bluuebunny/crossref_metadata_2025 huggingface dataset:
Replacement of Synthetic Acoustic Absorbers With Natural Fibers
Authors: Hosseini Fouladi Mohammad , Peng Sim Yeng , Wen Sin Yi , Xin Pang Zong , Mohd Nor Mohd Jailani , Mohd Saleh Mohd Afiq , Seng Tham Chan
Published: October 2013

The goal of this study was to implement Malaysian natural fibers as sound absorbers in acoustic panel. Four natural fibers, namely; coir, corn, sugar cane and grass were chosen and their acoustic absorption properties examined. Samples were tested in impedance tube complying with the standard ISO 10534-2. Increase in the thickness improved the absorption coefficient and samples of coir, corn and grass with 2 cm thickness absorbed more than 70% of normal incident sound at approximately f>1500 Hz. Comparison with synthetic materials having the same thickness showed that these fibers have better absorption coefficient throughout the frequency spectrum. Fiber-glass was an exception and still considered one of the best materials for acoustic insulation however it has adverse effects on human health and its utilization is no longer recommended. The results supported the viability of natural fibers as alternative to conventional synthetic absorbers in acoustic panels.
Modeling and Simulation of Performance of Stiffened Plates During Strength Analysis
Authors: Liu Yucheng , Wang Qingkui
Published: October 2013

This paper performs strength analysis on arbitrarily stiffened and regular stiffened plates to investigate the strengthening effects of stiffener’s height, number, and arrangement on the stiffened plates’ ultimate strength limit (USL). It is also found that the strengthening effects of an arbitrarily oriented stiffener (or oblique stiffener) can be decoupled to two perpendicular regular stiffeners which are located in appropriate positions. Nonlinear buckling analyses were performed on the arbitrarily stiffened plates with one and two arbitrarily oriented stiffeners to verify this finding. The outcome of this paper can be further extended and applied to develop simplified semi-analytical models for buckling strength analysis of constructional plates.
Research on Characteristics of Flow Field Inside Tangential Inlet Cyclone Separator
Authors: Luan Yigang , Liu Pengfei , Sun Haiou , Deng Yulin
Published: October 2013

Flow field inside tangential cyclone separator is a kind of complex three-dimensional rotation turbulent flow. To optimize the flow field structure and shorten the cycle of research and development, it is essential to find an appropriate calculation method to predict the flow field inside cyclone separators. In the article, FLUENT software is employed to obtain the internal flow field of tangential inlet cyclone separator by adopting different calculation models and different numerical simulation scheme. Also the simulation result was compared with that of existing experiment data to find a reasonable solution for the simulation of the flow field characteristics inside the cyclone. After the examination to the rationality of the different numerical simulation method, and the comparative analysis in the main flow field parameters of the simulated results which is the most reasonable combination, the flow characteristics of internal flow field of tangential inlet cyclone separator was obtained. The results show that: when the grid number of calculation domain reach 860000, it can cater to the calculation conditions of flow field, and the simulation results can agree with the experimental data better and will hardly change with the grid number; On the basis of standard k-ε model, the numerical simulation scheme was formulated by the orthogonal experiment method, through the comparison of results, the best combinations are 2 and 11; Applying the optimized combination to RNG k-ε model, Realizable k-ε model and RSM model and comparing simulation results with the existing one show that RSM was the ideal model used in simulation; With the change of the flow rate came a resistance characteristic curve of cyclone separator. The comparison between it and the predicted results of existing empirical formula of resistance characteristic drew the numerical simulation result, which is closest to Dirgo empirical formula; the first and second order upwind form have certain influence on the numerical simulation results, but the second one is more accurate in terms of simulating and predicting the parameters distribution inside flow field. This research result has certain reference value for cyclone separator design and performance optimization.
Energy Efficiency in Buildings: Think Pyramids
Authors: Khalil Essam E.
Published: October 2013

The developing communities in their path for rapid development is endeavoring to make all necessary and appropriate measures to enhance the efficiency of energy utilization and increase the beneficiation of the energy resources. The energy production, transmission, distribution and utilization efficiency becomes a vital factor and measure of national development. Governmental organizations were established earlier to be responsible for energy planning and efficient utilization, information dissemination and capacity building as well as devising the necessary codes and standards. Throughout the Nation, energy resources are widely used and consumption rates are in general exceeding the International accepted values. Energy rationalization and audit exercises were developed and monitored by Governmental Authorities, Universities and Research centers through the past two decades with a definitive positive energy reduction and beneficiation. The development of the relevant codes for Residential and Commercial Energy Efficiency in buildings is underway through the governmental bodies responsible for the research and development in the building Technology sector and is the umbrella under which the National and Unified Arab Codes are developed and issued. A proposed new Energy Performance in Buildings Directive (EPBD) would fulfill the following main targets of energy performance directive:

1. “Legestilative authorities shall ensure that, when buildings are constructed, sold or rented out, an energy performance certificate is made available to the owner or by the owner to the prospective buyer or tenant, as the case might be. …

2. The energy performance certificate for buildings shall include reference values such as currant legal standards and benchmarks in order to make it possible for consumers to compare and assess the energy performance of the building. The certificate shall be accompanied by recommendations for cost-effective improvement of the energy performance…” The following steps shall be required for the energy certification:

1. Develop methodologies for energy declaration of the buildings.

2. Develop reference values (key numbers) and /or systems for benchmarking.

3. Provide a labeling system for selected buildings.

4. Describe an energy signature for the building.
Effect of Riblets Geometry on Drag Reduction
Authors: Fayyadh Ekhlas M. , Mahdi Nibras M.
Published: October 2013

The effect of longitudinal riblet surface models (U, V and semi-Circular and U with fillet corner riblets) on the performance of unsymmetrical airfoil NACA23015 which has been investigated numerically and experimentally. Numerical investigation involve examining drag reduction by solving the governing equations (Continuity and Navier-Stokes equations) using the known package FLUENT in turbulent regime with appropriate turbulence model (κ-ε). Also measurement in experimental work will be carried out. The results indicate that the riblet surface models are the key parameters for controlling the boundary layer characteristics. The most effective riblet surface is U-riblet with fillet model (Mo.4, h = 0.1mm), by compare to smooth model, the results show a small increment in lift slope curve about 9% and total drag decrease 12% over the angles of attack range from (0° to 17°).
Evaluating Model Uncertainty Based on Probabilistic Analysis and Component Output Uncertainty Descriptions
Authors: Carlsson Magnus , Gavel Hampus , Ölvander Johan
Published: October 2013

To support early model validation, this paper describes a method utilizing information obtained from the common practice component level validation to assess uncertainties on model top level. Initiated in previous research, a generic output uncertainty description component, intended for power-port based simulation models of physical systems, has been implemented in Modelica. A set of model components has been extended with the generic output uncertainty description, and the concept of using component level output uncertainty to assess model top level uncertainty has been applied on a simulation model of a radar liquid cooling system. The focus of this paper is on investigating the applicability of combining the output uncertainty method with probabilistic techniques, not only to provide upper and lower bounds on model uncertainties but also to accompany the uncertainties with estimated probabilities.

It is shown that the method may result in a significant improvement in the conditions for conducting an assessment of model uncertainties. The primary use of the method, in combination with either deterministic or probabilistic techniques, is in the early development phases when system level measurement data are scarce. The method may also be used to point out which model components contribute most to the uncertainty on model top level. Such information can be used to concentrate physical testing activities to areas where it is needed most. In this context, the method supports the concept of Virtual Testing.
Analysis of Secondary Flows and Heat Transfer in Viscoelastic Flow With Viscous Dissipation in Non-Circular Tubes
Authors: Letelier Mario F. , Zapata Fernando N. , Siginer Dennis A. , Stockle Juan
Published: October 2013

The steady laminar non-isothermal flow of a non-linear viscoelastic fluid in tubes or arbitrary contour is analyzed under constant wall heat flux. Viscous dissipation is taken into account. Non-linear viscoelastic behavior is modeled by means of the Phan-Thien-Tanner model. The equations of motion and energy are solved analytically through a perturbation approach coupled with a one-to-one mapping of the boundary to map the circular shape into various axially symmetric cross-sectional shapes with the Weissenberg number as the perturbation parameter Longitudinal and transversal velocity components are determined for several cross-sectional shapes, for which the temperature field and the Nusselt number variation with the Prandtl, Brinkman and Reynolds numbers are computed.
Surface Topography Evolution During Long-Run Micro-Stamping of Bipolar Plates (BPPs) and Effects on Corrosion and Contact Resistance Characteristics
Authors: Peker M. F. , Cora Ö. N. , Koç M.
Published: October 2013

Micro-stamping, as a promising sheet metal forming process for mass production of small parts, can meet the expectations such as durability, strength, surface finish, and low cost for miniaturized metal products and features. The purpose of this research was set to investigate surface interactions during mass manufacturing of micro-stamped sheets, and its consequences; then establish correlations (if any) between surface interactions vs. corrosion and contact resistance of bipolar plates (BPPs) to be used in proton exchange membrane fuel cells (PEMFC).

In experimental part of this study, 10,000 SS316L sheet blanks were micro-stamped using a stamping die set with 750 μm-deep micro-channels under 200 kN stamping force, and with a constant stamping speed of 1mm/s. Surface inspections (surface roughness and micro-channel height measurements), corrosion and contact resistance tests were carried out on BPPs. Analysis of variance (ANOVA) technique was utilized to investigate the significance of surface roughness, channel heights, corrosion and contact resistance variations for BPPs. Moreover, three-dimensional (3D) finite element models of micro-stamping process were established to approximate the stress and strain levels as well as coefficient of friction value experienced at contact interface.

The results revealed that the roughness values for micro-stamping dies and BPPs followed similar trends during 10,000 micro-stampings. Since surface defects trigger corrosion, the correlation between surface roughness and corrosion resistance of BPPs was found to be direct. Increasing number of surface irregularities (asperities) lowered contact surface area that resulted in increased contact resistance. Finally, comparison of experimental and numerical channel height values showed that the coefficient of friction did not change considerably during the mass production of BPPs, at least within the 10,000 stamping cycle.
Course Module on Precision Control of Piezoelectric Actuators
Authors: Shih Hui-Ru , Walters Wilbur L.
Published: October 2013

Conventional mechanical actuation mechanisms, which have been used to drive nanoscale devices, have the drawback of requiring high power for operation. However, the piezoelectric actuation mechanism offers the advantages of extremely low power consumption. As piezoelectric materials change the practice of engineering and technology, providing undergraduate students with experiences with these materials has become necessary. This paper presents the design of a course module on precision control of piezoelectric actuators for undergraduate students. The course module incorporates lecture, experiment, and problem-based learning as pedagogical tools. Students are given opportunities to work directly with piezoelectric actuators to gain hands-on experience. Students can learn about actuation advantages of the piezoelectric materials along with their control problems. This course module can improve the knowledge of the students on how to design and analyze piezoelectric devices.
Estimation of Hourly Solar Loads on the Surfaces of Moving Refrigerated Tractor Trailers Outfitted With Phase Change Materials (PCMs) for Several Routes Across the Continental U.S.
Authors: Varadarajan Krupasagar , Medina Mario A.
Published: October 2013

The primary objective of this paper was to calculate solar loads and wind chill temperatures on the surfaces of moving refrigerated tractor trailers outfitted with phase change materials (PCMs) for several routes across the Continental United States. As food transportation vehicles, these trucks experience different environmental conditions as they are in motion. The study of PCMs on food transportation vehicles could lead to new findings related to energy conservation. In this research work, a solar model was developed based on synthesized weather data files obtained from the National Solar Radiation Data Base (NSRDB), which contains weather information from 1961 through 1990 for 239 locations (TMY2 data) and weather information from 1991 through 2005 for 1020 locations (TMY3 data). The solar model comprised two parts, data extraction and solar load calculations. The data extraction part separated and picked out the required fields from the TMY data and used them in the solar load calculations program, which was used to estimate the solar loads and wind chill temperatures of every exposed surface of a moving tractor trailer. These solar loads, and wind chill temperatures would then be used in selecting the adequate type of PCMs for a particular route and time of year. In conventional cargo trucks, the refrigeration units are operated by burning fossil fuels, mainly diesel. Therefore, a decrease in refrigeration load would have an impact in fuel consumption and/or in the reduction in size of the refrigeration equipment’s.
Investigation of Liquid Flow in a Multi-Pass Branching Microchannel System
Authors: Dede Ercan M.
Published: October 2013

The design and fabrication of a unique multi-pass branching microchannel heat sink is reviewed. The liquid flow inside of the cold plate is investigated both experimentally and numerically. The experiments are carried out over a range of flow rates, and the pressure drop across the cold plate is determined over the set of tested values. Comparisons are made between fluid flow simulations and the experimental results. Numerical predictions show good agreement with the measured data, and the effects of the connection taps, inlet/outlet manifolds, and flow behavior inside of the multi-pass region of the cooler are explained. Applications of the technology are briefly introduced, and recent progress toward heat transfer measurements is reported.
Numerical Analysis of a Gas Turbine Using Bio-Ethanol
Authors: Alfaro-Ayala J. Arturo , Gallegos-Muñoz Armando , Zaleta-Aguilar Alejandro , Rangel Hernandez Victor Hugo , Campos-Amezcua Alfonso
Published: October 2013

The change of the fuel to a bio-fuel in a gas turbine combustor is a defiant challenge due to there is not enough information about the thermal behavior into the combustor, even there is not information about the change of conventional fuel used. In these sense, a numerical analysis using Natural Gas, Diesel and Bio-Ethanol is presented. The results show a significant reduction of the Turbine Inlet Temperature (TIT) when the diesel and bio-ethanol are used in the gas turbine combustor (TITNatural Gas = 1,262.24 K, TITDiesel = 1,204.67 K and TITBio-ethanol = 918.24 K). This leads to an increment of the diesel and bio-fuel mass flow rate in order to reach the allowable condition of the gas turbine combustor. As it is well known, the reduction of the TIT means a reduction of the output power of the gas turbine, thus to avoid this, the increase of bio-ethanol was about 255.5% and diesel was about 112.2% (considering 3.6 kg/s of fuel as the full load). This paper gives an attempt to discover the viability to use bio-fuels in gas turbines from the thermal-fluid dynamic standpoint.
An Iterative Circular Contour Winding Number Integral Method and its Application in Wave Propagation Analysis of Infinite Fluid-Filled Cylinder
Authors: Yi Yang , Zhan Wang , Dong Longlei , Yan Guirong
Published: October 2013

In this article, an iterative circular contour winding number integral method (ICCWNI) is proposed. The error analysis and convergence proof is given. It overcomes the fault that the traditional circular winding number integral method can not locate the zeros accurately for the complex equation including function items of large-value derivative. In order to verify its reliability, the dispersion curves of infinite fluid-filled and fluid-loaded cylinder are computed. The results are in accord with the ones in the previous literatures.
A New Technique for Improving Heat Transfer in Forced-Convection Cooling Systems: Optimal Design of a Conjugate System
Authors: Hajmohammadi Mohammad Reza , Ostad Amir Masood , Nourazar Seyed Salman
Published: October 2013

In this paper, a new technique is proposed for improving heat transfer in forced-convection systems by designing an optimal conjugated heat transfer system. The conjugated heat transfer system is created by placing a highly conductive plate as a heat transfer interface between heat sources and the flowing fluid. Unlike the most common techniques used in practice, this technique does not interrupt the convective flow nor does it manipulate the design of the heat sources. Numerical work is carried out based on the SIMPLEC algorithm to compute the temperature field in the plate. Constructal theory is utilized to determine the optimal thickness of the highly conductive plate. The optimization objective is to maximize the heat transfer and improve the cooling performance by minimizing the hot spot temperature. The results show that if only a conductive interface plate is placed between the heat sources and the fluid flow without any changes in the flow characteristics or heat sources design, the cooling performance can be remarkably enhanced depending on the Reynolds number of the flow and the plate thermal conductivity.
Numerical Investigation of Convective Heat Transfer and Pressure Drop for Ribbed Surfaces in the Bend Part of a U-Duct
Authors: Salameh Tareq , Sunden Bengt
Published: October 2013

This work concerns two-dimensional numerical simulations of the flow and temperature fields inside smooth and ribbed bend (turn) parts of a U-duct with relevance for internal tip cooling of gas turbine blades. The ribs are placed internally on the outermost bend surface. The renormalization group (RNG) k-ε turbulence model was used to solve the momentum and energy equations inside the bend (turn) part as well in the supply and return straight parts of the U-duct. For the ribbed surface three different rib configurations were simulated, namely (a) single rib at three different rib positions, i.e., inlet, middle and outlet, (b) two ribs for three different configurations, i.e., at the inlet and middle, at the middle and outlet as well as at the inlet and outlet, and (c) three ribs. The rib height-to-hydraulic diameter ratio, e/Dh, was 0.1, the pitch ratios were 13.5 and 27 and the Reynolds number was 20000. The details of the duct geometry were as follows: the cross section area of the straight part was 50×50 mm2, the inside length of the bend part was 240 mm. The results were compared with experimental data obtained at similar conditions. The numerical results were closer to the experimental ones for those cases with the rib at the inlet position than for the cases with the rib at the middle position. The case of two ribs at the inlet and middle gave the highest heat transfer coefficients while the case of a single rib at the middle gave the highest local pressure coefficient of all cases.
An Investigation of Gurney Flap Effects on the Wake of an Airfoil in Plunging Motion
Authors: Ajalli Fariba , Gharakhanlou Mojgan , Mani Mahmoud , Daraeizadeh Sahar
Published: October 2013

Experimental measurements were conducted on a plunging Eppler 361 Gurney flapped airfoil to study wake structure and dynamic stall phenomenon in the wake. The heights of Gurney flap were 2.6% and 3.3% chord. All oscillation data were taken at the plunging amplitude of 6cm and Reynolds number 1.5×105. Special attention was focused on the temporal progressions of the plunging wake for the range of initial AOA (0 and 12deg) in prior and post stall flow conditions. The velocity in the wake was measured by hot-wire anemometry. Surface pressure-measurements as a supplementary data were also carried out to look into the link between the boundary layer flow and the shedding vortical flow. It was found that the hysteresis is detected between the plunging wake in the upstroke and down-stroke. The shape and width of the wake hysteresis loops strongly depend on the initial AOA and vertical positions of the sensor. At prior static stall AOA, positive camber effects of flapped airfoil shifted wake profiles downward and more velocity deficits were detected. In the post stall conditions the hysteresis loop widths for lower-than-centerline vertical positions were remarkably more than counterpart upper positions. The energetic dynamic stall vortex shedding was found to be main responsible for large hysteresis and velocity deficit at these positions. Furthermore the extent and strength of the stalled wake or flow separation was found to increase for the flapped case which results in a significant increase in the hysteresis loop widths.
Oscillating Viscoelastic Flow
Authors: Ashrafi Nariman , Samghani Sepideh
Published: October 2013

The flow of nonlinear viscoelastic fluids between oscillating parallel plates is investigated. The investigation features time-dependent analysis of a complicated viscoelastic material modeled based on the Johnson-Segalman constitutive relation. Given the rheological parameters of certain material known from experiments, the coefficients of Johnson-Segalman constitutive equation model for the material are evaluated by fitting the data. The problem is first formulated by writing the governing equations for the flow between two independently oscillating parallel plates, i.e. oscillating Couette flow. The velocity and stress are represented by symmetric and antisymmetric Chandrasekhar functions in space. Both inertia and normal stress effects are included. A numerical scheme is applied to solve the governing equations in time domain projected by Galerkin method. For given Reynolds number and viscosity ratio, one critical Weissenberg numbers is found at which an exchange of stability occurs between the Couette and other steady flows. The model is capable of predicting the nonlinear amplitude-dependent behavior of viscoelastic flows under single and multiple-frequency excitations.
Analysis of Gravity-Driven Slurry Flow
Authors: Ashrafi Nariman , Zeydabadi Haniyeh
Published: October 2013

The flow of slurry in a closed inclined circular channel is examined. The viscoelastic fluid is modeled as a derivative of typical Oldroyd-B relation of stress and velocity gradient. First, gravity is considered as the driving force for the fluid flow to simulate the existing sewage system. The complete flow field is evaluated for this case. Next, a pressure gradient is introduced to observe its effects on the flow. The effect of this pressure gradient on flow parameters is taken into account. Velocity profile as well as stress distributions are given for different scenarios of the nonlinear fluid flowing in a closed channel.
Influence of Nonlinear Effects on a Piezoelectric Energy Harvesting Device
Authors: Mineto Andreza T. , Varoto Paulo S.
Published: October 2013

In this paper we present an analytical investigation of a nonlinear energy harvester device. The device is composed of a cantilever beam partially covered by piezoelectric ceramics in a bimorph configuration with a magnetic lumped mass attached to the beam’s free end. The model accounts for the nonlinearity coming from the piezoelectric constitutive equations in addition to the nonlinear effect arising from the magnetic field generated by the magnetic properties of the tip mass and additional magnetic sources in the vicinity of the beam. The electromechanical coupled equations are solved numerically through the initial value problems for ordinary differential equations. The electrical power output is calculated by varying the amplitude of the base acceleration, the distance between the magnets and the load resistor. The stability of the system is also investigated. From the numerical results it is found that the influence of the parameters investigated in the frequency range of operation of the device and the nonlinear effects present on the device energy harvester extend the useful frequency range of these.
Numerical Analysis of Laminar Mixed Convection in a Lid Driven Square Cavity With an Isothermally Heated Square Internal Blockage
Authors: Islam Akand W. , Sharif Muhammad A. R. , Carlson Eric S.
Published: October 2013

Laminar mixed convection characteristics in a square cavity with an isothermally heated square blockage inside have been investigated numerically using the finite volume method of the ANSYS FLUENT commercial CFD code. Various different blockage sizes and concentric and eccentric placement of the blockage inside the cavity have been considered. The blockage is maintained at a hot temperature, Th, and four surfaces of the cavity (including the lid) are maintained at a cold temperature, Tc, under all circumstances. The physical problem is represented mathematically by sets of governing conservation equations of mass, momentum, and energy. The geometrical and flow parameters for the problem are the blockage ratio (B), the blockage placement eccentricities (εx and εy), the Reynolds number (Re), the Grashof number (Gr), and the Richardson number (Ri). The flow and heat transfer behavior in the cavity for a range of Richardson number (0.01–100) at a fixed Reynolds number (100) and Prandtl number (0.71) is examined comprehensively. The variations of the average and local Nusselt number at the blockage surface at various Richardson numbers for different blockage sizes and placement eccentricities are presented. From the analysis of the mixed convection process, it is found that for any size of the blockage placed anywhere in the cavity, the average Nusselt number does not change significantly with increasing Richardson number until it approaches the value of the order of 1 beyond which the average Nusselt number increases rapidly with the Richardson number. For the central placement of the blockage at any fixed Richardson number, the average Nusselt number decreases with increasing blockage ratio and reaches a minimum at around a blockage ratio of slightly larger than 1/2. For further increase of the blockage ratio, the average Nusselt number increases again and becomes independent of the Richardson number. The most preferable heat transfer (based on the average Nusselt number) is obtained when the blockage is placed around the top left and the bottom right corners of the cavity.
Hall Effects on Radiating MHD Flow Past an Accelerated Plate in a Rotating Fluid
Authors: Deka R. K. , Das S. K.
Published: October 2013

The effects of thermal radiation on the MHD flow past an accelerated infinite vertical plate in a rotating fluid, taking Hall effect into account, has been investigated. The solutions are obtained by Laplace transformation technique. Velocity distribution (both axial and transverse) are shown graphically, whereas the numerical values of the axial and transverse components of skin-friction are listed in a table.
Experimental Investigation on the Modal Characteristics of Rolling Thick Disk
Authors: Bashmal S. , Bhat R. , Rakheja S.
Published: October 2013

Analytical and experimental investigations are carried out to study the combined effect of rotation and support non-uniformity on the modal characteristics of circular thick disks. A three-dimensional model is implemented to study the coupled in-plane and out-of-plane modes of a thick disk and present the variations of the travelling waves with respect to rotating and fixed coordinates. The initial stiffening due to rotation is introduced by developing a non-linear model that permits the coupling between static and dynamic problems. The present formulation is generalized to account for the stiffening effects for disks subject to non-uniform boundary conditions, where the initial displacement cannot be considered as axisymmetric. The general non-linear problem of a rotating annular disk subject to non-uniform boundary conditions is, then, investigated. The laboratory experiments on stationary and rotating circular disks under selected boundary conditions are carried out to demonstrate the validity of the analytical methods in terms of vibration and acoustic emission behaviour. The experimental results examine the combined effect of rotation and point support on the disk. The experimental study confirms the split in natural frequencies of the disk that was observed in the analytical results due to both rotation and support non-uniformity.
Estimation of Long-Term Creep Rupture Life of T91 Alloy Superheater Tube in the Presence of Steam-Side Oxide Scales
Authors: Huang Junlin , Zhou Keyi , Xu Jianqun , Xu Xiaohu
Published: October 2013

Taking into account the effects that steam-side oxidation has on the effective load-bearing thickness and temperature of tube wall, a systematic probabilistic estimation method for the long-term creep rupture life of T91 alloy superheater tube is proposed in this work. The new creep strength assessment results of T91 alloy are utilized. Considering the influence of uncertain factors including the geometry dimensions and operational conditions, instead of usual deterministic methods, probabilistic life estimation is performed. A concept referred to as survival probability which reflects the possibility for the long-term creep rupture life to be longer than a given time is defined, and the effects of initial inner tube diameter, steam temperature and steam flow on the survival probability are analyzed. The results reveal that the increase of initial inner tube diameter or the steam temperature will decrease the survival probability, while the steam flow has an opposite effect. Measures that can be adopted to improve survival probability are also introduced. This work can provide reference for the design of high temperature steam generation components in coal-fired power plants. Besides, it is also expected that this work can guide the determination of metallographic inspection and replacement schedule of these components.
Vibration Analysis and Measurement in the Below Knee Prosthetic Limb: Part I — Experimental Work
Authors: Bedaiwi Bashar A. , Chiad Jumaa S.
Published: October 2013

The aim of this work is to study the effect of vibration on the amputee’s Comfort experimentally. The vibration transmitted from the artificial limb to the human body by free and forced vibration is taken into consideration. An experimental rig was constructed for this purpose and it consists of a shaking table equipped with a cam mechanism, AC motor, PLC speed variator (inventor) and suitable springs. A measurement device is used to collect the displacement, velocity, and acceleration spectrum with computer interface in different points along the prosthetic limb and the healthy limb. The experiments were carried out on an amputee whose amputation is in his leg during the Iraqi-Iranian war in the eighteens of the last century. This work is planned to serve the increasing number of amputee to supply them with more comfortable artificial limbs.
Micro-Electro-Mechanical Systems (MEMS) Micro-Heater
Authors: Janakos C. N. , Goericke F. T. , Pisano A. P.
Published: October 2013

This research addresses the problem of not having access to a localized heating device that easily integrates a variety of testing needs with MEMS packaging. This device can heat MEMS while simultaneously in vacuum, exposed to harsh gases and on a rate table. The solution is a micro-heater built directly into its packaging with the capability to test MEMS at vacuum, which can be pumped down to 1 Torr in a fraction of a second and heats the device to approximately 170 degrees Celsius to simulate the temperatures MEMS devices endure. This packaging integrated with a testing device can accommodate a broad range of MEMS devices.
Condensation Heat Transfer on Two-Tier Superhydrophobic Surfaces
Authors: Cheng Jiangtao , Vandadi Aref , Chen Chung-Lung
Published: October 2013

Superhydrophobic surfaces exhibit large contact angle (> 150°) and small hysteresis (< 5°) which facilitate liquid transport and are expected to enhance condensation heat transfer on the surfaces. By growing short carbon nanotubes (CNTs) on an array of microposts etched on a silicon wafer, we formed a two-tier multiscale texture mimicking the surface structure of lotus leaves. Compared to one-tier microtexture which energetically favors the Wenzel state, the two-tier texture with micro/nano-scale roughness favors the Cassie state, the desired superhydrophobic state. Using an environmental scanning electron microscope (ESEM), we investigated moisture condensation on the fluoropolymer-coated two-tier texture and we have observed continuous dropwise condensation on the engineered superhydrophobic surface. However, in a customer-designed vapor chamber our condensation measurements indicate that a film layer of condensate in Wenzel state was formed on the textured surface. In particular, due to the filmwise condensation, the condensation heat transfer coefficient of the lotus-leaf-like surface is lower than that of a smooth hydrophobic surface especially under high heat flux situations.
Experimental Investigation on Flow Characteristics in a Tube-Bundle Channel
Authors: Li Zhan , Lu Guangyao , Xiang Wenyuan
Published: October 2013

Experiments were carried out to investigate the flow characteristics with/without heat exchange in vertical and inclined tube-bundle channels. In the experiments, the influences of flow directions and heat exchange upon the flow characteristics were studied. Experiments showed that the flow friction in tube-bundle channels had relations to the flow directions, and the liquid temperature difference at the inlet and outlet of tube-bundle channels. And these influences were comparatively obvious in the laminar flow regime. In the experiments, the transition from laminar to turbulent flow was carefully observed. The flow characteristics of single phase flow through tube-bundle channels were different from those in circular tubes and those in annular channels. The flow friction in tube-bundle channel is larger than that in normal circular tube. And the transition from laminar flow to turbulent flow in tube-bundle channel is different from that in normal circular tube. The influences of flow direction and heat exchange on the friction were also studied. The results were gained to provide the basis for the further investigations on the two-phase flow in tube-bundle channels.
Investigation on Nonlinear Trends of Composite Laminated Plate
Authors: Zhang Wei , Chen Jianen , Wang Qian , Sun Min
Published: October 2013

The nonlinear trends of composite laminated plates are investigated. The governing equations of motion for the plate are derived with the von Karman strain-displacement relations for the geometric nonlinearity and the Reddy’s third-order shear deformation plate theory. The four dimensional nonlinear averaged equations with the case of 1/2-subharmonic resonance and principal parametric resonance for the first mode and primary resonance for the second mode are obtained by applying the method of multiple scales. The frequency-response curves are analyzed under consideration of strongly coupled of two modes. The influences of the coefficients in dynamic equations and the detuning parameters on the nonlinear trend are studied, and the results indicate that the composite laminated plate may have different trends of nonlinearity under aforementioned resonance conditions. The sweep experiment is conducted to find the softening and hardening nonlinearity. The different trends are obtained when the excitation amplitude is 1.2g. The spectrums of the different stages of the test show that the change of the nonlinear trend may be caused from the sub-harmonic resonance in this test.
Potential Well Escape of an Eccentric Disk
Authors: Lipp Genevieve M. , Mann Brian P.
Published: October 2013

This paper investigates the dynamic behavior of an eccentric disk rolling on a curve of arbitrary shape and then on a curve defined as a cubic function. Comparisons are made to a disk with no eccentricity and the related point mass approximation. The curve is subject to base excitation, and the system is considered from the perspective of a potential well problem where escape is possible on one side. The equations of motion are derived using a roll-without-slip constraint, and the behavior is investigated by means of simulated frequency and amplitude parameter sweeps and by considering the basins of attraction when initial conditions or forcing parameters are varied.
Effect of Multiwalled Carbon Nanotube on Compression Properties of Carbon Fiber Reinforced Epoxy
Authors: Zhou Yuanxin , Hosur Mahesh , Jeelani Shaik
Published: October 2013

In this study, a high-intensity ultrasonic liquid processor was used to obtain a homogeneous mixture of epoxy resin and multi-walled carbon nanotubes (CNTs). The CNTs were infused into epon 862 epoxy resin through sonic cavitation and then mixed with W curing agent using a high-speed mechanical agitator. The trapped air and reaction volatiles were removed from the mixture using a high vacuum. Nanophased epoxy with 0.3 wt.% CNT was utilized in a vacuum assisted resin transfer molding (VARTM) set up with carbon fabric to fabricate laminated composites. The effectiveness of CNT addition on matrix dominated properties of composites has been evaluated by compression and open hole compression tests. The compression strength and open hole compression strength were improved by 31% and 39%, respectively, as compared to the neat composite.
Evaporative Cooling Performance of a Brazed Microporous Coating on an Aluminum Surface
Authors: King Ryan M. , Amaya Miguel , You Seung M.
Published: October 2013

The effect of an aluminum microporous coating on evaporative cooling performance of water was studied. The coating consisted of aluminum powder brazed to a flat aluminum substrate. Coatings of average thicknesses of 175 μm, 270 μm, 900 μm, and of average aluminum particle sizes of 27 μm, 70 μm and 114 μm were tested. A hot water treatment of the coating insured repeatability of thermal performance. Wickability was measured and compared to Washburn’s equation for capillary flow. Evaporative cooling tests were then performed on coated and plain surfaces. The test surfaces were uniformly heated while kept vertically dipped in an isothermal pool of water. All microporous coatings increased evaporative heat transfer relative to that of the plain surface by their ability to wick fluid to the entire heated area. With particle size increase from 27 μm to 70 μm both the wickability and heat transfer were significantly increased, but no further significant gains in either were obtained with increase to 114 μm. The maximum heat transfer coefficient was increased ∼11 times and the temperature limit (dry-out) heat flux increased ∼10 times with the two larger particle sizes (70 μm and 114 μm). The heat transfer coefficient and dry-out heat flux similarly increased with thickness increase.
Bolt Bearing Strength of Commingled Boron/Glass Fiber Reinforced Aluminum Laminates
Authors: Yeh P. C. , Chang P. Y. , Yang J. M. , Wu P. H. , Liu M. C.
Published: October 2013

The bearing properties of recently developed hybrid fiber/metal laminates, or COmmingled Boron/glass fiber Reinforced Aluminum laminates (COBRA), are investigated in this study. The bolt-type bearing tests on GLass REinforced aluminum laminates (GLARE), non-commingled hybrid boron/glass/aluminum fiber/metal laminates (HFML) and COBRA were carried out as a function of e/D ratio, metal volume fraction, fiber volume fraction, and fiber orientation.

Experimental results show that with the same joint geometry and metal volume fraction, the commingling of boron fibers improves the bearing strength of fiber/metal laminates. The bearing strength of COBRA with longitudinal fibers is lower than that with transverse fibers due to the fact that shearout failure takes place before maximum bearing strength is reached. The experimental results show that, with only either transverse fiber orientation or longitudinal fiber orientation, COBRA with 18% boron fiber volume fraction possesses a higher bearing strength when compared to HFML with 6% boron fiber volume fraction. In addition to the properties in COBRA with parallel-plies commingled prepreg, the bearing properties of various COBRA with [0°/90°] and [0°/90°/90°/0°] cross-ply commingled prepregs are also discussed.
Theoretical Research of Thermal Conductivity Model of Metal Rubber Based on the Wire Helix
Authors: Ma Yan-Hong , Lu Hong-Wei , Ma Zheng-Dong , Zhu Bin , Hong Jie
Published: October 2013

The heat transfer process of the Metal Rubber is in combination with the modes of heat transfer and the characteristics of Metal Rubber micro-element structure. Under certain conditions, the heat transfer questions can be simplified to the thermal conductivity questions. Based on the Fourier law, the characteristics of the thermal conductivity of Metal Rubber micro-element structure were analyzed by using thermoelectric analogy method. Combined with the equivalent coefficient law of the thermal conductivity, the thermal conductivity model was established. The formula of the thermal conductivity coefficient was derived. The accuracy of the theoretical model was verified by the experimental results. This study provides strong theoretical support for the application of the heat insulation materials.
Numerical Simulation of Natural Convection of Water Near Its Density Maximum Around a Cylinder Inside a Concentric Triangular Enclosure
Authors: Hu Yu-Peng , Li You-Rong , Wu Chun-Mei
Published: October 2013

In this paper, a series of numerical simulations for natural convection of water near its maximum-density around a cylinder inside a concentric triangular enclosure were conducted using finite volume method. The effects of the density inversion parameter, the aspect ratio, the Rayleigh number and the inclination angle on natural convection were discussed. Furthermore, the flow and temperature fields, the local and average Nusselt numbers at different parameters were obtained and analyzed. The results show that the flow pattern and temperature distribution are unique for various density inversion parameters and inclination angles. The density inversion parameter, the aspect ratio, the Rayleigh number all have significant effects on the overall heat transfer rates, except for the inclination angle. The present results can also contribute further information on the natural convection of non-Boussinesq fluid in enclosures.
Random Gear Dynamics Based on Path Integration Method
Authors: Yang Jianming , Yang Ping
Published: October 2013

Gears exhibit vibrations during operation which contain apparently random components. Due to time-varying stiffness and backlash nonlinearity, it is very hard, if not impossible, to get a closed form response of gears under combination of deterministic and random loads. This paper employs a numerical method termed as path integration to obtain the probability density of the response at discrete time instants. The random excitation is assumed to be White noise. The response of the gear is a Markovian processes under the random excitation. In order to capture the probability density evolution, discretization is applied to both space and time. The transition probability between adjacent time instants is assumed to be Gaussian and the calculation of the probability density is made on a reduced finite space. The mean and variance, which are used to construct the Gaussian distribution, are obtained through a direct numerical integration scheme with one stochastic Newmark method. Statistic linearization technique is utilized within each individual time-step to find a linear equivalent of the original system with backlash nonlinearity. Through this method the evolution of the probability distribution function of the response displacement and the velocity is calculated. Three representative cases with different levels of constant load are investigated.
Numerical Study of Carbon Dioxide Gas Emission From an Urban Residential Kitchen in Developing Countries
Authors: Rahman M. Hamidur , Islam A. K. M. Sadrul , Amin M. Ruhul
Published: October 2013

Lack of proper ventilation of exhaust fumes from gas fired stoves in residential kitchens is a major health concern for some populations. It could even cause destruction of property, reduced quality of life and lifespan. In this study, a typical kitchen having a standard dimension of 21.3 m × 24.3 m × 30.5 m was modeled with single open door exit. Two heat sources were used for modeling the kitchen that resembles the double burner gas stove of an urban residential kitchen in developing countries. Steady state simulations were performed using a three dimensional CFD code with appropriate boundary conditions. The present numerical method was validated by comparing with the experimental data reported by Posner et al. [1]. The comparison showed very reasonable agreement. A grid independence test was also performed to determine the optimum grid resolution reflecting the accuracy of the numerical solution. The results are presented for carbon dioxide gas emission from the stove exhaust and dispersion within the kitchen space. A comparative analysis between the ventilation (natural and forced) and no ventilation conditions is also reported in this study. The location of the breathing zone was at a height of 73 cm and at a distance of 33 cm from the center of the two burners. Very high concentration (above 5000 PPM) of carbon dioxide gas was observed at the plane passing the breathing zone. Exposure to this environment for longer time may cause serious health damage of the occupants [2]. As per Wisconsin Department of Health Services of USA [2], over 5,000 PPM exposures to CO2 lead to serious oxygen deficit resulting in permanent brain damage, coma and even death.