bluuebunny/crossref_metadata_2025 huggingface dataset:
Buoyancy Driven Flow Between Vertical Parallel Plates of Finite Width
Authors: Olsson Carl-Olof
Published: April 2009

In the present investigation, three-dimensional (3D) simulations have been carried out in order to study the influence of Rayleigh number (Ra″, 0.1 to 1000) and the geometric proportions H/S (5 and 10) and W/S (2.5 to 20), where H is the duct height, S is the plate spacing, and W is the plate width. The Prandtl number is 0.72, and the thermal boundary condition is uniform heat flux. The results are compared to the corresponding two-dimensional (2D) situation that is approached when W/S is very large. The investigation is restricted to laminar flow. For H/S = 5, the 3D effects increase the Nusslet number (Nu3D) at low Ra″ as compared to the 2D situation. For increasing Ra″, Nu3D approaches the 2D correlation, however, for the largest Ra″, Nu3D is slightly larger than Nu2D and there is a local minimum in Nu3D/Nu2D in the range 1 < Ra″ < 100. The minimum occurs at smaller Ra″ for increasing W/S. In general, it seems as the buoyancy driven flow between parallel plates of finite width can be characterized by four regimes: conduction regime, pressure regime, boundary layer regime, and turbulent regime.
Numerical Study of Conjugate Heat Transfer Due to Growth of a Vapor Bubble During Flow Boiling of Water in a Microchannel
Authors: Mukherjee A.
Published: April 2009

The present study is performed to numerically investigate temperature distribution at the channel walls during growth of a vapor bubble inside a microchannel. The microchannel is of 200 μm square cross section and a vapor bubble nucleates at one of the walls, with liquid flowing in through the channel inlet. Constant heat flux boundary condition is specified at the bottom wall of the microchannel. The complete Navier-Stokes equations along with continuity and energy equations are solved using the SIMPLER method. The liquid vapor interface is captured using the level set technique. The conjugate heat transfer problem is solved at the bottom and side walls. The bubble grows rapidly due to heat transfer from the walls and soon turns into a plug filling the entire channel cross section. The temperature distribution at the channel walls is studied for different values of wall heat flux. The bubble growth rate is found to increase with increase in wall heat flux. High temperatures are noted at the wall below the bubble base due to vapor contact causing axial temperature gradients. Areas of high heat transfer are also seen to exist in the thin layer of liquid between bubble and the channel sidewalls.
Influence of Wall Heating on Turbulent Structure
Authors: Gajusingh Shivani T. , Siddiqui Kamran
Published: April 2009

An experimental study was conducted to investigate the impact of wall heating on the flow structure in the near-wall region inside a square channel. PIV was used to measure the two-dimensional velocity fields. The measurements were conducted for a range of mass flow rates that cover laminar and turbulent regimes. The results have shown that when a flow is unstably stratified via heating through a bottom wall, both the mean and turbulent characteristics are affected. The results have shown that the impact of wall heating on the flow behavior is significantly different for laminar and turbulent flow regimes. It was found that when a flow that is originally laminar is heated, the mean streamwise velocity in the near-wall region is significantly increased and turbulence is generated in the flow predominantly due to buoyancy. When the flow is in the turbulent regime, addition of heat reduces the magnitudes of mean streamwise velocity and turbulent properties. The reduction in the magnitudes of turbulent properties in this flow regime is due to the working of turbulence against the buoyancy forces.
Application of the 3ω Hot Wire Technique for Measurement of Fluid Thermophysical Properties
Authors: Olson Brandon W. , Fahham Ali
Published: April 2009

The popular 3ω method of measuring thermophysical properties of solids is adapted for the simultaneous measurement of thermal conductivity and heat capacity in both liquids and gases. This technique is experimentally simple and has a lower susceptibility to random experimental noise, bulk fluid motion, radiation losses, and non-linear effects than other transient hot wire measurement methods. The compactness of the 3ω hotwire allows it to be used with different fluids in a variety of circumstances with very little specialized experimental equipment. Both the experimental setup and theoretical model are detailed. Experimental 3ω measurements were made in a variety of common fluids (air, water, and mineral oil) using commercially drawn 10μm platinum and 5μm tungsten hot wires which serve as both heating element and resistance thermometer. Measurements taken over a range of frequencies are numerically reduced to provide both thermal conductivity and heat capacity information. Experimental measurements and the corresponding analytical model are presented in terms of impedance or thermal resistance; a more physically meaningful and intuitive basis of comparison. Fluid properties are determined by curve-fitting an analytical model to experimental data using a least-squares approach. This technique allows both thermal conductivity and heat capacity (or thermal diffusivity) to be uniquely determined from a single measurement sequence.
An Interfacial Tracking Method for Ultrashort Pulse Laser Melting and Resolidification of a Thin Metal Film
Authors: Zhang Yuwen , Chen J. K.
Published: April 2009

An interfacial tracking method is developed to model rapid melting and resolidification of a free-standing metal film subject to an ultrashort laser pulse. The laser energy is deposited to the electrons near thin film surface, and subsequently diffused into deeper part of the electron gas and transferred to the lattice. The energy equations for the electron and lattice are coupled through an electron-lattice coupling factor. Melting and resolidification are modeled by considering the interfacial energy balance and nucleation dynamics. An iterative solution procedure is employed to determine the elevated melting temperature and depressed solidification temperature in the ultrafast phase-change process. The predicted surface lattice temperature, interfacial location, interfacial temperature, and interfacial velocity are compared with those obtained by an explicit enthalpy model. The effects of the electron thermal conductivity models, ballistic range, and laser fluence on the melting and resolidification are also investigated.
On Selection of Reference Temperature of Heat Transfer Coefficient for Complicated Flows
Authors: Li X. C. , Zhou J. , Aung K.
Published: April 2009

One of the most fundamental concepts in heat transfer is the convective heat transfer coefficient, which is closely related with the flow Reynolds number, flow geometry and the thermal conditions on the heat transfer surface. To define the heat transfer coefficient, a reference temperature is needed besides the surface temperature and heat flux. The reference temperature can be chosen differently, such as the fluid bulk mean temperature (for internal flows) and the temperature at the far field (for external flows). For complicated flows, the adiabatic wall temperature, defined as the wall temperature when the surface heat flux is zero, is commonly adopted as the reference temperature. Other options can also be applied to complicated flows. This paper analyzed some of the potential selections of the reference temperature for different flow settings, including film cooling, jet impingement with cross flows and a mixing flow in a straight duct with or without internal heat source. Both laminar and turbulent flows are considered with different boundary conditions. Dramatic changes of heat transfer coefficient are observed with different reference temperatures. In some special conditions the heat transfer coefficient becomes negative, which means the heat flux has a different direction with the driving temperature difference defined. An innovative method is proposed to calculate the heat transfer coefficient of complicated flows with constant surface temperature.
Numerical Study on Heat Transfer of Inclined Jet Impingement With Explicit Crossflow
Authors: Li X. C. , Zhu Weihang , Corder Paul
Published: April 2009

Due to its high heat and mass transfer rate, especially near the stagnation region, jet impingement has been widely used in many applications, such as annealing of metal and plastic sheets, cooling of gas turbine blades and electronic components. However, the high heat transfer rate can be strongly affected by the crossflow coming from either the exhaust fluid in an array of jets or other sources. On the other hand, the inclination angle of injection also influences the jet impingement flow and heat transfer, and an inclined jet towards the crossflow may strengthen jet penetration. The combined effect of the crossflow and inclination angle on jet impingement heat transfer makes the problem even more complicated. This paper studied this effect numerically with various parameters, including the velocity ratio of jet to the crossflow, inclination angles, the crossflow temperature as well as the jet-to-target spacing. The heat transfer coefficient distribution and its peak value at the stagnation region are examined and compared. Results show that at small jet-to-target spacing the crossflow can enhance the heat transfer, while at large jet-to-target spacing the heat transfer is reduced due to the crossflow as well as inclination. In some cases jet impingement heat transfer can be higher with an inclined angle than that of a normal jet, given the same crossflow ratio.
Enhanced Saturation Boiling of HFE-7100 Dielectric Liquid on Extended Copper Surfaces
Authors: Parker Jack L. , El-Genk Mohamed S.
Published: April 2009

Experiments are performed, which investigated the enhancement in saturation boiling of HFE-7100 dielectric liquid on copper surfaces having a footprint of 10 × 10 mm and four 3 × 3 mm corner pins that are 2, 3 and 5 mm tall. These pins increase the geometrical surface area, by 96%, 144%, and 240%, respectively, and the surfaces are prepared using #400 and #1500 emery papers to investigate the effect of roughness on boiling heat transfer. Still photographs and video footage are recorded of the boiling processes. Nucleate boiling starts at a few isolated sites on the inside of the pins, close to the common line with the base surface, markedly reducing or eliminating the temperature excursion prior to boiling incipience. Measurable enhancements are obtained in both natural convection and nucleate boiling heat transfer. On the plane Cu surfaces prepared with emery paper #1500, the maximum nucleate boiling heat transfer coefficient, based on the foot print area, hB*, is 1.16 W/cm2.K and increases to 1.80, 2.03 and 2.37 W/cm2.K on the surfaces with 2, 3, and 5 mm tall pins. Similarly, the Critical Heat Flux (CHF), based on the foot print area, increases linearly with increased pin height, at a rate of ∼ 32% per mm. Increased surface roughness increases both hB* and CHF by additional 15% and 10% and markedly enhances nucleate boiling heat transfer at high surface superheats (ΔTsat > ∼10 K), but causes only little enhancement at lower superheats.
Evaluating LES Subgrid-Scale Models for High Heat Flux Flows
Authors: Hradisky Michal , Hauser Thomas
Published: April 2009

This work is concerned with the modeling of a strongly heated, low Mach number, gas flowing upward within a vertical tube with constant heat flux boundary conditions. Four large eddy subgrid models are compared in their ability to predict the temperature distribution in the heated pipe. All LES models predict the mean velocity profile reasonably well. The RMS values of the Smagorinsky-Lilly model and the WALE model show the same shape but different magnitude while the standard Smagorinsky model shows the maximum at a different location. The mean temperature profiles along the wall in the section with the prescribed heat flux are underpredicted by all LES models.
An Experimental Characterization of Miniature Scale Cold Plates for Electronics Cooling Applications
Authors: Jeffers N. , Punch J. , Walsh E.
Published: April 2009

Contemporary electronic systems are currently constrained by the high heat fluxes in which they generate at component level. It is evident that heat fluxes are currently approaching the limits of forced air cooling, and that liquid cooling is now under consideration. In this paper five commercially-available and one custom-made cold plates were characterised experimentally. The six cold plates utilized different geometries which included: an array of jets impinging onto a pin matrix; a fin structure; a pin fin structure; a large serpentine channel structure; a slot jet impinging onto wave shaped fins; and the custom cold plate having no significant geometry associated with it, as it was used as a bench mark. The bench mark is anticipated to be the minimum cost solution. The pressure drop, thermal resistance and hydrodynamic power consumption were determined for each solution as a function of flow rate. The results showed that there was a variety of operational power consumption costs coupled with a range of performance levels reached by the six cold plates. This emphasizes the need of a optimum cooling package for a specific application. A relationship of thermal resistance as a function of hydrodynamic power consumed was formulated, thus facilitating the selection of a cold plate for a practical application.
DNS and Turbulence Modeling for Turbulent Boundary Layers With Various Thermal Stratifications
Authors: Hattori H. , Nagano Y.
Published: April 2009

Direct numerical simulations (DNS) of boundary layers with various thermal stratifications are carried out to investigate the turbulent structures of these flows. The present DNSs quantitatively provide the characteristics of thermally stratified turbulent boundary layers. In particular, the counter gradient diffusion phenomenon is found in a strong, stable stratified boundary layer. On the other hand, in order to adequately predict turbulent boundary layers with various thermal stratifications, an appropriate turbulence model should be employed in the calculation. Thus, using a database obtained by DNS, the strict assessment of turbulent heat transfer model is made so as to construct a reliable advanced turbulence model. The results of in-depth turbulent model evaluation are indicated, in which we have explored the prediction potential of the proposed nonlinear eddy diffusivity models for momentum and heat in both stable and unstable stratified boundary layers.
Cryogenic Heat Exchanger With Photo-Etched Mini-Perforated Plates Allowing Flow-Bypass
Authors: Jung Jeheon , Jeong Sangkwon
Published: April 2009

A perforated plate heat exchanger can be made very compact by the reduced perforation size. Hence, it fits to the field where high effectiveness but small size is demanded, i.e., cryogenic applications. The compactness of a perforated plate heat exchanger can even reach that of a cryogenic regenerator. We are developing a compact perforated plate heat exchanger for replacing a low-temperature regenerator. In the compact perforated plate heat exchanger, small perforations (diameter: ∼ 150 μm) were patterned by photo-etching on thin copper plate (75 μm thick). Spacers were made of Kapton film (25 μm thick) or stainless steel plate (30 μm thick). Kapton film spacer is for an experimental heat exchanger which requires convenient disassembly, and stainless steel spacer is for the final product which will be diffusion-bonded. In this type of heat exchanger, stream-to-channel convection heat transfer coefficient is so large that conduction along the plate can rather restrict overall heat transfer rate between cold and hot streams. In order to avoid such conduction-restricted overall heat transfer, 14 strip-shaped channels were formed spirally to reduce effective conduction length and enhance lateral conduction. Transverse bypass among cold or hot stream channels were also adopted to relieve flow mal-distribution. Thermal performance of the heat exchanger was both analyzed and experimented between liquid nitrogen temperature and room temperature. The result shows quite good agreement.
Research on Flow and Condensation of Vapor With Non-Condensable Gas in an Inclined Tube
Authors: Wang Li , Li Hongying
Published: April 2009

A set of separate heat pipe (SHP) with water as medium has been built in this paper. The flow and condensation of vapor with non-condensable and high partial pressure air in the SHP are measured in the experiment. A series studies are made of the effect on the parameters-coolant water flux, vapor flux, the coolant inlet temperature and the inlet vapor temperature and a lot of reliable data are obtained to analyze the heat transfer process.The physical model of the flow and condensation of vapor-air mixture has been studied and the related numeral model is founded by using the two-fluid model in the Mathematical model. The numerical result agrees well with the experimental data.
Methodology for the Inline Die Attach Characterization of Power LEDs
Authors: Szabo P. , Farkas G. , Poppe A. , Rencz M.
Published: April 2009

Qualification of the die attach quality is a very important issue in case of Light Emitting Diodes (LEDs), as the operating temperature of these devices is usually much higher than that of usual silicon devices. Problems in the die attach quality result in significant reliability issues. For this reason the manufacturing line testing of these devices seems necessary. The usual structure function evaluation methodology that is regularly used for die attach qualification in after production testing is normally requiring several minutes for the testing of a device that is prohibitively long for inline testing. In this paper various solutions are proposed to overcome the lengthiness of the thermal transient testing and structure function evaluation methodology. With the proposed solutions the necessary time of problem detection is in the order of magnitude of milliseconds, enabling the methodology for production testing.
Characterisation of a Variable Conductance Heat Pipe Prototype for a Photonic Application
Authors: Cleary Martin , Grimes Ronan , Hodes Marc , North Mark T.
Published: April 2009

Thermoelectric modules (TEMs) consume a large amount of power when used for precision temperature control of high-power photonic devices, particularly when subjected to a wide range of ambient temperatures. The use of variable conductance heat pipes (VCHPs) as a lower power alternative to TEMs is investigated here. The performance of a methanol-argon VCHP with a non-wicked reservoir for both passive and active control is characterized. The concept of an “deal” working fluid for a gas-loaded VCHP is introduced. It has a liquid-vapor saturation curve resulting in perfect passive evaporator temperature control in the limit of an infinitely-large reservoir when the VCHP is subjected to changes in heat load and/or ambient temperature. The saturation curve of this ideal fluid is compared to that of the fluid used here, i.e., methanol, showing why perfect passive control is unrealistic for varying ambient temperature. An experimental prototype was constructed and measurements obtained from it were compared to the predictions of the flat front model. It was found that, even with active control, the evaporator temperature could not be maintained sufficiently at low ambient temperatures due to axial conduction through the adiabatic section of the prototype VCHP. However, excluding these low ambient temperatures, the VCHP provides a significant reduction in power consumption compared to a TEM.
Convective Heat Transfer of Nanofluids (DI Water-Al2O3) in Micro-Channels
Authors: Lee Joohyun , Flynn Roger D. , Goodson Kenneth E. , Eaton John K.
Published: April 2009

The convection performance of nanofluids in microchannels has received relatively little attention. This work reports convective heat transfer experiments of deionized water/Al2O3 nanofluids using 200μm hydraulic diameter MEMs fabricated microchannel structures and a stainless steel tube with 250μm inside diameter. The tube wall is heated electrically producing a constant heat flux boundary condition and an infrared camera is used to measure the outside tube wall temperature. A full numerical conjugate analysis of the apparatus is used to infer the fluid thermal conductivity from the temperature measurements. The effective thermal conductivity of nanofluids increased only by 4% for 4% volume concentration nanofluids in the MEMs fabricated microchannel and 5% for 3% volume concentration in the stainless steel tube under laminar flow conditions. The effective viscosity of the nanofluids increased 12% for 2% volume concentration. A dynamic light scattering system was used to measure the effective particle diameter and particle size distributions of nanoparticles with various pH values and surfactants. The measured mean diameter of Al2O3 nanoparticle is 170 nm, which is larger than the 40–50 nm nominal size.
Effects of Flow Field on Combustion Characteristics of Confined Jet Nonpremixed Flames
Authors: Noda Susumu , Nada Yuzuru , Parwatha I. Gede , Fukushige Shingo
Published: April 2009

Confined flames are widely used in the industrial field. The flame characteristics can be strongly dominated by the combination of a burner and furnace geometries, which were not paid much attention before. In the present study, flow fields in confined flames are discussed in terms of the flame characteristics. The flow characteristics of confined flames have been investigated for propane nonpremixed flames in cylindrical furnaces. The effects of the inner diameter of the cylindrical furnace D1, the turbulence at the flame boundary, and the global equivalence ratio φ are examined in terms of the relation between the emission of NOx and the flow fields. The emission index of NOx, EINOx, decreases roughly with these parameters. The decrease in EINOx is thought to be related to the dilution of mixtures by the burned gas and the flame stretch. The dilution is attributable to vortices formed at the bottom of the furnace, and the flame stretch is attributable to the air velocity difference ΔUa created by two air nozzles. In the present study, it was found that the increases in D1, ΔUa, and φ enlarge and strengthen recirculation vortices to dilute the flame.
The Effect of Molecular Orientation and Temperature on the Flow Dynamics of Water Molecules Through a Carbon Nanotube
Authors: Cannon James , Moore Natalie , Hess Ortwin
Published: April 2009

Temperature plays a significant role in determining the dynamics of flow on the nanoscale. This is particularly important with carbon nanotubes, which are likely to form an integral part of future nanofluidic and biological devices. We demonstrate through first-principles density-functional theory (DFT) that the energies and temperatures at which individual water molecules are able to enter the nanotube depends very strongly on their orientation. This has a number of implications for the flow of water through the nanotube at different temperatures and densities, particularly when considering low-density water vapour.
Gasification of Indian Coal in a Tubular Coal Gasifier
Authors: Ajilkumar A. , Sundararajan T. , Shet U. S. P.
Published: April 2009

In spite of the high ash content, Indian coals have been widely used for the generation of power and industrial steam in India. Being considered as the technology for future in terms of efficiency and cleaner environment, coal gasification carries much importance since India has a large amount of coal reserves. In this paper, the numerical simulations have been performed on gasification performance of three types of Indian coals in atmospheric as well as pressurized conditions in an entrained flow, air-blown tubular gasifier. In the model, continuous phase conservation equations are solved in an Eularian frame and those of particle phase are solved in a Lagrangian frame, with coupling between the two phases incorporated through interactive source terms. Phenomena such as devolatilisation, combustion of volatiles, char combustion & gasification and the dispersion of coal particles due to turbulence are taken into account. The P-1 model has been adopted for radiative heat transfer in which scattering is taken into account for the particles. It is observed that as the ash percentage increases, the heat and mass transfer are strongly affected and the gasification performance decreases. This is attributed to the lower char reactivity due to thick ash layers and lower oxygen and other gas diffusion rates. Various regions such as devolatilisation, combustion and gasification zones inside the gasifier have been identified using the temperature plots, devolatilisation plots and mass depletion histories of coal particles. The overall gasification performance indices such as carbon conversion, heating value of the exit gas and cold gas efficiency have been predicted.
Flame Spread Along PE-Insulated Wire in Sub-Atmospheric Pressure Enclosure
Authors: Nakamura Yuji , Yoshimura Nobuko , Matsumura Tomohiro , Ito Hiroyuki , Fujita Osamu
Published: April 2009

Flame spread over polymer-insulated wire in reduced (sub-atmospheric) pressure has been studied experimentally in order to evaluate the fire safety of electric circuit in the aircraft as well as the space habitats. Polyethylene (PE) insulated NiCr wire is used as the burning sample. Ambient gas is the mixture of nitrogen and oxygen, and the composition is fixed as air (79 vol.% of N2 and 21 vol.% of O2) throughout the study. Total pressure is reduced from atmospheric (101 kPa) to sub-atmospheric (20 kPa) in order to investigate the role of the reduced pressure on the flame spread along the wire. Spread event followed by the forced ignition is recorded by digital video camera to obtain any time-dependent flame behavior. Experimental results show that the flame shape is changed from typical “teardrop” to “round” (and even oval) with the decrease in total pressure. Flame spread rate increases in the reduced pressure although the partial pressure of oxygen is “reduced” with the total pressure. Such “pronounced” spread behavior is continuously observed until just before the extinction condition (∼25 kPa in the present study). The change in flame shape could enhance thermal input to the unburned PE through gas-phase conduction as well as conduction along the wire, and these should be responsible for the faster flame spread in sub-atmospheric pressure. Heat balance is roughly estimated with measured temperature and relative contribution of above two thermal input pathways is understood almost comparable. Importance of the presence of conductive material, such as metal wire, on flame spread is addressed in the current spread behavior.
A New Hybrid Full-Spectrum Correlated k-Distribution Method for Radiative Transfer Calculations in Nonhomogeneous Gas Mixtures
Authors: Pal Gopalendu , Modest Michael F.
Published: April 2009

The full-spectrum k-distribution (FSK) approach is a promising model for radiative transfer calculations in participating media. FSK achieves line-by-line (LBL) accuracy for homogeneous media at a tiny fraction of LBL’s high computational cost. However, inhomogeneities in gas temperature, total pressure and component-gas mole fractions change the spectral distribution of the absorption coefficient and can cause inaccuracies in the FSK method. In this paper, a new hybrid FSK method is proposed that combines the advantages of the multi-group FSK (MGFSK) method for temperature inhomogeneities in a single gas specie and the multi-scale FSK (MSFSK) method for concentration inhomogeneities in gas mixtures. In this new hybrid method the absorption coefficients of each gas specie in the mixture are divided into M spectral groups depending on their temperature dependence. New and accurate MGFSK databases are constructed for combustion gases, such as CO2 and H2O. This paper includes a brief mathematical development of the new method, method of database construction and sample heat transfer calculations for 1-D inhomogeneous gas mixtures with step changes in temperature and species mole-fractions. Performance and accuracy are compared to LBL and traditional FSK calculations. The new method achieves high accuracy in radiative heat transfer calculations in participating media containing extreme inhomogeneities in both temperature and mole fractions using as few as M = 2 spectral groups for each gas specie, accompanied by several orders of magnitude lower computational expense as compared to LBL solutions.
Fluid/Thermal Analysis of High Temperature Heat Exchanger and Chemical Decomposer for Hydrogen Production
Authors: Ponyavin Valery , Chen Yitung , Hechanova Anthony E. , Wilson Merrill
Published: April 2009

This paper presents fluid flow and heat transfer study of a high temperature heat exchanger and chemical decomposer. The decomposer will be used as a part of the plant for hydrogen production. The decomposer is manufactured using fused ceramic layers that allow creation of channels with dimensions below one millimeter. The main purpose for this study is to increase thermal performance of the decomposer which can help to intensify sulfuric acid decomposition rate. Effects of using various channel geometries of the decomposer on the pressure drop are studied as well. A three-dimensional computational model is developed for the investigation of fluid flow and heat transfer in the decomposer. Several different geometries of the decomposer channels such as straight channels, ribbed ground channels, hexagonal channels, and diamond-shaped channels are examined. Based on results of the calculation, the recommendations for the improved design of the decomposer are obtained.
Steady-State Network Thermofluid Models of Loop Heat Pipes
Authors: Atabaki Nima , Jesuthasan Nirmalakanth , Baliga B. Rabi
Published: April 2009

A loop heat pipe (LHP) with one evaporator, a vapor-transport line, a single condenser, a liquid-transport line, and a compensation chamber is considered. The evaporator is an internally grooved circular pipe, with an annular wick installed on its inner surface. The wick is made of sintered powder metal. The condenser is a horizontal tube that is fitted with excellent thermal contact inside a metallic sleeve that is immersed in a constant-temperature bath maintained at a fixed sink temperature. Two different network thermofluid models of this LHP operating under steady-state conditions are presented. In the first (basic) model, quasi one-dimensional mathematical models of the fluid flow and heat transfer in each of the elements of the LHP are used; the pressure drop in the two-phase region of the condenser is ignored; and a relatively simple correlation is used to model the heat transfer in the two-phase region of the condenser. In the second (segmented) model, quasi one-dimensional control volumes or cells are used for the simulation of fluid flow and heat transfer in the vapor-transport line, the condenser, and the liquid-transport line, in order to better account for the variation of fluid properties and the quality (in two-phase regions); and the pressure drops in the two-phase regions are accounted for. The working fluid considered in this investigation is ammonia, but the proposed models can be used with any suitable fluid. Results pertaining to the LHP performance for a range of operating conditions are presented. Some of these results are compared to corresponding results of an earlier experimental investigation in the literature: good agreement is obtained with both models.
Experiments and Analytical Simulation Work on an Innovative Steam-Injector-Driven Passive Core Injection Cooling System
Authors: Mori Michitsugu , Narabayashi Tadashi , Ohmori Shuichi , Watanabe Fumitoshi
Published: April 2009

A Steam Injector (SI) is a simple, compact, passive pump which also functions as a high-performance direct-contact compact heater. We are developing this innovative concept by applying the SI system to core injection systems in Emergency Core Cooling Systems (ECCS) to further improve the safety of nuclear power plants. Passive ECCS in nuclear power plants would be inherently very safe and would prevent serious accidents by keeping the core covered with water (Severe Accident-Free Concept). The Passive Core Coolant Injection System driven by a high-efficiency SI is one that, in an accident such as a loss of coolant accident (LOCA), attains a higher discharge pressure than the supply steam pressure used to inject water into the reactor by operating the SI using water stored in the pool as the water supply source and steam contained in the reactor as the source of pressurization energy. The passive SI equipment would replace large, rotating machines such as pumps and motors, so eliminating the possibility of such equipment failing. In this Si-driven Passive Core Coolant Injection System (SI-PCIS), redundancy will be provided to ensure that the water and steam supply valves to the SI open reliably, and when the valves open, the SI will automatically start to inject water into the core to keep the core covered with water. The SI used in SI-PCIS works for a range of steam pressure conditions, from atmosphere pressure through to high pressures, as confirmed by analytical simulations which were done based on comprehensive experimental data obtained using reduced scale SI. We did further simulations and evaluations of the core cooling and coolant injection performance of SI-PCIS in BWR using RETRAN-3D code, developed using EPRI and other utilities, for the case of small LOCA. Reactors equipped with passive safety systems — the gravity-driven core cooling/injection system (GDCS) and depressurization valves (DPV) — would inevitably end up having large LOCA, even if they are initially small LOCA, as depressurization valves are forcibly opened in order to inject coolant from the GDCS pool to the GDCS water head at up to ∼0.2MPa. On the other hand, our simulation demonstrated that SI-PCIS could prevent large LOCA occurring in reactors by having by coolant discharged into the core in the event of small LOCA or when DPV unexpectedly open.
Numerical Study of Heat Transfer Mechanism in Turbulent Supercritical CO2 Channel Flow
Authors: Li Xinliang , Hashimoto Katsumi , Tanahashi Mamoru , Miyauchi Toshio
Published: April 2009

Direct numerical simulation (DNS) of supercritical CO2 turbulent channel flow is performed to investigate the heat transfer mechanism of supercritical fluid. In the present DNS, full compressible Navier-Stokes equations and Peng-Robison state equation are solved. Due to effects of the mean density variation in the wall normal direction, mean velocity in the cooling region becomes high compared with that in the heating region. The mean width between high- and low-speed streaks near the wall decreases in the cooling region, which means that turbulence in the cooling region is enhanced and lots of fine scale eddies are created due to the local high Reynolds number effects. From the turbulent kinetic energy budget, it is found that compressibility effects related with pressure fluctuation and dilatation of velocity fluctuation can be ignored even for supercritical condition. However, the effect of density fluctuation on turbulent kinetic energy cannot be ignored. In the cooling region, low kinematic viscosity and high thermal conductivity in the low speed streaks modify fine scale structure and turbulent transport of temperature, which results in high Nusselt number in the cooling condition of the supercritical CO2.
Study on Comparison of Thermal Conductivities of Thermal Insulations Using Different Measurement Methods in Wide Range of Temperature
Authors: Ohmura Takahiro
Published: April 2009

Guarded hot plate method (GHP method) is the most popular way of measuring thermal conductivity of thermal insulation. However, there are large differences among the thermal conductivities measured by different apparatuses which are made in different institutions in the temperature range above 100 °C. It is considered the reason that we have no standard material for measurement of thermal conductivity. The standard material is only glass wool which are produced by NIST (National Institute of Standards and Technology) in a temperature range from about 7 to 67 °C. Then, I have researched how far the influence of the difference in measurement methods and apparatuses extends. Furthermore, I have investigated how to measure accurately thermal conductivity in the temperature range which there are few reference materials. In this study, I proposed to increase the accuracy of thermal conductivity of thermal insulation by comparing with values obtained using different methods. I investigated the practicality of the comparison of the results obtained by different methods, which are the GHP, cyclic heat, transient hot wire, and Hot Disk methods, for the accurate measurement at the temperature range from −170 to 1300 °C. First, I developed the three types of measurement apparatuses; one can measure thermal conductivity by using both the GHP and cyclic heat methods in the temperature range from 100 to 1300 °C, the second can measure using both the cyclic heat and transient hot wire methods in the temperature range from 100 to 1000 °C, and the third can measure using both the cyclic heat, transient hot wire, and Hot Disk methods in the temperature range from −170 to 25 °C. Next, I measured thermal conductivities of various thermal insulations using these apparatuses. In the temperature range above 100 °C, the results obtained by using the GHP and cyclic heat methods agree with each other within ± 10% deviations. In like manner, the results obtained by using the cyclic heat and transient hot wire methods agree with each other within ± 10% deviations. Furthermore, in the temperature range from −120 °C to 25°C, the results obtained by using the cyclic heat, transient hot wire, and Hot Disk methods agree with each other within ± 10% deviations. Therefore, it is thought that to compare the thermal conductivities obtained by the different measurement methods will be practical for improvement of the accuracy measurement at the temperature range in the absence of reference materials.
An Investigation of the Effect of Addition of Nanoparticles on the Properties of Lubricating Oil
Authors: Sajith V. , Mohiddeen Md. , Sajanish M. B. , Sobhan C. B.
Published: April 2009

Lubrication is essential to reduce friction and wear in mechanical parts thus minimizing the associated dissipative energy loss. Viscosity is the most important property of lubricating oil, which accounts for its flow resistance. Other important properties of lubricating oil include the flash point and the fire point, which are related to oil storage and handling. The present work is an attempt to study the effect of inclusion of nanoparticles on the kinematic viscosity and the flash point of lubricating oil. Copper oxide and aluminum oxide nanoparticles were suspended in two stroke Servo SAE 20 W-40 lubricating oil using standard ultrasonic agitation process, and the properties of the resulting suspension studied. The effects of the volume fraction of nanoparticles (dosing level varying from 0.02 to 0.2 percentage by volume) on the kinematic viscosity and flash point of the suspension were studied, treating the temperature as a parameter in the range 30°C to 65 °C. An initial increase and subsequent decrease was noticed in the kinematic viscosity as well as the flash point, with an increase in the volume fraction of the nanoparticles. Possible reasons for this behavior were understood to be the increase in density, and the agglomeration of nanoparticles as the dosing level increases.
CFD-Analysis of Fully Developed Turbulent Flow and Heat Transfer in a Unitary Cell of a Cross Corrugated Plate Pattern Heat Exchanger
Authors: Etemad Sassan , Sunde´n Bengt
Published: April 2009

The turbulent flow and the heat transfer in a unitary cell of a cross corrugated plate pattern heat exchanger has been studied using Chen’s high-Re k-ε model, Suga’s low-Re k-ε model, the RSM and the V2F model at a Reynolds number of 4930. The ability of these models in predicting the mean Nusselt number and Fanning friction factor has been investigated. The V2F model predicted higher heat transfer and friction factors than the other models. It was observed that the upper and lower flow in the unitary cell interact throw a shear process. This in turn initiates a complex secondary flow pattern which promotes the heat transfer. The V2F model predicted the strongest shear process. This may explain the fact that it also predicted the highest values of heat transfer and friction factor compared to the other models. The shear flow also caused high levels of turbulent kinetic energy in the centre of the unitary cell. The observed secondary motion is believed to be an efficient means of increasing the heat transfer coefficient with limited pressure drop penalty. It is also demonstrated that despite the geometrical complexity, high quality computational grids can be created and thereby details of the flow and heat transfer phenomena can be studied. The RSM appeared to be instable and gave results similar to Chen’s k-ε model. Therefore, its use is not motivated for such applications.
An Analysis of Local Quantities of Turbulent Premixed Flames Using DNS Databases
Authors: Tsuboi Kazuya , Nishiki Shinnosuke , Hasegawa Tatsuya
Published: April 2009

An analysis of local flame area was performed using DNS (Direct Numerical Simulation) databases of turbulent premixed flames with different density ratios and with different Lewis numbers. Firstly, a local flame surface at a prescribed progress variable was identified as a local three-dimensional polygon. And then the polygon was divided into some triangles and local flame area was evaluated. The turbulent burning velocity was evaluated using the ratio of the area of turbulent flame to that of planar flame and compared with the turbulent burning velocity obtained by the reaction rate.
Energy Conservation Based Spray Cooling CHF Correlation for Flat Surface Small Area Heaters
Authors: Silk Eric A. , Kim Jungho , Kiger Ken
Published: April 2009

A forced convection analysis that emphasizes heat transfer phenomena at the heat exchange surface during spray cooling was used to develop a CHF correlation by recasting the multiphase energy balance equation in the form of the Nusselt number. Although multiphase effects are accounted for, the correlation primarily applies to flow scenarios that are single phase dominated. Test cases from previously published and unpublished studies by various researchers were included. Results for comparison of predicted vs. measured CHF are presented for several different working fluids. Predictions for the modeled cases show an average mean error of ±18% with 88% of the data predicted within a range of ±30%. The correlation applies to both gassy and degassed conditions for perfluorocarbons, water, and methanol.
Thermal Conductivity Measurements and Modeling of Phase-Change GST Materials
Authors: Yang Yizhang , Jeong Taehee , Hamann Hendrik F. , Zhu Jimmy , Asheghi Mehdi
Published: April 2009

Phase-change technology has been widely used in rewritable disks for optical recording applications. Recently, it has also received attention as a candidate for future high storage density non-volatile random access memory, due to its much longer cycle life (∼1013) and fast data access time (∼100ns) compared with the existing Flash memory technology. In this paper, we present thermal conductivity data and models for phase-change GeSbTe material that would be helpful in performance optimization and improvement in the reliability (i.e., enhancement of data rate, cyclability, control of mark-edge jitter) of phase-change-based data storage devices and systems. We perform the thermal characterization of Ge4Sb1Te5 and Ge2Sb2Te5 phase-change materials for the application of optical recording and phase-change memory cell using the techniques of thermoreflectance and electrical resistance thermometry. The limits of lattice and electronic thermal conductivities are investigated to determine their relative contributions as a function of tellurium concentration at different crystalline structures.
Thermal Modeling and Luminosity Characterization of a Plasma Display Panel
Authors: Kahn Jeffry , Bar-Cohen Avram
Published: April 2009

Plasma Display Panels (PDPs) are a popular technology for large size television displays. Screen inefficiencies, which result in significant localized heat generation, necessitate the use of advanced thermal management materials to reduce both the peak temperatures and the spatial temperature variations across the screen. In the current study, infrared thermography was used to obtain thermal maps of a typical, 42", high-definition PDP screen for different illumination patterns and for several configurations of externally controlled heaters, simulating PDP heat generation. The results were used to validate a 3-dimensional numerical thermal model of the PDP which was then used to predict the beneficial effects of anisotropic graphite heat spreaders on the temperature distribution of the PDP. In addition, a color analyzer was used to determine the spatial and temporal variations in luminosity across the PDP when operated continuously for 1750 hours with different illumination patterns. The thermal model and experimental luminosity characteristics are used to evaluate the deleterious effects of temperature on PDP performance.
Theoretical Modeling and Optimized Design of a Packaged Liquid Chiller
Authors: Heydari Ali , Kargar Saeed
Published: April 2009

This work attempts to develop a physical simulation model for the purpose of studying the effect of various design parameters on the performance of a packaged liquid chiller. A computer model which simulates the steady-state cyclic performance of a vapor compression chiller is developed for the purpose of performing detailed physical design analysis of actual industrial chillers. The model can be used for optimizing design and for detailed energy efficiency analysis of packaged liquid chillers. The simulation model takes into account presence of all chiller components such as compressor, shell-and-tube condenser and evaporator heat exchangers, thermostatic expansion valve and connection pipes and tubing’s by thermal-hydraulic modeling of heat transfer, fluids flow and thermodynamics processes in the chiller’s components. To verify the validity of the developed model, a 7.5 USRT packaged-liquid chiller is used and a laboratory test stand for brining the chiller to its standard steady-state performance condition is build. Experimental results obtained from testing the chiller in different load and temperature conditions are shown to be in good agreement with those obtained from simulating the performance of the chiller using the developed computer model. To optimize the chiller design, an entropy-minimization-optimization analysis is performed based on the analytical performance model of the chiller. The variation of design parameters in construction of shell-and-tube condenser and evaporator heat exchangers are studied using the developed performance and optimization analysis and simulation model and a best-match condition between the physical design and construction of chiller heat exchangers and its compressor is found to exist. It is expected that manufacturers of chillers and research organizations interested in developing energy-efficient design and analysis of chillers can take advantage of the presented study and its results.
Modeling Optical Properties of Small Metallic Nanoparticles Based on Density Functional Theory
Authors: He Yi , Zeng Taofang
Published: April 2009

Optical properties of silver nanoparticles with different diameters are investigated based on the electronic structures of component silver atoms. Within the frame of tight binding method, the local density of states of each silver atom is obtained through a recursive approach that extracts the required information directly from the Hamilton matrix. Then the interaction between the electric field of incident light and electrons in the nanoparticles is simulated to characterize their optical features and the size effects were interpreted according the results.