bluuebunny/crossref_metadata_2025 huggingface dataset:
Current scenario of diabetes in India
Authors: RAMACHANDRAN Ambady , SNEHALATHA Chamukuttan
Published: December 2008

India, a country experiencing rapid socioeconomic progress and urbanization, carries a considerable share of the global diabetes burden. Studies in different parts of India have demonstrated an escalating prevalence of diabetes not only in urban populations, but also in rural populations as a result of the urbanization of lifestyle parameters. The prevalence of prediabetes is also high. Recent studies have shown a rapid conversion of impaired glucose tolerance to diabetes in the southern states of India, where the prevalence of diabetes among adults has reached approximately 20% in urban populations and approximately 10% in rural populations. Because of the considerable disparity in the availability and affordability of diabetes care, as well as low awareness of the disease, the glycemic outcome in treated patients is far from ideal. Lower age at onset and a lack of good glycemic control are likely to increase the occurrence of vascular complications. The economic burden of treating diabetes and its complications is considerable. It is appropriate that the Indian Government has initiated a national program for the management and prevention of diabetes and related metabolic disorders. Lifestyle modification is an effective tool for the primary prevention of diabetes in Asian Indians. The primary prevention of diabetes is urgently needed in India to curb the rising burden of diabetes.
Rate of peripheral glucose change during cognitive testing predicts performance in diabetes mellitus
Authors: PERLMUTER Lawrence Charles , SHAH Parinda Haresh , FLANAGAN Brian Patrick , SURAMPUDI Vijaya , KOSMAN Yevgeniya , SINGH Sant Parkash , AL‐JAGHBEER Eshraq
Published: December 2008

Background:  The reason for cognitive deterioration in diabetes mellitus (DM) remains unknown. One suggestion is that despite elevated glucose levels, patients with DM generally have difficulty utilizing glucose during cognitive tasks. This assumption was tested in the present study.

Methods:  Male outpatients with DM (n = 46; age 52–85 years) were administered a series of standard neuropsychological and cognitive tests. In addition to assessing the time to complete the series of tests, peripheral blood glucose levels were measured prior to and following testing.

Results:  The rate at which peripheral blood glucose levels changed was examined in relation to cognitive performance. Multiple linear regression analyses revealed significant relationships between the rate of glucose change and performance on tests measuring psychomotor skills, attention, visuoperceptual abilities, sequencing skills, mental flexibility, and planning. Higher rates of decline in peripheral blood glucose levels were associated with better performance on all cognitive measures, except verbal fluency.

Conclusions:  During cognitive testing, higher rates of decline in peripheral blood glucose levels may reflect stronger glucose utilization by the brain, thereby facilitating higher levels of cognitive performance. This non‐invasive measure may be useful in primary care settings to provide a link between blood glucose changes and cognitive status.
Teachers' Work Intensification and Educational Contradictions in Aboriginal Communities
Authors: WOTHERSPOON TERRY
Published: December 2008

L'auteur se penche sur l'évolution de la nature professionnelle de l'enseignement en relation avec les initiatives pour améliorer l'éducation chez les autochtones. Il examine les répercussions de plusieurs courants potentiellement contradictoires de réforme éducationnelle. Ceux‐ci contiennent en particulier des préoccupations concernant l'augmentation de la tâche des enseignants, la restauration professionnelle de l'enseignement, afin de satisfaire les besoins des sociétés fondées sur le savoir, et leurs conséquences pour les apprenants autochtones et leurs collectivités. Des résultats de sondages sur des enseignants travaillant dans des collectivités autochtones en Saskatchewan et au Manitoba soulignent l'émergence d'un professionnalisme fragmenté dans l'enseignement. Malgré que les enseignants aient exprimé leur engagement envers la réforme, des changements substantiels sont nécessaires pour que les intérêts professionnels des enseignants et les pratiques du système scolaire s'accordent entièrement pour assurer le genre de succès en éducation désiré par les collectivités autochtones. L'absence de mécanismes d'intégration forts pour lier les besoins professionnels des enseignants aux intérêts des autochtones et le manque d'engagement clair de la part du système envers l'équité en éducation pour les autochtones contribuent à créer des inégalités et des problèmes éducationnels potentiellement dommageables chez les élèves qui ont le plus besoin de soutien.

This paper explores the changing occupational nature of teaching in relation to initiatives to improve education for Aboriginal people. It examines the impact of multiple, potentially contradictory streams of educational reform. These include, in particular, concerns about the intensification of teachers' work, the professional reconstitution of teaching to meet the needs of knowledge‐based societies, and consequences for Aboriginal learners and communities. Results from surveys of teachers working in Aboriginal communities in Saskatchewan and Manitoba highlight the emergence of a fragmented professionalism within teaching. Despite teachers' expressed commitment to reform, substantial changes are required if teachers' professional interests and school system practice are to become fully aligned to produce the kinds of educational success desired by Aboriginal communities. The absence of strong integrative mechanisms to link teachers' professional needs, Aboriginal community interests, and clear system commitments to education equity for Aboriginal people contributes to uneven and potentially harmful educational consequences for students who are most in need of support.
Coriolis Effect on the Linear Stability of Convection in Solidifying Mushy Layers
Authors: Govender S.
Published: December 2008

We consider the solidification in a mushy layer subject to rotation and adopt a near-eutectic approximation. The linear stability is used to investigate analytically the Coriolis effect on convection for a new formulation of the momentum equation.
Thermal Design and Optimization of Harsh Environment Power Electronics in Natural Convection Heat Transfer
Authors: Arik Mehmet , Nagulapally Manoj , Brzozowski Steven , Glaser John
Published: December 2008

A study of thermal management of a harsh environment power electronics system is presented. The thermal environments were found to be between 65 °C and 90 °C that is considerably higher than many traditional electronics applications. A modular, low cost, and passive air-cooling system was desired. An analytical model was developed to obtain the heat transfer characteristics. Further performance verification of the thermal management solution was completed using a commercially available CFD tool. A small footprint area for thermal design of the power electronics connected with an electrically isolating low-conductivity material to the heat sink increased the challenge. A further thermal performance enhancement was achieved with the addition of a heat spreader between power electronics and the heat sink, and optimization of the heat spreader was achieved by utilizing FEM technique.
Numerical Simulation of a Spark Ignition Engine Using Liquid Fuels and Liquid Fuel Blends
Authors: Majmudar K. , Aung K.
Published: December 2008

The use of alternative fuels such as methanol and ethanol in spark-ignition (SI) engines is beneficial to the environment as it reduces emissions of pollutants such as NOx from these engines with slight penalty on the performance. This paper investigated the use of liquid fuel blends such as ethanol/gasoline blend in an SI engine by numerical simulations. The numerical simulations were based on the models of finite heat release, cylinder heat transfer, pumping losses, and friction losses. Simulations were carried out to evaluate the effects of compression ratio, equivalence ratio, ignition timing, and engine speed on the performance of the SI engine. The results of the simulations were compared with experimental data from the literature to validate the simulations. Good agreements between the computed and experimental results were obtained. The results showed that the current model could satisfactorily predict the performance of an SI engine fueled by liquid fuel blends.
Numerical Simulation of a Compression Ignition Engine Using Biodiesel Fuel
Authors: Purohit C. , Aung K.
Published: December 2008

Increasing concerns over pollutant emissions from diesel engines have prompted researchers to find replacement fuels for diesel engines. The use of alternative fuels such as biodiesel in compression-ignition (CI) engines is beneficial to the environment as it reduces emissions of pollutants with slight penalty on the performance. This paper investigated the use of biodiesel fuel (rapeseed oil) in a CI engine by numerical simulations. The numerical simulations were based on the models of finite heat release, cylinder heat transfer, and friction losses. Simulations were carried out to evaluate the effects of compression ratio, equivalence ratio, and engine speed on the performance of the CI engine. The results of the simulations were compared with experimental data from the literature to validate the simulations. Good agreements between the computed and experimental results were obtained. The results showed that the current model could satisfactorily predict the performance of a biodiesel-fueled CI engine.
Time-to-Market: A Practical CFD Application in the Telecom Industry
Authors: Champion Edward R.
Published: December 2008

This paper summarizes the practical use of CFD (Computational Fluid Dynamics) using a commercially available package, FLOTHERM [1], in a tight and highly competitive marketplace to produce a functional pre-production piece of telecom gear with no prototyping for thermal issues. The paper highlights the direct production, noprototype, analytical thermal performance verification of a small CMTS (Cable Modem Termination System) used in telecom applications.
Computational Modeling of Firmly Adhered Cell and Blood Flow Interactions in a Micro-Channel
Authors: Xu J. , Zhang H.
Published: December 2008

The interactions of cells with dynamic blood flow as they adhere firmly to a micro-channel wall are investigated. The cell is modeled either as a rigid solid or an elastic solid protrusion on a micro-channel wall. Blood is simulated using a validated non-Newtonian blood viscosity model (Walburn and Schneck model). We determine the effects of cell deformability on the force generated on the cell as the deformation progresses. The amplifications of mechanical stress and force on an adherent cell due to blood flow in a micro-channel are predicted. This two-dimensional model is solved by the finite volume package (CFDRC, CFD Research Corporation). This study shows that the pressure drop and drag force on the adherent cell are sensitive to the cell’s morphology, especially for the large ratio of cell diameter to channel height (d/D>0.5), the stresses and forces of deformable cells can be much smaller than that predicted based on the rigid cell model. These calculations may be used to predict blood flow interactions with cells in a micro-vessel. The modeling approach is useful in understanding the behaviors in cell adhesion and rolling.
Modeling Compact Exchangers for HVAC Applications
Authors: Scott Timothy C.
Published: December 2008

This paper presents equations for modeling the performance of compact air cooled heat exchangers when only limited supplier catalog performance information is available. Relations for the overall heat transfer coefficient under dry or wet surface operating conditions with water, steam, and refrigerants are presented. Equations for the air and water side pressure drop are also given. The coefficients in these equations may be determined using typical heat transfer vs. air face velocity data without the need for various surface and flow areas or air side convection coefficients. The model may then be used to predict performance at other conditions for which supplier data is not available.
Near Field Surface Wave Enhanced Photon Transport
Authors: Narayanaswamy Arvind , Chen Gang
Published: December 2008

Radiative energy transfer as described by the classical radiation transfer theory of Planck is valid only when the distance between the participating surfaces is larger than a few wavelengths of the characteristic radiation. When the spacing is comparable to the wavelength, electromagnetic theory and the fluctuation-dissipation theorem can be used to predict the energy transfer between the surfaces. We have used the electromagnetic Green’s function method to model the thermal energy transfer between two half planes with planar layers in between. With polar materials as the half planes, we see a narrowband energy transfer in the near field due to energy transfer by surface phonon polaritons. We have used this technique to show that such a resonance, however dampened, persists even with the presence of a layer of photovoltaic material. This results in not only an increased energy transfer to the photovoltaic material as compared to black body radiation but also imparts a narrowband characteristic to it. The implications for thermophotovoltaics are discussed.
Deformation and Solidification of Droplet Impact With Variable Thermal Contact Resistance
Authors: Wang W. , Qiu H.-H. , Cheng P.
Published: December 2008

Interfacial thermal contact resistance between the impinging flow of a molten droplet and a substrate, which is qualified by thermal contact conductance, plays an important role in the spreading and solidification of a droplet. In the present study, a simple correlation for the thermal contact conductance in the rapid contact solidification process was developed. With this correlation being directly used in numerical simulation, for the first time, a variable thermal contact resistance was taken into consideration to simulate both the dynamics and phase change responses during a molten droplet impingement. Numerical results were compared with that of the cases when thermal contact resistance was zero or a constant. The changes in spread factor with time and thermal contact conductance indicated that predictions from the computer simulation were sensitive to the values of thermal contact resistance. Experiment was conducted to demonstrate the validity of the present study. Comparison results showed that rather than using a constant average value, better agreement between the experimental and numerical results would be obtained if a variable thermal contact resistance were used in the numerical simulation.
CFD Simulation of Heat Transfer in SI Engine Combustion Chamber
Authors: Rashidi Manoochehr , Noori Ali Reza
Published: December 2008

The investigation reported in this paper includes the variation of transient and local heat transfer coefficient and heat flux in the combustion chamber of a spark ignition (SI) engine. Heat transfer characteristics are obtained from the Kiva-3v CFD (Computational Fluid Dynamics) code. Instantaneous results including the variations of mean heat transfer coefficient on the piston surface, combustion chamber, and wall of the cylinder are presented. Moreover, variations of the local heat transfer coefficient and heat flux along a centerline on the piston as well as a few locations on the combustion chamber surface are shown. It is illustrated that maximum heat transfer coefficient on the piston and combustion chamber surfaces varies with location and also it is observed that the initial high rate of increase of heat flux at any position is related to the instant of flame arrival at that position. In this work, the major focus is on the determination of the locations where heat flux and heat transfer are maximum.
Laminar Natural Convection in a Complicated Cavity With Spatially Variable Upper Wall Temperature
Authors: Dalal Amaresh , Das Manab Kumar
Published: December 2008

The study of natural convection inside a two-dimensional cavity with one and three undulations on the right vertical wall has been carried out where the top wall is heated by a spatially varying temperature and other three walls are cold walls. Non-orthogonal body-fitted coordinate system and SIMPLE algorithm with higher-order upwinding scheme are used. The streamline pattern shows two cells are formed separated at the middle vertical plane for both the configurations. The center of the cells is lifted upwards with increase in Ra. The heat rejection from the fluid to the right wall increases for the uppermost undulation whereas there is not much improvement of heat transfer for the other two in the three undulation case. For this particular configuration, the heat rejection increases with increase of Ra for the uppermost undulation and decreases with increase of Ra for the other two undulations. The overall improvement of heat rejection has been observed for three undulation case compared with one undulation case.
Investigation of Heat Transfer and Cure During the Unsaturated Flow in Woven, Stitched and Unbraided Mats
Authors: Jadhav Rajendra S. , Pillai Krishna M.
Published: December 2008

This numerical study investigates heat generation and cure during the unsaturated flow of thermosetting resins in woven, stitched or braided fiber mats during mold filling in liquid composite molding (LCM), a popular technology to manufacture polymer-matrix composites. This study is relevant to those mats, which can be characterized as a dual-scale porous medium. An iterative, control-volume approach, based on energy and cure balances in a two-layer model representing fiber tows and gaps between tows, is used for developing discretized equations for average temperatures and cures in the tows and gaps respectively. A significant difference in the temperatures and cures of the gap and tow regions is observed. The proposed model deviates significantly from the conventional single-scale model used in most LCM simulations and highlights the need to adopt a different approach in modeling cure and temperature in dual-scale fiber mats.
An Investigation Into the Effect of Subcooled Liquid Inertia on Flowrate Induced Transient Flow Surges in Horizontal Condensing Flow Systems
Authors: Kobus Chris J.
Published: December 2008

The objective of this research is to investigate large-scale transient flow surges of condensate leaving horizontal in-tube condensing flow systems, due to perturbations in the inlet vapor flowrate, and the influence of the subcooled condensate inertia on these surges. In a tube-type condenser involving complete condensation, it has been seen that small changes in the inlet vapor flowrate momentarily cause large transient flow surges in the outlet liquid flowrate. A System Mean Void Fraction (SMVF) Model is developed for predicting these flow surge characteristics. Experimental data are also presented, showing both the influence of subcooled liquid inertia, and the very good predictive capability of the SMVF Model. The salient feature of the SMVF Model is its simplicity that, with an experimentally verified predictive capability, enhances the models’ utility as an analytical tool as well as a tool for educational purposes.
Measurements of Turbulent Mixed Convection Flow Over a Vertical Forward-Facing Step
Authors: Abu-Mulaweh H. I. , Armaly B. F. , Chen T. S.
Published: December 2008

Measurements of turbulent mixed convection boundary-layer air flow over a two-dimensional, vertical forward-facing step are presented. The upstream and downstream walls and the step itself were heated to a uniform and constant temperature. Air velocity and temperature distributions and their turbulent fluctuations are measured simultaneously by using a two-component laser-Doppler velocimeter (LDV) and a cold wire anemometer were used, respectively. The present study treats buoyancy-dominated mixed convection over a vertical forward-facing step and examines the effect of a small free stream velocity on turbulent natural convection. It was found that the reattachment length increases while the heat transfer rate from the downstream heated wall decreases as the small free stream velocity increases.
Developing Fluid Flow and Heat Transfer in a Semi-Porous Square Channel
Authors: Jen Tien-Chien , Yan Tuan-Zhou , Chan S. H.
Published: December 2008

A three-dimensional computational model is developed to analyze fluid flow in a semi-porous channel. In order to understand the developing fluid flow and heat transfer process inside the semi-porous channels, the conventional Navier-Stokes equations for gas channel, and volume-averaged Navier-Stokes equations for porous media layer are adopted individually in this study. Conservation of mass, momentum and energy equations are solved numerically in a coupled gas and porous media domain in a channel using the vorticity-velocity method with power law scheme. Detailed development of axial velocity, secondary flow and temperature fields at various axial positions in the entrance region are presented. The friction factor and Nusselt number are presented as a function of axial position, and the effects of the size of porous media inside semi-porous channel are also analyzed in the present study.
Heat Transfer Characteristics of Steady Electroosmotic Flows in Two-Dimensional Straight Microchannels
Authors: Horiuchi Keisuke , Dutta Prashanta
Published: December 2008

Analytical solutions for the temperature distributions, heat transfer coefficients and Nusselt numbers of steady electroosmotic flows are obtained for two-dimensional straight micro-channels. This analysis is based on infinitesimal electric double layer (EDL) in which flow velocity becomes “plug-like” uniform except very close to the wall. Both constant surface temperature and constant surface heat flux conditions are considered in this study. Separation of variables techniques are applied to obtain analytical solutions of temperature distributions from the energy equation in which Joule heating is a significant contributor due to the applied electric field. The thermal analysis considers interaction among inertial, diffusive and joule heating terms in order to obtain the thermally developing behavior of electroosmotic flows. Heat transfer characteristics are presented for low Reynolds number microflows where the viscous and electric field terms are very dominant. For the parameter range studied here (Re ≤ 0.7), the Nusselt number is independent of the thermal Peclet number, except in the thermally developing region. In both isothermal and constant surface heat flux boundary conditions, the Nusselt number becomes constant in the fully developed region for a uniform volumetric heat generation. Analytical results for no Joule heating cases are also compared with the classical heat transfer results, and in the thermally fully developed region an excellent agreement is obtained between them.
Growth of Carbon Nanotubes and Carbon Nanofibers in Opposed Flow Oxy-Flame of Methane
Authors: Merchan-Merchan W. , Saveliev A. V. , Kennedy L. A.
Published: December 2008

Carbon nanotubes and carbon nanofibers formed on a Ni-based catalytic support positioned at the fuel side of opposed flow oxy-flame are characterized by electron microscopy. Observed nanoforms include multiwalled carbon nanotubes (MWNTs), MWNT bundles, helically coiled tubular nanofibers, and ribbon-like coiled nanofibers with rectangular cross-section. The electric field method is applied to control structure and purity of formed carbon nanomaterial. A coating layer of nanotubes possessing a thickness of 35 to 40 microns and a high degree of alignment was formed along the surface of the catalytic probe with variation of probe potential. The method shows a great promise in controlling the structure and formation rate of flame generated carbon nanomaterials.
Measurement of Temperatures on In-Flight Water Droplets by Laser Induced Fluorescence Thermometry
Authors: Salazar V. , Gonza´lez J. E. , Rivera L. A.
Published: December 2008

This work presents the use of laser induced fluorescence for instantaneous temperature measurements of a 200μm diameter water droplets monodispersed stream traveling downward in a standard stagnant atmosphere. The droplets are doped with small concentrations of a natural fluorescence dye (Pyrene), and with a surfactant substance, cetyldimetylbenzylammoniumchloride (CDBAC) to improve the fluorescence emission. The rate of the two-band pyreme emission (excimer to monomer) is used to determine the temperature. The temperature distribution along the stream of droplets determined for different initial temperatures: (30°C, 40°C and 50°C) at the exit of the nozzle compared very favorably with numerical results.
Thermal and Flow Field Characteristics in a Rectangular Duct With Broken V-Shaped Ribs
Authors: Wang Lieke , Gao Xiufang , Sunde´n Bengt
Published: December 2008

In the present study, the thermal and hydraulic characteristics of a rectangular duct with aspect ratio of 1/8 roughened by broken V-shaped ribs pointing upstream are investigated experimentally using Liquid Crystal Thermography (LCT) and Particle Image Velocimetry (PIV). The heat transfer distributions on the roughened wall were evaluated using liquid crystal images. It was found that the heat transfer coefficient had a spanwise variation on the ribbed wall, with high heat transfer coefficient at the upstream end of the rib and low value at the other end, similar to the continuous V-shaped ribs. However, the heat transfer distribution in the case of broken V-shaped ribs was observed more uniform, with local maxima due to the gap flow. In addition, the saw-tooth fashion of heat transfer distribution was also observed along the streamwise direction. The isothermal flow field measurements were obtained by PIV to catch the flow structures introduced by the ribs. The spanwise profile of the main flow velocity was found altered, and a complicated secondary flow was detected over the cross section. This flow phenomenon was caused by the ribs and the gaps between ribs.
LES Simulation in a Thin Liquid Film Subjected to High Thermal Stresses
Authors: Pham M. V. , Plourde F. , Doan S. K.
Published: December 2008

Thermal transfers occurring in the vicinity of an air-liquid interface have been studied numerically through a Large Eddy Simulation technique. Results obtained clearly show the unsteady response of the liquid film submitted to such thermal stress. Structures are created at the interface in a very small layer and it has been found that turbulence acts strongly in that layer. Moreover, even if the configuration studied tends to weaken buoyancy, the dissipation was found to obey a −3 power law. This clearly indicates that the buoyancy pilots the way turbulence behaves on the flow field; the latter is mainly characterized by a strong mixing phenomenon taking place in the already identified layer at the interface.
2-D Axisymmetric Finite Difference Modeling of Thermistor Probe Heating on the Kidney
Authors: Brown Fredericka , Boehm Robert , Shen Gary
Published: December 2008

Developing a means of determining whether or not there is adequate perfusion in a newly transplanted kidney is the impetus for this study. The concept analyzed is that of a self-heating thermistor probe located between the kidney and the adjacent body tissue, inserted during the transplant procedure. When appropriate perfusion is present in the kidney, more heat will be dissipated in the organ tissue than when perfusion is insufficient for transplant success. If the heat dissipation for a given probe temperature above the bulk tissue is monitored, this might be able to be used as an indicator of procedural success or failure. To assess the sensitivity of this approach a numerical model has been developed and is reported here. An axisymmetric two-dimensional finite-difference formulation is used. Results are shown using typical values of properties for perfused and non-perfused tissue. The sensitivity of the approach to these properties indicates the type of accuracy that will be required in the clinical application of the technique.
Numerical Simulation and Experimental Validation of the Dynamics of a Single Bubble During Pool Boiling Under Constant and Time-Varying Reduced Gravity Conditions
Authors: Abarajith H. S. , Qiu D. M. , Dhir V. K.
Published: December 2008

The numerical simulation and experimental validations of the growth and departure of a single bubble on a horizontal heated surface during pool boiling under reduced gravity conditions have been performed here. A finite difference scheme is used to solve the equations governing mass, momentum and energy in the vapor liquid phases. The vapor-liquid interface is captured by level set method, which is modified to include the influence of phase change at the liquid-vapor interface. The effects of reduced gravity conditions, wall superheat and liquid subcooling and system pressure on the bubble diameter and growth period have been studied. The simulations are also carried out under both constant and time-varying gravity conditions to benchmark the solution with the actual experimental conditions that existed during the parabolic flights of KC-135 aircraft. In the experiments, a single vapor bubble was produced on an artificial cavity, 10 μm in diameter microfabricated on the polished silicon wafer, the wafer was heated electrically from the back with miniature strain gage type heating elements in order to control the nucleation superheat. The bubble growth period and the bubble diameter predicted from the numerical simulations have been found to compare well with the data from experiments.
Experimental Investigation on Mixed Convection in a Channel With an Open Cavity Below
Authors: Manca Oronzio , Nardini Sergio , Pitzolu Ruggero , Vafai Kambiz
Published: December 2008

Mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The cavity has the heated wall on the inflow side. Mixed convection fluid flow and heat transfer within the cavity is governed by the buoyancy parameter, Richardson number (Ri), and the Reynolds number (Re). The results are reported in terms of wall temperature profiles of the heated wall and flow visualization for Re = 100 and 1000, Ri in the range 30–110 (for Re = 1000) and 2800–8700 (for Re = 100), the ratio between the length and the height of cavity (L/D) is in the range 0.5–1.5 and the ratio between the channel and cavity heights (H/D) equal to 0.5 and 1.0. The present results show that the maximum dimensional temperature rise values decrease as the Reynolds and the Richardson numbers decrease. The flow visualization points out that for Re = 1000 there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100 the effect of a stronger buoyancy determines a penetration of thermal plume from the heated plate wall into the upper channel. The dimensionless maximum wall temperatures in terms of L/D had values in ± 5% respect to an average function. Nusselt numbers increase when L/D increase in the investigated range of Richardson numbers.
Vapor Condensation and Absorption of SO2 in Wet Flue Gas
Authors: Jia Li , Peng Xiaofeng
Published: December 2008

The convection-condensation heat transfer mechanism of the gas mixture and its influence on SO2 absorption were theoretically analyzed with vapor fraction of 8% to 28%. A modified film model of mass transfer in mixture gas and Nusselt theory were used to describe the characteristics of mass, momentum and energy transfer at the phase interface. The effects of the velocities induced by mass transfer (vapor condensation and SO2 absorption) were included in conducting governing equations. Vapor condensation improves the SO2 absorption in the wet flue gas. Vapor fraction in the gas mixture would alter the mechanism of heat transfer modes, single-phase convection or condensation. But for high mass fraction of vapor the SO2 absorption will be an important phenomenon in the condensation process. Another important factor influencing the SO2 absorption is the Re number of bulk flow of wet flue gas.
Measurement of Dynamic and Equilibrium Surface Tension of Surfactant Solutions by the Maximum Bubble Pressure Method
Authors: Bahl Manish , Zhang Juntao , Manglik Raj M.
Published: December 2008

Surfactant solution systems are encountered in many different applications, including as a method to enhance the nucleate boiling performance of water. Characterizing the attendant interfacial phenomena requires precise predictions of their surface tension relaxation behavior. In this study, both the dynamic and equilibrium surface tension behavior of aqueous surfactant solutions has been investigated using the maximum bubble pressure method. The surface tension is measured as a function of concentration at room (23°C) and elevated (80°C) temperatures. The critical micelle concentration (c.m.c.) of each surfactant is calculated from their respective equilibrium adsorption isotherms. The dynamic surface tension measurements are obtained at a surface age of 50 ms, which simulates conditions typically encountered during nucleate boiling of water. Two anionic surfactants, Sodium Dodecyl Sulfate (SDS) and Sodium Lauryl Ether Sulfate (SLES), two cationic surfactants Dodecyl Trimethyl Ammonium Chloride (DTAC) and Ethoquad O12/PG, and one non-ionic surfactant Triton X-100 have been used. SLES, Ethoquad O12/PG and Triton X-100 have, respectively, 3, 2, and 9–10 degrees of ethoxylation, which tends to alter the interfacial rheology. The σ–C isotherms show marked variation based on the surfactant ionic nature and the number of ethoxy groups present, along with the effects of temperature, with considerably less surface relaxation under dynamic conditions compared to those at equilibrium.
Simulation of Flow and Heat Transport in a High-Temperature Reactor With Three-Dimensional Power Distribution
Authors: Laurien E. , Becker S.
Published: December 2008

A three-dimensional computational analysis is employed to investigate the transient flow and heat transport within an annular-core High-Temperature Reactor pebble bed, the blind core, and the surrounding graphite structures including 36 embedded coolant feeding channels. Well established models of pressure loss in the pebble bed, heat transfer between helium and the pebbles, and the heat transport within the porous medium by conduction and radiation (using an effective conductivity) have been implemented into an extended version of CFX-4. The graphite structures of the reflector are simulated closely coupled to the flow simulation as heat conducting solids. The model has been verified for axisymmetric power distributions by comparison with known results from 2D analysis. Various 3D-power distributions are assumed to represent a possible loss of forced cooling incident after unusual plant operation such as asymmetric positioning of absorber rods. It is confirmed, that 2D analysis is not adequate, because the predicted maximum temperature of the fuel elements after fission shutdown may exceed the maximum temperature predicted by 2D analysis.
Simulation of Heat Transfer in a Vertical Tubular CVD Reactor
Authors: Cai D. , Zheng L. L. , Wan Y. , Chandra M.
Published: December 2008

Polysilicon growth has increased due to its broad applications and market demand. The traditional method for polysilicon growth is based on the Siemens process. To improve the throughput, a new system with either large growth surface or other mechanism for high deposition rate is necessary. A novel design, using a vertical tubular CVD reactor has been recently proposed, in which an enlarged surface reaction area exits. This study is to investigate the optimal conditions for growth through numerical simulation of heat and mass transfer in the proposed vertical tubular CVD reactor. A complex computational model is developed that is capable of describing multi-component fluid flow, gas/surface chemistry, conjugate heat transfer, thermal radiation, and species transport. Different from the classical Siemens system, the bulk poly-silicon in a vertical tube growth has a complicated geometry. To accurately predict the various parameters covering broad range of scales, a multi-block grid generation system is used. Numerical computation has been conducted under different operating conditions, and in particular the effect of cooling gas flow direction and flow rate on the temperature distribution of the system and the polysilicon deposition rate has been investigated. Numerical results show that cooling from the top of the system is preferred.
An Inverse Method for Drying at High Mass Transfer Biot Number
Authors: Kanevce Gligor H. , Kanevce Ljubica P. , Dulikravich George S. , Colac¸o Marcelo J.
Published: December 2008

The inverse problem of using temperature measurements to estimate the moisture content and temperature-dependent moisture diffusivity together with the heat and mass transfer coefficients is analyzed in this paper. In the convective drying practice, usually the mass transfer Biot number is very high and the heat transfer Biot number is very small. This leads to a very small temperature sensitivity coefficient with respect to the mass transfer coefficient when compared to the temperature sensitivity coefficient with respect to the heat transfer coefficient. Under these conditions the relative error of the estimated mass transfer coefficient is high. To overcome this problem, in this paper the mass transfer coefficient is related to the heat transfer coefficient through the analogy between the heat and mass transfer processes in the boundary layer. The resulting parameter estimation problem is then solved by using a hybrid constrained optimization algorithm OPTRAN.
Computational and Experimental Study of Enhanced Laminar Flow Heat Transfer in Three-Dimensional Sinusoidal Wavy-Plate-Fin Channels
Authors: Zhang Jiehai , Muley Arun , Borghese Joseph B. , Manglik Raj M.
Published: December 2008

Enhanced heat transfer characteristics of low Reynolds number airflows in three-dimensional sinusoidal wavy plate-fin channels are investigated. For the computational simulation, steady state, constant property, periodically developed, laminar forced convection is considered with the channel surface at the uniform heat flux condition; the wavy-fin is modeled by its two asymptotic limits of 100% and zero fin efficiency. The governing equations are solved numerically using finite-volume techniques for a non-orthogonal, non-staggered grid. Computational results for velocity and temperature distribution, isothermal Fanning friction factor f and Colburn factor j are presented for airflow rates in the range of 10 ≤ Re ≤ 1500. The numerical results are further compared with experimental data, with excellent agreement, for two different wavy-fin geometries. The influence of fin density on the flow behavior and the enhanced convection heat transfer are highlighted. Depending on the flow rate, a complex flow structure is observed, which is characterized by the generation, spatial growth and dissipation of vortices in the trough region of the wavy channel. The thermal boundary layers on the fin surface are periodically disrupted, resulting in high local heat fluxes. The overall heat transfer performance is improved considerably, compared to the straight channel with the same cross-section, with a relatively smaller increase in the associated pressure drop penalty.
The Effect of Thermal Treatment on the Microstructural Evolution of an Al-Cu Alloy
Authors: Zoeller Tracie L. , Sanders Thomas H.
Published: December 2008

Following solidification, an aluminum alloy microstructure is highly segregated. The microstructure consists of cored dendrites with various soluble and insoluble phases present in the dendritic regions. The solidification rate has a marked effect on the amount of coring that an alloy experiences. Understanding the effects of the solidification rate is important in explaining differences in microstructures. Subsequent heat treatments are performed to homogenize the microstructure. The microstructure evolution after each processing step is dependent upon the previous microstructures. The variation in local chemical composition may promote or hinder precipitation of new phases. A large volume fraction of coarse insoluble phases can lead to the occurrence of recrystallized grains via particle stimulated nucleation, while inhomogeneous solute distribution can lead to the precipitation of an uneven distribution of dispersoid phases. The effect of solidification rate and subsequent thermal treatments on the microstructure of an Al-4Cu alloy will be investigated and experimental and numerical results will be presented.
Three-Dimensional Simulation of Plasma Spray Jet
Authors: Xiong H. , Zheng L. L. , Sampath S. , Fincke Jim , Williamson Richard
Published: December 2008

A three-dimensional computational model has been developed to describe the compressible, multi-component, turbulent, reacting plasma jet coupled with the orthogonal injection of carrier gas and particles. This model has been applied to plasma spray process that includes physical phenomena such as heating, melting, accelerating, and evaporation of in-flight particles. The entrained particles, NiCrAlY and ZrO2, are discretely treated in a Lagrangian coordinate and stochastically generated by sampling from the probability distributions of the particle size and its velocity at the injection nozzle. In this study, special attention has been directed to the effects of carrier gas injection on the characteristics of plasma jet. The computational results show that the injection of carrier gas from the orthogonal injector above the plasma jet introduce the 3-D phenomena of plasma gas flow. The plasma jet is defected and the thermo-fluid flow near the injector is locally deformed.
Forced Convective Boiling in Microchannels for kW/cm2 Electronics Cooling
Authors: Faulkner Daniel J. , Shekarriz Reza
Published: December 2008

This paper reports some of the results of our tests for the development of a high heat flux cooling system for thermal management of high power electronics. Our objective is to develop a practical design solution for achieving 1000 W/cm2 cooling. To achieve such high heat transfer rates, we have pursued and combined design advantages of a microchannel heat exchanger, high heat fluxes associated with forced convective nucleate boiling, and the use of a nanoparticles laden fluid for enhancement of heat transfer. A laboratory test module was designed, built, and tested to verify its performance. The experimental system employed sub-cooled as well as saturated forced convection boiling heat transfer in a high aspect ratio parallel microchannel heat sink. The working fluids tested were water and a selection of ceramic-based nanoparticle suspensions (nanofluids). The system was observed to readily dissipate heat fluxes in excess of 275 W/cm2 of substrate, while maintaining the substrate at or below 125°C. For optimized fin geometry, the current conditions would result in greater than 500 W/cm2. While the use of nanofluids was intended for boiling enhancement to push the envelop beyond 1000 W/cm2, we discerned limited improvement in the overall heat transfer rate. Future studies are planned for further exploitation of nanoparticles for enhancement of convective nucleate boiling.
Simulation of PCM Melting and Solidification in a Partitioned Storage Unit
Authors: Shatikian V. , Dubovsky V. , Ziskind G. , Letan R.
Published: December 2008

The present study explores numerically the processes of melting and solidification of a phase change material (PCM). The material used was a commercially available paraffin wax, which is non-toxic, recyclable, chemically inert, non-corrosive and can withstand an unlimited number of cycles. The phase-change material was stored in a rectangular box, open at the top. The bottom of the box could be heated or cooled. The inner space of the box was partitioned by vertical conducting plates attached to the bottom. Thus, heat was transferred to and from the PCM both through its melted/solidified layer and by conduction through the vertical plates. Transient two-dimensional numerical simulations were performed using the Fluent 6.0 software. The melting temperature of the wax, 23–25°C was incorporated in the simulations along with its other properties, including the latent and sensible specific heat, thermal conductivity and density in solid and liquid states. The simulations provided detailed temperature and phase fields inside the system as functions of time, showing evolution of the heat transfer in the system as the phase change material melts/solidifies. The dependence of the heat transfer rate on the properties of the system and on the PCM phase composition at various time instants is presented and discussed.
Flow and Heat Transfer in a Closed Rotating Circular Cylinder Heated From Top
Authors: Kahveci Kamil , Ece Mehmet Cem
Published: December 2008

Steady laminar centrifugally driven convective heat transfer in a spinning circular cylinder with top wall at higher and bottom and side walls at lower uniform temperatures were considered and the governing equations were solved numerically. Flow field is consist of a single eddy with clockwise rotation for all cases considered. Center of the eddy shifts from a location near the side wall to a location near the top disc as the aspect ratio increases.
Analytical Solution for the Prediction of Temperature Distributions During Radio-Frequency Ablation of Cardiac Tissue
Authors: Roper Ryan T. , Jones Matthew R.
Published: December 2008

One of the most effective methods of treatment for cardiac arrhythmias is radio-frequency (RF) ablation. Many studies have shown that the tissue temperature distribution is the key factor influencing lesion shape and size, and that accurate prediction of this distribution is essential to the further improvement of the procedure. Temperature distributions can be obtained by solving the bioheat equation, which has been done in several studies using numerical techniques. This paper describes the development of an analytical solution that can be used as a bench mark for subsequent numerical solutions. Using integral transforms, the bioheat equation is reduced to an ordinary differential equation with time as the independent variable. The solution has the form of a surface integral within another surface integral. An integration routine that extends the trapezoidal method of integration in two dimensions to an analogous method in three dimensions has been developed in order to evaluate the analytical solution. A C program was written to implement this method, and the program was validated using a surface integral with a known analytical solution. The program was then used to generate temperature profiles at various time values and for different convection coefficients.