bluuebunny/crossref_metadata_2025_split huggingface dataset:
Three-Dimensional Conjugate Heat Transfer in a Horizontal Channel
With Discrete Heating
Authors: Wang Qinghua , Jaluria Yogesh 
Published: September 2004

Abstract
Three-dimensional conjugate heat transfer in a rectangular duct with two discrete flush-mounted heat sources has been studied numerically in the context of cooling of electronic equipments. The Grashof number is fixed as 106 and the working fluid is taken as air. The effects of the spatial arrangement of heat sources, the thermal conductivity ratio of the bottom plate material to air, and the Reynolds numbers on the overall and local heat transfer in the duct are evaluated. The magnitudes of the conduction and the convection transport are compared for different parametric combinations. Of particular interest are the transverse variation in the flow, temperature and heat transfer, the interaction between the heat sources, and the effects of conjugate transport.
A Computational Study on Flame-Solid Radiative Interaction in Flame
Spread Over Thin Solid-Fuel
Authors: Kumar Amit , Tolejko Kevin , T'ien James S. 
Published: September 2004

Abstract
A detailed, two-dimensional, laminar, flame spread model over a thin solid is solved in both a normal gravity downward spread configuration and in a microgravity quiescent atmosphere configuration. The radiation transfer equation is solved using discrete ordinates methods. While flame radiation plays only a secondary role in normal gravity spread, it is crucial in microgravity. By using the solid fuel total emittance and total absorptance as parameters, systematic computations have been performed to isolate the roles of flame radiative loss to the ambient, absorption of flame radiation by the solid and solid emission. Computations show that depending on the values of the solid radiation parameters, trend reversals in spread rate and extinction limits between flames in normal gravity and in microgravity can occur.
A Dual-Scale Computational Method for Correcting Surface Temperature
Measurement Errors
Authors: Tszeng T. C. , Zhou G. F. 
Published: September 2004

Abstract
The present paper addresses the measurement errors in temperature due to the effects of surface-mounted temperature sensors like thermocouples. Heat conduction into or from the installed thermocouple wires can alter the temperature at the thermocouple junction as well as in its immediate vicinity. As a result, the emf appearing at the thermocouple terminals does not correspond to the actual surface temperature. In this paper, we present a dual-scale computational method that can be used to calculate the transient temperatures at the multiple thermocouple junctions during heating or cooling of an object. The basis of the method is a thermocouple submodel embedded in a FEM model for the parent object. The numerical results of the dual-scale computational model are compared with that of the conventional FEM models as well as the analytical solutions available. This paper also discusses the characteristics of surface-mounted thermocouples in a range of configurations.
Reverse Monte Carlo Method for Transient Radiative Transfer in
Participating Media
Authors: Lu Xiaodong , Hsu Pei-feng 
Published: September 2004

Abstract
The Monte Carlo (MC) method has been widely used to solve radiative transfer problems due to its flexibility and simplicity in simulating the energy transport process in arbitrary geometries with complex boundary conditions. However, the major drawback of the conventional (or forward) Monte Carlo method is the long computational time for converged solution. Reverse or backward Monte Carlo (RMC) is considered as an alternative approach when solutions are only needed at certain locations and time. The reverse algorithm is similar to the conventional method, except that the energy bundle (photon ensemble) is tracked in a time-reversal manner. Its migration is recorded from the detector into the participating medium, rather than from the source to the detector as in the conventional MC. There is no need to keep track of the bundles that do not reach a particular detector. Thus, RMC method takes up much less computation time than the conventional MC method. On the other hand, RMC will generate less information about the transport process as only the information at the specified locations, e.g., detectors, is obtained. In the situation where detailed information of radiative transport across the media is needed the RMC may not be appropriate. RMC algorithm is most suitable for diagnostic applications where inverse analysis is required, e.g., optical imaging and remote sensing. In this study, the development of a reverse Monte Carlo method for transient radiative transfer is presented. The results of non-emitting, absorbing, and anisotropically scattering media subjected to an ultra short light pulse irradiation are compared with the forward Monte Carlo and discrete ordinates methods results.
Three-Dimensional Instabilities of Natural Convection Flow in a
Vertical Cylinder With Partially Heated Sidewall
Authors: Rubinov A. , Erenburg V. , Gelfgat A. Yu. , Kit E. , Bar-Yoseph P. Z. , Solan A. 
Published: September 2004

Abstract
The three-dimensional axisymmetry-breaking instability of an axisymmetric convective flow in a vertical cylinder with a partially heated sidewall is studied numerically. The central part of the sidewall is maintained at constant temperature, while its upper and lower parts are thermally insulated. The dependence of the critical Grashof number on the cylinder aspect ratio (A=height/radius) is obtained for a fixed value of the Prandtl number, Pr=0.021, and fixed length of the heated central region, equal to the cylinder radius. Three different modes of the most dangerous three-dimensional perturbations, which replace each other with the variation of the aspect ratio, are found. Comparison with experiment shows a good agreement at the aspect ratio A=8 and 12, while at A=4 a significant disagreement is observed. Possible reasons for this disagreement are discussed. At A=4, the dependence of the critical Grashof number on the Prandtl number is studied in the range 0&lt;Pr&lt;0.05, to rule out the possibility that the disagreement is due to uncertainty in values of fluid properties. The similarities and differences of instabilities in the cylindrical and rectangular geometries are examined. The computations are carried out using two independent numerical approaches, which cross-validate each other.
Numerical Analysis of Natural Convection and Mixing in Two-Fluid
Stratified Pools With Internal Heat Sources
Authors: Gubaidullin A. A. , Sehgal B. R. 
Published: September 2004

Abstract
The heat transport in two-layer fluid systems has been investigated numerically for slice-type semicircular pools with internal heat sources. The fixed interface model has been applied to study natural convection in the system of the immiscible fluids. The double-diffusion model has been employed to describe the heat transfer and mixing for the miscible fluids. The numerical results are compared to data measured in the SIMECO experiments. Based on the numerical simulations, the effect of the ratio of the fluid properties has been quantified. The results are of interest for the corium melt coolability in a postulated severe accident scenario in a light water reactor.
A New Model for the Effect of Calcium Sulfate Scale Formation on Pool
Boiling Heat Transfer
Authors: Jamialahmadi M. , Müller-Steinhagen H. 
Published: September 2004

Abstract
Scale deposition on the heat transfer surfaces from water containing dissolved salts considerably reduces fuel economy and performance of heat transfer equipment. This problem is more serious during nucleate boiling due to the mechanisms of bubble formation and detachment. Using a precision pool boiling test apparatus, the effects of heat flux and calcium sulfate concentration on heat transfer coefficient and formation and growth of deposits are investigated. The transient change in heat transfer is closely related to wick boiling, and the associated changes in bubble departure diameter and bubble site density. A physically sound prediction model was developed for the prediction of heat transfer coefficients as a function of time during deposition processes. Based on comparison with experimental data over a wide range of foulant concentrations and heat fluxes, the model is considered to be sufficiently accurate for practical application.
Nano-Scale Machining Via Electron Beam and Laser Processing
Authors: Wong Basil T. , Mengüç M. Pinar , Vallance R. Ryan 
Published: September 2004

AbstractIt is recently conceptualized that nano-scale machining might be achieved by coupling electron emission with radiation transfer. A laser may be used to heat a workpiece to a threshold temperature, and a nano-probe might then transfer additional energy via electron emission to remove a minute amount of material. To investigate this hypothesis, a detailed numerical study is presented. The electron-beam transport is modeled using a Monte Carlo approach, and a radiation transfer model that includes Fresnel reflections is adapted to simulate laser heating. The numerical study suggests that approximately 0.5 W from a single electron-beam is sufficient to initialize local evaporation from a gold film. With the use of a laser, the required power can be halved if the film is sufficiently thin. This paper describes the details of the numerical study and establishes guidelines for such nano-scale machining processes.
Finite Size Effects in Determination of Thermal Conductivities: Comparing Molecular Dynamics Results With Simple Models
Authors: Chantrenne Patrice , Barrat Jean-Louis 
Published: September 2004

AbstractThe thermal conductivity of nanometric objects or nanostructured materials can be determined using nonequilibrium molecular dynamics (NEMD) simulations. The technique is simple in its principle, and resembles a numerical guarded hot plate experiment. The “sample” is placed between a hot source and a cold source consisting of thermostatted sets of atoms. The thermal conductivity is obtained from the heat flux crossing the sample and the temperature profile in the system. Simulation results, however, exhibit a strong dependence of the thermal conductivity on the sample size. In this paper, we discuss the physical origin of this size dependence, by comparing MD results with those obtained from simple models of thermal conductivity based on harmonic theory of solids. A model is proposed to explain the variation of the thermal conductivity with system size.
The Effects of Nozzle Diameter on Impinging Jet Heat Transfer and
Fluid Flow
Authors: Lee Dae Hee , Song Jeonghoon , Jo Myeong Chan 
Published: September 2004

Abstract
The effects of nozzle diameter on heat transfer and fluid flow are investigated for a round turbulent jet impinging on a flat plate surface. The flow at the nozzle exit has a fully developed velocity profile. A uniform heat flux boundary is created at the plate surface by using gold film Intrex, and liquid crystals are used to measure the plate surface temperature. The experiments are performed for the jet Reynolds number (Re) of 23,000, with a dimensionless distance between the nozzle and plate surface L/d ranging from 2 to 14 and a nozzle diameter (d) ranging from 1.36 to 3.40 cm. The results show that the local Nusselt numbers increase with the increasing nozzle diameter in the stagnation point region corresponding to 0⩽r/d⩽0.5. This may be attributed to an increase in the jet momentum and turbulence intensity level with the larger nozzle diameter, which results in the heat transfer augmentation. In the mean time, the effect of the nozzle diameter on the local Nusselt numbers is negligibly small at the wall jet region corresponding to r/d&gt;0.5.
Entropy Generation Minimization of Fully Developed Internal Flow With
Constant Heat Flux
Authors: Ratts Eric B. , Raut Atul G. 
Published: September 2004

Abstract
This paper uses the entropy generation minimization (EGM) method to optimize a single-phase, convective, fully developed flow with uniform and constant heat flux. For fixed mass flow rate and fixed total heat transfer rate, and the assumption of uniform and constant heat flux, an optimal Reynolds number for laminar and turbulent flow is obtained. The study also compares optimal Reynolds number and minimum entropy generation for cross sections: square, equilateral triangle, and rectangle with aspect ratios of two and eight. The rectangle with aspect ratio of eight had the smallest optimal Reynolds number, the smallest entropy generation number, and the smallest flow length.
The Condensation of Ammonia-Water Mixtures in a Horizontal Shell and
Tube Condenser
Authors: Philpott Chris , Deans Joe 
Published: September 2004

Abstract
The heat transfer rates that develop when ammonia water mixtures condense within a small, un-vented, horizontal, shell and tube condenser are examined. The vapor flow within the condenser was constrained by baffles and the condensate created formed a pool that flowed along the base of the condenser. During the test program the inlet ammonia vapor concentration to the condenser varied from 0 to 10 wt % and the maximum local vapor concentration measured was 26 wt %. The experimental results demonstrate that the condensation heat transfer rates generally decrease with increasing ammonia concentration, however at low ammonia concentrations (&lt;2 wt %) the local and overall heat transfer rates for the condenser were enhanced. When the ammonia concentration was 0.9 wt %, the vapor heat transfer rate was 34 percent greater than that predicted by the Nusselt analysis for steam at the same conditions. This enhancement is attributed to the disturbed morphology of the condensate film, created by Marangoni instabilities.
The Thermal Constriction Resistance for an Eccentric Spot on a
Circular Heat Flux Tube
Authors: Baïri A. , Laraqi N. 
Published: September 2004

Abstract
An analytical solution is proposed to calculate the thermal constriction resistance for an eccentric circular spot with uniform flux on a semi-infinite circular heat flux tube. This solution is developed using the finite cosine Fourier transform and the finite Hankel transform. It allows to calculate the stationary three-dimensional temperature distribution and the thermal constriction resistance. The results of proposed solution are in agreement with available theoretical and experimental studies. We show that the thermal constriction resistance for an eccentric contact is greater than the one of a centered contact (few tens percent), which is consistent with recent studies on random contacts. A simple correlation is also proposed to calculate the thermal constriction resistance as a function of the eccentricity and the relative contact size.
Local Pool Boiling Coefficients on the Inside Surface of a Horizontal
Tube
Authors: Kang Myeong-Gie 
Published: September 2004

Abstract
Nucleate pool boiling heat transfer of water on the inside surface of a horizontal tube of 51 mm internal diameter has been studied experimentally at atmospheric pressure. Experiments were performed at four different azimuthal angles (0 deg, 45 deg, 120 deg, and 180 deg from the tube bottom) to investigate variations in local heat transfer coefficients along the tube periphery. The local coefficient changes much along the tube periphery and the minimum was observed at the tube bottom. It is found that heat transfer on the inside surface is strongly dependent on the intensity of the liquid agitation and the evaporative mechanism.
Hydrophilic Domains of Scaffolding Protein CbpA Promote Glycosyl Hydrolase Activity and Localization of Cellulosomes to the Cell Surface of
Clostridium cellulovorans
Authors: Kosugi Akihiko , Amano Yoshihiko , Murashima Koichiro , Doi Roy H. 
Published: September 2004

ABSTRACT

CbpA, the scaffolding protein of
Clostridium cellulovorans
cellulosomes, possesses one family 3 cellulose binding domain, nine cohesin domains, and four hydrophilic domains (HLDs). Among the three types of domains, the function of the HLDs is still unknown. We proposed previously that the HLDs of CbpA play a role in attaching the cellulosome to the cell surface, since they showed some homology to the surface layer homology domains of EngE. Several recombinant proteins with HLDs (rHLDs) and recombinant EngE (rEngE) were examined to determine their binding to the
C. cellulovorans
cell wall fraction. Tandemly linked rHLDs showed higher affinity for the cell wall than individual rHLDs showed. EngE was shown to have a higher affinity for cell walls than rHLDs have.
C. cellulovorans
native cellulosomes were found to have higher affinity for cell walls than rHLDs have. When immunoblot analysis was carried out with the native cellulosome fraction bound to cell wall fragments, the presence of EngE was also confirmed, suggesting that the mechanism anchoring CbpA to the
C. cellulovorans
cell surface was mediated through EngE and that the HLDs play a secondary role in the attachment of the cellulosome to the cell surface. During a study of the role of HLDs on cellulose degradation, the mini-cellulosome complexes with HLDs degraded cellulose more efficiently than complexes without HLDs degraded cellulose. The rHLDs also showed binding affinity for crystalline cellulose and carboxymethyl cellulose. These results suggest that the CbpA HLDs play a major role and a minor role in
C. cellulovorans
cellulosomes. The primary role increases cellulose degradation activity by binding the cellulosome complex to the cellulose substrate; secondarily, HLDs aid the binding of the CbpA/cellulosome to the
C. cellulovorans
cell surface.
Transcriptional Regulation of
Vibrio cholerae
Hemagglutinin/Protease by the Cyclic AMP Receptor Protein and RpoS
Authors: Silva Anisia J. , Benitez Jorge A. 
Published: September 2004

ABSTRACT

Vibrio cholerae
secretes a Zn-dependent metalloprotease, hemagglutinin/protease (HA/protease), which is encoded by
hapA
and displays a broad range of potentially pathogenic activities. Production of HA/protease requires transcriptional activation by the quorum-sensing regulator HapR. In this study we demonstrate that transcription of
hapA
is growth phase dependent and specifically activated in the deceleration and stationary growth phases. Addition of glucose in these phases repressed
hapA
transcription by inducing
V. cholerae
to resume exponential growth, which in turn diminished the expression of a
rpoS-lacZ
transcriptional fusion. Contrary to a previous observation, we demonstrate that transcription of
hapA
requires the
rpoS
-encoded σ
s
factor. The cyclic AMP (cAMP) receptor protein (CRP) strongly enhanced
hapA
transcription in the deceleration phase. Analysis of
rpoS
and
hapR
mRNA in isogenic CRP
+
and CRP
−
strains suggested that CRP enhances the transcription of
rpoS
and
hapR
. Analysis of strains containing
hapR-lacZ
and
hapA-lacZ
fusions confirmed that
hapA
is transcribed in response to concurrent quorum-sensing and nutrient limitation stimuli. Mutations inactivating the stringent response regulator RelA and the HapR-controlled AphA regulator did not affect HA/protease expression. Electrophoretic mobility shift experiments showed that pure cAMP-CRP and HapR alone do not bind the
hapA
promoter. This result suggests that HapR activation of
hapA
differs from its interaction with the
aphA
promoter and could involve additional factors.
Adaptive Acid Tolerance Response of
Streptococcus sobrinus
Authors: Nascimento Marcelle M. , Lemos José A. C. , Abranches Jacqueline , Gonçalves Reginaldo B. , Burne Robert A. 
Published: September 2004

ABSTRACT

Streptococcus mutans
and
Streptococcus sobrinus
are the bacteria most commonly associated with human dental caries. A major virulence attribute of these and other cariogenic bacteria is acid tolerance. The acid tolerance mechanisms of
S. mutans
have begun to be investigated in detail, including the adaptive acid tolerance response (ATR), but this is not the case for
S. sobrinus
. An analysis of the ATR of two
S. sobrinus
strains was conducted with cells grown to steady state in continuous chemostat cultures. Compared with cells grown at neutral pH,
S. sobrinus
cells grown at pH 5.0 showed an increased resistance to acid killing and were able to drive down the pH through glycolysis to lower values. Unlike what is found for
S. mutans
, the enhanced acid tolerance and glycolytic capacities of acid-adapted
S. sobrinus
were not due to increased F-ATPase activities. Interestingly though,
S. sobrinus
cells grown at pH 5.0 had twofold more glucose phosphoenolpyruvate:sugar phosphotransferase system (PTS) activity than cells grown at pH 7.0. In contrast, glucose PTS activity was actually higher in
S. mutans
grown at pH 7.0 than in cells grown at pH 5.0. Silver staining of two-dimensional gels of whole-cell lysates of
S. sobrinus
6715 revealed that at least 9 proteins were up-regulated and 22 proteins were down-regulated in pH 5.0-grown cells compared with cells grown at pH 7.0. Our results demonstrate that
S. sobrinus
is capable of mounting an ATR but that there are critical differences between the mechanisms of acid adaptation used by
S. sobrinus
and
S. mutans
.
Osmosensitivity Associated with Insertions in
argP
(
iciA
) or
glnE
in Glutamate Synthase-Deficient Mutants of
Escherichia coli
Authors: Nandineni Madhusudan R. , Laishram Rakesh S. , Gowrishankar J. 
Published: September 2004

ABSTRACT

An ampicillin enrichment strategy following transposon insertion mutagenesis was employed to obtain NaCl-sensitive mutants of a
gltBD
(glutamate synthase [GOGAT]-deficient) strain of
Escherichia coli
. It was reasoned that the
gltBD
mutation would sensitize the parental strain even to small perturbations affecting osmotolerance. Insertions conferring an osmosensitive phenotype were identified in the
proU
,
argP
(formerly
iciA
), and
glnE
genes encoding a glycine betaine/proline transporter, a LysR-type transcriptional regulator, and the adenylyltransferase for glutamine synthetase, respectively. The

gltBD
+

derivatives of the strains were not osmosensitive. The
argP
mutation, but not the
glnE
mutation, was associated with reduced glutamate dehydrogenase activity and a concomitant NH
4
+
assimilation defect in the
gltBD
strain. Supplementation of the medium with lysine or a lysine-containing dipeptide phenocopied the
argP
null mutation for both osmosensitivity and NH
4
+
assimilation deficiency in a
gltBD
background, and a dominant gain-of-function mutation in
argP
was associated with suppression of these lysine inhibitory effects. Osmosensitivity in the
gltBD
strains, elicited either by lysine supplementation or by introduction of the
argP
or
glnE
mutations (but not
proU
mutations), was also correlated with a reduction in cytoplasmic glutamate pools in cultures grown at elevated osmolarity. We propose that an inability to accumulate intracellular glutamate at high osmolarity underlies the osmosensitive phenotype of both the
argP gltBD
and
glnE gltBD
mutants, the former because of a reduction in the capacity for NH
4
+
assimilation into glutamate and the latter because of increased channeling of glutamate into glutamine.