bluuebunny/crossref_metadata_2025 huggingface dataset:
Enhanced Thermal Conductivity of Ethylene Glycol-Based Suspensions in the Presence of Silver Nanoparticles of Various Sizes and Shapes
Authors: Fang Xin , Ding Qing , Fan Li-Wu , Yu Zi-Tao , Xu Xu , Cheng Guan-Hua , Hu Ya-Cai , Cen Ke-Fa
Published: December 2013

Engineered suspensions in the presence of highly-conductive nanoparticles, coined as nanofluids, have been studied extensively as a novel family of advanced heat transfer fluids. Attention has been paid primarily to the enhanced thermal conductivity of the suspensions that depends significantly on the material, size, shape, dispersion and loading of the nanoparticles. In this paper, the effects of adding silver (Ag) nanoparticles of various sizes and shapes on the thermal conductivity of ethylene glycol (EG)-based suspensions were investigated experimentally. These included Ag nanospheres (Ag NSs), Ag nanowires (Ag NWs) and Ag nanoflakes (Ag NFs). The suspensions were prepared at concentrations of 1, 5 and 10 mg/mL. The size and shape of the various Ag nanoparticles were observed by means of microscopy techniques. The dispersion and stability of the suspensions were also inspected. Measurements of the thermal conductivity of the suspensions were performed on a Hot Disk Thermal Constants Analyzer, which is based on the transient plane source technique, at elevated temperatures from 10 to 30 °C at an increment of 5 °C. It was shown that the thermal conductivity of the EG-based suspensions increases with raising the temperature. The Ag NWs of a very high aspect ratio (∼400) caused greatest relative enhancement up to 15.6% at the highest loading of 10 mg/mL (∼0.1 vol.%). The other two types of nanoparticles, Ag NSs and Ag NFs with much smaller aspect ratios, only led to enhancements up to 5%. The formation of a network of Ag NWs that facilitates heat conduction was likely responsible for their better performance. In addition, the relative enhancement was predicted by the Hamilton-Crosser (H-C) equation that takes the shape effect of the particles into consideration. It was shown that the predictions far underestimate the thermal conductivity enhancements but are qualitatively consistent with their shape dependence.
Effects of Channel Aspect Ratio on Convective Heat Transfer in an Electronics Cooling Heat Sink Having Agitation and Fan-Induced Throughflow
Authors: Agrawal Smita , Huang Longzhong , Simon Terrence , North Mark , Cui Tianhong
Published: December 2013

Fan-driven throughflow is frequently used for convective cooling of electronics. Channels with walls behaving like fins are common. In the present study, the flow inside the channels is agitated by means of translationally oscillating plates called agitators. Effectiveness of agitation by oscillating blades is found to be dependent on the channel width, a parameter studied herein. Heat sinks having narrower channels have a greater number of channels in total for the fixed size of heat sink and therefore greater heat transfer area than heat sinks with wider channels. Thus, with the same channel height, as the aspect ratio increases, channel width decreases, and it is found that opportunities for agitation are reduced and the generated turbulence is more strongly damped, thus reducing heat transfer coefficients. A study was carried out to find direction toward an optimal number of channels for a given heat sink using the agitation strategy. As part of the study, fluid damping and power consumption to drive the agitator assembly were addressed. The study was done numerically using ANSYS FLUENT on a representative single channel of the heat sink and the results were extended to the full size, multiple-channel heat sink system. Recommendations for moving toward an optimum geometry, based on thermal performance and agitator power are made.
Porous Media Thermal Modeling of an Electronic Chip With Non-Uniform Power Distribution and Cooled by Micro-Channels
Authors: Li Yubai , Zhang Yu , Yao Shi-Chune
Published: December 2013

Micro-channels are used for the cooling of electronic chips. However, the 3D-CFD modeling of the large number of channels in a full chip requires huge number of meshes and computation time. Although porous media modeling of micro-channels can significantly reduce the effort of simulation, most porous media models are based upon the assumption that the surface heat flux or temperature is uniform on the chip. In reality, the heat flux on the chip is usually highly non-uniform. As a result, the heat transfer coefficient along the micro-channel is not uniform. In the present study, the porous media model considers the simultaneously developing entrance effect at the micro-channel inlet, and the thermally developing entrance effect due to the severe heat flux variation along the channel. Duhamel integral is used to determine the heat transfer coefficient variation corresponding to the heat flux distribution along the channels, and comparisons are made with the rigorous conjugate conduction-convection modeling. The computing cost of this modeling method is only about 1% (including one time of iteration) of 3D-CFD simulation. To demonstrate this approach, a full scale electronic chip with realistic power distribution on the surface is modeled, and the temperature map on the chip’s heating surface is provided.
Computational and Experimental Study of Enhanced Mixing in a Gas Turbine Combustor Using Guide Vanes
Authors: Gupta Alka , Ibrahim Mohammed Saeed , Wiegand Benjamin , Amano Ryoichi
Published: December 2013

A number of studies have shown that the flow field exiting a combustor of a gas turbine cycle is highly non-uniform in pressure, velocity and, most importantly, temperature. Much research has been dedicated to the cooling of gas turbine blades using internal, film cooling, impingement jets, and pin/fin cooling technologies. Such designs allow for heated blades to be cooled from the inside out. While advancements in this type of blade cooling technology provide effective means to reduce the occurrence of blade failure due to material overheat conditions, the effect of externally reducing or eliminating the temperature non-uniformities in the exit flow from the combustor would assist in the solution. The goal of this study is to optimize the mixing of primary and dilution air in the dilution zone of the combustor using guide vanes. This improvement in mixing would lead to increase in the degree of temperature uniformity with respect to the radial position at the exit nozzle. To achieve this objective, both experimental and computational studies were performed to investigate the heat and flow behaviors with 45° spherically swept guide vanes attached to the dilution holes. These guide vanes were intended to direct the dilution jets into the primary flow and enhance mixing. A parameter was defined in terms of the temperatures of the dilution and primary flow streams at the inlet and the exit plane, called the mixture fraction. Based on the mixture fraction value, it was found that the guide vanes produce a more uniform exit temperature flow field as compared to the case when there were no guide vanes used. Also, the design was modified for different alignment orientations of the guide vanes — 0°, 30°, 60° and 90° with respect to the primary flow — with the 60° orientation fostering the best results.
Estimation of an Appropriate Lattice Structure for Phonon Transport Using Lattice Boltzmann Method
Authors: Chattopadhyay Ankur , Pattamatta Arvind
Published: December 2013

Heat transport at nanoscales departs substantially from the well established classical laws governing the physical processes at continuum level. The Fourier Law of heat conduction cannot be applied at sub-continuum level due to its inability in modeling non-equilibrium energy transport. Therefore one must resort to a rigorous solution to the Boltzmann Transport Equation (BTE) in the realm of nanoscale transport regime. Some recent studies show that a relatively inexpensive and accurate way to predict the behavior of sub continuum energy transport in solids is via the discrete representation of the BTE referred to as the Lattice Boltzmann method (LBM). Although quite a few numerical simulations involving LBM have been exercised in the literature, there has been no clear demonstration of the accuracy of LBM over BTE; also there exists an ambiguity over employing the right lattice configurations describing phonon transport. In the present study, the Lattice Boltzmann Method has been implemented to study phonon transport in miniaturized devices. The initial part of the study focuses upon a detailed comparison of the LBM model with that of BTE for one dimensional heat transfer involving multiple length and time scales. The second objective of the present investigation is to evaluate different lattice structures such as D1Q2, D1Q3, D2Q5, D2Q8, D2Q9 etc. for 1-D and 2-D heat conduction. In order to reduce the modeling complexity, gray model assumption based on Debye approximation is adopted throughout the analysis. Results unveil that the accuracy of solution increases as the number of lattice directions taken into account are incremented from D2Q5 to D2Q9. A substantial increase in solution time with finer directional resolutions necessitates an optimum lattice. A novel lattice dimension ‘Mod D2Q5’ has been suggested and its performance is also compared with its compatriots. It is also demonstrated that the inclusion of the center point within a particular lattice structure can play a significant role in the prediction of thermal conductivity in the continuum level. However, as the size of the device comes down to allow high Knudsen numbers, in the limiting case of ballistic phonon transport, the choice of lattice seems to have negligible effect on thermal conductivity.
Heat Transfer Analysis of Two Pass Cooling Channel of Gas Turbine Blade With Analytical Wall Function Turbulence Approach
Authors: Arakawa Hitoshi , Shen Shaohua , Amano Ryo S.
Published: December 2013

This paper reports experimental and computational studies of flow and heat transfer through a square duct with a sharp 180 degree turn. The main purpose of this research is to study flow and heat transfer predictions of the Analytical Wall-Function (AWF). To compare the predicting performance of the AWF, the standard Log-Law Wall-Function (LWF) and Low-Reynolds-number (LRN) k-ε model were applied. Their results were also compared with the experimental results for validation. In addition, three extended forms of the AWF were tested. Computational results showed better agreement with the experimental data, especially after the turn of the channel. It was also found that the wall-function (WF) models predicted more reasonable results as Reynolds number increased. The both wall-function models predicted similar results except for separation/reattachment regions where the LWF predicted lower Nusselt number than the other models.
Numerical Comparison of Operating Conditions and Nozzle Geometry on Injector Performance
Authors: Zhang Kun , Zhang Bo , Xiang Xu , Yang Yong
Published: December 2013

A model was established to discuss the effect of operating parameters and nozzle shapes on the performance of injectors. The comparison pointed out that heat load has worst effect on injector geometries, while little effect on area ratio. On the other hand, the area ratio is very sensitive to suction temperature, which is critical to injector performance. The least energy loss is achieved when nozzle converges gently at the same nozzle entrance and exit diameter.
Final Design Parameter Settings for a Physically-Realizable Uniform Temperature Boundary Condition Specification on a Wall of an Enclosure
Authors: Lee P. Y. C. , Leong W. H.
Published: December 2013

Design parameters based on a three-dimensional internal natural convection heat transfer in a cubical apparatus are presented so that a uniform temperature boundary condition specification on a wall of the apparatus can be physically achieved. Preliminary temperature measurements based on the initial design of the apparatus where the uniform boundary condition was prescribed revealed that a temperature non-uniformity existed in the excess of 4% error. In order to complete the objective of the benchmark internal natural convection study, the apparatus had to be modified so that the temperature non-uniformity can be reduced to less than 1% error. It was decided that the original design be modified by simply adding two auxiliary heaters in the vicinity of the wall where the uniform temperature profile was desired. Before the implementation of the auxiliary heaters onto the apparatus, a detailed mathematical analysis was conducted to determine the position and the contact width of the heaters, and to establish an appropriate heat flux required to reduce the temperature non-uniformity to less than 1% along the wall of the apparatus. This analysis was achieved by using the approximate analytical temperature solution obtained from the boundary value problem of a plate (which is one part of the apparatus) with boundary conditions prescribed to model the auxiliary heaters. Previously, a specific set of design parameters were used that reduced the temperature non-uniformity to less than 1% along a wall of the modified cubical apparatus. As an extension to the previous work, this paper presents a generalized set of design parameters that can equally prescribe a physically-realizable uniform temperature setting along a wall of an enclosure to within 1% error. With the range of design parameters, this would enable any designer with the flexibility in choosing what parameters can be allocated based on their need.
Computational Evaluation of the Effects of Voids on a Thermal Energy Storage System Using Molten Silicon as the Phase Change Material
Authors: Amundson Thomas R. , Scharfe David B. , Webb Rebecca N.
Published: December 2013

Latent heat energy storage is one of the most efficient ways to store solar thermal energy. A system capable of receiving, absorbing, and collecting solar energy and storing it within a high temperature phase change material has been designed as part of a power system to be used on a low Earth orbit satellite. The system employs silicon as the phase change material and thermophotovoltaic cells for the conversion of stored heat energy into electrical energy. The effect of a void, in the phase change material, on system temperature and the associated thermophotovoltaic power production is determined through computational evaluation.
Isothermal Physical Flow Modeling of a Gas Turbine Simple-Cycle Selective-Catalytic-Reduction (SCR) System
Authors: Swanson Larry , Zhang Hua , Byrd Doug
Published: December 2013

A physical flow model of a gas turbine (GT) simple-cycle Selective-Catalytic-Reduction (SCR) system was constructed to a 1/16 geometric scale to validate computational fluid dynamics (CFD) predictions and examine the impact of tempering air injection on system performance. Repeatable velocity contours and tempering air dispersion profiles were developed for baseline (no tempering air), and 12- and 6-lance tempering air injector configurations. The conclusions from the study are: (1) relative to the no lance baseline case, the 12-lance configuration tends to force more of the inlet flow towards the top of the duct, whereas the 6-lance configuration does not affect the upstream profile significantly, (2) adding tempering air does not have a significant impact on the diffuser inlet velocity distribution and has a minor effect on the velocity and dispersion profiles at the NOX-catalyst inlet, (3) at the NOX-catalyst inlet, the 6-lance configuration with tempering air exhibits a slightly skewed flow toward the lower right corner of the duct with a coefficient of variation (COV) of 19.4%, which is slightly better than that for the 12-lance configuration, (4) at the NOX-catalyst inlet, the 12-lance configuration disperses tempering air best because its COV is 20.8% relative to a 27.3% COV for the 6-lance configuration, and (5) a comparison between the local mixing-cup temperature contours for both 12- and 6-lance configurations, based on tracer injection into the tempering air flow, confirms that the CFD model does a good job of qualitatively predicting the heat and mass transport processes in the GT simple-cycle SCR system.
Boiling/Evaporation Heat Transfer Augmentation Using Subchannels-Inserted Metal Porous Media
Authors: Yuki Kazuhisa , Uemura Masahiro , Suzuki Koichi , Sunamoto Ken-ichi
Published: December 2013

Two-phase flow loop system using a metal porous heat sink is proposed as a cooling system of the future power electronic devices with a heat load exceeding 300W/cm2. In this paper, as the first step, the heat transfer performance of the porous heat sink is evaluated under high heat flux conditions and the applicability and some engineering issues are discussed. The porous medium, which is fabricated by sintering copper particles, has a functional structure with several sub-channels inside it to enhance phase-change as well as discharge of generated vapor outside the porous medium. This porous heat sink is attached onto a heating chip and removes the heat by evaporating cooling liquid passing through the porous medium against the heat flow. Experiments using 30 kW of heating system show that the heat transfer performance of a copper-particles-sintered porous medium with the sub-channels exceeds 800W/cm2 in both high and low subcooling cases and achieves 300W/cm2 at a wall temperature of 150 °C (Tin = 70 °C) and 130 °C (Tin = 70 °C). These results prove that this porous heat sink is applicable enough for cooling 300 W/cm2 class of power electronic devices.
Beam Splitting System for the Development of a Concentrating Linear Fresnel Solar Hybrid PV/T Collector
Authors: Crisostomo Felipe , Taylor Robert A. , Mojiri Ahmad , Hawkes Evatt R. , Surjadi Desiree , Rosengarten Gary
Published: December 2013

Investigations are underway around the world to make solar energy more competitive in the energy market [1–3]. One approach is to develop solar hybrid photovoltaic/thermal (PV/T) technologies which allow for maximal utilization of incident sunlight by integrating a PV cell and a thermal receiver in the same collector [4,5]. In this study, we will present a new PV/T design based on a compact linear Fresnel concentrator (LFC) coupled with a spectral beam-splitter. The beam-splitting approach avoids the efficiency drop in the PV cell while still obtaining high temperature thermal output. The design is analyzed numerically with respect to a worth factor which considers the intrinsically higher economic value of electrical energy at ∼3 times thermal energy. In order to predict optical performance, the geometry of this hybrid concentrating collector, which achieves 10–15 suns concentration, is modeled at various incident angles using the ray tracing software Zemax. Three different PV cells are considered (Si, GaAs and GaInP/GaAs). The reported spectral response of these cells is used to determine the optimal wavelength split for the fraction of the solar spectrum directed to the various PV cells. The results indicate that such designs can achieve 20–51% greater value of the power outputs — PV electrical power plus heat produced — relative to a stand-alone PV system.
Optimal Distribution of Discrete Heat Sources Under Mixed Convection: A Heuristic Approach
Authors: Hotta Tapano Kumar , Balaji C. , Venkateshan S. P.
Published: December 2013

Steady state experiments are conducted in a low speed horizontal wind tunnel under mixed convection regime, for five discrete heat sources (Aluminum) of different sizes arranged at different positions on a substrate board (Bakelite), to determine the optimal configuration. The characteristic length of heat sources varies from 0.005 to 0.011 m. The optimal configuration is one whose maximum temperature excess (temperature difference between the heat source and ambient) is minimum among all the possible configuration of heat sources mounted on the substrate board, and is determined by a heuristic non-dimensional geometric parameter λ. The maximum temperature excess is found to decrease with λ, signifying an increase of heat transfer coefficient. In view of this, configuration with the highest λ value is the optimal one. The effect of surface radiation on the heat transfer characteristic has also been studied by painting the surface of heat sources with black paint, which reduces their temperature by as much as 12%. An empirical correlation is developed for the non-dimensional temperature excess (θ) by taking into account the effect of surface radiation. The correlation when applied for the highest λ to the configuration, returns the maximum value of θ at the optimal value, which is a key engineering quality that is sought in problems of this class.
A Review of Hole Geometry and Coolant Density Effect on Film Cooling
Authors: Ekkad Srinath , Han Je-Chin
Published: December 2013

Improved film cooling hole geometries and effect of coolant density on film cooling have been a focus since the 1970s. One of the first studies on modifying hole exit to improve film cooling effectiveness and quantifying coolant density effect was from Prof. Goldstein’s group [1]. This paper traces the development and implementation of hole exit geometries as well as coolant density study from this landmark paper and its impact on future studies of advanced hole geometries under realistic engine-like coolant to mainstream density ratio conditions. This work is not intended to be a comprehensive review of the literature. It is aimed at providing an overview of the influence of ref. [1] over the past 4 decades.
Experimental Investigation on Fluid Flow in an Inclined Open Rectangular Microgrooves Heat Sink With Micro-PIV
Authors: Yu Dong , Hu Xuegong , Guo Chaohong , Tang Dawei , Sun Fangyuan , Hu Linghong , Gao Fei , Zhao Tao
Published: December 2013

The paper investigates the fluid flow in an inclined open rectangular microgrooves heat sink using LaVision-assembled micro-PIV system. The images of the accommodation stage and the corner flow stage at inclined 15 degrees angle with heat flux of 0.09W/cm2 were recorded by a CCD camera with the speed of 10 frames per second. The velocity profile at inclined 15 degrees angle with heat flux of 0.14W/cm2 was acquired by using the analyzing software DaVis 8.1. In accommodation stage, X-Y-Z scanning table was adjusted vertically and horizontally to investigate the velocity field of different focused planes. Results show that the experimental images of the accommodation stage and the corner flow stage verify the predictions proposed by Catton and Stroes that there exist accommodation stage and corner flow stage and no jump-like stage proposed by Nilson et al. Flow in microgroove driven by capillary force is very slow and the velocity is less than 1mm per second. In evaporating thin film region, from the left side to the right side of the microgroove, the velocity increases and velocity of the interface is the highest. In lower meniscus region, the velocity increases and then decreases.
Design and Verification of a PECVD Fabricated Multi-Layer Nano-Scale Photovoltaic Device
Authors: Hajimirza Shima , Howell John R. , Holt Milo , Saha Sayan , Akinwande Deji , Banerjee Sanjay
Published: December 2013

This paper summarizes the results of computational and experimental studies of an enhanced thin film solar structure. The cell structure consists of a reflective aluminum layer beneath an 80nm absorbing layer of amorphous silicon, coated with a top layer of transparent and conductive indium tin oxide (ITO). The structure is mounted on a glass substrate. We first use constrained optimization techniques along with numerical solvers of the electromagnetic equations to specify the layer thicknesses of the design for maximized efficiency. Numerical analysis suggests that solar absorptivity in the thin film silicon can be enhanced by a factor of 2. The proposed design is then fabricated using Plasma Enhanced Chemical Vapor Deposition techniques, along with a control sample of bare silicon absorber for comparison. AFM imaging and spectrophotometry experiments are applied to estimate the realized thin film dimensions, deposition error, unwanted oxidation volume and the resulting reflectivity spectra. Comparisons of the measured and simulated reflectivity spectra of the fabricated cells, as well as Monte Carlo simulations based on incorporating random geometry errors in the numerical simulations suggest that the measured spectra are in accordance with the expected curves from simulations.
Design a Wavelength-Selective Absorber for Solar Thermal Collectors With Two-Dimensional Nickel Gratings
Authors: Chen Yu-Bin , Han Sunwoo , Chiu Feng-Cheng , Lee Hyun Jin , Lee Bong Jae
Published: December 2013

The sunlight has been considered a promising alternative energy source because of its abundance and sustainability. A solar thermal collector can turn the solar irradiation into the usable heat, and thus, its performance highly depends on the efficiency of absorber. An ideal absorber should trap most incoming solar radiation in the visible and near-infrared spectral region, and minimize its emitted thermal energy at long wavelengths. One of the promising solutions for satisfying the aforementioned requirements is to employ periodic structured surfaces, whose tunable radiative properties were used in thermophotovoltaic devices and chemical sensors. Two-dimensional subwavelength gratings are thus proposed for the absorber surface profile in the present study. Design objectives are a broad-band peak in the absorption spectrum and a quasi-isotropic angular lobe at the incidence of both linear polarizations. Nickel is selected for its fabrication easiness and low cost. A SiO2 film sandwiched between gratings and a substrate is considered as extra design flexibility to possibly enhance performance without much difficulty. Radiative properties and electromagnetic fields will be obtained from programs based on the rigorous coupled-wave analysis (RCWA). The optimization is then realized with the Taguchi method.
Experimental Study on the Heat Transfer Characteristics of Water in Vertically-Upward Internally-Ribbed Tubes
Authors: Zhang Qing , Li Huixiong , Zhang Weiqiang
Published: December 2013

In the present paper, a systematic study of the heat transfer characteristics of water in a new-type vertically-upward internally-ribbed tube has been carried out experimentally. The ranges of the experimental parameters were as follows: the pressure at the inlet of the test section ranged from 12 to 28 MPa, and the mass velocity was from 400 to 1200 kg/m2s, and the internal wall heat flux varied from 300 to 600 kW/m2. The experimental results showed that no matter at subcritical pressures or at supercritical pressures, with the increase in pressure or heat flux, the heat transfer in the internally ribbed tube was weakened, while with the increase in mass velocity, the heat transfer was improved. A systematic comparison between the heat transfer of water in internally ribbed tubes and that in smooth tubes was made in this paper. It was found that compared with the smooth tube, the internally ribbed tube can effectively enhance the heat transfer at subcritical pressures, and also at supercritical pressures. In this paper, the heat transfer enhancement of the internally ribbed tube was attributed to the enlarged heat transfer area, disturbing effect of ribs and the rotational flow in the internally ribbed tube. On the basis of analysis of the effects of tube geometric structures on heat transfer in internally ribbed tubes, a new nondimensional parameter composed of the geometric parameters of the internally ribbed tube was put forward in the present paper to qualitatively compare the capacity of heat transfer enhancement of internally ribbed tubes with different geometric structures, and this new nondimensional parameter got verified by comparison of experimental data of different internally ribbed tubes from open literatures.
Spiral Microfluidics Device for Continuous Flow PCR
Authors: Salemmilani Reza , Cetin Barbaros
Published: December 2013

Polymerase-chain-Reaction (PCR) is a thermal cycling (repeated heating and cooling of PCR solution) process for DNA amplification. PCR is the key ingredient in many biomedical applications. One key feature for the success of the PCR is to control the temperature of the solution precisely at the desired temperature levels required for the PCR in a cyclic manner. Microfluidics offers a great advantage over conventional techniques since minute amounts of PCR solution can be heated and cooled with a high rate in a controlled manner. In this study, a microfluidic platform has been proposed for continuous-flow PCR. The microfluidic device consists of a spiral channel on a glass wafer with integrated chromium microheaters. Sub-micron thick microheaters are deposited beneath the micro-channels to facilitate localized heating. The microfluidic device is modeled using COMSOL Multiphysics®. The fabrication procedure of the device is also discussed and future research directions are addressed. With its compact design, the proposed system can easily be coupled with an integrated microfluidic device to be used in biomedical applications.
Cryomicroscopic and Calorimetric Assessment of Cell Response During Freezing Process
Authors: Zhu Kai , Wang Yabo , Liu Bin , Su Xinjun
Published: December 2013

Understanding the biophysical processes that govern freezing responds of cells is an important step in characterizing and improving the cryopreservation. The quantitative analysis on cell volume shrinkage during freezing helps us understand the mechanism of cryopreservation. Freezing studies were conducted using a Linkam cryostage fitted to an optical microscope cooled under controlled rates at 5, 10, 20, 50 and 100°C/min. The volume of renal cell at subzero temperature have been quantified by heat latent obtained from DSC data and compared to the microscopic data. Experimental data were fitted by nonlinear regression method to calculate the water transport parameters. Also, the final volume of cell was predicted. The ice crystal formation is the vital factor for cryopreservation. Cooling rate deeply affected ice formation temperature. The faster cells are cooled, the more their contents supercool, and at some subzero temperature that supercooled cytoplasm will freeze. Intracellular ice formation (IIF) plays a central role in cell injury during cooling. Cryomicroscope and differential scanning calorimeter were used to study the relationship between cooling rate and TEIF and TIIF. And morphological changes of renal cell were also obtained by cryomicroscope. According to cryomicroscope and DSC experiments, IIF did not occur in renal cells cooled at ≤10°C/min. High cooling rate could depress the ice formation temperature.
Creating an Application to Predict Operational Characteristics and Efficiency of Continuous Cross-Flow Corn Drying
Authors: Olson Matthew L. , Gent Stephen P. , Suess Taylor N. , Twedt Michael P.
Published: December 2013

The purpose of this study is to create a computer simulation which numerically predicts the drying conditions within a continuous cross-flow grain drying system. The model is based on a system of four partial differential equations using energy and mass balances for the air, grain, and moisture within the column. This simulation includes: (1) a graphical user interface for varying the operating conditions, (2) a numerical scheme for solving the system of equations based on a backwards finite difference scheme, and (3) graphical and tabular output data. The output includes graphs of moisture content, air temperature, and grain temperature inside the column, as well as the predicted energy consumption of the system. Using this program, the grain drying model is analyzed in order to gain insight towards the optimal operating conditions for the grain dryer. The study also makes adjustments to the model in order to improve accuracy and ease of use. In particular, the Page equation for single-kernel drying is implemented. Model assumptions are also analyzed for validity, and the solutions are verified using experimental data collected in a previous study. The overall goal of this research is to improve grain dryer design and optimize operating conditions in order to reduce energy costs, improve grain quality, and increase the understanding of deep bed grain drying models.
Feasibility Study for Ice-Slurry to District Cooling System in Korea
Authors: Chung Jae Dong , Lee Yoon-Pyo , Yoo Hoseon , Lee Jae-Heon , Lee Chang-Jun , Moon Seung-Jae
Published: December 2013

The district-cooling system (DCS) was in service in Sang-am in Seoul, Korea after 2005. The facility capacity of the DCS in Sang-am is 111Gcal/h at 2011 and 63Gcal/h of facility is planned to install till 2025. However, the cooling demand is increased due to new high-rise building blocks, and the required facility capacity is expected to be 101Gcal/h. A difficulty comes from building new plan in the existing plant. This paper is on the feasibility study for the new requirement under the restrictions of existing pipeline, limited space and regulation on the usage of electric driven chiller. Precise estimation of the diversity factor is essential to determine the required capacities. For this, every building in the area was categorized and the cooling loads were measured for the summer seasons of 2010 and 2011. The large energy capacity of ice slurry can potentially increase the cooling capacity in existing plants while maintaining the same flow rate and pumping power. Thus under the restriction of existing pipeline system, introducing ice slurry is expected as potential solution to the significantly increased cooling load without requiring increases in pipe size or system flow rates.
Optimization of Single Row Jet Impingement Array by Varying Flow Rates
Authors: Miller Nicholas , Siw Sin Chien , Chyu Minking K. , Alvin Mary Anne
Published: December 2013

The current detailed experimental study focuses on the optimization of heat transfer performance through jet impingement by varying the coolant flow rate to each individual jet. The test section consists of an array of five jets, which is individually fed and metered separately, and expels air through one exit. The jet diameter D, channel height to jet diameter H/D, and jet spacing to diameter S/D, are all held constant at 9.53 mm (0.375 in), 2 and 4 respectively. The Reynolds number, which is based on jet diameter and bulk mean velocity at each jet, ranges from 50,000 to 80,000. A transient liquid crystal technique is employed in this study to determine the local and overall-average heat transfer coefficient distribution on the target plate. Commercially available CFD software, ANSYS CFX, is used to qualitatively correlate the experimental results and to provide detailed insights of the flow field created by the array of jets. The results revealed higher heat transfer coefficients in the impingement area, while decreasing in the radial direction. The upstream region exhibited high heat transfer performance, which is ultimately driven by the jet impingement from the first jet to the third jet. Heat transfer performance decreases at the downstream region with the development of cross-flow. By varying the jet flow rates at approximately ±2%, local heat transfer at the downstream region is elevated and the total heat transfer enhancement on the target surface is enhanced up to 35% compared to the baseline case.
Forced Convection in a Square Duct With a Wavy Wall
Authors: Shmueli H. , Ziskind G. , Letan R.
Published: December 2013

In the present study, turbulent flow and heat transfer in a square duct with a heated wavy wall are investigated numerically using the Large Eddy Simulation (LES). A thorough validation of the numerical approach is done versus the existing results for both flat-wall square ducts and wavy-wall channels. It is demonstrated that a very good agreement is achieved with the literature in terms of global and local flow and heat transfer parameters.

Heated wavy surfaces of various amplitudes are explored. The results are compared with those for a completely flat duct in terms of the friction factor and Nusselt number. It is shown that the friction factor increases practically linearly with the wave amplitude. On the other hand, the Nusselt number, averaged over the entire duct length, increases more steeply for the relatively small wave amplitude, but almost reaches a plateau for a further increase in the amplitude.
Simplified Mathematical Model to Evaluate the Performance of the All-Vanadium Redox Flow Battery
Authors: Sathisha H. M. , Dalal Amaresh
Published: December 2013

All-vanadium redox flow battery is one of the promising rechargeable battery since it is able to withstand average loads, high energy efficiency and high power output. The battery exhibits the excellent transient behaviour and sustains sudden voltage drop. The dynamics of the battery is governed by the conservation equations of mass and charge. The simplified mathematical model includes major resistances, electrochemical reactions and recirculation of electrolyte through reservoirs. The mathematical model is able to predict the performance of the battery. The cell performance can be increased by increasing the concentration of the vanadium ions, the flow rate and the temperature inside the cell. The model results are validated with the available experimental result which shows better agreement.
Coupled Computational Heat Transfer and Reactor Physics for SCWR
Authors: Hughes Christopher R. , Schubring DuWayne , Jordan Kelly A. , Rätz Dominik
Published: December 2013

To fully model the physics present within the proposed supercritical water reactor (SCWR), the thermal hydraulics calculations (yielding temperatures and densities in each material as a function of space) must be coupled to the neutronic calculations (yielding reactivity and neutron flux shapes). To enable this full coupling, a 3D model of a supercritical water reactor is being implemented in the CFD software OpenFOAM with the same geometry as a 3D MCNP (neutronics) model. Coupling will performed through result exchange between the two codes — densities and temperatures from OpenFOAM to MCNP, with heat generation returned from the neutronics calculations. Use of a reduced-geometry model is advisable due to the high computational cost of each OpenFOAM/MCNP coupling iteration. In the present work, a 1.5D thermal model of a single fuel pin was coupled with a 3D MCNP model. The thermal model includes single channel analysis (cladding/coolant heat transfer) as well as heat transfer within the cladding, helium gas gap, and uranium dioxide fuel itself. These heat transfer zones provide specific data points of the radial temperature profile. Because no radial mesh is considered, full radial dependence is not possible. The model provides limited radial dependence unlike what a 1D code could provide; thus, 1.5D is used to indicate the incomplete radial dependence that is included in the model. Iteration between the two codes is performed until heat generation is converged to within 10% between successful MCNP results. A discussion of these 3D/1.5D coupled results and the path forward to fully 3D coupling is provided.
CFD Modeling of Single Bubble Collapse in Subcooled Boiling
Authors: Owoeye Eyitayo J. , Schubring DuWayne
Published: December 2013

The open-source software OpenFOAM has been employed to better understand the transport, deformation, and collapse of single, isolated bubbles in subcooled boiling. High pressure steam-water was selected as the fluid system of interest due to its relevance to the power generation industry. Ranges of bubble size, subcooling, pressure/saturation temperature, and mesh refinement have been employed. Both quantitative (bubble rise velocity and collapse times) and qualitative (bubble shape) results are discussed across the parameter ranges studied.
Research on Measurement of Spectral Emissivity Based on Fourier Infrared Spectrometer
Authors: Yue Kai , Niu Yongjian , Guo Xiaoming , Zhang Xinxin
Published: December 2013

As one of the basic parameters characterizing the radiation heat transfer of material surface, the emissivity is of important significance to perform non-contact thermometry research. Comparing with the traditional measurement method, measurement method of spectral emissivity based on the Fourier spectrometer has many advantages such as high accuracy and fast measurement. However, the measurement accuracy is subject to the influence of the radiant energy and the spectrometer electromagnetic radiation noise resulted from the environment. In this study, the geometric factor of the sample was defined and the reflectance of the background radiation in the surface of the sample was applied to accurately determine the energy of the radiation received on the detector. An emissivity measurement model was established and a mathematical formula was derived in this study to eliminate the influence of the background radiation noise. To improve the measurement accuracy of the surface temperature of samples, a heat conduction model is established so that the radiation heat transfer of the sample surface can be calculated and the surface temperature of the sample was obtained by equilibrium calculation. Moreover, we conducted emissivity measurement of black paint samples with high emissivity using the Fourier spectrometer and the proposed model is proven valid. Comparing the experimental results modified by the eliminating calculation formula with the experimental data obtained by the monochromator, it was found that there was good qualitative agreement between two sets of results.
A Novel Approach to Model Thermo-Fluids of Gearbox Systems
Authors: Yazdani Miad , Soteriou Marios , Botros Barbara , Wu Hailing , Liou Joe , Chaudhry Zaffir
Published: December 2013

Gearboxes are integral machine components that determine the capability and reliability of many aerospace and automobile industry systems. Continuous demand for higher efficiency and reliability, increased load-carrying capacity and endurance life, smaller size, lower weight, lower noise and vibrations, prolonged service intervals and low costs are the main driving forces in the development of gear drives in the future. For many gearboxes, the thermo-fluids of the gas/oil/solid system determine the gearbox performance and its durability and life. However, there is a very limited predictive capability of the thermo-fluid characteristics of gearbox due, in large part, to its excessive complexity.

In this paper, we present a coupled thermo-fluid model for the simulation of the two-phase flow along with the heat transfer within gearbox systems in a conjugate fashion. The primary challenge is the enormous separation of fluid-mechanics and heat-transfer time-scales which makes the conventional way of solving the coupled thermo-fluid system of equations computationally prohibitive. In contrast, the approximate approach developed in this study exploits this separation of scales to provide an accurate representation of the long-term, time dependent thermo-fluid state of the gearbox at a modest computational cost. The commercial package ANSYS FLUENT is used to solve URANS equations for fluid mechanics and VOF for the two-phase interface capturing, while the energy equation is modified through user-defined functions to solve for the temperature field inside the fluid and solid components. In addition, the heat generation raised by the meshing of the gears is provided by a separate model based on gear geometry and operating conditions. The approach is verified against a full-fidelity simulation for a simplified and accelerated gear system and is validated against experiments.
Advancement of Computational Heat Transfer in Fire Research in China
Authors: Fan Weicheng , Yao Wei , Zhang Hui , Liu Quanyi , Yang Rui , Zheng Lili
Published: December 2013

Computational heat transfer became one of the major tools for engineering system design in 1970’s. It has been introduced into Chinese society since 1980’s, especially after Brian Spalding’s first lecture in 1984 in China. As one of Brian’s a few early visiting scholars from China, Professor W. C. Fan has begun his endeavor to expand computational heat transfer to fire research. This paper will first briefly introduce the history of the development of computational modeling with particular applications in fire research — a state funded large project, and then present some representative research work in fire research including recent works on high altitude fire and performance based design.
Experimental Investigation of Heat Transfer Across a Thermoelectric Generator for Waste Heat Recovery From Automobile Exhaust
Authors: Pandit Jaideep , Thompson Megan , Ekkad Srinath V. , Huxtable Scott
Published: December 2013

The study investigates the temperature gradients achieved across a thermoelectric generator by using the exhaust gases from a vehicle as a heat source and the radiator coolant as the cold sink. Various heat transfer enhancement features are employed in order to achieve as high a temperature gradient as possible. Effect of flow Reynolds numbers and inlet temperatures are examined to create a body of data predicting total power output from the TEG. Data is normalized against results from baseline heat exchanger designs investigated in the past. The experiments are carried out at 1/5th scale of the previously examined geometry. Impingement geometry is employed on the coolant side to enhance heat transfer. The experimental test sections are fabricated using metal 3D printing. Water is used instead of radiator coolant and heated air is used for exhaust gases. The results from the experiments provide valuable data which can be used for system level optimization.
The Effect of Vertical and Horizontal Partitions on Natural Convection in a Heated Enclosure
Authors: Kruger Sunita , Pretorius Leon
Published: December 2013

In this paper, turbulent buoyancy induced convection in a partitioned square cavity with conducting baffles is numerically investigated to determine overall heat transfer performance. The finite volume method using polyhedral cells is used to solve the governing mass, momentum and energy equations and to predict the flow patterns and heat transfer in the cavity. The cavity consisted of two adiabatic vertical walls, an isothermal horizontal wall located at the bottom at Th and the top wall isothermal at Tc. The configuration was investigated for Ra = 9.1 × 107 to Ra = 1.9 × 109 (turbulent). The conducting baffles are assigned various values of effective thermal resistances, calculated using thermal conductivity. The effects of these conducting baffles and their effective thermal resistance are shown in terms of temperature and velocity contour plots and average Nusselt number. Results indicated that the presence of baffles influenced the heat transfer from the hot wall considerably, and it was concluded that a partitioned enclosure containing conducting partitions can be used to represent an enclosed greenhouse containing raised benches with single/multiple racks.