bluuebunny/crossref_metadata_2025 huggingface dataset:
Development of a Heat Transfer Correlation for the Transitional Flow in a Horizontal Tube Using Support Vector Machines
Authors: Tam L. M. , Ghajar A. J. , Tam H. K. , Tam S. C.
Published: July 2009

In this paper the Support Vector Machines (SVM) method is used to correlate the transitional forced and mixed convection experimental data of Ghajar and Tam (1994) that were obtained along a stainless steel horizontal circular tube fitted with re-entrant, square-edged, and bell-mouth inlets under uniform wall heat flux boundary condition. The SVM method has been chosen to further improve the accuracy of the correlations that were developed by Ghajar and his co-workers using the traditional least-squares method (Ghajar and Tam, 1994) and more recently the artificial neural networks (ANN) method (Ghajar et al., 2004). Using the ANN method improved the accuracy of their correlation. However, there are drawbacks associated with ANN method. One of the major problems with the ANN method is that it does not provide a unique correlation due to different coefficient matrices. The SVM method used in this study eliminated the drawbacks associated with the ANN method and provided a unique correlation with comparable accuracy as the ANN method. For the experimental data used, majority of the data points were predicted within 5% deviation. Comparisons were made regarding the accuracy of the developed correlation and its characteristic using SVM and ANN methods. The results showed that SVM is a good method to correlate complex heat transfer data.
Evaporating Interface in a Capillary Tube With High Heat Flux Induced by Micro Diffusion Flame
Authors: Chen J. , Peng X. F.
Published: July 2009

A series of experiments was conducted to understand the combustion characteristics and evaporating interface behavior of liquid fuel in capillary tubes. The flame shape, interface location of fuel front and tube outer surface temperature was visually observed and measured using CCD and IR camera, respectively. With fuel supply rate increasing, the interface location rose to tube exit and the temperature gradient of the outer tube surface increased, and consequently the evaporating interface tended to be unstable. The prediction of interfacial evaporation using available models was compared with the experimental measurements, indicating that this kind of highly non-equilibrium micro combustion with phase-change could not be described by normal mechanisms.
Transient Thermal and Hydrodynamic Performances of Flat Heat Pipe Subjected to Heating With Multiple Electronic Components
Authors: Sonan R. , Harmand S. , Pelle´ J. , Leger D. , Fake`s M.
Published: July 2009

This work is aimed to simulate the transient performances of a flat heat pipe (FHP) used to cool electronics components in automotive applications. A transient 3D thermal model (T3DTM) of the FHP wall is performed to calculate the heat transfer through the wall of the FHP. This model is coupled with a transient 2D hydrodynamic model (T2DHM) which determines the flows both in wick and vapour core. An energy balance and Clausius-Clapeyron law permit to represent the phase change mechanisms at the liquid-vapour interface. The performed T2DHM model includes the solution of the complete governing equations in both wick and vapor core. The T2DHM is able to predict the velocity and pressure distributions of the FHP working fluid and then the FHP transient response. That analysis helps determine the maximum pore radius of the wick necessary to support the total pressure drop in the FHP. The heat removal capability of the FHP is highlighted through a comparison with a solid copper plate of the overall dimensions as the FHP.
Calibration of Chemical Kinetic Models Using Simulations of Small-Scale Cookoff Experiments
Authors: Wemhoff Aaron P. , Becker Richard , Burnham Alan K.
Published: July 2009

Establishing safe handling limits for explosives in elevated temperature environments is a difficult problem that often requires extensive simulation. The largest influence on predicting thermal cookoff safety lies in the chemical kinetic model used in these simulations, and these kinetic model reaction sequences often contain multiple steps. Several small-scale cookoff experiments, notably Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), One-Dimensional Time-to-Explosion (ODTX), and the Scaled Thermal Explosion (STEX) have been performed on various explosives to aid in cookoff behavior determination. Past work has used a single test from this group to create a cookoff model, which does not guarantee agreement with the other experiments. In this study, we update the kinetic parameters of an existing model for the common explosive 2,4,6-Trinitrotoluene (TNT) using DSC and ODTX experimental data at the same time by minimizing a global Figure of Merit based on hydrodynamic simulated data. We then show that the new kinetic model maintains STEX agreement, reduces DSC agreement, and improves ODTX and TGA agreement when compared to the original model. In addition, we describe a means to use implicit hydrodynamic simulations of DSC experiments to develop a reaction model for TNT melting.
Prediction of Natural Convection Heat Transfer in Layered Porous Cavities by Homogeneous Anisotropic Model
Authors: Marvel R. L. , Lai F. C.
Published: July 2009

Steady-state heat transfer by natural convection in a layered porous cavity is examined by using homogeneous anisotropic model. The geometry considered is a two-dimensional square enclosure comprising of three or four porous layers with non-uniform thickness and distinct permeability. The cavity is subjected to differential heating from the vertical walls. The results, which include the flow patterns and temperature profiles as well as the heat transfer coefficients, are presented for a wide range of permeability ratio, sublayer thickness ratio, and Rayleigh number. Particularly, the heat transfer results obtained are compared with those reported from a rigorous numerical model for layered porous media. In addition, the results are compared with the lumped system model that was proposed recently. It has been found that homogeneous anisotropic model predicts the heat transfer coefficient reasonably well within the conductive flow regime. However, beyond this regime, the model fails to represent the layered case for the effective permeabilities and sublayer thickness ratios considered. On the other hand, it is observed that the lumped system model offers better agreement to the heat transfer coefficient of the actual layered porous system over a wider range of parameters and which also significantly reduces computational efforts.
Two-Phase Heat Transfer and Bubble Dynamics in a Microchannel Array
Authors: Lagus T. P. , Kulacki F. A.
Published: July 2009

Heat transfer coefficients and bubble dynamics are reported for two-phase water flow in an array of 13 equally spaced microchannels over an area of 1 cm2. Each channel has Dh = 451 ± 3 8 μm, W/H = 0.8, and L/Dh = 22.2. Uniform heat flux is applied through the base, and wall temperatures are determined from thermocouple readings corrected for heat conduction effects. The upper surface is insulated and transparent. Single-phase heat transfer coefficients are obtained for 216 < Re < 2530 and 216 < G < 4100 kg/m2s and are in good agreement with comparable trends of existing correlations for developing flow and heat transfer, although a difference is seen due to the insulated upper surface. Two-phase experiments are run to determine overall heat transfer coefficients and bubble dynamics for a mass flux of 221 < G < 466 kg/sm2 and heat flux of 25 < q < 178 W/cm2. Heat transfer coefficients normalized with mass flux exhibit a trend comparable to that of available studies that use similar thermal boundary conditions. Two-phase flow visualization via shows expanding vapor slug flow as the primary flow regime, but bubbly flow and nucleation leading to elongated bubble flow are also observed. Analysis of bubble dynamics reveals a t1/3 dependence for bubble growth, and flow reversal is observed and quantified. Different speeds of the phase fronts are observed at the leading and trailing edges of elongated slugs once a bubble diameter equals the channel width. Bubble formation, growth, coalescence and detachment at the outlet of the array are characterized by the Weber number.
Investigation of a Split-Dimple Fin Geometry for Heat Transfer Augmentation
Authors: Elyyan Mohammad A. , Tafti Danesh K.
Published: July 2009

The use of an interrupted plate fin with surface roughness in the form of split-dimples is investigated. Time-dependent high-fidelity simulations are conducted for laminar, early turbulent, and fully turbulent flows, ReH = 360, 800, and 2000. Detailed analysis of the domain’s flow structure, turbulent statistics, and heat transfer distribution is presented. Regions of high heat transfer occur at the fin and protrusion leading edges, at flow impingement on the protrusion faces, and flow acceleration region between protrusions. Flow separation and large wakes induced by the large protruding surfaces of the split-dimples, increase friction losses and reduce heat transfer from the fin. The split-dimple fin has a heat conductance 60–175% higher than that of the plate fin, but at 4–8 times the pressure drop.
On Relativistic Transformation of Coordinates and Exact Solution of Damped Wave Conduction and Relaxation Equation
Authors: Sharma Kal Renganathan
Published: July 2009

Analytical solution to the hyperbolic damped wave conduction and relaxation equation is developed by a novel method called the relativistic transformation method. The hyperbolic PDE is decomposed into a time decaying damping component and a Klein-Gardon type equation for the wave temperature. The PDE that describes the wave temperature is transformed to a Bessel differential equation by using the relativistic transformation. The relativistic transformation, η = τ2 − X2 is symmetric in space and time. The solution obtained for the transient temperature to a semi-infinite medium was compared with success to a Laplace transform solution reported by other investigators. A approximate analytical solution is obtained for the transient temperature by realizing that the integration constants from the solution of Bessel differential equation in the transformation variable is with respect to the transformation variable which is a function of space and time. So the boundary conditions can be used to solve for integration “constants” that are functions of one variable. The solution consists of three regimes. There is no discontinuity at the wave front. A inertial zero transfer regime, a second rising regime characterized by Bessel composite function of the zeroth order and first kind and a third falling regime characterized by modified Bessel composite function of the zeroth order and first kind.
Bessel Composite Function of the Third Order and First Kind Solution to Damped Wave Conduction and Relaxation
Authors: Sharma Kal Renganathan
Published: July 2009

The damped wave conduction and relaxation equation in three dimenions in spherical coordinates was solved for by using the relativistic transformation. Approximate analytical solutions were obtained in the creeping transfer limit in spherical infinite coordinates. The solution consist of three regimes. A inertial zero transfer regime. A second regime that is characterized by the Bessel composite function of the third order and first kind. The third regime is characterized by the modified composite function of the third order and first kind. Without the creeping transfer limit assumption the order of the Bessel composite solution can be seen to be 7/2.
Transport Processes Governing the Drawing of a Hollow Optical Fiber
Authors: Yang Jing , Jaluria Yogesh
Published: July 2009

This paper presents a mathematical model to simulate the silica hollow optical fiber drawing process. Two neck-down profiles, which represent the inner and outer surfaces of the hollow fiber, are generated by using an iterative numerical scheme. The zonal method is applied to calculate the radiative transport within the glass. The effects of variable properties for air and buoyancy are investigated and results indicate that these can be neglected for simulating the draw process. The validation of the model is carried out by comparing the results with those obtained by using the optical thick method as well as those for a solid-core fiber. The effect of drawing parameters like the temperature of the furnace, feeding speed and drawing speed on the temperature and velocity distributions and on the draw tension are studied. It is found that the geometry and qualities of the final hollow optical fiber are highly dependent on the drawing parameters, especially the drawing temperature and the feeding speed.
Jet Impingement Melting With Vaporization: A Numerical Study
Authors: Jain Jayesh , Dey Subhrajit , Muralidharan L. , Leach Andrew M. , Ardenkjaer-Larsen Jan Henrik
Published: July 2009

The objective of this work was to develop a computational model for better understanding of the process of producing contrast agent, used in Magnetic Resonance Imaging (MRI). Contrast agents are used to provide high-resolution anatomical and functional information to identify tumor growth for prostrate and breast cancers. The production process for the contrast agents involves melting and dissolution of the imaging agent (maintained at very low temperature ∼1K to retain its polarization capability) by injecting the jet of alkaline solvent. Dissolution should happen in minimum time to allow for time required to inject contrast agent into the patient with sufficient time to travel to the targeted organ. This process involves multi-phase, multi-species and chemically reacting fluid dynamics. The intricacy and complexity of the melting process and very small time scales (order of a few milliseconds) poses practical challenges of collecting enough experimental data for the better understanding of such processes. It creates a need for looking at these kinds of processes from a numerical point of view. A computational model was developed in commercial software to capture the relevant physics involved in the flow-thermal process. System was analyzed to guide design changes with the objective of minimizing the melting time of imaging agent. Model predictions were validated against experiments and sensitivity studies were carried out pertaining to operating parameters such as solvent flow rate, temperature and other geometrical parameters. The predictions from model gave an insight into the process. It was found that melting time is not only a function of operating conditions and geometrical parameters but also a function of nature of the multiphase flow. Other than solid and molten phase, vapor phase (vaporization of the alkaline solvent) also coexist in the system under certain operating conditions; which further complicates the process. Desired operating conditions and geometrical changes were recommended to minimize the melting time. It is believed that current findings and numerical modeling approach could be utilized in other similar processes.
A Compact Thermal Resistance Model for Determining Effective Thermal Conductivity in the Fibrous Gas Diffusion Layers of Fuel Cells
Authors: Sadeghi E. , Bahrami M. , Djilali N.
Published: July 2009

Accurate information on the temperature field and associated heat transfer rates are particularly important in devising appropriate heat and water management strategies in proton exchange membrane (PEM) fuel cells. An important parameter in fuel cell performance analysis is the effective thermal conductivity of the gas diffusion layer (GDL). Estimation of the effective thermal conductivity is complicated because of the random nature of the GDL micro structure. In the present study, a compact analytical model for evaluating the effective thermal conductivity of fibrous GDLs is developed. The model accounts for the salient geometric features, effects of bipolar pressure variation, gas rarefaction effects, and spreading resistance. The model predictions are in good agreement with existing experimental data over a wide range of porosities. Parametric studies are performed using the proposed model to investigate the effect of bipolar plate pressure, aspect ratio, fiber diameter, fiber angle, and operating temperature.
Characterization of Microstructures for Heat Transfer Performance in Passive Cooling Devices
Authors: Ranjan Ram , Garimella Suresh V. , Murthy Jayathi Y.
Published: July 2009

The topology and geometry of microstructures play a crucial role in determining heat transfer performance in passive cooling devices such as heat pipes. It is therefore important to characterize microstructures based on their wicking performance, the thermal conduction resistance of the liquid filling the microstructure, and the thin-film characteristics of the liquid meniscus. In the present study, the free-surface shapes of the static liquid meniscus in common microstructures have been modeled using the program, Surface Evolver, for zero Bond number. Four well-defined topologies, viz., surfaces with parallel rectangular ribs, horizontal parallel cylinders, vertically aligned cylinders, and spheres (the latter two in both square and hexagonal packing arrangements), have been modeled. Non-dimensional capillary pressure, average distance of the free liquid surface from solid walls (a measure of the conduction resistance of the liquid), total exposed area and thin-film percentage of surface area of the liquid meniscus have been computed. These parameters are presented as functions of the non-dimensional geometrical parameters of the microstructures, volume of the liquid filling the structure, as well as the contact angle between the liquid and solid. Based on these non-dimensional performance parameters, the microstructure, contact angle and non-dimensional liquid volume for the best performance are identified.
Study of the Gas Combustion LP in an Atmospheric Burner
Authors: Gallegos-Mun˜oz Armando , Balderas-Bernal Armando , Rami´rez-Barro´n Alejandro , Prince-Avelino J. C.
Published: July 2009

The study of the gas combustion LP in an atmospheric burner to bake ceramics is presented. The study includes different models from combustion and turbulence to find the best interaction chemistry-turbulence, applying Computational Fluids Dynamics (CFD) through FLUENT®. For the study different models of combustion were considered, where the finite speed of the reaction is important by means of kinetic chemistry from Arrhenius. The different models of combustion were; a generalized model of speed of Finite Rate/Eddy dissipation, non-premixed combustion Laminar Flamelet and Eddy dissipation. Each one of these models represents the combustion non-premixed of gas LP, to simulate the combustion of turbulent diffusive flames. For the study of the turbulence the model k-epsilon was applied. The results obtained for each combination turbulence-chemistry were compared with experimental measurements of temperature within the furnace. This comparison allowed making adjustments in the modeling of the process of combustion, identifying the best interaction between combustion and turbulence. According to the obtained results, the k-epsilon model represents adequately the fluid-dynamic development of the flame within the furnace. The models of combustion Finite Rate/Eddy dissipation and Laminar Flamelet show the best approach to the experimental results, where the k-epsilon model is applied to modeling the turbulence-chemistry interaction.
Thermal Model of a Gas Fired Generator for an Absorption GAX Cooling System
Authors: Vidal A. , Barrera-Chavarri´a M. A. , Go´mez V. H. , Cervantes J. , Best R.
Published: July 2009

A numerical model of a direct fired generator is presented. The objective is to provide a baseline for designing the prototype of a gas fired generator, aimed to drive a GAX absorption cooling system. The model was carried out using Fortran 90. The gas fired generator will be part of the hybrid 10.5 kW GAX cooling system, which is being designed to operate with solar energy and direct fired by LPG combustion. The prototype is designed in two sections. In the first section, the “U” form combustion chamber is flooded with ammonia-water solution, the heat radiation from the flame and the hot combustion gases are absorbed by the tube walls and transferred to the solution. In the second section (the convection zone), the combustion gases are used to increase the concentration of the ammonia refrigerant. Thermal design results in the radiation, boiling and convection zones are presented and discussed, while the manufacturing strategies are being analyzed to produce a compact and efficient prototype.
Pin-Fin Heat Sink With Horizontal Base and Blocked Edges
Authors: Sahray D. , Shmueli H. , Segal N. , Ziskind G. , Letan R.
Published: July 2009

In the present work, horizontal-base pin fin heat sinks exposed to free convection in air are studied. They are made of aluminum, and there is no contact resistance between the base and the fins. For the same base dimensions the fin height and pitch vary. The fins have a constant square cross-section. The edges of the sink are blocked: the surrounding insulation is flush with the fin tips. The effect of fin height and pitch on the performance of the sink is studied experimentally and numerically. In the experiments, the heat sinks are heated using foil electrical heaters. The heat input is set, and temperatures of the base and fins are measured. In the corresponding numerical study, the sinks and their environment are modeled using the Fluent 6 software. The results show that heat transfer enhancement due to the fins is not monotonic. The differences between sparsely and densely populated sinks are analyzed for various fin heights. Also assessed are effects of the blocked edges as compared to the previously studied cases where the sink edges were exposed to the surroundings.
Numerical Study on Forced Convective Heat Transfer in Porous Pin Fin Channels
Authors: Yang Jian , Zeng Min , Wang Qiuwang
Published: July 2009

Pin fin heat exchanges are often used in cooling of high thermal loaded electronic components due to their excellent heat transfer performance. However, the pressure drop in such heat exchanges is usually much higher than that in others, so their overall heat transfer performance is seriously reduced. In order to reduce the pressure drop and improve the overall heat transfer performance for pin fin heat exchangers, porous metal pin arrays are used and the performance of fluid flow and heat transfer in heat exchanger unit cells are numerically studied. The Forchheimer-Brinkman extended Darcy model and two-equation heat transfer model for porous media are employed and the effects of Reynolds number (Re), permeability (K) and pin fin cross-section forms are studied in detail. The results show that, with proper selection of governing parameters, the overall heat transfer performance of porous pin fin heat exchanger is much better than that of traditional solid pin fin heat exchanger; the overall heat transfer performance of long elliptic porous pin fin heat exchanger is the best, that is, the heat transfer per unit pressure drop of such heat exchanger is the highest and the maximum value of the heat transfer over pressure drop is obtained at K = 2×10−7 m2.
Numerical Studies of a Novel Combined Multiple Shell-Pass Shell-and-Tube Heat Exchanger With Helical Baffles
Authors: Wang Qiuwang , Chen Guidong , Chen Qiuyang , Zeng Min , Zhang Dahai
Published: July 2009

In order to simplify the manufacture and improve heat transfer performance of shell-and-tube heat exchangers (STHXs), we have invented a combined multiple shell-pass STHX with continuous helical baffles. The novel combined multiple shell-pass STHX with continuous helical baffles (NOVEL STHX) is compared with the conventional STHX with segmental baffles by Computational Fluid Dynamics (CFD) method. The numerical results show that, under the same mass flow rate M and the same overall heat transfer rate Qm in the shell side, the overall pressure drop DP of the NOVEL STHX is lower than that of the STHX with segmental baffles by about 13%. The heat transfer rate Qm of the NOVEL STHX is higher than that of the STHX with segmental baffles by about 6% under the same overall pressure drop DP. The NOVEL STHX might be used to replace the conventional STHX with segmental baffles in industrial applications to save energy, reduce cost and prolong service life.
Variation of the Thermal Conductivity of Elastomeric Foam With Pressure
Authors: Bardy Erik R. , Mollendorf Joseph C.
Published: July 2009

In a previous study, the authors used well-known upper and lower bounds to develop the form of an empirical correlation for the thermal conductivity of foam insulation as a function of ambient pressure. The correlation was in terms of three constants which were determined by performing a nonlinear regression on experimentally measured thermal conductivity values of foam neoprene insulation at varying ambient pressure. In this previous work, the thermal conductivity of neoprene rubber was determined using the three constants, one of which is the reciprocal of the thermal conductivity of air. In the present paper, we show that the three correlation constants can, alternately, be determined by using values of the constituent thermal conductivities (e.g. air and rubber), and the effective thermal conductivity at one pressure only. Previously reported values of the measured effective thermal conductivity of foam neoprene insulation under applied pressure, up to 1.18 MPa, were found to have a maximum difference of about 14% of the values predicted using the correlation. It was also found that the accuracy of the correlation did not depend strongly on the reference pressure used.
Slip-Flow and Conjugate Heat Transfer in Rectangular Microchannels
Authors: Hettiarachchi H. D. Madhawa , Golubovic Mihajlo , Worek William M. , Minkowycz W. J.
Published: July 2009

Slip-flow and conjugate heat transfer in rectangular microchannels are studied numerically for thermally developing laminar flow subjected to constant wall temperature (T) and constant wall heat flux (H2) boundary conditions. A three-dimensional numerical code based on finite volume method is developed to solve the coupled energy equations in the wall and fluid regions together with temperature jump at the wall-fluid boundary. A modified convection-diffusion coefficient at the wall-fluid interface is defined to incorporate the temperature-jump boundary condition. The numerical code is validated by comparing the present results with the published data. The effect of rarefaction and wall conduction on the heat transfer in the entrance region is analyzed in detail. Results show that the wall conduction has a considerable influence on the developing Nusselt number along the channel for the H2 boundary condition, particularly at low Knudsen numbers. In the case of the T thermal boundary condition, negligible influence of wall conduction on the Nusselt number is observed for all Knudsen numbers considered.
Developing Forced and Free Convection for Inclined Semicircular Ducts
Authors: El. Hasadi Yousef M. F.
Published: July 2009

Laminar mixed convection in the entrance region for inclined semicircular ducts with the flat wall in the vertical position has been investigated numerically. The governing momentum and energy equations were solved numerically using a marching technique with finite control volume approach following the SIMPLER algorithm. Results were obtained for the thermal boundary condition of uniform heat input axially and uniform wall temperature circumferentially (H1 thermal boundary condition), with Pr = 7.0 (i. e. water), Reynolds number equals 500, inclination angles 0°, 20°, 40°, 60°, 80°, and a wide range of Grashof numbers. These results include velocity, and temperature distributions, at different axial locations, as well as, the axial development of the Nusselt numbers, and the wall friction factor a long the duct length. It was found that the Nusselt numbers were close to the forced convection values near the entrance region and then decreases to a minimum as the distance from the entrance increases and than rises up due to the effect of free convection before reaching a constant value (fully developed value). It is observed that at inclination angles 0° and 20° the values of Nusselt number are higher in the developing and fully developed regions, than those corresponding to 40°, 60°, and 80° at the same Grashof number, however, it was found that at the same Grshof number the values of friction factors increases in the developing and fully developed regions with the increase of the inclination angle.
Study of Co-Injection of Natural Gas and Pulverized Coal in Blast Furnace Under Pure Oxygen Environment
Authors: Gu Mingyan , Li Jiaxin
Published: July 2009

Using pure oxygen in blast furnace is a developing method in blast furnace in order to lower the emission of waste gases. Numerical simulation has been applied to analyze the combustion process of co-injection of natural gas (NG) and pulverized coal (PC) in a blast furnace while the blast is pure oxygen gas. The effect of injection NG and blast flow rate on the coal and coke combustion processes is examined. The predicted results provide a better understanding of reactions inside blast furnace.
Modeling of Polarization-Specific Phonon Transmission Functions Through Interfaces
Authors: Huang Zhen , Murthy Jayathi , Fisher Timothy
Published: July 2009

The atomistic Green’s function (AGF) method has been used successfully in previous research to predict the transmission function for energy carriers at interfaces. In this work, the method is extended to capture the transmission function for each phonon polarization. The inputs for this extension are the same as for the original AGF method. Furthermore, this method does not require any complex manipulation of harmonic matrices and can be applied to different materials and geometries. The eigenvectors and eigenvalues of the overall density of states matrices are manipulated to yield the density of states matrix for each polarization. A decomposed self-energy is calculated from the density of states matrix for each polarization and used to calculate the transmission function for a particular phonon branch. In a pure bulk material such as silicon, each transmission function exhibits a frequency-independent value of unity, which matches the theoretical prediction. In heterogeneous bulk materials, the transmission function is reduced significantly due to the contact of dissimilar materials. The summation of the decomposed transmission functions is shown to reproduce the result from a direct AGF calculation in which all branches were treated together.
Errors in Skin Temperature Measurements
Authors: Dugay M. V. , Boetcher S. K. S. , Sparrow E. M.
Published: July 2009

Numerical simulation is used to investigate the accuracy of a widely used direct-contact device for measuring skin-surface temperature. The device incorporates a foam pad which functions as a de facto thermal resistance to heat flow from the skin surface to the environment. The temperature at the interface of the measurement device and the skin surface is sensed by a micro thermocouple or thermistor. The multidimensional bioheat equation was solved numerically to obtain the temperature field both in the tissue beneath the device and in the device proper. Parametric variations were made of the thermal conductivity of the foam pad and of the blood perfusion rate. Of these, the former was found to have the greater effect on the results. In the limiting case where the thermal conductivity of the foam pad is zero, an error of 1.5 °C in the measured temperature was identified. For foam pad conductivities of 0.03 and 0.06 W/m-°C, the numerical solutions gave temperature measurement errors of 0.5 and 0.15 °C, respectively.
Negatively Buoyant Plume Flow in a Baffle
Authors: Boetcher S. K. S. , Kulacki F. A.
Published: July 2009

Transient two-dimensional negatively buoyant flow into a straight adiabatic baffle beneath an isothermal circular cylinder is numerically simulated. The surrounding fluid is considered infinite in extent and at constant temperature. Governing parameters are the baffle width and the offset of the entrance of the baffle beneath the center of the cylinder. Overall characteristics of the flow and entrainment of the surrounding fluid are found to be dependent on the baffle offset; however, the attachment length of the flow to the baffle wall is relatively insensitive to the offset. Heat transfer rates to the cylinder are calculated for various times for various baffle offsets. There is a weak dependence on baffle-offset distance with heat transfer rate.
Dependence of Heat Transfer Coefficient on Porous Structure in Porous Media
Authors: Matsui Akira , Yuki Kazuhisa , Hashizume Hidetoshi
Published: July 2009

Detailed heat transfer characteristics of particle-sintered porous media and metal foams are evaluated to specify the important structural parameters suitable for high heat removal. The porous media used in this experiment are particle-sintered porous media made of bronze and SUS316L, and metal foams made of copper and nickel. Cooling water flows into the porous medium opposite to heat flux input loaded by a plasma arcjet. The result indicates that the bronze-particle porous medium of 100μm in pore size shows the highest performance and achieves heat transfer coefficient of 0.035MW/m2K at inlet heat flux 4.6MW/m2. Compared with the heat transfer performance of copper fiber-sintered porous media, the bronze particlesintered ones give lower heat transfer coefficient. However, the stable cooling conditions that the heat transfer coefficient does not depend on the flow velocity, were confirmed even at heat flux of 4.6MW/m2 in case of the bronze particle-sintered media, while not in the case of the copper-fiber sintered media. This signifies the possibility that the bronze-particle sintered media enable much higher heat flux removal of over 10MW/m2, which could be caused by higher permeability of the particle-sintered pore structures. Porous media with high permeability provide high performance of vapor evacuation, which leads to more stable heat removal even under extremely high heat flux. On the other hand, the heat transfer coefficient of the metal foams becomes lower because of the lower capillary and fin effects caused by too high porosity and low effective thermal conductivity. It is concluded that the pore structure having high performance of vapor evacuation as well as the high capillary and high fin effects is appropriate for extremely high heat flux removal of over 10MW/m2.
Simultaneous Production of Hydrogen and CNTs by In-Liquid Plasma, and Its Discharge Characteristics
Authors: Nomura Shinfuku , Toyota Hiromichi , Mukasa Shinobu , Hattori Yoshiaki , Takahashi Yoshiyuki , Ueda Naoharu , Yamashita Hiroshi , Tanaka Muneo
Published: July 2009

The plasma in liquid is generated by applying High-Frequency (HF) irradiation of 27.12 MHz or Microwave (MW) irradiation of 2.45 GHz from an electrode, namely, a monopole-antenna electrode inserted into a reactor vessel. n-dodecane, methanol, and water are used as test liquids. The glow discharge plasma can be kept in spite of atmospheric pressure due to the cooling effect of liquid itself. The light emission from the plasma changes substantially according to the behavior of the bubble. The present Chemical Vapor Deposition (CVD) process also enabled simultaneous production of hydrogen gas and the synthesis of the Carbon Nano-Tubes (CNTs) in hydrocarbon liquids. The actual production of hydrogen per unit energy by this process corresponds to approximately 1% of that by conventional steam reforming method and about 32% of that by the alkaline water electrolysis. Moreover, this process can make the solid carbon of about 14 g/h at the same time.
Accounting for Sensor Errors in Estimation of Surface Heat Flux by an Inverse Method
Authors: Woolley Jonathan W. , Woodbury Keith A.
Published: July 2009

Thermocouples or other measuring devices are often embedded into a solid to provide data for an inverse calculation. It is well-documented that such installations will result in erroneous (biased) sensor readings, unless the thermal properties of the measurement wires and surrounding insulation can be carefully matched to those of the parent domain. Since this rarely can be done, or doing so is prohibitively expensive, an alternative is to account for the sensor dynamics with an appropriate model. In this paper we simulate a thermocouple embedded in a sand mold near the interface of a solidifying aluminum casting. The effect of sensor errors is accounted for by generating correction kernels from a detailed model of the embedded thermocouple. The corrected sensor readings are used in the inverse heat conduction solution. The magnitude of the effect is shown by comparing surface heat fluxes computed with measured temperatures to the heat fluxes computed with corrected temperatures.
Effectiveness of Parallel Flow Microchannel Heat Exchangers With External Heat Transfer and Internal Heat Generation
Authors: Mathew B. , Hegab H.
Published: July 2009

In this paper the thermal performance of balanced parallel flow microchannel heat exchangers subjected to external heat transfer and internal heat generation have been numerically analyzed. The governing equations were numerically solved to obtain the axial temperatures of the fluids. The effectiveness of each fluid was determined using the inlet and outlet temperatures obtained from the numerical analysis. Moreover, the heat transferred between the individual fluids and the ambient as well as that between the fluids were numerically determined. The effectiveness depended on NTU, ambient temperature, thermal resistance between the ambient and the fluids, and the internal heat generation. When NTU is zero, the effectiveness depends only on the internally generated heat. At a particular ambient temperature and NTU the effectiveness of the hot and cold fluids degraded and improved, respectively, with increase in the internally generated heat. On the other hand with increase in ambient temperature the effectiveness of the hot and cold fluids decreased and increased, respectively, for a specific amount of heat generation. The model developed in this paper has been validated using existing models which consider the individual effect of external heat transfer and internal heat generation on the performance of parallel flow microchannel heat exchangers.
An Analysis of Natural Convection in Leading Edge Wing Compartments
Authors: Egan V. , Moore D. , Newport D. , Lacarac V. , Estebe B.
Published: July 2009

Enclosure natural convection has applications in many engineering disciplines such as electronic component cooling, building ventilation and heating, and renewable energy systems such as solar collectors. To date there has been little research on its application in the aeronautical industry where it plays an important role in aircraft heat transfer. Standard civil aircraft comprise of a number of vented and non-vented compartments. One such compartment is the leading edge which houses the main aircraft bleed duct and several electronic devices. Natural convection heat transfer in the leading edge compartment is important during aircraft turn around while systems are running and the exterior of the aircraft is subjected to solar loading. The objective of this paper is to investigate the heat transfer in a leading edge. The effect of an internal heat generating source, a bleed duct, is also investigated. A dimensional analysis of the governing equations is carried out to determine the appropriate scaling groups for the natural convection cases and a numerical simulation is run on a commercial CFD package. The numerical results are compared with experimental measurements obtained from a leading edge test facility. The effect of bleed duct placement is also investigated both experimentally and numerically with good agreement achieved. It was found that bleed duct placement can have a significant effect on the overall temperature distribution within a leading edge compartment. The results provide a basis for the optimisation of natural convection in such aircraft wing compartments.
Velocity Field Measurements in Leading Edge Wing Compartments
Authors: Egan V. , Newport D. T. , Larcarac V. , Estebe B.
Published: July 2009

For many applications the optimisation of natural convection cooling is a major design consideration due to factors such as weight, accessibility, cost and power consumption. In aircraft wing compartments, natural convection is the dominant mode of heat transfer due to high wall temperatures resulting from solar loading and heat dissipating internal electronics. This paper investigates the flow structures in a leading edge compartment subject to various thermal boundary conditions. The experimental configuration consisted of two leading edge enclosures; the first is a single compartment while the second has an attached wing box. Particle image velocimetry (PIV) was employed to obtain velocity measurements of the flow in both leading edge enclosures. The second compartment investigated the effect of an adjacent fluid filled enclosure on the flow regime in the leading edge compartment. Higher local velocities were found in the second compartment due to an increase in buoyancy forces resulting from a lower of the average fluid temperature within the compartment. The introduction of a heat dissipating component gave rise to two separate convection structures and in general increased the fluctuations in the both temperature and velocities within the compartment.
Numerical Investigation on Thermal and Fluid Dynamic Behaviors of Air Conditioning in Aircraft Cabin
Authors: Balducci G. , Bianco V. , Manca O. , Nardini S. , Roma M.
Published: July 2009

The thermo-hygrometric comfort in the environments is strictly connected with thermo fluid dynamic fields inside them. Jet position and inlet air velocity could origin uncomfortable air distribution and temperature level. In order to avoid this, a preliminary study to determine the best jet position and air velocity is necessary. In this study the transient thermo and fluid dynamic field are analyzed for an executive aircraft. The aim of this study is the numerical visualization of the thermo and fluid dynamic fields in the cabin, with the target to optimize the thermo-hygrometric comfort of the passengers. The main focus is on the velocity and temperature fields, because the proper pressure level is guaranteed by the pressurization system. The analysis is performed on a cabin section, considering seats influence. An average conductance and heat transfer coefficient are considered for the skin, in order to properly simulate the heat exchange with external environment. A k-ε model is used to take into account the turbulence effect, due to the cabin configuration and air velocity. The results are presented in form of velocity and temperature fields; moreover, air temperature and velocity profiles are shown at different positions, in order to well evaluate the comfort conditions in the examined aircraft section.
Stability Analysis and Network Design of Evaporative Micro-Channels
Authors: Lee Hee Joon , Yao Shi-Chune
Published: July 2009

During the operation of evaporative micro-channels, flow instability could be encountered. This phenomenon usually occurs when the Bond number of the fluid in the micro-channels is less than unity, so that a growing bubble is severely squeezed in the narrow channel and expands towards both upstream and downstream simultaneously. To reduce the flow instability, installation of an inlet orifice at the upstream, or making the micro-channel expanding at the downstream are found to be effective. An instability model for micro-channels was established, which takes into account the effects of both the inlet orifice and the channel expansion. Experiments of evaporating water micro system of 48 parallel micro-channels with 353 μm hydraulic diameter were conducted. The instability criterion of evaporative micro-channels with the effects of inlet orifice and expanding channel area are validated. Furthermore, to assist the general design of complex micro-channel network systems, a computational scheme is developed.
Radiative Properties of GaAs From First Principles Calculations
Authors: Bao Hua , Ruan Xiulin
Published: July 2009

Spectral reflectance of GaAs from infrared (IR) to ultra-violet (UV) bands is calculated from first principles. We first calculate the spectral dielectric function which is determined by the response of GaAs to external electromagnetic field. Two mechanisms exist for different wavelengths, namely, phonon absorption in the far-IR region and the electronic absorption in the near-IR to UV region. With plane-wave pseudopotential method, we determined the dielectric function of GaAs with the the initial structure as the only input. For the far-IR region, phonon calculations are carried out. By analyzing the phonon modes, low-frequency dielectric constant is calculated. For the near-IR to UV band, the electronic band structure of GaAs is calculated, and the imaginary part of the dielectric function is determined from the band structure using Fermi’s Golden rule. The real part of spectral dielectric function is then derived from Kramer-Kronig transformation. The reflectance is then calculated using Maxwell’s equations.
Characteristics of Cooling of the Leading Edge With a Row of Dual Impinging Jets
Authors: Li X. C. , Corder P.
Published: July 2009

The leading edge of turbine blades is one of the critical areas that need to be cooled effectively because of the high local heat transfer rate of the main flow. Film cooling with different shaped holes as well as internal cooling by impinging jets has successfully been applied in modern gas turbine applications. This paper numerically studies the cooling of the leading edge with a row of dual impinging jets — two jets close to each other. Heat transfer of the dual jets is compared to that of a single jet (in a row) based on the same flow rate or jet velocity. The effect of the distance between the dual jets and the jet inclination angle is examined to seek the best geometric parameters. In addition, the curvature of the leading edge surface is considered to examine the heat transfer difference between curved and flat walls. Various jet-to-target spacing and Reynolds numbers are also studied. Results show that the dual impinging jets generally produce two high heat transfer regions in the stagnation point, and the peak value is slightly higher than the single row of jets with the same Reynolds number. When the distance between two jets is 3d, the jet flow after bouncing back from the symmetry line affects the heat transfer as a crossflow. The target surface curvature has little effect on the overall heat transfer, but the peak heat transfer coefficient is lower on the curved surface than that on the flat surface. The dual impinging jets present a higher average heat transfer around the stagnation region.