bluuebunny/crossref_metadata_2025 huggingface dataset:
Flow Visualization of Airflow Through a Rectangular Duct With Combined Heat and Mass Transfer
Authors: Fauchoux M. T. , Simonson C. J. , Torvi D. A.
Published: March 2011

Radiant ceiling panels have been shown to provide good thermal comfort for occupants and reduce energy consumption in large buildings. A disadvantage of radiant panels however, is the inability to alter the relative humidity (RH) of a space, which can also lead to occupant discomfort. A new panel is being developed which will transfer both heat and moisture to a room, to moderate space temperature and RH simultaneously. In order to determine how this panel performs, a test panel has been created and tested in an experimental facility. The panel is situated in the top of a rectangular duct. The surface of the panel is made of a porous membrane, which allows moisture to transfer between the air and the panel. Air passes through the duct and underneath the panel, at low Reynolds numbers (Re). As heat and moisture are transferred between the panel and the air, temperature and concentration gradients form in the duct. If these gradients become large, free convection will occur. Depending on which type of convection is dominant, free or forced, the air will flow in different patterns. In order to understand the performance of the panel, flow visualization is used to determine how the airflow is affected by temperature and concentration gradients. Test conditions include heating, cooling, humidification and dehumidification.
Using Quantum Dots for Liquid-Phase Thermometry at Near-Infrared Wavelengths in Silicon Devices
Authors: Kim Myeongsub , Yoda Minami
Published: March 2011

The need for new thermal management technologies to cool electronic components with their ever-increasing density and power requirements has renewed interest in techniques for measuring liquid-phase coolant temperatures, especially nonintrusive techniques with micron-scale spatial resolution. A variety of optical liquid-phase thermometry techniques exploit the changes in the emission characteristics of fluorescent, phosphorescent or luminescent tracers suspended in a liquid-phase coolant. Such techniques are nonintrusive and have micron-scale spatial resolution, but they also require optical access to both excite and image the emissions. Silicon (Si), the leading material for electronic devices, is opaque at visible wavelengths, but is partially transparent in the near-infrared (IR). To date, the only tracers that emit at near-IR wavelengths with reasonable quantum yield are IR quantum dots (IRQD), colloidal nanocrystals of semiconductor materials such as lead sulfide (PbS). Previous work has shown that the intensity of emissions at 1.55 μm from PbS IRQD suspended in toluene are temperature-sensitive, decreasing by as much as 15% as the temperature increased from 20 °C to 60 °C. The accuracy of temperature measurements using PbS IRQD was estimated to be about 5 °C, based on 95% confidence intervals, where the major limit on the accuracy of the technique was the poor photostability of this material [1]. Recently, a new method for creating a cadmium sulfide (CdS) overcoat layer on PbS “cores” has been developed [2]. The experimental results presented here on the temperature sensitivity of these PbS/CdS core-shell infrared quantum dots with an emission peak around 1.35 μm and a diameter of 5.7 nm (with a core diameter of 4 nm) suggest that these new core-shell structures are more temperature-sensitive than the PbS cores. These core-shell quantum dots, when suspended in toluene, were found to have a 0.5% decrease in emission power per °C increase in temperature at suspension temperatures ranging from 20 °C to 60 °C. The uncertainty in the liquid-phase temperatures derived from these emissions was estimated to be less than 0.3 °C based on the standard deviation. Furthermore, the PbS/CdS quantum dots were highly photostable, with a consistent response more than 100 days after suspension. These results imply that that these new IRQD can be used to measure liquid-phase coolant temperatures without disturbing the flow of coolant at an accuracy comparable to commercially available thermocouples in monolithic Si devices.
Thermoelectric Energy Recovery From Power Amplifier Transistors
Authors: Kim Kyoung Joon
Published: March 2011

A thermoelectric energy recovery module (TERM) is proposed. The TERM seeks to generate electrical energy from waste heat of power amplifier transistors. The TERM consists of a thermoelectric generator (TEG), a heat spreader, and a heat sink. A fully-coupled thermoelectric (TE) model of the TERM is developed to predict the power generation and the thermal performance of the TERM. A first order prototype of the TERM and a measurement setup are constructed to demonstrate the TERM performance. Power generation values and junction temperatures of a heat source are measured at various source heat flows. The measured results are used to verify the predicted results and to demonstrate the TERM performance. Load resistance effects to the TERM performance are also investigated utilizing the TE model and the measurement setup.
Numerical Solutions Control by Entropy Analysis
Authors: De Giorgi Luigi , Bertola Volfango , Cafaro Emilio , Cima Carlo
Published: March 2011

The rate of entropy generation is used to estimate the average error of approximate numerical solutions of conductive and convective heat transfer problems with respect to the corresponding exact solutions. This is possible because the entropy analysis of simple problems, which have exact analytical solutions, shows that the rate of entropy generation behaves similarly to the average error of approximate solutions. Two test cases (transient two-dimensional heat conduction with Dirichlet boundary conditions and free convection between two plates at different temperatures with internal heat source) are discussed. Results suggest to use entropy analysis as a tool for the assessment of solution methods and to estimate the error of numerical solutions of thermal-fluid-dynamics problems.
Development of Surface Plasmon Resonance Immuno-Sensors at Mid-Infrared Range
Authors: DiPippo William , Lee Bong Jae , Park Keunhan
Published: March 2011

This paper reports the design analysis of a novel doped-silicon infrared-surface plasmon resonance (IR-SPR) platform. The structure combines the advantages of both conventional grating and prism surface plasmon couplers while providing several intrinsic beneficial aspects. In combination with a Fourier transform infrared spectrometer, the biosensor is shown to compare favorably in trace analyte detection with visible range SPR devices while still maintaining the advantageous characteristics of IR-SPR. A numeric analysis of the structure was completed using a rigorous coupled wave analysis method to determine the geometric parameters of the diffraction grating as well as assess the sensor’s performance. Finite element analysis simulations were used to model the electromagnetic field distributions during the plasmon resonance. The results demonstrate that surface binding concentrations of biochemical species as small as 70 pg/mm2 can be measured. The large probing depth resulting from the IR spectrum facilitates the study of larger analyte (e.g. living cells). Additionally, the structure offers unequaled adaptability for a user’s specific biosensing needs while remaining inexpensive owing to the microelectromechanical systems (MEMS) batch protocols used in fabrication.
Evaluation of Directional Flame Thermometer for Real-Time Inversion of Heat Flux
Authors: Kokel Philip , Weinschenk Craig , Ezekoye O. A.
Published: March 2011

The Directional Flame Thermometer (DFT) is often used to measure heat flux during room fire testing. In literature and practice, heat transfer solutions for the DFT have been post processed. It is important to develop real-time capability for calculating heat flux based on measured temperatures as such capability will allow control of fire testing furnaces. In this study, we show that if a user will accept moderate errors in the heat flux, then a simple forward solution methodology allows heat flux measurements to be made in real-time. Essentially, the “inverse” problem is sufficiently well-conditioned to allow for a simple solution. Both a simple spreadsheet type solution and a finite difference code were used to generate the heat flux. The code was verified in both forward and inverse senses. The calculations were verified through a convergence study of both the forward and inverse solutions in spatial discretization (dx) and temporal discretization (dt). The inverse solution showed expected convergence behavior in both spatial and temporal discretization. In all cases, the solution for the front plate produced a maximum error of around 5%, which decreased as the DFT reached a steady state temperature. The forward and inverse models were validated through experimental testing using a radiant heater panel. The inverse model’s calculations were compared to measurements from a Schmidt-Boelter gage. The front plate heat flux measurements of the DFT matched reasonably well with the Schmidt-Boelter gage (2–6% difference) during the majority of the testing. The heat flux was then used to drive a forward simulation, and the forward model’s calculations were compared to actual temperature data acquired by the tests, producing a difference no greater than 4%. The DFT was also placed into a room fire to evaluate its effectiveness in this environment. The DFT was placed near a sand burner and in a panel fire test. The DFT produced reasonable heat flux values, but had more noise than results from those in front of the radiant heater panel (standard deviation of 1500 W/m2 compared to 400–600 W/m2).
Computational Study of Gas Turbine Blade Cooling Channel
Authors: Amano R. S. , Guntur Krishna , Martinez Lucci Jose
Published: March 2011

It has been a common practice to use cooling passages in gas turbine blade in order to keep the blade temperatures within the operating range. Insufficiently cooled blades are subject to oxidation, to cause creep rupture, and even to cause melting of the material. To design better cooling passages, better understanding of the flow patterns within the complicated flow channels is essential. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. Power output and the efficiency of turbine are completely related to gas firing temperature from chamber. The increment of gas firing temperature is limited by the blade material properties. Advancements in the cooling technology resulted in high firing temperatures with acceptable material temperatures. To better design the cooling channels and to improve the heat transfer, many researchers are studying the flow patterns inside the cooling channels both experimentally and computationally. In this paper, the authors present the performance of three turbulence models using TEACH software code in comparison with the experimental values. To test the performance, a square duct with rectangular ribs oriented at 90° and 45° degree and placed at regular intervals. The channel also has bleed holes. The normalized Nusselt number obtained from simulation are validated with that of experiment. The Reynolds number is set at 10,000 for both the simulation and experiment. The interactions between secondary flows and separation lead to very complex flow patterns. To accurately simulate these flows and heat transfer, both refined turbulence models and higher-order numerical schemes are indispensable for turbine designers to improve the cooling performance. The three-dimensional turbulent flows and heat transfer are numerically studied by using several different turbulence models, such as non-linear low-Reynolds number k-omega and Reynolds Stress (RSM) models. In k-omega model the cubic terms are included to represent the effects of extra strain-rates such as streamline curvature and three-dimensionality on both turbulence normal and shear stresses. The finite volume difference method incorporated with the higher-order bounded interpolation scheme has been employed in the present study. The outcome of this study will help determine the best suitable turbulence model for future studies.
Tangential Gas Injection Into a Supersonic Stream
Authors: Vasilevskiy Eduard B. , Ezhov Ivan V. , Novikov Andrey V.
Published: March 2011

An experimental and numerical study of a tangential gas injection effect on a flow pattern and heat flux was carried out. The cooling gas (air) was injected in the flow (air) through the tangential axis-symmetric slot on the spherically blunted cylinder streamlined longitudinally. Experiments were conducted in TsAGI shock wind tunnel at free-stream Mach number M∞ = 6, Reynolds number Re∞, Rw = 0.76×106 (calculated for free-stream parameters and bluntness radius Rw = 37.5 mm), cylinder angle of attack α = 0…30°, slot width h* = hk/Rw = 0–0.021, free-stream stagnation temperature T0 = 710 K, pressure behind the normal shock ps = 0.5 bar. The mass rate of the injected gas G* = gj/πρ∞u∞rw2 = 0…0.12. It is shown, that maximum of the heat flux toward the sphere surface could be sufficiently decreased. For example, for coolant mass rate G* = 0.03 and angle of attack α = 0 the heat flux maximum is reduced by factor of two.
Interfacial Thermal Fluid Phenomena in Thin Liquid Films
Authors: Kabov Oleg A.
Published: March 2011

Films are ubiquitous in nature and play an important role in our daily life. The paper focuses on the recent progress that has been achieved in the interfacial thermal fluid phenomena in thin liquid films and rivulets through conducting experiments and theory. Phase shift schlieren technique, fluorescence method and infrared thermography have been used. A spanwise regular structures formation was discovered for films falling down an inclined plate with a built-in local rectangular heater. If the heating is low enough, a stable 2D flow with a bump at the front edge of the heater is observed. For lager heat flux this primary flow becomes unstable, and the instability leads to another steady 3D flow, which looks like a regular structure with a periodically bent leading bump and an array of longitudinal rolls or rivulets descending from it downstream. The heat flux needed for the onset of instability grows almost linearly with the increase of Re number. Strong surface temperature gradients up to 10–15 K/mm, both in the streamwise and spanwise directions have been measured. For a wavy film it was found that heating may increase the wave amplitude because thermocapillary forces are directed from the valley to the crest of the wave. Thin and very thin (less than 10 μm) liquid films driven by a forced gas/vapor flow (stratified or annular flows), i.e. shear-driven liquid films in a narrow channel are a promising candidate for the thermal management of advanced semiconductor devices in earth and space applications. Development of such technology requires significant advances in fundamental research, since the stability of joint flow of locally heated liquid film and gas is a rather complex problem. Experiments with water and FC-72 in flat channels (height 0.2–2 mm) have been conducted. Maps of flow regimes were plotted. It was found that stratified flow exists and stable in the channels with 0.2 mm height and 40 mm width. The critical heat flux for a shear driven film may be up to 10 times higher than that for a falling liquid film, and reaches 400 W/cm2 in experiments with water at atmospheric pressure. Some experiments have been done during parabolic flight campaigns of the European Space Agency under microgravity conditions. It was found that decreasing of gravity leads to a flow destabilization.
Effect of Density Variation on the Dynamic Characteristic of Coaxial Swirling Jet Flows
Authors: Adzlan Ahmad , Matsubara Suguru , Gotoda Hiroshi , Ueda Toshihisa
Published: March 2011

We experimentally investigated the effect of density variation on the dynamic behavior of coaxial co-rotating swirling jets, focusing on how the difference of density between the inner and outer jets affect the flow at a high swirl number. When the density of the inner jet is higher than that of the outer jet (ρi/ρo ≈ 1.64. Here, ρi and ρo is the density of the inner and outer jet respectively.), both large-scale vortical structure and stagnating flow is induced by the hydrodynamic shear layer instability become easier to form when compared to that obtained for the case of iso-density jet (ρi/ρo = 1). The velocity field at the inner swirl number, Si = 0.6 is obtained using the Particle Image Velocimetry (PIV) analysis. The velocity field shows the absence of velocity vectors pointing towards the jet core downstream of the CO2 jets stagnation point. In contrast, when the density of the inner jet is lower than that of the outer jet (ρi/ρo ≈ 0.15), the inner jet does not form a stagnating point even at a high inner swirl number (Si = 0.6), and does not significantly change in response to swirl of inner jet.
Numerical Simulation of Flow and Heat Transfer in the Base Region of Martian Descent Vehicle
Authors: Egorov Ivan
Published: March 2011

Numerical investigation of hypersonic flow and heating over two models of an interplanetary probe was carried out at Mach numbers from 6 to 20 and Reynolds numbers Re∞,D from 0.7×105 to 16×105. The models differ mainly by the shape of the back surface simulating the payload container. The Reynolds number, at which laminar-turbulent transition takes place in the near wake, was defined at Mach numbers M = 6–8. It was shown that at turbulent base flow, the heat flux to the back surface of a blunted body can be comparable with the heat flux at the forward stagnation point. The results of numerical flow within the framework of Navier-Stokes and Reynolds equations simulation were compared with the experimental data.
Ballooning of Pressure Tube Under LOCA in an Indian Pressurised Heavy Water Reactor
Authors: Kumar Ravi , Nandan Gopal , Sahoo P. K. , Chatterjee B. , Mukhopadhyay D. , Lele H. G.
Published: March 2011

A study has been carried out by experimental simulation of the loss of coolant accident (LOCA) in an Indian pressurized heavy water reactor (IPHWR). The experiment has been carried out taking a completely voided fuel channel of Indian PHWR at 40 bar inside pressure as test-section. In order to simulate the rate of heat generation during LOCA, the pressure tube (PT) was electrically heated with a 12VDC/3500A rectifier. Initially the set-up was maintained at 300 °C temperature by resistance heating of PT. After attaining nearly steady state a step input of 21 kW electrical heating was given to the test-section which resulted in the temperature rise of PT with a gross rate of 2.8 °C/s. The ballooning deformation of test-section tube i.e. PT initiated at 575 °C temperature. With the progress of ballooning the rate of temperature rise was reduced due to high heat transmission to CT and subsequently to water in the tank surrounding CT. The pressure tube (PT) and calendria tube (CT) contact established at the average PT temperature of 680 °C. The contact was also confirmed from the average temperature profile of CT.
Numerical Investigation of Non-Newtonian Flow and Heat Transfer in Tubes of Heat Exchangers With Reciprocating Insert Devices
Authors: Marti´nez D. S. , Solano J. P. , Pe´rez J. , Viedma A.
Published: March 2011

Non-Newtonian flow and heat transfer in tubes of heat exchangers with reciprocating insert devices have been numerically investigated. The heat exchanger is mechanically assisted by a reciprocating cylinder, which moves the scraping rods inserted in the tubes. An array of semi-circular elements is mounted on each rod, with a pitch p = 5D. These elements fit the internal diameter of the tubes. During the reciprocating motion, they scrape the inner tube wall, avoiding fouling. Additionally, the movement of the inserted device generates macroscopic displacements of the flow, which continuously mix core regions with peripheral flow. A power law model with temperature dependent properties is implemented in FLUENT, for a Carboxymethil cellulose (CMC) solution in water with concentration of 2%. Flow pattern and pressure drop mechanisms are analyzed in static and dynamic conditions, and heat transfer enhancement features are discussed.
Thermal Conductivity of Mesoporous MCM-41 Studied by Molecular Dynamics Methods and Kinetic Theory
Authors: Huang Congliang , Feng Yanhui , Zhang Xinxin , Wang Ge , Yang Mu
Published: March 2011

MCM-41 consists of a hexagonal array of long, unconnected cylindrical pores with diameters that can be tailored within the range 1.6–10nm. As a porous silica nano-material, MCM-41 is thought to have a special thermal conductivity and is a promising porous substrate for mesoporous composites with high or low thermal conductivity. The Equilibrium Molecular Dynamics numerical simulations of thermal conductivity of MCM-41 are performed in this paper. FB potential equation and procedure of annealing are employed to get the structure of MCM-41. The Green-Kubo method is used to calculate the thermal conductivity of MCM-41. At the same time, the kinetic method is used to predict the thermal conductivity of MCM-41 for comparison. It turns out that the shell thermal conductivities of MCM-41 distribute within a reasonable range and increases linearly as porosity decreases, approaching the thermal conductivity of aerogels.
Organic Compounds Thermal Conductivity in the Liquid Phase: A Prediction Method in the Temperature Range From the Melting Point to Near the Critical Temperature
Authors: Latini Giovanni , Sotte Marco
Published: March 2011

In this work a new equation for liquid thermal conductivity prediction is proposed; its goal is to overcome the existing relations’ limitations, being reliable for many compounds in a wide temperature range and requiring few parameters to be used. The equation allows thermal conductivity calculation along or near the saturation line by the knowledge of the reduced temperature and two parameters characteristic of the organic family and of the single investigated compound. Also the “golden ratio” appears in the formula and an investigation on this number is carried out, proposing it as a characteristic value of the liquid state. The results of the formula’s test on the best available experimental values of more than 120 organic compounds, belonging to 13 different families (including the most used refrigerants) are presented. In the investigated reduced temperature range (going from the melting point to close the critical temperature, Tr = 0.30 ÷ 0.95) mean absolute deviations between calculated and experimental thermal conductivity data are generally less than 3% and maximum ones usually close to 8%.
Experimental Investigation on the Heat Transfer Performance of a Scraped Surface Heat Exchanger for Highly Viscous Foods
Authors: Bozzoli Fabio , Rainieri Sara , Mordacci Marco , Pagliarini Giorgio
Published: March 2011

Scraped Surface Heat Exchangers (SSHEs) provide an interesting solution in order to actively enhance the convective heat transfer mechanism when highly viscous fluids have to be treated. The investigations available in literature about these heat exchangers are rare, especially under laminar flow regime conditions. Moreover, due to the specificity of each product, it is difficult to generalize the few data available, by making the thermal design of these apparatuses a critical point. This paper concerns with a pilot plant designed in order to evaluate the performance of a concentric SSHE, especially intended for highly viscous fluid foods. Preliminary experimental results are compared to the prediction of an analytical model and to the few empirical heat transfer correlations available in literature suitable for this application.
Transport Process Study in Sodium Alanate Hydrogen Storage System During Desorption
Authors: Bhouri Maha , Goyette Jacques , Hardy Bruce J. , Anton Donald L.
Published: March 2011

Transport processes in a sodium alanate hydrogen storage system during desorption are presented. The mathematical model, which considers heat conduction and convection, hydrogen flow governed by Blake-Kozeny law and the chemical kinetics, is solved using the COMSOL Multiphysics® finite element software. The numerical simulation is used to present the time-space evolutions of the temperature, pressure and hydride concentration. The results are discussed for two cases: a finned storage system and a finless one. It is shown that the whole process occurring in the bed is governed and controlled by heat transfer from the heating fluid to the storage media and strengthened by axial heat transfer through the fins. The importance of the hydride bed thermal conductivity has also been evaluated. It was observed that the hydrogen discharge rate in a finless system can be improved if we find ways of increasing the thermal conductivity of the storage media. On the other hand, for a reservoir with fins, heat transfer is good enough that the discharge rate is limited by the kinetics.
Electrokinetic Flow and Heat Transfer in Microchannel
Authors: Elias Ezra
Published: March 2011

Electrokinetic heat in a narrow slit between two parallel plates with uniformly charged walls is investigated by considering the exact analytical solution of the Poisson-Boltzmann (PB) equation. It is demonstrated that the temperature field depends strongly upon interfacial electrokinetic effects resulting from the presence of an interfacial electric double layer (EDL) in the liquid. Thermal parameters are evaluated in systems for which the EDL thickness is comparable with or larger than the hydraulic diameter of the flow channel. Results are compared with existing approximate solutions and experimental results.
Measurements of Local Heat Transfer Coefficients in Heat Exchangers With Inclined Flat Tubes by Means of the Ammonia Absorption Method
Authors: Ahrend Ulf , Hartmann Angelika , Koehler Juergen
Published: March 2011

For high efficiency compact heat exchangers one needs to gain detailed knowledge of the distribution of the local heat transfer. For a profound assessment of heat enhancing mechanisms like secondary flow structures which are often found at rather small scales it is necessary to perform heat transfer measurements with high spatial resolution. A technique that satisfies this need is the ammonia absorption method (AAM). It is based on the analogy between heat and mass transfer. The here presented paper describes a new calibration approach for the AAM. It is done through the use of a well established heat transfer correlation for the hydrodynamic and thermal entry in parallel plate channels. This calibration approach is applied to heat transfer measurements in compact heat exchangers with inclined flat tubes and plane fins at Redh = 3000. The heat transfer performance is compared to fin-and-tube heat exchangers with round tubes. It is found that the novel devices show consistently higher global Nusselt numbers than comparable round tube heat exchangers.
Analysis and Design of Dye Sensitized Solar Cells
Authors: Nithyanandam Karthik , Pitchumani Ranga
Published: March 2011

Dye sensitized solar cells (DSC) are an attractive alternative to the conventional photovoltaic cell because of their low cost electricity production from solar radiation. The advantages of a DSC include the ability to generate power without emitting pollutants and requiring no fuel. While modeling of the physical and transport phenomena in DSC has been widely reported in the literature, a thorough analysis to quantitatively determine the optimal design and operating configuration in installation is lacking. The present study incorporates a model of the DSC coupled with a model to predict global irradiance on a terrestrial surface to analyze the hourly, daily, monthly and annual performance of a DSC installation over a wide range of design and operating parameters. Optimum design and operating parameters are derived from the analysis.
Test Facility to Study the Chill Down Phase of a Liquified Gas Flow
Authors: De Salve Mario , Panella Bruno
Published: March 2011

The paper presents some experimental data of the cool down by means of liquid nitrogen of the components in a small facility equipped with two cold boxes connected by an horizontal transfer channel. Temperature transients, pressure and pressure drops, heat transfer and flow rates are investigated.
Development of High Performance Thin Heat Pipe for Cooling Small Form Factor Devices
Authors: Mochizuki Masataka , Nguyen Thang , Saito Yuji , Nguyen Tien , Wuttijumnong Vijit , Ahamed Mohammad Shahed
Published: March 2011

The fast development in computing technology and the trend towards miniature architecture has created a more challenging task for cooling high-powered electronic components in further confined spaces. Thermal solution providers are required to develop higher performance and thinner heat pipes for their cooling devices. This paper shows the detail development of 1 mm thick heat pipe. In order to improve and characterize the heat pipe performance, various parameters were investigated such as wick structures; heat pipe length and thickness; operating temperatures; water-surface wettability and operation against gravity. In general, for a low-profile device, the heat pipe length is usually less than 150 mm and the operating temperature less than 80 °C. Based on this condition, if using a diameter 4 mm heat pipe flattened to 1 mm thick, the maximum heat transfer is about 11 watts.
Wall Thermal Conductivity Effects on Nucleation Site Interaction During Boiling: An Experimental Study
Authors: Jiang Yu Yan , Osada Hiroshi , Inagaki Masahide , Horinouchi Nariaki
Published: March 2011

The past decades have witnessed the diverse applications of boiling heat transfer enhancement in the removal of high density heat flux released by electronic components or power devices. People have developed many enhanced surfaces to obtain the highest heat transfer coefficient in nucleate boiling or to raise the CHF. In the boiling arena bubbling and nucleation site density play core parts, and hence it is crucial to correlate them quantitatively with surface structure and heat transfer conditions. For example one can determine by that correlation the best arrangement of boiling cavities for a given heat flux. However, the bubbling is highly influenced by inter-bubble actions. It has been found that the interactions can considerably change the bubble’s size, frequency and spatial distribution. The interactions are needed to be taken accounts of for a good correlation. Researchers tried to formulate the interactions as a single function of the inter-site spacing but have obtained contradictory conclusions, as suggests that they depend also on other parameters. In the present study we conducted a saturated boiling heat transfer experiment to investigate the interactions with respects to both the inter-site spacing and the wall thermal conductivity. The test section was fabricated by both copper and stainless steel, whose surface has two cylindrical artificial cavities of 50μm in diameter. It was heated with a uniform heat flux. The results show that both the bubble diameter Db and frequency f are functions of the inter-cavity distance s, but they vary in different manners in the copper and the stainless steel surfaces. In the copper surface, we observed evident enhancement of the boiling heat transfer at 1> S >0.4 and a slight inhibitive effect at 1.6> S >1, where S = s/Db. On the contrary the two nucleate sites in the stainless steel surface interfere with each other giving rise to evident suppression of boiling heat transfer at 1.6> S >0.65 and only slight enhancement at 0.65> S >0.3. Note that the copper’s thermal conductivity is 22 times larger than the stainless steel. Numerical simulation has revealed that the temperature variation beneath the copper cavities is much less than the stainless steel, which partly explains the differences in our experimental results. It is suggested that modeling the bubble interactions should take accounts of not only the distance-to-diameter ratio but also the fluid and wall properties.
Nucleate Boiling Performance of Azeotropic Binary Mixtures in a Saturate Pool Boiling System
Authors: Matsumura Kunihito , Kaminaga Fumito
Published: March 2011

Nucleate boiling of binary mixtures is of particular importance in chemical and process industries. The purpose of the present study is to provide experimental data and prediction method for nucleate boiling heat transfer in two types of anti-freeze solutions, Propylene-glycol (PG)/water and Ethylene-glycol (EG)/water, under atmospheric pressure. The experiments were performed in a saturated condition. The concentrations of solutions are varied from 10 to 40 wt%. It was found that the heat transfer coefficient gradually decreases as increasing the addition of anti-freeze. An addition of small amount of propylene-glycol and ethylene-glycol to water also decreases the CHF value far below that of pure water. It is concluded that the correlation proposed by Fujita for several binary mixtures can well predict the heat transfer coefficients within almost ±5% accuracy for every concentration of mixture solutions.
Heat Transfer Correlations for Thermally Developing Flow in Rectangular Micro-Channels Subject to Four-Sided and Three-Sided H1 Boundary Conditions
Authors: Hwu Ruey , Qu Weilin
Published: March 2011

In this study, heat transfer to laminar hydrodynamically fully developed flow in the thermally developing region of rectangular micro-channels is analyzed for four-wall and three-wall circumferentially uniform temperature and axially uniform heat flux (H1) boundary conditions. The temperature and wall heat flux distributions are solved numerically and used to calculate the local average Nusselt number. Based on the numerical results, new correlations capable of predicting heat transfer in the thermally developing region continuously into the fully developed region are developed. The correlations are compared with other correlations and available experimental data, and show good agreement.
Thermal and Electrochemical Cell Design and Its Experimental Assessment for Micro SOFC System
Authors: Usui Satoshi , Nishi Mina , Shikazono Naoki , Kasagi Nobuhide
Published: March 2011

A numerical simulation tool to predict the performance of a tubular SOFC is developed. For the convenience of the infrastructure, it has become more important to consider feeding hydrocarbon fuels like methane, which would be widely used, rather than hydrogen. Although it is well known that the performance of an SOFC drops largely when methane is fed compared with hydrogen, the reason for this is not yet well explained and thus prevents efficiently constructing an optimized SOFC system. Therefore, the present investigation is carried out to clarify how an SOFC performs when different fuels are fed. The calculation based on one-dimensional computation is carried out by introducing the parameters of actual electrode microstructures, obtained from the images taken by the focused ion beam scanning electron microscope (FIB-SEM). Values are adapted in calculating the ohmic, activation and concentration overpotentials. Proper experiments were also carried out to verify the validity of the numerical simulation. Although slight errors are found in the calculation results for fuels with high steam concentration, performances of hydrogen and methane fed cells were well predicted. Temperature distribution within the cell is also clearly shown. Through the present investigation, the performance drop, when the fuel is changed from hydrogen to methane, is found mainly caused by the temperature distribution of the cell that gives a concrete guide to construct an SOFC system.
Experimental Analysis of Air Dehumidification System With Liquid Desiccant
Authors: Zhang Li , Chitose Tanaka , Hihara Eiji
Published: March 2011

The performance of an air dehumidification system with lithium chloride solution used as a desiccant was studied experimentally. First, the mass-transfer coefficients were measured for a structured packed dehumidifier/regenerator. It was shown that the overall mass-transfer coefficients varied from 2.5 to 7.8 g/(m2·s) when the air velocity was increased from 0.5 to 1.5 m/s in the dehumidifier and varied from 1.2 to 2.7 g/(m2·s) in the regenerator. Second, experiments on the air dehumidification system were conducted. The experimental results showed that higher humidity in summer and lower humidity in winter resulted in decreased dehumidifying (humidifying) efficiency.
Study of Interaction Energy Between Nanoparticles and Cell Membrane
Authors: Guan Yingxue , Zhang Aili , Xu Lisa X.
Published: March 2011

Applications of nanoparticles in the bio-medical field like nano-medicine, molecular imaging probes, fluorescence marker, gene carriers, are developing quickly owing to the unique characteristics of nanoparticles. Among these applications, the interaction of nano-particles with the living cells is of critical importance. The complex chemical properties and biological activities of the particles bring about undesirable cytotoxic potentials and special cell internalization. According to previous studies, the cell uptake kinetics of nanoparticles mainly depend on the concentration difference between extracellular and intracellular nanoparticles, the surface electric charge of the nanoparticle, and the active transport of the cell. For example, Ginzburg’s thermodynamic simulation and Park’s three-dimensional phase-field model quantitatively explain the transitions in membrane morphology after exposure to nanoparticles with different surface charge, respectively. However, recent studies have shown that the gold nanoparticles coated with hydrophilic and hydrophobic functional groups with the same concentration but in different orders, completely exhibit quite different intrusion ability at 4°C when the active transport of the cell is greatly inhibited. The results suggest that the interaction energy of nanoparticles and cell membranes may be another driving force for the nanopartcles’ mass transfer across the cell membrane. Thus, in this paper, the interaction energy of the differently coated nanoparticles (P) with cell membrane (M) in water (W) is studied theoretically and results are used to explain the former experimental findings.
Heat Transfer Enhancement in Corrugated Pipes
Authors: Siginer Dennis A. , Akyildiz F. Talay
Published: March 2011

The temperature distribution and heat transfer coefficient are investigated in forced convection with Newtonian fluids in pressure gradient driven hydrodynamically and thermally fully developed steady laminar flow in transversally corrugated pipes. The governing equations are solved by means of the epitrochoid conformal mapping and exact analytical solutions are derived for the velocity and temperature fields without viscous dissipation. The effect of the corrugations and the number of waves on the friction factor, the temperature distribution and the heat transfer enhancement is discussed.
Quantitative Visualization of the Thermoacoustic Effect
Authors: Herman Cila
Published: March 2011

Thermoacoustic energy conversion was introduced into engineering systems during the past three decades as a new, alternative, environmentally safe energy conversion technology. It uses noble gases and mixtures of noble gases as working fluids rather than hazardous refrigerants required for the vapor compression cycle. A thermoacoustic system can operate both as a prime mover/engine (a temperature gradient and heat flow imposed across the stack lead to the generation of acoustic work/sound in the resonator) and, when reversing the thermodynamic cycle, as a refrigerator (acoustic work is used to pump heat from the low temperature reservoir and release it into a higher temperature ambient). Energy transport in thermoacoustic systems is based on the thermoacoustic effect. Using an acoustic driver, the working fluid in the resonance tube is excited to generate an acoustic standing wave. When introducing a stack of parallel plates of length Δx into the acoustic field at a suitable location, a temperature difference ΔT develops along the stack plates. This temperature difference is caused by the thermoacoustic effect. In this paper the thermoacoustic effect is visualized using real-time holographic interferometry combined with high-speed cinematography. In holographic interferometry both temperature and pressure variations impact the refractive index and both of these variations are present in our thermoacoustic system. In our analysis temperature variations are uncoupled from pressure variations to quantitatively visualize the oscillating temperature fields around the stack plate.
Properties and Performance of Quantum Well Thermoelectric Materials
Authors: Jovanovic Velimir , Ghamaty Saeid , Elsner Norbert B. , Krommenhoek Daniel
Published: March 2011

New and more efficient thermoelectric (TE) materials that make use of nanotechnology have been developed. These new materials, called quantum wells (QW), are composed of alternating layers of 10 nm thick silicon and SiGe films. They can be deposited by various techniques and magnetron sputtering was used to obtain uniform layered structures that exhibited no degradation of the TE properties or microstructure after thermal aging. For QW thin films, the heat and current flow are “in plane” and in this orientation all of the thermoelectric properties (the Seebeck coefficient, electrical resistivty, and the thermal conductivity) are improved to increase the TE Figure of Merit, ZT (see equation 3, p. 4, for the definition of Z). From the most recent QW test data, ZTs greater than 3 at room temperature have been obtained which constitutes a significant improvement over the state-of-the-art (SOTA) bulk thermoelectrics which have ZTs less than 1. QW materials have the best measured TE power factor (Seebeck coefficient squared divided by electrical resistivity) and, combined with low thermal conductivity substrates, should provide very high efficiency TE modules. The QW TE materials with ZTs greater than 3 lead to conversion efficiencies greater than 20 percent, which allows for much wider commercial applications, particularly in the applications such as the waste-heat recovery from truck engines, refrigeration, and air conditioning, where the SOTA bulk TE modules were shown to be technically feasible but economically unjustified due to low conversion efficiencies. With higher efficiency QW materials, these applications become economically attractive. For the refrigeration and air conditioning applications, the QW TE materials are predicted to have higher coefficients of performance (COP) than the SOTA vapor compression systems, with the additional advantages of having no compressors, no moving parts, no refrigerants, no vibrations, no noise, and practically no maintenance. With such significant advantages, it is very important to have independent confirmation of the QW TE properties that lead to such improved performance. Three independent researchers have confirmed the previously measured QW TE properties using conventional test techniques, and a totally new test technique was developed to measure the TE properties and performance and the results provided yet another confirmation of the superior TE performance of the QW materials versus the SOTA bulk thermoelectrics. The temperature range for the applications is anticipated to be as low as −150C to the upper temperature of 1000C, with the power generation capacity ranging from milliwatts to kilowatts and cooling capacity ranging from watts to several tons of refrigeration.
Molecular Dynamics Modeling of Heat Transport in Metals and Semiconductors
Authors: Narumanchi Sreekant , Kim Kwiseon
Published: March 2011

Interfacial thermal transport is of great importance in a number of practical applications where interfacial resistance between layers is frequently a major bottleneck to effective heat dissipation. For example, efficient heat transfer at silicon/aluminum and silicon/copper interfaces is very critical in power electronics packages used in hybrid electric vehicle applications. It is therefore important to understand the factors that govern and impact thermal transport at semiconductor/metal interfaces. Hence, in this study, we use classical molecular dynamics modeling to understand and study thermal transport in silicon and aluminum, and some preliminary modeling to study thermal transport at the interface between silicon and aluminum. A good match is shown between our modeling results for thermal conductivity in silicon and aluminum and the experimental data. The modeling results from this study also match well with relevant numerical studies in the literature for thermal conductivity. In addition, preliminary modeling results indicate that the interfacial thermal conductance for a perfect silicon/aluminum interface is of the same order as experimental data in the literature as well as diffuse mismatch model results accounting for realistic phonon dispersion curves.
Experimental Investigation of Metal-Diamond Thermal Interface Conductance With Different Diamond Surface Terminations
Authors: Collins Kimberlee C. , Chen Gang
Published: March 2011

Synthetic diamond has potential as a heat spreading material due to its uniquely high thermal conductivity. In small-scale devices, interfaces can dominate the resistance to heat transport, and thus play an important role in determining device performance. Here we use transient thermoreflectance techniques to measure the thermal interface conductance at metal-diamond interfaces. We study single crystal diamond samples with various surface terminations. We measure thermal interface conductance values over a range of temperatures from 88 K to 300 K, and find roughly 60 percent higher thermal interface conductance between Al and oxygenated diamond samples as compared to hydrogen terminated samples. The results reported here will be useful for device design and for advancing models of interfacial heat transport.
Heat Transfer to Foods: Safety and Structure
Authors: Fryer Peter J. , Bakalis S.
Published: March 2011

Heat transfer in foods is a commonplace operation in the home and restaurant, but is also the basis for a very large industry. Foods are complex non-Newtonian soft solids or structured liquids whose thermal behaviour is difficult to model; but engineering understanding is needed to develop processes that are safe and products that are attractive to the consumer. The increasing incidence of obesity in the developed world, and of food shortage elsewhere, demands that the industry adopts processes that give nutritious products in environmentally acceptable ways. This paper reviews the heat transfer problems that are found in food processing, with particular reference to the modelling of heating operations to ensure safety, problems that are found in the fouling and cleaning and process plant, and how heating and cooling are used to generate structure. Research challenges for the future are outlined.
Y thin films grown by pulsed laser ablation
Authors: Lorusso A. , Fasano V. , Perrone A. , Lovchinov K.
Published: March 2011

The effects of laser fluence on the growth characteristics and surface morphology of yttrium films grown by pulsed laser deposition are investigated. The presence of droplets in the deposited films, which is the main drawback of pulsed laser deposition technique, was studied at different laser fluences. The morphology and the structure of the grown films were studied by scanning-electron microscopy and x-ray diffraction, respectively. Careful scanning-electron microscope investigations obtained by tilting the samples show that the droplets arrive to the substrate in the molten phase. The ablation rate measured at five different laser fluences (0.9–7.6 J/cm2) shows a nonlinear trend correlated with the presence of the plasma-shielding effect. The present interest in the deposition of yttrium thin films by laser ablation is due to the well-known photoemission characteristics of this metal. Depositing good-quality thin films with high adhension and low droplet density will improve the performance of photocathodes by reducing both the dark current and the thermal emittance of the photoemitted current.