bluuebunny/crossref_metadata_2025 huggingface dataset:
Detailed Numerical Modeling of a Hybrid PCM-Air Heat Sink
Authors: Kozak Y. , Ziskind G.
Published: December 2013

The ability of phase-change materials (PCMs) to absorb large amounts of heat without significant rise of their temperature during the melting process may be utilized in thermal energy storage and passive thermal management. This paper deals with numerical modeling of a hybrid PCM-air heat sink, in which heat may be either absorbed by the PCM stored in compartments with conducting walls, or dissipated to the air using fins, or both.

Under the assumptions of perfect insulation (except for the air fins), identity and symmetry between all PCM channels, and negligible 3-D boundary effects, a 2-D model of the problem for half a PCM compartment of the heat sink is solved, saving calculation time and yet taking into account the essential physical phenomena. A commercial program, ANSYS Fluent, is used in order to solve the governing conservation equations. Phase-change is solved using the enthalpy-porosity method. PCM-air interface is modeled using the volume-of-fluid (VOF) approach. The model takes into account natural convection in the liquid PCM and air, volume change, phase- and temperature-dependence of thermal properties, and PCM-air interface interaction.

Various scenarios for the hybrid heat sink operation are simulated and compared. The difference in the melting patterns is analyzed for the cases of heating with and without the fan operating. The solidification process with the fan operating is also simulated. It is shown that the VOF model enables simulating realistic void formation in the solidification process.
Natural Convection of Viscoplastic Fluids in an Enclosure With Localized Heating and Symmetrical Cooling
Authors: Hassan Mohd. Ashique , Pathak Manabendra , Khan Mohd. Kaleem
Published: December 2013

In this study a computational investigation of two-dimensional, steady-state, natural convection of viscoplastic fluid in a square enclosure has been presented. The enclosure has been locally heated from the bottom wall using a constant heat flux source and symmetrically cooled from both the side walls. The other walls are maintained as insulated surfaces. Finite volume based code has been used in the simulation and Bingham model has been used to model the rheology of the enclosed viscoplastic fluids. Simulations have been made for three different heating lengths of the bottom wall. The flow phenomenon and heat transfer inside the enclosure have been investigated for different properties of viscoplastic fluid, heating conditions and heated length. It has been observed that for a particular thermal condition the heat transfer coefficient or the Nusselt number decrease with the increase in yield stress value of the fluid due to weakening of convective circulation.
Measurement of Thermal Conductivity for Insulation Materials in High Temperature Based on Transient Hot-Plane Method
Authors: Pan Guanfu , Yu Fan
Published: December 2013

Acquiring the thermal conductivity in high temperature accurately has important implications for using insulation materials. In this paper, the principle of the measurement of the transient hot plane method is introduced. For rising the operating temperature, the plane heat source with film is changed to no film one. So the measurement errors caused by film can be eliminated. Because of the low thermal conductivity of insulation materials and that the sample should be heated up to a high temperature, the preheating time will be too long. In order to shorten the time of preheating sample before measuring, this text introduces an original preheating method called center preheating method which is verified by the numerical simulating result. After the experimental apparatus has been established, practical measurements about thermal conductivity and thermal diffusivity have been made with ceramic fiber material in environment temperature at 23.9∼746.9°C. These experiments demonstrate favorable reproducibility and accuracy under the established apparatus in high temperature environment.
Predictions of Adsorption Enthalpy on Graphitic Surfaces Using Statistical Thermodynamics
Authors: Wemhoff Aaron P.
Published: December 2013

A method is proposed to estimate the enthalpy associated with the desorption of liquid molecules away from a solid surface as a function of temperature using a generic statistical thermodynamic formulation with known intermolecular potentials. This paper specifically focuses on coupling the well-known Redlich-Kwong fluid model with the interactive pair potential models between fluid molecules and a graphite surface. An example is applied where an approximate Lennard-Jones 6–12 intermolecular model dictates fluid-fluid molecule interaction, while the Steele potential is applied for the graphite-fluid interaction. Predictions suggest that the adsorption enthalpy of methanol on graphite is approximately 0.1 J/m2. A new metric is also established that suggests the qualitative magnitude of adsorption enthalpy for a variety of fluids, with alcohols and acetone appearing to be the most favorable.
Simulation of Blob Dynamics Inside a Channel Under Acoustic Excitation
Authors: Randive Pitambar , Dalal Amaresh , Mukherjee Partha P.
Published: December 2013

The displacement of a three-dimensional immiscible blob subject to oscillatory acoustic excitation in a channel is studied with the Lattice Boltzmann method. The effects of amplitude of the force, viscosity and frequency on blob dynamics are investigated. The trend for variation of mean displacement of blob and frequency response is in agreement to that of the previous two-dimensional studies reported in literature. The response of the blob with pinned contact line shows underdamped behavior. It is also found that increasing the amplitude of the force increases the mean displacement and frequency response.
Condensing Heat Transfer Coefficients for R134a at Different Saturation Temperatures in Inclined Tubes
Authors: Adelaja Adekunle O. , Dirker Jaco , Meyer Josua P.
Published: December 2013

This paper presents the effects of saturation temperature and inclination angle on convective heat transfer during condensation of R134a in an inclined smooth copper tube of inner diameter of 8.38 mm. Experiments were conducted for inclination angles ranging from −90° (vertical downward) to +90° (vertical upward) for mass fluxes between 100 kg/m2s and 400 kg/m2s and vapour qualities between 0.1 and 0.9 for saturation temperatures ranging between 30 °C and 50 °C. The results show that saturation temperature and inclination angles strongly influence the heat transfer coefficient. With respect to saturation temperature, an increase in saturation temperature generally leads to a decrease in heat transfer coefficient irrespective of the inclination angle. The effect of inclination angle was found to be more pronounced at mass fluxes of 100 kg/m2s and 200 kg/m2s for the range of vapour qualities considered. Within the region of influence of inclination there is an optimum angle which is between 15° and −30° (downward flow). The inclination effect corresponds to the predominance of the effect of gravity on the flow distribution.
Effect of Morphology on Spectral Radiative Properties of Three-Dimensionally Ordered Macroporous Ceria Packed Bed
Authors: Ganesan Krithiga , Randrianalisoa Jaona , Lipiński Wojciech
Published: December 2013

In this paper, radiative characterization of a packed bed of novel three-dimensionally ordered macroporous (3DOM) ceria particles is performed in the spectral range relevant to solar thermochemical processes, 0.35–2.2μm. Normal–hemispherical transmittance and reflectance of three samples of various thicknesses are measured. Monte Carlo ray-tracing and discrete ordinate methods are employed to identify transport scattering albedo and transport extinction coefficient in the spectral range corresponding to weak absorption in the semi-transparency band of ceria. 3DOM ceria particles are characterized by weaker scattering in comparison to sintered ceria ceramics, and increased transparency in the near-infrared spectral range 0.7–2 μm. The ordered pore-morphology of the 3DOM ceria after thermochemical redox cycling between temperatures 1373 K and 1073 K is altered due to sintering of walls of the 3DOM structure. The absorption coefficient of the packed bed is found to be practically independent of morphology. Radiative characterization of 3DOM ceria ceramics before and after thermochemical cycling suggests that preserving the 3DOM structure can lead to scattering characteristics that permit longer attenuation path lengths of incident concentrated solar radiation in the material, as well as be favorable for confinement of the near-infrared radiation during thermochemical cycling leading to favorable thermochemical conditions for fuel production.
Effect of Inclination Angle on the Closed Loop Pulsating Heat Pipe Thermal Performance
Authors: Pachghare Pramod R. , Mahalle Ashish M.
Published: December 2013

The closed loop pulsating heat pipe (CLPHP) is a passive two-phase heat transfer device, patented by Akachi (1990). Due to its excellent features, PHP has been considered as one of the promising technologies for electronic cooling, heat exchanger, etc. This paper presents an experimental study shows the effect of inclination angle on the thermal performance of CLPHP, which consist of 10 turns of copper tubes having inner and outer diameter 2 mm and 3.6 mm respectively. The equal lengths of evaporator, condenser and adiabatic sections are 50 mm each. Different working fluids are used as R-134a, Methanol and Water. For all experimentations, an optimum filling ratio was maintained 50% by volume. The thermal performance have been investigated with different inclination angles (viz. 0°, 20°, 40°, 60° and 90°) at various heat input from 5 to 50W in the steps of 5W. The thermal resistance (which is inversely proportional to thermal performance) of CLPHP at various heat input are plotted for different working fluids. The result shows that, the thermal resistance decreases as heat input increases. But at low heat input i.e. upto 25W, the thermal resistance decreases rapidly and the PHP performance is more sensitive to the inclination angle whereas high heat input i.e. above 25W, the thermal resistance decreases smoothly and less independent to the inclination angle. In all inclination angles, vertical bottom heat position (at 90°) of CLPHP gives best thermal performance due to presence of gravity force. At all inclination angles, the working fluid R-134a show best thermal performance followed by methanol and water.
The Shock Tube Autoignition of Biodiesels and Biodiesel Components
Authors: Wang Weijing , Oehlschlaeger Matthew A.
Published: December 2013

The autoignition of fatty-acid methyl ester biodiesels and methyl ester biodiesel components was studied in gas-phase shock tube experiments. Ignition delay times for two reference methyl ester biodiesel fuels, derived from methanol-based transesterification of soybean oil and animal fats, and four primary constituents of all methyl ester biodiesels, methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate, were measured behind reflected shock waves for fuel/air mixtures at temperatures ranging from 900 to 1350 K and at pressures around 10 and 20 atm. Ignition delay times were determined by monitoring pressure and chemiluminescence from electronically-excited OH radicals around 310 nm. The results show similarity in ignition delay times for all methyl ester fuels considered, irrespective of the variations in organic structure, at the high-temperature conditions studied and also similarity in high-temperature ignition delay times for methyl esters and n-alkanes.
Design and Optimization of High Performance Adsorption-Based Thermal Battery
Authors: Narayanan Shankar , Li Xiansen , Yang Sungwoo , McKay Ian , Kim Hyunho , Wang Evelyn N.
Published: December 2013

Electric vehicle (EV) technology faces a substantial challenge in terms of driving range, especially when the vehicle’s climate control system relies entirely on the onboard electric battery. Therefore, we are developing an advanced adsorption-based thermal battery (ATB) capable of delivering both heating and cooling for electric vehicles with minimal use of the electric battery bank. While adsorption based climate control systems offer the advantage of direct usage of primary thermal energy sources for operation, they typically have low COP values, and are often bulky and heavy. A compact and lightweight ATB is necessary to replace existing climate control systems in EVs that use electric battery for operation. In this paper, we present a detailed computational analysis of adsorption kinetics taking place within an adsorption bed that is capable of delivering large cooling and heating capacities by making use of novel adsorbents. The overall design of the adsorption bed, which is a critical element in achieving a high performance thermal battery, is also discussed. To make performance predictions, we characterized the adsorbents to obtain their thermophysical and transport properties as well as adsorption characteristics. The model consequently incorporates these measured properties to predict the performance variation as a function of time. This work provides the critical parameters affecting heating and cooling rates, and identifies avenues for further improvement in the overall performance of the thermal battery.
Molecular Dynamics Study of the Interfacial Thermal Conductance at the Graphene/Paraffin Interface in Solid and Liquid Phases
Authors: Babaei Hasan , Keblinski Pawel , Khodadadi J. M.
Published: December 2013

By utilizing molecular dynamics (MD) simulations, we study the interfacial thermal conductance at the interface of graphene and paraffin. In doing so, we conduct non-equilibrium heat source and sink simulations on systems of parallel and perpendicular configurations in which the heat flow is parallel and perpendicular to the surface of graphene, respectively. For the perpendicular configuration, graphene with different number of layers are considered. The results show that the interfacial thermal conductance decreases with the number of layers and converges to a value which is equal to the obtained conductance by using the parallel configuration. We also study the conductance for the solid phase paraffin. The results indicate that solid paraffin-graphene interfaces have higher conductance values with respect to the corresponding liquid phase systems.
Buoyancy Driven Heat Transfer Behavior of Zinc Oxide (ZnO)–Water Nanofluids
Authors: Paul Titan C. , Morshed A. K. M. M. , McCants Dale A. , Khan Jamil A.
Published: December 2013

The systematic experiments were performed for buoyancy driven heat transfer of zinc oxide (ZnO)-water nanofluids with volume fraction 0.5%, 1%, and 2% in rectangular (50×50×75mm) cavity heated from below. In addition to determining the convective heat transfer coefficients, this study also included experimental determination of density, effective thermal conductivity, and rheological behavior of nanofluids. For all the properties and natural convection behavior De-Ionized (DI) water was used as the baseline data. The results show that density measurements agree well with predicted values by equation, thermal conductivity enhanced by ∼14% for 2 vol% nanofluids, and shear thinning behavior of nanofluids. The natural convection behavior shows degradation of heat transfer and degradation increases with the volume fraction of nanoparticles. Probable reasons of degradation are discussed in the paper.
Modeling of Conduction and Natural Convection in Ice-Water Systems Containing Porous Metal Foams
Authors: Bories Sylvain , Baliga B. Rabi
Published: December 2013

Mathematical models and numerical predictions of heat conduction and laminar natural convection in ice-water systems containing porous metal foams are presented, in the context of computationally convenient two-dimensional steady-state problems with rectangular calculation domains. The Darcy-Brinkman-Forchheimer equations were used to model momentum transfer in the liquid-water-metal-foam region. For modeling the heat transfer, volume-averaged equations governing two intrinsic-phase-average temperature fields were used: one for the metal foam and the other for the water (solid or liquid). The following improvements are proposed: novel expressions for the interfacial (metal-water) heat transfer coefficient in both the convection and conduction regimes; and effective thermal conductivity correlations that provide consistency between the formulations of one-temperature and two-temperature models in the limit of local thermal equilibrium. A well-established fixed-grid, co-located, finite volume method (FVM) was adapted and used for the numerical solutions. The proposed models and FVM were used to solve the test and demonstration problems involving conduction and laminar natural convection in ice-water-aluminum-foam systems contained in rectangular enclosures. The findings and results of these investigations are presented and discussed in this paper.
Computational Investigation of Gallium Nitrite Ammonothermal Crystal Growth
Authors: Mirzaee Kakhki Iman , Charmchi Majid , Sun Hongwei
Published: December 2013

This paper presents a rigorous approach to the simulation of the GaN growth process, which involves dissolution kinetics, transport by thermal convection and crystallization kinetics. So far, a wide range of numerical efforts have been published which provide valuable information on the flow field and temperature distribution in the hydrothermal crystal growth processes; however, no research has attempted to model the mass transfer in the nutrient porous basket nor did they present a modeling of the nutrient/mineralizers/solvent chemical reactions. In addition, the rate of crystallization was not numerically considered in the model. This paper shows the feasibility of developing a robust numerical code based on models that accurately account for the rate of nutrient dissolution and crystallization kinetics. Numerical simulation results revealed that chemical reaction kinetics can directly affect the crystallization rate and is a dominant factor in this phenomenon.
Interfacial Resistance Measurement of High Performance Thermal Interface Materials
Authors: Smith Andrew N. , Jankowski Nicholas , Boteler Lauren , Meyer Christopher
Published: December 2013

Advancements in thermal interface materials have reached the resolution limit of typical ASTM D5470 based testers, which is around ±1×10−6 m2K/W. As the interfacial resistance is reduced, the temperature difference at the interface decreases and ultimately becomes difficult to measure. Standard ASTM testers utilize precise temperature sensors and knowledge of the thermal conductivity of the heat meter bar to resolve the temperature difference at the interface. It is difficult to resolve interface resistances on the order of 1×10−6 m2K/W, even when precision RTDs with a resolution of ±0.001°C are utilized, as the location uncertainty of the sensor can become important. Increasing the temperature difference across the interface is necessary for further improvement in the resolution.

This work presents a miniature ASTM type tester that was developed to address the resolution limits of standard testers by reducing the heat meter bar thickness, using a chip resistor as the heater element, and using an IR camera to measure the temperature gradient along the meter bar. Reducing the length of the heat meter bars reduces the overall resistance, and increases the resistance of the interface relative to that of the meter bars. Because of the reduced size scale of the miniature tester, measurement of the temperature profile using the typical ASTM approach of embedding temperature probes along the length of the meter bar was not feasible but instead was achieved using a relatively inexpensive uncooled long wavelength infrared camera with a microscope attachment in order to focus down to ∼100 microns. Although the IR camera increases the uncertainty of the measured temperatures, this method is shown to measure a thermal interfacial resistance of 1.45×10−6 m2K/W with an uncertainty of ±1.1×10−7 m2K/W, where the sample interface was a 2 mil AuSn preform soldered interface.
In Situ Evaluation of Vanguard Technologies for High Performance Residential Buildings
Authors: Sailor David J. , Rodriguez Santiago , Lauck Jeff
Published: December 2013

High performance buildings demand innovative and often untested strategies for improving thermal performance and reducing energy consumption while maintaining indoor environmental quality. The Passive House design standard is increasingly being implemented in residential and small commercial construction. This standard results in buildings with airtight envelopes, high levels of insulation, very high performance windows, and energy efficient appliances.

The intent of this paper is to evaluate the performance of several cutting-edge high performance building technologies as implemented in a Passive House duplex constructed in Portland, Oregon, USA. We provide an overview of the performance of the entire structure from multiple viewpoints, but focus largely on the performance of the heat recovery ventilator and heat pump water heater. Interactions of these systems with occupant behavior and indoor environmental quality are also discussed.
Effect of Channel Geometry on Ammonia Boiling Heat Transfer of a Plate-Type Evaporator
Authors: Koyama Kohei , Chiyoda Hirotaka , Arima Hirofumi , Ikegami Yasuyuki
Published: December 2013

The ocean thermal energy conversion (OTEC) is attracted attention as one of the promising renewable energy. OTEC uses small temperature difference between surface and deep sea water. Plate-type heat exchangers, or evaporators, are usually used for OTEC to obtain vapor for electric generator. Ammonia is used for OTEC as a working fluid. It is important to improve thermal performance of an evaporator for the OTEC. Channel dimension is one of the important factors to improve heat transfer performance of an evaporator. In this study, the measurement and comparison of local heat transfer coefficient for three channels are experimentally performed. The experiments are conducted for a range of mass flux (5 and 7.5 kg/m2s), heat flux (10 to 25 kW/m2), and pressure (0.7 and 0.9 MPa). The results show that the heat transfer coefficient increases as decreases channel height. The modified emprical correlation for a plate-type evaporator is proposed.
Design of a Microscale Combustor-Heat Exchanger for Low Temperature Applications
Authors: Ghazvini Mohammad , Narayanan Vinod
Published: December 2013

A design of a compact, integrated combustor and heat exchanger for low temperature applications is presented in this paper. The design involves use of several repeating unit cells that each performs three unit operations — combustion, recuperation, and heat exchange. Heat from combustion is transferred to a cold gas stream entering the device at 200K. Heterogeneous catalytic combustion occurs on the walls of microchannels in the presence of a platinum catalyst. Two levels of numerical simulations are performed to realize the design. The first level represents a single unit cell consisting of a combustor, exhaust gas, and heat exchange fluid channels. At the unit cell level, a two-dimensional numerical model with detailed surface chemistry is used to provide high unit cell thermal efficiency. It is shown that with the help of a novel distributed catalyst arrangement, extinction of the reaction due to the cold gas stream is prevented and a high hydrogen conversion (greater than 95 percent) is achieved for a range of operating conditions. The second level of simulations is at the device scale, consisting of multiple unit cells connected together with appropriate fluidic headers. At this device level, three dimensional simulations of fluid flow were performed to ensure uniformity in flow distribution while maintaining low pressure drop through the device. Fabrication constraints were also incorporated into the device level design and simulations.
Glovebox Fire Suppression Experimental and Computational Characterization
Authors: Cabrera Jan-Michael , Overholt Kristopher J. , Abbasi Mustafa , Granzow Howard N. , Gordon Derek J. , Ezekoye Ofodike A.
Published: December 2013

Gloveboxes are generally used to protect workers from the potential hazards that arise in the materials they are working with. In the middle of the 20th century gloveboxes were mainly used to protect workers against radioactive materials. Factory Mutual investigated accidents involved in gloveboxes at nuclear facilities from 1956 to 1965 that resulted in damages and contamination clean up efforts reported at $1,232,000 ($8.5 million in 2012 dollars) [1]. Fire suppression systems are therefore a key aspect to glovebox safety. Use of water based systems generally result in undesired transport of hazardous materials [2]. Halon suppression systems were used but due to its large potential to deplete ozone was phased out in the latter part of the 20th century. Activation tests of a commercial automatic fire suppression system (Fire Foe™) containing heptaflouropropane (FE-36) fire suppressant were conducted within a glovebox at the University of Texas Fire Research Group’s burn structure. Ten tests were conducted at four different fire sizes: three 13 kW, one 20 kW, three 25 kW, and three 50 kW. Activation times and gas temperatures were recorded. Gas temperatures from experiments were compared against NIST’s Fire Dynamics Simulator (FDS) gas temperatures with good agreement. More stratification was observed in experimental temperatures compared to FDS temperatures. The time and spatially averaged net heat flux on a virtual Fire Foe™ tube from the FDS simulations were passed to a thermo-physical semi-empirical submodel to predict activation. The submodel did not capture the exponential nature observed in the data of activation times versus fire heat release rate. Work is continuing on improving the submodel to capture the observed events.
Development of a Compensation Chamber for Use in a Multiple Condenser Loop Heat Pipe
Authors: Roche Nicholas A. , Cleary Martin , Peters Teresa B. , Wang Evelyn N. , Brisson John G.
Published: December 2013

We report the design and analysis of a novel compensation chamber for use in PHUMP, a multiple condenser loop heat pipe (LHP) capable of dissipating 1000 W. The LHP is designed for integration into a high performance air-cooled heat sink to address thermal management challenges in advanced electronic systems. The compensation chamber is integrated into the evaporator of the device and provides a region for volumetric expansion of the working fluid over a range of operating temperatures. Additionally, the compensation chamber serves to set the liquid side pressure of the device, preventing both flooding of the condensers and dry out of the evaporator. The compensation chamber design was achieved through a combination of computational simulation using COMSOL Multiphysics and models developed based on experimental work of previous designs. The compensation chamber was fabricated as part of the evaporator using Copper and Monel sintered wicks with various particle sizes to achieve the desired operating characteristics. Currently, the compensation chamber is being incorporated into a multiple condenser LHP for a high performance air-cooled heat sink.
Molecular Dynamic Simulation of Thermal Conductivity of Carbon Nano-Peapods
Authors: Cui Liu , Feng Yanhui , Zhang Xinxin , Li Wei
Published: December 2013

The thermal conductivity of carbon nano-peapods, carbon nanotube (10,10) filled with fullerene molecules, is investigated by Equilibrium Molecular Dynamic Simulation based on Green-Kubo’s equation. Carbon nano-peapods structures are built by HyperChem. C-C bonding interactions are determined by the AIREBO potential, and the Lennard-Jones potential is used for expressing nonbonding interactions. The results show that filled fullerenes lead to the increment of thermal conductivity, relative to the bare carbon nanotubes. The thermal conductivity of carbon nano-peapods always increases with the rising filling ratio only if the filling ration is less than 100%. Once the nanotube is fully filled with fullerene molecules, a sudden drop in the thermal conductivity appears due to the restriction of molecules’ axially translational motion. Thermal conductivity of carbon nano-peapods reduces first and then increases with the increasing temperature. In addition, the thermal conductivity increases sharply with the increasing length. The length of thermal conductivity convergence for carbon nano-peapods seems much shorter than for bare carbon nanotubes.
Parametric Study of the Transport Properties of Wicking Micro-Pillar Arrays
Authors: Tej Sai , Horner David , Moghaddam Saeed
Published: December 2013

Two-phase passive heat carriers/spreaders are effective thermal management tools. However, their thermal performance is limited due to the transport characteristics of their wick structure. To enhance the performance of passive heat spreaders and expand their use to applications with high heat loads and severe operating environments, better wick structures are being developed. Advancements in the design of these structures have been hampered by a lack of models that can predict fluid flow rate in wicks over a wide range of geometrical parameters. The focus of this study is to find such a model for micro-pillar arrays. The model is intended for use in optimizing an array to achieve maximum liquid permeability at a given hydrostatic pressure. Two wicking devices with different pillar spacings were fabricated. The maximum heat transfer capacities of the devices at various wicking lengths were compared with predictions of selected correlations. A model by Byon et al. [1] predicted the experimental results with reasonable accuracy.
Discriminating Composite Panels by Use of a Spectral Reflectometer
Authors: Brown Alexander L.
Published: December 2013

Carbon fibers are being increasingly used in composites for aircraft. They are bound together with a binder, often an epoxy. There are many grades of binders, and many different types of composites sold on the market. They are expensive. We have some donated materials of unknown type, and would like to be able to be cost-effective and use them without incurring a large cost to analyze the materials using laboratory methods. Visual inspection is not normally sufficiently accurate to be able to tell one composite from another. Optical methods that involve a broader spectrum have commonly been used to discriminate organic materials. A five-band spectral reflectometer is used to measure reflectivity of the surfaces, and is a simple way of extracting data into the infrared bands. The instrument used in these tests is less resolved than a narrow band spectrometer, but is easier to deploy because it is a hand-held device that only requires a flat surface of approximately 3 cm diameter.

Reflectivity of many different composite materials, including a bismaleimide, several thermoset epoxies, and some low temperature epoxies from various manufacturers is measured. Other materials are also included to demonstrate that non-composites can be rejected by the methods. Analysis shows that the reflectometer measurements are capable of discriminating some materials, but have difficulty with discriminating others. The raw reflectivity data are likely to be helpful for future radiation modeling of composite surfaces.
Numerical Methods for Simulating the Reduction of Iron Ore in Blast Furnace Shaft
Authors: Fu Dong , Chen Yan , Zhou Chenn Q.
Published: December 2013

The blast furnace process is a counter-current moving bed chemical reactor to reduce iron oxides to iron, which involves complex transport phenomena and chemical reactions. The iron ore and coke are alternatively charged into the blast furnace, forming a layer by layer structural burden which is slowly descending in the counter-current direction of the ascending gas flow. A new methodology was proposed to efficiently simulate the gas and solid burden flow in the counter current moving bed in blast furnace shaft. The gas dynamics, burden movement, chemical reactions, heat and mass transfer between the gas phase and solid phase are included. The new methodology has been developed to explicitly consider the effects of the layer thickness thermally and chemically in the CFD model.
Microscale Phase Separation Through Nanoporous Membranes
Authors: Fazeli Abdy , Moghaddam Saeed
Published: December 2013

This paper presents an experimental study on bubbles extraction from a two-phase flow in microchannels. The bubbles were extracted through a hydrophobic porous membrane covering the microchannels. The two-phase flow was generated through mixing water and air at a T-junction positioned before a microchannel on a microfabricated device. To study the effect of different parameters on the extraction rate, an extensive parametric study was conducted. The parametric space included variations of the channel depth, pressure difference across the membrane, and water and air flow rates. Differential pressure across the membrane was found to be the most critical factor impacting the bubbles extraction rate. Also, the effect of flow quality on the extraction rate was determined to be insignificant. Furthermore, it was found that at a critical velocity a liquid layer forms between the bubbles and the membrane and consequently the bubbles cease to extract.
Natural Convection in an Enclosure With Blend of Micro Encapsulated Phase Change Materials
Authors: Khakpour Yasmin , Seyed-Yagoobi Jamal
Published: December 2013

This numerical study investigates the effect of using a blend of micro-encapsulated phase change materials (MEPCMs) on the heat transfer characteristics of a liquid in a rectangular enclosure driven by natural convection. A comparison has been made between the cases of using single component MEPCM slurry and a blend of two-component MEPCM slurry. The natural convection is generated by the temperature difference between two vertical walls of the enclosure maintained at constant temperatures. Each of the two phase change materials store latent heat at a specific range of temperatures. During phase change of the PCM, the effective density of the slurry varies. This results in thermal expansion and hence a buoyancy driven flow. The effects of MEPCM concentration in the slurry and changes in the operating conditions such as the wall temperatures compared to that of pure water have been studied. The MEPCM latent heat and the increased volumetric thermal expansion coefficient during phase change of the MEPCM play a major role in this heat transfer augmentation.
Comparison of Mixed and Stratified Ventilation Systems in Production Areas: Experimental and Simulation Studies
Authors: Schäfer Mirko , Wagner Johannes , Hesselbach Jens , Phan Long , Lin Cheng-Xian
Published: December 2013

Ventilation system can have significant influences on the energy consumption, especially in factories with high thermal loads. To remove generated thermal and mass loads from manufacturing areas, several mechanisms can be applied: mixing and layering ventilation.

This paper shows experimental studies to compare mixed and stratified ventilation systems for industrial buildings. These experiments were conducted in a factory model with a scale of 1:2.5. The measurements consist of vertical distribution of carbon dioxide concentration and temperature in the ambient room. Additionally, a simulation study was conducted based on the same factory model to predict the annual energy demand of mixed and stratified ventilation systems in different climatic regions. The simulation models were validated with measurements from machines and devices in the authors’ laboratories and in the factories of project partners.

The results show advantages in airflow, air quality, cooling capacity and energy demand at different climatic zones when using stratified ventilation.
Cryogenic Single-Phase Heat Transfer in a Microscale Pin Fin Heat Sink
Authors: Truong Eric D. , Rasouli Erfan , Narayanan Vinod
Published: December 2013

A combined experimental and computational fluid dynamics study of single-phase liquid nitrogen flow through a microscale pin-fin heat sink is presented. Such cryogenic heat sinks find use in applications such as high performance computing and spacecraft thermal management. A circular pin fin heat sink in diameter 5 cm and 250 micrometers in depth was studied herein. Unique features of the heat sink included its variable cross sectional area in the flow direction, variable pin diameters, as well as a circumferential distribution of fluid into the pin fin region. The stainless steel heat sink was fabricated using chemical etching and diffusion bonding. Experimental results indicate that the heat transfer coefficients were relatively unchanged around 2600 W/m2-K for flow rates ranging from 2–4 g/s while the pressure drop increased monotonically with the flow rate. None of the existing correlations in literature on cross flow over a tube bank or micro pin fin heat sinks were able to predict the experimental pressure drop and heat transfer characteristics. However, three dimensional simulations performed using ANSYS Fluent showed reasonable (∼7 percent difference) agreement in the average heat transfer coefficients between experiments and CFD simulations.
Prediction of the Effective Thermal Conductivity of Discretely Inhomogeneous Media
Authors: Ramos-Negrete Mario , Mackowski Daniel W.
Published: December 2013

An exact mathematical formulation and associated parallel computational scheme is developed by use of regular harmonics and the addition theorem for the harmonics to calculate the effective thermal conductivity of discretely inhomogeneous media consisting of spherical particles embedded in a continuous matrix. Exact calculations of the temperature field and heat transfer (with high harmonics orders of sphere interactions) are performed in various particulate configurations in which the number of particles is sufficiently large to represent a continuous inhomogeneous medium. Effective medium principles are applied to determine the effective conductivity of the medium. Reported experimental results in the literature are compared with the results from our analytical formulation.
Parametric Study of Simultaneous Radiative Transfer in Plane-Parallel Scattering Medium With Variable Refractive Index by Spectral Collocation Method
Authors: Ma Jing , Sun Yasong , Li Benwen
Published: December 2013

In this work, a spectral collocation method is developed to simulate radiative transfer in a refractive planar medium. The space and angular domains of radiative intensity are discretized by Chebyshev polynomials, and the angular derivative term and the integral term of radiative transfer equation are approximated by spectral collocation method. The spectral collocation method can provide exponential convergence and obtain high accuracy even using few nodes. There is a very satisfying correspondence between the spectral collocation results and available data in literatures. Influence of the extinction coefficient, the scattering albedo, the scattering phase function, the gradient of refractive index and the emissivity of boundary are investigated for the plane-parallel scattering medium with variable refractive index.
Application of Coupled Lattice Boltzmann and Phase-Field Methods for Multiphase Flow Simulations
Authors: Premnath Kannan N. , Patil D. V. , Banerjee Sanjoy
Published: December 2013

Coupling of lattice Boltzmann (LB) and phase-field (PF) methods is discussed for simulation of a range of multiphase flow problems. The local relaxation and shifting operators make the LB method an attractive candidate for the simulation of the single-phase as well as multiphase flows. For simulating interface dynamics, LB methods require to be coupled with an appropriate scheme representing interfacial dynamics. To this end, we have used a model based on the order parameter, which could be either an index function or a phase-field variable, and coupled it with a LB solver for the simulation of various classes of complex multi-physics and multiphase flows. The LB method is used to compute the flow-field, and, in the case of electrodeposition process modeling, the electro-static potential-field. The application of such a coupled LB-PF is illustrated by the solution of a variety of examples. Finally, fast simulation of such a coupled algorithm is achieved using the state-of-art numerical solution acceleration techniques involving preconditioning and multigrid approaches.
Lattice Boltzmann Simulation of Frost Formation Process
Authors: Sun Jinjuan , Gong Jianying , Li Guojun , Gao Tieyu
Published: December 2013

Compared with the conventional mathematical and physical models, the lattice Boltzmann (LB) method is an effective method to simulate the heat and mass transfer in porous media. Frost crystallization aggregation is a very complex process involving inconsistency of frost structures, crystal size distributions, the complex transient shapes, and other numerous influential factors. Assuming the frost is a special porous medium consists of ice crystals and humid air, a mesoscopic model is established to predict the behavior of frost formation based on the lattice Boltzmann equation. The moving boundary condition is adopted in the two-dimensional nine-speed (D2Q9) lattices. The influences of the cold flat surfaces temperature on frost formation process are investigated. The variation laws of frost density and frost layer height are obtained and discussed. Simulation results by the LB model are in agreement with the experiment data from the references.
Vortex Ring Formation on Drop Coalescence With Underlying Liquid
Authors: Ray Bahni , Biswas Gautam , Sharma Ashutosh
Published: December 2013

Numerical simulations using coupled level-set and volume-of-fluid (CLSVOF) method has been carried out to capture the vortex ring when a drop coalesces on a pool of liquid. A study has been done for the formation and motion of vortex rings generated when drops of liquid are allowed to come into contact at zero velocity with a quiescent flat surface of the same liquid.
Numerical Simulation of Flow and Heat Transfer of a Direct Air-Cooled Condenser Cell in a Power Plant
Authors: Wen Juan , Tang Dawei , Wang Zhicheng , Zhang Jing , Li Yanjun , Sun Fangyuan
Published: December 2013

The classical A-frame condenser cell and the complicated flow field at the exit of the axial flow fan bring on the air mal-distribution on the finned tube bundles and poor efficiencies. This paper addresses the detailed characteristics of the thermo-flow in the A-shaped frame condenser cell and the influence of the ambient temperature on the performance of the condenser cell. A three dimensional coupled air flow field calculation is carried out for the rotational fan and the stock-still A-shaped frame-work with the computational fluid dynamics code ANSYS FLUENT12.0. Results show that the coupled computation not only could give boundary conditions conveniently, but also could reflect many important flow phenomena, such as flow backward, biased flow and the air flow field in the chamber is rather complex. The distribution of velocity and temperature in A-frame at different cross sections are presented. Furthermore, the inlet air velocity of the finned tube bundles under different ambient temperature are compared. These simulations provide basis for both understanding the existing deficiencies of the A-frame condenser cell and moreover provide direction for improved designs in the future.
Natural Convection in Cubic and Rhomb-Shaped Enclosures
Authors: Dzodzo Milorad B.
Published: December 2013

Laminar natural convection in cubic and rhomb–shaped enclosures (rhomb angles 59°, 44° and 28.2°) with two opposite vertical walls kept at different temperatures was investigated experimentally and numerically. The enclosures were filled with glycerol and the Rayleigh (Ra) and Prandtl (Pr) numbers ranged from 2,000<Ra<369,000 and 2,680<Pr<7,000. The visualization of the velocity and temperature fields was obtained by using Plexiglass and liquid crystal particles as tracers. The finite volume method based on the finite difference approach was applied for numerical analysis. The velocity and temperature fields and average Nusselt numbers were found as a function of the Reyleigh and Prandtl numbers. Comparison of the average Nusselt numbers for cubic and rhomb-shaped enclosures indicates decrease of heat transfer for the cases when the lower and upper vertical walls of the rhomb-shaped enclosures are at lower and higher temperatures, respectively. This is due to the tendency of fluid stratification in the lower and upper corners.
Experimental Study on the Combustion Process and Performance of Diesel Engines Fueled by Emulsion Diesel With Novel Organic Additives
Authors: Yang Wenming , An Hui , Li Jing , Maghbouli Amin , Chua Kian Jon
Published: December 2013

Transportation is one of the major contributors to the world’s energy consumption and greenhouse gases emissions. The need for increased efficiency has placed diesel engine in the spotlight due to its superior thermal efficiency and fuel economy over gasoline engine. However, diesel engines also face the major disadvantage of increased NOx emissions. To address this issue, three types of emulsion fuels with different water concentrations (5%, 10% and 15% mass water) are produced and tested. Novel organic materials (glycerin and ployethoxy-ester) are added in the fuel to provide extra oxygen for improving combustion. NP-15 is added as surfactant which can help to reduce the oil and water surface tension, activates their surface, and maximizes their superficial contact areas, thereby forming a continuous and finely dispersed droplets phase. The stability of the emulsion fuels is tested under various environmental temperature for one year, and no significant separation is observed. It is better than normal emulsion fuel which can only maintain the state for up to three months. The combustion process and performance of the emulsion fuels are tested in a four-stroke, four cylinder diesel engine. The results indicate that the water droplets enclosed in the emulsion fuel explode at high temperature environment and help to break up the big oil droplets into smaller ones, thereby significantly increase the surface area of the oil droplets and enhance the heat transfer from hot gas to the fuel. As a result, the fuel evaporation is improved and the combustion process is accelerated, leading to an improved brake thermal efficiency (up to 14.2%). Meanwhile, the presence of the water causes the peak temperature of the flame to drop, thereby significantly bringing down the NOx emissions by more than 30%.