delta wings. The velocity profiles and turbulent dissipation rate calculations suggest that delta wings are a viable method of increasing vertical motion. However, the mixing time results for the configuration of delta wings tested suggest that the additional mixing was insignificant to the raceway as a whole. Additional work on optimizing the use of delta wings is suggested.
Numerical Analysis of Pressure Fluctuation in Circulating Water Pump Using CFD
Authors: Dai Cui , Kong Fan-Yu , Dong Liang
Published: July 2013

Pressure fluctuations acting on centrifugal pump contain a lot of dynamic information, such as rotor-stator interaction, vortex, backflow, and so on. By CFD method, calculations of three-dimensional unsteady flow in the suction chamber, impeller, annular chamber, inlet and outlet were conducted with sliding mesh technology. For the simulation of inner flow field, a commercial code Fluent had been used to predict the pulsating pressures. The shear stress transport turbulence model (SST k-ω) was confirmed through comparison with the hydraulic performance experiment. The change of static pressure was recorded by means of virtual sensors placed at the impeller-annular chamber interface and the tongue. And the pulsating pressures in the impeller passage were recorded to reflect its flow state. Then, amplitude domain analysis and frequency domain analysis were conducted to process those fluctuating pressure signals obtained under different opening conditions. The results indicate that the effect of rotor-stator interaction and vortexes to pressure fluctuations in flow field is obvious. The pressure fluctuation around impeller-chamber interface and tongue is affected by the interaction between blade and tongue definitely, and the various positions of the blade relative to the tongue lead to different trends of variation of pressure distribution. The primary source of pressure fluctuation in the impeller passage is associated with vortexes.
Thrust Measurements and Flow Field Analysis of a Piezoelectrically Actuated Oscillating Cantilever
Authors: Eastman Andrew , Kiefer Jacob , Kimber Mark
Published: July 2013

Although not identical to the motion employed by nature’s swimmers and flyers, the simple harmonic oscillations of cantilever-like structures have been shown to provide efficient low power solutions for applications ranging from thermal management to propulsion. However, in order to quantify their true potential, the resulting flow field and corresponding thrust must be better understood. In this work, a thin, flexible cantilever is actuated via a piezoelectric patch mounted near its base and caused to vibrate in its first resonance mode in air. The flow field is experimentally measured with Particle Image Velocimetry while the thrust produced from the oscillatory motion is quantified using a high resolution scale. The trends observed in the data are captured using an oscillating Reynolds number and a clear relationship is defined between the operating parameters and the resulting thrust. Two dimensional flow fields are extracted from the x-y and y-z planes, and are primarily used to motivate future geometry and sidewall configurations that could greatly enhance the thrust capabilities of the cantilever by directing the flow downstream in a more effective manner.
Investigation of Multiphase Unsteady Flow in a Double-Channel Pump by CFD Simulation and PIV Measurement
Authors: Zhao Binjuan , Yuan Shouqi , Huang Zhongfu , Hou Duohua
Published: July 2013

The multiphase unsteady flow fields in a double-channel pump have been investigated both numerically and experimentally for the design condition and also off-design conditions. Three-dimensional, unsteady Reynolds-averaged Navier–Stokes equations are solved on high-quality unstructured tetrahedral mesh with the shear stress transport turbulence model by using the CFD code Fluent 6.4. Furthermore, PIV measurements are successfully conducted in the impeller, in order to capture the complex flow with abundant measurement data and to validate the CFD results. The main conclusions include: 1) The velocity field changes according to the blade orientation. When the impeller channel is near to the outlet of volute, the velocity distribution is relatively regular than when the impeller channel is far from the outlet of volute. 2) At the tongue of the volute, the fluid discharged from the impeller mixes with the re-circulating fluid in the volute, which contributes a lot to the impeller-volute interaction. 3) The pressure vibration in the volute is very obvious, pressure fluctuation on monitors far from the volute outlet is more obvious than those near to the volute outlet, and becomes stronger as drawing near the tongue. 4) The sand volume fraction distribution is extremely inhomogeneous in both impeller and volute. Particles mainly flow along the pressure surface and hub of the impeller; Particles mainly accumulate in the region near to the exit of volute, and the largest sand volume fraction is observed at the tongue. 5) Particle diameter has great influence on the particle distribution, and particles tend to accumulate on the pressure surface of the balde with the increase of particle diameter. 6) The total pressure difference of the pump declines with the increase of inlet sandy volume fraction or particle diameter. 7) PIV measurement results correspond well with the CFD simulation results, which in turn gives a good validation of the simulation accuracy. This work offers a good data set to develop the comprehension of the unsteady multiphase flow in the double-channel pump.
Effect of Low Reynolds Number Mixed Convection on Channel Flows Structure
Authors: Elatar Ahmed , Siddiqui Kamran
Published: July 2013

The effect of wall heating on low Reynolds numbers channel flow has been investigated experimentally. The experiments were conducted at heated bottom wall temperatures from 30 °C to 50 °C for two flow rates 0.0210 and 0.0525 kg/s, corresponding to the Reynolds number range of 150 and 750 (in the absence of heating). The results showed that the initially laminar flow became turbulent due to wall heating, and that wall heating has a significant influence on both the mean and turbulent velocity fields. The mean velocity profiles were altered by the convective currents. The magnitude of mean streamwise velocity near the heated wall increased with an increase in the wall temperature. A back flow near the upper channel wall was also observed primarily at the lower flow rate which diminished for the high flow rate. The magnitude of backflow increased with an increase in the wall temperature. The turbulent intensities were found to increase with an increase in the wall temperature for both flow rates. The result also showed the presence of strong vortices originating from the heated wall and advecting towards the central core of the channel.
Overview of Particle Transport and Deposition in Environmental and Industrial Applications
Authors: Ahmadi Goodarz
Published: July 2013

Overview of particle transport and deposition in flows in environmental and industrial applications was presented. Aerosol transport including particle deposition, removal and re-entrainment in turbulent flows were discussed. The numerical simulation airflow through the Reynolds averaged Navier-Stokes equation was described. The approximate stochastic models for simulation of instantaneous flow were discussed. The Lagrangian particle equation of motion was presented. It was shown that the particle deposition and removal processes in turbulent flows are strongly affected by the near wall flow structures. Wind tunnel studies of particle transport and deposition were also discussed. Examples of computational modeling of gas-solid flows in indoor and out door air were described. It was shown that computational modeling was an efficient tool for studying alternative scenarios. A simulation procedure for pollutant transport through human upper airways was discussed and sample results were presented.
The Influence of Oscillating Jet on the Liquid Jet Gas Pump’s Performance
Authors: Xiang Qingjiang , Wu Yanlan , Li Hong , Yun Qianglong
Published: July 2013

When the liquid jet gas pump was used in gas absorption or jet aeration, there is a characteristic of jet mixing in its inner flow. In order to improve the effect of liquid-gas two phase mixing, an oscillating jet form was put forward and compared with the straight jet form. The oscillating jet was produced by a kind of fluidic element. The range of oscillating frequency was measured by the wall pressure pulsation. Factors which affect the oscillating frequency were analyzed, which mainly considered the change of working pressure and the length of signal pipe. The liquid jet gas pump was vertically installed on test rig, as the model pump’s working performance was experimentally studied. The results showed that the working pressures and the oscillating jet frequencies had great influence on the pump’s performance. When the oscillating frequency of the given model pump was set constant, the approximate linear h∼q performance curves had the close maximal h. When the working pressure was kept constant, the performance curves increased with the oscillating frequencies. As the area ratio of throat to nozzle m increased, the performance curves changed from steep to flat. The pump’s efficiency was low and the causes were analyzed. The study on oscillating liquid jet gas pump’s performance can help to improve the effect of jet mixing in pump and can make the pump to work more efficiently.
Numerical Optimal Design of a Non-Overload Centrifugal Pump
Authors: Hu Bo , Yuan Shouqi , Lu Weigang , Li Tong , Guo Chenxu
Published: July 2013

Shaft power characteristics of centrifugal pumps attract extensive attentions in order to improve the operating reliability of pumps. TS-50-32-250 type low specific speed centrifugal pumps are selected as the research subjects. Three parameters of impeller including blade outlet angle β2, outlet width b2 and wrapping angle of blade θ are selected for the impeller shape optimization. Maximum flow design method and non-overload design method are adopted to design 7 impellers. Numerical simulation with CFX 12.1 is used to reduce the cost and shorten the design period. The time-averaged Navier-Stokes equations of 3D steady flow in the pump are calculated by CFX 12.1 based on the standard k-ε turbulence model together with standard wall function. The structured grids of different qualities are used in unmodified impeller for comparison to confirm that the results are not influenced by the quality of mesh.

The optimal impeller is obtained when β2, b2, θ are 18°, 7mm, 175°, respectively. The performances of NCPs at other working conditions satisfy the requirements of heads and efficiencies obtained from China National Standard. The shaft power reaches to 15 kW which is the power rating of the matched motor, at 1.45QR (35m3/h), showing that the non-overload performance of the pump is also significantly improved after modifying impeller geometries. Impeller 6 is considered as the optimal one and produced for experiments. Experiment results prove that it is effective and reliable to improve a non-overload pump’s performance by maximum flow design method and non-overload pump design method. The results provide a reference for increasing the efficiencies and heads of non-overload pumps at multiple operating conditions.
Hydrodynamics of Multiple Jet Systems in a 2D Gas Solid Fluidized Bed
Authors: Brown Steven L. , Lattimer Brian Y.
Published: July 2013

An experimental 2-D fluidized bed was developed to study gas-solid hydrodynamics. The effects of multiple jet systems were examined using Particle Image Velocimetry (PIV) combined with Digital Image Analysis (DIA). Flow regimes were classified through pressure drop spectral analysis. The combination of these non-intrusive techniques allowed for the development of a solid volume fraction correlation. The experimental results show new void fraction regimes of multiple interacting jets. Jet systems combined to promote gas solid mixing and decrease particle dead zones within the bed. It was determined that the validation of multiple jet Discrete Particle Model simulations cannot be exclusively confirmed from single jet studies.
Passive Control of Flow in an A-Pillar Region in the Presence of Uniform or Turbulent Upstream Flow
Authors: de Moraes Luis F. G. , Sicot Christophe , Paille François , Borée Jacques
Published: July 2013

The flow at the level of A-pillar region is characterized by complex and unsteady three-dimensional separated areas. They are mainly responsible for pressure fluctuations which are the source aerodynamic noises radiated outward or transmitted in the passenger compartment. This noise can make the driver tired and stress the passengers in the cabin. Therefore, one of the technological challenges for ground vehicles is the reduction of noise generated by these aerodynamic sources. At the present time, active control devices are wanted to control the vortex and its interaction with the wall (lateral windows). However, fixed devices can also be installed to a form of passive control which will play on the relative position of the vortex and its dynamics. In the present work, simple geometric devices were installed on the A-pillar strut of a model body to modify the development of the conical vortex and its fluctuating pressure footprint. Two strategies were tested. The first consisted in a narrow plate running along the A-pillar, expected to modify the A-pillar strength and its position relative to the side wall. The second consisted in generating a secondary vortex, intense enough to interact with the main structure. The efficiency of these devices has been tested in the presence of a uniform upstream flow and a turbulent upstream flow. The isotropic and homogeneous turbulent flow was generated using a grid placed in the entry of test section, generating an intensity of 4% and an integral length scale of the magnitude of the A-pillar vortex diameter.

For a uniform upstream flow, it was observed that the simple geometric devices used made the vortex core more energetic and coherent. Moreover, the group of devices acting as a vortex generator was able to very significantly reduce the coefficient of fluctuating pressure. Such an improvement was however not obtained in the presence of upstream turbulence.
Thermodynamic Parameter on Cavitation in Space Inducer
Authors: Yoshida Yoshiki , Kikuta Kengo , Niiyama Kazuki , Watanabe Satoshi
Published: July 2013

Cavitation is physically “a vaporization of liquid” which needs latent heat for phase change. A cavity grows in the liquid, so the latent heat of vaporization can only be supplied by the liquid surrounding the cavity. Thus, the liquid close to the interface region of the cavity is cooled down.

In general, cryogenic liquids are very thermosensitive. For liquid hydrogen and oxygen used in rocket propulsion, the temperature in the cavity, i.e., the vapor pressure in the cavity, is lower than those of the liquid bulk. Thanks to this thermal effect, cavitation in cryogenic liquids is less developed than that in water at room temperature. This thermal effect on cavitation is beneficial in that it improves cavitation performance and alleviates cavitation instability in space inducers.

In previous works, we investigated the relationship between the thermodynamic effect and the cavitation instabilities, e.g., rotating cavitation and cavitation surge, with a focus on the cavity length as an indication of cavitation. In the present work, first, aspects of cavitation in the inducer were observed by direct optical visualization in liquid nitrogen. Second, joint experiments in liquid nitrogen and cold water were conducted on a cavitaing inducer. In nitrogen experiments, operating conditions, i.e., rotational speed and liquid temperature, were varied to determine the cavitation scaling law. Through these experimental results, characteristic times, namely, the transit time for bubble growth and the characteristic thermal time introduced from the thermal property, were investigated as a cavitation thermodynamic parameter. It was found out that the adjustment of cavitation number has a good correlation with the ratio of the transit time and the characteristic thermal time.
Laser Interferometric Determination of Thermal Diffusivity of Transparent Soft Glassy Materials
Authors: Bhandari S. S. , Joshi Y. M. , Muralidhar K.
Published: July 2013

Many soft materials of industrial importance such as pastes, gels, concentrated dispersions and emulsions fail to attain thermodynamic equilibrium over practical time scales due to jamming of constituent entities. Such soft materials, known as soft glassy materials, have very high viscosity and show extremely slow relaxation behavior. In this work heat transport behavior of a model soft glassy material, namely aqueous suspension of laponite is studied. Laponite is synthetic nanoclay with particles of disc-like shape, diameter 25 nm and thickness 1 nm. For concentrations above 1 volume % the aqueous system forms a space filling gel that supports its weight. In the present work, thermal diffusivity of laponite suspension in deionized water is investigated with laser interferometry. A sample is placed in an octagonal cavity comprising fixed copper plates on the top and bottom sides. Initially, the sample is at a uniform temperature. Collimated laser light beam generated from He-Ne laser with 632.8 nm wavelength is passed through the test cell. The interferometer is aligned in the infinite fringe setting, obtained by balancing the refractive index of the laponite suspension against a reference cell filled with glucose solution. At certain time instant (t = 0), the temperature of top surface is increased by 1–3°C. The interference patterns are analyzed to obtain the time dependent temperature field. This data is regressed against the analytical solution of the unsteady heat conduction problem to determine the thermal diffusivity of the solution. Results show a strong dependence of thermal diffusivity on laponite concentration.
Effects of Blade-End Open Ratio on Aerodynamic Performance of Multi-Blade Fan
Authors: Lee Ho Ho , Choi Hang Cheol , Jung Jae Gu , Lee Yoon Pyo , Shin Youhwan , Chung Jin Taek
Published: July 2013

This paper is studied to the performance characteristics and the flow behavior of multi-blade fan according to blade-end open-ratio (k) of near the shroud side. Firstly, the properties related to performance of the fan have been measured in a test rig. In the next, numerical calculations are conducted to explain the complex, three-dimensional flow behavior and performance of the fan using CFX 12.0 commercial code. The validation of numerical results has been performed in comparison with the experimental results. The numerical results provide a comprehensive understanding of the flow behavior inside the fan. By changing the open ratio of blade-end near the shroud side, the flow behavior and inactive zone is respectively different. The separated flows are strongly occurred in a blade passage and the inactive zones are formed near the shroud as k = 0 and 20% cases, relatively. The flow separation and inactive zone reduce fan’s efficiency because they cause internal loss. The best efficiency and flow behavior of the fan is appeared to be at k = 70% case. According to open ratio of blade-end near shroud side, the flow behavior can be changed and the efficiency of a fan can be increasing. The objective of this study is to understand of the complex flow behavior inside the fan and offer guidance for fan designing.
Characterization of the Behavior of Confined Laminar Round Jets
Authors: Landfried D. Tyler , Jana A. , Kimber M. L.
Published: July 2013

Confined laminar fluid jets have many practical applications in industry. Several examples include expansions in pipes and flow of gas into a large plenum. While much consideration has been given experimentally to heat transfer and pressure gradients within the confinement, little attention has been paid to quantify the velocity profiles and transitions between various flow behaviours. Using a finite volume CFD code, OpenFOAM ®, the Navier-Stokes equations were solved for varying expansion ratio, 1/ε = renclosure/rj, and varying Reynolds numbers. In the present analysis, Reynolds number based on the inlet jet diameter is varied from 30 to 70, well within the accepted range for laminar jet behavior. The expansion ratio, 1/ε is varied from 20–200. Of primary focus in the current study are compact correlations for the jet centreline velocity as a function of jet Reynolds number, Rej and expansion ratio. Similar functional dependences for the “linear” decay region of the jet, and the location of the stagnation point on the enclosure wall, are also investigated. These are all important features of the global flow field for the confined jet. Results suggest that initially, the flow characteristics are identical to a free jet. At some downstream location, the presence of the enclosure is felt by the jet and deviations begin to be seen from free jet behavior. This transition region continues until at a sufficiently large downstream location, the flow becomes fully developed, internal Poiseuille flow. In this paper, we analyse these transition regions and offer explanations and practical correlations to successfully predict the important flow physics that occur between free jet behavior and Poiseuille flow. Key dimensionless parameters are identified, the magnitude of which can be used to classify the flow conditions.
A Multi-Objective Optimization for a Centrifugal Fan Impeller
Authors: Lee Yu-Tai , Cooper Paul
Published: July 2013

A reduced-order flow analysis method is developed to predict impeller flow field and impeller performance characteristics for a high-specific-speed centrifugal fan attached with a double-discharge volute. The method is validated by comparing its performance prediction for a baseline fan with measurements. The flow analysis calculation not only predicts impeller flow field, but also generates impeller configurations based on given impeller design parameters. A multi-objective genetic algorithm is also developed and coupled with the reduced-order flow analysis to perform a direct online search of the nominal (deterministic) optimum impeller design envelope. An existing fan serving as the baseline fan was reverse engineered to regenerate its geometry using the current method. The optimization calculations were used to explore design variables including blade inlet and outlet angles, shroud angle and blade leading-edge span as 2, 3 and 4-variable design calculations. The 2-variable prediction concludes that the fan is limited in its performance improvement if only the blade shape is changed, which agrees with early CFD prediction results of the baseline fan. Comparing 3 and 4-variable predictions with the 2-variable predictions, larger ranges of improvement in fan performance are feasible by only considering fan aerodynamics. Furthermore the conflicting nature of design variables with regard to the fan performance improvement is also demonstrated by the prediction results.