bluuebunny/crossref_metadata_2025 huggingface dataset:
Efficient Heat Transfer by Phase Transition in Microstructured Devices
Authors: Maikowske Stefan , Brandner Juergen J. , Dittmeyer Roland
Published: March 2011

Devices with microchannels or similar structures with dimensions in the range of a few 100 micrometers, so-called microstructured devices, have become a powerful tool in modern process engineering for transferring huge amounts of thermal energy. The high internal surface of these devices, caused by small characteristic channel dimensions, lead to very high specific heat transfer rates. Additional increase of these high heat transfer capabilities is enabled by taking advantage of the latent heat of evaporation. During fundamental research activities phase transition and accompanying phenomena in arrays out of straight microchannels as well as novel microstructures were investigated to obtain new and additional information about these processes. A novel microstructure which is based on a new innovative design away from straight channels is able to enhance evaporation. This design, based on semicircular and semi-elliptical microstructures, leads to mixing effects as well as flow acceleration by pressure release effects including increased heat transfer properties. This novel microstructure reaches highly enhanced evaporation performance compared to linear microchannels.
Flow Boiling Characteristics for R1234ze in 1.0 and 2.2 mm Circular Channels
Authors: Tibiric¸a´ Cristiano Bigonha , Ribatski Gherhardt , Thome John Richard
Published: March 2011

Experimental flow boiling heat transfer results are presented for horizontal 1.0 and 2.2 mm I.D. (internal diameter) stainless steel tubes for tests with R1234ze, a new refrigerant developed as a substitute for R134a with a much lower GWP (Global Warming Potential). These two tube diameters were chosen due the necessity to a better investigation the macro to microchannel transition boundary. The experimental campaign includes mass velocities ranging from 50 to 1500 kg m−2s−1, heat fluxes from 10 to 300 kW m−2, exit saturation temperatures of 25, 31 and 35 °C, vapor qualities from 0.05 to 0.99 and heated lengths of 180 mm and 361 mm. Flow pattern characterization was performed using high-speed videos. Data for heat transfer coefficients, critical heat fluxes and flow pattern transitions were obtained. R1234ze demonstrated similar thermal performance to R134a data when running at similar conditions. For critical heat flux the correlation of Katto and Ohno (1984) best predicted the database with a mean absolute error of 6.3%. For the heat transfer coefficients, the Thome et al. (2004) three-zone model predicted the data for slug flow with 15.9% and Saitoh et al. (2007) predicted data for other flow regimes with mean absolute error of 19.4%.
CFD Modelling With Buoyancy Effects for a Heat and Moisture Transfer Ceiling Panel
Authors: Fauchoux Melanie , Simonson Carey , Torvi David , Talukdar Prabal
Published: March 2011

A heat and moisture transfer panel (HAMP) capable of simultaneously transferring heat and moisture to/from a space to improve indoor air conditions is being developed at the University of Saskatchewan. Experiments have been performed for different air conditions to simulate heating, cooling, humidification and dehumidification of the air by the HAMP. A latent effectiveness value is calculated for each test to show the performance of the HAMP. The HAMP has the highest effectiveness (∼45%) when used to cool the airflow. When used to heat the airflow, the effectiveness is much lower (∼25%). This difference can be attributed to the presence of large buoyancy forces during cooling in comparison to heating. To observe the flow field characteristics under the varying test conditions, a computational fluid dynamics (CFD) model is developed. The CFD model is able to provide a better insight into the features of the flow field. The presented streamlines and isotherms exhibit the effect of buoyancy for various conditions and help in understanding the experimentally determined effectivenesses.
Nanofluid Extinction Coefficients for Photothermal Energy Conversion
Authors: Taylor Robert A. , Phelan Patrick E. , Adrian Ronald , Prasher Ravi , Otanicar Todd P.
Published: March 2011

Suspensions of nanoparticles in liquids (i.e. nanofluids) have been shown to dramatically affect thermal and optical properties of the base liquid at low particle loadings [1–3]. Recent studies by the co-authors have indicated that selected nanofluids are promising as solar energy harvesters [4,5]. In order to determine the effectiveness of nanofluids in solar applications, their ability to convert light energy to thermal energy must be known. That is, the extinction coefficient of real nanofluids must be established. Although it is relatively straight-forward to model these properties from knowledge of bulk properties, with the help of some simplifying assumptions, real spectroscopy tests do not always match these calculations. This study compares model predictions of extinction coefficients to spectroscopic measurements. Unfortunately, the models and the optical testing data do not show very good agreement. Some possible reasons for this are discussed. Also, some simple experiments are presented to investigate the extent of scattering in nanoparticle suspensions. As alluded to above, all of these tests are conducted on nanofluid compositions which are considered to be suitable for solar thermal collectors.
An Annular Impinging Jet Alternated by Pulse-Modulated Synthetic Jets
Authors: Tra´vni´cˇek Zdeneˇk , Tesarˇ Va´clav
Published: March 2011

The present experimental study focuses on a generation and control of annular impinging jets. The used working fluid is air. An active flow control system is designed with six radial synthetic jets, which are generated by a common actuator located in the central body of the annular nozzle. The synthetic jets are pulse-modulated. Flow visualization and measurements of the wall pressure and wall heat transfer have been performed. Two flowfield steady patterns A and B (small or large recirculation bubbles, respectively) are recognized. The pattern B exists without the actuation, the unmodulated actuation causes the flowfield switching into the pattern A, and the pulse-modulated actuation generates an alternating flowfield. The present results indicate that the area of higher heat transfer can be slightly spread by means of flow alternation. However, the penalty for this slight gain is a substantial reduction of the heat transfer in the central area.
A Hybrid SN-PN Formulation for Solution of the Boltzmann Transport Equation for Phonons
Authors: Mittal Arpit , Mazumder Sandip
Published: March 2011

A generalized form of the Ballistic-Diffusive Equations (BDE) for approximate solution of the Boltzmann Transport Equation (BTE) for phonons is formulated. The formulation presented here is new and general in the sense that, unlike previously published formulations of the BDE, it does not require a priori knowledge of the specific heat capacity of the material. Furthermore, it does not introduce artifacts such as media and ballistic temperatures. As a consequence, the boundary conditions have clear physical meaning. In formulating the BDE, the phonon intensity is split into two components: ballistic and diffusive. The ballistic component is traditionally determined using a viewfactor formulation, while the diffusive component is solved by invoking spherical harmonics expansions. Use of the viewfactor approach for the ballistic component is prohibitive for complex large-scale geometries. Instead, in this work, the ballistic equation is solved using two different established methods that are appropriate for use in complex geometries, namely the discrete ordinates method (DOM), and the control angle discrete ordinates method (CADOM). Results of each method for solving the BDE are compared against benchmark Monte Carlo results, as well as solutions of the BTE using standalone DOM and CADOM for a two-dimensional transient heat conduction problem at various Knudsen numbers. It is found that standalone CADOM (for BTE) and hybrid CADOM-P1 (for BDE) yield the best accuracy. The hybrid CADOM-P1 is found to be the best method in terms of computational efficiency.
Modeling Compressive Reaction in Shock-Driven Secondary Granular Explosives
Authors: Brundage Aaron L.
Published: March 2011

Hexanitrostilbene (HNS) is a secondary, granular explosive with a wide usage in commercial and governmental sectors. For example, HNS is used in the aerospace industry as boosters in rockets, in the oil and gas industry in linear shaped charge designs in wellbore perforating guns, and in a number of applications in the US Department of Energy (DOE) and Department of Defense (DoD). In many of these applications, neat granules of HNS are pressed without binder and device performance is achieved with shock initiation of the powdered bed. Previous studies have demonstrated that powdered explosives do not transmit sharp shocks, but produce dispersive compaction waves. These compaction waves can induce combustion in the material, leading to a phenomenon termed Deflagration-to-Detonation Transition (DDT). The Baer-Nunziato (B-N) multiphase model was developed to predict compressive reaction in granular energetic materials due to shock and non-shock inputs using non-equilibrium multiphase mixture theory. The B-N model was fit to historical data of HNS, and this model was used to predict recent impact experiments where samples pressed to approximately 60% of theoretical maximum density (TMD) were shock loaded by high-velocity flyers [1]. Shock wave computations were performed using CTH, an Eulerian, multimaterial, multidimensional, finite-volume shock physics code developed at Sandia National Laboratories [2]. Predicted interface velocities using the B-N model were shown to be in good agreement with the measurements. Furthermore, an uncertainty quantification study was performed and the computational results are presented with best estimates of uncertainty.
Band-Gap Tuned Direct Absorption for Hybrid Concentrating Solar Photovoltaic/Thermal System
Authors: Otanicar Todd P. , Chowdhury Ihtesham , Prasher Ravi , Phelan Patrick E.
Published: March 2011

Two methods often proposed for harnessing renewable energy, photovoltaics and solar thermal, both utilize the power of the sun. Each of these systems independently present unique engineering challenges but when coupled together the challenge intensifies due to competing operating requirements. Recent research has demonstrated these hybrid systems for low-temperature applications but there exists limited studies at higher concentration ratios, and thus higher temperatures. What these studies have shown is that keeping the PV cell temperature low keeps the overall system efficiency relatively high but results in low efficiencies from the thermal system. This study presents a unique design strategy for a hybrid PV/thermal system that only has mild thermal coupling which can lead to enhanced efficiency. By creating a fluid filter that absorbs energy directly in the fluid below the band-gap and a PV cell with a passive cooling strategy combined efficiencies greater than 38% can be achieved.
Performance Tests for Development of a Dry Low NOx Combustor
Authors: Kim Hyungmo , Park Poomin , Yang Sooseok , Ko Youngsung
Published: March 2011

A 5MW-gas turbine engine (DGT-5) for power generation is currently under development by Doosan Heavy Industries, funded under a national R&D program. Tests of its combustor performance are carried out by the Korea Aerospace Research Institute (KARI). The combustor is a Dry Low NOx (DLN) type premixed combustor consisting of dual radial swirl burners, air-cooled liner, transition piece, and torch system. It uses natural gas as fuel. Measured characteristics of the combustor include emissions, pressure pulsation, and exit temperature distribution. The optimal operation point of the combustor is found by investigating parameters such as the fuel ratio between the pilot and the main burner and various total fuel rates. The test results show that the combustor performance satisfies the requirements for a gas turbine system. The following results are obtained from the test: pressure loss<4.3; NOx emissions<20ppm; PF<7.6%; Pressure pulsation amplitude <2kPa at low pressure (3bar, a), 100% load and FR 0.2 conditions.
Combustion of Bio-Coke (Highly Densified Biomass Fuel) Block in High-Temperature Air Flow
Authors: Ito Hiroyuki , Sakai Yuto , Ida Tamio , Nakamura Yuji , Fujita Osamu
Published: March 2011

Bio-coke (BIC, highly densified biomass briquette), a newly developed biomass fuel as an alternative to coal coke which utilized in blast furnace, is employed in this study. This fuel is manufactured in highly compressed and moderate temperature conditions and has advantages in its versatility of biomass resources, high volumetric calorific value and high mechanical strength. Japanese knotweed is chosen as a biomass resource and is shaped into cylinder (48 mm in diameter and 85 mm in length). One of the most important characteristics of BIC is its high apparent density (1300 kg/m3; twice or more than that of an ordinary wood pellet). In the present study, combustion characteristics of a single BIC fuel in high temperature air flow (473–873 K, 550–750 NL/min.) are investigated. Air is preheated and blown to the bottom surface of the BIC. Ignition and subsequent combustion behavior are observed with monitoring gas temperature near the BIC, surface and inside the BIC temperature, and time dependent mass loss of the BIC is measured. In the case with low air temperature, low heat flux from the fuel surface leads to the broad temperature distribution inside the BIC accompanied by the increase in ignition delay time and, then, once ignition takes place degradation rate becomes larger than the case with high temperature air. On the other hand, mass loss rate for the case of solid surface combustion in the high temperature air does not depend on the air temperature but does depend on the air flow rate, which is a result of reduced degradation rate relating to narrow temperature distribution in depth caused by short ignition delay time. Consequently, it is suggested that the history of preheating, i.e. the preheated condition which is determined by air temperature and air flow rate, is an essential factor to determine the ignition mode in the early stage of BIC combustion and the mass burning velocity in the period of main combustion with flame. It is found that the mass loss rate of BIC in the gas-phase combustion period increases with decrease in supplied air temperature in this study.
Design Concept and the Performance of a Metal Hydride Hydrogen Storage Tank in Totalized Hydrogen Energy Utilization System
Authors: Maeda Tetsuhiko , Nishida Keiichi , Yamazaki Shiro , Kawakami Yoshiaki , Masuda Masao , Tange Manabu , Hasegawa Yasuo , Ito Hiroshi , Nakano Akihiro
Published: March 2011

We have proposed the Totalized Hydrogen Energy Utilization System (THEUS) for applying to commercial buildings. THEUS consists of fuel cells, water electrolyzers, metal hydride tanks and their auxiliaries. The basic operation of the THEUS is as follows: In the nighttime, hydrogen is produced by water electrolysis and stored in metal hydride tanks. In the daytime, it conducts fuel cell power generation using the stored hydrogen to meet the electric power demand of a building. The chilled and hot water generated in this process are also utilized. It is also possible to use the electric power from renewable energy. That is, THEUS has not only the load leveling function but the function to stabilize the grid system. The metal hydride tank is an important component of THEUS as hydrogen storage. The tank was designed as a thermally driven type, which be able to absorb/desorb hydrogen at normal temperature and pressure and utilize the endothermic reaction during hydrogen desorption as chilled water for air-conditioning. The tank with 50 kg AB5 type metal hydride alloy was assembled to investigate the hydrogen absorbing/desorbing process. The experimental results of the heat utilization ratio using this metal hydride tank are about 43%. Since the reaction heat is consumed to heat and to cool the tank up to the temperature of possible heat utilization. The heat utilization ratio can be improved by reduced the heat capacity of the tank and exchanging heat with multiple tanks.
The Actual Operation of Multiple Metal Hydride Hydrogen Storage Tanks in Totalized Hydrogen Energy Utilization System
Authors: Kawakami Yoshiaki , Masuda Masao , Maeda Tetsuhiko , Nakano Akihiro , Tange Manabu , Takahashi Atsushi , Shoji Masakazu , Aoki Hideyuki , Miura Takatoshi
Published: March 2011

As a method for simultaneously increasing efficiency of energy use and stability of energy supply in commercial buildings, we have proposed Totalized Hydrogen Energy Utilization System (THEUS) that uses hydrogen as a high potential for energy carrier. The hydrogen storage method used by this system adopts metal hydride that excels in volumetric storage density. In this paper, as the model case for electric power load leveling operation, the optimum design and optimum operation method for multiple metal hydride tanks are described with a mathematical model which can simulate operation of the metal hydride tank and experimental equipment. As a result, the combination of tank specifications and operating conditions that produce the effective simultaneous utilization of 1) hydrogen, 2) metal hydride and 3) heat are identified. Furthermore, an operating method to make the most of the metal hydride tank flexibility with respect to tank selection is determined.
Cooling-Induced Depressurization of a Steam-Filled Chamber
Authors: He Pengfei , Patel Rajesh , Zhu Chao , Lin Chao-Hsin
Published: March 2011

Depressurization can be realized by condensing saturated vapor of a pure substance inside a confined chamber. The depressurization rate depends directly upon the effectiveness of cooling to the condensing vapor. The objective of this study is to develop modeling approaches for cooling-controlled depressurization, which will assist the optimization of process design and operation. To this end, an experimental system is set up to provide sets of data for model validations. A simple mechanistic model based on assumption of thermodynamic-equilibrium inside the system has been developed to show the limiting depressurization characteristics with instant heat balance. This simplified model has a merit of quick evaluation on comparisons among various parametric effects. Yet the model is inadequate for real-time quantification in depressurization. The gaps between the measurements and model predictions indicate the importance of local non-uniform heat transfer and condensation. To close the gaps, a complicated full-field computational fluid dynamics modeling and simulation (CFD) is needed, in which the local condensations (especially surface condensation) must be fully account for. The difficulty in CFD approach is the unavailability of condensation-coupled boundary conditions in most commercial CFD codes. Hence, in this paper, we have also proposed the modeling of condensation-based boundary conditions that will be used for CFD simulations.
Role of Chemical Ordering on Phononic Transport in Binary Alloys
Authors: Duda John C. , English Timothy S. , Soffa William A. , Jordan Donald A. , Norris Pamela M.
Published: March 2011

Many random substitutional solid solutions (alloys) will display a tendency to chemically order given the appropriate kinetic and thermodynamic conditions. Such order-disorder transitions will result in major crystallographic reconfigurations, where the atomic basis, symmetry, and periodicity of the alloy change dramatically. Consequently, phonon behavior in these alloys will vary greatly depending on the type and degree of ordering achieved. To investigate these phenomena, the role of the order-disorder transition on phononic transport properties of Lennard-Jones type binary alloys is explored via non-equilibrium molecular dynamics simulations. Particular attention is paid to regimes in which the alloy is only partially ordered. It is shown that, through exploitation of the long-range order parameter, thermal conductivity of binary alloys can be effectively tuned across half an order of magnitude at low-to-moderate temperatures.
Film-Cooling Performance of Anti-Vortex Hole on a Flat Plate
Authors: Narzary Diganta P. , LeBlanc Christopher , Ekkad Srinath
Published: March 2011

Film cooling performance of two hole geometries is evaluated on a flat plate surface with steady-state IR (infrared thermography) technique. The base geometry is a simple cylindrical hole design inclined at 30° from the surface with pitch-to-diameter ratio of 3.0. The second geometry is an anti-vortex design where the two side holes, also of the same diameter, branch out from the root at 15° angle. The pitch-to-diameter ratio is 6.0 between the main holes. The mainstream Reynolds number is 3110 based on the coolant hole diameter. Two secondary fluids — air and carbon-dioxide — were used to study the effects of coolant-to-mainstream density ratio (DR = 0.95 and 1.45) on film cooling effectiveness. Several blowing ratios in the range 0.5 –4.0 were investigated independently at the two density ratios. Results indicate significant improvement in effectiveness with anti-vortex holes compared to cylindrical holes at all the blowing ratios studied. At any given blowing ratio, the anti-vortex hole design uses 50% less coolant and provides at least 30–40% higher cooling effectiveness. The use of relatively dense secondary fluid improves effectiveness immediately downstream of the anti-vortex holes but leads to poor performance downstream.
Experimental Verification of Expedited Freezing of Nanoparticle-Enhanced Phase Change Materials (NEPCM)
Authors: Fan Liwu , Khodadadi J. M.
Published: March 2011

Highly-conductive nano-sized particles are dispersed into phase change materials (PCM) to improve their effective thermal conductivity, thus leading to suspensions that are referred to as nanoparticle-enhanced PCM (NEPCM). In order to assess the extent of expedited phase change due to the enhanced thermal conductivity, the one-dimensional unidirectional freezing process of NEPCM in a finite slab was investigated experimentally. Thermocouple readings were recorded at several equally-spaced locations along the freezing direction in order to monitor the progress of the freezing front. As an example, cyclohexane (C6H12) and copper oxide (CuO) nanoparticles were chosen to develop the NEPCM with three different volume fractions (0.5, 1.0, and 2.0 vol%). It was shown that the freezing rate for the 0.5 vol% NEPCM is considerably raised as compared to pure cyclohexane. However, further increase of the fraction of nanoparticles to 1.0 and 2.0 vol% did not linearly expedite freezing. Significant sedimentation of nanoparticles was observed for the 2.0 vol% NEPCM. Additionally, in this case the undesirable supercooling phenomenon was enhanced, which suppresses the growth rate of the solidified NEPCM.
Development of a High Performance Thermal Interface Material With Vertically Aligned Graphite Platelets
Authors: Zhao Y. , Strauss D. , Liao T. , Chen Y. C. , Chen C. L.
Published: March 2011

This paper introduces a high performance thermal interface material (TIM) with vertically aligned graphite. The main structure of the TIM is a vertically laminated structure, in which thin solder layers are laminated with aligned graphite layers. Unlike traditional TIMs infiltrated with randomly oriented high conductive fillers, the laminated TIM with vertically aligned graphite provides extraordinarily high z-axis thermal conductivity and controllable stiffness by simply setting the thickness of each component layer to match different surfaces. Thus, this design greatly improves the overall heat transfer performance. In addition, using metallic-graphite composites greatly improves the bonding between the graphite and the metallic host compared to nonmetallic materials, and thus the thermal boundary resistance can be significantly reduced. Moreover, compared to organic hosts, solders have much smaller phonon spectra mismatch with graphite nanoplatelets (GNPs), and thus offer significantly higher interface conductance. Furthermore, vertically connected solder layers can also lock the graphite layers in place and reinforce the strength of the entire package. A series of experimental tests was conducted to evaluate the effects of processing pressure and surface roughness on the overall thermal performance of the graphite TIMs. The results indicated that the overall thermal resistance of two smooth surfaces soldered by a 200 μm-thick graphite TIM was reduced from 0.12 to 0.03 cm2•K/W when the compression pressure applied during the soldering process was increased from 7 to 68 psi. Increased surface roughness appeared to improve heat transfer across the interface by enlarging the contact areas between the surface and the graphite TIMs. A preliminary numerical simulation verified this trend.
Development of Advanced Combustor for Biomass
Authors: Urashima Masato , Torii Shuichi
Published: March 2011

Biomass is a renewable energy source in that the energy that it contains comes from the sun. One of sources of biomass is municipal solid waste. The final goal of the study is to develop the combustor for the micro gas-turbine using the biomass as a fuel. Here, it is very important to remove ashes (10μm or more in diameter) in the gas because its size affects the strength or erosion of the turbine blade. The aim of the present study is to observe the combustion phenomena relevant to a mixture of waste liquid and waste oil. Emphasis is placed on the ash size which is produced from the combustion chamber developed here. It is found that the ash size obtained at the exit of the combustor is less than 10 μm.
Reburning of Cattle Manure-Based Biomass With Coals in a Small Scale Boiler Burner Facility for NOx and Hg Reduction
Authors: Oh Hyukjin , Annamalai Kalyan , Sweeten John
Published: March 2011

Reburning of cattle manure-based biomass (CB) with coals is performed to develop environmentally friendly thermo-chemical energy conversion technologies for NOx reductions and Hg captures and removals from existing pulverized coal-fired power plants. A small-scale (30 kWth) down-fired boiler burner facility has been used for burning most types of pulverized solid fuels including coal and biomass. Blends of CB and coals are used as reburn fuels. It has hypothesized that a major fraction of the fuel-N in the CB is released in the form of NH3 or urea. In the reburn process, therefore, it is believed that NOx produced by coal is reduced to molecular nitrogen by NH3 released from the pyrolysis of CB under slightly fuel-rich conditions. The CB also contains larger amounts of chlorine (Cl) than most types of coals. Hence gaseous mercury (Hg) in the flue gas is oxidized by large amounts of Cl species mainly from the CB combustion. Consequently, the results indicate that the CB can serve as a very effective fuel supplementing coals on NOx reductions and Hg captures and removals in pulverized coal-fired boilers. It was also found that the auto-gasification occurred during the pyrolysis due to the oxygen available in the fuel mainly helped for burning fixed carbon.
Development of Diesel Engine Emissions Control Models Based on Heat Release Rate Analysis of Combustion Processes
Authors: Wang Dong , Zhang Chao
Published: March 2011

Linear control models to control the Nitrogen Oxides (NOx) and soot emissions from a diesel engine were developed through numerical simulations. A modified KIVA-3V code was used to calculate the NOx and soot formations in a direct injection diesel engine under different operating conditions. The following relationships between the pollutant formations and the heat release rate were observed: 1) NOx formation amount is related to the peak value of the heat release rate and the timing of the premixed combustion; 2) soot formation amount is related to the peak heat release rate and the soot oxidation amount is related to the timing of the premixed combustion. Based on the above observations, linear control models for NOx and soot emissions were constructed. The NOx control model developed through the numerical simulations was implemented into the controller of an EGR valve on a small diesel engine. The experimental results showed that the NOx control model was effective in reducing NOx emissions under high RPM conditions.
Marangoni Convection in Water Isopropanol Mixture in the Presence of Soret Effect
Authors: Rahman M. A. , Saghir M. Z.
Published: March 2011

In the present study, the onset of Marangoni convection in a liquid layer overlaying a porous layer where the whole system is being laterally heated is investigated. Two different cases are analyzed in this paper. In the first case, the Marangoni convection in the absence of the Soret effect is studied. Results revealed, when the liquid layer and the porous layer have identical thickness, the convective flow remains in the liquid layer. However, the flow covers the entire cavity when the liquid layer thickness is very small (less than 1/10th of the porous layer). For the case of Marangoni convection in the presence of Soret effect, it has been found that the isopropanol component enriches near the cold wall.
Optimized Ionic Wind-Based Cooling Microfabricated Devices for Improving a Measured Coefficient of Performance
Authors: Ongkodjojo Andojo , Abramson Alexis R. , Tien Norman C.
Published: March 2011

This work is a continuation of previous investigations aimed at developing an innovative microfabricated air-cooling technology that employs an electrohydrodynamic corona discharge (i.e. ionic wind pump) [1], [2]. This technology enables the miniaturization of cooling systems for next generation electronics. Our single ionic wind pump element consists of two parallel collecting electrodes between which a single emitting tip is positioned. Two-dimensional (2-D) and three-dimensional (3-D) simulations using COMSOL Multiphysics™ are additionally employed to predict the temperature distribution, the flow field, and the heat removal capacity of the device in operation. One such model utilizes a small gap between collector and emitter electrodes and demonstrates an improvement in the COP (coefficient of performance) of a single device. Comparisons are made with experimental temperature data on an actual device. The purpose of this work is therefore to optimize the performance of a single microfabricated ionic wind pump to enable the development of an array of these elements for use in larger-scale heat transfer applications.
Effect of Cooling Water Temperature on Impinging Jet Heat Transfer on Hot Steel Plate
Authors: Lee Jungho , Yu Cheong-Hwan , Do Kyu Hyung
Published: March 2011

Water impinging jet has been widely used in a variety of engineering applications; especially in the hot steel cooling of steelmaking processes and heat treatment in hot metals. The effects of cooling water temperature on water impinging jet cooling are mainly investigated for hot steel plate cooling in this study. The heat flux are measured by a novel experimental technique that has a function of high-temperature heat flux gauge in which test block assemblies are used to measure the heat flux distributions on the hot surface. The water impinging jet is produced by a straight pipe nozzle and experiments are performed at fixed water flow rate and fixed nozzle-to-target spacing. The results show that effects of water temperature on impinging jet transfer characteristics are presented for five different water temperatures between 5 to 45°C. The heat flux curves and heat transfer coefficients are also provided to a benchmark data for the actual impinging jet cooling applications of hot steel plate.
Influence of Inserting the Heat Pipe Into the MH Particle Bed on Refrigeration Performance
Authors: Bae Sangchul , Morita Eiji , Ishikawa Keisuke , Haruna Yusuke , Katsuta Masafumi
Published: March 2011

In the refrigeration and air conditioning fields, the needs of energy conservation and renewable energy spread have become stronger recently. In this study, we aim at the development of the heat driven type metal hydride (abbr, MH) that can be driven by the low temperature exhausted heat or solar heat under 100°C. In order to commercialize this system, the heat transfer characteristics and the activation characteristics of MH particle bed must be more improved, and production cost must be more reduced. In this study, we use the two heat transfer enhancement methods for improving the low effective thermal conductivity of MH particle bed. One is by heat pipe (abbr., HP) and another is by brush type carbon fiber. HP is inserted into heat source part MH (abbr., MH1). By this method, we aim not only to enhance the heat transfer of MH1 particle bed but also to achieve the temperature uniformity of MH1 particle one. The effective thermal conductivity of cooling part MH (abbr., MH2) particle bed is enhanced by inserting the brush type carbon fiber. The influence of these heat transfer methods on our MH refrigeration system is estimated by measurement and calculation.
Simultaneous Heat Transfer and Pressure Drop Measurements for a Horizontal Micro-Tube
Authors: Tam Lap Mou , Tam Hou Kuan , Ghajar Afshin J.
Published: March 2011

Heat transfer and pressure drop measurements for horizontal macro-tubes under uniform wall heat flux boundary condition have been conducted by various researchers in recent years. From their studies, it was shown that good agreements were observed in the laminar and turbulent regions. However, for the transition region, the heat transfer and pressure drop characteristics depended on various factors, such as inlet configuration, buoyancy effect, and surface roughness. In a recent study by Tam et al. (2010), they measured the heat transfer and pressure drop simultaneously for a horizontal macro-tube with and without internally micro-fins and concluded that under the heating condition, the transition Reynolds number range for heat transfer and pressure drop were completely different. The transition Reynolds number range was documented in their research in great detail. However, for horizontal micro-tubes, there is no information in the literature on the simultaneous behavior of the heat transfer and pressure drop, especially in the transition region. In order to fill in this gap, an experimental setup was built to measure the heat transfer and pressure drop simultaneously for a horizontal micro-tube under uniform wall heat flux boundary condition. Water was used as the test fluid and the test section was a stainless steel micro-tube with 1000μm diameter. For heat transfer, the results indicated that the micro-tube had an earlier start and end of transition compared to the macro-tube and, in the turbulent region, an increase in heat transfer due to the surface roughness was observed. For friction factor under isothermal condition, the micro-tube had a narrower transition range due to the roughness compared to the macro-tube. For friction factor under heating condition, the laminar data and the start of transition were different from the isothermal case, and the effect of heating was not seen on the end of transition.
Flame Fractal Dimension Induced by Hydrodynamic Instability
Authors: Wada Yukari , Kuwana Kazunori
Published: March 2011

Premixed flames self-turbulized due to hydrodynamic instability have self-similar, fractal-like structures as evidenced by the acceleration of spherically-propagating flames. The fractal dimension of a self-turbulized premixed flame needs to be known if its apparent flame speed is to be estimated. CFD simulations of outwardly-propagating flames have been conducted to predict their fractal dimensions. There are, however, difficulties in accurately determining fractal dimension based on the flame-propagation behavior of such an outwardly-propagating flame. This paper demonstrates a newly proposed method to determine the fractal dimension based on the CFD simulation of a planar flame. The fractal dimension is computed from the dependency of apparent flame speed on the computational domain size. The computed fractal dimension well agrees with the experimental value. The box-counting method is also applied to calculate the flame’s fractal dimension. The fractal dimensions obtained by these two methods agree well, confirming the fractal nature of the self-turbulized flame.
Influence of Flame Front Instability on Flame Propagation Behavior
Authors: Mukaiyama Kenji , Kuwana Kazunori
Published: March 2011

This paper discusses flame acceleration due to flame instability mechanisms. In particular, the diffusive-thermal instability and hydrodynamic instability mechanisms are considered. The Sivashinsky equation is used to compute two-dimensional flame propagation behaviors, and the influence of each instability mechanism is separately considered. The effect of flame size on flame speed (accelerated due to the instability mechanisms) is particularly investigated. It is found that the flame propagation velocity (Vf) is independent of flame size under the influence of diffusive-thermal instability, whereas Vf increases with flame size under the influence of hydrodynamic instability. The fractal nature of the flame under the influence of hydrodynamic instability is confirmed based on the dependence of Vf on flame size. Fractal dimension is then calculated as a function of volume expansion ratio, the parameter that controls the hydrodynamic instability mechanism. An FFT analysis is conducted to further understand the flame’s fractal structure.
High Temperature Thermal Characterization of Ge2Sb2Te5 for Phase Change Memory
Authors: Lee Jaeho , Reifenberg John P. , Asheghi Mehdi , Goodson Kenneth E.
Published: March 2011

We propose a novel design of Joule heating thermometry to measure thermal properties of Ge2Sb2Te5 (GST) films at temperatures relevant for the switching of phase change memory devices. Vertically stacked micro-fabricated heaters control temperature and measure thermal conductivity of thin films using the 3ω method. The thermal time constant of the experimental structure enables studies of short time scale crystallization and cycling effects for phase change materials. This work reports the thermal conductivity of GST films from the room temperature to above 400 Celsius in amorphous, face-centered cubic, and hexagonal close-packed phases.
Evaluation of Effective Thermal Conductivity of Multilayer Printed Circuit Board
Authors: Tomimura Toshio , Shiotsu Yoshihiro , Koito Yasushi , Ishizuka Masaru , Hatakeyama Tomoyuki
Published: March 2011

To perform a rational thermal design of a printed circuit board (PCB) with highly anisotropic heat transfer nature in its initial stage, effective thermal conductivities in thickness direction and in in-plane direction must be given depending on the electric circuit of the board. However, a simple evaluation method for the effective thermal conductivities of such PCB has not been developed yet. In this study, as the first step to propose a simple evaluation method, the heat transfer coefficient by natural convection around a horizontal disk, which is indispensable for measuring the effective thermal conductivity, has been evaluated. Furthermore, the thermal conductivity of the glass epoxy resin in in-plane direction has been evaluated by applying the evaluated heat transfer coefficient, and then, the validity of the proposed thermal conductivity measurements of the anisotropic PCB has been confirmed.
Thermal Fluid-Structure Coupling for Atmospheric Entries
Authors: Joshi Ojas , Leyland Pe´ne´lope
Published: March 2011

This paper deals with the modeling of aero-thermal aspects of a space vehicle during its entry phase into an atmosphere. We treat the numerical coupling techniques between the external and internal aero-thermo-dynamics (ATD) produced by the interaction of ATD fields with the structural components. The thermal properties induced within the structure via heat transfer mechanisms of convection, conduction and radiation is taken into account presenting multi-disciplinary coupling between the aero-thermo-dynamics, the heat loads and the structural thermal response.
Numerical Simulations of Heat Fluxes for Atmospheric Re-Entries
Authors: Savajano Romain , Potter Daniel F. , Leyland Pe´ne´lope
Published: March 2011

During atmospheric (re-)entries, planetary probes encounter huge heat fluxes due to their significant speed (up to 13 km/s for an Earth re-entry). The total heat flux received by the probe can be divided into two main components: a convective one (coming from the conduction and diffusion phenomena occuring in the shock layer) and a radiative one (due to the radiation of certain species). Numerical simulations have been performed for both Titan (Huygens mission) and Earth (Fire II mission) entries. The main parameters influencing the results are the atmosphere composition, the chemical reaction scheme, the transport model and the radiative model. The results obtained gave us information on the flowfield (temperature, pressure, species densities...) and values for the heat fluxes on the wall that are useful for experimental or flight data comparison.
Application of Immersed-Boundary Method to Complex Geometry Flows With Heat Transfer
Authors: Liao Chuan-Chieh , Lin Chao-An
Published: March 2011

In the present study, an immersed-boundary method is adopted to simulate natural and forced convection within a domain with complex geometry. The method is based on the direct momentum and energy forcing on a Cartesian grid and issues involving implementation of both the thermal (Dirichlet and Neumann) and dynamic (stationary and nonstationary) boundary conditions are addressed. The second order accuracy of the present method was validated based on natural convection in an annulus between horizontal concentric cylinders. Simulations of flow over a stationary cylinder with heat convection were further conducted to validate the capability of present technique for both temperature boundary conditions. Finally, the influence of the lock-on phenomenon in heat transfer is investigated for flow over a transversely oscillating cylinder. All computed results are in generally good agreement with previous experimental measurements and numerical simulations.
A Design for Loop Thermosyphon Including Effect of Non-Condensable Gas
Authors: Toyoda Hiroyuki , Nakajima Tadakatsu , Kondo Yoshihiro , Idei Akio , Sato Shigemasa
Published: March 2011

We have developed a loop thermosyphon for cooling electronics devices. Its cooling performance changes with the ambient temperature and amount of input heating. Especially it deteriorates with non-condensable gas (NCG) increase. NCG leakage of thermosyphon cannot detect below under 10−10 Pa-m3/s, though we have to design the thermosyphon considering these characteristics to provide guaranteed performance for 5–10 years. In this study, the effect of the amount of NCG in each component of a thermosyphon was measured while changing the amount of heater input, and the amount of NCG. As a result, we obtained some useful design information. The performance of air cooling part does not depend on the NCG amount in this case. The performance of evaporation part depends on the total pressure that includes the partial pressure of vapor and the partial pressure of NCG. The performance of condensation part is deteriorated strongly by NCG amount increase. Additionally, we expressed these performances as approximations. These expressions let us predict the total thermal resistance of this thermosyphon by the NCG amount and the input heating amount. Then, using the leakage of a thermosyphon and the amount of dissolved NCG in water, we predicted the amount of NCG that will be in the thermosyphon after 10 years. These results also let us predict the thermosyphon’s total thermal resistance after 10 years. Though there is a slight leakage on thermosyphon, using this technique, we are able to design a thermosyphon that is guaranteed the cooling performance for a long term.
Flow Characteristics Over a Backward-Facing Step in a Duct in Low Reynolds Number Range
Authors: Suyama Nobuyuki , Inaoka Kyoji , Senda Mamoru
Published: March 2011

Velocity measurements have been done in order to grasp the flow reattachment locations over a 3D backward-facing step in a duct by PIV for various Reynolds numbers from 200 to 1000. The aspect ratio and the expansion ratio of the stepped duct were 16 and 2, respectively. It was found that the flow reattachment location varies in the spanwise direction in every case. In the range of Re<400, flow near the bottom wall is stable. The longest flow reattachment length appears at the center of the duct while the shortest appears near the side wall. In the range of 400<Re<550, the flow reattachment length turns to be shorten and begins to vary largely near the center of the duct. This variation of the flow reattachment extends to the near wall region around 600<Re<700 and relatively uniform and short flow reattachment is realized in the range of 800<Re. The largest difference in the reattachment length between the center of the duct and near the side wall is generated at Re = 400.
VAT Based Modeling of Plate-Pin Fin Heat Sink and Obtaining Closure From CFD Solution
Authors: Zhou Feng , Hansen Nicholas , Catton Ivan
Published: March 2011

A plate-pin fin heat sink (PPFHS) is composed of a plate fin heat sink (PFHS) and some pin fins planted between the flow channels. Just as the other kinds of heat sinks, it is a hierarchical multilevel device with many parameters required for its description. Volume Averaging Theory (VAT) is used to rigorously cast the point-wise conservation of energy, momentum and mass equations into a form that represents the thermal and hydraulic properties of the plate-pin fin (porous media) morphology and to describe the hierarchical nature of the heat sink. Closure for the upper level is obtained using VAT to describe the lower level. At the lower level, the media is described by a representative elementary volume (REV). Closure terms in the VAT equations are related to a local friction factor and a heat transfer coefficient of the REV. The terms in the closure expressions are complex and relating experimental data to the closure terms resulting from VAT is difficult. In this work, we model the plate-pin fin heat sink based on Volume Averaging Theory and use CFD to obtain detailed solutions of flow through an element of PPFHS and use these results to evaluate the closure terms needed for a fast running VAT based code. The VAT based code can then be used to solve the heat transfer characteristics of the higher level heat sink. The objective is to show how plate-pin fin heat sinks can be modeled as porous media based on Volume Averaging Theory and how CFD can be used in place of a detailed, often formidable, experimental effort.
A Proposal of Waste Heat Recovery System Through Methanol Steam Reforming Integrated With Absorption Heat Pump
Authors: Kawasaki Shunsuke , Yanto Wijaya Willy , Watanabe Hirotatsu , Okazaki Ken
Published: March 2011

Through the methanol steam reforming (MSR), the energy of low temperature waste heat (100–150°C) can be recovered into that of hydrogen. However, actual MSR requires over 200°C to enable the high conversion of methanol into hydrogen. In this research, two types of combined absorption heat pump (AHP) and MSR systems were proposed: one-pass system and steam recycling system. The role of the AHP is to enhance the temperature level of the waste steam up to 230°C, which is used for the MSR. To evaluate the performances of these systems, “energy enhancement factor” was defined. As a result, the recovered energy of the waste heat was almost three times as much as the required work for the AHP when the reaction temperature and waste heat temperature and S/C ratio were 210°C and 150°C and 4.0, respectively. It was also indicated that the steam recycling was more effective at the higher reaction temperature and lower waste heat temperature and higher S/C ratio.