bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of Three-Dimensional Electric Field and Heat Conduction to Electrodes on the Temperature Rise During Irreversible Electroporation
Authors: Nomura Seiji , Kurata Kosaku , Takamatsu Hiroshi
Published: March 2011

The irreversible electroporation (IRE) is a novel method to ablate abnormal cells by applying a high voltage between two electrodes that are stuck into abnormal tissues. One of the advantages of the IRE is that the extracellular matrix (ECM) may be kept intact, which is favorable for healing. For a successful IRE, it is therefore important to avoid thermal damage of ECM resulted from the Joule heating within the tissue. A three-dimensional (3-D) analysis was conducted in this study to predict temperature rise during the IRE. The equation of electric field and the heat conduction equation were solved numerically by a finite element method. It was clarified that the highest temperature rise occurred at the base of electrodes adjacent to the insulated surface. The result was significantly different from a two-dimensional (2-D) analysis due to end effects, suggesting that the 3-D analysis is required to determine the optimal condition.
The Effect of Distance Between Fuel and Oxidizer Nozzles on NOx Emission From High Temperature Air Combustion
Authors: Nada Yuzuru , Zenman Yasutomo , Ito Takahiro , Noda Susumu
Published: March 2011

This study describes NOx emission characteristics of a high temperature air combustion furnace operating with parallel jet burner system. In the parallel jet burner system, fuel nozzles are separated with a distance from an oxidizer nozzle. Objectives of this study are to clarify the effect of the distance between the fuel nozzle and the oxidizer nozzle on NOx emission. The emission index of NOx (EINOx) decreases with the increase in the distance. This is due to the dilution through entrainment of burned gas. A scaling concept is proposed to assess the dilution effect on the NOx emission. Scaling parameters employed here are the global residence time of fuel and the flame temperature evaluated on a modified flamelet model in which the dilution effect is included. The overall EINOx production rate is scaled with the flame temperature. This scaling indicates the importance of the distance between the nozzles for NOx emission.
Effects of the Nanostructural Geometry at a Liquid-Solid Interface on the Interfacial Thermal Resistance and the Liquid Molecular Non-Equilibrium Behaviors
Authors: Shibahara Masahiko , Ohara Taku
Published: March 2011

The effects of the structural geometry at the nanometer scale on the thermal resistance at a liquid molecule-solid interface, as well as the interfacial energy transport mechanism of liquid molecules, were investigated directly by the nonequilibrium classical molecular dynamics simulations. The 12-6 Lennard-Jones potential energy functions for liquid molecules and the channel structure at the nanometer scale are employed so as to discuss the effects of the surface geometry at the nanometer scale on the interfacial thermal resistance in comparison with a flat surface. The thermal resistance between solid and liquid molecules was calculated by the temperature discontinuity at the liquid-solid interface and the energy flux that was added or subtracted by the Langevin method per unit area so as to maintain a constant boundary temperature of solid walls. The substantial interfacial thermal resistance reduction depending on the interaction parameters between solids and liquid molecules was observed in the case of the nanostructure surface in comparison with the flat surface. The liquid-solid interfacial thermal resistance reduction in the case of nanostructure surface relates to the energy transport mechanism change at the liquid-solid interface and the surface area magnification.
Study of Thermo-Diffusive Effects on Iso-Octane/Air Flames at Fixed Turbulence Karlovitz Number
Authors: Hayakawa Akihiro , Takeo Tomohiro , Miki Yukito , Nagano Yukihide , Kitagawa Toshiaki
Published: March 2011

Spherically propagating laminar and turbulent flames were studied using iso-octane / air mixtures with and without dilution. The main purpose of this study is to clarify the influence of thermo-diffusive effects on the turbulent flames. In order to examine the thermo-diffusive effects solely by separating them from the effects of flame stretch, turbulent burning velocities were compared at constant flame stretch factors. The mean flame stretch factor acting on turbulent flame front may be represented by the turbulence Karlovitz number. Thus, turbulent explosions were carried out at fixed turbulence Karlovitz numbers. The ratio of turbulent burning velocity to unstretched laminar burning velocity increased with the equivalence ratio for non-diluted mixtures at fixed turbulence Karlovitz numbers. And this ratio for CO2 diluted mixtures was larger than N2 diluted mixtures. The Markstein number that denotes the sensitivity of the flame to thermo-diffusive effects depends on the equivalence ratio and diluents of the mixture. The ratio of turbulent burning velocity to unstretched laminar one increased with decreasing Markstein number. Especially, it changed stepwise around Markstein number of zero. However, the burning velocity ratios did not increase with increasing mixture pressure although the Markstein number decreased with pressure.
Natural Convection Heat Transfer in Vertical Fluid Layers of High Aspect Ratio
Authors: Masuoka Takashi , Kakimoto Yasushi , Ito Hirokazu , Inoue Koichi
Published: March 2011

A two-dimensional numerical analysis is made on the effect of aspect ratio on flow and heat transfer characteristics of natural convection in a slender fluid layer enclosed between two vertical plates of different temperatures. It is shown that the boundary layer instability induces the hook-shaped flows and that its growth disrupts the large-scale circulatory flow into cellular flows of smaller scales, which in part include the renewed boundary layers. Then it is suggested that there exists a transition region where the average heat transfer coefficient increases with the increase of the height of a vertical fluid layer, as is seen in the transition region from laminar to turbulent natural convection along a single vertical plate. Discussion is also made on the nature of instability to yield cellular flows of smaller scales.
Numerical Study of Thermal Convection in Boussinesq-Stokes Suspension Occupying a Rectangular Box
Authors: Manjunath S. , Chandrashekara N. P.
Published: March 2011

This paper is a Fourier–series assisted numerical study of two-dimensional thermal convection in Boussinesq–Stokes suspensions occupying a cavity. The suspension is modeled as a couple stress liquid. The horizontal walls of the cavity are assumed to be perfectly heat conducting and the vertical walls are non-uniformly heated to establish a linear temperature in the vertical direction. The critical Rayleigh number is obtained numerically as a function of couple stress parameter and aspect ratio, and the same is plotted graphically. The results of slender vertical cavity, classical Rayleigh-Be´nard convection, rectangular and square cavities of finite aspect-ratio heated from below are obtained as limiting cases of the study.
Analysis of One-Dimensional Hyperbolic Heat Conduction in a Functionally Graded Thin Plate
Authors: Raveshi Mohammad Reza , Amiri Shayan , Keshavarz Ali
Published: March 2011

This paper presents the analytical solution of one-dimensional non-Fourier heat conduction problem for a finite plate made of functionally graded material. To investigate the influence of material properties variation, exponential space-dependant functions of thermal conductivity and specific heat capacity are considered. The problem is solved analytically in the Laplace domain, and the final results in the time domain are obtained using numerical inversion of the Laplace transform. The trial solution method with collocation optimizing criterion has been applied to solve the hyperbolic heat conduction equation based on polynomial shape function approximation. Due to the reflection and interaction of the thermal waves, the temperature peak happens on the insulated wall of the FGM plate, so the major aim of this paper is to find the amount of temperature peak and the time at which it happens. It has been shown that the dimensionless temperature peak and its happening time increase along with an increase in the dimensionless relaxation time. The results are validated by comparison with the results from an exact available solution solved at special case which shows a close agreement.
Investigating the Effect of Pipe Inclination on Two-Phase Gas-Liquid Flows Using Advanced Instrumentation
Authors: Abdulahi Abolore , Abdulkareem Lokman A. , Sharaf Safa , Abdulkadir Mukhtar , Hernandez Perez Valente , Azzopardi Barry J.
Published: March 2011

Pipes that make up oil and gas wells are not vertical but could be inclined at any angle between the vertical and the horizontal which is a significant technology of modern drilling. Hence, this study has been undertaken to look at the effect of inclination on flow characteristics especially at 10 degrees from both horizontal and vertical. Air/silicone oil flows in a 67 mm slightly deviated pipe have been investigated using advanced instrumentation: Wire Mesh Sensor Tomography (WMS) and Electrical Capacitance Tomography (ECT). They provide time and cross-sectionally resolved data on void fraction. Both the ECT probes and WMS were mounted on the inclined pipes upstream just at the point where flows were fully developed. By keeping the liquid flow rate constant at 10 litres/min (or liquid superficial velocity of 0.052m/s), gas flow rate was varied from 10 litres/min to 1000 litres/min (or gas superficial velocity from 0.05m/s to 4.7m/s). Then other values of liquid superficial velocity were considered. Visual observations were considered. Time series and void fraction were then measured for WMS while time series and liquid holdup were measured for ECT. The raw data were processed and then interpreted for proper analysis. From an analysis of the output from the tomography equipment, flow patterns were identified using both the reconstructed images as well as the characteristic signatures of Probability Density Function (PDF) plots of the time series of cross-sectionally averaged void fraction as suggested by some authors. Bubbly, slug and churn flows were observed for 10° from vertical pipe while bubbly, plug as well as slug flow when the pipe was inclined at 10° from horizontal. Examples of the PDFs are well illustrated which compares the use of ECT with WMS. In addition, statistical data such as Power Spectral Density (PSD), dominant frequency, mean void fraction as well as the structure velocities from cross correlation of the two planes of ECT have been identified.
FDTD Analysis of Ultra Short Pulse Laser Propagation in Transient Lens Effect
Authors: Chijiiwa Munehiro , Fushinobu Kazuyoshi , Okazaki Ken
Published: March 2011

Recent advances in measurement techniques using the photo-thermal effect have drawn attention to the application in various fields. We focus on the transient lens effect, which is a well-known photo-thermal phenomenon. As this effect is caused by the change of thermal properties or other physical properties, the measurements using this effect have the possibility to measure various materials information. This phenomenon has the optical property of a concave lens since the refractive index distribution on the optical axis is formed when the sample is irradiated. One reason for the refractive index distribution in sample is the effect of the nonlinear effect when irradiated by ultra-short pulse laser. In this research, we investigate two-dimensional propagation of ultra short pulse laser in the sample with nonlinear effect by using FDTD method. Effect of the third-order susceptibility on the two-dimensional pulse propagation has been demonstrated.
Ultrasound Characteristics in High-Temperature Fluid
Authors: Ihara Tomonori , Kikura Hiroshige , Takeda Yasushi , Ochi Eiji , Inagaki Akira
Published: March 2011

To investigate the ultrasound characteristics in high-temperature (over 1000 °C) viscous fluid such as molten glass, we developed an experimental apparatus. This apparatus consists of an electric furnace, a glass container and a transducer employing buffer rod with a cooling jacket to use room-temperature ultrasonic transducers. An ultrasonic velocity and its attenuation in molten glass are measured using the pulsed echo method. To derive the desired echoes, the buffer rod with grooves and cross-correlation analysis are applied.
Numerical Predictions of Thermal and Hydraulic Performances of Heat Sinks With Enhanced Heat Transfer Capability
Authors: Zhou Feng , Hansen Nicholas , Catton Ivan
Published: March 2011

The plate-pin fin heat sink (PPFHS) is composed of a plate fin heat sink (PFHS) and some pin fins planted between the flow channels. In this paper, a numerical investigation was performed to compare the thermal and hydraulic performances of the PPFHSs and PFHS. PPFHSs with five forms of pin cross-section profiles (square, circular, elliptic, NACA 0050, and dropform) were numerically simulated. The influence of pin fin cross-section profile on the flow and heat transfer characteristics was presented by means of Nusselt number and pressure drop. It is found that the Nu number of a PPFHS is at least 35% higher than that of a PFHS used to construct the PPFHS at the same Reynolds number. Planting circular and square pins into the flow channel of heat sinks enhances the heat transfer at the expense of high pressure loss. Using the streamline shaped pins, not only the pressure drop of the compound heat sinks could be decreased considerably, the heat transfer enhancement also makes a step forward. The present numerical simulation provides original information of the influence of different pin-fin cross-section profiles on the thermal and hydraulic performance of the new type compound heat sink, which is helpful in the design of heat sinks.
Experimental Study on Characteristics of Methane-Coal Dust Mixture Explosion and Its Mitigation by Ultra-Fine Water Mist
Authors: Xu Hongli , Wang Xishi , Gu Rui , Zhang Heping
Published: March 2011

This paper presents the results of experimental investigation on characteristics of methane-coal dust mixture explosion and its mitigation by ultra-fine water mist. Four E12-1-K type fast response thermocouples, two PCB piezotronic pressure transducers were used to obtain the temperature and pressure history of methane-coal dust mixture explosion and its mitigation by ultra-fine water mist, while a GigaView High-speed camera was used to visualize the processes. Different methane concentrations, coal dust concentrations, diameters of coal particles and volumes of ultra-fine water mist were considered for their effects on methane-coal dust mixture explosion. The temperature of explosion flame, the maximum explosion overpressure, the maximum rate of overpressure rise, and the critical volume flux of ultra-fine water mist were experimentally determined. The results show that the characteristics of the methane-coal dust mixture explosion and the mitigating efficiency by ultra-fine water mist are influenced by the methane concentration, the coal dust concentration, the coal dust diameter and the applied volume flux of ultra-fine water mist. For example, both the maximum explosion overpressure and rate of overpressure rise increased with increasing of coal dust concentrations and methane concentrations. All of the test cases indicate that ultra-fine water mist can mitigate the mixture explosion and suppress the flame propagation efficiently from the images record by high speed video camera.
Testing of Rectangular Channels With Perturbed Entrances for Temperature Difference Under Constant Heat Flux
Authors: Matyja Jacek Marek , Bello-Ochende Tunde
Published: March 2011

In this paper convective heat transfer performance of various duct geometries are compared using theoretical and experimental analyses. The experiments stretch further by perturbing the entrance region of the 2:1 rectangular duct (both inwards and outwards) and to obtain the effect on heat transfer performance. The cross-sectional area and length of the ducts are fixed and constant heat flux is applied to the ducts while cold water is used as the flow stream. The laminar flow regime is analysed. The theoretical and experimental cases are in agreement, with slight deviances attributed to certain assumptions made during the theoretical analysis and non-ideal testing conditions. The analyses concludes that perturbing the entrance region of a standard rectangular duct, both inwards and outwards, has a visible increase in heat transfer performance. The inward perturbed duct shows the highest increase in performance. The average variation between the theoretical and experimental case is about 18% for constant heat flux. The average error imposed on the results due experimental equipment is about 3% for constant heat flux experiments.
Impact on Thermal Conductivities of Nanostructured Bismuth Telluride Based Thin Films
Authors: Tanaka Saburo , Takashiri Masayuki , Miyazaki Koji
Published: March 2011

Nanostructured bismuth telluride based thin films, including nanoparticle and nanocrystalline have been prepared and measured their thermal conductivities. These thin films exhibit an average grain size of from 10 nm to 150 nm. The cross-plane thermal conductivities are measured by 3-omega method at 300 K. The determined nanostructured bismuth telluride thermal conductivities are 0.18 W/(m·K) and nanoparticle bismuth telluride thin film thermal conductivities are from 0.61 W/(m·K) to 0.80 W/(m·K). As compared with bulk alloys at the same atomic composition, both the nanoparticle and nanocrystalline thin films exhibit a reduction in the thermal conductivity. For more detail analysis, the reduction of the thermal conductivity is examined by a simplified phonon gas model on single crystal of bulk bismuth telluride, antimony telluride and bismuth selenide, The analytical model is consistent with the experimental results, and thus we consider that the thermal conductivity is reduced by the strong phonon scattering.
NO Reduction Mechanism Peculiar to O2/CO2 Coal Combustion Characterized by High CO2 Concentration
Authors: Watanabe Hirotatsu , Marumo Takashi , Yamamoto Jun-ichiro , Okazaki Ken
Published: March 2011

The characteristics of NOx reduction in O2/CO2 combustion were investigated experimentally and numerically. Experiments showed that the exhaust CO concentration in O2/CO2 combustion was almost twice as much as that in air combustion. This was because high CO2 concentration enhanced the reaction (CO2 + H → CO + OH). A mass of OH radicals led to the oxidation of NH3 and HCN. The sum of the nitrogen-species in O2/CO2 combustion was less than that in air combustion. It meant that NO formation suppression effect was high in O2/CO2 combustion. N2 conversion ratio became an effective guide to show NO formation suppression effect quantitatively. Calculations showed that N2 conversion ratio was high in O2/CO2 combustion and the unique NO reduction scheme caused by high CO2 concentration. This scheme proceeded under high CO and OH concentration. It was shown that O2/CO2 combustion was suited for reducing nitrogen-oxide due to the unique NO reduction scheme.
A Study of HCCI Combustion Characteristics by Using Light Emission and Absorption Spectroscopy
Authors: Iijima Akira , Yoshida Koji , Shoji Hideo
Published: March 2011

Light emission and absorption spectroscopic measurements of chemical species were made to investigate the effects of the fuel octane number, residual gas state and intake air temperature on the ignition characteristics of a Homogeneous Charge Compression Ignition (HCCI) engine. The results revealed that the activity level of low-temperature oxidation reactions and the tendency for autoignition to occur can be ascertained by making simultaneous spectroscopic measurements of light emission and absorption at wavelengths corresponding to those of formaldehyde (HCHO). The measured results showed that light absorption attributable to HCHO and faint light emission occur coincidentally with the cool flame. Once the cool flame degenerates, light absorption and emission are moderated. Absorbance declines sharply when autoignition occurs, indicating the consumption of HCHO. Increasing the octane number, raising the intake air temperature and increasing the residual gas fraction all have the effect of weakening the absorbance and light emission intensity of HCHO at the time the cool flame occurs, thereby lengthening the interval from the cool flame to autoignition.
Numerical Simulation for Infrared-Assisted Freeze Drying of Solution Products
Authors: Song Chi Sung , Nam Jin Hyun , Kim Charn-Jung
Published: March 2011

This study numerically investigated the one-dimensional freeze drying of a solution product assisted with infrared radiation heating. In order to accurately consider the spectral radiative transfer inside the moisture-rich product, the two-flux radiation model was incorporated with our previous freeze drying analysis model based on the fixed grid method. Thus, this model fully takes into account the spectral absorption characteristics of ice and the spectral composition of light emitting from an infrared heater. The infrared-assisted freeze drying characteristics were investigated in detail, along with the spatial variation of radiation intensity inside the product. Then, the effects of infrared heater temperature on freeze drying behaviors were parametrically studied, and the results were discussed in relation with the spectral effects in the radiative transfer in the moisture-rich product.
DNS Analysis on Local Burning Velocity and Flame Displacement Speed of Turbulent Premixed Flames With Different Density Ratio
Authors: Tsuboi Kazuya , Hasegawa Tatsuya
Published: March 2011

To investigate the relationship between local burning velocity and flame displacement speed with different density ratio, a numerical analysis was performed using DNS databases of statistically steady and fully developed turbulent premixed flames. The local burning velocity based on fuel consumption rate is considered to be most appropriate as the definition of burning rate because combustion is a kind of chemical reactions. Since it is impossible, however, that the local burning velocity is obtained experimentally by using any present measurement technology, the numerical results using the local burning velocity cannot be compared with any experimental data. Hence the flame displacement speed, which can be obtained and compared easily with experiments, has previously been used for numerical analyses. Thus, to realize comparison of numerical results using the local burning velocity with some experimental ones, it is necessary to reveal the relationship between the local burning velocity and the flame displacement speed.
Development and Characterization of an Electroplated Copper Nickel Alloy–Platinum Micro-Thermocouple
Authors: Loane S. , Selvaganapathy P. R. , Ching C. Y.
Published: March 2011

A cost effective electrodeposition technique was developed to microfabricate copper nickel alloy (CuNi)-platinum micro thermocouples. A flat smooth silicon wafer with a 9000 Å layer of oxide was chosen as the substrate material. Gold was used for the thermocouple electroplating base because of its high resistance to electrochemical corrosion and oxidation. Since gold does not adhere to the silicon substrate, a chromium layer was deposited as a seed layer for the gold deposition. The substrate is patterned using a lithography process to create a mould for the plating with junction sizes in the range 50 μm to 500 μm. The CuNi leg was electroplated onto the exposed gold surface. The platinum leg of the thermocouple was metal deposited. The CuNi composition of the microfabricated thermocouples was 16.3 percent nickel and 83.7 percent copper as determined through energy dispersive spectroscopy. The sensitivity of the microthermocouple was determined using a thermal bath, with the platinum leg as a reference. The sensitivity was 39 μV/°C for ice bath compensated and 41 μV/°C for non compensated thermocouples.
Efficiency Improvement in Entrained Flow Gasification
Authors: Bhatnagar Ankit , Pushpavanam S.
Published: March 2011

In this work a one dimensional steady state model is developed for a single stage and two-stage bottom fed entrained flow coal gasifier for. The single stage model was first analysed for two different oxidants (i) oxygen and (ii) air to study their effects on gasification. Analysis proved oxygen to be the better oxidant. The model is then extended to a two stage gasifier. Here 30 (70) percent of the coal is fed in the first stage (second stage). The first (second) stage operates in oxidant rich (lean) environment. The performances of single stage and two-stage models are compared in terms of their cold gas efficiencies for the same coal feed rates. It is observed that a two-stage system has better cold gas efficiency (77%) than a single stage system (72%) with lower oxygen consumption. The two-stage model is used to optimise the O2/Coal ratio as the H2O/Coal ratio is varied in the 2nd stage. The optimum yields the highest cold gas efficiency with minimum possible oxygen consumption.
Laminar Mixed Convection Nanofluids Flow in a Elliptic Duct Using Two Phase Approach
Authors: Akbarinia A. , Shariat M. , Laur R.
Published: March 2011

Laminar mixed convection Al2O3-Water nanofluid flow in elliptic ducts with constant heat flux boundary condition has been simulated employing two phase mixture model. Three-dimensional Navier-Stokes, energy and volume fraction equations have been discretized using the Finite Volume Method (FVM). The Brownian motions of nanoparticles have been considered to determine the thermal conductivity and dynamics viscosity of Al2O3-Water nanofluid, which vary with temperature. Simulation effects of solid volume fraction and nanoparticles mean diameter on thermal and hydraulics behaviors of nanofluid flow in elliptic ducts have been presented and discussed. The calculated results show good agreement with the previous numerical data. Results show that in a given Reynolds number (Re) and Richardson number (Ri), increasing solid nanoparticles volume fraction increases the Nusselt number (Nu) while the skin friction factor decreases. Increasing nanoparticles mean diameter augments the local skin friction factor whereas it causes the Nusselt number to reduce. But these effects are significant for nanoparticles diameter equal to 13nm especially.
Investigating the Performance of Bi-Porous Disk-Shaped Wick With the Restricted Vapor Space by Developing an Electric Analogue Method
Authors: Amouzegar Ladan , Reilly Sean W. , Catton Ivan
Published: March 2011

In this work, we build up a model applying our analogy strategy to investigate the performance of the Bi-porous wicks which are intended to eventually be used as the substrate in the TGP (Thermal Ground Plane) devices which function like thin heat pipes. In order to more closely simulate the operating conditions in a TGP, the vapor space above the wick is restricted, and consequently inserting vapor grooves in the wick is required to maintain the vapor removal. Further, adding a mono-porous layer at the bottom aids in delaying dry out by enhancing the liquid supply. [1] Here, we present our effort improving an electric analogue model to simulate the bi-porous wick described above. The model is based on the similarity between the differential equations governing the two systems. The analog model is initially improved for a disk-shaped bi-porous wick with a restrictor on top and grooves introduced in the bi-porous region. Moreover, the analogue technique is employed as a tool to investigate the performance of the wick with the vapor restrictor mounted thoroughly on top, to compare the experimental data achieved in a boiling chamber versus TGP device, and to estimate the required data for the bi-porous evaporator calculations.
Predicting Phonon Properties From Molecular Dynamics Simulations Using the Spectral Energy Density
Authors: Turney Joseph E. , Thomas John A. , McGaughey Alan J. H. , Amon Cristina H.
Published: March 2011

Using lattice dynamics theory, we derive the spectral energy density and the relation between the spectral energy density and the phonon frequencies and relaxation times. We then calculate the spectral energy density and phonon frequencies and relaxation times for a test system of Lennard-Jones argon using velocities obtained from molecular dynamics simulations. The phonon properties, which can be used to calculate thermal conductivity, are compared to predictions made using (i) anharmonic lattice dynamics calculations and (ii) a technique that performs normal mode analysis on the positions and velocities obtained from molecular dynamics simulations.
Introduction of Object Oriented FEM Model Developed for Solving Thermal-Hydraulic Processes
Authors: Frydrych D. , Hokr M.
Published: March 2011

Building of a model which could be used for optimization of design of nuclear waste storage, is one of biggest challenges in field of coupled processes modeling. Such a model have to take in consideration several fully-coupled processes. These processes are from field of Thermal, Hydro, Mechanical and Chemical science in short, they are described as THMC processes. Most of all, it is interaction of heat, generated by residual radiation in the waste, reacting with underground water and eventual chemical reaction in these water-solution. And all these actions being still a subject of eventual physical movements in the bedrock. In addition, model must take into consideration that values of a given process can change dramatically importance of this process characteristics for the safety of the storage. None of existing models is reaching the level of model complexity needed to address these issues. In this article is presented an object oriented model ISERIT. Model ISERIT is able to solve multidimensional task THH, where HH is for water, and water being present in 2 phases. The first phase is water vapor and the second phase is water absorbed by clay particles of the container buffer. In theoretical part of the article are defined governing equations. The governing equations are based on the conservation equations of heat and mass. The continuum equations are discretized in space by using the Galerkin finite element formulation. The time discretization is solved by implicit finite difference scheme. The main part of the article describes implementation of model ISERIT. Main structure of the model is defined with functionality of significant classes. The temperature, the water vapor concentration and the water concentration in solid phase are chosen as the three primary variables. The parameters, such as heat conductivity, heat capacity and water vapor diffusion coefficient, could be taken to be constants, or could be allowed to vary with temperature and water vapor concentration, without requiring fundamental modifications to the code. Article also describes how model can be enlarged to incorporate eventually other processes. This thanks to the fact, that model was build as object designed. At the end, article presents verification of the model against the experimental results, laboratory experiment BenchMark 1.3, as well as against full-scale experiment BenchMark 2.1.
Spray Cooling Heat Transfer Enhancement and Degradation Using Fractal-Like Micro-Structured Surfaces
Authors: Tulchinsky Alex , Pence Deborah V. , Liburdy James A.
Published: March 2011

In the present study, spray cooling curves are presented for two micro-structured surfaces and are compared to smooth surface results. The micro-structured surfaces consisted of bio-inspired fractal-like geometries, denoted as grooves or fins, extending in a radial direction from the center to the periphery of a 37.8 mm circular disc. Depending on the location on the surface, dimensions of groove widths and heights varied from 100 to 500 μm, and 30 to 60 μm, respectively. Fin width and height dimensions remained constant over the surface at 127 and 60 μm, respectively. Results are presented as heat flux versus the surface-to-exit spray temperature difference at each of five volume flux conditions ranging from 0.54 to 2.04 × 10−3 m3/m2-s. Convection heat transfer coefficients are also presented for each case as a function of heat flux. Results indicate that at low and high volume fluxes, an improvement in heat transfer occurs in the single phase regime for the fin geometry. Enhancement in the single phase regime does not occur at the intermediate volume flux condition. In the two phase regime for the fin structure significant enhancements, up to 50%, are observed. Whereas the groove structure performs similarly to the smooth surface in the single phase regime and exhibits large degradation in the two phase and critical heat flux regimes, up to 50%. Critical heat flux for the fin surface compares well to that of the flat surface, with a slightly increase at high volume flux conditions.
Measurements of the Intrinsic Thermal Conductivity of Individual Multi-Wall Carbon Nanotubes
Authors: Yang Juekuan , Waltermire Scott W. , Yang Yang , Li Deyu , Chen Yunfei
Published: March 2011

Thermal transport through carbon nanotubes (CNTs) attracted a lot of attention over the past decade. Several experimental studies have been carried out to determine the thermal conductivities of CNTs [1–3]. However, the measurements are based on an individual CNT sample between two suspended membranes and the results actually include both the intrinsic thermal resistance of the CNT and the contact thermal resistance between the CNT and the two suspended membranes that serve as a heat source and a heat sink. Hence, the effective thermal conductivity extracted from these measurements should be lower than the intrinsic thermal conductivities of the CNTs measured. To minimize the contact thermal resistance, electron beam induce deposition (EBID) of different metals has been used to increase the contact area between the CNT and the heat source and sink [3,4]. However, it is still not clear how effective this treatment is and to what level the effective thermal conductivity obtained after the EBID treatment reflects the intrinsic one.
Transient Analysis of Microorganism Temperature and Evaporative Losses in an Algae Biofilm Photobioreactor
Authors: Murphy Thomas E. , Berberoglu Halil
Published: March 2011

This study describes the thermal modeling of a novel algal biofilm photobioreactor aimed at cultivating algae for biofuel production. The thermal model is developed to assess the photo-bioreactor’s thermal profile and evaporative water loss rate for a range of environmental parameters, including relative humidity, ambient air temperature, solar irradiation, and wind speed. First, a 24 hour simulation of the system has been performed using environmental data for Memphis, TN, USA on a typical spring day to assess the diurnal variations in system performance. Then, a sensitivity analysis is performed to assess the effect of each environmental parameter on the temperature and evaporative losses of the photobioreactor. It is observed that because of the high surface area-to-volume ratio of the system, the temperature of the system exceeds that of the maximum ambient temperature during daylight hours by approximately 0.5 °C and is lower than the minimum ambient temperature at night by approximately 1.4 °C because of evaporative and radiative cooling. Furthermore, without active cooling, the characteristic evaporative water loss from the system is approximately 4.8 L/m2-day.
Constrained Optimization of One-Dimensional Two-Phase Flow in Fractal-Like Branching Microchannel Heat Sinks
Authors: Heymann Douglas B. , Pence Deborah V.
Published: March 2011

The performance of two-phase flow through fractal-like heat sinks, subject to both geometrical and flow constraints was assessed. Constraints are crucial in order to satisfy physical requirements of a design. A one-dimensional model of two-phase flow through fractal-like branching microchannels was used to estimate pressure drop, wall temperature and critical heat flux. Water is employed as the working fluid. The exit pressure is varied between 6 kPa and 101.3 kPa (absolute) in order to achieve two-phase flow at temperatures lower than the maximum wall temperature constraint of 70°C. Preliminary results show that the benefit to cost ratio of two-phase flow is on the same order of magnitude as single-phase flow, both with a 70°C wall temperature constraint. Alternatively, a critical heat flux model is used to constrain the flow rate in order for the imposed heat flux to be 50% of the critical heat flux.
An Exergy-Based Metric for Evaluating Solar Thermal Absorber Technologies for Gas Heating
Authors: Ruiz Maritza , Carey Van P.
Published: March 2011

The energy conversion effectiveness of the central receiver absorber in concentrating solar thermal power systems is dictated primarily by heat losses, material temperature limits, and pumping power losses. To deliver concentrated solar energy to a gas for process heat applications or gas cycle power generation, there are a wide variety of compact heat exchanger finned surfaces that could be used to enhance the convective transfer of absorbed solar energy to the gas stream flowing through the absorber. In such circumstances, a key design objective for the absorber is to maximize the heat transfer thermodynamic performance while minimizing the pumping power necessary to drive the gas flow through the fin matrix. This paper explores the use of different performance metrics to quantify the combined heat transfer, thermodynamic and pressure loss effectiveness of enhanced fins surfaces used in solar thermal absorbers for gas heating. Previously defined heat exchanger performance metrics, such as the “goodness factor”, are considered, and we develop and explore the use of a new metric, the “loss factor”, for determining the preferred enhanced fin matrix surfaces for concentrated solar absorbers. The loss factor, defined as the normalized exergy loss in the receiver, can be used for nondimensional analysis of the desirable qualities in an optimized solar receiver design. In comparison to previous goodness factor methods, the loss factor metric has the advantage that it quantifies the trade-off between trying to maximize the solar exergy transferred to the gas (high heat transfer rate and delivery at high temperature) and minimizing the pumping exergy loss. In this study, the loss factor is used to compare current solar receiver designs, and designs that use a variety of available plate-finned compact heat transfer surfaces with known Colburn factor (j) and friction factor (f) characteristics. These examples demonstrate how the loss factor metric can be used to design and optimize novel solar central receiver systems, and they indicate fin matrix surfaces that are particularly attractive for this type of application.
Liquid Supply and Heat Transfer Performance of Sintered Cu Monolayer Wicks for Phase Change Heat Transfer Applications
Authors: Sharratt Stephen , Nam Youngsuk , Ju Y. Sungtaek
Published: March 2011

When combined with a bi-porous or a vertical liquid artery structure, thin porous layers of high thermal conductivity materials can provide high critical heat flux while maintaining low thermal resistance. They are therefore are very promising for applications in advanced heat pipes and vapor chambers. The present study characterizes the liquid supply and heat transfer performance of monolayers of sintered Cu powders. Three sets of monolayer samples are prepared by sintering Cu powders with different diameters (29, 59, 71 um). The measured heat transfer performance is relatively insensitive to the powder diameter in the low flux regime. At relatively high heat fluxes (> 20 W/cm2) monolayers with the two large diameter powders show similar liquid supply and heat transfer performance while the sample with the smallest powder size shows significantly degraded heat transfer performance due to local dryouts.
Thermo-Wetting and Friction Reduction Characterization of Microtextured Superhydrophobic Surfaces
Authors: Kim Tae Jin , Glass Phillip , Hidrovo Carlos H.
Published: March 2011

Microtextured superhydrophobic surfaces have become ubiquitous in a myriad of engineering applications. These surfaces have shown potential in friction reduction applications and could be poised to make a big impact in thermal management applications. For instance higher heat transfer rate with less pumping power might be achievable through the aid of superhydrophobic surfaces. However, past and current research on superhydrophobic surface has focused mainly on modifying either the chemical component or the roughness factors of such surfaces. The purpose of this paper is to account for the thermal effects of the heated fluid flowing in superhydrophobic microfluidic channels. Herein we characterize the wetting behavior as a function of temperature of microtextured superhydrophobic surfaces, for both active and passive thermal management applications. A series of PDMS microtextured samples were fabricated using micromachining and soft lithography techniques. Flow measurements were performed using the superhydrophobic microfluidic channel. The channel surface roughness was large enough to induce the Cassie-Baxter state, a phenomenon in which a liquid rests on top of a textured surface with a gas layer trapped underneath the liquid layer. This gas layer induces a two-phase flow, and friction reduction can be achieved for the liquid channel flow. With this channel, flow rates were measured by varying the equilibrium temperature of the substrate. The temperature in the constant pressure source was controlled by circulating the water through a water-bath. As the heating reached a certain threshold the curvature of the liquid-gas interface was reversed and dewetting of the penetrated liquid layer was observed. This result suggests that the Cassie state in fluid flow can be prolonged even under increased pressure drops by increasing the temperature in the gas layer.
Fundamental Study of Turbulence-Radiation Interaction in Turbulent Channel Flow Using Direct Numerical Simulation
Authors: Sakurai Atsushi , Matsubara Koji , Maruyama Shigenao
Published: March 2011

Importance of turbulence and radiation interaction (TRI) has been investigated in a turbulent channel flow by using direct numerical simulation (DNS) to clarify detailed turbulent flow structure and heat transfer mechanisms. To investigate the effect of correlation functions between gas absorption and temperature fluctuation, the two cases of correlation are tested. Consequently, the TRI effect can be clearly observed when the correlation is positive. This fact provides the evidence that radiative intensity is enhanced by the turbulent fluctuation. The DNS results suggest the significance in the fundamental aspect of TRI. Furthermore, effects of frictional Reynolds number, Reτ, are investigated. Comparing with the case of Reτ = 150, the location of the enhancement peaks of Reτ = 300 shifts toward the walls. It is found that the relative importance of the TRI correspond to the structure of temperature fluctuation intensity originated from the differences of the Reτ.
Experimental Study of Thermal Performance of Nanofluids During Flow in Microchannels Using Surface Temperature-Nano-Sensors
Authors: Kang Seok-Won , Jeon Saeil , Banerjee Debjyoti
Published: March 2011

The thermal performance of nanofluids in microchannel of rectangular cross-section was experimentally investigated in this study. In the previous studies, a threshold nanoparticle concentration exists where the critical concentration separates the heat transfer performance of the nanofluid during a flow through microchannels. Thus, the emphasis of our study is to find the optimum concentration value of nanoparticles for enhancing the forced convective heat transfer coefficients. In this study, thin-film thermocouple array (TFTA) of K-Type (Chromel/ Alumel) was employed to measure the temperature profile on the heated surface in the microchannel (while the top and wall was sufficiently insulated). The TFTA deposited on a silicon wafer is bonded with a polymer substrate containing the molded microchannel. The microchannel was made using the Poly Di-Methyl Siloxane (PDMS). The mold for the microchannel in order to cure the PDMS onto it was fabricated using soft-lithography technique on an atomically stable silicon substrate. To assess the thermal performance of nanofluids in micro-channels, the temperature profiles in the heated bottom wall of the micro-channel was monitored using the TFTA which was then used to estimate the wall heat flux values. The concentration and size of the silica nanoparticles in the aqueous nanofluids are parametrically varied in this study (e.g. at weight concentrations of 0.5%, 0.1% and 0.2%). These parametric experiments were performed by varying the wall temperatures (e.g. 30, 50 and 70 °C) and flow rates (e.g. 5, 7 and 9 μl/min).
Characterization of Activated Carbon for Carbon Laden Flows in a Solar Reactor
Authors: Ozalp Nesrin , Shilapuram Vidyasagar
Published: March 2011

Carbon is not only a major product of the methane decomposition but also a catalyst for the heterogeneous methane decomposition reaction. It is highly desirable that the morphology and surface properties of the product carbon be controlled to maximize their catalytic effects. In this paper, we characterize the physical properties of two activated carbon samples by sizes, and crystallographic structures using scanning electron microscope, x-ray diffraction, particle size analyzer, and surface area measurement. The paper also includes high temperature thermogravimetric experiment results on the carbon–hydrogen reaction to show if the injected carbon particles reacts with the formed hydrogen, which has not been studied in solar thermal hydrocarbon decomposition before. Results show that carbon does not react with hydrogen to form methane or any other intermediate compounds up until 900°C, which explains the favorable effect of carbon laden flow experiments for catalytic methane decomposition at lower temperatures. These results will be used to identify the optimal operating conditions for our solar reactor.
Heat Transfer Analysis of a Novel Piezoelectric Air Pump
Authors: Eastman Andrew , Kimber Mark , Hirata Atsuhiko , Kamitani Gaku
Published: March 2011

With the propagation of ever faster and more powerful electronics, the need for active, low power, cooling is becoming apparent. Piezoelectric materials exhibit reasonable performance with very little power consumption. Therefore a promising potential solution lies in utilizing piezoelectric materials via fans or pumps. However, piezoelectric pumps have mainly been employed in the transport of liquids and aqueous solutions through small microchannels. The structures typically consist of both an outlet nozzle and an inlet nozzle that are geometrically disposed to promote flow in one direction. Device construction is generally simplified compared to mechanically actuated openings, however much of the potential flow is lost due to backflow. The piezoelectric pump studied in this paper consists of a single outlet nozzle with a large inlet. Its unique construction allows it to overcome relatively high pressures as well as promoting better manufacturability. Experimental investigations were undertaken in order to characterize the cooling potential of the device. A thin film heater provided a constant heat flux and an infrared camera was used to determine the resulting temperatures of the heated surface. Full-field data of the convection coefficient were analyzed as a function of vibration amplitude of the piezoelectric diaphragm and distance from the nozzle to the heated target. A maximum heat transfer coefficient was found when the blower was approximately 30 mm from the heated surface and this distance was independent of vibration amplitude. Correlations have been developed which account for both variables considered and can be used to predict the performance of future designs which rely on the same physical characteristics.