bluuebunny/crossref_metadata_2025 huggingface dataset:
The proximal cis‐regulatory region of the RHD/RHCE promoter is 105 bp and contains a 55‐bp core devoid of known binding motifs but necessary for transcription
Authors: Denomme Gregory A. , Wang Duncheng , Matheson Kimberly A. , Titolo Danny
Published: April 2009

BACKGROUND: The RhD and RhCE polypeptides are erythroid‐specific members of the RH gene family. Little is known about the promoter cis‐regulatory proximal region responsible for transcription.

STUDY DESIGN AND METHODS: The 1246‐bp 5′‐flanking regions of the RHD and RHCE promoter were amplified and ligated to a luciferase reporter vector and erythroid‐specific transcription was evaluated in K562, HEL, U937, and HeLa cell lines. Deletion and substitution promoter‐reporter constructs were generated to define the minimal cis‐regulatory region.

RESULTS: Deletion analysis in K562 cells revealed that the cis‐regulatory region extended to a position between −78 and −120 relative to the site of initiation of transcription. Electrophoretic mobility shift assays confirmed binding motifs for Sp1, GATA‐1, and E2F transcription factors. The use of 15‐bp substitution mutagenesis showed that the minimal region required for transcription extended to −105 bp, and 6‐bp substitution mutants from −35 to −90 identified a region necessary for transcription yet devoid of known cis‐regulatory binding motifs.

CONCLUSION: The proximal RHD/RHCE promoter regions contain cis‐regulatory binding motifs and an internal sequence‐dependent region that together regulate transcription. The results suggest that this region may be relevant in the weak expression of RhD.
Clinical practice recommendations for bipolar disorder
Authors: Malhi G. S. , Adams D. , Lampe L. , Paton M. , O’Connor N. , Newton L. A. , Walter G. , Taylor A. , Porter R. , Mulder R. T. , Berk M.
Published: April 2009

Objective:  To provide clinically relevant evidence‐based recommendations for the management of bipolar disorder in adults that are informative, easy to assimilate and facilitate clinical decision‐making.

Method:  A comprehensive literature review of over 500 articles was undertaken using electronic database search engines (e.g. MEDLINE, PsychINFO and Cochrane reviews). In addition articles, book chapters and other literature known to the authors were reviewed. The findings were then formulated into a set of recommendations that were developed by a multidisciplinary team of clinicians who routinely deal with mood disorders. These preliminary recommendations underwent extensive consultative review by a broader advisory panel that included experts in the field, clinical staff and patient representatives.

Results:  The clinical practice recommendations for bipolar disorder (bipolar CPR) summarise evidence‐based treatments and provide a synopsis of recommendations relating to each phase of the illness. They are designed for clinical use and have therefore been presented succinctly in an innovative and engaging manner that is clear and informative.

Conclusion:  These up‐to‐date recommendations provide an evidence‐based framework that incorporates clinical wisdom and consideration of individual factors in the management of bipolar disorder. Further, the novel style and practical approach should promote their uptake and implementation.
Predicting future distributions of mountain plants under climate change: does dispersal capacity matter?
Authors: Engler Robin , Randin Christophe F. , Vittoz Pascal , Czáka Thomas , Beniston Martin , Zimmermann Niklaus E. , Guisan Antoine
Published: April 2009

Many studies have investigated the potential impacts of climate change on the distribution of plant species, but few have attempted to constrain projections through plant dispersal limitations. Instead, most studies published so far have simplified dispersal as either unlimited or null. However, depending on the dispersal capacity of a species, landscape fragmentation, and the rate of climatic change, these assumptions can lead to serious over‐ or underestimation of the future distribution of plant species.

To quantify the discrepancies between simulations accounting for dispersal or not, we carried out projections of future distribution over the 21st century for 287 mountain plant species in a study area of the western Swiss Alps. For each species, simulations were run for four dispersal scenarios (unlimited dispersal, no dispersal, realistic dispersal, and realistic dispersal with long‐distance dispersal events) and under four climate change scenarios.

Although simulations accounting for realistic dispersal limitations did significantly differ from those considering dispersal as unlimited or null in terms of projected future distribution, the unlimited dispersal simplification did nevertheless provide good approximations for species extinctions under more moderate climate change scenarios. Overall, simulations accounting for dispersal limitations produced, for our mountainous study area, results that were significantly closer to unlimited dispersal than to no dispersal. Finally, analysis of the temporal pattern of species extinctions over the entire 21st century revealed that important species extinctions for our study area might not occur before the 2080–2100 period, due to the possibility of a large number of species shifting their distribution to higher elevation.
Biological Safety of LipoFullerene composed of Squalane and Fullerene‐C60 upon Mutagenesis, Photocytotoxicity, and Permeability into the Human Skin Tissue
Authors: Kato Shinya , Aoshima Hisae , Saitoh Yasukazu , Miwa Nobuhiko
Published: April 2009

Abstract:  Fullerene‐C60 (C60) is mainly applied in the aqueous phase by wrapping with water‐soluble polymer or by water‐solublizing chemical‐modification, whereas C60 dissolved in oil is scarcely applied; still less explicable is its toxicity. We dissolved C60 in squalane at near‐saturated or higher concentrations (220–500 ppm), named LipoFullerene (LF‐SQ), and examined its biological safety. LF‐SQ was administered at doses of 0.49–1000 µg/ml to fibroblast cells Balb/3T3, and showed that cell viability was almost equal to that of the control regardless of the UVA‐ or sham‐irradiation, indicating no phototoxicity. Reverse mutation by LF‐SQ was examined on four histidine‐demanding strains of Salmonella typhimurium and a tryptophan‐demanding strain of Escherichia coli. As for the dosages of LF‐SQ (313–5000 µg/plate), the dose‐dependency of the number of reverse mutation colonies of each strain did not show a marked difference when compared with the negative control, regardless of the metabolic activation, in contrast to twice or more differences for five positive controls (sodium azide, N‐ethyl‐N′‐nitro‐N‐nitrosoguanidine, 2‐nitrofluorene, 9‐aminoacridine, and 2‐aminoanthracene). In human skin biopsy built in a diffusion chamber, C60 permeated into the epidermis at 33.6 nmol/g tissue (24.2 ppm), on administration with LF‐SQ containing 223 ppm of C60, but not detected in the dermis even after 24 hrs, as analysed by HPLC. It is presumed that LF‐SQ can permeate into the epidermis via the corneum but can not penetrate the basement membrane, and so can not reach into the dermis, suggesting no necessity for considering a toxicity of C60 due to systemic circulation via dermal veins. Thus, C60 dissolved in squalane may not give any significant biological toxic effects such as photocytotoxicity, bacterial reverse mutagenicity, and permeability into the human skin.
Predictive Heat Exchanger Efficiency Monitoring
Authors: Prasad Vijaysai , Osborn Mark D. , Au Shirley S. , Reddy K. Ravi Chandra , Shah Sunil S. , Vora Nishith P. , Gryscavage Anthony
Published: April 2009

The performance of heat exchangers degrades with time due to fouling or deposition of material on the heat transfer surface. The fouling of critical exchangers in manufacturing plants results in a significant cost impact in terms of production losses, energy efficiency, and maintenance costs. While most plants monitor their exchangers to some degree, the ability to effect real and sustainable improvements requires four components: (1) real time monitoring; (2) an advance warning mechanism; (3) the ability to diagnose the cause of fouling; and (4) the ability to treat the cause in order to slow or reverse the degradation. CHeX is a comprehensive tool which monitors, predicts, and diagnoses heat exchanger performance. The unique features of this advanced technology include: numerous data cleaning steps to improve data quality and isolate a net fouling trend, an adaptive model which learns from the past to predict performance three years in advance, and knowledge-based diagnostics which identify the probable cause(s) of fouling and recommend corrective actions. The final control action is performed by a field engineer in adjusting the fouling treatment. The scope of the current paper includes only the detection and prediction features. To date, CHeX has been validated at three chemical processing plants, for fourteen exchangers. Selected case studies shall be presented to demonstrate the power of its algorithms over traditional calculations.
Laser Flash Method for Non-Opaque Materials
Authors: Lin Bochuan , Ban Heng , Li Chao , Scripa Rosalia N. , Su Chinghua , Lehoczky Sandor L.
Published: April 2009

The laser flash method for thermal diffusivity measurement is a standard method for opaque solid materials. It can also be used to measure liquid in a specially designed cell. The theoretical basis for the method is established based on pulse heating of one side of a thin opaque sample and measure the temperature response of the other side. In cases where the material is non-opaque or semi-transparent for the laser wavelength, existing theoretical models cannot be used directly. One way to overcome the problem is to coat a thin layer of graphite on the sample surface. The coating can absorb the laser energy and create a surface heating effect. However, coating may not be possible for special cases due to concerns of contamination of liquid samples. This paper reports the development of a theory that includes the transmission and absorption of the laser energy through out the sample thickness. The theory can be applied for samples with different absorption coefficient to obtain simultaneously thermal diffusivity and thermal conductivity of the sample. The original theory of the laser flash method becomes a limiting case of the current theory with an infinitely large absorption coefficient. The uncertainty analysis was performed and results indicated that that laser flash method can be used on non-opaque samples.
Numerical Simulation of Flow Field and Heat Transfer of Streamlined Cylinders in Crossflow
Authors: Li Zhihua , Davidson Jane , Mantell Susan
Published: April 2009

The use of streamlined tubes to reduce pressure drop across polymer tube bundles is considered because of the relative ease of fabrication. The drag and convective heat transfer coefficients along the outer surface of lenticular and elliptical tubes with minor-to-major axis ratios of 0.3, 0.5, and 0.8 are determined numerically for cross-flow Reynolds numbers from 500 to 10,000. An isothermal surface is assumed. The two-dimensional, unsteady Navier-Stokes equations and energy equation are solved using the finite volume method. Laminar flow is assumed from the front stagnation point up to the point of separation. Turbulent flow in the wake is resolved using the shear stress transport k-omega model. Local heat transfer, pressure and friction coefficients as well as a total drag coefficient and average Nusselt number are presented. The results for streamlined tubes are compared to published data for circular and elliptical cylinders. Drag of the elliptical and lenticular cylinders is similar and lower than a circular cylinder. Reductions in drag may be increased by making the streamlined cylinders more slender. Over the range of Reynolds number considered, an elliptical cylinder with an axis ratio equal to 0.5 reduces pressure drop by 30 to 40 percent compared to that of a circular cylinder. The lenticular and elliptical geometries have nearly identical average of Nusselt number. The average Nusselt number of an elliptical or lenticular cylinder with axis ratio of 0.5 and 0.3 is 15 to 35% lower than that of a circular cylinder. A case study for an automotive radiator is presented to illustrate comparison of shaped and circular tubes in terms of both heat transfer and pressure drop.
Direct Numerical Simulation of Two Phase Flows in Liquid Cooled Engine Valves
Authors: Sander W. , Weigand B. , Beerens C.
Published: April 2009

Future designs of combustion engines for motor-vehicles require modern high performance valves. Internally cooled valves have been used in engines for more than 90 years. Water was initially used as coolant and later mercury, but finally, after difficulties with these liquids, sodium was found to be an appropriate working fluid. The technique of using a liquid to carry the heat from the hot valve head to the valve stem, where it can pass through the valve guide, is now well established in industry. However, the design of such valves is mostly based on empirical knowledge within the industry. A simulation of the processes during the movement of the valve including detailed information about the highly transient two phase flow and the heat transfer in this system has not been realized so far. For this, an inhouse 3D DNS (direct numerical simulation) program (FS3D) was used to simulate the flow phenomena. The simulations have been performed on an equidistant rectangular computational grid in 2D. It was found that a typical fill level of sodium between 50% and 60% of the stem volume provides the best results for the averaged time evolution of the kinetic energy and also of the heat flux in the system. Furthermore, detailed descriptions of the realtime movement in the flow are shown for different fill levels. These results can be used to enhance and improve future designs.
Preconditioning and Solver Optimization Ideas for Radiative Transfer
Authors: Carrington David B. , Mousseau Vincent A.
Published: April 2009

In this paper, radiative transfer and time-dependent transport of radiation energy in participating media are modeled using a first-order spherical harmonics method (P1) and radiation diffusion. Partial differential equations for P1 and radiation diffusion are discretized by a variational form of the equations using support operators. Choices made in the discretization result in a symmetric positive definite (SPD) system of linear equations. Modeling multidimensional domains with complex geometries requires a very large system of linear equations with 10s of millions of elements. The computational domain is decomposed into a large number of subdomains that are solved on separate processors resulting in a massively parallel application. The linear system of equations is solved with a preconditioned conjugate gradient method. Various preconditioning techniques are compared in this study. Simple preconditioning techniques include: diagonal scaling, Symmetric Successive Over Relaxation (SSOR), and block Jacobi with SSOR as the block solver. Also, a two-grid multigrid-V-cycle method with aggressive coarsening is explored for use in the problems presented. Results show that depending on the test problem, simple preconditioners are effective, but the more complicated preconditioners such as an algebraic multigrid or the geometric multigrid are most efficient, particularly for larger problems and longer simulations. Optimal preconditioning varies depending on the problem and on how the physical processes evolve in time. For the insitu preconditioning techniques—SSOR and block Jacobi—a fuzzy controller can determine the optimal reconditioning process. Discussions of the current knowledge-based controller, an optimization search algorithm, are presented. Discussions of how this search algorithm can be incorporated into the development of data-driven controller incorporating clustering and subsequent construction of the fuzzy model from partitions are also discussed.
Film Cooling System Numerical Design: Adiabatic and Conjugate Analysis
Authors: Andreini Antonio , Carcasci Carlo , Gori Stefano , Surace Marco
Published: April 2009

Film cooling is certainly the most diffused system to protect metal surface against hot gases, both in turbogas blades and combustors. Although being very diffused, there are still several aspects of its behavior which need a better understanding. Mainly, the performance of multi-row holes configurations are still estimated correcting single-row correlations. Heat transfer coefficient modifications due to the presence of injected coolant are hard to evaluate, and even now few studies in literature take into account this factor. The present work is a detailed numerical study of some effects of film cooling. 3D CFD-RANS simulations have been performed to infer interesting trends of adiabatic superposition effects and conjugate heat transfer performances. In particular, several calculations have been carried out to evaluate single row and multi-row film cooling behavior in terms of heat transfer coefficient, overall and adiabatic effectiveness. Test were conducted with blowing ratios between 0.5 and 5.5, coolant Reynolds from 1000 to 16000.
Heat Transfer Enhancement of Steam-Reformation by Passive Flow Disturbance Inside the Catalyst Bed
Authors: Liao Chang-Hsien , Erickson Paul Anders
Published: April 2009

Because of the potential for high efficiency and low emissions, hydrogen powered fuel cell systems are considered to be the next generation power source for both stationary and transportation applications. Providing a hydrogen source to feed a fuel cell is a critical challenge. Steam reforming processes are demonstrated for producing hydrogen for fuel cell and other applications. Generating hydrogen via steam reformation requires that heat energy be transferred to the reactants to support the endothermic reaction. For a cylindrical steam-reforming reactor, large thermal gradients between the heat source (reactor wall) and reactor centerline create a non-ideal condition for complete conversion. This gradient is caused by insufficient heat transfer inside the catalyst bed. Passive flow disturbance inside the catalyst bed provides a potential to enhance the heat and mass transfer in the steam reforming process. This paper presents experimental research that investigates the effect of changing the flow pathway inside the reactor to improve the heat and mass transfer and thus enhance fuel conversion. The results of this study contribute to the improvement of reformer design for better fuel processing system performance.
Thermal Transport Due to Phonons in Nano-Particulate Media in the Multiple and Dependent Elastic Scattering Regime
Authors: Prasher Ravi
Published: April 2009

Effects of multiple and dependent elastic scattering of phonons due to nano particles on thermal transport due to phonons in nano particulate media are investigated in this paper under various approximations. Multiple scattering means that the scattered wave from one particle is incident on another particle to be scattered again. Dependent scattering means far-field interference of the scattered waves due to phase difference, which is ignored in the independent scattering regime. Results show that multiple scattering primarily affects the velocity and density of states of phonons and dependent scattering primarily affects the mean free path of phonons. Effects of both multiple and dependent scattering increases with increasing volume fraction of the elastic scatterers. Modification of these parameters affects the equilibrium phonon intensity and the thermal conductivity of phonons. Finally a new simplified model called dependent effective field approximation is introduced in this paper. This model accurately captures the effects of both multiple and dependent scattering.
Multiscale Analysis of Silicon LPCVD Reactor
Authors: Sakiyama Yukinori , Takagi Shu , Matsumoto Yoichiro
Published: April 2009

We demonstrate the multiscale analysis of the transport phenomena in a low pressure reactor. In this method, the macroscopic phenomena such as the temperature and the density distribution are related to the microscopic electronic structure of atom/molecule. By connecting the different scales with physical models, the macroscopic properties are obtained starting from the first principle calculation without any empirical parameters. Here, we take the silicon epitaxial growth from a gas mixture of silane and hydrogen as an example. As the first step of this method, we calculated the intermolecular potential energy of SiH4/H2 using the ab initio molecular orbital calculations. Then, an analytical pair potential model was constructed to reproduce the potential energy surface obtained from the ab initio calculation. We have confirmed the validation of the potential model by comparing the experimental data of the transport properties with the molecular dynamics simulation using the potential model. Subsequently, the binary molecular collision models were constructed by the classical trajectory calculation using the potential model as the second step of the multiscale analysis. The trajectory calculations were conducted for the various combinations of the initial translational and the rotational energy. Through the statistical analysis of the trajectory calculations, the elastic/inelastic collision cross section and the scattering angle model were constructed. Finally, the direct simulation Monte Carlo simulation of flow field in a low parssure reactor was executed. The thin film thickness distribution was also investigated and discussed. This method was extended to analyze the surface reaction, which is an ongoing research work and only the current progress is reported here.
Experimental Study on Frost Formation on a Vertical Hydrophobic Cold Surface Under Natural Convection Conditions
Authors: Liu Zhongliang , Zhang Xinhua , Wang Hongyan , Meng Sheng , Ma Chongfang
Published: April 2009

Micro-observation of frost formation and deposition processes on a vertical hydrophobic cold surface was made under free convection conditions. The formation and shape variation of frost crystals during the initial period are described and the frost thickness variation with time on both hydrophobic and plain copper cold surfaces are presented. The various influencing factors are discussed in depth. The mechanism of frost formation on hydrophobic surfaces was analyzed theoretically. This revealed that increasing the contact angle can increase the potential barrier and restrain crystal nucleation and growth and thus frost deposition. The experimental results show that the initial water drops formed on a hydrophobic surface are smaller in size and remain in the liquid state for a longer time compared with ones formed on a plain copper surface. It is also observed that the frost layer deposited on a hydrophobic surface is loose and weak. Though the hydrophobic surface can retard frost formation to a certain extent and causes a looser frost layer, our experimental results show that it does not depress the growth of the frost layer.
The Performance of Methanol and Water Heat Pipes for Electronics Cooling Applications in Spacecraft Instrumentation
Authors: Bernardin John D.
Published: April 2009

Increases in the power density of electronics and the corresponding decreases in packaging space have driven the development and enhancement of numerous electronics cooling strategies. The design of cooling systems for electronics are particularly challenging in spacecraft environments where there exists the additional requirements of minimal mass and volume, high reliability, reduced complexity and number of moving parts, and ability to operate in a reduced or gravity-free environment. One cooling technique that has proven to satisfy these demanding and integrated requirements for spacecraft electronics cooling applications, involves the use of heat pipes. The heat pipe is a passive heat transport device that requires no moving parts, is highly compact and reliable, and is an efficient mover of thermal energy in reduced gravity environments. Despite all of these positive features, heat pipes do have limitations and functional characteristics that designers must be keenly aware of when incorporating them into the development of electronic cooling systems. These include, in part, limits on the heat transport capacity and operational temperature, as well as performance variations between seemingly identical heat pipes due to contamination or manufacturing flaws. This paper discusses thermal analyses and performance testing of commercial copper heat pipes that utilize a sintered copper wick with either methanol or water as the working fluid. First, the electronic cooling application, thermal operating requirements, and commercial heat pipe designs are introduced. Next, the models and analyses used to predict the heat transport limits for the heat pipes are discussed. Following this, the experimental apparatus and procedures used to characterize the thermal performance of the heat pipes are presented. Finally, with the aid of empirical data, assessments of the thermal performance of each heat pipe, the range of performance variation between heat pipes, as well as the applicability and accuracy of the analytical performance models are provided.
Numerical Investigation of Heat Transfer in Forced Convection in a Helical Pipe Filled With a Porous Medium
Authors: Cheng Liping , Kuznetsov Andrey V.
Published: April 2009

This paper investigates numerically heat transfer in a helical pipe filled with a fluid saturated porous medium. The analysis is based on the full momentum equation for porous media that accounts for the Brinkman and Forchheimer extensions of the Darcy law as well as for the flow inertia. Numerical computations are performed in an orthogonal helical coordinate system. The effects of the Darcy number, the Forchheimer coefficient as well as the Dean and Germano numbers on the axial flow velocity, secondary flow, temperature distribution, and the Nusselt number are analyzed.
Thermal-Fluid Characteristics of an Automotive Radiator Used as the External Heat Exchanger in an Auto Air Conditioning System
Authors: Jokar Amir , Hosni Mohammad H. , Eckels Steven J.
Published: April 2009

The thermal-fluid characteristics of an automotive radiator, used as the external heat exchanger in an auto air conditioning system, are experimentally analyzed and discussed in this article. The radiator in this study is a compact heat exchanger with parallel rectangular minichannels and louvered thin-plate fins. A 50% glycol-water mixture flows through the minichannels with staggered surface enhancements on the walls. On the other side, air flows through the radiator openings with the louvered thin-plate fins sandwiched between the minichannels. Single-phase heat transfer and pressure drop correlations for glycol-water flow within the minichannels and for air flow through the louvered fins are obtained and presented. The Wilson plot technique is applied to find the heat transfer coefficients on both the glycol-water and air sides. The frictional pressure drop for the glycol-water flow within the minichannels is also obtained using the Fanning equation. The uncertainty estimates for both measured and calculated parameters are then presented, and finally the results are plotted, discussed and compared with the relevant previous studies. These results show that the heat transfer rate is increased in the glycol-water side due to the surface enhancements in comparison with smooth rectangular channels. The heat transfer is enhanced on the air side as well, as compared with the flat smooth surfaces, due to the use of louvered fins.
Numerical Investigation of Laminar Impinging Jet Heat Transfer to Finned Heat Sinks
Authors: Lou Z. Q. , Yap C. , Mujumdar A. S.
Published: April 2009

A numerical study has been carried out to examine the conjugate heat transfer under a confined impinging jet using a plate-fin heat sink as the target plate. Effects of geometric parameters such as fin number, fin height and fin-to-spacing ratio are examined over a range of jet Reynolds numbers using dielectric fluid FC-72 as the fluid medium. Thermal resistance, pressure drop and Nusselt number are the main criteria used to evaluate the thermal and fluid dynamic performance of this flow system. Furthermore, the effects of fin height, fin-to-spacing ratio and jet Reynolds number on impinging jet heat transfer are obtained. The concept of an effective Nusselt number is introduced for computing the heat transfer effectiveness of heat sinks with different fin numbers.
Stability of Solutal Convection in a Gravity Modulated Mushy Layer During the Solidification of Binary Alloys
Authors: Govender S.
Published: April 2009

The linear stability theory is used to investigate the effects of gravity modulation on solutal convection in mushy layers found in solidifying binary alloys. The gravitational field is modeled to consist of constant part and a sinusoidally varying part. The linear stability results are presented for both the synchronous and subharmonic solutions, and it is demonstrated that up to the transition point between the synchronous and subharmonic regions, increasing the frequency of vibration rapidly stabilizes the solutal convection. However, beyond the transition point, further increases in the frequency tends to destabilize convection. It is also demonstrated that the effect of increasing the ratio of the Stefan number and the solid composition (ηo) is to destabilize the solutal convection.
Microscopic Effective Medium Model for Thermal Conductivity of Two Dimensional Nano-Porous and Micro-Porous Media
Authors: Prasher Ravi , Song David
Published: April 2009

Two-dimensional Nano-porous (NP) and micro-porous (MP) materials are currently used in a variety of applications which require the knowledge of the thermal conductivity (k). In NP and MP materials, two pertinent length scales determine the phonon thermal conductivity: 1) the ratio of inter-pore distance, δ, and the mean free path (m.f.p.) of phonons, 1, 2) the ratio of the pore diameter, d, and the m.f.p. of phonons. This is schematically shown in Fig. 1. In the traditional diffusion-approximation (macroscopic models) based models (1 ≪ d, δ) for the thermal conductivity of porous materials, the effective thermal conductivity, keff, of the porous material for a given shape of the pores and direction of the heat flow is only a function of the volume fraction (φ) of the pores. Therefore, in the diffusion approximation, keff can be written as keff=kmf(φ)(1) where km is the thermal conductivity of the host medium. Our focus is on cylindrical pores. We only consider the heat flow in the transverse direction as shown in Fig. 1a. For example, if φ <40%, Maxwell-Garnett effective medium model (MG EMM) can be used. f(φ) for MG EMM is given by f(φ)=1−φ1+φ(2) Experimental data on two-dimensional micro-porous silicon made of cylindrical pores have shown that the macroscopic model given by Eq. (1) grossly over predicts keff of the porous materials. In MP and NP materials, the phonon transport is ballistic in nature because of the dominant scattering of phonons from the pore boundaries. Ballistic transport becomes dominant when m.f.p is comparable to or larger than d and δ. In this regime, the Boltzmann Transport Equation (BTE) must be solved without invoking the diffusion approximation. Solving the BTE for such a complex network of pores is a challenging task, and a few previous works exist where BTE was solved numerically under various simplifying assumptions regarding the geometry and the arrangement of the pores. Both of these investigations assumed rectangular pores for two-dimensional composite or cubical pores for three-dimensional composites; however, in reality, these pores are never so simple in their geometry. Typically, these pores are cylindrical in shape for two-dimensional composites and nearly spherical in shape for three-dimensional composites. The solution of BTE for the multitude of non-planar pores, although achievable, will be a very tedious task.
Modeling of Phonon Thermal Conductivity of Two Dimensional Nano and Micro Composites in the Longitudinal Direction
Authors: Prasher Ravi
Published: April 2009

The three important length scales in composites made from nano/micro wires and fibers are: 1) the ratio of inter fiber distance and mean free path of the phonons in the host medium 2) the ratio of the diameter of the fiber or the wire and the mean free path of the phonons in the host medium and 3) the ratio of the diameter of the fiber and the mean free path of phonons in the fiber. Modeling of longitudinal thermal conductivity of two-dimensional nano and micro composites has not been attempted in the literature. This paper develops analytical modeling for the longitudinal thermal conductivity of nano and micro composites by solving the Boltzmann transport equation (BTE) for phonons. The paper shows the scattering of phonons in the host medium by the fiber boundaries play a very important role in deciding the thermal conductivity of nano and micro composites. The model is in good agreement with data on thermal diffusivity of Bismuth Telluride nanowire/ Alumina composite.
Piezoelectric Actuating Sprayed Phase-Change Cooling Technique for VLSI Chips
Authors: Huang Yu-Lin , Chang Shuo-Hung , Wang Chin-Horng , Lee Chiung-I
Published: April 2009

To develop high performance cooling systems for high heat generation electronic devices, such as CPU, the spray cooling technique using piezoelectric (PZT) actuator in vacuum with its experimental results will be described. The water droplets were ejected through an circular orifice array membrane vibrating at high frequency bending mode which was excited by a ring-shape PZT actuator. Two parts of experiment has been conducted that including the driving conditions for PZT and the heat transfer of the micro scale water droplet. Furthermore, the maximum heat transfer rate has been evaluated at different ambient pressure. The cooling capability at a wide range of operation conditions was measured. The experimental results indicate that the stability of the spray flow rate will affect the heat transfer rate dramatically. In our experiment, the water was used as the coolant and 30 μm diameter orifice array. At a flow rate of 1.2 ml/min will remove the heat over 50.3 W/cm2, and the copper surface would be 123.18°C. When vacuum technique is used to reduce the operation pressure to 21.33 kPa, the copper surface temperature can decrease to 85.78°C at 50.3 W/cm2 heat flux. The described cooling technique demonstrates competitive potential for next generation cooling for CPU applications.
Comparison of a New Numerical Model With the Published Data for Enthalpy Wheel and Air Dehumidifier: Study of Optimum Speed and Wall Effects
Authors: Esfandiarinia Fatemeh , van Paassen Dolf , Saidi Mohamad Hassan
Published: April 2009

In this paper the analytical and simulation modelling of the combined heat and mass transfer processes that occur in a solid desiccant wheel is carried out. Using the numerical method, the performance of adiabatic rotary dehumidifier and enthalpy wheels are parametrically studied, and the optimal rotational speed is determined by examining the outlet adsorption-side humidity profiles. A comparison of solutions for different conditions used in the air dehumidifier has been investigated according to the previously published studies. These approaches have been developed for enthalpy wheels. The simulated results have been compared with the published actual values of an experimental work. This substantiates the validity of the model. In addition, the effect of wall thickness on outlet water content and the wheels efficiency for different rotation speeds and different sorption characteristics are taken into consideration. The model accuracy with respect to the key variables (outlet and inlet temperatures and humidity) is optimized to minimize margin of error. This method is useful to study and model solid desiccant dehumidification and cooling systems.
Flow Structure and Heat Transfer Numerical Study in a Rotor-Stator System Air-Gap
Authors: Pelle´ Julien , Boutarfa Rachid , Harmand Souad
Published: April 2009

This paper deals with flow structure and heat transfer modeling in a two coaxial disk air-gap. Numerical estimations for the local Nusselt number on the rotor, for the radial and tangential velocities are compared with experimental results obtained using PIV and infrared thermography. Models used for the numerical approach are then validated for a turbulent Reynolds Number.
Velocity and Temperature Fields Measurement of Natural Convection Flow Using Thermochromic Liquid Crystals
Authors: Me´nard Vale´rie , Stitou Adel , Le Masson Ste´phane , No¨rtersha¨user David , Millan Pierre
Published: April 2009

Based on a particular property of some liquid crystal to reflect a specific wavelength for a specific temperature, Particle Image Velocimetry and Thermometry (PIVT) is a method allowing to measure simultaneously velocity and temperature fields. In a first part, this study discusses PIVT calibration methods and especially the effect of liquid crystal particle deposition on hue and intensity response. An experimental set-up is designed and the results confirm the high variations of intensity response with time and the need to use a simple relationship between hue and temperature. In a second place, these results are used to apply PIVT to an unsteady natural convection flow in a cavity containing an internal heat source.
Natural Convective Heat Transfer From an Unconfined or a Confined Heated Surface
Authors: Liu L. K. , Lin T. W. , Wu M. C. , Peng C. H. , Hung Y. H.
Published: April 2009

A series of experimental investigations with a stringent measurement method on the natural heat transfer from an unconfined or confined smooth and extended surface have been successfully conducted. From the results, the maximum transient-/steady-state local Nusselt number exists in the region near the edge of the heated smooth or extended surface, and the transient-/ steady-state local Nusselt number decreases along the distance from the surface edge toward the surface center. The transient-/steady-state local and average Nusselt number increases with increasing Grs, H/W or Hes/W. The effects of Grs, H/W and Hes/W on the Nus/Nus,o distribution are not significant; and the Nus/Nus,o distribution can be expressed as a generalized bowl-shaped profile, which is independent of Grs, H/W and Hes/W. By the statistical sensitivity analysis of ANOVA F-test, the steady-state average Nusselt number for unconfined/confined smooth or extended surface is significantly affected by either one of Grs, H/W and Hes/W. Among them, Grs has the most significant effect. Four new correlations of steady-state average Nusselt number in terms of relevant influencing parameters for unconfined/ confined smooth or extended surfaces are proposed, respectively. Furthermore, two normalized steady-state average Nusselt numbers for confined smooth or extended surfaces are proposed, respectively. As compared with the steady-state average Nusselt numbers for unconfined/confined smooth surface, the steady-state heat transfer enhancement for unconfined/confined extended surface can be achieved between 93.99% and 254.65%.
Radiation Heat Transfer in SOFC Electrolytes
Authors: Daun K. J. , Beale S. B. , Liu F. , Smallwood G. J.
Published: April 2009

Due to their high operating temperature, there has been speculation that thermal radiation may play an important role in the overall heat transfer within the electrode and electrolyte layers of solid oxide fuel cells (SOFCs). This paper presents a detailed characterization of the thermophysical and radiative properties of the composite materials, which are then used to define a simple 2-D model incorporating the heat transfer characteristics of the electrode and electrolyte layers of a typical planar SOFC. Subsequently, the importance of thermal radiation is assessed by comparing the temperature field obtained using a conduction model with fields obtained using coupled conduction/radiation models. Contrary to some published literature, these results show that radiation heat transfer has a negligible effect on the temperature field within these components, and does not need to be accommodated in comprehensive thermal models of planar SOFCs.
Development of a Convective Heat Transfer Measurement Technique for Flow Downstream of Support Grids in Rod Bundles
Authors: Holloway Mary V. , Beasley Donald E. , Conner Michael E.
Published: April 2009

Convective heat transfer coefficients are measured for flow downstream of support grids in a rod bundle. The rod bundle geometry consists of a 5×5 square array of parallel rods that are held on a constant pitch by a series of support grids spaced axially along the rod bundle. The rods are heated using direct resistance heating, and a bulk axial flow of air is used to cool the rods in the rod bundle. The support grid designs are modified to enhance the local heat transfer in the rod bundles. The present study examines the heat transfer enhancement downstream of standard, disc, and split-vane pair support grid designs. Results indicate that the heat transfer downstream of the support grid designs is enhanced for up to 10 hydraulic diameters downstream of the support grid. The heat transfer enhancement for the disc and split-vane pair support grid designs is greater than that of the standard support grid design. The heat transfer development downstream of the split-vane pair support grid designs indicates a decreased region of heat transfer below that of the fully-developed heat transfer for the Reynolds numbers investigated. The heat transfer results are the first presented in the open literature for flow downstream of a fully-heated span for disc and split-vane pair support grid designs.
Discrete Optimization of Radiant Heaters With Simulated Annealing
Authors: Porter Jason M. , Larsen Marvin E. , Howell John R.
Published: April 2009

The simulated annealing algorithm is used to seek optimal radiant heater configurations that provide a desired distribution of incident radiant energy onto a surface. The problem is motivated by a need to create well-understood boundary conditions that simulate fire environments. A bank of halogen lamps irradiates the back of a thin black plate (called a shroud), which simulates the fire environment. For such fire simulations, shroud temperatures routinely exceed 1000 °C and thermal radiation is the dominant mode of heat transfer. The test specimen is then heated by placing it in front of the shroud. The panel, accommodating the radiant heaters (lamps), provides equally spaced slots all of which are powered at the same voltage. Lamp positioning is crucial to obtaining a uniform temperature on the shroud, but determining the best positioning of the lamps experimentally through trial and error has proven difficult. The discrete optimization problem searches possible lamp configurations by simulating adding or removing lamps from the panel. Inverse heat transfer methods have been successfully applied to similar problems. Applying inverse heat transfer methods to this problem, the desired boundary conditions on the shroud are used to solve for the required heater settings. Two boundary conditions are needed: the temperature profile and the heat flux profile on the shroud. The heat flux profile is determined by calculating the radiation heat transfer between the shroud and the test object. However, because the heaters used in the design can only assume discrete positions and are all maintained at the same power level, traditional inverse methods fail. A discrete inverse radiation heat transfer solution method is needed. In this study, a simulated annealing optimization routine is used to determine optimal heater positions given desired boundary conditions on the shroud. Computational characteristics of simulated annealing are presented as well as results of the optimization.
Partial Melting and Resolidification of Single-Component Metal Powder With a Moving Laser Beam
Authors: Xiao Bin , Zhang Yuwen
Published: April 2009

Partial melting and resolidification of single-component metal powders with a moving laser beam is investigated numerically. Since laser processing of metal powder is a very rapid process, the liquid layer and solid core of a partially molten powder particle may not at thermal equilibrium and have different temperatures: the temperature of the liquid part is higher than the melting point, and the temperature of the solid core is below the melting point. Therefore, the local temperature of regions with partial molten particles is within a range of temperature adjacent to the melting point, instead of at the melting point. The partial melting of the metal powder is also accompanied by shrinkage that drives out the gas in the powder bed and the powder structure is supported by the solid core of the partially melted powder particles. Melting with shrinkage and resolidification are described using a temperature transforming model. The convection driven by capillary and gravity forces in the melting liquid pool is formulated by using Darcy’s law. The effects of laser beam intensity and scanning velocity on the shape and size of the heat affected zone and molten pool are investigated.
Thermal Transport in Nanotube Composites for Large-Area Macroelectronics
Authors: Kumar Satish , Alam Muhammad A. , Murthy Jayathi Y.
Published: April 2009

Thermal transport in a new class of nanocomposites composed of isotropic 2D ensembles of nanotubes or nanowires in a substrate is considered for use as the channel region of thin film transistors. The random ensemble is generated numerically and simulated using a finite volume scheme. The effective thermal conductivity of a nanotube network embedded in a thin substrate is computed. Percolating conduction in the composite is studied as a function of wire/tube densities and channel lengths. The conductance exponents are validated against available experimental data for long channels devices. The effect of tube-tube contact conductance, tube-substrate contact conductance and substrate-tube conductivity ratio is analyzed for various channel lengths. It is found that beyond a certain limiting value, contact parameters do not result in any significant change in the effective thermal conductivity of the composite. It is also observed that the effective thermal conductivity of the composite saturates beyond a limiting channel-length/tube length ratio for the range of contact parameters under consideration.