bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical and Experimental Investigation on Thermal Management of an Outdoor Battery Cabinet
Authors: Meng X. Z. , Lu Z. , Su L. J. , Luo X. L. , Wei L. C. , Jin L. W. , Chai J.
Published: August 2016

Many forms of electronic equipment, of necessity, must be located in an outdoor environment. Such equipment in typical form may be battery packs or telecom-equipment. It is essential that these facilities be protected from a wide range of ambient temperatures and solar radiation. To this end, cabinet enclosures with proper thermal management have been developed to house such electronic equipment in a highly weather tight manner, especially for battery cabinet. Often the batteries are of a lead-acid construction which is known to be adversely affected by temperature extremes in terms of battery performance and life. Therefore, it is important to maintain the cabinet temperature ideally for ensuring battery stability and extending battery lifespan.

In this paper, physical and mathematical models are established to investigate the flow field and temperature distribution inside an outdoor cabinet, which contains 24 batteries with two configurations of two-layer and six-layer respectively. The cabinet walls are maintained at a constant temperature by a refrigeration system and the ambient temperature is up to 50 °C according to the practical situation. The flow field and temperature distribution are analyzed with and without consideration of solar radiation. An experimental facility is then developed to measure the battery surface temperatures and to validate the numerical simulation. The differences between the CFD and experimental results are within 2%, which confirms the CFD model.
Measurement of Thermal Conduction Through Polymeric Nanowires With the Dual Cantilever Technique
Authors: Canetta Carlo , Narayanaswamy Arvind
Published: August 2016

Bi–material microcantilevers, with their high sensitivity to thermal stimuli, are ideally suited sensors for investigating nanoscale heat transfer. We have designed and fabricated low thermal conductance bi–material microcantilevers by minimizing their width and thickness. Using such cantilevers, we have demonstrated heat flux resolution of less than 1 picowatt. A pair of such cantilevers is proposed as a configuration for measuring thermal conductance of a nanostructure suspended between the two. In this technique, two lasers are focused, one on each cantilever. One laser is modulated to vary the temperature at the end of one cantilever, while the second laser senses variation in heat flow through the second cantilever due to thermal conduction along the nanowire. We have determined the resolution of such a conductance measurement by measuring the background conductance between the two cantilevers in the absence of a nanostructure suspended between them. The background conductance is due to other pathways for heat transfer between the cantilevers besides nanostructure conductance. We have measured the background conductance to be as low as 0.05 nWK−1.

We present measurements of thermal conductance of polystyrene nanowires performed using the dual cantilever technique. The nanowires are fabricated via electrospinning technique with diameters varying in the range of 150–300 nm. While the polystyrene nanowires present a demonstration of the cantilever technique for measuring thermal conductance, the technique we have developed can be extended to other types of nanostructures so long as they can be suspended between two cantilever ends.
High Pressure Pool Boiling on a Hydrophobic Surface
Authors: Li Nanxi , Betz Amy Rachel
Published: August 2016

The purpose of this research is to investigate heat transfer enhancement on a Teflon© coated hydrophobic surface compared to a plain copper surface at increased pressures with deionized water. Previous research has shown that hydrophobic surfaces promote bubble nucleation and increase heat transfer coefficient. However, heat transfer enhancement on hydrophobic surfaces at high pressures is not widely studied. To carry out the experiments, we designed and fabricated a special experimental facility that will withstand the high pressures (up to 20 bar/ 290 psi) and high temperatures (270 °C /518 °F). A copper surface is coated with Telfon© AF solution using dip coating. Boiling tests are done on a plain copper surface and the Teflon© coated hydrophobic surface at elevated pressures. Test results show that both high pressure and hydrophobic coating will enhance the boiling performance. Bubble nucleation on the hydrophobic surface starts at lower heat fluxes. The effect of pressure on the Teflon© coated surface is smaller compared to the plain copper surface. Approximately 40% of increase of heat transfer coefficient is observed for the Teflon© coated copper surface at 15 psig.
Validation of a Unified Nondiffusive-Diffusive Phonon Transport Model for Nanoscale Heat Transfer Simulations
Authors: Ramu Ashok T. , Ma Yanbao
Published: August 2016

Heat transfer in the vicinity of nanoscale hot-spots is qualitatively different from that in the macroscale, which effect stems from the breakdown of Fourier law due to phonon nondiffusive transport. In this work, we validate a recently proposed alternative, high-fidelity phonon transport model, the unified nondiffusive-diffusive (UND) model, which takes into account the mixed ballistic-diffusive nature of heat transport, as well as reduces to the Fourier law as a limiting case. In the UND model, the nondiffusive phonons are treated using the Boltzmann transport equation, while the diffusive phonon gas is treated by the Fourier law. The numerical results of Maznev et al. for the geometry and spatial dependence of variables corresponding to the transient gratings experiments of Johnson et al. are used for validation of the model.
Experimental Study of Buckling Behavior of Octagonal Thin-Walled Silicon Tube Grown by Edge-Defined Film-Fed Method
Authors: Wei Guanghua , Ma Ronghui , Zhang Hui , Zheng Lili
Published: August 2016

Edge-defined Film-fed Growth (EFG) is a promising technology for production of silicon wafers with minimum loss of silicon material for photovoltaic applications. The growth of the hollow tubes by the EFG method is a very high temperature gradient along the direction of tube growth at the melt-solid interface. As this high temperature gradient is necessary to sustain the high speed of silicon growth through dissipating latent heat at the melt-solid interface, it generates substantial amount of thermal stresses that are associated with defect generation and deformation of the structure. With increase of the tube diameter and reduction of wall thickness, the large thermal stresses lead to significant buckling of the tube.

In this study, the buckling behavior of the growing silicon tube is studied experimentally by monitoring deflection of two pairs of opposite faces of an octagonal tube during the growth. Four capacitance sensors were placed on a fixed plane normal to the translation of the tube to measure the varying thickness of the air between the sensor and the tube surface throughout the tube growth. The recorded data reveal the buckling behavior of tubes for several growth runs. Despite the different growth conditions in the EFG systems, similar patterns of buckling behavior have been observed in octagonal silicon tubes with face width of 12.5 cm. A typical buckling pattern observed can be divided into three distinctively different stages, namely seed holder-influenced stage, tube growth stage, and a random fluctuation stage. Each stage has different amplitude of deflection and covers different length of the tube. More interestingly, the recorded surface deflection reveals the displacement of the center of the tube, suggesting off-centered growth and possible instability of the meniscus. It is considered that these mechanisms may contribute to the special buckling pattern observed during growth.
Using POD to Characterise Panel Backside Heat Losses
Authors: Emery A. F.
Published: August 2016

Repairing composite structures requires heating the repair site to a specific temperature and holding it at this temperature for a length of time. This is usually accomplished by placing a heating blanket over the repair site or by thermally radiating it. In either case, significant heat conduction occurs through the composite repair zone resulting in spatial variations in temperature. In general, one has access only to one side of the structure and is not aware of the specific nature of conditions on the backside. It is not uncommon for the backside structure in the neighborhood of the repair site to be such that the heat transfer is inhibited by pockets of trapped air or increased by metal structures. If the applied heat can be spatially controlled it is possible to eliminate temperature variations in the repair zone. This short paper describes attempts to estimate backside heat losses, or at a minimum to detect the presence/magnitude of these losses. Early attempts to estimate these losses by parameter estimation proved not to be adequate. The test was modified to include a backside heat sink, but thermocouple measurements suggested that there was negligible effect. The use of proper orthogonal decomposition of thermographic images taken during heating and cooling was considered as an alternative analysis. The POD indicated that there was no substantial heat loss to the sink because of the high thermal resistance of the panel. Given this finding, it appears that eliminating spatial temperature variations can only be done by active control of the heat source.
Thermo-Economic Limitations of Passive Air-Cooled Ambient Heat Rejection Systems
Authors: Gallandat Noris , Mayor J. Rhett
Published: August 2016

This paper presents the preliminary results of a thermo economic optimization of passive air-cooled ambient heat rejection systems. Although a lot of effort has been put into the thermal efficiency of various cooling technologies, there is a need for a comprehensive thermo-economic study cross comparing the different options. This study considers passive ambient heat rejection from bonded and extruded fin arrays. The outcome is a general Pareto front showing the limitations of different passive cooling technologies such as natural convection through extruded and bonded fin arrays or enhanced heat transfer via chimney effect. The obtained Pareto front allows making cost effective decisions regarding which technology to implement depending on the thermal requirements of the system. A bi-objective optimization is carried out using genetic algorithms. The two parameters to minimize are the overall thermal resistance and the total cost of the system. It is shown that, generally, there is a negative correlation between the cost of the system and the thermal resistance. At low heat flux, natural convection through extruded fin arrays is the most economical choice. As more stringent thermal loads act on a system, the thermal resistance of the heat sink can be reduced at an additional cost by enhancement of convective heat transport through buoyancy-driven flows. For the considered geometry, the maximal cooling power without a chimney amounts 1887W at a heat flux of 0.87W/cm2. By adding a 5m chimney, a 43% increase in the cooling power is reached, allowing the removal of up to 2695W at a heat flux of 1.26 W/cm2.
Transient Heat Conduction and Thermal Coefficient of Ceramic Coated Fabrics
Authors: Teimoori Khashayar , Sadegh Ali M.
Published: August 2016

Ceramic coated fabrics have been employed for heat resistant clothing such as fire-fighters gears, fire-proof insulators, and heating and cooling insulators. Thus, transient heat conduction and thermal properties of such fabrics are needed for the design of the clothing. The goal of this study is to measure the transient heat conduction and the coefficient of thermal expansion of ceramic coated fabrics with different woven morphologies. This has been accomplished through an experimental setup consists of a hotplate assembly, applying a uniform temperature, with the accuracy of +/− 1 °C in less than 500 msec, a ceramic coated fabric and an infra-red thermometer assembly. This set up has been validated by using a known material such as aluminum and copper for the coefficient of thermal expansion measurement. The hot plate temperature was varied between 30 to 400°C within 300 seconds.

The transient heat conduction and the thermal coefficient of the woven ceramic coated fabrics were compared with ceramic nonwoven fabrics materials. Finally, upon comparing different samples and measuring the coefficients of thermal expansion, K’s, the level of delay in heat transfer with respect to time has been determined.
Jet Interaction in Cross Flow: Experimental and Numerical Model
Authors: Almeida Celso , Nunes António A. , Teixeira Senhorinha , Teixeira José Carlos , Lobarinhas Pedro
Published: August 2016

Ventilation of wide spaces often requires a correct mixing of a jet in a cross flow. The present paper describes the application of Computational Fluid Dynamics (CFD) to model the interaction of a free stream jet with a cross flow, taking into account temperature gradients between the two streams. The model uses the finite volume technique for solving the conservation equations of fluid: mass, momentum and energy. Buoyancy is described by the Boussinesq approximation. The convergence of the solution required a high mesh refinement in the region of flow interaction.

The data were compared with experimental results obtained in a subsonic wind tunnel. The experiments were carried out along the 4.0 m long test section of a 1.4×0.8 low speed wind tunnel. The jets were injected at 90° through orifices 25 mm in diameter drawn from a plenum either at the same or higher temperature the free stream. The jet velocity to the free stream velocity ratio was set at 8 for a single jet and between 4 and 16 for multiple injections. Data include velocity, pressure and temperature.

The results show that the injection of relatively small cross-flow rates can cause the development of large regions of interaction with the main flux, accompanied by the creation of large scale flow structures, which contribute effectively to rapid mixing of the two streams.

A CFD simulation of temperature showed that a jet 30 diameters downstream (30D) is an extension of the plume covering almost half of the cross section and a good homogeneity, then the extension of the plume 120D which covers almost the entire cross section and an optimum mixing occurs.

The CFD simulation temperature of 13 jets showed that a toroidal extension of the plume and a good homogenization as early as 30D downstream of the injection point, occurs.
Velocity Based Defrost and Frost Inhibition of Evaporator Coils of Heat Pump
Authors: Muthusubramanian Kamalakkannan , Dessiatoun Serguei V. , Shooshtari Amir H. , Ohadi Michael M.
Published: August 2016

Researchers in the past have reported various methods to either retard frost formation or minimize energy expenditure during defrosting, but the methods reported in this paper is novel. Use of air flow during heating and defrosting cycles has not been studied and reported so far.

The effect of using air flow during heating and defrosting cycles of heat pump were investigated experimentally.

In the heating cycle, it is found that at higher air flow velocities, it is possible to retard the rate at which frost grows on the evaporator coils of the heat pump. Changing the air velocity from 0.8 m/s to 2 m/s caused a significant reduction in the frost growth rate. The ΔT of the working fluid for the 2 m/s experiment stayed at least 0.5 ∼ 1.0 °C more than the corresponding value of the 0.8 m/s experiment for the entire 90 minute duration of the heating cycle.

In the defrost cycle, it is found that using air flow in the direction opposite to the normal air flow on the evaporator coil provides an energy saving opportunity by increasing the time interval between subsequent defrosting. It was seen that a reduction of 1 ∼ 2 defrost cycle was possible in 1 hour of operation, depending on the level of frost formation.
Heavy Duty Vehicle Cooling System Auxiliary Load Management Control: An Application of Linear Control Strategy (MIMO and SISO)
Authors: Sermeno Salvador , Bideaux Eric , Brun Xavier , Ameur Omar
Published: August 2016

Vehicle Thermal Management covers the engineering field of solutions that maintain the complete vehicle in acceptable operating conditions regarding components and fluid temperatures in an engine. The maximum efficiency rating of a Diesel engine reaches up to 45%; a vast amount of the energy produced is transformed into heat. This heat is partly rejected in the exhaust gases and partly transmitted to the engine cooling circuit. The latter can be seen in two different ways, on the one hand, cooling is necessary to regulate the fluids and component temperature to an optimum operating point for fuel efficiency and maintain engine performance. On the other hand it constitutes a loss since the coolant system actuators are engine driven (pump, fan, etc.).

In order to improve the fuel efficiency of the vehicle one can reduce the losses generated by the cooling system. Ideally, the full motive force of the engine should be used for propulsion, and new and more efficient energy sources have to be explored to power the secondary systems (cooling, compressed air…). The electrification of some components in the cooling system can limit losses and improve component energy efficiency but it is not the only answer and in many cases this approach might be a limited. Recent studies have shown that by improving the control strategy of the cooling system the fuel consumption can be improved, however no real data is available since its implementation has been limited.

In keeping with latter approach, this paper introduces a novel control which aims at a more efficient regulation of the cooling system operation of a Heavy Duty Truck cooling system. The main complexity in such a system remains the interactions between actuators. In this paper we propose a way to solve this using a control based on model inversion and decoupling strategy. It needs to be noted that any new approach requires the current control specifications to be modified. This enables also a better understanding of the system. However, other goals can be exploited through the use of an advanced control and the new control specifications such as a reduction of thermal shock, reduction of thermal fatigue, minimization of system overcooling (directly impacts fuel consumption but also the noise levels).

Finally, the controller has been tested on a Simulation Platform using a Matlab/Simulink (Controller) and compared to the existing system control using a reference driving cycle.
Optimization of Data Center Cooling Efficiency Using Reduced Order Flow Modeling Within a Flow Network Modeling Approach
Authors: Fouladi K. , Wemhoff A. P. , Silva-Llanca L. , Ortega A.
Published: August 2016

Much of the energy use by data centers is attributed to the energy needed to cool the data centers. Thus, improving the cooling efficiency and thermal management of data centers can translate to direct and significant economic benefits. However, data centers are complex systems containing a significant number of components or sub-systems (e.g., servers, fans, pumps, and heat exchangers) that must be considered in any synergistic data center thermal efficiency optimization effort. The Villanova Thermodynamic Analysis of Systems (VTAS) is a flow network tool for performance prediction and design optimization of data centers. VTAS models the thermodynamics, fluid mechanics, and heat transfer inherent to an entire data center system, including contributions by individual servers, the data center airspace, and the HVAC components. VTAS can be employed to identify the optimal cooling strategy among various alternatives by computing the exergy destruction of the overall data center system and the various components in the system for each alternative. Exergy or “available energy” has been used to identify components and wasteful practices that contribute significantly in cooling inefficiency of data centers including room air recirculation — premature mixing of hot and cold air streams in a data center. Flow network models are inadequate in accurately predicting the magnitude of airflow exergy destruction due to simplifying assumptions and the three-dimensional nature of the flow pattern in the room. On the other hand, CFD simulations are time consuming, making them impractical for iterative-based design optimization approaches. In this paper we demonstrate a hybrid strategy, in which a proper orthogonal decomposition (POD) based airflow modeling approach developed from CFD simulation data is implemented in VTAS for predicting the room airflow exergy destruction. The reduced order POD tool in VTAS provides higher accuracy than 1-D flow network models and is computationally more efficient than 3-D CFD simulations. The present VTAS – POD tool has been applied to a data center cell to illustrate the use of exergy destruction minimization as an objective function for data center thermal efficiency optimization.
Analysis of the Forced Convection in a Porous Channel Saturated by a Nanofluid: Effects of Brownian Diffusion and Thermophoresis
Authors: Rossi di Schio Eugenia
Published: August 2016

The Darcy-Graetz problem for a channel filled by a nanofluid saturated porous medium is studied. The flow is assumed to be fully developed, and a boundary temperature linearly varying with the longitudinal coordinate in the thermal entrance region is prescribed. A study of the thermal behaviour of the nanofluid is performed by solving numerically the fully–elliptic coupled equations. For the model of the nanofluid, both thermophoresis and Brownian diffusion are taken into account. The governing equations have been solved separately for the fully developed region and for the thermal entrance region. With reference to the fully developed region the solution has been obtained analytically, while for the thermal entrance region it has been obtained numerically, by a Galerkin finite element method implemented through the software package Comsol Multiphysics (© Comsol, Inc.). The analysis shows that for physically interesting values of the Péclet number the concentration field depends very weakly on the temperature distribution. Indeed, the homogeneous model could be employed effectively, since the effects of thermophoresis and Brownian diffusion are negligible.
The Modulation of Interfacial Thermal Resistance in Graphite
Authors: Liu Chenhan , Wei Zhiyong , Chen Weiyu , Yang Juekuan , Chen Yunfei
Published: August 2016

It is demonstrated through the nonequilibrium Green’s function method that the interfacial thermal resistance (Ω) of graphite can be modulated by loading pressure in x direction, x and y directions and all three directions respectively in this paper. For graphite without pressure, the interfacial thermal resistance is about 8×10−9 m2K/W. The pressure in the z direction from tensile −1GPa to compressive 10GPa can reduce the Ω by one order of magnitude, which is caused by the increase in the phonon transmission possibility resulting from the increase in the interlayer interaction strength. And the phonon transmission function has the phenomenon of blue shift in the low-frequency range during the process. The pressure in the x-y plane changes from −10GPa to 1.5GPa has slight impact on the phonon transmission and interfacial thermal resistance Ω while there has no pressure or a small pressure in the z direction. So pressure in the basal plane has slight effect on the interfacial thermal conductance and phonon transmission in the graphite. Furthermore, the discrete layer in the graphite separates mutually when the pressure reaches to the critical value 1∼2GPa in the basal plane or to −2∼−1GPa in the z direction. It is worth noted that low-frequency phonons have larger phonon transmission due to longer mean free path and the soft van der Waals interaction between the neighboring layers. Our results suggest that the interfacial thermal resistance of graphite or few-layer graphene can be modulated in a large scope and then can be applied for both heat dissipation and insulation through the pressure engineering.
Visual and Numerical Study for Dropwise Condensation Heat Transfer Mechanism of Steam-Air Mixture Vapor
Authors: Ma Xuehu , Rongfu Wen , Lan Zhong , Zhou Xingdong
Published: August 2016

Non-condensable gas (NCG) is well known for degrading condensation heat transfer due to the accumulation of NCG near the gas-liquid interface. It has been found that a small amount of NCG results in a significant reduction of heat transfer performance. In the present work, dropwise condensation heat and mass transfer mechanism of steam-air mixture were studied on a vertical plate experimentally and theoretically. Considering the dynamic interaction of condensate and gas-vapor diffusion layer, the study focused on the interfacial effect on heat and mass transfer of condensation in the presence of NCG. Comparison of growth rates of new nucleated droplets in different regions showed the enhancement of mass transfer by the gas phase perturbation. Taking advantage of visualization, the influences of droplet curvature, departure movement and transversal suction effect on mass transfer in the interfacial mass diffusion layer were investigated. The numerical simulation subsequently revealed the mixing characteristic of steam and air in the mass diffusion layer which was corroborated by the visual results inspected by PIV technology. Due to the relative motion of condensed droplet and steam-air mixture vapor, eddy flow occurred in the gas phase resulting in a perpendicular velocity of the bulk vapor to the condensing surface and a perpendicular velocity of the accumulated NCG to the vapor bulk which enhanced the heat and mass transfer in dropwise condensation.

The study provides an insight into the disturbance of the diffusion boundary layer by droplet departure movement, as well as the need to design specific surface to promote the droplet departure movement and achieve enhanced heat and mass transfer during dropwise condensation in the presence of NCG.
Numerical Investigation on Thermal and Fluid Dynamic Behavior of Laminar Slot-Jet Impinging on a Surface at Uniform Heat Flux in a Confined Porous Medium in Local Thermal Non-Equilibrium Conditions
Authors: Buonomo Bernardo , Manca Oronzio , Nardini Sergio , Lauriat Guy
Published: August 2016

A numerical investigation on a single slot jet impinging in a porous parallel-plate channel containing an air-saturated high permeability porous medium is accomplished. The wall opposite the slot jet is partially heated at uniform heat flux and the buoyancy effects are taken into account. The fluid flow is assumed two dimensional, laminar and steady. The porous medium is modeled using the Brinkman–Forchheimer-extended Darcy model and the Boussinesq approximation. The local thermal non-equilibrium (LTNE) hypothesis is invoked. The results are discussed in terms of streamlines, fluid and solid phase temperature fields, wall temperature profiles and local and average Nusselt numbers.

The porous medium allows a more significant heat transfer close to the end of the heated part of the plate. For low Peclet numbers, forced flow and natural convection are opposite and the mean Nusselt number shows a decrease in heat transfer, whereas they are aiding for high Peclet numbers. Porosity effects on the mean Nusselt numbers were found weak.
Sub-Grid Filtering Model for Multiphase Heat Transfer With Immersed Tubes
Authors: Lane William A. , Ryan Emily M. , Sarkar Avik , Sundaresan Sankaran
Published: August 2016

Adequately resolving the hydrodynamics and heat transfer in gas-solid flow simulations typically requires computational grids on the order of 1–10 particle diameters. This requirement is not feasible for most full-scale applications. To overcome these impracticalities, we consider a sub-grid filtering approach where the microscopic heat transfer mechanisms are approximated through coarse grid simulations using constitutive relations. Using the open source CFD code Multiphase Flow with Interphase Exchanges (MFIX), we simulate a periodic unit cell domain with immersed horizontal heat transfer cylinders under varying solid-phase fractions and temperatures. The simulation results are averaged over the domain and are used to fit functional forms describing relations between the flow properties and input conditions. The result is a constitutive function that is added as a source term to the solid-phase energy conservation equation to approximate the effective heat transfer between the cylinders and flow with coarse grid simulations.
An Experimental Study of Marangoni Convection in Confined and Volatile Binary Liquids: The Effect of Noncondensables
Authors: Li Yaofa , Yoda Minami
Published: August 2016

Marangoni convection in a liquid layer subject to a horizontal temperature gradient due to variations in the surface tension at the liquid-vapor interface and confined in a rectangular enclosure is a basic problem of heat transfer and fluid mechanics, with applications in evaporative cooling. In general, surface tension increases as temperature decreases, giving rise to thermocapillary stresses that drive liquid coolant away from hot regions. In a volatile binary-fluid mixture, however, the two components can be chosen so that the surface tension of the mixture increases as temperature increases due to differential evaporation, giving rise to solutocapillary stresses that can drive liquid instead towards hot regions, and hence oppose the thermocapillary stresses.

It is of course well-known that noncondensables suppress phase change. Yet there have been few, if any studies of how noncondensables affect the Marangoni convection of volatile binary fluids in a confined geometry, where evaporation and condensation must balance. An experimental study was therefore performed of Marangoni convection in a layer of methanol-water (MeOH-H2O) mixture confined in a sealed rectangular cuvette. The cuvette was symmetrically heated on one end and cooled on the other end using Peltier devices, giving temperature differences of ∼6 °C over a horizontal distance of 4.9 cm, and two-dimensional, two-component particle-image velocimetry (2D-2C PIV) was used to measure the velocity fields in this steady flow. The study focuses on convection in liquid layers with a depth of ∼0.3 cm (vs. a test cell height of 1 cm), and how this flow is affected by changes in the relative concentration of noncondensables (i.e., air) in the gas space above the liquid. The results suggest that changing the concentration of noncondensables, which also has a marked effect on the pressure, in the gas space, can be used to “adjust” the relative importance of solutocapillary and thermocapillary stresses.
3D Examination of the Thermal Properties of Carbon-Carbon Composites
Authors: Patrick Melanie , Saad Messiha
Published: August 2016

Thermal characterization of composites is essential for their proper assignment to a specific application. Specific heat, thermal diffusivity, and thermal conductivity of carbon-carbon composites are essential in the engineering design process and in the analysis of aerospace vehicles, space systems and other high temperature thermal systems. Specifically, thermal conductivity determines the working temperature levels of a material and is influential in its performance in high temperature applications.

There is insufficient thermal property data for carbon-carbon composites over a range of temperatures. The purpose of this research is to develop a thermal properties database for carbon-carbon composites that will contain in-plane (i-p) and through-the-thickness (t-t-t) thermal data at different temperatures as well as display the effects of graphitization on the composite material. The carbon-carbon composites tested were fabricated by the Resin Transfer Molding (RTM) technique, utilizing T300 2-D carbon fabric and Primaset PT-30 cyanate ester resin.

Experimental methods were employed to measure the thermal properties. Following the ASTM standard E-1461, the flash method enabled the direct measurement of thermal diffusivity. Additionally, differential scanning calorimetry was performed in accordance with the ASTM E-1269 standard to measure the specific heat. The measured thermal diffusivity, specific heat, and density data were used to compute the thermal conductivity of the carbon-carbon composites. The measured through-the-thickness thermal conductivity values of all the materials tested range from 1.0 to 17 W/m·K, while in-plane values range from 3.8 to 4.6 W/m·K due to the effect of fiber orientation. Additionally, the graphitized samples exhibit a higher thermal conductivity because of the nature of the ordered graphite structure.
1-D Model of a Real Stirling Engine Calibrated by Experiments
Authors: Vavra Jiri , Cervenka Libor , Takats Michal , Broz Josef
Published: August 2016

In this study the results of a detailed thermodynamic investigation of a real Stirling engine are presented. A combined experimental and simulation approach was applied. A detailed 1-D thermodynamic model of a real Stirling engine was built and calibrated to match experimental data. The experimental data were collected on a prototype engine at the manufacturer’s test laboratory. The set of calibration parameters included energy balance inputs and outputs in the form of integral data and the crank angle based pressure data from the working volumes of the Stirling engine. Unconventional data acquisition and analysis was developed due to the specific nature of the Stirling engine. The procedure for calibrating the Stirling engine model is described in detail, and the resulting tuned model is used to predict the operation of the Stirling engine beyond the measured range. Further design optimization will be performed by the model in future studies. Although the experiments focused on the acquisition and evaluation of instantaneous pressures, the calibration of the model revealed a need for more detailed measurements of the temperature distribution within the regenerator.
Parametric Study on Transient Pool Boiling Heat Transfer Using Metal Rodlet
Authors: Lee Chi Young , Shin Chang Hwan , Oh Dong Seok , Chun Tae Hyun , In Wang Kee
Published: August 2016

The transient pool boiling heat transfer of zircaloy and stainless steel rodlets was investigated using a quenching method. The influences of quenchant temperature, test specimen size, and material property were examined. The groove-structured surface was also prepared and tested, which could be a valuable attempt to study the effect of a machined surface structure of a vertical rodlet on the rapid cooling heat transfer performance. A test specimen with a small volume-to-heat transfer surface area and small heat capacity showed a shorter quenching time. In the low quenchant temperature condition, a stable film boiling regime was likely to be hardly observed. The grooved surface appeared to have a shorter quenching duration, which could be due to its small volume-to-area ratio. In addition, the groove-structured portion seemed to help the liquid make contact with the heated wall earlier than the plain portion. Based on this work, it was found that the quenching duration and the position of vapor film rupture can be controlled by the surface structure.
Simulation of Free Convection in a Porous Enclosure Using the One-Temperature Approach
Authors: de Lemos Marcelo J. S. , Carvalho Paulo H. S.
Published: August 2016

This article investigates the influence of porosity and thermal conductivity ratio on the Nusselt number in a heated vertical cavity. Heat transfer modeling across the enclosure assumed the hypothesis of thermal equilibrium between the solid matrix and the fluid phase. Transport equations were discretized using the control-volume method and the system of algebraic equations was relaxed via the SIMPLE algorithm. Results showed that, when using the one temperature model under the turbulent regime, the cavity Nusselt number is reduced for higher values of the ratio ks/kf as well as when the material porosity is increased. In both cases, conduction through the solid material overwhelms convection across the medium.
Effects of Al2O3-Water Nanofluid and Angular Orientation on Entropy Generation and Convective Heat Transfer of an Elliptical Micro-Pin-Fin Heat Sink
Authors: Rajab Husam , Yin Da , Ma Hongbin
Published: August 2016

This paper presents an investigation of the effect of nanofluid on the heat transfer performance in an elliptical micro-pin-fin heat sink including the influence of entropy generation and pin orientation. The orientation angle of pins is decreased with the number of pins in the array with a 90 degree angle for the first pin and a 0 degree angle for the last pin. To study the flow and heat transfer behaviors in a micro-pin-fin heat sink, steady Navier-Stokes and energy equations were discretized using a finite volume approach and were solved iteratively. Deionized (DI) water was used as a base coolant fluid while aluminum oxide (Al2O3) nanoparticles were used in the present study with mean diameters of 41.6 nm. The results showed that (1) changing the angular orientation of pins can cause significant enhancement in heat transfer, (2) a significant enhancement of heat transfer can be attained in the system due to the suspension of Al2O3 nanoparticles in the base fluid in comparison with pure water, (3) enhancement of heat transfer is intensified with increasing volume fraction of nanoparticles and Reynolds and Prandtl numbers, (4) increasing volume fraction of nanoparticles, which is responsible for higher heat transfer performance, leads to a higher pressure drop, (5) using nanofluids as coolant can cause lower heat transfer entropy generation due to their high thermal properties, and (6) with increasing volume fraction and Reynolds and Prandtl numbers, overall entropy generation rate decreases.
Liquid Film Boiling Heat Transfer in the Presence and Absence of Gravity
Authors: Patel Viral K. , Robinson Franklin , Seyed-Yagoobi Jamal , Didion Jeffrey
Published: August 2016

Liquid film boiling is an effective method of heat removal from a flat surface and has many terrestrial applications. It is an attractive technique for microgravity thermal control but cannot be sustained in the absence of gravity, according to theoretical prediction. However, this has not been experimentally confirmed to date for various reasons such as difficulty of performing experiments in microgravity and the associated cost. This paper presents new terrestrial and microgravity experimental results of liquid film boiling in a radial heat transport device. The microgravity experiments were performed on board a variable gravity parabolic flight. The data were expected to show that absence of gravity results in very high heater surface temperatures and eventual dryout compared to results in the presence of gravity at a given heat flux. However, this only occurred during the transition phase from 1.8-g to 0-g in the parabolic maneuver and the heater temperatures remained normal during the 0-g phase. Despite this, the results still add valuable information to the overall understanding of the liquid-vapor phase-change process in the absence of gravity. They have also laid the foundation for further experimental work such as using electrohydrodynamic (EHD) conduction pumping to facilitate liquid film boiling in microgravity, which we have presented in another study.
The Impact of Reference Frame Orientation on Discrete Ordinates Solutions in the Presence of Ray Effects and a Related Mitigation Technique
Authors: Tencer John
Published: August 2016

The discrete ordinates method is a popular and versatile technique for deterministically solving the radiative transport which governs the exchange of radiant energy within a fluid or gas mixture. It is the most common ‘high fidelity’ technique used to approximate the radiative contribution in combined-mode heat transfer applications. A major drawback of the discrete ordinates method is that the solution of the discretized equations may involve nonphysical oscillations due to the nature of the discretization in the angular space. These ray effects occur in a wide range of problems including those with steep temperature gradients either at the boundary or within the medium, discontinuities in the boundary emissivity due to the use of multiple materials or coatings, internal edges or corners in non-convex geometries, and many others. Mitigation of these ray effects either by increasing the number of ordinate directions or by filtering or smoothing the solution can yield significantly more accurate results and enhanced numerical stability for combined mode codes. When ray effects are present, the solution is seen to be highly dependent upon the relative orientation of the geometry and the global reference frame. This is an undesirable property. A novel ray effect mitigation technique is proposed. By averaging the computed solution for various orientations, the number of ordinate directions may be artificially increased in a trivially parallelizable way. This increases the frequency and decreases the amplitude of the ray effect oscillations. As the number of considered orientations increases a rotationally invariant solution is approached which is quite accurate. How accurate this solution is and how rapidly it is approached is problem dependent. Uncertainty in the smooth solution achieved after considering a relatively small number of orientations relative to the rotationally invariant solution may be quantified.
Characterization of thin film deposits on tungsten filaments in catalytic chemical vapor deposition using 1,1-dimethylsilacyclobutane
Authors: Shi Yujun , Tong Ling , Mulmi Suresh
Published: August 2016

Metal filament plays a key role in the technique of catalytic chemical vapor deposition (Cat-CVD) as it serves as a catalyst in dissociating the source gas to form reactive species. These reactive species initiate the gas-phase reaction chemistry and final thin film and nanostructure formation. At the same time, they also react with the metal itself, leading to the formation of metal alloys and other deposits. The deposits on the tungsten filaments when exposed to 1,1-dimethylsilacyclobutane (DMSCB), a single-source precursor for silicon carbide thin films, in the process of Cat-CVD were studied in this work. It has been demonstrated that a rich variety of deposits, including tungsten carbides (W2C and WC), tungsten silicide (W5Si3), silicon carbide, amorphous carbon, and graphite, form on the W filament surfaces. The structural and morphological changes in the tungsten filaments depend strongly on the DMSCB pressure and filament temperature. At 1000 and 2000 °C, the formation of WC and W2C dominates. In addition, a thin amorphous carbon layer has been found at 1500 °C with the 0.12 and 0.24 Torr of DMSCB and a lower temperature of 1200 °C with the 0.48 Torr of DMSCB. An increase in the DMSCB sample pressure gives rise to higher Si and C contents. As a result, the formation of SiC and W5Si3 has been observed with the two high-pressure DMSCB samples (i.e., 0.24 and 0.48 Torr). The rich decomposition chemistry of DMSCB on the W surfaces is responsible for the extensive changes in the structure of the W filament, providing support for the close relationship between the gas-phase decomposition chemistry and the nature of alloy formation on the metal surface. The understanding of the structural changes obtained from this work will help guide the development of efficient methods to solve the filament aging problem in Cat-CVD and also to achieve a controllable deposition process.
Distinct microenvironmental cues stimulate divergent TLR4-mediated signaling pathways in macrophages
Authors: Piccinini Anna M. , Zuliani-Alvarez Lorena , Lim Jenny M. P. , Midwood Kim S.
Published: August 2016

Macrophages exhibit distinct phenotypes when a shared receptor is stimulated by molecules associated with either infection or injury.
Genomic Analysis of the Evolution of Fluoroquinolone Resistance in Mycobacterium tuberculosis Prior to Tuberculosis Diagnosis
Authors: Zhang Danfeng , Gomez James E. , Chien Jung-Yien , Haseley Nathan , Desjardins Christopher A. , Earl Ashlee M. , Hsueh Po-Ren , Hung Deborah T.
Published: August 2016

Fluoroquinolones (FQs) are effective second-line drugs for treating antibiotic-resistant tuberculosis (TB) and are being considered for use as first-line agents. Because FQs are used to treat a range of infections, in a setting of undiagnosed TB, there is potential to select for drug-resistant
Mycobacterium tuberculosis
mutants during FQ-based treatment of other infections, including pneumonia. Here we present a detailed characterization of ofloxacin-resistant
M. tuberculosis
samples isolated directly from patients in Taiwan, which demonstrates that selection for FQ resistance can occur within patients who have not received FQs for the treatment of TB. Several of these samples showed no mutations in
gyrA
or
gyrB
based on PCR-based molecular assays, but genome-wide next-generation sequencing (NGS) revealed minority populations of
gyrA
and/or
gyrB
mutants. In other samples with PCR-detectable
gyrA
mutations, NGS revealed subpopulations containing alternative resistance-associated genotypes. Isolation of individual clones from these apparently heterogeneous samples confirmed the presence of the minority drug-resistant variants suggested by the NGS data. Further NGS of these purified clones established evolutionary links between FQ-sensitive and -resistant clones derived from the same patient, suggesting
de novo
emergence of FQ-resistant TB. Importantly, most of these samples were isolated from patients without a history of FQ treatment for TB. Thus, selective pressure applied by FQ monotherapy in the setting of undiagnosed TB infection appears to be able to drive the full or partial emergence of FQ-resistant
M. tuberculosis
, which has the potential to confound diagnostic tests for antibiotic susceptibility and limit the effectiveness of FQs in TB treatment.