bluuebunny/crossref_metadata_2025 huggingface dataset:
Regulation of Salmonella enterica pathogenicity island 1 (SPI‐1) by the LysR‐type regulator LeuO
Authors: Espinosa Elena , Casadesús Josep
Published: December 2013

LeuO is a quiescent LysR‐type regulator belonging to the H‐NS regulon. Activation of leuO transcription represses expression of pathogenicity island 1 (SPI‐1) in Salmonella enterica serovar Typhimurium and inhibits invasion of epithelial cells. Loss of HilE suppresses LeuO‐mediated downregulation of SPI‐1. Activation of leuO transcription reduces the level of HilD protein, and loss of HilE restores the wild type HilD level. Hence, LeuO‐mediated downregulation of SPI‐1 may involve inhibition of HilD activity by HilE, a view consistent with the fact that HilE is a HilD inhibitor. In vivo analyses using β‐galactosidase fusions indicate that LeuO activates hilE transcription. In vitro analyses by slot blotting, electrophoretic mobility shift analysis and DNase I footprinting show that LeuO binds the hilE promoter region. Although residual SPI‐1 repression by LeuO is observed in the absence of HilE, the LeuO‐HilE‐HilD ‘pathway’ appears to be the major mechanism. Because both leuO and SPI‐1 are repressed by H‐NS, activation of leuO transcription may provide a backup mechanism for SPI‐1 repression under conditions that impair H‐NS‐mediated silencing.
“Gliomatosis encephali” as a novel category of brain tumors by the first autopsy case report of gliomatosis cerebelli
Authors: Nakahara Asa , Yoshida Toshikazu , Yazawa Masanobu , Ehara Takashi , Nakayama Jun , Kakita Akiyoshi , Ogura Ryosuke , Asakawa Mika , Suzuki‐Kouyama Emi , Oyanagi Kiyomitsu
Published: December 2013

Gliomatosis cerebri is a rare diffuse glioma that is neither mass‐forming nor necrotic, and does not disrupt existing structures. Gliomatosis occurring in the cerebellum is known as gliomatosis cerebelli, and only three such cases examined by biopsy have been reported. Here we describe the first autopsy findings of a patient who was diagnosed as having gliomatosis in the cerebellum. Neuropathological examination identified the tumor cells as being positive for glial fibrillary acidic protein, vimentin and nestin, with atypical nuclei that were cashew‐nut‐ or dishcloth‐gourd‐shaped. These tumor cells were dense in the right cerebellum, but also spread broadly throughout the brain including the left cerebrum and optic nerve. Mitotic figures were frequently seen in the cerebellum, brain stem and cerebrum. Scherer's secondary structures were evident not only in the cerebellum but also the cerebrum. No necrosis, microvascular proliferation or destruction of anatomical structures was detected in the whole brain. Differences in the origin of the tumors of the gliomatoses cerbri and cerebelli suggests these tumors are different types of brain tumors. Thus the findings support that the gliomatosis cerebelli is a novel type of brain tumor classification. Furthermore, by the similarities of the histological features among the tumors, it appears appropriate to establish a novel category of “gliomatosis encephali” which includes both gliomatosis cerebri and gliomatosis cerebelli.
Preferential secretion of inducible HSP70 by vitiligo melanocytes under stress
Authors: Mosenson Jeffrey A. , Flood Kelsey , Klarquist Jared , Eby Jonathan M. , Koshoffer Amy , Boissy Raymond E. , Overbeck Andreas , Tung Rebecca C. , Le Poole I. Caroline
Published: December 2013

Inducible HSP70 (HSP70i) chaperones peptides from stressed cells, protecting them from apoptosis. Upon extracellular release, HSP70i serves an adjuvant function, enhancing immune responses to bound peptides. We questioned whether HSP70i differentially protects control and vitiligo melanocytes from stress and subsequent immune responses. We compared expression of HSP70i in skin samples, evaluated the viability of primary vitiligo and control melanocytes exposed to bleaching phenols, and measured secreted HSP70i. We determined whether HSP70i traffics to melanosomes to contact immunogenic proteins by cell fractionation, western blotting, electron microscopy, and confocal microscopy. Viability of vitiligo and control melanocytes was equally affected under stress. However, vitiligo melanocytes secreted increased amounts of HSP70i in response to MBEH, corroborating with aberrant HSP70i expression in patient skin. Intracellular HSP70i colocalized with melanosomes, and more so in response to MBEH in vitiligo melanocytes. Thus, whereas either agent is cytotoxic to melanocytes, MBEH preferentially induces immune responses to melanocytes.
Speaking under pressure: Low linguistic complexity is linked to high physiological and emotional stress reactivity
Authors: Saslow Laura R. , McCoy Shannon , van der Löwe Ilmo , Cosley Brandon , Vartan Arbi , Oveis Christopher , Keltner Dacher , Moskowitz Judith T. , Epel Elissa S.
Published: December 2013

What can a speech reveal about someone's state? We tested the idea that greater stress reactivity would relate to lower linguistic cognitive complexity while speaking. In Study 1, we tested whether heart rate and emotional stress reactivity to a stressful discussion would relate to lower linguistic complexity. In Studies 2 and 3, we tested whether a greater cortisol response to a standardized stressful task including a speech (Trier Social Stress Test) would be linked to speaking with less linguistic complexity during the task. We found evidence that measures of stress responsivity (emotional and physiological) and chronic stress are tied to variability in the cognitive complexity of speech. Taken together, these results provide evidence that our individual experiences of stress or “stress signatures”—how our body and mind react to stress both in the moment and over the longer term—are linked to how complex our speech under stress.
Berberine Ameliorates Experimental Autoimmune Neuritis by Suppressing both Cellular and Humoral Immunity
Authors: Li H. , Li X.‐L. , Zhang M. , Xu H. , Wang C.‐C. , Wang S. , Duan R.‐S.
Published: December 2013

Berberine (BBR), an isoquinoline derivative alkaloid, has been extensively used in traditional Chinese medicine for the treatment of diarrhoea, rheumatic diseases, diabetes, etc. Recent studies have demonstrated new biological properties of BBR and suggested the possibility of BBR to be a therapeutic agent for some autoimmune diseases. To explore the effect of BBR on the development of experimental autoimmune neuritis (EAN), BBR was administered intragastrically daily to Lewis rats immunized with P0 peptide 180–199 in Freund's complete adjuvant. We found BBR treatment resulted in amelioration of EAN, accompanied by suppressed lymphocyte (in particular CD4+ T cell) proliferation, downregulated Th1 (TNF‐α) and Th2 (IL‐10) cytokines and reduced anti‐P0 peptide 180–199 IgG1 and IgG2a. In brief, BBR played a role in ameliorating EAN by suppressing both cellular and humoral immunity. Thus, our study suggests that BBR may be a potential therapeutic agent for the autoimmune disease in the peripheral nervous system, such as Guillain–Barré syndrome.
Specific muscle–tendon architecture in elite Kenyan distance runners
Authors: Kunimasa Y. , Sano K. , Oda T. , Nicol C. , Komi P. V. , Locatelli E. , Ito A. , Ishikawa M.
Published: December 2013

The Achilles tendon moment arm (MA_AT) and foot lever ratio (FLR) can play important roles for force production and movement economy during locomotion. This notion has become more relevant, and suggestion has been given that the Kenyan runners belonging to the world elite would have specific anatomical, mechanical, and functional properties in their lower limbs and that this feature could be responsible for their high running economy. The present study aimed to characterize the AT of elite Kenyan distance runners as compared with Japanese ones, and to examine the potential relationship with their running performance. Ultrasonography was used to measure AT cross‐sectional area and AT soleus and gastrocnemius lengths. MA_AT and FLR were calculated from the position of anatomical landmarks using sagittal plane photographs. MA_AT was significantly longer and the FLR lower in Kenyans than in Japanese. Independently of the group, the running performance was positively related to the MA_AT (r = 0.55, P < 0.001) and negatively to the FLR (r = −0.45, P = 0.002). These results suggest that longer MA_AT and lower FLR could be advantageous in elite Kenyan runners, by contributing to effective endurance running performance in a protective and economical way.
Variational Discrete Developable Surface Interpolation
Authors: Gong Wen-Yong , Liu Yong-Jin , Tang Kai , Wu Tie-Ru
Published: December 2013

Modeling using developable surfaces plays an important role in computer graphics and computer aided design. In this paper, we investigate a new problem called variational developable surface interpolation (VDSI). For a polyline boundary P, different from previous work on interpolation or approximation of discrete developable surfaces from P, the VDSI interpolates a subset of the vertices of P and approximates the rest. Exactly speaking, the VDSI allows to modify a subset of vertices within a prescribed bound such that a better discrete developable surface interpolates the modified polyline boundary. Therefore, VDSI could be viewed as a hybrid of interpolation and approximation. Generally, obtaining discrete developable surfaces for given polyline boundaries are always a time-consuming task. In this paper, we introduce a dynamic programming method to quickly construct a developable surface for any boundary curves. Based on the complexity of VDSI, we also propose an efficient optimization scheme to solve the variational problem inherent in VDSI. Finally, we present an adding point condition, and construct a G1 continuous quasi-Coons surface to approximate a quadrilateral strip which is converted from a triangle strip of maximum developability. Diverse examples given in this paper demonstrate the efficiency and practicability of the proposed methods.
A New Laparoscopic Morcellator Using an Actuated Wire Mesh and Bag
Authors: Isakov Alexander , Murdaugh Kimberly M. , Burke William C. , Zimmerman Sloan , Roche Ellen , Holland Donal , Einarsson Jon I. , Walsh Conor J.
Published: December 2013

Laparoscopic morcellation is a technique used in gynecological surgeries such as hysterectomy and myomectomy to remove uteri and uterine fibroids (leiomyomas) through a small abdominal incision. Current morcellators use blades or bipolar energy to cut tissue into small pieces that are then removed through laparoscopic ports in a piecewise manner. These existing approaches have several limitations; (1) they are time consuming as the tissue must be manually moved over the devices during the cutting step and removal is piecewise, (2) they can lead to accidental damage to surrounding healthy tissue inside the body and (3) they do not provide safe containment of tissue during the morcellation process which can lead to seeding (spreading and regrowth) of benign or potentially cancerous tissue. This paper describes a laparoscopic morcellator that overcomes these limitations through a new design that is based on an enclosed, motor-actuated mesh that applies only an inward-directed cutting force to the tissue after it has been loaded into the protective mesh and bag. The deterministic design approach that led to this concept is presented along with the detailed electromechanical design. The prototype is tested on soft vegetables and an animal model to demonstrate successful morcellation and how the device would be compatible with current clinical practice. Results show that the time required to morcellate with the new device for a set of tests on animal tissue is relatively uniform across samples with widely varying parameters. Including tissue manipulation and extraction time, the new device is shown to have an improvement in terms of speed over current morcellators. The mean time for cutting animal tissue ranging from 100 g to 360 g was 30 s with small variations due to initial conditions. The time for cutting is expected to remain approximately constant as tissue size increases. There is also minimal risk of the protective bag ripping due to the inward-cutting action of the mesh, thereby potentially significantly reducing the risk of seeding during clinical procedures; thus, further increasing patient safety. Finally, this design may be applicable to other procedures involving removal of tissue in nongynecologic surgeries, such as full or partial kidney or spleen removal.
A Model of Micro Electro-Discharge Machining Plasma Discharge in Deionized Water
Authors: Mujumdar Soham S. , Curreli Davide , Kapoor Shiv G. , Ruzic David
Published: December 2013

For successful commercial adaptation of the μ-EDM (micro electro-discharge machining) process, there is a need to increase the process efficiency by understanding the process mechanism. This paper presents a model of the plasma discharge phase of a single discharge μ-EDM event in deionized water. The plasma discharge is modeled using global model approach in which the plasma is assumed to be spatially uniform, and equations of mass and energy conservation are solved simultaneously along with the dynamics of the plasma bubble growth. Given the input discharge voltage, current and the discharge gap, complete temporal description of the μ-EDM plasma during the discharge time is obtained in terms of the composition of the plasma, temperature of electrons and other species, radius of the plasma bubble and the plasma pressure. For input electric field in the range of 10–2000 MV/m and discharge gap in the range of 0.5–20 μm, time-averaged electron density of 3.88×1024m-3-30.33×1024m-3 and time-averaged electron temperature of 11,013–29,864 K are predicted. Experimental conditions are simulated and validated against the spectroscopic data from the literature. The output from this model can be used to obtain the amount of heat flux transferred to the electrodes during the μ-EDM process.
Thermodynamic Simulation and Prototype Testing of a Four-Stroke Free-Piston Engine
Authors: Lin Jiming , Xu Zhaoping , Chang Siqin , Yin Ningxia , Yan Hao
Published: December 2013

In order to achieve higher-energy conversion efficiency, a free-piston engine with an improved four-stroke thermodynamic cycle is investigated in this paper. This cycle is optimized according to the variable strokes feature and is characterized by the short intake stroke, the complete expansion stroke, the external pressurization, and the intercooling. The development of a four-stroke free-piston engine system simulation model was described, and the effects of the cycle on the system performances were qualitatively analyzed. According to the experiment of the prototype, the generating efficiency of 33.4% can be achieved when the system is fueled with gasoline and the output power is significantly increased from 1.62 to 2.68 kW. The simulation and experiment results are analyzed in detail, giving insight into the performances of the system. Studies show that the energy-saving and environmental protection performances of the system can be significantly promoted by using the improved thermodynamic cycle.
Modeling and Parameter Estimation of Robot Manipulators Using Extended Flexible Joint Models
Authors: Moberg Stig , Wernholt Erik , Hanssen Sven , Brogårdh Torgny
Published: December 2013

This paper considers the problem of dynamic modeling and identification of robot manipulators with respect to their elasticities. The so-called flexible joint model, modeling only the torsional gearbox elasticity, is shown to be insufficient for modeling a modern industrial manipulator accurately. Another lumped parameter model, called the extended flexible joint model, is therefore used to improve the model accuracy. In this model, nonactuated joints are added to model the elasticity of the links and bearings. The unknown elasticity parameters are estimated using a frequency-domain gray-box identification method. The conclusion is that the obtained model describes the movements of the motors and the tool mounted on the robot with significantly higher accuracy than the flexible joint model. Similar elasticity model parameters are obtained when using two different output variables for the identification, the motor position and the tool acceleration.
Synchronization of Chaotic Systems Using Sampled-Data Polynomial Controller
Authors: Lam H. K. , Li Hongyi
Published: December 2013

This paper presents the synchronization of two chaotic systems, namely the drive and response chaotic systems, using sampled-data polynomial controllers. The sampled-data polynomial controller is employed to drive the system states of the response chaotic system to follow those of the drive chaotic system. Because of the zero-order-hold unit complicating the system dynamics by introducing discontinuity to the system, it makes the stability analysis difficult. However, the sampled-data polynomial controller can be readily implemented by a digital computer or microcontroller to lower the implementation cost and time. With the sum-of-squares (SOS) approach, the system to be handled can be in the form of nonlinear state-space equations with the system matrix depending on system states. Based on the Lyapunov stability theory, SOS-based stability conditions are obtained to guarantee the system stability and realize the chaotic synchronization subject to an H∞ performance function. The solution to the SOS-based stability conditions can be found numerically using the third-party Matlab toolbox SOSTOOLS. Simulation examples are given to illustrate the merits of the proposed sampled-data polynomial control approach for chaotic synchronization problems.
Nusselt Numbers for Thermally Developing Couette Flow With Hydrodynamic and Thermal Slip
Authors: Steigerwalt Lam Lisa , Melnick Corey , Hodes Marc , Ziskind Gennady , Enright Ryan
Published: December 2013

The effects of hydrodynamic and thermal slip on heat transfer in a thermally developing, steady, laminar Couette flow are investigated. Fluid temperature at the inlet to a parallel plate channel is prescribed, as various combinations of isothermal and adiabatic boundary conditions are along its surfaces. Analytical expressions incorporating arbitrary slip are developed for temperature profiles, and developing and fully developed for Nusselt numbers. The results are relevant to liquid and gas flows in the presence of apparent and molecular slip, respectively.
Numerical Modeling of Two-Phase Flow Distribution Inside Evaporator Headers
Authors: Yazdani Miad , Alahyari Abbas A. , Wu Hailing , Radcliff Thomas D.
Published: December 2013

Two-phase flow distribution inside evaporator headers has been a challenging problem for a long time and having a robust predictive tool could substantially alleviate the costs associated with experimentation with different concepts and configurations. The use of a two-phase CFD model to predict flow distribution inside the header and at the discharge ports is demonstrated in this paper. The numerical domain is comprised of an inlet pipe and a distributor tube representing the header with a series of discharge ports. The flow distribution was initially verified using an air–water experiment, where the two-phase modeling approach, mesh requirements, and discretization schemes were defined. Next, the model was used to predict distribution of R134a in a typical heat exchanger distributor. The flow distribution across the discharge ports was provided to a discretized correlation-based heat exchanger model to predict the temperature and quality distribution along the length of the heat exchanger. The resultant temperature distribution is validated against IR imaging results for various operating conditions and header orientations.
Normal and Explosive Boiling of Argon on Nanostructured Copper Surface: A Molecular Dynamics Study
Authors: Seyf Hamid Reza , Zhang Yuwen
Published: December 2013

Nonequilibrium molecular dynamics (NEMD) is carried out to investigate the normal and explosive boiling of thin film adsorbed on a metal substrate whose surface is structured by an array of nanoscale spherical copper particles. It is found that superheat degree and size of nanoparticles have significant influences on the location of atoms at multiple times and net evaporation rate. For the cases with nanostructure, liquid respond very quickly and evaporation rate increase with increasing the size of particles from 1 to 2 nm while it decreases for particles diameter of 3 nm.
Computational Modeling of Transverse Peltier Coolers
Authors: Ali Syed Ashraf , Mazumder Sandip
Published: December 2013

Transverse thermoelectric effect can be produced artificially by stacking at an angle layers of a thermoelectric material with another material that may or may not be a thermoelectric material. In this exploratory computational study, a new metamaterial, comprised of tilted alternating layers of an n-type thermoelectric alloy and a metal, is investigated to gain an understanding of how much cooling can be produced by transverse thermoelectric effect and the conditions under which maximum cooling is attainable. The governing conservation equations of energy and electric current, with the inclusion of thermoelectric effects, are solved on an unstructured mesh using the finite-volume method to simulate a transverse Peltier cooler under various operating conditions. First, the code is validated against experimental data for a n-Bi2Te3-Pb metamaterial, and subsequently explored. It is found that intermediate applied currents produce maximum temperature depression (ΔT). Optimum values of the geometric design parameters such as tilt angle and device aspect ratio are also established through parametric studies. Finally, it is shown that the ΔT can be amplified by constricting the phonon (heat) transport cross-section while keeping the electron (current) transport cross-section unchanged — a strategy that cannot be employed in conventional thermoelectric devices where electrons and phonons follow the same path. This makes transverse Peltier coolers particularly attractive for generating large ΔT without multi-stage cascading.
Numerical Simulations on Natural Convection From a Circular Cylinder in Oscillating Flows
Authors: Su Yan
Published: December 2013

Natural convection from a circular cylinder in oscillating flows has been simulated by projection method with two dimensional exponential stretched staggered cylindrical meshes. Present numerical results are validated by comparing the heat transfer results of free convection over a circular cylinder to published experimental and numerical results. The effects of wave directions, amplitudes, frequencies and buoyancy forces on the enhancement of heat transfer have also been presented. Based on turning points of the curves of the overall Nusselt numbers versus Reynolds numbers, the heat transfer can be divided into three linear regimes (conduction, laminar convection and turbulent convection dominated regimes) and two non-linear transient regimes. The valid ranges of the governing parameters for heat transfer enhancement have been identified. The effects of wave directions, amplitudes, frequencies, and buoyancy forces on the enhancement of heat transfer are also investigated. The effective ranges of the governing parameters for heat transfer enhancement are identified.
An Open Loop Pulsating Heat Pipe for Integrated Electronic Cooling Applications
Authors: Kearney Daniel , Griffin Justin
Published: December 2013

Increasing trends towards integrated power electronic systems demand advancements in novel, efficient thermal management solutions to cope with the increasing the power density. This paper investigates the performance of a novel open loop pulsating heat pipe embedded in an FR4 organic substrate. The heat pipe and is comprised of 26 parallel minichannels with 13 turns, an average hydraulic diameter of 1.9mm and maximum surface roughness of 2.5μm. The bulk thermal performance of three saturated working fluids — Novec 649, Novec 7200 and Ethanol (99.8%) — is investigated in terms of fill ratio, three angles of orientation, and applied heat fluxes ranging from 0.4 to 2.5W/cm2 at sub-ambient pressures. Novec 649 achieved quasi-stable pulsations at lower heat fluxes due to lower (dp/dT)sat. In addition, the dielectric Novec 649 fluid showed significant potential for integrated heat spreading applications demonstrating heat transfer of up to 176W and thermal resistances as low as 0.25°C/W for a filling ratio of 30% — a 16× improvement to that of a standard dry FR4 substrate.
Combined Experimental-Numerical Approach to Determine Radiation Properties of Particle Suspensions
Authors: Marti Jan , Roesle Matthew , Steinfeld Aldo
Published: December 2013

A combination of experimental measurements with a numerical model is used to find the intensive radiation properties — extinction coefficient, scattering albedo and scattering phase function — of SiC particle suspensions with varying particle loadings. The experimentally determined angular radiation distribution of irradiated SiC samples is applied to fit a collision-based Monte Carlo model with a continuous participating media defining the particle suspension. A validation case with glass microspheres and Mie theory is used to verify the modeling procedure. Two types of SiC particles with dissimilar optical characteristics are examined and the respective radiation properties are determined for porosities between 0.70–0.95. The extinction coefficients of both types of SiC particle are in good agreement with the dependent scattering correlation of Kaviany and Singh.
A Space-Time Meshless Method for Heat Transfer Problems With High Discontinuities
Authors: Da Silva Arthur , Sophy Tonino , Kribèche Ali
Published: December 2013

The aim of this research is the development of a space-time driscretization method based on Diffuse Approximation Meshless method. This method, devoted to transient heat transfer problems presenting high temporal discontinuities, avoids any Finite-Difference time stepping procedure. The space-time discretization proposed here seems to be convenient for continuous transient heat transfer. Nevertheless, for problems including temporal discontinuities, some spurious oscillations, whose amplitudes depend on source power, appear. A new weight function respecting the principle of causality, based on a modification of the involved node’s selection and a normalisation of the distances, is developed. The use of this new weight function both improves the accuracy and vanishes the oscillations. The method is validated by a source free transient heat transfer problem presenting convective exchanges. Then problems including a constant and a discontinuous heat source are solved. Temperatures fields obtained when using the classical weight function are closer to those obtained with a backward Finite Difference scheme when the heat source is continuous. In case of discontinuous sources, when using the classical weight function, temperature fields present some spurious oscillations which disappear when choosing the new one. The proposed method associated to a grid refinement procedure will lead to adaptive grids in space and/or time, independently.
Effect of Cavity Size on Confined Slot Jet Impingement Cooling
Authors: Hamdan Mohammad O. , Hayek Ahmad Y.
Published: December 2013

The paper investigates experimentally the heat transfer characteristic for internal flow inside a semicircular channel due to confined slot-jet impingement. The effect of varying the channel diameters to slot-jet width is evaluated. The average and local Nusselt numbers is calculated by reporting the heater thermal map obtained via an infrared camera, the inlet/ outlet flow temperature are measured via thermocouples, the flow rates are reported via rotameter and the pressure drop is measured across the inlet and outlet flow via pressure transducers. The single enclosed jet flow is used to create a double cyclones inside the semicircular channel to promote heat transfer at different jet Reynolds numbers (ReJet = 100 to 1,000). A semicircular cavity with variable diameter are used to evaluate the effect of channel size on the cyclone flow which directly affect the heat transfer. It is found that the cavity size has two opposite effects on the heat transfer. In one side, as cavity size decreases, the distance between the jet and the curved surface decreases and hence heat transfer improves. On the other hand, as the cavity size increases the swirl size inside the cavity increases and hence heat transfer improves.
Scale/Analytical Analyses of Freezing and Convective Melting With Internal Heat Generation
Authors: Siahpush Ali , Crepeau John , Sabharwall Piyush
Published: December 2013

Using a scale/analytical analysis approach, we model phase change (melting) for pure materials which generate constant internal heat generation for small Stefan numbers (approximately one). The analysis considers conduction in the solid phase and natural convection, driven by internal heat generation, in the liquid regime. The model is applied for a constant surface temperature boundary condition where the melting temperature is greater than the surface temperature in a cylindrical geometry. The analysis also consider constant heat flux (in a cylindrical geometry). We show the time scales in which conduction and convection heat transfer dominate.
Recent Advances in High-Flux, Two-Phase Thermal Management
Authors: Mudawar Issam
Published: December 2013

Recent developments in applications such as computer data centers, electric vehicle power electronics, avionics, radars and lasers have led to alarming increases in heat dissipation rate, which now far exceeds the capability of air cooling schemes and even the most aggressive single-phase liquid cooling schemes. This trend is responsible for a recent transition to two-phase cooling, which capitalizes upon the coolant’s latent heat rather than sensible heat alone to achieve several order-of-magnitude increases in heat transfer coefficient. Three two-phase cooling configurations have surfaced as top contenders for the most demanding applications: mini/micro-channel, jet and spray. This study will explore the implementation of these configurations into practical cooling packages, assess available predictive tools, and identify future research needs for each. It is shown that the design and performance assessment of high-flux, two-phase cooling systems are highly dependent on empirical or semi-empirical predictive tools and, to a far lesser extent, theoretical mechanistic models. A major challenge in using such tools is the lack of databases for coolants with drastically different thermophysical properties, and which cover broad ranges of such important parameters as flow passage size, mass velocity, quality and pressure. Recommendations are therefore made for future research to correct any critical knowledge gaps, including the need for robust computer algorithms. Also discussed is a new class of ‘hybrid’ cooling schemes that capitalize upon the merits of multiple cooling configurations. It is shown that these hybrid schemes not only surpass the basic cooling configurations in heat dissipation rate, but they also provide better surface temperature uniformity.
Heat Transfer Study on Multiple Walls of an Impingement Channel With Variable Jet Heights
Authors: Claretti Roberto , Hossain Jahed , Harrington J. T. , Bernstein J. A. , Verma S. B. , Kapat J. S.
Published: December 2013

The present work studies the relationship between target and sidewall surfaces of a single row impingement channel at various jet-to-target distances. Temperature sensitive paint and constant flux heaters are used to gather heat transfer data on the target and side walls. Jet-to-target distance is set to 1, 2, 3, 5, 7 and 9 jet diameters. The spanwise jet spacing is 4 jet diameters and the streamwise jet spacing is 5 jet diameters. All cases were run at average jet Reynolds numbers ranging from 5,000 to 30,000. Pressure data is also gathered and used to calculate the channels mass flux profiles, used to better understand the flow characteristics of the impingement channel. While target plate heat transfer profiles have been thoroughly studied in the literature, side wall data has only recently begun to be studied. The present work shows the significant impact the side walls provide to the overall heat transfer capabilities of the impingement channel. When only the target wall heat transfer is considered, the Z/D = 2 channel performs the best; however, it was found that, when both the target and side wall channels were taken into account, the Z/D = 3 channel provides with the largest overall heat transfer rate through the target wall and the side walls out of all channel heights.
Compact Gravity Driven and Capillary-Sized Thermosyphon Loop for Power Electronics Cooling
Authors: Agostini Francesco , Gradinger Thomas , Cottet Didier
Published: December 2013

A novel two-phase thermosyphon based on automotive technology is presented as a valid solution for the cooling of power-electronic semiconductor modules. A horizontal evaporator configuration is investigated. This solution is based on a 90°-shaped thermosyphon that allows an optimal geometrical arrangement of the cooler with limited volume occupancy, reduced air pressure drop, and weight as well as optimal thermal performance compared to standard heat-sink technology. The 90°-shape refers to the mutual arrangement of the evaporator body and the condenser; which are in a horizontal and vertical position, respectively. The evaporator cools three power modules with a total power loss between 500 and 1500 W. Experimental results are presented for inlet air temperatures ranging from 20 to 50 °C and for different air volume flow rates between 200 and 400 m3/h. The working fluid is refrigerant R245fa. The maximum thermal resistance (cooler base to air) attained values between 40 and 50 K/kW.
Analysis of Composite Fouling in Corrugated Plate Heat Exchangers
Authors: Zhang Guanmin , Li Guanqiu , Li Wei
Published: December 2013

Experimental and theoretical investigations of water-side fouling have been performed inside four corrugated plate heat exchangers. They have different geometric parameters, such as plate height, plate spacing, and plate angle. Heat transfer coefficients and friction factors have been obtained in clean tests. Composite fouling experiments have also been performed. The tests are primarily focused on the effects of average velocity. Scanning electron microscope (SEM) was used to investigate the microscopic structures of composite fouling and analyze the fouling characteristics in composite fouling tests. The plate heat exchanger with the largest de and height to pitch ratio shows the best anti-fouling performance.
Experimental Study on Heat Transfer of Fuel-Particle Mixtures in a Vertical Tube at Supercritical Pressure
Authors: Wu Xiao-Yu , Huang Dan , Li Wei , Xu Guo-Qiang , Tao Zhi , Jiang Pei-Xue
Published: December 2013

Regenerative cooling system is thought to be an effective and practical solution to better thermal management for high heat flux applications. In this paper, we examined the effects of solid particles mixed with fuels on the heat transfer performances of supercritical fuel coolant. Two-step method was applied to prepare Fe3O4-kerosene fluids. Experiments were carried out to study the heat transfer characteristics of fuel-particle mixtures flowing in a vertical tube at supercritical pressures. Results show that there are three different heat transfer mechanisms at the in-, mid- and ex-sections along the tube; increasing the flow rate or the working pressure could enhance the heat transfer performances, yet higher heat flux leads to poorer heat transfer performances. Besides, the addition of solid particles deteriorates the heat transfer performances of the fuel coolant through the modification of inner wall surfaces. As the particle content increases, the heat transfer performance becomes worse.
Thermal Transport in the Gallium Nitride Chemical Vapor Deposition Process
Authors: Meng Jiandong , Jaluria Yogesh
Published: December 2013

A numerical study has been carried out to characterize the metalorganic chemical vapor deposition (MOCVD) growth of Gallium Nitride (GaN) in a rotating-disk reactor. The major objective of this work is to examine the dependence of the growth rate and thin film uniformity on the primary parameters. First of all, for a rotating-disk system, the governing equations involved are obtained. Then, with the effect of thermal buoyancy included and based on the detailed mathematical model and chemical reaction mechanisms, the 3D simulation study is conducted for a rotating reactor. A comparison between the predicted growth rate and experimental data is presented. In addition, the effect of various primary operating and design parameters on the growth rate of GaN and thin-film uniformity is also examined. This provides further insight into the reactor performance and the characteristics of the entire process. The results obtained can also form the basis for the future design and optimization of this system.
A Comparative Study of the Kinetics of Ethyl and Methyl Esters in Diffusion Flame Extinction
Authors: Diévart Pascal , Gong Jing , Ju Yiguang
Published: December 2013

The rapid growth of eco-friendly biomass derived fuels in transportation requires a fundamental understanding of the uniqueness of their oxidation and combustion characteristics. This paper focuses on one specific class of biofuels, namely Fatty Acids Ethyl Esters (FAEE). A counterflow configuration was employed to measure the extinction limits of the diffusion flames of four ethyl esters (ethyl-butanoate, pentanoate, heptanoate, and nonanoate). The results were compared to that of methyl esters (Diévart et al., 2012, Proceedings of the Combustion Institute, 34). It was observed that both methyl esters and ethyl esters exhibit similar high temperature reactivity against extinction. The use of the transport-weighted enthalpy metric has revealed that all esters share similar chemical kinetics in the near extinction conditions of the present study. A previous detailed kinetic model has been extended to include the oxidation chemistry of ethyl esters, and used to interpret the experimental observations. Good agreement between the computed and experimental extinction limits was observed. The rates of consumption pathway analysis have shown that ethyl esters exclusively decomposed into ethylene and a carboxylic acid through an endothermic six-centered unimolecular decomposition reaction, while methyl esters oxidation preferentially progresses through H abstraction reactions. However, the growth of the radical pool was observed to be driven indifferently between ethyl and methyl esters, therefore resulting in similar global flame reactivity.
Experimental Investigation on Operating Limitation of an Oscillating Heat Pipe
Authors: Ji Yulong , Chang Chao , Li Gen , Ma Hongbin , Sun Yuqing
Published: December 2013

This research represents an experimental investigation on the operating limitation of an oscillating heat pipe (OHP). The OHP has six turns and three sections: evaporator, condenser and adiabatic sections with lengths of 40 mm, 64 mm and 51 mm, respectively. Water or a mixture of water and alumina (Al2O3) making up a nanofluid served as the working fluid. Filling ratios ranging from 30% to 70%, and tilt angles (orientation) ranging from 0° to 90° were studied. The experimental results showed (1) the water/Al2O3 nanofluid can enhance the OHP heat transfer performance, i.e., the highest input power (operating limitation) increased when the OHP was charged with water/Al2O3 nanofluid; (2) the operating limitation increased as the filling ratio increased from 30% to 70%, but the optimum filling ratio of the OHP is 30% or 50% when the working power is lower or higher; and (3) the thermal resistance of the OHP decreased as the tilt angle increased, and the operating limitation increased as the tilt angle increased.
Numerical Analysis of Cooling Tower Water Fouling in Enhanced Tubes
Authors: Fu Ping , Li Hong-Xia , Li Wei , Du Yi-Lin , Xiao Sheng-Lan
Published: December 2013

This paper provides particulate and precipitation fouling data in five 15.54 mm I.D. copper, helically ribbed tubes taken at the condition of Re = 16000 and 800 ppm concentration. The geometries of the helical-rib tubes provided a class of internal enhancement that is typical of commercially enhanced tubes presently used in water chillers, and the ranges of geometric parameters were number of rib starts (10 to 30), helix angle (25° to 45°), and height (0.40 to 0.55 mm). A semi-theoretical model was developed to investigate the main factors of fouling formation from the fouling tests. The fouling model which started from the mass balance model considered the influences of the mass transfer coefficient, wall shear stress, sticking probability and deposit bond strength factor. The model analysis results fit the experiment data well. 3D numerical models for the experimental tubes were established, in which volume-control method and standard k-ω model were used. To explain the diversity of anti-fouling performance in different tubes, the influences of velocity field near wall to the cooling tower fouling deposition were also discussed. It is found that the fouling resistance increases with the increase of the number of starts and helix angle. The numerical results had reasonable deviations with the experimental data.
Tuning Near Field Radiation by Doped Silicon
Authors: Shi Jiawei , Shen Sheng
Published: December 2013

In this letter, we demonstrate theoretically and experimentally that bulk silicon can be employed to overcome the challenge of tuning near field radiation. Theoretical calculation shows that the nanoscale radiation between bulk silicon and silicon dioxide can be tuned by changing the carrier concentration of silicon. Near field radiation measurements are carried out on multiple bulk silicon samples with different doping concentrations. The measured near field conductance agrees well with theoretical predictions, which demonstrates a tuning range from 2 nW/K to 6 nW/K at a gap of ∼60 nm.
Modeling Temperature Distributions in a Nuclear Fuel Rod With the Integral Technique
Authors: Kobus Chris J.
Published: December 2013

There is a large amount of research in the modeling of nuclear reactor fuel rods for various parameters amongst which the temperature is high on the list, reason being the critical temperature limit above which control of geometry will be lost as a meltdown or a partial meltdown may occur. Much of this research involves complex numerical models that are of little help especially to students learning the basics of nuclear engineering and heat transfer. This paper will explore the possibility of utilizing the integral technique for such modeling. The advantage of the technique is its simplicity which comes at the cost of some accuracy. An example is given here for a simplified cross-sectional geometry to illustrate how this modeling is done, and why it may be a superior technique to at least introduce students to the concept, but which may have applications to research in the field as well.
Indirectly Measuring the Convective Heat Transfer Coefficient Utilizing Thermistors for Education and Research
Authors: Kobus Chris J.
Published: December 2013

A primary parameter of interest in many heat transfer problems is the convective heat transfer coefficient, which is dependent upon several fundamental parameters like fluid properties, velocity, temperature distribution, etc. As such, empirically determining this parameter can be complicated, especially in educational settings. The classical method includes many physical temperature sensors and heating pads distributed throughout a body that necessitates complex control schemes and data acquisition systems. This paper details a far simpler method of indirectly measuring the convective heat transfer coefficient by utilizing thermistors of various geometries. In calibrating these thermistors for their temperature-resistance characteristics, the convective heat transfer coefficient can be backed out without directly measuring the temperature of the thermistror itself, which has the effect of simplifying the experimental requirements to a large enough degree to make the technique suitable for introductory educational courses in heat transfer. In addition, the technique is also accurate enough to where the experimental data is worthy of publication in the archival literature.
Application of Schlieren Photography to Study Neutral Plane in a Compartment Fire With Scale Models
Authors: Su Chung-Hwei , Ke Yu-Pei , Chow W. K. , Hsu Ming-Chih
Published: December 2013

In this paper, the neutral plane in a compartment fire was measured by Optical Schlieren Photography. This is a highly sensitive, optical, nonintrusive and remote technique to visualize fluid flow, utilizing refraction when light passes through air of different densities. The positions and variations of hot air flowing out of an opening can be determined clearly. A 1/14 scale model room burning candles inside was used. Hot air induced by the candle flame flowing out a 15 cm opening was observed. Thermocouples were also placed at the opening to compare with the neutral plane determined by the Schlieren Photography method. Simulations with Computational Fluid Dynamics were performed to justify the observed locations of the neutral planes.
Boiling of Dilute Emulsions on a Heated Strip
Authors: Roesle Matthew L. , Lunde David L. , Kulacki Francis A.
Published: December 2013

Measurements of heat transfer coefficients in pool boiling of a dilute emulsion on a short vertical surface are reported. The vertical surface is a thin steel ribbon of 1.35 mm height × 101 mm length. Direct current resistance heating produces boiling either on the surface or in the free convection boundary layer of dilute emulsions of pentane and FC-72 in water. Single phase and boiling heat transfer coefficients are measured for emulsions with a volume fraction of the dispersed component of 0.1 and 0.5 percent in an isothermal pool at approximately 25 degrees Centigrade. The dispersed component is created by a simple atomization process, and no surfactants are employed to maintain the droplets of the dispersed phase in suspension. In free convection, the presence of the dispersed component slightly decreases the overall heat transfer coefficient, but when boiling commences, an enhancement of the heat transfer coefficient is observed. Boiling is observed in the emulsions at lower surface temperatures than for water alone, and significantly more superheat is required to initiate boiling of the dispersed component than would be needed for a pool of the dispersed component alone. Consequently, a temperature over shoot is observed prior to initiation of boiling, and such an over shoot has been observed in several prior studies. Heat transfer coefficients are compared to recently published measurements of boiling in similar emulsions on a small diameter horizontal wire. Quantitative comparison of the boiling curves for the wire and plate geometries is made and discussed. The magnitude of the increase in heat transfer coefficient is smaller for emulsion boiling on the surface of the heated strip than is reported for boiling on the wire. The shape of the boiling curve is nearly the same for both geometries.