bluuebunny/crossref_metadata_2025 huggingface dataset:
An Analysis of a Direct Contact Ice Slurry Generator
Authors: Wahed M. A. , Hawlader M. N. A.
Published: July 2009

Attempts have been made to study an ice slurry generation system where two immiscible liquids, water and a coolant, are used to produce ice slurry by direct contact heat transfer. A mathematical model has been developed to evaluate the heat transfer phenomena between the coolant drops and the water in the ice slurry generation system. In this process, all the important variables that affect the direct contact heat transfer between these two fluids were incorporated into the simulation model to evaluate thermal performance of the system. Experiments were performed on an ice slurry generator using water and an immiscible liquid coolant, Fluroinert FC-84. The coolant at about −10°C to −15°C was delivered to the top of the ice slurry generator containing water and collected from the bottom for recirculation. The measured temperature profiles of water in the ice slurry generator for different coolant flow rates (8 lit/min to 12 lit/min) showed a good agreement with those temperature profiles obtained from the simulation model. These results validated the simulation model developed for the ice slurry generator. The analysis showed that during sensible cooling, the estimated heat transfer coefficients between water and the coolant were in the range of 3.0 to 6.5 kW/m2 for coolant flow rates varying from 8 lit/min to 12 lit/min. Higher coolant flow rates also enhanced the ice formation process due to the increased heat transfer rate. In addition, it was also observed that the ice production increased significantly when the nozzle was placed at the bottom of the ice slurry generator.
Convective Boiling Between 2D Plates: Shear Flow Influence on Bubble Growth, Detachment and Evolution
Authors: Serret D. , Brutin D. , Rahli O. , Le Niliot C. , Tadrist L.
Published: July 2009

The experiment detailed in this paper presents results obtained on the nucleation, growth and detachment of HFE-7100 vapor bubbles confined in a two-dimensional plane created on an artificial nucleation site. The experiments were performed by varying the shear flow and the bubble nucleation rate through the heat flux supplied under normal gravity and microgravity. The distance between the plates was kept constant at 1 mm. The first results of these experiments are mainly related to the formation of a bubble on an isolated site with or without convection and to the associated heat transfer when confinement is imposed on a bubble. To this effect, we implemented an experimental device allowing the observation of the flow by means of both a visible video camera and an infrared video camera. Here, we present the first results obtained from the campaign performed in December 2007 concerning the influence of gravity on the bubble detachment diameter and the first images of 2D bubbles obtained in microgravity by means of an infrared camera.
Experimental Study of Thermal Response of LPG Tanks Subjected to External Fire
Authors: Xing Zhi Xiang , Zhao Xiao Fang
Published: July 2009

The experimental research on thermal response of LPG tank exposed to fire is carried out. A experimental apparatus to simulate real accident of LPG tank is designed and manufactured. A series of experiments for different fill levels, different type of tanks subjected to different type of fires are performed with this apparatus. From the results of the experiments, the obvious stratification of temperature in the ladings of the tank is observed. And the pressure is increased due to the stratification. Thermal response of the LPG is affected by various factors such as fire type, tank type and fill level etc. The liquid could be superheated or sub-cooled in fire exposure situation. The pressure can be fitted to time by cube polynomial equation.
Modeling and Testing of an Integrated Evaporator-Condenser Device for CPU Cooling
Authors: Chan Mark Aaron , Yap Christopher R. , Ng Kim Choon
Published: July 2009

CPUs with high clock rates can dramatically increase heat dissipation within their encapsulation due to internal Joule heat from the transistors. The conventionally used air cooling systems for CPUs, such as the aluminum or copper extruded heat sink types, have severe heat transfer “bottlenecks” due to high thermal resistances and they easily reach their thermal design limits (TDL). Alternative cooling devices such as heat pipes and liquid cooling tends to have externally attached radiator/condenser and/or pump and such designs are cumbersome. This paper describes the modeling, design, and testing of a compact (about the size of the Intel stock cooler, diameter: 96mm, height: 50mm), fully integrated, orientation-free, evaporator-condenser device for CPU cooling, with excellent attributes of low thermal resistance from phase change phenomena and minimal vapor pressure drop. The prototype fabricated is designed to reject 200 W (twice the capacity of conventional heat sinks). It is made of copper and uses distilled water as the working fluid. The working fluid boils inside a porous structure clad evaporator and is transported radially to nearby air-cooled condenser sections; this unique arrangement minimizes space while providing adequate area for air convection. Testing was done by subjecting it to varying heat loads and air flow rates. A best performance of 0.206 K/W of the device’s thermal resistance was achieved at a fan air flow rate of 34.5 CFM under 203 W of cooling load, and moreover, these results are in good agreement with the simulation. Further improvement of the current design could yield significantly better performance as the device has yet to reach its full potential, especially with regard to the design of its air-cooled curvilinear fins and boiling enhancement.
The Effect of Partitions on the Laminar Natural Convection in a Square Cavity
Authors: Wu Wenjiang , Ching Chan Y.
Published: July 2009

The effect of a partition on the laminar natural convection flow in an air-filled square cavity driven by a temperature difference across the vertical walls was investigated experimentally. Two partitions with non-dimensional heights of 0.0625 and 0.125 was attached either to the upper half of the heated vertical wall or the top wall at different locations. The experiments were performed for a global Grashof number of approximately 1.24×108 and non-dimensional top wall temperatures of approximately 0.48 to 2.28. At the higher top wall temperatures, a secondary flow circulation region formed between the partition attached to the top wall and the heated vertical wall of the cavity. This secondary flow circulation region was sensitive to the location and height of the partition, in addition to the top wall temperature of the cavity. The secondary flow circulation region moved the location where the upward boundary layer flow along the heated vertical wall turned over to be further away from the top wall, than in the cavity without the partition. A thermal boundary layer was observed to move along the rear surface of the partition attached to the top wall. In the region close to the top wall, the partitions caused the non-dimensional temperature outside of the boundary layer and the local Nusselt number along the heated vertical wall to be different from that in the cavity without the partition. There were no significant effects of the partition on the flow and heat transfer characteristics in the lower half of the cavity.
Mid-Infrared Properties of Nanoscale Metallic Slit Arrays
Authors: Chen Y.-B. , Fu K. , Chen C.-H. , Hsu P.-F. , Lee Y.-C.
Published: July 2009

Sub-wavelength periodic structures have demonstrated wavelength- or polarization-selective transmittance, which is critical for many optical devices and thermal applications. For example, linear polarizers composed of metallic wire grids on a transparent substrate have been used for a long time [1]. Near-field microscopy and photon extraction also much benefited from two-dimensional hole arrays [2]. Specifically, nanolithography and energy conversion devices recently made significant progresses with the help of one-dimensional periodic metallic slit arrays [3]. In fact, the unique transmittance spectrum through slit arrays was attributed to several physical mechanisms, including Wood’s anomaly, cavity resonance, surface plasmon polaritons, and effective medium behavior [4,5]. Either only one or the interplay of multiple mechanisms can tailor the spectrum depending strongly on slit features and the wavelength. Though correlations between tailoring mechanisms and unique radiative properties attracted abundant research interests, exactly rectangular cross-section is usually assumed for gratings in most numerical investigations with feature variation in slit width, slit depth, or period [4–7]. Other types of feature variation include the combination of two rectangular gratings made of different materials [8] or the rectangular gratings themselves filled with both metal and dielectrics [9].
Numerical Study on High Temperature Air Combustion in U-Type Tube
Authors: Li Xing , Jia Li , Zhang Tiantian , Yang Lixin
Published: July 2009

In this paper, the combustion characteristics of natural gas with high-temperature air combustion technology in a U-type combustion chamber were investigated by the numerical method. The results of the CFD-based mathematical modeling of rated condition were compared with experimental data including the maximum temperature, average temperature and NO emission. The research indicates that the combustion can be well simulated using the suggested numerical model. The temperature distribution, velocity distribution in the combustion chamber and NO emission were attained. In addition, the effects of some parameters such as oxygen concentration, excessive air ratio and combustion air temperature were discussed in detail. It provided primarily theoretic basis for further study of natural gas high temperature air combustion.
Numerical Simulation of the Impact of Both Air Conditioning System and Train’s Movement on Platform Air Temperature Distribution
Authors: Yang Hui , Jia Li , Yang Lixin
Published: July 2009

The three dimensional air temperature distributions on subway platform under both natural ventilation mode and over-platform supply/ under-platform exhaust (OSUE) air conditioning system were simulated during a single train entering, staying and departing processes by using Computational Fluid Dynamics (CFD) method. On basis of the simulation, the comprehensive influences of both the train’s piston effect and the air conditioning mode on the air environment in different part of the platform were analyzed.
Natural Convection Around a Horizontal Heated Square-Section Cylinder in an Enclosure: Visualization and Dynamic Characterization of Instabilities by Particle Image Velocimetry
Authors: Leplat Gillian , Barricau Philippe , Reulet Philippe , Millan Pierre
Published: July 2009

Consider an air-filled square cavity with cold top and bottom walls, adiabatic side walls and a centered heated sharp-edged source (a square-section cylinder). An unstable behavior has been highlighted previously while studying the effects of confinement (with different cylinder sizes) on the topology of the flow. A transition occurs from a bi-dimensional, steady regime to a three-dimensional, unsteady regime when the aspect ratio reaches the value of 0.4 for a Rayleigh number of 5.74 × 104. Time-resolved 2D particle image velocimetry is used to characterize the dynamics of the flow in this configuration. The evolution of the instability is particularly investigated.
Optimum Flashing Pressure in Single and Double Flash Geothermal Power Plants
Authors: Amiri Shahin , Shokouhmand Hossein , Kahrobaian Ahmad , Amiri Shayan
Published: July 2009

In this paper an analytical investigation has been reported on determination of the optimum flashing pressures to get maximum efficiency in flash geothermal power plants. Also, two different views on efficiency have been considered; thermal efficiency and exergy efficiency. Both views anticipate very close optimum flashing pressure and in this pressure, exergy efficiency is between 3 to 5.5 times more than thermal efficiency. It is observed that the optimum flashing pressure in a single flash power plant is between the optimum flashing pressures of two separators in a double flash power plant. Also both views predict an increase of 20–29 percent for the efficiency of double flash power plants than the efficiency of single flash power plants.
Direct Radiation From Wildfires Through Square Woven Screens
Authors: Sharifian Ahmad , Buttsworth David R.
Published: July 2009

The positioning of a metal mesh between a property and a wildfire not only reduces the threat of ember attack, but can also be effective in reducing the radiation heat flux from the fire to the property. A computational technique is used to establish a view factor correlation for the object-screen-wildfire arrangement for screens consisting of woven wire, square-celled elements. The view factor between the object and fire is calculated separately for each square-celled element of the screen and the results are added. The results indicate that the average view factor between an infinite fire and an object of the same size as the square cell is only related to the porosity of screen and is independent of distance of the object from the screen (when the object is in the proximity of the mesh). The results also show the view factor is less than screen porosity, particularly at lower porosities.
Validation of Mist/Steam Cooling CFD Model in a Horizontal Tube
Authors: Dhanasekaran T. S. , Wang Ting
Published: July 2009

Mist cooling concept has been considered for cooling turbine airfoils for many years. This concept has been proven experimentally as an effective method to significantly enhance the cooling effectiveness with several fundamental studies in the laboratory under low pressure and temperature conditions. However, it is not certain the same performance can be harnessed in the real gas turbine environment under the condition of elevated temperature, pressure, heat flux, and Reynolds number. This paper aims at validating a CFD model against experimental results in a circular tube and then applies the validated CFD model to simulate mist/steam cooling performance at elevated gas turbine working conditions. The results show that the standard k-ε and a RSM turbulence models are the best-suited model for this application. The mist with smaller droplet diameter is found achieving higher cooling enhancement than the flows with bigger droplets, while mist with a distributed droplet size matches the data slightest better than with uniform droplets. Both the wall-film and the reflect droplet boundary conditions are employed and their effects on the cooling result is not significant at the studied cases. The validated CFD model can predict the wall temperature within 2% in steam-only flow and 5% in the mist/steam flow. Applying the calibrated CFD model to the actual gas turbine working environment shows that the mist/steam cooling technique could harness an average 50–100% cooling enhancement.
Effects of Triangular Rough Elements on Flow and Heat Transfer in Micro-Channels
Authors: Feng Yan-Hui , Wang Ai-Guo , Lin Lin , Zhang Xin-Xin , Liu Xin
Published: July 2009

The flow and heat transfer of rarefied gas in rough microchannels, which are confined between two infinite large parallel plates with uniformly distributed triangular rough elements, are simulated by DSMC method with Delaunay triangulation meshes. Analysis and comparison are carried out on smooth and rough channels with rough elements of different size or/and distribution density. Roughness in micro-channels affect the gas flow and heat transfer greatly. As the size or/and the number of rough elements increases, the gas velocity jumps more seriously, even being accompanied by some vortices; furthermore, the gas temperature increases, but both the mass flux and the heat transfer rate decrease. In the flow direction, the gas temperature rises first and then falls; the local pressure increases at the windward of rough elements and decreases at the leeward side; moreover, the heat flux at the surface shows violent fluctuation, that is, the heat flux at the rough element surface is much smaller than that at the channel wall surface.
Numerical and Experimental Investigation on Thermal Characteristics of Deformable Thin Film Mirrors Package and Its Performance Optimization
Authors: Kim Jae Choon , Chung Jin Taek , Min Jae Hong , Lee Dong Jin , Yu Ji-Hyuk , Lim JuHwan , Ju Byeong-Kwon , Hwang SungWoo
Published: July 2009

This paper presents the thermal characteristics of a microelectro-mechanical deformable thin film mirrors package for the optical modulators used in mobile equipment such as cellphones, lab tops and PDA. One critical factor which affects the performance of the package is the ambient temperature change. To reduce the effect of the ambient temperature change, the temperature control system by a micro heater and a temperature feedback circuit was developed. The thermal characteristics histories were numerically modeled, the results of which were validated by the experimental data. The magnitude of the fluctuation was reduced within 1°C under the controlled system. In addition, required time to reach the steady state temperature was reduced by using the proposed control system.
Flame Holding and Combustion Characteristics of a Geometrical Flame Holder
Authors: Ahmed K. A. , Forliti D. J.
Published: July 2009

Flame Stabilization in a high-speed premixed environment requires the presence of a mechanism to stabilize the flame. Bluff bodies or geometrical flame holders introduce a recirculation zone that anchor the flame. The current study considers the influence of equivalence ratio and the boundary layer state at the trailing edge of the flame holder on the flowfield and combustion characteristics. It was found that the recirculation zone is shortened as the equivalence ratio increases towards unity. A secondary shear region emerges downstream of the recirculation zone and is caused by the accelerated low-density combustion products. The emergence of the secondary shear region moves upstream with increasing equivalence ratio. Tripping the boundary layer causes a dramatic reduction in the length of the recirculation zone, and the secondary shear region is greatly augmented. Visualizations show that tripping the boundary layer resulted in a greatly disturbed flame near the trailing edge and large flame scales. Flowfield measurements suggest that the heat release is increased by approximately 50% when the boundary layer tripped.
Axial Heat Conduction in Counter Flow Microchannel Heat Exchangers
Authors: Mathew B. , Hegab H.
Published: July 2009

This paper analyzes the effect of axial heat conduction on the thermal performance of a balanced counter flow microchannel heat exchanger. The ends of the wall separating the coolants are subjected to the mixed-boundary condition. Analytical equations were developed for predicting the axial temperature of the fluids and the wall as well as the effectiveness of the fluids. Moreover, equations for determining the heat transferred between the heat exchanger and its surroundings have been provided in this paper. The effectiveness of the fluids depended on the NTU, axial heat conduction parameter, manifold fluid temperatures and Biot numbers (of the manifolds). By varying the Biot number the model presented here can be used for designing a MCHXCF with Dirichlet, Neumann or mixed boundary condition at the ends of the wall separating the coolants. At very low values of Biot number the end walls act as if they are insulated. At these values of Biot numbers the effectiveness of the fluids degraded with increase in axial heat conduction parameter for a particular NTU. At very high values of Biot number the end walls assume a temperature that is close to the temperature in the manifold. At high values of Biot number the effectiveness of the fluids can either improve or degrade depending on the manifold temperatures. Moreover, the model developed in this paper has been verified using existing models that consider either adiabatic or isothermal condition at the end walls.
Computational Study of Reactive Flow in Halide Chemical Vapor Deposition of Silicon Carbide Epitaxial Film
Authors: Wang Rong , Ma Ronghui
Published: July 2009

In this study, a comprehensive transport model is developed for Halide Chemical Vapor Deposition (HCVD) system which includes gas dynamics, heat and mass transfer, gas-phase and surface chemistry, and radio-frequency induction heating. This model addresses transport of multiple chemical species in high temperature environment with large temperature difference and complex chemical reactions in gas-phase and on the deposition surface. Numerical modeling of the deposition process in a horizontal hot-wall reactor using SiCl4/C3H8/H2 as precursors has been performed over a wide range of operational parameters to quantify the effects of processing parameters on the film growth. The simulations of the deposition process provide detailed information on the gas-phase composition as well as the distributions of gas velocity and temperature in the reactor. The deposition rate on the substrate surface is also predicted. The results illustrate that deposition temperature and the flow rate of carrier gas play an important role in determining the processing conditions and deposition rate. A high concentration of HCl exists in the growth chamber and the etching of the SiC films by HCl has significant effect on the deposition rate. The modeling approach can be further used to improve reactor design and optimization of processing conditions.
Numerical Investigation on Forced Convection in Circular Tubes With Septa
Authors: Corrente D. , Manca O. , Nardini S. , Ricci D. , Masullo G.
Published: July 2009

Heat transfer in fluids is very important in many industrial heating and cooling equipments. Convective heat transfer can be enhanced passively by changing flow geometry, boundary conditions or by increasing thermal conductivity of the fluid. Another possibility to increase heat transfer with gas is to employ extended surfaces. When gas flows in a tube, septa with one or more openings can be used as fins. Furthermore, if the openings are arranged to give a spiral motion around the cylinder axis wall-fluid contact area increases. As a consequence the presence of the septa can significantly augment pressure drops. In this paper a numerical investigation is carried out on forced convection in circular isothermal tubes. The fluid is air and ideal gas model is employed. Septa are introduced and several shapes and arrangements are analyzed. The investigation is accomplished by means of the commercial code Fluent. A turbulence model is used. Results are presented in terms of temperature and velocity fields, local and average heat transfer coefficients and pressure drops. The aim of this study is to find the shape and arrangement of septa such to give high heat transfer coefficients and low pressure drops.
Heat Transfer Experiments and Process Development Measurements in the Production of Aerospace Wire
Authors: Varela Guillermo , Whitley Joshua , Cox Daniel , Roy Tom
Published: July 2009

Measurement methods to obtain process models from the ovens to a specific type of aerospace wire are described to model the manufacturing process of the wire. Study and measurement of the heat transfer of the system enables observation and insight into the temperature changes of the wire as it goes through a set of temperature controlled ovens. Different measurement techniques are used to obtain temperature data in order to model the heat transfer for the production of the wire. The measurement techniques include oven mapping, cooling curves, and dimension analysis. This data is used to for model procedures to create a relationship between oven temperature and wire processing temperature.
Vibration/Shock-Tolerant Capillary Two-Phase Loop Technology for Vehicle Thermal Control
Authors: Tang Xudong , Park Chanwoo
Published: July 2009

Two-phase thermal management technologies are promising cooling solutions for the high performance electronics in the next generation military and commercial vehicles. However, vibrations (∼ 10Grms in commercial automobile engines and transmissions) and shocks (30G to 1,200G in military combat vehicles, caused by gun firing, ballistic launch and abrupt maneuvering) present a severe challenge to any capillary-driven (i.e., passive) two-phase devices. A low-cost, vibration/shock-tolerant Capillary Two-Phase Loop (CTPL) technology was developed as a cooling alternative for the future military vehicles. Unlike the traditional two-phase cooling loops such as Loop Heat Pipes (LHP) and Capillary Pumped Loops (CPL), the CTPL offers the following advantages: (1) lower manufacturing cost by sintering the evaporator wick in-situ; (2) improved tolerance to vibrations and shocks due to the improved mechanical strengths of the in-situ sintered wick; (3) improved heat flux performance because of the non-inverted meniscus wick. Small-scale proof-to-concept CTPL prototypes were successfully tested up to 120W of heat input and under multiple, consecutive shocks of up to 6.6G.
Performance of Vertical Cracked Air Plasma Spray Processed Thermal Barrier Coatings: Thermo-Physical Properties Measurements, and Effects of Thermal Stress on Thermal Cycling Failure
Authors: Mensah Patrick F. , Uppu Nalini , Diwan Ravinder
Published: July 2009

In this study two variations of Air plasma spray (APS) coated Inconel738 (IN738) materials are evaluated for their thermal cycling and spalling behavior as well as thermo-physical properties variations as a function of temperature. The emphasis in this study was to investigate two different processing regimes that yield a standard APS and vertically oriented columnar microstructures in terms of their thermomechanical performance. The thermal cycling studies involved ramping the samples from 25°C to a temperature of about 1125°C in duration of 30 minutes, and followed by maintaining the samples at that temperature for 5 hours, followed by cooling down from 1125°C to 25°C for 30 minutes. The thermal properties measurements involved using Laser Flash method to measure thermal diffusivity and thermal conductivity from 100°C to 900°C. A thermal stress analytical study was also conducted in order to draw inference in the above studies as to the plausible causes of failure in the samples. Preliminary results of this thermal cycling and thermo-physical properties study are presented in this paper. The results are being correlated with the stress analysis results.
Methodology for the Numerical Simulation of Natural Gas, Coal, and Coke Combustion in a Blast Furnace
Authors: Walker William , Gu Mingyan , D’Alessio John , Macfadyen Neil , Zhou Chenn
Published: July 2009

A blast furnace is a reaction vessel in which iron ore is converted to molten iron. High rate pulverized coal injection (PCI) into a blast furnace (BF) is an existing process that is known to decrease the amount of coke in the ironmaking process. Natural gas co-injection with pulverized coal increases the burnout and devolatilization rates of pulverized coal. Also, hydrogen produced from natural gas combustion is a powerful reducing agent of iron (III) oxide, releasing pure iron that trickles down and is eventually removed through the taphole. Due to the inherent complexity of the blast furnace ironmaking process, numerical simulation can prove to be quite difficult. This paper describes a three step methodology for modeling blast furnace combustion, and its application to a furnace in operation at USSC Hamilton Works.
Permeability and Thermal Transport in Compressed Open-Celled Foams
Authors: Annapragada S. Ravi , Murthy Jayathi Y. , Garimella Suresh V.
Published: July 2009

A computational methodology is proposed to describe the fluid transport in compressed open-celled metallic foams. Various unit-cell foam geometries are numerically deformed under uniaxial loads using a finite element method. An algorithm is developed and implemented to deform the fluid domain mesh inside the unit-cell foam based on the deformed solid unit-cell geometry. Direct simulations of the fluid transport in these deformed meshes are then performed over a range of Reynolds numbers used in practical applications. The model is validated against available experimental results and correlations. A corrected model is proposed for the permeability of compressed foams as a function of strain for flows transverse to the direction of compression. The thermal conductivity of fluid-saturated foams is also computed. Compression of foams increases the conductivity transverse to the direction of compression and decreases the conductivity parallel to it.
Determination of Dimensionality of Pool Boiling on a Thin Horizontal Disk Under Subcooled Conditions Using Thin-Film Thermocouples
Authors: Sathyamurthi Vijaykumar , Banerjee Debjyoti
Published: July 2009

Subcooled pool boiling experiments are conducted at subcooling levels of 10 °C on a thin silicon disk (∼ 400μm thickn, 3 – inch diameter) with in situ micro-machined K-type thin film thermocouples (TFT) using a perfluorocarbon liquid refrigerant (PF-5060) with a boiling point of 56 °C. The experimental apparatus is of constant heat flux type. Surface temperature (from TFT) and heat flux data is obtained at each steady state condition to generate the pool boiling curve. The time – delay embedding technique is used to re-construct higher dimensional vectors with the optimal delay being estimated from the first minimum of mutual information. The correlation dimension measure is then estimated from the delay re – constructed phase space vectors. In this preliminary study correlation dimension measures are seen to vary from ∼ 12 in nucleate boiling, to ∼ 7 – 9 near Critical Heat Flux (CHF) condition, and ∼ 7 – 8 in film boiling. The results suggest that the attractors underlying thermal transport mechanisms in nucleate boiling are affected by a greater number of parameters than that at CHF. The dimension of the attractor is reduced further in the film boiling regime.
Hysteresis in Spray Cooling of Micro-Structured Surfaces
Authors: Bostanci Huseyin , Rini Daniel P. , Kizito John P. , Chow Louis C.
Published: July 2009

Spray cooling experiments were performed in a closed loop with ammonia using RTI’s vapor atomized spray nozzles. Thick film resistors, simulating heat source, were mounted onto 1cm × 2cm heater surfaces and heat fluxes up to 500 W/cm2 (well below critical heat flux (CHF) limit) were removed. Two nozzles each spraying 1 cm2 of heater area utilized 96 ml/cm2-min (9.7 gal/in2-hr) liquid and 13.8 ml/cm2-s (11.3 ft3/in2-hr) vapor flow rate with only 48 kPa (7 psi) pressure drop. A smooth surface and two types of micro-structured surfaces with indentations and protrusions were used as test surfaces. Comparison of cooling curves in the form of surface superheat (ΔTsat = Tsurf − Tsat) vs. heat flux in the heating-up and cooling-down modes (for increasing and decreasing heat flux conditions) demonstrated substantial performance enhancement for both micro-structured surfaces over a smooth surface. Moreover, results showed that smooth surface gives nearly identical cooling curves while micro-structured surfaces experience a hysteresis phenomenon depending on the surface roughness level and yields lower surface superheat in the cooling-down mode, compared to the heating-up mode, at a given heat flux. Micro-structured surface with protrusions was tested using two approaches to gain better understanding on hysteresis. Data mainly indicated that micro-structured surface helps retain established three-phase contact line, the region where solid, liquid and vapor phases meet, resulting in consistent cooling curve and hysteresis effect at varying heat flux conditions (as low as 25 W/cm2 for the present work). Data furthermore confirmed a direct connection between hysteresis and thermal history of the heater.
The Double-Diffusive Convection in the Process of Water Mist Fire Suppression
Authors: Xu Kai , Lu Wen-Qiang
Published: July 2009

In the research of the mechanism of water mist fire suppression, thermal buoyancy has important effects on smoke movement and temperature distribution, but the effects of the smoke diffusion are less considered. In this paper, a computational method couple dual reciprocity boundary element method (DRBEM) with finite volume method (FVM) is developed to study the thermal and smoke diffusion effects on the smoke movement, temperature and CO2 concentration distribution. And the interaction between the smoke and a water spray is calculated using FVM with the PSIC scheme. The DRBEM is employed to calculate the inner temperature of the droplet and radius variation, and the results show that when the droplet radius less than 1mm, the uniformly temperature assumption is reasonable. Numerical results also show the gradients of temperature and smoke concentration drive double-diffusive convection have different effects on the smoke temperature and CO2 concentration with and without water spray.
Tomographic Reconstruction of Unsteady Fields Using Proper Orthogonal Decomposition
Authors: Singh Dhruv , Srivastava Atul , Muralidhar K.
Published: July 2009

An algorithm for the reconstruction of unsteady three dimensional concentration field from path-integrated data has been discussed. We propose the use of Proper Orthogonal Decomposition (Karhunen Loe´ve Expansion) to completely decouple the spatial and temporal components of the image sequence (projections) obtained from a typical experiment enabling the analysis of an asynchoronous time-dependent data set. We apply the algorithm to experimental data from a Laser Interferometric study of convection in a cylindrical annulus to capture transients that are invariably faster than the camera speed. The strength of the technique is demonstrated in the reconstruction of the flow field (related to concentration gradients) from model (simulated) Schlieren projections. Tomographic reconstruction based on Convolution Back Projection (CBP) has been coupled with Proper Orthogonal Decomposition to enable the reconstruction of unsteady concentration gradient field from asynchronous projections.
Effect of Brownian and Thermophoretic Diffusions of Nanoparticles on Nonequilibrium Heat Conduction in Nanofluids
Authors: Zhang Yuwen , Li Ling , Ma H. B.
Published: July 2009

Effects of Brownian and thermophoretic diffusions on nonequilibrium heat conduction in a nanofluid layer with periodic heat flux on one side and specified temperature on the other side are investigated numerically. The problem are described by eight dimensionless parameters: density ratio, heat capacity ratio, Lewis number, Soret coefficient, initial volume fraction of nanoparticles, initial temperature, Sparrow number, and period of the surface heat flux. Effects of Brownian and thermophoretic diffusions of nanoparticles on nonequilibrium heat conduction in nanofluid obtained by dispersing copper nanoparticles into ethylene glycol are investigated. The results showed that the Brownian and thermophoretic diffusions only affect the nanoparticle temperature but their effect on the heat transfer enhancement is negligible.
Performance of Thermal Enhancement Materials in High Pressure Metal Hydride Storage Systems
Authors: Pourpoint Timothe´e L. , Sisto Aaron , Smith Kyle C. , Voskuilen Tyler G. , Visaria Milan K. , Zheng Yuan , Fisher Timothy S.
Published: July 2009

Over the past two years, key issues associated with the development of realistic metal hydride storage systems have been identified and studied at Purdue University’s Hydrogen Systems Laboratory, part of the Energy Center at Discovery Park. Ongoing research projects are aimed at the demonstration of a prototype large-scale metal hydride tank that achieves fill and release rates compatible with current automotive use. The large-scale storage system is a prototype with multiple pressure vessels compatible with 350 bar operation. Tests are conducted at the Hydrogen Systems Lab in a 1000 ft2 laboratory space comprised of two test cells and a control room that has been upgraded for hydrogen service compatibility. The infrastructure and associated data acquisition and control systems allow for remote testing with several kilograms of high-pressure reversible metal hydride powder. Managing the large amount of heat generated during hydrogen loading directly affects the refueling time. However, the thermal management of hydride systems is problematic because of the low thermal conductivity of the metal hydrides (∼ 1 W/m-K). Current efforts are aimed at optimizing the filling-dependent thermal performance of the metal hydride storage system to minimize the refueling time of a practical system. Combined heat conduction within the metal hydride and the enhancing material particles, across the contacts of particles and within the hydrogen gas between non-contacted particles plays a critical role in dissipating heat to sustain high reaction rates during refueling. Methods to increase the effective thermal conductivity of metal hydride powders include using additives with substantially higher thermal conductivity such as aluminum, graphite, metal foams and carbon nanotubes. This paper presents the results of experimental studies in which various thermal enhancement materials are added to the metal hydride powder in an effort to maximize the effective thermal conductivity of the test bed. The size, aspect ratio, and intrinsic thermal conductivity of the enhancement materials are taken into account to adapt heat conduction models through composite nanoporous media. Thermal conductivity and density of the composite materials are measured and enhancement metrics are calculated to rate performance of composites. Experimental results of the hydriding process of thermally enhanced metal hydride powder are compared to un-enhanced metal hydride powder and to model predictions. The development of the Hydrogen Systems Laboratory is also discussed in light of the lessons learned in managing large quantities of metal hydride and high pressure hydrogen gas.
CFD Analysis of a Notebook Computer Thermal Management Solution
Authors: Yalc¸ın Fidan S. , Sert Cu¨neyt , Tarı I˙lker
Published: July 2009

The thermal management system of a commercially available notebook computer is investigated by using a commercial finite volume Computational Fluid Dynamics (CFD) software. After taking the computer apart, all dimensions are measured and all major components are modeled as accurately as possible. Heat dissipation values and some characteristics of the components are obtained from the manufacturer’s specifications. Different heat dissipation paths utilized in the design are investigated. Two active fans and aluminum heat dissipation plates as well as the heat pipe system are modeled according to their exact specifications. Under different operating powers, adequacy of the existing thermal management system is observed. Average temperatures of the sides of the casing, the keyboard and the internal components are reported in the form of tables. Thermal resistance networks for five different operating conditions are obtained from the analysis of the CFD simulation results.
The Numerical Mirage Method for Photothermal Characterization of Materials
Authors: Demko Michael T. , Hostler Stephen R. , Abramson Alexis R.
Published: July 2009

Photothermal measurements are increasingly attractive for thermal analysis of fragile nano-structured materials or as an in situ measurement for investigation of coupled thermal and mechanical properties. The most common thermal property measurements, including the laser flash and photothermal reflectance methods, have limited applicability due to stringent requirements on geometry, thermal, and optical properties of the material. In contrast, the mirage method typically does not require any sample modification and places a minimum number of restrictions on the sample geometry. This method uses a periodically modulated pump laser to heat a sample material and a probe beam to observe the resulting change in index of refraction of a gas above the sample. In this work, the experimental methodology and data analysis are generalized to allow more accurate measurement of low thermal diffusivity materials. The method expands upon the work of Ravi et al. (2002), but alternatively uses a numerical solution to the heat equations, more accurately capturing a square-wave heat application from the pump laser and non-zero probe beam height.
Experimental Investigation of an Evaporator Enhanced With a Micro-Porous Structure in a Two-Phase Thermosyphon Loop
Authors: Furberg Richard , Khodabandeh Rahmatollah , Palm Bjo¨rn , Li Shanghua , Toprak Muhammet , Muhammed Mamoun
Published: July 2009

Following is an experimental study of six different evaporators in a closed two-phase thermosyphon loop system, where the influence of various evaporator dimensions and surfaces was investigated. The evaporators featured a 30 mm long rectangular channel with hydraulic diameters ranging from 1.2–2.7 mm. The heat transfer surface of one of the tested evaporators was enhanced with copper nano-particles, dendritically connected into an ordered micro-porous three dimensional network structure. To facilitate high speed video visualization of the two-phase flow in the evaporator channel, a transparent polycarbonate window was attached to the front of the evaporators. Refrigerant 134A was used as a working fluid and the tests were conducted at 6.5 bar. The tests showed that increasing channel diameters generally performed better. The three largest evaporator channels exhibited comparable performance, with a maximum heat transfer coefficient of about 2.2 W/(cm2K) at a heat flux of 30–35 W/cm2 and a critical heat flux of around 50 W/cm2. Isolated bubbles characterized the flow regime at peak performance for the large diameter channels, while confined bubbles and chaotic churn flow typified the evaporators with small diameters. In line with previous pool boiling experiments, the nucleate boiling mechanism was significantly enhanced, up to 4 times, by the nano- and micro-porous enhancement structure.
Carbon Nanotube Array Thermal Interfaces Enhanced With Paraffin Wax
Authors: Cola Baratunde A. , Hodson Stephen L. , Xu Xianfan , Fisher Timothy S.
Published: July 2009

Vertically oriented carbon nanotube (CNT) arrays can increase real contact in thermal interfaces and efficiently transfer heat between the mating solids. In this study, a paraffin wax that changes phase at approximately 50°C was applied to interfaces with CNT arrays directly synthesized on one side of the interface, and to foil/CNT interfaces with CNT arrays directly synthesized on one side and both sides of the foil. The bulk thermal resistances of single-sided CNT array/wax interfaces were measured using a transient photoacoustic (PA) technique to range from approximately 2 to 3 mm2·K/W under moderate pressures. The bulk thermal resistances of foil/CNT/wax interfaces were measured with the PA technique to range from approximately 10 to 20 mm2·K/W under moderate pressures. For each sample structure, the addition of paraffin wax to the CNT arrays produced significant reductions in thermal resistance. We surmise that this improved thermal performance could be a function of the wettability of paraffin wax to CNTs. A hydrophilic wetting angle of approximately 47° was observed at the interface of liquid wax and the free tips of a CNT array at 60°C, and field-emission scanning electron microscope images taken after PA testing revealed individual CNTs that were blanketed with a wax coating.
Integrated Gas Dynamic and Thermodynamic Computational Modeling of Multicylinder 4-Stroke Spark Ignition Engine Using Gasoline as Fuel
Authors: Tirkey J. V. , Gupta H. N. , Shukla S. K.
Published: July 2009

This paper presents a computational tool for the evaluation of engine performance and exhaust emissions for four stroke multi-cylinder spark ignition engine which uses gasoline as fuel. Gas dynamics flow in multi-cylinder intake and exhaust systems are modeled by using one dimensional unsteady compressible flow equations. The hyperbolic partial differential equations are transferred into a set of ordinary differential equations by using method of characteristics and solved by finite difference method. Compatibility relationships between local fluid velocity (U) and sonic velocity (a) are expressed in terms of Riemann variables, which are constant along the position characteristics. The equations are solved numerically by using rectangular grid in the flow direction (x) and time (t). In this model Nitric Oxide concentration is predicted by using the rate kinetic model in the power cycle and along the exhaust pipes. Carbon Monoxide is computed under chemical equilibrium condition and then empirical adjustment is made for kinetic behaviors based upon experimental results. A good agreement is obtained in the comparison of computed and experimental results of instantaneous cylinder pressure, manifold pressure and temperature, and NO, CO emissions level.
Design and Cost of the Sulfuric Acid Decomposition Reactor for the Sulfur Based Hydrogen Processes
Authors: Hu Tzu-Yu , Connolly Sarah M. , Lahoda Edward J. , Kriel Willem
Published: July 2009

The key interface component between the reactor and chemical systems for the sulfuric acid based processes to make hydrogen is the sulfuric acid decomposition reactor. The materials issues for the decomposition reactor are severe since sulfuric acid must be heated, vaporized and decomposed. SiC has been identified and proven by others to be an acceptable material. However, SiC has a significant design issue when it must be interfaced with metals for connection to the remainder of the process. Westinghouse has developed a design utilizing SiC for the high temperature portions of the reactor that are in contact with the sulfuric acid and polymeric coated steel for low temperature portions. This design is expected to have a reasonable cost for an operating lifetime of 20 years. It can be readily maintained in the field, and is transportable by truck (maximum OD is 4.5 meters). This paper summarizes the detailed engineering design of the Westinghouse Decomposition Reactor and the decomposition reactor’s capital cost.