bluuebunny/crossref_metadata_2025 huggingface dataset:
Management and environmental factors involved in equine influenza outbreaks in Ireland 2007–2010
Authors: GILDEA S. , ARKINS S. , CULLINANE A.
Published: March 2011

Reasons for performing study: Outbreaks of equine influenza (EI) in endemic populations continue to cause economic loss despite widespread vaccination.

Hypothesis: To identify the key management and environmental factors that determine the risk of horses contracting EI in an endemic country and to identify control strategies.

Methods: Real time‐polymerase chain reaction (RT‐PCR), virus isolation and haemagglutination inhibition were carried out on nasopharyngeal swabs and clotted blood samples collected from horses and ponies showing signs of respiratory disease. On premises where a diagnosis of EI was confirmed, the attending veterinary surgeon was asked to participate in an epidemiological investigation.

Results: Between June 2007 and January 2010, EI outbreaks were diagnosed on 28 premises located in 13 of the 32 counties of Ireland. Veterinary advice was sought on average more than 5 days after the first clinical signs were observed. The majority of diagnoses were made by RT‐PCR. Data from 404 horses on 16 premises were used in the epidemiological analysis. In 15 premises, EI was identified following movement of horses. Housing type, teaser stallions or fomites/personnel contributed to virus spread. Vaccination status, number of years vaccination, time since last vaccination and age influenced disease expression. Isolation and vaccination were effective control measures on the premises where they were implemented.

Conclusions: Preventative measures include: isolation, clinical monitoring, serological testing and vaccination of new arrivals, booster vaccination of horses at 6 monthly intervals, maintenance of effective boundaries between equine premises and avoidance of stabling in single air spaces. Control measures include: prompt isolation of suspected cases, rapid diagnosis by RT‐PCR, booster vaccination of cohorts and implementation of biosecurity measures to avoid transmission by fomites and personnel.

Potential relevance: Implementation of these preventative and control measures should reduce the economic losses associated with outbreaks of EI.
Influence of Dissipated Energy on Shear Band Spacing in HY-100 Steel
Authors: Oussouaddi O. , Daridon L. , Ahzi S. , Chrysochoos A.
Published: March 2011

To analyze the formation of multiple shear bands in HY-100 steel, we consider an infinitely extended layer of finite thickness subjected to shear loading. The perturbation approach, associated with numerical methods, is used to determine the instability modes. The criteria of Wright–Ockendon and Molinari are used to determine the shear band spacing. The hypothesis consisting in considering the proportion of plastic work dissipated as heat (quantified by the Taylor–Quinney coefficient β) as independent of the loading path is now recognized as highly simplistic. The present study attempts to provide a systematic approach to the inelastic heat fraction evolution for a general loading within the framework of thermoviscoplastic standard modeling, including a number of material parameters as strain hardening, strain rate sensitivity, and thermal softening. The effect of each material parameter on the shear band spacing is determined by using a power law constitutive relation. The Johnson–Cook and power law models are used to illustrate the influence of the constitutive relation on the results for the adiabatic shear band spacing by studying the response of HY-100 steel. We have compared our results with available experimental results in the literature over a very wide range of strain rates (103–105 s−1). In this study, we show that the variation in the Taylor–Quinney parameter β(γ) as a function of shear strain is an important parameter that plays a significant role in the calculation of the shear band spacing.
Film Thickness and Heat Transfer Measurements in a Spray Cooling System With R134a
Authors: Martínez-Galván Eduardo , Ramos Juan Carlos , Antón Raúl , Khodabandeh Rahmatollah
Published: March 2011

Experimental measurements in a spray cooling test rig have been carried out for several heat fluxes in the heater and different spray volumetric fluxes with the dielectric refrigerant R134a. Results of the heat transfer and the sprayed refrigerant film thickness measurements are presented. The film thickness measurements have been made with a high speed camera equipped with a long distance microscope. It has been found that there is a relation between the variation in the average Nusselt number and the film thickness along the spray cooling boiling curve. The heat transfer regimes along that curve are related not only with a variation in the average Nusselt number but also with changes in the film thickness. The qualitative analysis of those variations has served to understand better the heat transfer mechanisms occurring during the spray cooling.
Iterative Methods for Eigenvalues of Viscoelastic Systems
Authors: Adhikari Sondipon , Pascual Blanca
Published: March 2011

This paper proposes a new iterative approach for the calculation of eigenvalues of single and multiple degree-of-freedom viscoelastic systems. The Biot model of viscoelasticity is assumed. With this model, the viscoelastic forces depend on the past history of motion via convolution integrals over exponentially decaying kernel functions. Current methods to solve this type of problem normally use the state-space approach involving additional internal variables. Such approaches often increase the order of the eigenvalue problem to be solved and can become computationally expensive for large systems. The method proposed in this paper is aimed to address this issue. In total, five iterative algorithms for the real and complex eigenvalues of single and multiple degree-of-freedom systems have been proposed. The results are obtained in terms of explicit closed-form expressions. This enables one to approximately calculate the eigenvalues of complex viscoelastic systems using the eigenvalues of the underlying elastic systems. Representative numerical examples are given to verify the accuracy of the derived expressions.
Modeling Analysis of Different Renewable Fuels in an Anode Supported SOFC
Authors: Andersson Martin , Paradis Hedvig , Yuan Jinliang , Sundén Bengt
Published: March 2011

It is expected that fuel cells will play a significant role in a future sustainable energy system due to their high energy efficiency and possibility to use as renewable fuels. Fuels, such as biogas, can be produced locally close to the customers. The improvement for fuel cells during the past years has been fast, but the technology is still in the early phases of development; however, the potential is enormous. A computational fluid dynamics (CFD) approach (COMSOL MULTIPHYSICS) is employed to investigate effects of different fuels such as biogas, prereformed methanol, ethanol, and natural gas. The effects of fuel inlet composition and temperature are studied in terms of temperature distribution, molar fraction distribution, and reforming reaction rates within a singe cell for an intermediate temperature solid oxide fuel cell. The developed model is based on the governing equations of heat, mass, and momentum transport, which are solved together with global reforming reaction kinetics. The result shows that the heat generation within the cell depends mainly on the initial fuel composition and the inlet temperature. This means that the choice of internal or external reforming has a significant effect on the operating performance. The anode structure and catalytic characteristic have a major impact on the reforming reaction rates and also on the cell performance. It is concluded that biogas, methanol, and ethanol are suitable fuels in a solid oxide fuel cell system, while more complex fuels need to be externally reformed.
CFD Modeling: Different Kinetic Approaches for Internal Reforming Reactions in an Anode-Supported SOFC
Authors: Paradis Hedvig , Andersson Martin , Yuan Jinliang , Sundén Bengt
Published: March 2011

Fuel cells are electrochemical devices that convert chemical energy into electricity. Solid oxide fuel cells (SOFCs) are a particularly interesting type because they can reform hydrocarbon fuels directly within the cell, which is possible, thanks to their high operating temperature. The purpose of this study is to develop an anode-supported SOFC theoretical model to enhance the understanding of the internal reforming reactions and their effects on the transport processes. A computational fluid dynamics approach, based on the finite element method, is implemented to unravel the interaction among internal reforming reactions, momentum, and heat and mass transport. The three different steam reforming reaction rates applied were developed and correlated with experimental studies found in the literature. An equilibrium rate equation is implemented for the water-gas shift reaction. The result showed that the reaction rates are very fast and differ quite a lot in size. The pre-exponential values, in relation to the partial pressures, and the activation energy affected the reaction rate. It was shown that the anode structure and catalytic composition have a major impact on the reforming reaction rate and cell performance. The large difference between the different activation energies and pre-exponential values found in the literature reveals that several parameters probably have a significant influence on the reaction rate. As the experiments with the same chemical compositions can be conducted on a cell or only on a reformer, it is important to reflect over the effect this has on the kinetic model. To fully understand the effect of the parameters connected to the internal reforming reaction, microscale modeling is needed.
A Solution for the Stabilization of Electrodynamic Bearings: Modeling and Experimental Validation
Authors: Tonoli Andrea , Amati Nicola , Impinna Fabrizio , Detoni Joaquim Girardello
Published: March 2011

Electrodynamic bearings are a kind of passive magnetic bearings based on eddy currents that develop between a rotating conductor and a static magnetic field. Relative to active magnetic bearings, their passive nature implies several advantages such as the reduced complexity, improved reliability, and smaller size and cost. Electrodynamic bearings have also drawbacks such as the difficulty in ensuring a stable levitation in a wide speed range. The most common solution to improve the stability is to add a nonrotating damping between the rotor and the stator. Although effective, this solution implies the installation of a dedicated magnet on the rotor. This increases the rotor weight and complexity and rises some concerns about the mechanical resistance. The aim of the present work is to experimentally validate the model of an electrodynamic bearing proposed by the same Authors in a previous paper and to investigate a new solution for the stabilization of electrodynamic bearings based on the introduction of compliant and dissipative elements between the statoric part of the bearing and the ground. The performances of the proposed solution are studied in the case of a simple Jeffcott rotor by means of root loci to investigate the stability of the system. The results show an improved stability relative to the test cases reported in the literature.
Effect of Cyclic Strain on the Mechanical Behavior of a Thermoplastic Polyurethane
Authors: Avanzini A. , Gallina D.
Published: March 2011

Thermoplastic polyurethanes (TPUs) are polymeric materials employed in a wide array of applications in the industrial field. Knowledge of their mechanical behavior is essential in order to obtain an accurate prediction of stresses and deformations resulting from loading. Mechanical and physical properties of these materials have been studied in the past, but their stress-strain behavior in the presence of cyclic loading has comparatively received much less attention. In this paper, experimental and constitutive modeling aspects concerning cyclic mechanical response of a TPU are investigated. The effect of imposing a cyclic strain on a TPU is studied by means of an experimental procedure based on alternate-symmetric tests in strain control at different strain levels and frequencies. During the tests, the increase in temperature due to the hysteretic heating can also be controlled by means of a compressed air cooling apparatus specifically devised. By taking advantage of the possibility of controlling and stabilizing temperature, the cyclic mechanical response can then be investigated at different temperatures and strain levels. A transient thermal analysis using finite element method (FEM) was also carried out to investigate temperature distribution on the specimen. TPU exhibited cyclic softening, and by comparing stabilized material response at different temperatures, cyclic softening was shown to be composed of a mechanical contribution and a thermal component. The TPU’s stress-strain curve changed considerably under cyclic loading conditions. In particular, cyclic softening was observed to increase with temperature and imposed cyclic strain, with a progressive shrinking of hysteresis loop passing from virgin condition to stabilized cyclic condition. Based on the experimental data, the cyclic curve could be determined as a function of temperature and could be fitted with a hyperelastic law in which material parameters are temperature dependent. The TPU exhibited significant sensitivity to cyclic loading, and this study demonstrated the importance of considering mechanical response in cyclic condition for design purposes. In particular, the identification of mechanical and thermal contributions to cyclic softening can be useful when studying fatigue failure mechanisms of these materials. Knowledge of cyclic curve can help when developing constitutive model for polymers to better predict a long-term behavior when cyclic loading is expected. The introduction of a dependence of cyclic curve on temperature allows considering simultaneously the new “material state” of the cycled polymer and, with some limitations, the thermal influence on mechanical response.
Posture, Workspace, and Manipulability of the Metamorphic Multifingered Hand With an Articulated Palm
Authors: Cui Lei , Dai Jian S.
Published: March 2011

This paper presents a novel multifingered hand with an articulated palm that makes the hand adaptable and reconfigurable. The posture of the new multifingered hand is enhanced by the additional motion of the palm and the workspace of fingers is augmented by the palm workspace. To analyze this integrated workspace, this paper introduces finger-operation planes to relate the finger motion to the palm motion and its configuration. Normals of these operation planes are used to construct a Gauss map. Adding an additional dimension, a four-dimensional ruled surface can be generated from this map to illustrate variation of posture. With the change of palm configurations, a posture manifold can be developed from the posture ruled surfaces. The workspace analysis is developed by introducing a palm workspace-triangle. This workspace-triangle evolves into a helical workspace-triangle tube when palm inputs vary and further develops into a four-dimensional presentation. This progresses into a set of workspaces of the multifingered hand by varying the palm configuration, leading to a larger workspace of the new multifingered hand as the union of the workspaces corresponding to individual palm configuration. This paper further investigates manipulability of the multifingered hand by modeling the contact point as a hypothetical spherical joint. Based on reciprocity relationship of screw systems, the finger Jacobian matrices and the hand Jacobian matrix are established. With singular value decomposition, manipulability of each finger is explored and the hand manipulability is revealed by the diagonal nature of the Jacobian matrix of the hand.
Evaluation of Turbulence Models Using Direct Numerical and Large-Eddy Simulation Data
Authors: Raiesi Hassan , Piomelli Ugo , Pollard Andrew
Published: March 2011

The performance of some commonly used eddy-viscosity turbulence models has been evaluated using direct numerical simulation (DNS) and large-eddy simulation (LES) data. Two configurations have been tested, a two-dimensional boundary layer undergoing pressure-driven separation, and a square duct. The DNS and LES were used to assess the k−ε, ζ−f, k−ω, and Spalart–Allmaras models. For the two-dimensional separated boundary layer, anisotropic effects are not significant and the eddy-viscosity assumption works well. However, the near-wall treatment used in k−ε models was found to have a critical effect on the predictive accuracy of the model (and, in particular, of separation and reattachment points). None of the wall treatments tested resulted in accurate prediction of the flow field. Better results were obtained with models that do not require special treatment in the inner layer (ζ−f, k−ω, and Spalart–Allmaras models). For the square duct calculation, only a nonlinear constitutive relation was found to be able to capture the secondary flow, giving results in agreement with the data. Linear models had significant error.
Simulation on Flow and Heat Transfer in Diesel Particulate Filter
Authors: Yamamoto Kazuhiro , Nakamura Masamichi
Published: March 2011

To reduce particulate matters including soot, a diesel particulate filter (DPF) has been developed for the after-treatment of exhaust gas. Since the filter is plugged with particles that would cause an increase of filter back-pressure, filter regeneration process is needed. However, there is not enough data on the phenomena in DPF because there are many difficulties in measurements. In this study, the flow in DPF is simulated by the lattice Boltzmann method. To focus on a real filter, the inner structure of the filter is scanned by a 3D X-ray computed tomography technique. By conducting tomography-assisted simulation, the local velocity and pressure distributions in the filter can be visualized, which is hardly obtained by measurements. Results show that, even in cold flow, the complex flow pattern is observed due to the nonuniformity of pore structure inside the filter. Based on the flow characteristics in the range of 0.2–20 m/s, simulation results show a good agreement with the empirical equation of Ergun equation. In the combustion simulation, the time-dependent temperature field inside the filter is visualized. As the temperature of inflow gas is increased, the filter regeneration process is promoted.
Cooling Characteristics of Regenerative Magnetic Refrigeration With Particle-Packed Bed
Authors: Kawanami Tsuyoshi , Hirano Shigeki , Ikegawa Masahiro , Fumoto Koji
Published: March 2011

The aim of our study was to elucidate the fundamental cooling characteristics and to improve the cooling characteristics of a room-temperature magnetic refrigerator operated under an active magnetic regenerator (AMR) cycle. The AMR refrigeration cycle, which includes a thermal storage process and a regeneration process, is used to realize a practical magnetic refrigerator operating near room-temperature. The basic components of the target AMR system are a magnetic circuit, test section, fluid-displacing device, and associated instrumentation. Spherical gadolinium particles are packed in the test section as the magnetic working substance, and air and water are used as heat transfer fluids. The cooling characteristics of the target AMR system under various operating conditions are investigated. The results show that the AMR cycle is very effective in improving the cooling performance of the room-temperature magnetic refrigerator.
Convective Boiling Heat Transfer Enhancement by Microgrooves in Plate Evaporator
Authors: Arima Hirofumi , Matsuo Nobuhiko , Shigyou Keita , Okamoto Akio , Ikegami Yasuyuki
Published: March 2011

In this experimental study, we investigate the enhancement of heat transfer in ammonia on a new plate evaporator whose surface is configured with microgrooves. The microgrooves have a depth of 30 μm and a width of 200 μm. The local boiling heat transfer coefficients were measured on the evaporator. To compare the heat transfer characteristics of the evaporator, the local boiling heat transfer coefficient on a flat surface and on two microgrooved surfaces—one vertical and one horizontal to the direction of the ammonia flow—were measured at different ranges of mass flux (2–7.5 kg/m2s), heat flux (10–20 kW/m2), and saturation pressure (0.7–0.9 MPa). The results show that the local boiling heat transfer coefficient of the horizontal and vertical microgrooved surfaces was larger than that of a flat surface. In particular, the horizontal microgrooved surface had the best heat transfer coefficient.
Multidimensional Modeling of Temperature Distribution in Engine Combustion Chamber
Authors: Li Yuanhong , Kong Song-Charng
Published: March 2011

Heat conduction calculations are coupled with in-cylinder combustion modeling for engine simulation in this study. Heat transfer on the fluid-solid interface will affect the in-cylinder combustion process, emissions formation, and thermal loading on the combustion chamber surface. Full knowledge of heat fluxes on the interface is important in helping improve engine efficiency, reduce exhaust emissions, and reduce combustion chamber thermal stresses. To account for the unsteady, non-uniform temperature distributions on the combustion chamber surface, a fully coupled numerical procedure was developed and applied to calculate in-cylinder flows and heat conduction in solids simultaneously. The current approach was first validated against analytical heat conduction solutions. The model was then applied to simulate diesel engine combustion under different operating conditions. Unsteady, non-uniform temperature distributions on the piston surface were successfully predicted. Global engine parameters including in-cylinder pressure, heat release rate, and emissions were also comparable to the experimental data.
A Numerical Algorithm and a Graphical Method to Size a Heat Exchanger
Authors: Berning Torsten
Published: March 2011

This paper describes the development of a numerical algorithm and a graphical method that can be employed in order to determine the overall heat transfer coefficient inside heat exchangers. The method is based on an energy balance and utilizes the spreadsheet application software Microsoft Excel™. The application is demonstrated in an example for designing a single pass shell and tube heat exchanger that was developed in the Department of Materials Technology of the Norwegian University of Science and Technology (NTNU) where water vapor is superheated by a secondary oil cycle. This approach can be used to reduce the number of hardware iterations in heat exchanger design.
Thermal Conductivity of Amorphous and Crystalline Mesoporous Titania Thin Films From 30 to 320 K
Authors: Fang Jin , Pilon Laurent , Reitz Christian , Brezesinski Torsten , Nemanick E. Joseph , Tolbert Sarah H.
Published: March 2011

This paper reports, for the first time, the cross-plane thermal conductivity of amorphous and crystalline templated cubic mesoporous titania thin films from 30 to 320 K. Both sol-gel and nanocrystal-based films were synthesized by evaporation-induced self-assembly with porosity of 30% to 35%, respectively. The pore diameter in sol-gel mesoporous films ranged from 14 to 25 nm and film thickness from 120 to 370 nm. Crystalline domains in crystalline mesoporous films were 9 to 13 nm in diameter. The thermal conductivity was measured between 30 and 320 K using the 3ω method. The experimental setup and the associated analysis were first validated by comparing experimental measurements with data reported in the literature for high purity silicon substrate and thermal oxide films over the temperature range considered. The thermal conductivity of sol-gel dense and mesoporous TiO2 films was found to increase with increasing temperature. The thermal conductivity of polycrystalline dense film was strongly dependent on temperature while that of dense amorphous and mesoporous films increased slowly with increasing temperature. The amorphous mesoporous TiO2 films featured very small thermal conductivity due to the fact that heat was mainly transferred by very localized non-propagating vibrational modes. Despite the particles crystallinity, the nanocrystal-based film showed significantly lower thermal conductivity than that of the sol-gel polycrystalline mesoporous thin films due to the strong phonon scattering at the nanocrystal boundaries.
Influence of Particle Alignment on Thermal Diffusivity in Transformer Cores Made of Polymer Bonded Soft Magnetic Composites
Authors: Anhalt M. , Weidenfeller B.
Published: March 2011

Measurements of thermal diffusivity α by laser flash method (LFA) have been performed on polypropylene-iron composites with filler particle content from 10vol.% to 70vol.% at temperatures from 305K to 410K. Experimental data of thermal diffusivity have been compared with existing mathematical models whereas best congruent fit is a model by Hashin and Shtrikman. Additionally to composites containing randomly distributed filler material, composites containing aligned particles where produced. LFA measurements where performed on samples in longitudinal and perpendicular direction of particle alignment. Values of thermal diffusivity in longitudinal direction of alignment where always higher than unaligned samples and in perpendicular direction of the alignment, respectively, with a maximum of 1.64: 1 (αlongitudinal: αunaligned) at a filler content of about 30vol.%.
Charging Station of a Planar Miniature Thermal Ground Plane
Authors: Ababneh Mohammed T. , Gerner Frank M. , Hurd Doug , de Bock Peter , Chauhan Shakti , Deng Tao
Published: March 2011

Thermal ground planes (TGPs) are flat thin (less than 1 mm thick) heat pipes that can be used as a thermal spreader in a variety of microelectronic cooling applications. Like conventional heat pipes, TGP’s utilize two-phase cooling. Major advantages, include the ability to integrate directly with the microelectronic substrate for a wide range of applications; and the ability to operate in an adverse gravity environment of up to 20g. Other advantages include a very high thermal conductivity, reliability, no moving parts, electrodes, or need for external power. A key factor in the design of the TGP is evacuation prior to filling and introduction of the proper amount of working fluid (water) into the device. The major challenge of this work is to fill heat pipes with a total liquid volume of less than 1 ml, without being able to see into the device. The current filling station is an improvement over the current state of the art as it allows for accurate filling of micro liter sized volumes. Tests were performed to validate performance of the system and to verify that little to no non-condensable gasses were introduced to the system. Careful calibration of the amount of liquid introduced is essential. Therefore, calibration of the burettes utilized for a liquid fill range of 0.1 ml to 100ml was important. The magnitude of the pressure inside the TGP envelope is also an important factor. Calibration curves for the burettes and error characterization curves for a range of liquid charging volumes will be presented and discussed.
Experimental Research of Boiling Heat Transfer Phenomena on Metal Surface in State of Low Gravitational Acceleration Field Between 0g and 1g
Authors: Nemoto Eiji , Saitoh Tomohiro
Published: March 2011

The paper deals with the characteristics of boiling heat transfer phenomena on the metal surfaces where gravitational acceleration between 0g and 1g acts. To conduct the experiment in the field where the gravitational acceleration between 1g and 0g acted accurately, we produced the Atwood machine that was able to obtain the fixed gravitational acceleration field known by physics well. The metallic materials used by the experiment were brass, stainless steel, aluminum, copper and these materials were processed to 10mm in the diameter, and we put these samples in liquid nitrogen and experimented on the boiling phenomenon. As a result, it has been understood that there is the feature shown next in boiling heat transfer phenomena on the metal surface in gravitational acceleration field between 0g and 1g. (1) When brass, copper, stainless steel, and aluminum of the sample were put in the liquid nitrogen, the temperature differentiation coefficient on the sample surface showed the tendency to decrease in proportion to gravitational acceleration changed from 1g into 0g. (2) In boiling heat flux curve in these metals (brass, stainless steel, aluminum and copper), it was clarified for gravitational acceleration 1g to indicate maximum heat flux value qmax.
Scaling Thermocapillary Surface Velocity in Weld Pool
Authors: Wei P. S. , Lin C. L. , Ting C. N.
Published: March 2011

In this study, the peak surface velocity driven by thermocapillary force in melting or welding pool irradiated by a distributed low-power-density beam is determined from a scale analysis. In view of different distances of diffusion between momentum and energy, the effects of Prandtl number on surface velocity are of interest. A low-power-density-beam heating implies no deep and narrow cavity (or keyhole) taking place in the pool. The results find that the peak surface velocity is proportional to the first power and 2/3 power of the surface tension coefficient or Marangoni number for high and low Prandtl number, respectively. The free surface velocity is determined by Prandtl and Marangoni numbers for given dimensionless beam power and Peclet numbers. The predictions agree with numerical computations.
Micro-Patterned Substrates With Nano-Scale Elements for Pool Boiling
Authors: Hunter Chad N. , Glavin Nicholas R. , Muratore Chris , Fisher Timothy S. , Jones John G. , Putnam Shawn A. , Khramov Alexander N. , Li Calvin H.
Published: March 2011

The critical heat flux values of copper substrates were increased from 87 to 125 W/cm2 by using a simple chemical process resulting in growth of micro and nano-scale copper structures on the surface. Pre- and post-test surface analysis revealed that the morphology of the micro and nano-scale features of these copper structures changed during the boiling process accompanied by a change in oxide layer composition. Boiling performance of the micro and nano-structured samples was repeatable when testing at lower heat fluxes.
Proposal and System Design for a Chemical Dehumidification Process
Authors: Shirai Koichi , Matsumura Yukihiko , Kitahara Hiroyuki
Published: March 2011

When used to dehumidify indoor air, ordinary air-conditioners demand abundant energy and expend it inefficiently. The mechanism of dehumidification on which they rely, the cooling of air to below its dew point to remove moisture by condensation, significantly limits the efficiency, as the air reheats once the moisture is removed. To solve this problem, our group has proposed to use desiccant. The system dehumidifies air using sodium carbonate monohydrate, a chemical that absorbs moisture and changes into decahydrate at low temperature. The compound polyethylene glycol (PEG) is added to the system as a water-transfer medium to increase the contact between the air and sodium carbonate hydrates. In earlier work our group proposed a basic system design and evaluated its efficiency. In doing so, we identified three important points neglected in the design: the power consumption for the circulation pump, the mass transfer characteristics of the spray column, and the hydration reaction rate. In the current study we evaluate a renewed design for the proposed chemical humidity-conditioning system taking these points into account. According to calculations of the system energy balance, the system enables dehumidification with higher COP by 1.5, and practical rates of mass transfer and hydration are expected from the experimental results.
The Model of Temperature Field and Chemical Heterogeneity of Solidifying Ductile-Cast-Iron Roller
Authors: Dobrovska Jana , Kavicka Frantisek , Stransky Karel , Sekanina Bohumil
Published: March 2011

The quality of the working rollers used for rolling rails of different profiles is determined by the chemical and structural composition of the material of the rollers and the production technology. It is therefore necessary to find and ensure optimal relationships between the matrix structure and the resultant values of the mechanical properties of the rollers in order to maximize the length of life. The requirements introduced here cannot be ensured without perfect knowledge of the course of solidification, cooling and heat treatment of the cast rollers as well as the kinetics of the temperature field of the casting and mould. The kinetics of the solidification has a measurable and non-negligible influence on the chemical and structural heterogeneity of the investigated type of cast-iron. Tying on to the results of the model of the temperature field of the cast rollers, an original methodology was developed for the measurement of chemical microheterogeneity.
A Study of Critical Heat Flux During Flow Boiling in Microchannel Heat Sinks
Authors: Chen Tailian , Garimella Suresh V.
Published: March 2011

The cooling capacity of two-phase transport in microchannels is limited by the occurrence of critical heat flux (CHF). Due to the nature of the phenomenon, it is challenging to obtain reliable CHF data without causing damage to the device under test. In this work, the critical heat fluxes for flow boiling of FC-77 in a silicon thermal test die containing 60 parallel microchannels were measured at five total flow rates through the microchannels in the range of 20–80 ml/min. CHF is caused by dryout at the wall near the exit of the microchannels, which in turn is attributed to the flow reversal upstream of the microchannels. The bubbles pushed back into the inlet plenum agglomerate; the resulting flow blockage is a likely cause for the occurrence of CHF which is marked by an abrupt increase in wall temperature near the exit and an abrupt decrease in pressure drop across the microchannels. A database of 49 data points obtained from five experiments in four independent studies with water, R-113, and FC-77 as coolants was compiled and analyzed. It is found that the CHF has a strong dependence on the coolant, the flow rate, and the area upon which the flux definition is based. However, at a given flow rate, the critical heat input (total heat transfer rate to the coolant when CHF occurs) depends only on the coolant and has minimal dependence on the details of the microchannel heat sink (channel size, number of channels, substrate material, and base area). The critical heat input for flow boiling in multiple parallel microchannels follows a well-defined trend with the product of mass flow rate and latent heat of vaporization. A power-law correlation is proposed which offers a simple, yet accurate method for predicting the CHF. The thermodynamic exit quality at CHF is also analyzed and discussed to provide insights into the CHF phenomenon in a heat sink containing multiple parallel microchannels.
Water-Heating Pool Boiling of Different Refrigerants on the Outside Surface of a Horizontal Smooth Tube
Authors: Chen Tailian
Published: March 2011

Heat transfer coefficients during pool boiling of five different refrigerants (R123, R245fa, R236fa, R134a, and R22) on the outside surface of a smooth copper tube were measured at the saturation temperature 6.7°C. Water flows inside the tube and provides heat to the refrigerants to boil. Measurements showed that the refrigerant of a higher vapor pressure has a higher heat transfer coefficient with the exception that R22 performs nearly the same as R134a. Compared with the predictions by the correlation developed from the data of electric-heating pool boiling on cylindrical tubes, the boiling heat transfer coefficients of the five refrigerants measured in this work are 30–46% higher. Among the pool boiling correlations reviewed in this work, the Cooper correlation (for pool boiling on cylindrical tubes) predicts the boiling heat transfer coefficients of R22 and R245fa reasonably well (within ±8.5%), but not as well for the other three refrigerants (R123, R236fa, and R134a). It is found that the predicted boiling heat transfer coefficients of the five refrigerants by the modified Gorenflo correlation (simply adding a constant multiplier of 1.47 to the correlation) are in excellent agreement with their respective measurements.
From Chip to Cooling Tower Data Center Modeling: Influence of Air-Stream Containment on Operating Efficiency
Authors: Breen Thomas J. , Walsh Ed J. , Punch Jeff , Shah Amip J. , Bash Cullen E. , Rubenstein Brandon , Heath Scot , Kumari Niru
Published: March 2011

In the drive to enhance data center energy efficiency, much attention has been placed on the prospect of airflow containment in hot-aisle cold-aisle raised floor arrangements. Such containment prevents airflow recirculation, eliminating the mixing effects of the hot and cold air streams that can cause an undesirable temperature rise at the inlet of the equipment racks. The intuitive assessment of the industry has been that the elimination of such mixing effects increases the energy efficiency of the data center cooling system by enabling delivery of air at higher inlet temperatures, thus reducing the amount of infrastructure cooling required. This paper employs an end-to-end modeling approach to analyze the effect of air stream containment in the computer room and its impact on the holistic system efficiency. Dimensionless heat index parameters are employed to characterize the effects of containment, recirculation and mixing within the computer room environment. The extent of recirculation is shown to primarily influence the operation of the rack and CRAC level cooling systems, with the chiller systems also impacted. The overall effect on the complete cooling system performance and data center efficiency requires balancing of these effects. Through this model analysis, it is shown that containment may negatively impact overall energy efficiency in some circumstances, and that recirculation may actually be beneficial to overall energy efficiency under certain system dependent operating thresholds.
Functional Materials for Energy Storage: Fabrication of Shape Stabilized Polymeric Phase Change Composites and the Determination of Their Thermophysical Properties for Use in Energy Conservation Applications
Authors: Saleem Anjum , Frormann Lars
Published: March 2011

Several polymeric thermal energy storage composites of high density polyethylene and polypropylene with two commercial paraffin waxes (PCM) P27 and P31 were prepared. The compounds were further reinforced with carbon fibers and carbon nanotubes to improve their thermal conductivity and heat transfer efficiency. The impact penetration behavior, service temperature and solvent resistance of the composites were improved by the addition of SEBS. DSC, optical microscopy, SEM, impact penetration and time–temperature history studies of the materials were done to determine the structure and thermal properties of these composites. The paraffins provide energy storage effect by solid–liquid phase change. The polymers encapsulate the paraffins so that the fluid motion of the PCMs is reduced during an application. The composites prepared were used for the construction of a small prototype swimming pool (laboratory scale). The time–temperature history of the composites, water in the container with and without energy storage materials and the environment was recorded. It was found that the composites significantly prolonged the cooling down time for water in the PCM pool. The difference between the cooling down temperature of water in a container with and without PCM composite was almost 4 hours. Moreover a computer program in C++ was written to solve the heat flow equations for the calculation of theoretical temperature–time curves.
Fluidised Bed Combustion of Blends of Coal and Pressed Sugar Beet Pulp
Authors: Ward John , Akram Muhammad , Garwood Roy
Published: March 2011

It can be difficult to burn relatively cheap, poor quality, unprepared biomass materials in industrial heating processes because of their variable composition, relatively low calorific values and high moisture contents. Consequently the stability and efficiency of the combustion process can be adversely affected unless they are co-fired with a hydrocarbon support fuel. There is a lack of information on the “optimum” conditions for co-firing of coal and high moisture biomass as well as on the proportions of support fuel which should be used. This paper is therefore concerned with the pilot scale (<25 kW thermal input) fluidised bed combustion of blends of coal with pressed sugar beet pulp, a solid biomass with an average moisture content of 71%. The experimental work was undertaken in collaboration with British Sugar plc who operate a coal-fired 40 MW thermal capacity fluidised bed producing hot combustion gases for subsequent drying applications. The project studied the combustion characteristics of different coal and pressed pulp blends over a wide range of operating conditions. It was found that stable combustion could only be maintained if the proportion of pulp by mass in the blended fuel was no greater than 50%. However evaporation of the moisture in the pressed pulp cools the bed so that the excess air which is necessary to maintain a specified bed temperature at a fixed thermal input can be reduced as the proportion of biomass in the blended fuel is increased. Therefore, with a 50/50 blend the bed can be operated with 20% less fluidising air and this will be beneficial for the output of the full scale plant since at present the flow rate of the air and hence the amount of coal which can be burnt is restricted by supply system pressure drop limitations. A further benefit of co-firing pressed pulp is that NOx emissions are reduced by about 25%. Agglomeration of the bed can be a problem when co-firing biomass because of the formation of “sticky” low melting point alkali metal silicate eutectics which result in subsequent adhesion of the ash and sand particles. Consequently longer term co-firing tests with a 50/50 blended fuel by mass were undertaken. Problems of bed agglomeration were not observed under these conditions with relatively low levels of alkali metals in the ash.
Quasi-Ballistic Heat Transfer From Metal Nanostructures on Sapphire
Authors: Minnich Austin , Chen Gang
Published: March 2011

Quasi-ballistic phonon transport, where heat transfer does not obey Fourier’s law, occurs when length scales become comparable to the phonon mean free path (MFP). Understanding this regime of heat transport is of fundamental interest, as the manner in which the heat transport deviates from Fourier’s law reveals important information about the phonon mean free path distribution. While ultrafast techniques can provide the time resolution to observe heat transfer in this regime, the minimum size of the heated region is restricted by diffraction to approximately 1 μm, which is larger than phonon MFPs in many materials. To circumvent this limit, we study heat transfer from metallic dot arrays with sub-micron diameters on sapphire fabricated using electron beam lithography. We describe heat transfer models which allow us to determine how the heat transfer in sapphire deviates from Fourier’s law at these small length scales. Our results indicate that quasi-ballistic transport occurs in sapphire when length scales are on the order of hundreds of nanometers.
Variable Pressure Humidification Dehumidification Desalination System
Authors: Narayan G. Prakash , McGovern Ronan K. , Lienhard John H. , Zubair Syed M.
Published: March 2011

Nature uses air as a carrier gas to desalinate seawater through evaporation and rain. Several investigators have previously studied desalination cycles based on carrier gas processes. However, single pressure carrier gas cycles suffer from low energy recovery and hence low performance. Here we discuss a novel carrier gas cycle which operates under varied pressure. This cycle operates the evaporation process under a reduced pressure and the condensation process at an elevated pressure to enhance energy recovery. The pressure is varied by using a mechanical compressor. This cycle has been found to be several times as efficient as the existing carrier gas cycles. In this paper, the salient features of this cycle are analyzed in an on-design sense by defining a component effectiveness for the simultaneous heat and mass exchange components and an isentropic efficiency for the compressor and the expander. Based on this study, ways to improve the cycle are proposed. The possibility of using a throttle valve instead of an expander and the effect this would have on the overall performance is reported. Comparison of the new desalination cycle with existing ones is also performed in terms of specific work consumption.
Development of Heat Sinks for Air Cooling and Water Cooling Using Lotus-Type Porous Metals
Authors: Chiba H. , Ogushi T. , Nakajima H.
Published: March 2011

In recent years, since heat dissipation rates and high frequency electronic devices have been increasing, a heat sink with high heat transfer performance is required to cool these devices. Heat sink utilizing micro-channels with several ten microns are expected to provide an excellent cooling performance because of their high heat transfer capacities due to small channel. Therefore, various porous materials such as cellular metals have been investigated for heat sink applications. However, heat sink using conventional porous materials has a high pressure drop because the cooling fluid flow through the pores is complex. Among the described porous materials, a lotus-type porous metal with straight pores is preferable for heat sinks due to the small pressured drop. In present work, cooling performance of the lotus copper heat sink for air cooling and water cooling is introduced. The experimental data for air cooling show 13.2 times higher than that for the conventional groove fins. And, the data for the water cooling show 1.7 times higher than that for the micro-channels. It is concluded that lotus copper heat sink is the most prospective candidate for high power electronics devices.
A Mechanistic Heat Transfer Correlation for Non-Boiling Two-Phase Flow in Horizontal, Inclined and Vertical Pipes
Authors: Tang Clement C. , Ghajar Afshin J.
Published: March 2011

A mechanistic heat transfer correlation is proposed to estimate heat transfer coefficient for non-boiling two-phase flow in horizontal, slightly inclined, and vertical pipes using the analogy between friction factor and heat transfer. Local heat transfer coefficients, pressure drops and flow parameters were measured for air-water flow in a 27.9 mm stainless steel pipe. The heat transfer and pressure drop data were collected by carefully coordinating the gas and liquid superficial Reynolds numbers. The proposed mechanistic correlation is validated by using experimentally measured heat transfer data. Evaluation of the mechanistic correlation with the measured heat transfer data indicated that the analogy between friction factor and heat transfer can be used with reasonable accuracy for heat transfer predictions in non-boiling two-phase pipe flow. Comparison with experimental results showed that the bulk of the data points were predicted within ±30% by the mechanistic model.