bluuebunny/crossref_metadata_2025 huggingface dataset:
Improving the Performance of a Thermal Compressor in a Steam Evaporator via CFD Analysis
Authors: Li Xianchang , Wang Ting , Day Benjanmin
Published: July 2010

Ejectors have been widely used in many applications such as water desalination, steam turbine power generation, refrigeration systems, and chemical plants. The advantage of an ejector system lies in its extremely reliable and stable operation due to the complete absence of moving parts. However, the performance depends on a number of factors, among which the flow channel configuration/arrangement is very critical. A comprehensive study mainly focusing on the sensitivity of performance on the geometric arrangement was conducted in this paper to improve an existing thermal compressor performance in a steam evaporator. The performance is measured by the suction (secondary) flow rate of the primary steam jet from a low-pressure vapor plenum. Numerical simulation is employed to investigate the thermal-flow behavior. It is observed that any downstream resistance will seriously impede the suction flow rate. In addition, the suction rate is found to be sensitive to the location of the jet exit, and there is an optimum location where the jet should be issued. A well-contoured diffuser can increase the suction rate significantly. However, the size of suction opening to the plenum is less important, and a contoured annular passage to guide the entrained flow shows little effect on the overall performance. Based on the numerical results the steam suction rate of the best case in the confinement of the current study is approximately 430% the jet flow rate, while some cases with mediocre design can only produce an entrainment of 24% the jet flow.
Vibration Analysis of Wind Turbine via a Multibody Dynamics Approach
Authors: Duan Shanzhong Shawn
Published: July 2010

In this paper, a lumped model of horizontal axis wind turbines (HAWT) is presented for modal and vibration analysis. Motion modes such as tower fore and aft, tower side to side, blade flap, blade edge, and tower axial torsion are considered. A multibody modeling approach is used to represent the structure and components of a HAWT. A continuous component in wind turbines may be divided as discrete rigid bodies linked by proper types of joints with springs and dampers for couplings. Joints are used to describe the degrees of freedom of the component’s deformation. Springs and dampers are added to accommodate the component’s elastic and plastic properties. For example the tower is modeled as discrete rigid bodies linked by universal joints, which allow three degrees of freedom (DOF) from one torsional and two bending motions of the tower, and torsional springs are added between bodies to accommodate elastic property of the tower. The potential energy of the springs equals to the potential energy of the continuous tower, which may be represented by Timoshenko-beam model. Thus the spring stiffness is calculated based on the potential energy equivalence. Equations of motion of wind turbines are derived via Kane’s dynamical method. Modal and vibration analysis are further carried out based on this lumped multibody model. As a comparison with other approaches such as finite element analysis (FEA) that requires high data storage and long simulation time, this approach may provide a low fidelity simulation model and tool, which is suitable for analysis of dynamic loads, modal, and vibration of wind turbines with respect to fixed and moving references at high computational efficiency and low simulation costs. The approach is also a good candidate for simulating dynamical behaviors of wind turbines and preventing their fatigue failures in time domain.
A Distributional Approach of the Impact Between a Rigid Sphere and an Elastic Beam
Authors: Barbulescu Ion-Horatiu , Barbulescu Ion
Published: July 2010

This paper is a study of the normal impact between a rigid sphere and an elastic beam using the theory of distributions. The governing equation of transverse motion of the beam is firstly stated using the classical mathematical approach. This equation that includes the force of impact is then transposed and solved in the space of distributions using the method given by Tataru. Two cases of different boundary conditions are considered. In the first case, the elastic beam is simply supported at one end and cantilever at the other end. In the second case, the elastic beam is cantilever at both ends. For both cases, the analytical expressions of the normalized eigenfunctions are found with the exact values of the coefficients of normalization. The transverse displacements of the elastic beam are calculated and then represented with time and along the length of the beam. Also, the first derivatives with respect to time (velocities) are calculated and represented. Numerical simulations are performed for the two cases studied.
Numerical Simulations on Turbulent Heat Transfer Characteristics of Supercritical Pressure Fluids
Authors: Nakatsuka Toru , Takase Kazuyuki , Yoshida Hiroyuki , Misawa Takeharu
Published: July 2010

As one of next generation nuclear reactors, development of a supercritical pressure water reactor (SCWR) has been performed. In order to design the SCWR, it is necessary to investigate thermal-hydraulic characteristics in the SCWR core precisely. As for those characteristics, many experimental studies have been conducted from the former in each country using circular tubes, annular channels, and the simulated fuel bundles. An objective of this study is to clarify the prediction accuracy of the turbulent heat transfer characteristics in the supercritical pressure fluids for the SCWR design. From the experimental results of the supercritical pressure fluids flowing upward in a vertical circular tube, it was confirmed that the turbulent heat transfer coefficient suddenly decreases under the high heat flux condition. Although many numerical studies have been done in order to confirm the deterioration of turbulent heat transfer in supercritical pressure fluids, it is important to choose a suitable turbulence model to obtain high prediction accuracy. Then, the present study was performed to investigate numerically the effect of turbulent models on the deteriorated turbulent heat transfer.
Design and Fabrication of a Substrate Integrated Phase Change Thermal Buffer Heat Sink
Authors: Jankowski Nicholas R. , Morgan Brian C. , McCluskey F. Patrick
Published: July 2010

Recent power electronics cooling efforts have shown that bringing the cooling mechanism directly into the device substrate can achieve reduced package thermal resistance and reduced system pumping requirements while maintaining traditional circuit manufacturing processes. At the same time, it has been demonstrated that effective compact methods of managing electronic temperature excursions from brief power surges or other transient events include the use of a solid-liquid phase change material (PCM), but tight integration into the electronics package without degrading overall cooling has proven difficult. Recognizing that such a thermal buffer heat sink (TBHS) would enable lighter weight, more compact cooling hardware for vehicle power electronic modules, the U.S. Army Research Laboratory has developed a method for integrating and assembling a PCM-based TBHS within a power electronics substrate. The TBHS design builds upon both the author’s previous efforts in substrate integrated cooling and design trade studies sponsored by the Department of Energy. By fabricating the PCM cavities alongside the fluidic passages on the backside of a ceramic substrate, the PCM thermal bottleneck can be minimized, and a compact solution can be found. Low fabrication temperature limits imposed by the presence of an integrated PCM can be circumvented by using a room temperature curing silicone bonding layer for assembly. The prototype fabrication plan is presented along with steady and transient thermal models to verify performance of the integrated heatsink. A representative design is shown to have a steady state thermal resistivity of less than 0.4 cm2K/W, with the convective rate of the cooling fluid being the dominant factor. Transient analysis shows peak temperature suppression due to the effect of phase change heat absorption, including a 4°C reduction under a pulsed loading condition.
Innovative Engineering Technology Curriculum Integrated With Web-Based Technology in Robotics, Mechatronics, and E-Quality
Authors: Chiou Richard , Mauk Michael , Danley William , Kizirian Robin , Yang Yueh-Ting , Kwon Yongjin
Published: July 2010

This paper discusses the integration of an innovative engineering technology curriculum with Web-based technology in robotics, mechatronics, and E-quality at Drexel University. The School of Technology and Professional Studies in the Goodwin College has offered a co-op-based Applied Engineering Technology (AET) major since 2002. The program comprises three concentrations in Electrical, Mechanical, and Industrial Engineering Technology and provides an integrated educational experience directed toward developing the ability to apply the knowledge gained in college to the solution of practical problems in engineering technology fields. The majority of courses are fully integrated with training and laboratory experience to provide students with a strong foundation of engineering practices and to stimulate students’ interests by using a problem solving approach in state-of-the-art laboratories. Key efforts in the development process include creation of the Network-based laboratories that can significantly contribute to the development of new courses integrated with the Internet-based technology in robotics, automation, and E-quality. Development of Web-based technology laboratories and capstone courses such as Robotics and Mechatronics, Engineering Quality Methods, Thermodynamics, and Manufacturing Information Management are described in this paper.
Flow Boiling Experiments of R-134A Refrigerant in a Pressurized System
Authors: Murshed S. M. Sohel , Vereen Keon , Kumar Ranganathan
Published: July 2010

This paper reports an experimental investigation of the effect of heat flux and system pressure on bubble nucleation of a refrigerant in a flow boiling environment. A high pressure test loop was built with easy physical and optical access to the test section. The test section is vertical with thermochromic liquid crystal (TLC) applied to the back of the heater for high resolution and accurate surface temperature measurement. Refrigerant R-134 is used as the test fluid at different pressures ranging from 690 to 827 kPa and different heat fluxes to quantify the nucleation process. Two synchronized high resolution and high speed cameras are used to simultaneously capture TLC images as well as bubbling events such as bubble nucleation, growth and departure at high frame rates (up to 1200 fps). In order to use TLC for temperature measurement, hue versus temperature relationship was first established through in-situ calibration. By varying flow rate and inlet temperature, TLC and bubble images were captured and analyzed. Results show that the bubble generation frequency and size increase with heat flux. An increase in pressure of 137 kPa (from 690 to 827 kPa) increased the bubble frequency and size by about 32 Hz and 20 μm respectively.
Wavelet Analysis of the Pressure Fluctuations of Bottom Outlet of Kamal-Saleh Dam
Authors: Liaghat M. , Abdollahi A. , Daneshmand F. , Liaghat T.
Published: July 2010

Non-stationary signals are frequently encountered in a variety of engineering fields. The inability of conventional Fourier analysis to preserve the time dependence and describe the evolutionary spectral characteristics of non-stationary processes requires tools which allow time and frequency localization beyond customary Fourier analysis. The spectral analysis of non-stationary signals cannot describe the local transient features due to averaging over the duration of the signal [1]. The Fourier Transform (FT) and the short time Fourier transform (STFT) have been often used to measure transient phenomena. These techniques yield good information on the frequency content of the transient, but the time at which a particular disturbance in the signal occurred is lost [2, 3]. Wavelets are relatively new analysis tools that are widely being used in signal analysis. In wavelet analysis, the transients are decomposed into a series of wavelet components, each of which is a time-domain signal that covers a specific octave band of frequency. Wavelets do a very good job in detecting the time of the signal, but they give the frequency information in terms of frequency band regions or scales [4]. The main objective of this paper is to use the wavelet transform for analysis of the pressure fluctuations occurred in the bottom-outlet of Kamal-Saleh Dam. The “Kamalsaleh Dam” is located on the “Tire River” in Iran, near the Arak city. The Bottom Outlet of the dam is equipped with service gate and emergency gate. A hydraulic model test is conducted to investigate the dynamic behavior of the service gate of the outlet. The results of the calculations based on the wavelet transform is then compared with those obtained using the traditional Fast Fourier Transform.
Determination of Solid Fraction Evolution During Solidification of Aluminum Alloy in Presence of Linear Electromagnetic Stirring
Authors: Kumar Pramod , Lakshmi Hamsa , Dutta Pradip
Published: July 2010

In many industrial casting processes, knowledge of the solid fraction evolution during the solidification process is a key factor in determining the process parameters such as cooling rate, stirring intensity and in estimating the total solidification time. In the present work, a new method of estimating solid fraction is presented, which is based on calorimetric principles. In this method, the cooling curve data at each point in the melt, along with the thermal boundary conditions, are used to perform energy balance in the mould, from which solid fraction generation during any time interval can be estimated. This method is applied to the case of a rheocasting process, in which Al-Si alloy (A356 alloy) is solidified by stirring in a cylindrical mould placed in the annulus of a linear electromagnetic stirrer. The metal in the mould is simultaneously cooled and stirred to produce a cylindrical billet with non-dendritic globular microstructure. Temperature is measured at key locations in the mould to assess the various heat exchange processes prevalent in the mould and to monitor the solidification rate. The results obtained by energy balance method are compared with those by the conventional procedure of calculating solid fraction using the Schiel equation.
Shooting Method for Good Estimates of the Eigenvalue in the Rayleigh-Be´nard-Marangoni Convection Problem With General Boundary Conditions on Velocity and Temperature
Authors: Siddheshwar P. G. , Revathi B. R.
Published: July 2010

The paper presents a numerical study of Rayleigh-Be´nard-Marangoni convection in a Newtonian liquid that is bounded on the underside by a permeable boundary and on the upperside by a free boundary. General boundary conditions arise in the study on both the velocity and temperature and hence the problem is not amenable to analytical treatment. First the single-term Galerkin technique is used to obtain an estimate of the critical value of the Marangoni and wave numbers as a function of Rayleigh, Darcy and Biot numbers. The estimates are then improved upon by the shooting method which is based on the Runge-Kutta-Fehlberg and Newton-Raphson methods. The results are documented in 4 figures and a table, and some conclusions are made on comparing the present results with those of the classical Rayleigh-Be´nard, Be´nard-Marangoni and Rayleigh-Be´nard-Marangoni convection problems.
Experience With Introducing Robotics Toolbox for MATLAB in a Senior Level Undergraduate Course
Authors: Nagchaudhuri Abhijit
Published: July 2010

While most K-12 students associate the field of “Robotics” with mobile robots, undergraduate and basic graduate level courses in the subject tend to focus on serial link manipulator arms on fixed bases. Senior level “Robotics” course discussed in this paper, emphasize the latter. In the study of serial link manipulator arms, linear algebra, fundamentals of kinematics and dynamics, control systems, trajectory planning, programming languages, robotic sensors (particularly vision) play a dominant role. The abstract mathematical concepts are often difficult for the undergraduate students to fathom. Laboratory demonstration using industrial robotic arms provides some physical insight; however, it is seldom practical to let undergraduate students work on these machines on their own without appropriate supervision. Time constraints associated with credit/contact hours is also a deterrent and a practical reality. A combination of laboratory demonstration and use of software environment such as MATLAB and in particular the “Robotics Toolbox” integrated with the course lectures help convey important ideas related to spatial transformations, forward and inverse kinematics, forward and inverse dynamics, control, robotic vision and programming concepts related to the field of robotics to the undergraduate students in a meaningful framework. The “Robotics Toolbox” allow students to work on simulations of different manipulator arms, as well as create their own. The schematic visualization of the simulations reinforces important concepts covered in course lectures, as well as laboratory demonstration.
Application of the Modified Differential Approximation (MDA) for Radiation Transport to Arbitrary Three-Dimensional Geometry
Authors: Ravishankar Mahesh , Mazumder Sandip
Published: July 2010

The first-order spherical harmonics method (or P1 approximation) has found prolific usage for approximate solution of the radiative transfer equation (RTE) in participating media. However, the accuracy of the P1 approximation deteriorates as the optical thickness of the medium is decreased. The Modified Differential Approximation (MDA) was originally proposed to remove the shortcomings of the P1 approximation in optically thin situations. This article presents algorithms to apply the MDA to arbitrary geometry—in particular, three-dimensional (3D) geometry with obstructions, and inhomogeneous media. The wall-emitted component of the intensity was computed using a combined view-factor and ray-tracing approach. The Helmholtz equation, arising out of the medium-emitted component, was solved using an unstructured finite-volume procedure. The general procedure was validated against benchmark Monte Carlo results. The accuracy of MDA was found to be far superior to the standard P1 approximation in optically thin situations, and comparable to the P1 approximation in optically thick situations. Calculation and storage of the view-factor matrix was found to be a major shortcoming of the MDA, and several strategies to reduce both memory and computational time are discussed and demonstrated. In addition, for inhomogeneous media, calculation of optical distances requires a ray-tracing procedure, which was found to be a bottleneck from a computational efficiency standpoint.
The Effect of the Combustor-Turbine Slot and Mid-Passage Gap on Vane Endwall Heat Transfer
Authors: Lynch Stephen P. , Thole Karen A.
Published: July 2010

Turbine vanes are generally manufactured as single- or double-airfoil sections that are assembled into a full turbine disk. The gaps between the individual sections, as well as a gap between the turbine disk and the combustor upstream, provide leakage paths for relatively higher pressure coolant flows. This leakage is intended to prevent ingestion of the hot combustion flow in the primary gas path. At the vane endwall, this leakage flow can interfere with the complex vortical flow present there, and thus affect the heat transfer to that surface. To determine the effect of leakage flow through the gaps, heat transfer coefficients were measured along a first-stage vane endwall and inside the mid-passage gap for a large-scale cascade with a simulated combustor-turbine interface slot and a mid-passage gap. For increasing combustor-turbine leakage flows, endwall surface heat transfer coefficients showed a slight increase in heat transfer. The presence of the mid-passage gap, however, resulted in high heat transfer near the passage throat where flow is ejected from that gap. Computational simulations indicated that a small vortex created at the gap flow ejection location contributed to the high heat transfer. The measured differences in heat transfer for the various mid-passage gap flowrates tested did not appear to have a significant effect.
High Pressure Fan Design for Biogas Plants
Authors: Epple Philipp , Miclea Mihai , Schmidt Harald , Delgado Antonio , Russwurm Hans
Published: July 2010

High pressure fans for thermal power generation stations, especially biogas plants, usually operate in a spiral casing at high pressures of about p = 12.000–15.000 Pa and low flow rates of around Q = 100–600 m3/s. The motor drive has a constant speed of 3.000 l/min. This corresponds to specific speeds of nq = 3–6 min−1, which is already beyond the conventional range of single stage radial machines. Nowadays these fans for biogas plants usually operate at higher flow rates than specified or are multiple stage radial fans. Therefore a new class of radial impellers has been developed. These single stage impellers have a unique high pressure at a low flow rate operating point. In this work several impellers of this new class have been designed and validated with a commercial Navier-Stokes solver (ANSYS CFX). The design process is described in detail. It is based on a new extended analytical and numerical design method. It is shown that the prescribed unusual operating point can be achieved with single stage radial impellers. An in detail flow analysis is given showing the fundamental flow physics of these impellers.
Dynamics of Pipes Conveying Fluid With a Non-Uniform Velocity Profile
Authors: Hellum Aren M. , Mukherjee Ranjan , Hull Andrew J.
Published: July 2010

Previous work on stability of fluid-conveying cantilever pipes assumed a uniform velocity profile for the conveyed fluid. In real fluid flows, the presence of viscosity leads to a sheared region near the wall. Earlier studies correctly note that viscous forces drop out of the system’s dynamics since the force of fluid shear on the wall is precisely balanced by pressure drop in the conveyed fluid. The effect of shear has therefore not been ignored in these studies. However, a uniform velocity profile assumes that the sheared region is infinitely thin. Prior analysis was extended to account for a fully developed non-uniform profile such as would be encountered in real fluid flows. A modified equation of motion was derived to account for the reduced momentum carried by the sheared fluid. Numerical analysis was carried out to determine a number of velocity profiles over the Reynolds number range of interest and a simple set of curve fits was used when finer discretization was required. Stability analysis of a pipe conveying fluid with these profiles was performed, and the results were compared to a uniform profile. The mass ratio, β, is the ratio of the fluid mass to the total system mass. At β = 0.2, the non-uniform case becomes unstable at a critical velocity, ucr, that is 5.4% lower than the uniform case. The critical frequency, fcr, is 0.36% higher than the uniform case. A more sensitive region exists near β = 0.32. There, the nonuniform velocity ucr is 23% lower than the uniform case and the non-uniform critical frequency fcr is 49% of the uniform case.
Design of a Digital Wireless Energy Meter for Residential Energy Monitoring Using Wireless Sensor Networks
Authors: Koplow Michael , Redfern Andrew , Cheng John , Wright Paul K.
Published: July 2010

This paper presents a prototype application for residential energy monitoring using a digital energy meter coupled with a wireless sensor. The current measuring meter is designed to be placed in-line with household appliances. The data are then sent using a wireless sensor node to a low cost server. The system allows end users to measure energy expenditure and visualize the data in real time with a forward prediction of cost for running the appliance. The system is an enabling technology for a global architecture of dynamic electricity pricing schemes and load reduction programs, called Demand Response. The new system allows residents to become self aware about power consumption levels in their home and enables users to make informed decisions about demand response events.
Optimization of a Leaching Tank for Hydrometallurgical Recovery of Metals
Authors: Vilarinho M. C. L. G. , Gonc¸alves N. M. B. , Teixeira J. C. F.
Published: July 2010

The sludge wastes generated by the metal plating industries are classified as hazardous wastes because of their high concentration of heavy metals. Amongst the various routes for their treatment, the hydrometallurgical processes are highly attractive because they can be tailored to the wide compositional range of such wastes and assure its metals recovery and/or toxicity reduction. In these processes the leaching operation is paramount to the overall efficiency. In this, the mixing of the leaching solution with sludge has to be effective in order to obtain high levels of metal extraction and make the process attractive. Most of the available data refers to laboratory tests. This paper reports on the use of CFD model to optimize the operation of a pilot size leaching tank. The results regarding the velocity field were compared with experimental data and proved that such techniques can be effectively applied to improve the process. A leaching experiment, with the best configuration for the mixing, yielded a high metal extraction, suggesting that this technique can be successfully implemented for the treatment of such wastes.
An Interpretive Assessment of Engineering Science Core Courses
Authors: Ghosh Amitabha , Hensel Edward C.
Published: July 2010

This paper provides a mapping of common conceptual difficulties in learning fundamentals of engineering analysis from two different core courses in mechanical engineering—fluid mechanics and statics. For analysis, examples from actual test questions and student performance on them are presented with interpretations of the subject areas and source of difficulties. Properly designed multiple choice questions can provide an effective evaluation of student comprehension. The paper discusses the structure of good questions, and describes how improperly designed questions may hinder learning and accurate assessment.
In-Situ and Ex-Situ Investigation of Lateral Current Density Variations in a PEM Fuel Cell With Serpentine Flow Field
Authors: Higier Andrew , Liu Hongtan
Published: July 2010

One of the most common types of flow field designs used in proton exchange membrane (PEM) fuel cell is the serpentine flow field. It is used for its simplicity of design, its effectiveness in distributing reactants and its water removal capabilities. The knowledge about where current density is higher, under the land or the channel, is critical for flow field design and optimization. Yet, no direct measurement data are available for serpentine flow fields. In this study a fuel cell with a single channel serpentine flow field is used to separately measure the current density under the land and channel on the cathode. In this manner, a systematic study is conducted under a wide variety of conditions and a series of comparisons are made between land and channel current density. Results show that under most operating conditions, current density is higher under the land than that under the channel. However, at low voltage, a rapid drop off in current density occurs under the land due to concentration losses. In order to investigate the cause of the variations of current density under the land and channel and series of ex-situ and in-situ experiments were conducted. In the ex-situ portion of the study, the contact resistance between the gas diffusion electrode (GDE) and the graphite flow plate were measured using an ex-situ impedance spectroscopy technique. The values of the contact resistance under the channel were found to be larger than that under the land. This implies that the contact resistance under the land and channel vary greatly, likely due to variations in compression under different section of the flow field. These variations in turn cause current density variations under the land and channel.
Non Linear Correlation Optimized for Estimating Enthalpy of Modified Packages in a Cooling and Freezing Temperature Range
Authors: Lo´pez B. Marle´n Eliana , Valencia Guillermo E. , Turizo John C. , Bula Antonio J.
Published: July 2010

An optimization and a statistical analysis are presented in order to obtain a mixture based on commercial and inexpensive components, which represents the enthalpy behavior of the package described in UNE-EN441 standard. The enthalpy of the M package, which represents the thermal characteristics of lean meat used in test of refrigerated display cabinets, is estimated as a function of temperature. The package is used to analyze the heat transfer process in packages undergoing cooling or freezing conditions. The package is composed of hard wood sawdust, brine and a preservative. The points required for experimentation are determine according to D-Optimal experiment design, taking into account the concentration of each component. The β’s parameters for the semi-theoretical non linear correlation of the modified package enthalpy are estimated with nonlinear least square approach. Gauss-Newton algorithm with Levenberg-Marquardt modifications for global convergence is used. Correlation for the enthalpy package is presented and suggestions for future experimentation are presented in order to increase the accuracy of the regression.
Simulation and System Identification of a Biomethanol Production Plant
Authors: Garci´a Jaime R. , Romero Iva´n D. , Posada Jose D. , Bula Antonio J. , Sanjua´n Marco E.
Published: July 2010

Biomethanol is simply methanol produced from non-fossil feedstock. The process requires gasification of biomass, black liquor, or the gas can be obtained from landfill or animal waste. Typically, Biodiesel production requires methanol as a main feedstock, and the latter can be obtained from biomass waste, turning the biodiesel production process even more sustainable, as the necessary materials involved come from renewable sources. This investigation addresses the need to develop a simulation model of a biomethanol production process, to determine the feasibility of the plant by analyzing different operating conditions at the process units. Also, a subspace system identification technique is used to capture the dynamics of the process at one operating condition for further optimization of operational costs. The results showed that H2/CO ratio significantly affects the final amount of biomethanol (CH3OH) obtained.
Numerical Study of Mist Film Cooling in Combustor at Operating Conditions
Authors: Para Srinivasa Rao , Li Xianchang , Subbuswamy Ganesh
Published: July 2010

To improve the gas turbine thermal performance, apart from using a high compression ratio, the turbine inlet temperature must be increased. Therefore, the gas temperature inside the combustion chamber needs to be maintained at a very high level. Hence, cooling of the combustor liner becomes critical. Among all the cooling techniques, film cooling has been successfully applied to cool the combustor liner. In film cooling, coolant air is introduced through discrete holes and forms a thin film between the hot gases and the inner surface of the liner, so that the inner wall can be protected from overheating. The film will be destroyed in the downstream flow because of mixing of hot and cold gases. The present work focuses on numerical study of film cooling under operating conditions, i.e., high temperature and pressure. The effect of coolant injection angles and blowing ratios on film cooling effectiveness is studied. A promising technology, cooling with mist injection, is studied under operating conditions. The effect of droplet size and mist concentration is also analyzed. The results of this study indicate that the film cooling effectiveness can increase ∼11% at gas turbine operating conditions with mist injection of 2% coolant air when droplets of 10μm and a blowing ratio of 1.0 are applied. The cooling performance can be further improved by higher mist concentration. The commercial CFD software, Fluent 6.3.26, is used in this study and the standard k-ε model with enhanced wall functions is adopted as the turbulence model.
A Numerical Study of Unsteady Natural Convection in a Rectangular Enclosure: The Effect of Variable Thermodynamic and Transport Properties
Authors: Akyuzlu K. M. , Chidurala M.
Published: July 2010

A two-dimensional, mathematical model is adopted to investigate the development of buoyancy driven circulation patterns and temperature contours inside a rectangular enclosure (with aspect ratio of one) filled with a compressible fluid (Pr = 0.72). One of the vertical walls of the enclosure is kept at a higher temperature than the opposing vertical wall. The top and the bottom of the enclosure are assumed insulated. The physics based mathematical model for this problem consists of conservation of mass, momentum (two-dimensional, unsteady Navier-Stokes equations for compressible flows) and energy equations for the enclosed fluid subjected to appropriate boundary conditions. The compressibility of the working fluid is represented by an ideal gas relation. Thermodynamic and transport properties of the fluid are assumed to be function of temperature. The governing equations are discretized using second order accurate central differencing for spatial derivatives and second order finite differencing based on Taylor expansion for time derivatives. The resulting nonlinear equations are then linearized using Newton’s linearization method. The set of algebraic equations that result from this process are then put into a matrix form and solved using a Coupled Modified Strongly Implicit Procedure (CMSIP) for the unknowns of the problem. Grid independence and time convergence studies were carried out on different mesh sizes and also on a stretched orthogonal mesh to determine the accuracy of the square mesh adopted for the present study. Numerical experiments were carried out for a benchmark case (driven cavity flows) to verify the accuracy of the CMSIP, the proposed solution procedure. Numerical experiments were then carried out to simulate the development of the buoyancy driven circulation patterns for Rayleigh (Ra) numbers between 103 and 106. Also a parametric study was carried out (where Ra number was kept constant) to determine the effect of variations in wall temperature difference and reference length on the velocity and temperature fields. The effects of variable fluid properties on circulation patterns, temperature distributions, vertical and horizontal velocity profiles, and heat transfer from the walls of the enclosure were determined in a separate set of numerical experiments. Finally, unsteady thermal and hydrodynamic behavior of the working fluid was studied by imposing a sudden wall temperature change in the square enclosure. It is concluded that there is notable difference between the results of the variable property and the constant property models. Also, the variable property model predicts lower values for wall heat fluxes and Nu number than the constant property one. This seems to be more true when the temperature difference between the hot and cold walls of the enclosure is larger.
Development of Complex Thermal Models Using Global Sensitivity and MCMC
Authors: Bardot D. M. , Emery A. F.
Published: July 2010

In order to simulate the behavior of a thermal protection system exposed to a sudden heat flux it was necessary to develop a model of the thermal degradation of the insulating foam. The model was based upon measured mass losses, Thermal Gravimetric Analysis (TGA) data. Models can range from the simplest one chemical reaction to a complex, pressure dependent lattice model incorporating as many as sixteen reactions. The paper describes the development of a model, calibration using a fixed set of data, an analysis of the sensitivity based upon the concepts of global sensitivity and the evaluation of the uncertainty of estimated parameters.
Optimum Solar Panel Tilt Angle for Maximum Annual Irradiation
Authors: Naraghi Mohammad H.
Published: July 2010

This work presents a simple numerical model, based on a spreadsheet, to optimize solar panel tilt angle for given panel azimuth angle. This approach uses ASHRAE’s solar irradiation model, which presents a comprehensive model for calculating solar irradiation based on direct, reflected, diffuse and scattered components of solar irradiation. It includes the atmospheric extinction coefficient and sky clearness number (index). By calculating the monthly total irradiation from January to December the present model calculates the total annual irradiation on an incline solar panel. Then by implementing spreadsheet’s solver, the tilt angle to yield maximum annual solar irradiation per square area of panel is evaluated. Due to its general formulation the present model can be used to optimize solar tilt angle for any location (latitude) as long as the clearness index and ground reflectivity are known. The results of this model were compared with some existing location specific optimum tilt angles. The results are comparable within three degrees of tilt angle.
Use of Low/Mid-Temperature Solar Heat for Thermochemical Upgrading of Energy, With Application to a Novel Chemically-Recuperated Gas-Turbine Power Generation (SOLRGT) System
Authors: Zhang Na , Lior Noam
Published: July 2010

This paper presents the concept of indirect thermochemical upgrading of low/mid temperature solar heat, and demonstration of its integration into a high efficiency novel hybrid power generation system. The proposed system consists of an intercooled chemically recuperated gas turbine (SOLRGT) cycle, in which the solar thermal energy collected at about 220°C is first transformed into the latent heat of vapor supplied to a reformer and then via the reforming reactions to the produced syngas chemical exergy. The produced syngas is burned to provide high temperature working fluid to a gas turbine. The solar-driven steam production helps to improve both the chemical and thermal recuperation in the system. Using well established technologies including steam reforming and low/mid temperature solar heat collection, the hybrid system exhibits promising performance: the net solar-to-electricity efficiency, based on the gross solar thermal energy incident on the collector, was predicted to be 25–30%, and it can reach up to 35% when the solar share is reduced. In comparison to conventional CRGT system, 30% of fossil fuel saving is feasible with the solar thermal share of 26%, and the system overall efficiency reaches 51.2% to 53.6% when the solar thermal share is increased from 11 to 28.8%. The overall efficiency is about 5.7%-points higher than that of a comparable intercooled CRGT system without solar assist. Due to the introduction of steam into the combustion chamber, production of NOx is near zero, and the reduction of fossil fuel use results in a commensurate 23% reduction of CO2 emissions as compared with the comparable intercooled CRGT system without solar assist.
Subsystem Level Optimal Control and Filtering of Non-Classically Damped Matrix Second-Order Linear Mechanical Stochastic Systems
Authors: Radisavljevic Verica , Skataric Dobrila , Su Wu-Chung
Published: July 2010

Matrix second-order damped linear dynamic systems are frequently encountered in mechanical, structural, civil, aerospace engineering, and related fields. In this paper, we show how to optimally control matrix second-order systems using locally optimal Kalman filters corresponding to scalar second-order subsystems and how to find the corresponding filter and linear-quadratic (LQ) controller optimal gains at the subsystem level. The globally optimal linear-quadratic controller and the globally optimal Kalman filter and obtained in terms of locally optimal LQ controllers and locally optimal scalar second-order parallel Kalman filters. Conditions are established under which the presented procedure is applicable. Examples are included to demonstrate the efficiency of the proposed technique.
Exact Decoupling of Non-Classically Damped Matrix Second-Order Linear Mechanical Systems
Authors: Radisavljevic Verica , Skataric Dobrila
Published: July 2010

Matrix second-order damped linear dynamic systems are frequently encountered in mechanical, structural, civil, aerospace engineering, and related fields. This class of systems is also obtained by approximating dynamics of systems described by partial differential equations (distributed parameter systems). There are many papers in the engineering literature on analysis and control of matrix second-order linear damped systems. They provide either approximate (simplified) analytical results or accurate numerical results (usually computationally involved). In this paper, we show how to decouple exactly a matrix second-order linear system into scalar second-order subsystems and study exactly the corresponding system dynamics at the subsystem level using simple analytical tools. Conditions are established under which the presented procedure is applicable. An example is included to demonstrate the efficiency of the proposed technique.
From a Traditional Combustion Course to an Alternative and Renewable Energy Course
Authors: So¨zen Mehmet
Published: July 2010

With the increased interest and focus on sustainability and energy independence, utilization of renewable energy resources has been receiving a lot of attention. A new course on Alternative and Renewable Energy has been developed in the School of Engineering at Grand Valley State University as both a new technical elective course in thermofluids area as well as an alternative to the existing Combustion Applications course. While this course emphasizes alternative and renewable energy sources and applications, it also encompasses the basics of combustion of hydrocarbon fuels that is not covered in the single compulsory four credit hour thermodynamics course in the mechanical engineering curriculum. In this sense it serves a unique purpose of filling in an important gap in the curriculum. The laboratory used for the combustion course has been enhanced and transformed to be a Combustion and Energy Applications Laboratory. The experimental course that was developed and offered for the first time in fall 2008 tries to utilize to the maximum extent the existing laboratory and the essential and relevant topics of the combustion course, and builds on these with topics and experiments on alternative and renewable energy in forming a coherent course. In this regard, new equipment including a Hy-Expert™ Instructor Fuel Cell System, portable self-contained educational training units for solar photovoltaic, wind energy, and hydrogen energy have been purchased and added to the lab to complement the existing equipment. Other additions that are under way for enhancing this course are also described in this paper. This paper also discusses how the course and the laboratory were developed, the difficulties encountered, feedback obtained from the students as well as the overall experience and recommendations of the instructor.
A Time-Resolved PIV Study of Vortical Structures in the Near-Wall Region of an Impinging Round Jet
Authors: Hammad Khaled J. , Milanovic Ivana M.
Published: July 2010

Time-Resolved Particle Image Velocimetry (TR-PIV) was used to study the vortical structures resulting from a submerged water jet impinging normally on a smooth and flat surface. A fully developed turbulent jet, exiting a long pipe, and a semi-confined flow configuration ensured properly characterized boundary conditions, which allows for straightforward assessment of turbulence models and numerical schemes. The Reynolds number based on jet mean exit velocity was 23,000. The pipe-to-plate separation was varied between 2D and 7.6D. Turbulent velocity fields are presented using Reynolds decomposition into mean and fluctuating components. Proper Orthogonal Decomposition (POD) analysis was used to identify the most energetic coherent structures of the turbulent flow field. Three velocity gradient-based vortex identification techniques, 2nd invariant Q, λ2, and swirling strength, were found to perform equally well in identifying vortical structures along the impingement wall. The results clearly demonstrate the shortcomings of local vorticity as a vortex identifier in an impinging jet flow field.
Regenerative Braking Potential and Energy Simulations for a Plug-In Hybrid Electric Vehicle Under Real Driving Conditions
Authors: Martins L. A. S. B. , Brito J. M. O. , Rocha A. M. D. , Martins J. J. G.
Published: July 2010

There are several possible configurations and technologies for the powertrains of electric and hybrid vehicles, but most of them will include advanced energy storage systems comprising batteries and ultra-capacitors. Thus, it will be of capital importance to evaluate the power and energy involved in braking and the fraction that has the possibility of being regenerated. The Series type Plug-in Hybrid Electric Vehicle (S-PHEV), with electric traction and a small Internal Combustion Engine ICE) powering a generator, is likely to become a configuration winner. The first part of this work describes the model used for the quantification of the energy flows of a vehicle, following a particular route. Normalised driving-cycles used in Europe and USA and real routes and traffic conditions were tested. The results show that, in severe urban driving-cycles, the braking energy can represent more than 70% of the required useful motor-energy. This figure is reduced to 40% in suburban routes and to a much lower 18% on motorway conditions. The second part of the work consists on the integration of the main energy components of an S-PHEV into the mathematical model. Their performance and capacity characteristics are described and some simulation results presented. In the case of suburban driving, 90% of the electrical motor-energy is supplied by the battery and ultra-capacitors and 10% by the auxiliary ICE generator, while on motorway these we got 65% and 35%, respectively. The simulations also indicate an electric consumption of 120 W.h/km for a small 1 ton car on a suburban route. This value increases by 11% in the absence of ultra-capacitors and a further 28% without regenerative braking.
Thermo-Economic Optimization in the Design of Small-Scale and Residential Cogeneration Systems
Authors: Lea˜o C. P. , Teixeira S. F. C. F. , Silva A. M. , Nunes M. L. , Martins L. A. S. B.
Published: July 2010

In recent years, gas-turbine engines have undergone major improvements both in efficiency and cost reductions. Several inexpensive models are available in the range of 30 to 250 kWe, with electrical efficiencies already approaching 30%, due to the use of a basic air-compressor associated to an internal air pre-heater. Gas-turbine engines offer significant advantages over Diesel or IC engines, particularly when Natural Gas (NG) is used as fuel. With the current market trends toward Distributed Generation (DG) and the increased substitution of boilers by NG-fuelled cogeneration installations for CO2 emissions reduction, small-scale gas turbine units can be the ideal solution for energy systems located in urban areas. A numerical optimization method was applied to a small-scale unit delivering 100 kW of power and 0.86 kg/s of water, heated from 318 to 353K. In this academic study, the unit is based on a micro gas-turbine and includes an internal pre-heater, typical of these low pressure-ratio turbines, and an external heat recovery system. The problem was formulated as a non-linear optimisation model with the minimisation of costs subject to the physical and thermodynamic constraints. Despite difficulties in obtaining data for some of the components cost-equations, the preliminary results indicate that the optimal compressor pressure ratio is about half of the usual values found in large installations, but higher than those of the currently available micro-turbine models, while the turbine inlet temperature remains virtually unchanged.