bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Study on Turbulent Drag Reduction and Polymer Concentration Distribution With Blowing Polymer Solution From the Channel Wall
Authors: Motozawa Masaaki , Kurosawa Taiki , Xu Hening , Iwamoto Kaoru , Ando Hirotomo , Senda Tetsuya , Kawaguchi Yasuo
Published: March 2011

Experimental study on turbulent drag reduction (DR) and polymer concentration distribution with blowing polymer solution from whole surface of the channel wall was carried out. A set of measurements for drag reduction were performed with blowing rate for the sintered porous metal plate (0.45m × 0.45m × 3) adjusted from 0.5 L/min to 4.0 L/min, and concentration of polymer solution varied from 10 ppm to 200 ppm. Reynolds number based on the channel height was chosen for 20000 and 40000 in this experiment. The polymer concentration distribution in the near-wall region (0.5 mm < y < 20 mm) at three locations of the downstream from the leading edge of the blower wall was also measured. Polymer concentration can be analyzed via Total Organic Carbon (TOC) analyzer. Through the analysis of mass transfer by polymer concentration distribution, we found that polymer which exists in buffer layer (10 < y+ < 70) has important influence on drag reduction.
The Effect of Surface Structure on Microwave Heating
Authors: Akahori Masatoshi , Aoki Kazuo , Taniguchi Shinya
Published: March 2011

In microwave heating, interference of transmission wave and reflection wave in a sample has an important meaning. We focus on the high performance of the heating efficiency due to changing the surface structure of the sample. Using the microwave of TE10 mode and frequency of 2.45GHz in rectangular waveguide, we have investigated the effect of the surface structure of the material on the characteristics of microwave heating, and have indicated the guideline for the optimization of microwave heating by controlling reflected and transmitted waves. It was found that the rectangle surface structure was effective for the high performance of the heating efficiency, by considering the relationship between the mode and the surface structure.
Growth of Single-Walled Carbon Nanotubes at Low Temperature and Low Pressure CVD Conditions
Authors: Chiashi Shohei , Inoue Taiki , Okabe Hiroto , Shiomi Junichiro , Maruyama Shigeo
Published: March 2011

Controlling the detailed structures of single-walled carbon nanotubes (SWNTs) is imperative for realizing many SWNT applications, and understanding the SWNT growth mechanism is important to improve the growth techniques. In the present study, we performed SWNT growth by a catalytic chemical vapor deposition (CVD) method in wide temperature and pressure ranges, using a high-vacuum CVD chamber. We focused on low CVD gas pressure and low temperature conditions and investigated the SWNT growth mechanism. SWNTs were synthesized by using ethanol gas as the carbon source. As the catalyst, Co and Mo metal nano-particles deposited onto silicon substrates were used. SWNTs were grown via the reaction between ethanol gas and the catalytic metal nano-particles at high temperature. The ethanol gas pressure ranged from 10−3 Pa to 102 Pa, and the CVD temperature ranged from 400 to 900 °C. The yield of SWNTs was assumed to be proportional to the G-band intensity, which was measured by Raman scattering spectroscopy. SWNT samples were observed by scanning electron microscopy and transmission electron microscopy. An optimum CVD temperature existed for each ethanol gas pressure, and decreased with decreasing ethanol gas pressure. Moreover, SWNTs were grown even at 500 °C, when the ethanol gas pressure was low (less than 10−2 Pa). In this study, the minimum temperature and pressure at which SWNTs could be grown were 450 °C and 10−3 Pa. At low temperature and low CVD gas pressure, the activity of the catalyst and the growth rate of SWNTs were low, while the catalyst lifetime was long.
Heat Transfer Performance of Finless Flat Tube Heat Exchanger With Vortex Generator
Authors: Onishi Hajime , Yonekura Haruka , Tada Yukio , Takimoto Akira
Published: March 2011

As the longitudinal vortex is known to be effective in enhancing heat transfer, a three-dimensional unsteady numerical analysis has been made especially for the flow and thermal fields in a unit element of flat tube heat exchanger with vortex generator (VG) in so-called middle Reynolds number range. Both staggered and in-lined arrangements of the tubes with VG are considered and results obtained from the case with VG are compared with those without VG. The study was aimed at the influence of Reynolds number and some geometrical parameters on the heat transfer and the pressure drop. Moreover, as little research has been considered the interaction between transverse vortices and longitudinal vortices in the literatures, the effect is also investigated. It is found that the longitudinal vortex plays an important role in enhancing the local heat transfer by exchanging the fluid from the tube surface region to the fresh fluid of the main flow region and lasts over long distances. Moreover, the longitudinal vortices restrain unsteady transverse vortex shedding. As a result, heat transfer rate for the flat tube with VG case is larger compared to that without VG case. From the view point of pressure drop, increase in pressure drop for the case with VG is not so much larger due to the restraint of transverse vortex shedding. Finally, heat transfer performance becomes higher for the flat tube with VG case compared to that without VG case for the same pumping power.
Numerical Study of Air Forced Convection in a Rectangular Channel Provided With Ribs
Authors: Manca O. , Nardini S. , Ricci D.
Published: March 2011

Heat transfer enhancement technology has the aim to develop more efficient systems as demanded in many applications, like heat exchangers for refrigeration, automotives, process industry, solar heater etc.. Convective heat transfer may be enhanced passively by adopting different solutions. A possibility for increasing the heat transfer is to employ rough surfaces. When a fluid flows in a channel, ribs break the laminar sub-layer and create local turbulence, due to flow separation and reattachment between consecutive ribs, which reduce thermal resistance and augment heat transfer. This behaviour overcomes the effect linked to the increased heat transfer area due to the ribs. However, higher friction losses are expected and turbulence must be created only in the region very close to the heat transferring surface and the core flow should not be unduly disturbed. In this paper a numerical investigation is carried out on air forced convection in a rectangular channel with constant heat flux applied on the bottom and upper external walls. Properties of fluid are considered temperature-dependent and flow regime is turbulent. The investigation is accomplished by means of the commercial code Fluent. A three-dimensional model is developed in order to study the effect of the angle between the fluid flow direction and the ribbed surfaces. In fact, secondary turbulence is promoted in the orthogonal direction to the channel longitudinal axis. Three different inclination angles of the ribbed surfaces have been considered and the channel is provided with rectangular ribs. Simulations have shown that Nusselt numbers as well as the pressure drops increase as the inclination angles increase.
Thermal Conductivity of Nano-Porous Bismuth Antimony Telluride
Authors: Tanaka Saburo , Takashiri Masayuki , Miyazaki Koji
Published: March 2011

Bismuth antimony telluride (Bi0.4Te3.0Sb1.6) nano-porous thin films have been prepared and measured their thermal conductivities. The thin films exhibit an average grain size of 50 nm and random crystal orientation. The cross-plane thermal conductivity is measured by a differential 3ω method at temperature range from 100 to 300 K, and the determined thermal conductivities are from 0.09 to 0.18 W/(m·K). As compared with bulk alloys at the same atomic composition, the nano-porous thin films exhibit an eightfold reduction in the thermal conductivity. For more detail analysis, the reduction of the thermal conductivity is examined by a simplified phonon gas model on a single crystal of bulk Bi2Te3. The analytical model fairly agreed with the experimental results, and thus we consider that the thermal conductivity is reduced by the strong phonon scattering at the nano-pores.
CFD Modeling of Environmental System Options Used for Cooling of Telecommunication Shelters
Authors: Muralidharan Bharathkrishnan , Iqbal Mariam Feroz Ahamed , Menon Abhilash Ramachandran , Mynampati Venkata Naga Poornima , Agonafer Dereje , Hendrix Mark
Published: March 2011

Telecommunication shelters form an important component at different levels of the wireless access network. They are commonly used as transmission hubs and base transceiver stations. The telecom shelter protects wireless transmitters and receiver electronics in the wireless network. They are stand-alone, modular structures that are supported with their own electrical and HVAC systems. Based on their locations they are designed to work over a wide range of environmental conditions with temperatures ranging from −40°C to 55°C and may be exposed to high humidity, and saline and corrosive environments. Cooling/heating systems typically consume 30% of the energy required to operate a wireless cell site. There is, therefore, an impetus to embark on initiatives to reduce this percentage as part of an effort to both save money, and to reduce the carbon footprint. In this paper various thermal design options to cut down on cooling/heating energy loads for these shelters are discussed. The effect of substituting active cooling/heating equipments used in shelter with a hybrid one. The hybrid cooling system consists of both the air conditioner and a blower. CFD analysis is performed to compare these designs and come up with a robust design solution. The best cooling methodology showed an energy saving of 40% with minimal impact on design temperature.
Formation of a Counter-Rotating Vortex Pair in a Plume in a Cross-Flow
Authors: Shinohara Masahiko
Published: March 2011

Numerical simulations are performed to study the formation of a counter-rotating vortex pair (CVP), a dominant flow feature in plumes inclined in a cross-flow. The unsteady three-dimensional flow fields are calculated by a finite difference method using the Boussinesq approximation. A plume rises from an isothermally heated square surface facing upward in air. Calculations show that the CVP originates not from horizontal spanwise vorticity in the velocity boundary layer on the bottom wall around the heated area, but from horizontal streamwise vorticity just above each side of the heated area. When the cross-flow begins after a plume forms a vortex ring in the cap above the heated area in a still environment, the vortex ring does not form a CVP. However, as the cap and the stem of the plume move downwind, a rotation about the streamwise axis appears just above each side edge of the heated area and grows into the CVP. We discuss the effect of entrainment into the stem and cap on the formation of the streamwise rotation that causes the CVP.
Enhancement of Heat Transfer With Pool and Spray Impingement Boiling on Microporous and Nanowire Surface Coatings
Authors: Thiagarajan Suraj Joottu , Narumanchi Sreekant , King Charles , Wang Wei , Yang Ronggui
Published: March 2011

The National Renewable Energy Laboratory (NREL) is leading a national effort to develop next-generation cooling technologies for hybrid vehicle electronics, as part of the Advanced Power Electronics and Electrical Machines program area in the U.S. Department of Energy’s (DOE’s) Vehicle Technologies Program. The overarching goal is to reduce the size, weight, and cost of power electronic modules that convert direct current from the batteries to alternating current for the motor, and vice versa. Aggressive thermal management techniques help in achieving the goals of increased power density and reduced weight and volume, while keeping the chip temperatures within acceptable limits. The viability of aggressive cooling schemes such as spray and jet impingement in conjunction with enhanced surfaces is being explored as part of the program. In this work, we present results from a series of experiments with pool and spray boiling on enhanced surfaces, such as a microporous layer of copper and copper nanowires, using HFE-7100 as the working fluid. Spray impingement on the microporous coated surface showed an enhancement of 100%–300% in the heat transfer coefficient at a given wall superheat with respect to spray impingement on a plain surface under similar operating conditions. The critical heat flux also increased by 7%–20%, depending on the flow rates. Heat transfer coefficients obtained on the nanowire-grown surface are considerably better than those obtained on the plain surface, although the enhancement is lower than those obtained on the microporous surface. The critical heat flux is also considerably lower for the nanowire surface than for the plain surface.
Thermal Conductivity Measurement of Graphene Exfoliated on Silicon Dioxide
Authors: Seol Jae Hun , Moore Arden L. , Jo Insun , Yao Zhen , Shi Li
Published: March 2011

Since graphene was first exfoliated from graphite, the monatomic layer of carbon atoms has attracted great interest for fundamental studies of unique two dimensional transport phenomena. Meanwhile, graphene is being explored for nanoelectronic applications because of the superior electron mobility and mechanical strength as well as compatibility with existing planar silicon-based microelectronics. The ultrahigh thermal conductivity suggested recently for suspended graphene is another attractive feature that may potentially address the increasingly severe heat dissipation problems in nanoelectronic devices. However, little is known about thermal transport properties of supported graphene that is used in most graphene device configurations. To better understand thermal transport in supported graphene, we have developed a device to measure the thermal conductivity of graphene exfoliated on a silicon dioxide beam. The obtained peak thermal conductivity is about 600 W/m-K near room temperature. This value is lower than the basal plane values for graphite and suspended graphene, but still considerably higher than common electronic materials. The measurement results at low temperatures further reveal intriguing low dimensional behaviors. Here, we present a detailed analytical and numerical heat transfer analysis of the thermal measurement method.
Numerical Study of 3D Nonlinear Disturbance Growth in Transitional Natural Convection
Authors: Aberra Tilek , Armfield Steven W. , Behnia Masud , Maruyama Shigenao , Komiya Atsuki
Published: March 2011

Three dimensional boundary layer disturbance growth in natural convection adjacent to a uniformly heated vertical plate has been studied using a finite volume direct numerical simulation (DNS). The sequence of events associated with the intermediate stage of the spatial laminar-turbulent-transition for water, with Prandtl number Pr = 6.7, for the Rayleigh numbers in the range Rax ≈ 1 × 1010 – 4 × 1013, with perturbation parameters closely matching the experiment reported in [1], is investigated. Preliminary calculations confirm that this stage is characterized by the development of spatially periodic inner and outer span-wise vortices (shear layers), which travel in a differing fashion and speed; and a secondary mean flow system. The important route to natural convection flow breakdown, the arising of a double vortex mean longitudinal system, repeatedly suggested by past experiments, seems to be related to the complex and opposing behavior of these two layers.
Effect of Nano-Structured Surface on Meniscus Evaporation at Nanoscale
Authors: Maroo Shalabh C. , Chung J. N.
Published: March 2011

Evaporation of a nanoscale meniscus on a nano-structured heater surface is simulated using molecular dynamics. The nanostructures are evenly spaced on the surface and rectangular-shaped with a length and height of 0.41 nm and 0.96 nm respectively, and stretching throughout the width of the domain. The simulation results show that the film breaks during the early stages of evaporation due to the presence of nanostructures and no non-evaporating film forms (unlike a previous simulation performed in absence of nanostructures where non-evaporating film forms on the smooth surface). High heat transfer and evaporation rates are obtained. We conclude that heat transfer rates can be significantly increased during bubble nucleation and growth by the presence of nanostructures on the surface as it breaks the formation of non-evaporating film. This will cause additional chaos and allow the surrounding cooler liquid to come in contact with the surface enhancing heat transfer coefficients.
Thermal Anisotropy in Injection Molded Polymer Composite Fins
Authors: Bar-Cohen Avram , Luckow Patrick , Cevallos Juan G. , Gupta S. K.
Published: March 2011

An integrated molding-heat transfer modeling methodology is used to study the thermal characteristics of polymer composite fins subjected to convective heat transfer coefficients. Numerical predictions of the fiber orientation in a representative, injection-molded plate fin, based on the Folgar-Tucker model, are used, via the classic Nielsen model, to determine the anisotropic variation of thermal conductivity in the fin. Thermal simulations are then performed to determine the effect of both global and local thermal anisotropy on the temperature distribution and heat transfer rate of the anisotropic fin. It is also shown that the harmonic mean conductivity, in the axial direction, can be used to represent the heat loss of an anisotropic fin to better than 10% accuracy.
Thermoelectric Self-Cooling on Germanium Chip
Authors: Wang Peng , Bar-Cohen Avram
Published: March 2011

Growing interest in germanium solid-state devices is raising concern over the effects of on-chip, micro-scaled, high flux hot spot on the reliability and performance of germanium chips. Current thermal management technology offers few choices for such on-chip hot spot remediation. However, the good thermo-electric properties of single crystal germanium support the development of a novel thermal management approach, relying on thermoelectric self-cooling by an electric current flowing in a thin planar layer on the back of the germanium chip. Use of metal-on-germanium fabrication techniques can yield a very low thermal contact resistance at the micro cooler/chip interface and the current flow can transfer the energy absorbed from a hot spot to the edge of the chip, thus substantially reducing the detrimental effect of thermoelectric heating on the temperature of the active circuitry. In this paper three-dimensional thermo-electric simulations are used to investigate the self-cooling of hot spots on a germanium chip for a wide range of input current, doping concentration, hot spot heat flux, micro cooler size, and germanium chip thickness. Results suggest that localized thermoelectric self-cooling on the germanium chip can significantly reduce the temperature rise resulting from micro-scaled high-flux hot spots.
Analysis of Transient Conjugate Heat Transfer From a Hemispherical Plate During Liquid Jet Impingement
Authors: Rahman Muhammad M. , Hernandez Cesar F.
Published: March 2011

Transient heating of a hemispherical solid plate of finite thickness during impingement of a free liquid jet is studied. A constant heat flux is imposed at the inner surface of the hemispherical plate at t = 0 and heat transfer is monitored for the entire duration of the transient until a steady state condition is reached. Calculations are done for Re = 500–1500 and b/dn = 0.083–1.5 using water (H2O) as the coolant and various solid materials such as silicon, Constantan, and copper. It was found that the time for the plate to achieve the steady-state condition decreases and Nusselt number increases with Reynolds number. A plate material with higher thickness provides higher average Nusselt number and longer transient period.
Interactions of Porosity-Magnetic Field and Viscous Dissipation in an Inclined Channel Type Flow
Authors: Havzali Murat , Komurgoz Guven , Arikoglu Aytac , Keser Haci Ibrahim , Ozkol Ibrahim
Published: March 2011

In this work, entropy generation due to laminar viscous incompressible flow of a conducting fluid in the presence of a transverse magnetic field in a porous inclined channel is investigated. Fully developed flow field is solved analytically whereas the solution of the energy equation is obtained by Finite Difference Method (FDM). The boundary conditions at the walls are considered to be constant heat flux. The influence of the applied magnetic field, porous medium and the viscous dissipation on velocity, temperature and entropy generation is examined. The dependence of flow and thermal characteristics on Peclet number (Pe), Brinkman number (Br), Darcy number (Da) and Hartman number (Ha) is analyzed through velocity and temperature distribution as well as Entropy generation number (Ns) and Bejan Number (Be) profiles.
An Exploration of the Effects of Dissolved Ionic Solids on Bubble Merging in Water and Its Impact on the Leidenfrost Transition
Authors: Gan Yu , Carey Van P.
Published: March 2011

Theoretical models and MD simulation studies suggest that dissolved salts tend to alter the surface tension at liquid vapor interfaces and affect the stability of the free liquid film between adjacent bubbles. Recent modeling of the Leidenfrost phenomenon also indicates that bubble merging is a key mechanism affecting the Leidenfrost transition conditions. This investigation summarizes the results of an investigation of the effects of dissolved salts on liquid film stability and bubble merging in the aqueous solution. The interaction of pairs of bubbles injected into solution with different dissolved salt concentrations was studied experimentally to determine the probability of merging from statistics for ensembles of bubble pairs. The results of these experiments indicate that very low dissolved salt concentrations can strongly reduce the tendency of adjacent bubbles to merge, implying that the presence of the dissolved salt in such cases strongly enhances the stability of the free liquid film between adjacent bubbles. The trends are compared to predictions of free liquid film stability by wave instability theory and MD simulations. These trends are also compared to experimental data indicating the effects of dissolved salt on the Leidenfrost transition. These comparisons indicate that the suppression of merging due to the effects of some dissolved salts can significantly alter the Leidenfrost transition conditions. The implications of this in quenching of cast aluminum or steel parts using water of variable hardness are also discussed.
Pressure Drop and Two Phase Flow During Boiling of FC-72 in a High Aspect Ratio Micro-Channel
Authors: Wang Yuan , Sefiane Khellil , Bennacer Rachid
Published: March 2011

Liquid-vapour interface behaviours and the pressure drop fluctuation during flow boiling in a single rectangular micro-channel with high aspect ratio were experimentally investigated in the present study. A micro-channel with the hydraulic diameter of 727 μm was chosen, the aspect ratio of which was 10. FC-72 was used as the working liquid. Wide ranges of mass fluxes and heat fluxes were tested to study bubble dynamics and hydraulic instabilities during flow boiling. With the aid of high speed camera, various liquid-vapour interface behaviours during flow boiling were captured, such as bubble nucleation and growth, interface deformation, recoiling and rewetting. Based on the interface movement, the evaporation rate of the liquid was discussed. Evaporation rates of bubble nose and bubble tail at different mass fluxes and heat fluxes were compared. Besides, the effects of thermal and flow conditions on bubble geometry were discussed. Moreover, the pressure fluctuations resulting from boiling instabilities was remarkable. Fluctuation frequency was largely affected by the heat and mass fluxes.
Some Experimental Results of Free Convection From Horizontal Heated Wires Below Atmospheric Pressure
Authors: Milano Guido
Published: March 2011

The cooling of horizontal wires by natural convection of air is investigated. Experiments are carried out with the use of an apparatus designed for thermal testing of electric cables for aerospace vehicles. Two wire diameters are considered: D = 0.155 mm and 0.593 mm with a length of about 2.45 m. Air pressure is varied from the atmospheric value down to 0.4 mbar, to which corresponds a Knudsen number ranging from 2·10−4 up to 2 while the Rayleigh number covers ten order of magnitude, from 10−10 up to 1. On the basis of the value of the Knudsen number, three regimes of heat transfer are identified: free convection in fully continuum fluid regime, the combined free molecule conduction close to the wire surface and free convection in the remaining space and the conductive regime at low pressure, when the rarefied gas is nearly quiescent. An attempt is also made to correlate the heat transfer results in all three regimes.
Heat and Mass Transfer Issues in the Design of Solid State Hydrogen Storage Devices
Authors: Murthy S. Srinivasa
Published: March 2011

Metal hydrides are formed when certain metals or alloys are exposed to hydrogen at favorable temperatures and pressures. In order to sustain the sorption of hydrogen during this exothermic process, the generated heat has to be removed effectively. Release of hydrogen is an endothermic process needing supply of heat to the metal hydride matrix. Depending on the application, the heat transfer medium can be either a liquid or a gas. Reduction of the total weight of hydrogen storage devices is essential towards utilization of hydrogen for mobile and portable applications. While a variety of new storage materials with desirable sorption characteristics are being suggested, optimal thermal design of the storage device remains a major challenge. Lack of thermodynamic, transport and thermophysical property data of the material particles and of the bed is another drawback which needs to be addressed.
History, Advances, and Challenges in Liquid Flow and Flow Boiling Heat Transfer in Microchannels: A Critical Review
Authors: Kandlikar Satish G.
Published: March 2011

As the scale of devices becomes small, thermal control and heat dissipation from these devices can be effectively accomplished through the implementation of microchannel passages. The small passages provide a high surface area to volume ratio that enables higher heat transfer rates. High performance microchannel heat exchangers are also attractive in applications where space and/or weight constraints dictate the size of a heat exchanger or where performance enhancement is desired. This survey article provides a historical perspective of the progress made in understanding the underlying mechanisms in single-phase liquid flow and two-phase flow boiling processes and their use in high heat flux removal applications. Future research directions for (i) further enhancing the single-phase heat transfer performance, and (ii) enabling practical implementation of flow boiling in microchannel heat exchangers, are outlined.
Eddie Leonardi Memorial Lecture: Natural Convection from Earth to Space
Authors: Timchenko Victoria
Published: March 2011

This lecture is dedicated to the memory of Professor Eddie Leonardi, formerly International Heat Transfer Conference (IHTC-13) Secretary, who tragically died at an early age on December 14, 2008. Eddie Leonardi had a large range of research interests: he worked in both computational fluid dynamics/heat transfer and refrigeration and air-conditioning for over 25 years. However starting from his PhD ‘A numerical Study of the effects of fluid properties on Natural Convection’ awarded in 1984, one of his main passions has been natural convection and therefore the focus of this lecture will be on what Eddie Leonardi has achieved in numerical and experimental investigations of laminar natural convective flows. A number of examples will be presented which illustrate important difficulties of numerical calculations and experimental comparisons. Eddie Leonardi demonstrated that variable properties have important effects and significant differences occur when different fluids are used, so that non-dimensionalisation is not an appropriate tool when dealing with fluids in thermally driven flows in which there are significant changes in transport properties. Difficulties in comparing numerical solutions with either numerically generated data or experimental results will be discussed with reference to two-dimensional natural convection and three-dimensional Rayleigh-Be´nard convection in bounded domains with conducting boundaries. For a number of years Eddie Leonardi was involved in a joint US-French-Australian research program — the MEPHISTO experiment on crystal growth — and studied the effects of convection on solidification and melting under microgravity conditions. The results of this research will be described. Finally, results of experimental and numerical studies of natural convection for Building Integrated Photovoltaic (BIPV) applications in which Eddie Leonardi had been working in the last few years will also be presented.
Heat Transfer Generated by the Interaction of Single and Multiple Tandem Jets in Crossflow
Authors: Radhouane Amina , Mahjoub Nejla , Mhiri Hatem , Lepalec George , Bournot Philippe
Published: March 2011

“Twin jets in Crossflow” is a common configuration that finds application in several large and/or small scale industrial fields. The interest in such a configuration is further enhanced by its dependence in several parameters, that may be geometric, dynamic, thermal, or relative to the handled fluid composition. We propose to focus in the present work on the effect of the number of the emitted jets on the generated heat transfer, in presence of an unchanged uniform crossflow. To reach this goal, single, double and triple jet configurations were simulated, based upon the resolution of the Navier Stokes equations by means of the RSM (Reynolds Stress Model) second order turbulent closure model, together with a non uniform grid system particularly tightened near the emitting nozzles. After validation, we tried to find out the impact of the number of the handled jets on their cooling “power” by tracking the temperature distribution of the resulting flowfield. Since in practically all applications we are in need of higher efficiencies and then of higher operating temperatures, we are constantly concerned about not going beyond the shielding material melting temperature. If the use of cooling jets proves to be efficient, this may bring a significant progress in the technological field.
Inundation Effect and Its Elimination in Shell and Tube Condenser
Authors: Ma Zhixian , Zhang Jili , Sun Dexing
Published: March 2011

Inundation effect, decrease of condensation heat transfer coefficient (CHTC) induced by both falling condensate from the neighboring tubes above and condensing condensate form the vapor, significantly affects the CHTC of tube bundles composed of smooth and enhanced tubes. This paper experimentally studied the inundation effect of smooth tube and three kinds of enhanced tubes (3D-A, 3D-B and 2D-A), put forward a scheme to eliminate the inundation effect caused by falling condensate and check it by experimental investigation. HFC134a and HFC245fa (substitutes of CFC12 and CFC11, respectively) were condensed in the experiment. Nominal diameter and active length of each test tube is 19.05mm and 500mm, respectively. Diversion ducts were fixed into the test tube bundle to eliminate tube row effect (part of the inundation effect caused by the falling condensate). Drainage strip was equipped on the test tubes to abate the inundation effect induced by condensed condensate. The (These) experimental results show: (1) Inundation effect of HFC 134a and HFC245fa on smooth tube bundle is not as severe as that predicted by Kern’s model. (2) 3D-B enhanced tube is dramatically affected by the inundation effect caused by falling condensate; (3) The equipped diversion ducts can eliminate tube row effect and improve the CHTC of tube bundles composed of smooth and 3D-B tubes. (4) The equipped drainage strip can further enhance the CHTC of 3D-A and 2D-A tubes in the tube bundle.
Quantitative Study on Model and Basic Concepts of Thermodynamic System
Authors: Wang Zhiguo , Yang Wenzhe , Song Yongchen
Published: March 2011

Drawing on relevant theories, a quantitative study on model and basic concepts for thermodynamic system has been conducted. It Includes following concepts: thermodynamic system (system interior, system border and system outside), the border (border wall and border gate), the open degree (not only the function of space and time, but also related to energy, quality and information), the exchange rate (including quality, energy and information exchange rate; and it is a composite function, correlated to the opening degree of border, the state inside the system, time and space and so on). Accordingly, the relationship between the opening degree and the exchange rate of system has been analyzed, and the system stability (opening degree) criterion is derived.
Computational Heat Transfer in Complex Systems: A Review of Needs and Opportunities
Authors: Murthy Jayathi Y.
Published: March 2011

During the few decades, computational techniques for simulating heat transfer in complex industrial systems have reached maturity. Combined with increasingly sophisticated modeling of turbulence, chemistry, radiation, phase change and other physics, powerful computational fluid dynamics (CFD) and computational heat transfer (CHT) solvers have been developed which are beginning to enter the industrial design cycle. In this paper, an overview of emerging simulation needs is first given, and currently-available CFD techniques are evaluated in light of these needs. Emerging computational methods which address some of the failings of current techniques are then reviewed. New research opportunities for computational heat transfer, such as in sub-micron and multiscale heat transport, are reviewed. As computational techniques and physical models become mature, there is increasing demand for predictive simulation, that is, simulation which is not only verified and validated, but whose uncertainty is also quantified. Current work in the area of sensitivity computation and uncertainty propagation is described.
The Finite Element Method for Microchannel Flow and Heat Transfer Calculations
Authors: Nithiarasu Perumal
Published: March 2011

In this paper, the finite element method for modelling of microchannel flow and heat transfer is discussed. The situations that need unstructured mesh technology are highlighted in addition to the flexible nature of the finite element method for problems with the need for adaptive refinement. Many of these aspects are demonstrated by solving flow and heat transfer through microchannels. Both mechanically driven and electrokinetically driven single phase flows in microchannels are considered. A brief discussion is provided on enhancement methods in which the finite element modelling can help. Only a selection of results are presented in this paper. More results will be presented during the conference.
Current and Future Needs in Electric Drive Vehicle Batteries
Authors: Pesaran Ahmad A.
Published: March 2011

Batteries are considered to be a critical component for making future transportation more energy-efficient and less dependent on petroleum through hybrid, plug-in hybrid, electric, and fuel cell vehicles. In this paper, the current status of batteries for electric drive vehicle applications will be discussed. Special attention will be given to the thermal issues associated with batteries in vehicle environment. We will also discuss future needs of batteries for further development.
Optimization of the Fin-and-Tube Heat Exchanger Design for Non-Standard Applications
Authors: Orozaliev Janybek , Budig Christian , Vajen Klaus
Published: March 2011

This paper describes an optimization procedure of the heat exchanger design, which is based on cost effectiveness. In the procedure, a genetic optimization algorithm varies the heat exchanger geometry and operating conditions. The influence of the heat exchanger design on its costs, heat transfer and friction performance has been evaluated economically by determining investment and operation costs of the system. For this purpose, a specific approach for setting up of cost functions of the heat exchanger, fans and pumps is presented as well. It has been shown on a non-standard application, that the heat transfer costs of the optimized heat exchanger design is 30% lower than that of the reference configuration, which was designed by a heat exchanger producer.
Prediction of Temperature Distribution in a Food Self-Heating System
Authors: Ho Son H. , Rahman Muhammad M. , Sunol Aydin K.
Published: March 2011

This paper presents a numerical modeling and simulation of heat transfer in a food self-heating unit for group meals. A model of a water-activated heater based on an exothermic reaction was developed. The resulting governing equations of heat conduction and chemical reaction were solved for an analytical approximate solution, to which experimental data found from literature were compared and curve fitted. Then a model of a complete food-heating unit, which includes a stack of four sets of food tray, heating tray, and heater sandwiched between them, as well as the cardboard container, was developed. A system of governing equations for heat transfer in the composite medium for the complete model was solved. Numerical solution of temperature distribution within the food-heating unit is presented. The responses in thermal performance of the heating system to the parameters that influence heating profiles of the heater such as decay constant and heat generation were studied in order to improve the thermal performance of the heating system. The results are useful for designing and optimizing self-heating systems for food served to groups of many people.
Turbulent Natural Convection Inside a Square Enclosure With Baffles
Authors: Mushatet Khudheyer S.
Published: March 2011

In this paper, the turbulent natural convection heat transfer and fluid flow inside a square enclosure having two conducting solid baffles has been numerically investigated. Fully elliptic Navier-Stockes and energy equations are disrectized using finite volume method along with a staggered grid techniques. The resulting algebraic equations were solved by using semi-implicit line by line Guase elimination scheme. The effect of turbulence was incorporated to treat the regions near the walls. The flow and thermal fields are investigated for different parameters such as the relative baffles height, Rayleigh number and the distance between baffles. The conducted results indicated that the resulting vortices are decreased in number and elongated with the decrease of the dimensionless relative baffle heights. Also the results show that the rate of heat transfer is increased with the increase of Ra especially for the region near the baffles.
Influence of Force Fields and Flow Patterns on Boiling Heat Transfer Performance
Authors: Di Marco Paolo
Published: March 2011

Recent experimentation of boiling in different environments, namely in reduced or enhanced gravity and/or in the presence of electric fields, have shed new light on the comprehension of boiling phenomena and have focused the objectives of future investigation. The recent results achieved by the author and other research groups around the world are reported and discussed in the paper. After a short introduction on some fundamental phenomena and their dependence on force fields, pool and flow boiling are dealt with. In particular, it is stressed that due to increased coalescence peculiar flow regimes take place in reduced gravity, influencing the heat transfer performance. The application of an electric field may, in some instances, delay or avoid these regime transitions. In boiling at high flowrate, the phenomena are dominated by inertia and thus gravity-independent; however the threshold at which this occurs has still to be determined.
Improved Pyroelectric Energy Converter for Waste Heat Energy Harvesting Using Co-Polymer P(VDF-TrFE) and Olsen Cycle
Authors: Nguyen Hiep , Navid Ashcon , Pilon Laurent
Published: March 2011

This study is concerned with pyroelectric energy conversion to directly convert waste heat into electricity. The pyroelectric effect refers to the flow of charges to or from the surface of a material upon heating or cooling. A prototypical pyroelectric energy converter was designed, built, and tested. It performed the Olsen cycle consisting of two isothermal and two isovoltage processes in the charge-voltage diagram. Co-polymer poly(vinylidene fluoride-trifluoroethylene) [P(VDF-TrFE)] thin films sandwiched between metallic electrodes were used as the pyroelectric elements. Their temperature oscillation, charge, and voltage along with the overall heat input and output were measured experimentally. Then, the electrical power generated and the energy efficiency of the device were computed. The effects of channel width, frequency, and stroke length on temperature swing, heat input, and energy and power densities were investigated. Reducing the channel width and increasing the stroke length had the largest effect on device performance. A maximum energy density of 130 J/L of P(VDF-TrFE) was achieved at 0.061 Hz frequency with temperature oscillating between 69.3 and 87.6°C. Furthermore, a maximum power density of 10.7 W/L of P(VDF-TrFE) was obtained at 0.12 Hz between 70.5 and 85.3°C. In both cases, the voltages in the Olsen cycle were 923 and 1732 V imposed on a 45.7 microns thick 60/40 P(VDF-TrFE) films. To the best of our knowledge, this is the largest energy density achieved by any pyroelectric energy converter using P(VDF-TrFE). It also matches performances reported in the literature for more expensive lead zirconate stannum titanate ceramic films operated at higher temperatures between 110 and 185°C.
Experimental Investigation of Silicon-Based Oblique Finned Microchannel Heat Sinks
Authors: Lee Yong-Jiun , Lee Poh-Seng , Chou Siaw-Kiang
Published: March 2011

Sectional oblique fins are employed in contrast to the continuous fins in order to modulate the flow in microchannel heat sink. Experimental investigation of silicon based oblique finned microchannel heat sink demonstrated a highly augmented and uniform heat transfer performance against the conventional microchannel. The breakage of continuous fin into oblique sections leads to the re-initialization of the thermal boundary layers at the leading edge of each oblique fin, effectively reducing the boundary-layer thickness. This regeneration of the entrance effect causes the flow to be always in a developing state thus resulting in better heat transfer. In addition, the presence of smaller oblique channels diverts a fraction of the flow into the adjacent main channels. The secondary flows thus created improve fluid mixing which serves to further enhance the heat transfer. The average Nusselt number, Nuave, for the silicon microchannel heat sink which uses water as the working fluid can increase as much as 55%, from 8.8 to 13.6. Besides, the augmented convective heat transfer leads to reduction in both maximum chip temperature and its temperature gradient, by 8.6°C and 47% respectively. Interestingly, there is only little or negligible pressure drop penalty associated with this novel heat transfer enhancement scheme in contrast to conventional enhancement techniques.
Dry-Out CHF Characteristics of R134a Flow Boiling in a Horizontal Helically-Coiled Tube
Authors: Chen Chang-Nian , Han Ji-Tian , Shao Li , Jen Tien-Chien
Published: March 2011

An experimental study was carried out to investigate the dry-out critical heat flux (CHF) characteristics of R134a flow boiling in a horizontal helically-coiled tube. The test section was heated uniformly by DC high-power sources and the geometrical parameters are the outer diameter of 10 mm, inner diameter of 8.4 mm, coil diameter of 300 mm, helical pitch of 75 mm and valid heated length of 1.89 m. The experimental conditions are the outlet pressures of 0.30–0.95 MPa, mass fluxes of 60–500 kg/m2s, inlet qualities of −0.36–0.35 and heat fluxes of 7–50 kW/m2. In total of sixty-eight 0.2 mm T-type thermocouples were set along the tube to measure wall temperatures exactly. A method based on the event-driven Agilent BenchLink Data Logger Pro software was developed to determine the occurrence of CHF. It was found that the wall temperatures jumped abruptly once the CHF occurred. The CHF usually starts to form at the front and offside (270° and 90°) of the sections near outlet. The CHF value increases largely with increasing mass flux and decreases slightly with increasing pressure. It decreases nearly linearly with increasing inlet qualities, while it decreases acutely with increasing critical qualities under larger mass flux conditions. An experimental correlation was developed to estimate dry-out CHF of R134a flow boiling in horizontal helically-coiled tubes under current conditions compared with the calculated results of Bowring and Shah correlations.
Atomic ordering and phase separation in MBE GaAs1−xBix
Authors: Norman Andrew G. , France Ryan , Ptak Aaron J.
Published: March 2011

Transmission electron microscopy studies of GaAs1−xBix layers grown at low temperature by molecular beam epitaxy have revealed evidence of both atomic ordering and phase separation. In layers containing up to ∼10% Bi, the two variants of CuPtB-type atomic ordering on {111}B planes were observed and this is believed to be associated with the surface reconstruction present during growth. In a sample containing ∼13% Bi, no atomic ordering was observed but instead an anisotropic platelike structure was present that is believed to result from phase separation, possibly associated with the surface segregation of excess Bi during growth. Both of these effects are expected to have significant effects on the electrical and optical properties of the material.
High-quality global hydrogen silsequioxane contact planarization for nanoimprint lithography
Authors: Büyükköse Serkan , Vratzov Boris , van der Wiel Wilfred G.
Published: March 2011

The authors present a novel global contact planarization technique based on the spin-on-glass material hydrogen silsequioxane (HSQ) and demonstrate its excellent performance on patterns of 70 nm up to several microns generated by UV-based nanoimprint lithography. The HSQ layer (∼165 nm) is spin coated on the imprinted organic layer and planarized by pressing it with a flat wafer at room temperature. Before retracting the planarization wafer, the HSQ is hardened by baking at 120 or 70 °C, depending on the underlying material. Fluorine-based reactive ion etching (RIE) is used to etch the HSQ (etch-back) down to the top of the features in the organic imprint layer. Subsequently, oxygen-based RIE is used to etch the organic imprint layer in the exposed regions, thereby transferring the imprinted pattern down to the substrate. The etch selectivity between the HSQ and the underlying layers is found to be more than 1:100, enabling very accurate pattern transfer with excellent critical dimension control and well-defined undercut profile suitable for further metal liftoff processes. The dependence of the contact planarization quality on the HSQ spinning speed and pressure is investigated, achieving a global planarization degree as good as 93%, an improvement of 45% compared to standard spin-coating planarization.