bluuebunny/crossref_metadata_2025 huggingface dataset:
Thermal Performance of Heat Pipe Drill: A New Simulation Model for Heat Pipe
Authors: Jen Tien-Chien , Liao Quan , Chen Qinghua , Li Longjian , Cui Wenzhi
Published: April 2009

It is well known that drilling is one of the most difficult metalwork cutting operations, not only from the viewpoint of manufacturing process, but also from the thermal management point of view of the drill. For the drilling process, due to its long time continuous metal-to-metal friction between drill tip edge and work piece, a significant amount of heat is generated on the interface, which is in a confined space compared to other machining processes, such as cutting or milling. This makes it very difficult to keep the temperature of drill tip under a certain but acceptable range since the coolant is unable to penetrate deep enough into the hole. Also, based on the environmental considerations and the cost reduction requirement, the conventional flooding coolant method become highly inefficient and expensive due to high maintenance costs. A new approach, dry drilling method (i.e., no coolant is employed during the drilling process) is investigated in this study. In dry drilling, we used heat pipe technology to accomplish the goal of efficient heat removal from the drill tip. It is heat pipe’s unique and excellent advantages such as, high reliability, supreme equivalent thermal conductivity, flexible adaptability and so forth, that make it possible for dry drilling by combining the drill and heat pipe. From the numerical simulation viewpoint of heat pipe drill, how to correctly model the heat pipe in the drill is one of the crucial tasks because it will directly influence the accuracy of the simulation results. So far, there are few different kinds of simulation models for heat pipe drill and each of them works well in some kinds of special situations. The present paper studied and compared these different simulation models of heat pipe and then proposed a general, simple but robust and more accurate approach to simulate the heat transfer process in the heat pipe drill. Furthermore, this kind of the heat pipe model can be used in many other heat pipe applications.
Diode Laser Cladding on A5052 Aluminium Alloy for Wear Resistance
Authors: Iwatani Shingo , Ogata Yasuhito , Uenishi Keisuke , Kobayashi Kojiro F. , Tsuboi Akihiko
Published: April 2009

In order to improve a wear resistance of aluminium alloy, we proposed a diode laser cladding on the surface of a A5052 aluminium alloy. Firstly, an applicability of diode laser to laser cladding was evaluated. In this result, application of diode laser made it possible to obtain stable beads in low heat input compared with CO2 laser. According to the increase in aluminium content in the obtained clad layer, the microstructure of the clad layer changed as γ (8∼20%) → γ + α (10∼30%) → Fe3Al (30%∼). At the interface between the clad layer and the aluminium alloy substrate, the reaction layer consisting of Fe2Al5 and FeAl3 formed. In the abrasion wear the obtained clad layers exhibited a higher wear resistance compared with the aluminium alloy.
Impinging Jet Heat Transfer in the Transitional Wall Jet Region
Authors: O’Donovan Tadhg S. , Murray Darina B. , Torrance Andrew A.
Published: April 2009

Convective heat transfer to an impinging air jet is known to yield high local and area averaged heat transfer coefficients. Such jets are of interest in the cooling of electronic components and of turbine blades and in manufacturing processes such as grinding. The current research is concerned with the measurement of heat transfer to an impinging air jet over a wide range of test parameters. These include Reynolds numbers, Re, from 10000 to 30000 and nozzle to impingement surface distance, H/D, from 0.5 to 8. The current research reports both mean and fluctuating heat transfer distributions up to 6 diameters from the geometric centre of the jet. The heat transfer results are compared to local velocity data. At low nozzle to impingement surface spacings the heat transfer distributions exhibit peaks at a radial location that varies with both Re and H/D. These peaks are shown to be due to an abrupt increase in turbulence in the wall jet boundary layer. At certain test configurations vortices that initiate in the shear layer impinge on the surface and move along the wall jet before being broken down into smaller scale turbulence. The effects of the vortical flow on the heat transfer mechanisms in an impinging jet flow are discussed.
Evaporation in Capillary Tubes of Square Cross Section
Authors: Coquard Typhaine , Camassel Bruno , Prat Marc
Published: April 2009

Modeling of evaporation of a pure liquid within a capillary tube of circular cross section is a classic problem which has been the subject of many studies. Here we consider the case of tubes of polygonal cross section. This case leads to much greater evaporation rates owing to the liquid flow along the tube edges induced by the capillary forces. We concentrate on slow evaporation situations for which evaporation is controlled by mass transfer. Various evaporation regimes are distinguished depending on the competition between capillary, gravity and viscous forces. When the capillary forces are dominant, it is shown that the position of the bulk meniscus scales linearly with time (and not as the square root of time as in a capillary tube of circular cross section). The effect of viscous or gravity forces is to thin out the corner liquid fingers as the bulk meniscus recedes into the tube. This contributes to reduce the evaporation rate compared to the capillarity dominated regime. Then the case of faster evaporations inducing significant temperature variations is briefly discussed.
Transient Thermal Measurements Using Thermographic Phosphors for Temperature Rate Estimates
Authors: Crim P. R. , Walker D. G. , Allison S. W.
Published: April 2009

This paper addresses the potential for predicting heat flux from thermographic phosphor measurements. Temperature can be measured using thermographic phosphors by extracting the intensity decay of the phosphor, which is temperature dependent. This measured temperature can then be used to estimate boundary heat fluxes, which is often called the inverse heat conduction problem. Heating rate can also be estimated with the use of thermographic phosphors, from which heat flux can also be determined. In this case, the solution to the inverse problem appears more stable. The purpose of this work is to demonstrate the feasibility of measuring change in decay rates and the ability to determine the first derivative of temperature from these measurements. Preliminary analysis shows that by determining dT/dt instead of temperature, a better estimate of heat flux can be made. The experiment uses a millisecond phosphor, excited by an LED pulsed at 100 Hz. The phosphor is painted on a tungsten filament, which can be heated to hundreds of degrees in under a second. The temperature change during a single pulse is significant enough to affect the decay rate, which is necessary to achieve reasonable heating rate measurement. The measurements of heating rate are used to determine the volumetric generation rate (Joule heating) and the heat transfer loss from the system by convection and radiation. Early data show that estimates from heating rate data, as opposed to temperature data, result more accurate predictions with less error.
Interfacial Area Transport of Vertical Upward Annular Two-Phase Flow
Authors: Hazuku Tatsuya , Takamasa Tomoji , Hibiki Takashi , Ishii Mamoru
Published: April 2009

Accurate prediction of the interfacial area concentration is essential to successful development of the interfacial transfer terms in the two-fluid model. The interfacial area concentration in annular flow and annular mist flow is especially relevant to the transition process to the liquid film dryout, which might lead to fatal problem in the safety and efficient operation of boiling heat transfer system. However, very few experimental and theoretical studies focusing on the interfacial area concentration in annular flow region have been conducted. From this point of view, accurate measurements of annular flow parameters such as local liquid film thickness, one-dimensional interfacial area concentration of liquid film, and local interfacial area concentration profile of liquid film were performed by a laser focus displacement meter at 21 axial locations in vertical upward annular two-phase flow using a 3-m-long and 11-mm-diameter pipe. The axial distances from the inlet (z) normalized by the pipe diameter (D) varied over z/D = 50 to 250. Data were collected for preset gas and liquid flow conditions and for Reynolds numbers ranging from Reg = 31,800 to 98,300 for the gas phase and Ref = 1,050 to 9,430 for the liquid phase. Axial development of the one-dimensional interfacial area concentration and the local interfacial area concentration profile of liquid film were examined with the data obtained in the experiment. Total interfacial area concentration including liquid film and droplets was also discussed with help of the existing drift-flux model, entrainment correlation, and droplet size correlation.
Simultaneous Heat and Mass Transfer During Evaporation/Condensation on the Surface of a Stagnant Droplet in the Presence of Inert Admixtures Containing Non-Condensable Solvable Gas
Authors: Elperin Tov , Fominykh Andrew , Krasovitov Boris
Published: April 2009

In this study we investigated numerically simultaneous heat and mass transfer during evaporation/condensation on the surface of a stagnant droplet in the presence of inert admixtures containing non-condensable solvable gas. The performed analysis is pertinent to slow droplet evaporation/condensation when Mach number is small (M≪1). The system of transient conjugate nonlinear energy and mass conservation equations was solved using anelastic approximation. Transport coefficients of the gaseous phase were calculated as functions of temperature and concentrations of gaseous species. Thermophysical properties of the liquid phase are assumed to be constant. Using the material balance at the droplet surface we obtained equations for Stefan velocity and the rate of change of the droplet radius taking into account the effect of solvable gas absorption at the gas-liquid interface. We derived also boundary conditions at gas-liquid interface taking into account the effect of gas absorption. The governing equations were solved using a method of lines. Numerical calculations showed essential change of the rates of heat and mass transfer in water droplet-air-water vapor system under the influence of solvable species in a gaseous phase. Consequently, the use of additives of solvable noncondensable gases to enhance the rate of heat and mass transfer in dispersed systems allows to increase the efficiency and reduce the size of gas-liquid contactors.
The Smallest Temperature Scales in a Turbulent Channel Flow at High Prandtl Numbers
Authors: Bergant R. , Tiselj I.
Published: April 2009

The object of this paper is to perform the numerical simulations of the temperature fields at low Reynolds numbers, i.e. Reτ = 150 and Reτ = 170.8, and at Prandtl numbers, Pr = 1 and Pr = 100. The spatial scales of the velocity field can be successfully described with DNS accuracy, meanwhile the scales of temperature fields decreasing approximately with Pr3/2 and cannot be resolved for entire energy scalar spectra due to the computer limitations. To overcome these obstacles, filtering and damping of the highest temperature wave number modes in homogeneous directions are introduced rather than modeling the unresolved subgrid scales. First, numerical simulations at Pr = 1 are performed in order to make comparison of the temperature field described with DNS accuracy and filtered and damped temperature fields described with coarser numerical grids. Obtained results show that at least first and second order statistics are comparable to the DNS ones. Next step is to analyze this approach at two orders of magnitude higher Prandtl numbers, i.e: Pr = 100. Comparison is a little bit difficult because no real DNS of the temperature fields at such high Prandtl number has been performed so far. But we estimate that results are still accurate at least in the proximity of the wall.
Numerical Analysis of an Electromagnetic CZ-Si Growth Process by 3D Global Modeling
Authors: Liu Lijun , Nakano Satoshi , Kakimoto Koichi
Published: April 2009

Three-dimensional (3D) thermal flow of silicon melt in an electromagnetic Czochralski (CZ) system was numerically investigated with a recently developed 3D global model. The electromagnetic CZ system was established with a transverse magnetic field and an injected electric current applied on the melt surface. Different azimuthal and radial positions of the electrode on the melt surface were taken into account to investigate their influences on the heat and mass transfer in the melt, as well as on the melt-crystal interface. The influence of the electric current direction on the melt flow pattern and temperature distribution was also demonstrated. The results showed that the position of the electrode on the melt surface and the direction of the applied electric current play an important role in controlling the heat and mass transfer in the silicon melt.
Free Jet in Confined Combustion Chamber: Numerical Model for Industrial Application in Low NOx Burners
Authors: Colombo Emanuela , Inzoli Fabio , Malfa Enrico
Published: April 2009

The present work is focused on the prediction of the fluid dynamics behaviour for natural gas burners characterized by low NOx emissions. The fluid dynamics in the combustion chamber is investigated in order to look for the condition under which it is possible to obtain a diluted combustion. The experimental data used as reference come from two set of tests related to different isothermal flow behaviour: high Reynolds number (Re = 68000) and lower Reynolds number (Re = 5427). Many turbulence models are examined in order to validate high and low Reynolds case. The k-ω models implemented by Wilcox in 1998 seems to properly predict the fluid dynamics behaviour of the jet for high Reynolds numbers, while, for low Reynolds jets, a modification needs to be introduced. The numerical analysis for low Reynolds number, based on an unstructured 2D axial symmetrical grid, shows that no two-equation turbulence models fit the experimental data for low Reynolds jet. Based on the evidence that at low Reynolds number the hypothesis of homogeneous isotropic small turbulence eddy is not valid a modification of k-ω turbulence model’s closure constant has been proposed. This leads to a better agreement with the experimental data. The results demonstrate that great attention needs to be taken and invested in the identification of the turbulence models used in CFD and in the proper tunneling (of the closure coefficient for the turbulence model) that need to be computed case by case accordingly with the specific turbulence level and fluid dynamic features of the jet itself.
Film Boiling on Downward Facing Flat Plates With Varying Inclination Angles
Authors: Kim Chan S. , Yu Mong J. , Suh Kune Y. , Rempe Joy L. , Cheung F. Bill , Kim Sang B.
Published: April 2009

The effect of inclination angle of the downward facing flat plate on the interfacial wavy motion is investigated utilizing the water test apparatus DELTA FS (Downward Ebullient Laminar Transition Apparatus Flat Surface) in a quasi-steady state. Film boiling heat transfer coefficients are obtained on the relatively long surface in the flow direction. The measured heat transfer coefficients are compared with those predicted by the laminar film boiling and interfacial wavy film boiling correlations at the same experimental condition. Visualization of the vapor film revealed that the interfacial wavelength decreases as the flat plate moves from the vertical to downward facing locations.
Mixed Convection in Air in an Open Ended Cavity With a Moving Plate Parallel to the Cavity Open Surface
Authors: Andreozzi Assunta , Bianco Nicola , Naso Vincenzo , Manca Oronzio
Published: April 2009

In this study, a numerical investigation of mixed convection in air in an open ended cavity, with a moving plate parallel to the cavity open surface, is carried out. The moving plate has a constant velocity, whereas a vertical plate of the open cavity is heated at uniform heat flux. All the other walls are adiabatic. The numerical analysis is obtained by means of the commercial code FLUENT. Two configurations, assisting and opposing, are analyzed. In the assisting configuration, natural convection is supported by the plate motion, whereas, in the opposing configuration, natural convection and plate motion have opposing effects. The effect of different geometrical parameters, heat flux and moving plate velocity are analyzed. Results in terms of heated plate and moving plate temperature profiles are presented and simple monomial correlation equations for both the configurations are proposed between the terms Nu/Re0.6 and Ri.
Heat and Mass Transfer in a CVD Optical Fiber Coating Process by Propane Precursor Gas
Authors: Huang Wei , Chiu Wilson K. S.
Published: April 2009

This study investigates the chemical vapor deposition (CVD) process used to hermetically coat optical fibers during draw using propane as the precursor gas. Temperature is calculated by coupling radiation and convection heat transfer from the reactor walls and gas flow with a radially-lumped conduction heat transfer model for the moving optical fiber. Multi-component species diffusion is modeled by the Dixon-Lewis method, which is based on the molecular theory for ideal gases. Gas-phase reaction kinetics is modeled using a 3-step gas phase chemical kinetics mechanism. Surface reaction kinetics is described using collision theory in which a sticking coefficient is used as an empirical parameter to predict surface reactions. A parameter study is carried out with various optical fiber inlet temperature and drawing speed, and validated with experiment results.
Hemispherical Emittance of a Semitransparent Fiber Coated With a Submicron Absorbing Film
Authors: Tian Weixue , Huang Wei , Chiu Wilson K. S.
Published: April 2009

This study presents a model to predict the directional and hemispherical emittance of a fiber coated with up to 2 μm film. The fiber is composed of semitransparent media with a small extinction coefficient. Transmittance and reflectance of the thin film is calculated based on the flat thin film assumption, because the thickness of the film is much less than the fiber radius, and the curvature can be neglected. Predicted emittance from wave optics is compared to geometric optics for modeling radiative transfer in thin film. Steep changes in emittance are predicted by wave optics for films that are nanometers thick. This effect was not observed from geometric optics analysis. Effects of film and fiber substrate optical properties are also studied.
Experimental Analysis of Opposing Flow in Mixed Convection in a Channel With an Open Cavity Below
Authors: Manca Oronzio , Nardini Sergio , Vafai Kambiz
Published: April 2009

In this paper mixed convection in an open cavity with a heated wall bounded by a horizontal unheated plate is investigated experimentally. The cavity has the heated wall on the opposite side of the forced inflow. The results are reported in terms of wall temperature profiles of the heated wall and flow visualization for Reynolds number (Re) from 100 to 2000 and Richardson number (Ri) in the range 4.3–6400; the ratio between the length and the height of cavity (L/D) is in the range 0.5–2.0 and the ratio between the channel and cavity height (H/D) is equal to 1.0. The present results show that at the lowest investigated Reynolds number the surface temperatures are lower than the corresponding surface temperature for Re = 2000, at same the ohmic heat flux. The flow visualization points out that for Re = 1000 there are two nearly distinct fluid motions: a parallel forced flow in the channel and a recirculation flow inside the cavity. For Re = 100 the effect of a stronger buoyancy determines a penetration of thermal plume from the heated plate wall into the upper channel. Moreover, the flow visualization points out that for lower Reynolds numbers the forced motion penetrates inside the cavity and a vortex structure is adjacent to the unheated vertical plate. At higher Reynolds number the vortex structure has a larger extension at same L/D value.
A Model for Condensation Inside Minichannels
Authors: Cavallini Alberto , Del Col Davide , Doretti Luca , Matkovic Marko , Rossetto Luisa , Zilio Claudio
Published: April 2009

Present authors have measured heat transfer coefficients (Cavallini et al. [1, 2]) and pressure drops (Cavallini et al. [3, 4]) during condensation of R134a, R410A and R236ea inside a flat multiport mini-channel tube with a 1.4 mm hydraulic diameter. The experimental heat transfer coefficients (α) have been compared against correlations available in the literature and no correlation was able to predict α in all the experimental conditions. The present paper suggests a heat transfer model for condensation inside minichannels, based on analogy between heat and momentum transfer. The proposed procedure takes into account the effect of the entrainment rate of droplets from the liquid film. The model is applied to the annular, annularmist flow. A simplified version of the model is also presented. Comparisons between present authors’ data and predicted values show the satisfactory behaviour of both versions of the models.
Discontinuous Finite Element Modeling of Grain Growth Behavior of Polycrystalline Material
Authors: Shu Y. , Ai X. , Li B. Q.
Published: April 2009

In this paper, a discontinuous finite element solution to the phase-field equations for the microstructure evolution of polycrystalline material is presented. The mathematical formulation and numerical implementation are discussed. Numerical studies are conducted on the interactions between multiple grain seeds with different orientations during solidification. The discontinuous numerical scheme is validated by the results reported in literature. The effects the pulling rate, the size and orientation of the grain seeds on the microstructure formation of interface are investigated using the presented model. Results show that the initial orientation of the grain seed plays a dominant role in the final crystallography of the crystals.
Thermal Conduction in Ultra-Thin Pure and Doped Single Crystal Silicon Layers at High Temperatures
Authors: Liu Wenjun , Asheghi Mehdi
Published: April 2009

This work presents the in-plane thermal conductivity data for pure as well as boron (1.6 × 1021 /cm3), arsenic (2.3 × 1020 /cm3) and phosphorus (2.3 × 10 20/cm3) doped silicon layers of thickness 30 and 50 nm at high temperature. The steady-state Joule heating and electrical resistance thermometry is used to measure lateral thermal conductivity of suspended silicon layers. Thermal conductivity data for pure and lightly doped single crystalline silicon layers can be interpreted using thermal conductivity integral and relaxation time approximation for phonon-boundary and phonon-impurity scattering rates. No additional fitting parameters are used in this work; in contrast with previous studies that required an unusually large phonon-impurity scattering coefficient to match the predictions to the thermal conductivity data for bulk doped silicon.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
A Numerical Study of a Single Bubble Sliding on a Downward Facing Heating Surface
Authors: Li Ding , Manickam Sathish , Dhir Vijay K.
Published: April 2009

In this study, a complete 3D numerical simulation of single bubble sliding on a downward facing heater surface is carried out. The continuity, momentum and energy equations are solved using finite difference method and the level-set method is used to capture the liquid-vapor interface. The shape of sliding bubble changes from initially spheroids, to ellipsoids and finally to bubble-cap. The temperature gradient downstream the sliding bubble is much larger than that upstream the bubble. This indicates the sliding bubble enhances the heat transfer significantly. The bubble shape and sliding distance predicted from numerical analysis is compared with the experimental data.
Stability of Axisymmetric Thermocapillary Flows in an Open Vertical Cylinder With Lateral Heating
Authors: Xu B. , Ai X. , Li B. Q.
Published: April 2009

Instability of Marangoni-Rayleigh-Be´nard convection of low Prandtl number fluid in an open vertical cylinder subjected to lateral heating is investigated using higher order finite difference scheme. Radiative boundary condition is applied to the free surface and bottom of the cylinder is adiabatic. The axisymmetric base flow is solved and then linear stability analysis is conducted to determine the critical points at which the flow becomes asymmetric. It is revealed that the Marangoni flow plays a stabilizing role to the Rayleigh-Be´nard convection.
Inverse Design of Time Dependent Solidification Processes
Authors: Okamoto Kei , Li Ben Q.
Published: April 2009

An inverse algorithm is developed for the design of the solidification processing systems. The algorithm entails the use of the Tikhonov regularization method, along with an appropriately selected regularization parameter. Both the direct solution of moving boundary problems and the inverse design formulation are presented, along with the L-curve method to select an optimal regularization parameter for inverse design calculations. The design algorithm is applied to determine the optimal boundary heat flux distribution in order to obtain a unidirectional solidification front moving at a constant velocity in a 2-D cavity by eliminating the effect of natural convection. The inverse calculation is also performed for the case in which the solid-liquid interface is prescribed to vary with sine functions. The L-curve based regularization method is found to be reasonably accurate for the purpose of designing time dependent solidification processing systems.
Use of Contact Resistance Algorithm to Implement Jump Boundary Conditions for the Radiation Diffusion Approximation
Authors: Larsen Marvin E.
Published: April 2009

Thermal conduction codes can be used as solvers for the diffusion approximation for radiation heat transfer. Energy fluxes and temperature distributions that result from thermal radiation in an optically-thick participating medium can be estimated. Allowing dependence on temperatures from either side of the interface, a contact resistance algorithm can be used to implement “jump” (or slip) boundary conditions appropriate for the diffusion approximation in solving the radiation transfer equation. For steady, pure radiation (no conduction) systems analytical expressions exist to specify the temperature in the radiating medium at the wall as a function of the wall temperature, wall emissivity, and extinction coefficient. Radiation and conduction solutions for gray, absorbing/emitting and conducting media bound by diffuse surfaces for the simple case of the steady planar layer are considered. Reference solutions are developed by detailed zone-methods solving the coupled differential forms of both the radiation and conduction heat transfer equations. From the reference solutions, empirical relations are developed for surface resistance as functions of the local wall and adjacent media temperatures, the wall emissivity, the absorptivity, and the thermal conductivity of the medium. Performance of the approximate solution is compared to the reference solutions.
Conduction Heat Transfer Problem Solution Using the Method of Fundamental Solutions With the Dual Reciprocity Method
Authors: Erdo¨nmez Cengiz , Saygın Hasan
Published: April 2009

The method of fundamental solutions (MFS) is first proposed in 1964 by Kupradze and theoretical basis of this method is constructed at the end of 1980’s. As a meshless method, no domain meshing is required for MFS. Fundamental solutions are used to solve problems without coping with the singularity on the boundary because of the fictitious boundary defined containing the domain of the problem. In this paper effectiveness of the MFS will be introduced by two test problem for the homogeneous and inhomogeneous modified helmholtz equations. In-homogeneous terms are approximated by using the method of particular solutions through the dual reciprocity method. The conduction heat transfer problem is defined and transformed to the corresponding elliptic partial differential equation by using finite difference and the method of lines method which gives an inhomogeneous helmholtz equation. Then the problem is solved iteratively by using the MFS. Two test problem are solved by both the finite element method (FEM) and MFS and compared in the figures. It can be seen that as a meshless method, MFS gives very good results for the test problems. The thermal shock problem presented here also gives accurate solutions by using MFS and agrees well with the FEM solution.
Jet Impingement Cooling of an Inverter Module in the Harsh Environment of a Hybrid Vehicle
Authors: Bhunia Avijit , Chen Chung-Lung
Published: April 2009

This paper presents a study of liquid jet impingement cooling technique and its system level implementation for thermal management of an inverter module in a hybrid vehicle. Clusters of anti-freeze liquid jet array impinge on the base plate of a 450V (DC Link voltage)/400A (RMS current) module, made by Semikron, Inc. In the harsh environment of an automobile, the ambient temperature of the coolant is 105°C, and the maximum allowable flow rate and pressure drop are 2.5GPM and 1.6bar respectively. The impingement cooling technique demonstrates 1623 Watts of heat dissipation for 20°C device temperature rise above ambient. This translates to a chip level dissipation power density of 56W/cm2, approximately 1.8X improvement over forced convection liquid cooling in the state-of-the-art pin fin cold plate. At the highest power, the less than 3°C temperature variation among the twelve IGBT measurements indicates a high degree of reliability in module operation. The efficient phase change heat transfer mechanism sets in at local base plate temperatures between 109–111°C, which accounts for more than 10% of the total heat dissipation at 1600W level.
The Response of Portable Electronics to Transient Conditions of Temperature and Humidity
Authors: Punch Jeff , Grimes Ronan , Heaslip Greg , Galkin Timo , Va¨keva¨inen Kyo¨sti , Kyyhkynen Vesa , Elonen Erkko
Published: April 2009

The design of portable electronic systems for use in hot and humid conditions represents a significant design challenge for packaging engineers. Humidity drives a range of failure mechanisms: the alteration of material properties; hygro-mechanical stress phenomena; and the acceleration of corrosion and material migration. Moreover, portable electronic products such as mobile phones, CD players and digital cameras can experience rapidly varying conditions of temperature and humidity which, in certain conditions, can cause condensation to form on the internal and external surfaces of the product. Condensation — or even very high relative humidity — is a severe stimulus because it greatly accelerates corrosion and migration mechanisms. This paper considers the response of portable electronics to transient variations of temperature and humidity in order to assess the conditions under which condensation is likely to occur. A first-order coupled hygrothermal model is developed to represent the temperature and humidity response of a typical portable product using simple time constants. Experimental characterisation of a sample product is performed to evaluate the parameters of the model, and it is demonstrated how movement from one environment to another can precipitate condensation.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Heat Transfer Dynamics During Treatment of Port Wine Stain Birthmarks With Multiple-Intermittent Cryogen Spurts and Laser Pulses
Authors: Jia Wangcun , Aguilar Guillermo , Nelson J. Stuart
Published: April 2009

Port wine stain (PWS) is a congenital, progressive vascular malformation of human skin. Presently, all PWS patients are treated using single cryogen spurt and single laser pulse exposure (SCS-SLP), which does not produce complete lesion blanching in the vast majority of patients. In this study, the feasibility of applying multiple cryogen spurts intermittently with multiple laser pulse exposures (MCS-MLP) is studied numerically. Laser therapy of PWS was simulated with finite element heat diffusion and Monte Carlo light distribution models. Epidermal and thermal damage of PWS blood vessels of various diameters (50–130 μm) were calculated with an Arrhenius-type kinetic model. The results show that the proposed MCS-MLP approach can provide sufficient epidermal protection while at the same time achieving higher core intravascular temperatures over longer periods of time. PWS patients may benefit from the MCS-MLP approach, depending on PWS vessels diameter.
Steady-State Hydrodynamic and Thermal Interactions Between Secondary User-Loops in a Hydraulic Network
Authors: Franco Walfre , Cai Weihua , Sen Mihir , Yang K. T.
Published: April 2009

Hydraulic networks constitute a fundamental part of heating, ventilating and air conditioning systems in buildings and high rises. In order to optimize large and complex networks it is important to understand the effects of operational changes in one loop on the others. The objective of this study is to investigate the time-independent flow and thermal interactions between secondary user-loops, in a hydraulic network that is used for cooling, when the system goes from one steady state to another. The study is experimental and was carried out on a facility which has a primary cooling loop, three secondary loops, and a primary heating loop. The flow was abruptly changed by actuating a valve in one of the loops causing changes in the other two loops. Results show that the change of flow rates and pressure differences in the other two loops are linearly dependent on that in the actuating loop. The dependence is also affected by the initial operational condition of the network. The thermal interaction, however, is different in that it is nonlinearly coupled with the hydrodynamic interaction.
Noninvasive Measurement of Thermal Property Parameters of Cylindrical Living Tissues
Authors: Yue Kai , Zhang Xinxin , Yu Fan
Published: April 2009

A new noninvasive measurement method is proposed to simultaneously determine the thermal parameters of cylindrical living tissues. The corresponding two-dimensional mathematic model is established based on the Pennes’ bioheat transfer equation. With respect to the measuring points on the surface of the given living tissue, the effects of thermal parameters on the temperature variations, the sensitivity coefficients of the key thermal parameters to the model temperatures and the relativities of these sensitivity coefficients are analyzed and calculated. The results show that the thermal parameters concerned can be estimated with high measuring precision and can be simultaneously estimated. The experimental system of the dynamic tissue phantom is established to validate the presented method. A number of experiments are carried out under different conditions and the experimental results indicate that the measured parameters are in good agreement with the reference values.
Heat Transfer Analysis in a Blast Furnace Tuyere Nose
Authors: Roldan David , Tetrault Clifford , Zhao Yongfu , Atkinson Mark , Zhou Chenn Q.
Published: April 2009

The Blast furnace process is a counter current moving bed chemical reactor to reduce iron oxides to iron for iron/steel making. In the process, tuyeres are used to introduce hot air (blast) and fuel (gas or pulverized coal) into the furnace for combustion. The nose of a tuyere, composed of copper material, that is exposed to a high temperature environment and a cooling water pipe is embedded to prevent melting of the material. In this work, heat transfer and temperature distributions have been analyzed using the computational fluid dynamics commercial software, FLUENT®. The computations have included the cooling water flow and conjugate heat transfer in the tuyere nose. Both convection and radiation heat transfer on the surfaces are included. Different geometry and operating conditions were considered. The results have indicated that insufficient cooling in a large area between the nose inlet and outlet pipe can cause failures of the tuyere nose.
Visualization of Pool Boiling From Plain and Enhanced Structures
Authors: Ghiu Camil-Daniel , Joshi Yogendra K.
Published: April 2009

A visualization study of pool boiling at atmospheric pressure from plain and enhanced structures was conducted with PF 5060 as working fluid. The single layer enhanced structures were fabricated in copper and were 1 mm thick. The parameters investigated in the present study are heat flux, width of microchannels and overall structure width. A monochrome CCD camera with attached magnifying lens served as the main tool for observation of the boiling process from the structures. The nucleate boiling regime for a plain surface is usually divided into two sub-regimes: the isolated bubbles regime and the coalesced bubbles regime. For enhanced structures, the increase in geometric complexity leads to different flow regimes that may establish under different heat fluxes. This study evaluates these regimes using movies and still photographs. A comparison with the plain case is made and the differences highlighted.
A Comparison Between Computational Simulation and Measurement of Acoustically Enhanced Heat Transfer
Authors: Oh Yool-Kwon , Yang Ho-Dong
Published: April 2009

The strong upward flow called as “acoustic streaming”, when ultrasonic waves were applied in a medium, occurred near to ultrasonic transducer and enhanced the heat transfer. That is, applying ultrasonic waves in a medium may cause the flow velocity of the medium to increase: an effect known as acoustic streaming promotes heat transfer through convection and affects the thermal boundary layer. So, this study was compared with the pressure variations and enhancement of heat transfer by computational simulations and experiments in acoustic field. For the computational simulations, structural vibration simulator (SVS) programmed with a fortran language and based on a coupled finite element-boundary element method (coupled FE-BEM) was used. The results of this study reveal that the acoustic pressure is higher near two ultrasonic transducers than other points where no ultrasonic transducer was installed. The enhancement trend of heat transfer is similar with the profile of the pressure variations. It is concluded that the pressure variations are related to the enhancement of heat transfer in acoustic field.
Comparison of Heat Transfer Rates Around Moving and Stationary Bubbles During Nucleate Boiling
Authors: Christopher David M. , Wang Hao , Peng Xiaofeng
Published: April 2009

Nucleate boiling is known to be a very efficient method for generating high heat transfer rates from solid surfaces into liquids; however, the fundamental physical mechanisms governing nucleate boiling heat transfer are not well understood. This paper describes a numerical analysis of the heat transfer mechanisms around stationary and moving bubbles on a very thin microwire. The numerical analysis accurately models the experimentally observed bubble movement and fluid velocities. The analytical model was then used to study the heat transfer mechanisms around the bubbles. The analysis shows that the primary heat transfer mechanism is not the direct heat transfer to the bubble, but rather the large amount of convection around the outside of the bubble induced by the Marangoni flow that transfers at least twice as much energy from the wire than the heat transfer directly under the bubble. The enhanced heat transfer due to the Marangoni flow was evident for both stationary and moving bubbles.
A Mathematical Model for the Performance of a Horizontal Convective Solar Still
Authors: Feng M. , Tao Y.-X.
Published: April 2009

A mathematical model is developed to predict the rate of distilled water production for a solar still with convective, double-deck configuration. The model is based on the one-dimensionally distributed formulation in the flow direction and two media treatment in the vertical direction. Different operating conditions are investigated to include different airflow rates, variable rates of solar radiation and ambient temperature. The effects of materials used in the still canopy and physical phenomena such as solar radiation absorption of liquid film on the performance are also investigated. The comparisons between the model results and fully two-dimensional CFD model results are presented.
Multi-Objective Shape Optimization of Convective Wavy Channels
Authors: Nobile Enrico , Pinto Francesco , Rizzetto Gino
Published: April 2009

In this paper we describe a procedure for the multi-objective shape optimization of periodic wavy channels, representative of the repeating module of an ample variety of heat exchangers. The two objectives considered are the maximization of heat transfer rate and minimization of friction factor. Since there is no a single optimum to be found, we use a Multi-Objective Genetic Algorithm and the so-called Pareto’s dominance concept. The optimization of the periodic channel is obtained, by means of an unstructured Finite Element solver, for a fluid of Prandtl number Pr = 0.7, assuming fully developed velocity and temperature fields, and steady laminar conditions. For the two-dimensional case, the geometry is parameterized either by means of linear-piecewise profiles, or NURBS, and their control points represent the design variables. The three-dimensional channels are obtained by simple extrusion of the two-dimensional geometries. The results obtained are very encouraging, and the procedure described can be applied, in principle, to even more complex problems.
Heat Transfer Analysis of Human Cell Culture Under RF Exposure
Authors: Khalid Muhammad , Zhou Chenn , Bassi Ashish , Wang San Ming , Gerber Howard , Tseng Charles
Published: April 2009

A 2.45 GHz radio frequency (RF) exposure system was designed and used to study the RF effects on the genome-wide gene expression in cultured human cells. In this system, a T-25 culture flask, which contains 10 × 106 cells in a 10ml medium, is placed in a WR 340 waveguide. The waveguide serves as an environmental chamber. The source is a pulsed magnetron for obtaining a high electric field with the specific absorption rate (SAR) at approximately 10 W/kg. In order to ensure the non-thermal effect, the system was designed to maintain a temperature of 37°C. In this research, the heat transfer analysis of the system was conducted using the computational fluid dynamic (CFD) software FLUENT® coupled with the finite element software, High Frequency Structural Simulation (HFSS) by Ansoft. The electric field was first analyzed by using HFSS to calculate the SAR distribution as a heat source input for CFD calculations. The fluid flow and temperature distributions within the flask were then analyzed using FLUENT®. The results were validated experimentally by measuring the temperatures with fluoroptic thermometer probes as well as by examining the level of heat shock gene expression. These results provide useful information for a better understanding and controlling of the operating conditions of the system.
Thermal Transport Network Model for High-Porosity Materials: Application to Nanoporous Aerogels
Authors: Smith Brian R. , Beutler Peter D. , Amon Cristina H.
Published: April 2009

Nanoporous thin films have received attention in the microelectronics field for their application as next-generation low-k inner-layer dielectric (ILD) materials due dielectric constants approaching 1.4. In addition, emerging applications as thermal insulation for microsystems aim to exploit the materials’ unique thermal properties in sensor and component products. However, its thermal properties can vary greatly depending on fabrication processes and material morphology. In addition, a variety of transport phenomena are present and delineation among them is difficult. In this work, we examine heat transport in aerogel, one of the most common embodiments of nanoporous materials, to identify the main modes of energy transport. We employ a modified diffusion-limited cluster aggregation (DLCA) technique to simulate aerogel’s highly porous, amorphous solid structure. Network models then simulate heat transport through the structure to extract effective thermal conductivity. The models are verified by comparing calculated bulk data to published aerogel literature. Preliminary models yield thermal conductivity on the order of 0.010 W/m*K, which is consistent with published data for aerogel films. These values vary inversely with porosity of the aerogel following an inverse power law often used to fit aerogel experimental data. This methodology is most useful for examining the sensitivity of thermal conductivity to salient structural features such as porosity, pore size distribution, solid thermal properties, average branch width, and sub-continuum phenomena. The results of this study can be used as a predictive tool in optimizing aerogel fabrication process to yield morphologies that best-suit the requirements of the application.
Self-Heating Modeling of Magnetic Recording Read Head
Authors: Yang Y. , Baril L. , Schreck E. , Wallash A. , Asheghi M.
Published: April 2009

The performance and reliability of the GMR heads are adversely affected by self-heating due to the aggressive scaling of its dimensions to increase areal density. In this manuscript, the self-heating of the GMR head during the normal operation is investigated. An analytical model is developed to estimate the temperature rise in the GMR sensor due to self-heating for magnetic recording areal densities from 2.8 to 80 Gbits/in2, which agrees well with the FEM simulations. This model is subsequently used to investigate the influence of the GMR head constituent materials’ thermal properties on the device temperature rise. A 3-D finite element analysis was also performed to predict the level of self-heating in lead-overlaid (LOL) design, which agrees well with the experimental data obtained using steady-state and transient measurements.   This paper was also originally published as part of the Proceedings of the ASME 2005 Pacific Rim Technical Conference and Exhibition on Integration and Packaging of MEMS, NEMS, and Electronic Systems.
Optimization of the Absorption Performance of a Vertical Absorber
Authors: Kim Jungkuk , Cho Keumnam
Published: April 2009

The present study experimentally and numerically investigated the enhancement of absorption performance due to the waviness of falling film in the vertical absorber tube. The momentum, energy and mass diffusion equations were utilized to find out temperature and concentration profiles at both the interface of liquid solution and refrigerant vapor and the wall. Flow visualization was done to find out the wetting characteristics of the falling film. The maximum absorption rate was obtained for the wavy flow using spring as an insert device through both numerical and experimental studies. Based on the numerical and experimental results, the maximum absorption rate was found for the wavy-flow using spring as the insert device. The differences between experimental and analytical results were ranged from 5.8 to 12% when Ref > 100.