bluuebunny/crossref_metadata_2025 huggingface dataset:
Modeling Convective Boiling in Single Diverging Channel With In-Situ Vapor Extraction
Authors: Salakij Saran , Liburdy James A. , Pence Deborah V.
Published: July 2013

The present work shows the potential of using a diverging channel with in-situ vapor extraction as a means to reduce flow instability in microscale flow boiling. It has been shown that diverging channel helps stabilize convective boiling flow. In-situ vapor extraction is proposed as an alternative method that helps further stabilize flow boiling. The main concept of in-situ vapor extraction is to reduce the vapor available inside the channel where it forms by locally extracting vapor through a hydrophobic porous membrane that forms a wall of the channel to stabilize the flow and reduce pressure drop along the channel. In-situ vapor extraction of boiling flow in a microchannel also has the potential to reduce the required pressure to drive the flow through the channel without losing the benefit of convective boiling heat transfer. In this study, four microchannels, each with a range extraction pressures, are evaluated using a one-dimensional predictive model. Each channel is 50 mm and has a mid-channel width of 500 microns and height of 500 microns. The half angle of divergence of the channels varies: 0, 0.11, 0.23, and 0.34 degrees. Wall heat flux values range from 13.3 to 133 W/cm2. Extracted mass flow rates, global pressure drop across the channels, and quality at the channel outlet are presented as a function of heat flux and extraction pressure. Local variations of pressure, quality and bulk fluid temperature are also presented. Stability is predicted by a newly proposed criterion applicable for a diverging channel with in-situ vapor extraction. The results show that in-situ vapor extraction significantly reduces pressure drop for all channel configurations. Although the drop in pressure across the diverging channels is less influenced by vapor extraction than the non-diverging channel, the coupling of diverging channels and vapor extraction considerably improves the predicted stability of the flow.
An Experimental Study on the Effects of Agitation in Generating Flow Unsteadiness and Enhancing Convective Heat Transfer
Authors: Agrawal Smita , Simon Terrence , North Mark , Cui Tianhong
Published: July 2013

Agitation is produced inside a channel by a plate that is periodically oscillating normal to the channel side walls. The test channel is a rectangular cavity open on one end to allow inflow and outflow of air, as driven by the plate movement. Heat transfer and velocity measurements are made within different regions of the channel to study the effectiveness of agitation in promoting heat transfer from the channel side wall. The purpose of agitation is to strongly mix the near-wall flow, to thin the thermal boundary layer and increase the convective heat transfer coefficient. Velocity measurements using laser Doppler velocimetry are made to document the fluctuations of velocity within the agitated cavity. Variations of ensemble-averaged velocity throughout the cycle identify the unsteady sloshing of the flow. Cycle-to-cycle variations about the ensemble mean computed as an RMS and resolved in time within the cycle period present the changing turbulence levels throughout the agitation cycle. The ensemble-averaged mean velocity variations show periods of acceleration, deceleration and flow reversal during a cycle as a result of agitator movement. Turbulence is found to increase toward the end of the acceleration phase and persist through the deceleration phase. Intensities of sloshing and turbulence are used to explain the measured convective heat transfer coefficients. ANSYS FLUENT simulations supply velocity contours and flow visualization. This study finds application in electronics cooling where agitation can be used inside air-cooled heat sinks to enhance heat transfer to through-flow driven by a fan.
Heat Transfer Enhancement by Synthetic Jet Arrays in Air-Cooled Heat Sinks for Use in Electronics Cooling
Authors: Huang Longzhong , Simon Terrence , Zhang Min , Yu Youmin , North Mark , Cui Tianhong
Published: July 2013

A synthetic jet is an intermittent jet which issues through an orifice from a closed cavity over half of an oscillation cycle. Over the other half, the flow is drawn back through the same orifice into the cavity as a sink flow. The flow is driven by an oscillating diaphragm, which is one wall of the cavity. Synthetic jets are widely used for heat transfer enhancement since they are effective in disturbing and thinning thermal boundary layers on surfaces being cooled. They do so by creating an intermittently-impinging flow and by carrying to the hot surface turbulence generated by breakdown of the shear layer at the jet edge. The present study documents experimentally and computationally heat transfer performance of an array of synthetic jets used in a heat sink designed for cooling of electronics. This heat sink is comprised of a series of longitudinal fins which constitute walls of parallel channels. In the present design, the synthetic jet flow impinges on the tips of the fins. In the experiment, one channel of a 20-channel heat sink is tested. A second flow, perpendicular to the jet flow, passes through the channel, drawn by a vacuum system. Surface- and time-averaged heat transfer coefficients for the channel are measured, first with just the channel flow active then with the synthetic jets added. The purpose is to assess heat transfer enhancement realized by the synthetic jets. The multiple synthetic jets are driven by a single diaphragm which, in turn, is activated by a piezoelectrically-driven mechanism. The operating frequency of the jets is 1250 Hz with a cycle-maximum jet velocity of 50 m/s, as measured with a miniature hot-film anemometer probe. In the computational portion of the present paper, diaphragm movement is driven by a piston, simulating the experimental conditions. The flow is computed with a dynamic mesh using the commercial software package ANSYS FLUENT. Computed heat transfer coefficients show a good match with experimental values giving a maximum difference of less than 10%. The effects of amplitude and frequency of the diaphragm motion are documented. Changes in heat transfer due to interactions between the synthetic jet flow and the channel flow are documented in cases of differing channel flow velocities as well as differing jet operating conditions. Heat transfer enhancement obtained by activating the synthetic jets can be as large as 300% when the channel flow is of a low velocity compared to the synthetic jet peak velocity (as low as 4 m/s in the present study).
Enhanced Heat Transfer in Single-Phase Forced Convection in Tubes due to Helical Swirl Generated by Twisted-Tape Inserts
Authors: Bergles Arthur E. , Manglik Raj M.
Published: July 2013

Very high heat transfer enhancement can be achieved in single-phase flows by using twisted-tape inserts in circular tubes. The primary convection mechanism is the generation of helical swirl or secondary fluid motion that is induced by the helical curvature of the tape insert. This promotes cross-stream mixing and sharper wall gradients, which are further aided by the increased flow velocity due to the tube partitioning and blockage along with an effectively longer helical flow length. These phenomena are scaled for both laminar and turbulent flow regimes, and an evaluation of the transition is also given to highlight the damping effects of tape-generated swirl. The nature of swirl and its dimensionless scaling, and concomitant development of predictive correlations for heat transfer coefficients and friction factors are discussed. Finally, a brief discussion of the quantification of heat transfer enhancement by means of twisted tapes is given so as to extend their application in heat exchanger design.
Developments in Enhanced Heat Transfer Technology From a Petroleum Industry Perspective in 2012
Authors: Rudy Matthew P. , Rudy Thomas M. , Joshi Himanshu M. , Wanni Amar S.
Published: July 2013

Within the past 30 years, many Enhanced Heat Transfer (EHT) technologies have become available in a number of forms for application in heat exchangers. These technologies are used in various industries to widely different extents. In 1999, H. Joshi, T. Rudy, and A. Wanni, former Ph.D. students of Dr. Ralph L. Webb and specialists in the application of EHTs in the Petroleum Industry prepared a paper for the Journal of Enhanced Heat Transfer that reviewed the extent of use of EHT Technologies in the Petroleum Industry [1]. The current paper reviews how the application of EHT in the Petroleum Industry has changed in the last 14 years.
Dynamic Modeling of Vapor Compression Cycles Using a Novel Lagrangian Approach
Authors: Miller Eric S. , Patnaik Soumya S. , Jog Milind A.
Published: July 2013

Vapor compression cycles-based systems (VCS) are being adapted for thermal management of modern aircraft. Predicting dynamic behavior is critical to the design and control of these systems, which are likely to experience large dynamic changes in heat load. To meet this demand, a novel Lagrangian method to model the dynamic behavior of vapor compression cycles has been developed. The approach described in this paper considers the basic VCS as 4 fluid sides: one high pressure and one low pressure refrigerant side and external fluids which interact with each respectively. Sides are further divided into some number of material volumes. The model simulates compressible, unsteady flow by allowing each volume to translate and displace other elements, expanding and contracting in response to changes in mass, enthalpy and pressure. At every timestep, heat transfer to each mass element is determined and corresponding changes in thermodynamic properties are evaluated. The model predicts transient system response during normal operation as well as startup mode. Results from a dynamic evaporator simulation are presented and discussed. These results show the low-pressure refrigerant and external fluid response to changes in valve position, external fluid inlet temperature, and refrigerant inlet enthalpy. The conclusion drawn from these results is that the modeling framework described in this paper can reproduce the basic dynamics of a two-phase heat exchanger at a rate less than real time.
Effect of Cross Groove on Flow Boiling in a Microgap
Authors: Morshed A. K. M. M. , Paul Titan C. , Khan Jamil A.
Published: July 2013

Flow boiling performance of a microgap channel has been investigated experimentally. Experimental studies were carried out on a bottom surface heated single microgap channel having 5×0.372 mm cross sectional area using DI water as coolant. Four rectangular grooves were cut along the flow direction and surface morphology of the microgrooves was modified by depositing ZnO nanoparticles from a nanofluid using electrophoresis deposition technique. Flow boiling experiments were conducted for different mass flux. The results from the microgap channel having no cross grooves have been used as the baseline data. Cross grooves have been found effective in reducing boiling incipience temperature and enhancing heat transfer coefficient. Up to 50% enhancement in two-phase heat transfer coefficient was observed for the cross groove. Nanoparticles deposition reduces boiling incipient temperature but does not show any significant effect on two-phase heat transfer coefficient.
Experimental Investigation of Microexplosion Phenomena in Emulsified Vegetable Oil-Methanol Blends
Authors: Alvarado Jorge L. , Nam Hyungseok
Published: July 2013

Secondary atomization is one of the most attractive and misunderstood effects in the combustion of microemulsified fuel blends. The occurrence of secondary atomization has been studied to determine its effects on improved combustion efficiency especially when low vapor pressure fuels are used. Several methods to detect microexplosion as alternative to secondary atomization have been considered including acoustic signal processing. As part of the physical characterization of an emulsified vegetable oil-methanol blend, microexplosion behavior of fuel blend droplets has been observed to take place under certain environmental conditions. Droplets microexplode as methanol surrounded by vegetable oil molecules flashes or microexplodes under intense temperature and intense droplet pressure. The droplets of emulsified methanol-in-oil break up forming tiny droplets with greater surface-to-volume ratio in the process. To understand the effects of emulsification on microexplosion, characterization of secondary atomization has been performed using a temperature probe, a high-speed camera and an acoustic sound signal processor. Experiments have been conducted at temperatures similar to those encountered in liquid fuel boilers. The acoustic signal data were analyzed using Fast Fourier Transform (FFT) to define and understand the overall microexplosion process. Also, the effect of temperature, droplet sizes and the percentage of methanol in the vegetable oil blend have been studied to understand what leads to a higher probability of microexplosion occurrence. A correlation between the analyzed acoustic signal data and high speed images were used to differentiate between the different microexplosion events. The results of the study can be useful in predicting the occurrence of microxplosion in liquid fuel boiler which should result in more complete combustion processes, reducing contaminant levels significantly.
2-D Simulation of Hot Electron-Phonon Interactions in a Submicron Gallium Nitride Device Using Hydrodynamic Transport Approach
Authors: Fan Angie , Tarau Calin , Bonner Richard , Palacios Tomas , Kaviany Massoud
Published: July 2013

In this study, a thermal and electrical coupled device solver is developed to simulate the energy transfer mechanism within a GaN FET with a gate length of 0.2 μm. The simulation simultaneously solves a set of hydrodynamic equations (derived from the Boltzmann Transport Equation) and the Poisson equation for electron, optical phonon and acoustic phonon energies, electron number density, electric field and electric potential. This approach has been previously established for gallium arsenide (GaAs) devices [36,37], but has not been extended to GaN due to the lack of readily available property values for GaN devices that are required. Via extensive literature study, high-fidelity properties for GaN were collected in analytical forms with respect to many dependencies, e.g. lattice temperature, electrical field, electron number density, doping rate, defects rate. These properties are then implemented into the developed code to provide a high accuracy sub-micron GaN device simulation.

Simulations show that non-equilibrium heat generation is exhibited in a typical device while the drain current is reduced due to the decrease in electron mobility. Future analysis is needed to quantify the hot-electron effect on reducing the drain current and to discover more effective ways of heat removal.
Hybrid Eigenfunction-Discretization Methodology for Solving Convective Heat Transfer Problems
Authors: Chalhub D. J. M. N. , Sphaier L. A. , de B. Alves L. S.
Published: July 2013

This paper presents a novel methodology for the solution of problems that include diffusion and advection effects, as naturally occur in convective heat transfer problems. The methodology is based on writing the unknown temperature field in terms of eigenfunction expansions, as traditionally carried-out with the Generalized Integral Transform Technique (GITT). However, a different approach is used for handling advective derivatives. Rather than transforming the advection terms as done in traditional GITT solutions, upwind discretization schemes (UDS) are used prior to the integral transformation. With the introduction of upwind approximations, numerical diffusion is introduced, which can be used to reduce unwanted oscillations that arise at higher Péclet values. This combined methodology is termed the GITT-UDS for convective problems. The procedure is illustrated for a simple case of one-dimensional Burgers’ equation with temperature-dependent velocities. Numerical results are calculated, showing that augmenting the upwind approximation parameter can effectively reduce solution oscillations for higher Péclet values.
Experiments and Simulation of an Impinging Synthetic Jet Designed to Eliminate Actuator Artifacts
Authors: Silva Luis , Ortega Alfonso , Ebrahim Mahsa
Published: July 2013

Synthetic jets are created by periodically ejecting and injecting fluid from an orifice or channel. Despite delivering no net mass flow per cycle, a synthetic jet delivers flow with net positive momentum. Small, compact synthetic jet actuators can be fabricated to operate in the subaudible acoustic range and can be packaged in orientations that allow them to deliver cooling air flow to electronic devices. The most promising orientation is one that delivers the jet flow in a direction normal to the heated surface such that it impinges on the surface as a periodic jet. In previous studies, numerical simulations have been performed by the authors, utilizing a canonical geometry, with the purpose of eliminating actuator artifacts from the fundamental physics that drive the problem. The present paper reports on laboratory experiments that have been performed in order to nearly replicate the idealized synthetic jet geometry and thus allow comparison to the previous numerical investigations. The periodic volume change in an upstream plenum required to produce the synthetic jet is accomplished with an acoustic speaker operated at low frequencies. The amplitude and the frequency at which the jet is actuated determine the Reynolds and Strouhal numbers, which are the dominant non-dimensional groups that control the behavior of the impinging synthetic jet. By maintaining the Re and the St in the laboratory experiments to match those of the small scale actuators, the laboratory experiments have been geometrically scaled up to allow highly resolved measurements of the unsteady velocity field and the local time-dependent Nusselt number on the target heated surface. Experiments were performed at variable jet Re, frequencies, and height from the target surface. The dependence of the surface averaged Nu to jet parameters generally agrees with the computational results. However, discrepancies found between numerical and empirical local data are under revision.
A Correlation for Critical Heat Flux in Submerged Jet Impingement
Authors: Cardenas Ruander , Narayanan Vinod
Published: July 2013

Data from an extensive experimental study of submerged jet impingement boiling performed with water at sub-atmospheric pressures and with FC-72 at atmospheric pressure are used to develop a predictive critical heat flux (CHF) correlation for use in thermal management of electronic components. The configuration was that of a circular submerged jet impinging on a high-thermal-capacity copper surface with a standoff distance of 6 nozzle diameters. Varied parameters included the Reynolds numbers (Re) from 0 (pool boiling) to 14000, surface-to-nozzle diameter ratios (by varying the nozzle diameter) from 25 to 6, system pressures (0.2, 0.3, 0.5, 1 bar), surface roughness (123 nm, 33 nm), and system subcooling. CHF is found to increase with Re, system pressure, subcooling, and roughness and decreases with increase in nozzle diameter for a fixed Re.

Comparison with correlations in literature indicated that data of sub-atmospheric jet impingement of water were poorly predicted by existing correlations while the Monde and Katto correlation [1] was found to predict the atmospheric jet impingement data with FC-72 within 10 percent at Re >4000. Data from the experiments were fitted to a submerged forced convective CHF model proposed by Haramura and Katto [2] to develop a correlation for submerged jet impingement boiling over a wide range of density ratios. Using this model, the entire CHF dataset from experiments can be predicted with a maximum error of less than 11 percent and an average error of less than 2.6 percent.
Modeling Transient/Steady-State Convection From Isoflux Vertical Plates
Authors: Ahmadi Mehran , Bahrami Majid
Published: July 2013

A new compact analytical model is developed to predict transient heat convection from isoflux vertical plates into a constant property surrounding region. The proposed model is based on a blending of the two asymptotes corresponding to transient diffusion into a half-space and the steady-state convection heat transfer from an isoflux vertical plate. A compact relation for transient and steady-state average Nusselt numbers is proposed. The proposed model is successfully verified with existing experimental data of Goldstein and Eckert. The maximum difference between the proposed compact analytical model and the experimental data is less than 6%.
Thermal and Flow Visualization of Submerged Jet Impingement Boiling With FC-72
Authors: Mani Preeti , Narayanan Vinod
Published: July 2013

Dielectric fluids like FC-72 have been popularly used as electronic coolants owing to their chemical inertness and low saturation temperatures at atmospheric pressure. This work visualizes the heat transfer characteristics of FC-72 during submerged jet impingement boiling on a silicon surface heated by means of a thin film serpentine heater. Infrared thermography is used to obtain quantitative thermal maps of the boiling process from beneath the surface. Simultaneous high-speed visualization is used to record the corresponding bubble dynamics on the top surface. Experiments for two jet Reynolds numbers are compared with pool boiling under saturated conditions at a fixed surface to nozzle diameter ratio. Area-averaged temperatures evaluated from the thermal maps are used to describe the boiling trends for increasing and decreasing heat flux. Wall superheat required for phase-change varies randomly with increasing jet Reynolds numbers. Incipience overshoot as high as ∼21°C is observed and visually documented for the lower jet flow rate. Radial temperature profiles along the surface indicate that locally overshoots may vary significantly (∼8–21°C) for conditions with extremely high incipient superheats.
Experimental Investigation of Nanofluid Flow Boiling in a Single Microchannel
Authors: Edel Zachary , Mukherjee Abhijit
Published: July 2013

The trends of decrease in size and increase in power dissipation for micro-electronic systems present a significant challenge for thermal management of modern electronics. The preferable cooling solution could be micro heat exchangers based on forced flow boiling. Nanoparticle deposition can affect nucleate boiling heat transfer coefficient via alteration of surface thermal conductivity, roughness, capillary wicking, wettability, and nucleation site density. It can also affect heat transfer by changing bubble departure diameter, bubble departure frequency, and the evaporation of the micro and macrolayer beneath the growing bubbles. In this study, flow boiling was investigated for 0.001 vol% aluminum oxide nanofluids in a brass microchannel and compared to results for regular water. For the case of nanofluid flow boiling, high speed images were taken after boiling durations of 25, 75, 125, and 150 min. Bubble growth rates were measured and compared for each case. Flow regime oscillation was observed and regime duration was split into two periods: single-phase liquid and two-phase. The change in regime timing revealed the effect of nanoparticle suspension and deposition on the Onset of Nucelate Boiling (ONB) and the Onset of Bubble Elongation (OBE). The addition of nanoparticles was shown to stabilize bubble growth as well as the transition of flow regimes between liquid, two-phase, and vapor.
Current Progress in Enhanced Heat and Mass Transfer
Authors: Bergles Arthur E. , Manglik Raj M.
Published: July 2013

Heat transfer enhancement, which is often also referred to as augmentation or intensification, has evolved into an important component of thermal science and engineering. The accumulated literature in enhanced heat and mass transfer includes thousands of references, and it continues to grow. To give an overview of the current state of this important technology, representative developments over the past ten years in each category of enhancement techniques are cited and commented on. The discussion is divided into the literature, passive enhancement techniques, active enhancement techniques, and compound enhancement techniques.
Numerical Simulation on Gas Turbine Film Cooling of Curved Surface With Backward Injection
Authors: Shetty Shashank , Li Xianchang , Subbuswamy Ganesh
Published: July 2013

Due to the unique role of gas turbine engines in power generation and aircraft propulsion, significant effort has been made to improve the gas turbine performance. As a result, the turbine inlet temperature is usually elevated to be higher than the metal melting point. Therefore, effective cooling of gas turbines is a critical task for engines’ efficiency as well as safety and lifetime. Film cooling has been used to cool the turbine blades for many years. The main issues related to film cooling are its poor coverage, aerodynamic loss, and increase of heat transfer coefficient due to strong mixing. To overcome these problems, film cooling with backward injection has been found to produce a more uniform cooling coverage under low pressure and temperature conditions and with simple cylindrical holes. Therefore, the focus of this paper is on the performance of film cooling with backward injection at gas turbine operating conditions. By applying numerical simulation, it is observed that along the centerline on both concave and convex surfaces, the film cooling effectiveness decreases with backward injection. However, cooling along the span is improved, resulting in more uniform cooling.
Experimental and Numerical Study of Methanol-Water Mixture Single-Phase Heat Transfer in a Micro-Channel Heat Sink
Authors: Kwok Chun K. , Asada Matthew M. , Mita Jonathan R. , Qu Weilin
Published: July 2013

This paper presents an experimental study of single-phase heat transfer characteristics of binary methanol-water mixtures in a micro-channel heat sink containing an array of 22 microchannels with 240μm × 630μm cross-section. Pure water, pure methanol, and five methanol-water mixtures with methanol molar fraction of 16%, 36%, 50%, 63% and 82% were tested. Key parametric trends were identified and discussed. The experimental study was complemented by a three-dimensional numerical simulation. Numerical predictions and experimental data are in good agreement with a mean absolute error (MAE) of 0.87%.
Investigation of Heat Transfer in Evaporator of Microchannel Loop Heat Pipe
Authors: Yakomaskin Alexander A. , Afanasiev Valery N. , Zubkov Nikolay N. , Morskoy Dmitry N.
Published: July 2013

Loop heat pipes (LHP) are closed loop heat transfer devices which use evaporation and condensation of a working fluid to transfer heat and use capillary forces to provide fluid circulation. One of the main applications of LHP is cooling of electronics components. Further development in this field is associated with miniaturization. Therefore in electronics cooling there are strict limits imposed upon size of elements of heat transfer devices. One of such elements is evaporator of LHP, its main element. This paper deals with LHP evaporator and aims to find ways of reducing its thickness. An open loop experimental setup was created to investigate heat transfer phenomena in evaporator. Experiments were carried out with variety of configurations. Evaporator consists of microchannel plates with groove width 100 and 300 micrometers, wick (metal and non-metal porous materials were used) and compensation chamber (CC). Heat load varied from 20 to 140 W by steps of 20 W. The area of heater was equal to 19 mm × 19 mm. Working fluid — deionised water. Experiments resulted in data on temperature distribution across wick’s height, temperature of microchannel’s surface and temperature of water in compensation chamber. The results reveal potentials to perform optimization of evaporating zone to produce thinner evaporators.
Numerical Simulation of Different Coal Combustion in Two Tiny-Oil Ignition Burners With Oxygen-Enriched
Authors: Zhang Yongsheng , Wu Haisu , Liu Xueqi , Zhou Chenn Qian , Fu Zhongguang
Published: July 2013

Two tiny-oil ignition combustion burners with oxygen-enriched were studied in this paper. One is adding oxygen directly into primary air, and the other is adding oxygen by extra adding-oxygen tube. The bituminous coal, the lignite, and the meager coal, are simulated in these burners. By comparing the two different combustion characteristics, the simulation results show that, for bituminous coal, the high temperature zone congregates in the first directly added oxygen burner, while, for the meager coal, it is difficult to burn in the first directly added oxygen burner. As to the lignite, because of its characteristics of high volatility and low heating value, the first directly added oxygen burner provide oxygen timely for its high volatile, its flame combust more quickly and directly.
Simulation of Nanofluid Heat Transfer Enhancement With LBM
Authors: Guo Yali , Qin Daoyang , Shen Shengqiang , Xu Hehan , Yang Yong , Li Yeqing
Published: July 2013

Heat transfer and fluid flow in a two-dimensional enclosure filled with nanofluids is investigated using multi-phase LBM, where the influences of external and internal forces, for example, the Bromnian force, gravitational force, drag force, buoyancy force and the interactions among particles on the molecular levels, are considered. The velocity field and the temperature field are obtained at different nanoparticles volume fractions, different buoyancy parameters. The simulation results show that nanofluids could enhance the heat transfer compared to pure liquid.
Shear Heating of High-Viscosity Grade Lubricant in Piston Skirts: EHL at Idling Speeds in Initial Engine Start Up
Authors: Qasim Syed Adnan , Khan Mumtaz Ali , Malik M. Afzaal
Published: July 2013

A few initial cold engine start up cycles at low idling speeds do not prevent wear due to the absence of a fully established elastohydrodynamic lubrication (EHL) film between the piston skirts and the cylinder liner. It happens when the thermal loading due to combustion may be ineffective initially, and shear heating becomes significant as a result of the sliding motion of the piston. This study models the 2-D piston skirts EHL at the idling speeds in the initial engine start up by using a high-viscosity grade engine oil and incorporating the shear heating effects. The 2-D heat transfer equation is used with no source term effects to study the temperature changes and their effects on the viscosity of a Newtonian lubricant at the different idling speeds in the initial start up of an internal combustion engine. The 2-D Reynolds equation is solved numerically to generate the hydrodynamic pressures as the function of 720 degrees crank rotation cycle. Under the flooded lubrication conditions the inverse solution technique is employed to generate the hydrodynamic pressures in the EHL regime. The numerical analysis at the two different idling initial engine start up speeds is presented based on the 2-D heat equation having adiabatic conduction and convective heat transfer with no source term effects. Viscous dissipation coupled with the piston motion, the pressure fields generation, the temperature effects on the viscosity of the lubricant and the subsequent oil film thickness profiles in the contact region are examined. The influence of the low-temperature shear heating on the hydrodynamic and EHL film thickness at the time of initial engine start up are investigated. This study suggests that by using a high-viscosity grade oil in the idling speed engine start up the film temperature rises non-uniformly due to shear heating in the hydrodynamic and EHL regimes. The low temperature rise affects the pressure and temperature dependent oil viscosity, and the secondary transverse eccentric displacements of the piston. Resultantly, the piston skirts lubrication is affected despite the initial engine start up at the idling speeds.
Evaluating Liquid-Cooled Heat Sink Resistance Data for Electronic Applications
Authors: Manteufel Randall D.
Published: July 2013

A number of experimental studies have been published for single-phase liquid cooling for electronic heat sources. These include flow though various sized channels and configurations. Results are expressed using a thermal resistance as a function of liquid volumetric (or mass) flow rate. This paper discusses the regression of experimental data. Two simple thermal resistance models are evaluated, each having a combination of conduction and convection components. The models are applicable to a wide set of data. A preferred model is identified having three parameters: (1) overall resistance at a nominal flow, (2) percentage of resistance due to conduction at the nominal flow, and (3) convective exponent for the liquid flow rate. The preferred model has lower correlation between its parameters and reproduces the trends in experimental data. The model is used to quantify the relative contribution of the convective and conductive sources of thermal resistance. It is also useful in design to evaluate the effectiveness of increasing the liquid flow rate which can be accomplished with increased pressure drop and pumping costs. The best-fit estimates and their approximate 95% confidence intervals are calculated using experimental data. A few experimental results yield discrepant values for the model parameters. In some cases the rate of reduction of the thermal resistance with increasing flow rate appears beyond what can be reasonably expected. Sources of discrepant results are discussed. The results of the paper are helpful in evaluating experimental data and guiding the design of liquid-cooled heat sinks.
Surface Characterization Studies of Thiols as a Blocking Mechanism for Specific Adsorption for Application of Charge Selective Membrane Transport
Authors: Agonafer Damena D. , Chainani Edward , Oruc Muhammed E. , Lee Ki Sung , Shannon Mark A.
Published: July 2013

This paper proposes the use of electrochemical impedance spectroscopy (EIS) to measure characteristics of gold (Au)-coated membranes and their inherent limitations. In this work, the fabrication of a membrane permeate flow cell is described with the aim of subsequently studying the transport of ions through conductive polycarbonate track etched membrane (PCTE) by interrogating the system using EIS and CV measurements. In particular, we would like to ascertain the voltage range that can be applied to the Au-coated membrane without getting a considerable faradaic activity; the difference between platinum and Au electrode; the effects of different electrolyte concentrations and various applied DC potentials.

We extend our previous work done [1] by studying the differences of using a hrydroxyl and methyl terminated self assembled monolayer (SAM). We also extend the quality of the monolayer with respect to the amount of time in which the monolayer is grown. Finally, finding the voltage in which a ‘defect free’ monolayer transforms from insulative to ‘leaky’ behavior extends a detailed analysis of the critical voltage of an alkane thiol.
Numerical Investigation of Laminar Natural Convection Heat Transfer From an Isothermal Body: Concave vs. Convex Shapes
Authors: Jafarpur K. , Jayhooni S. M. H.
Published: July 2013

In this article a numerical simulation is employed to obtain dimensionless heat transfer in laminar natural convection condition for isothermal bodies which are similar to sphere and cylinder. Then, the numerical results for different bodies are compared with each other to figure out the effect of convexity / concavity on laminar natural convection. A computational fluid dynamics (CFD) codes is used for solving the relevant mathematical expressions for natural convection heat transfer from isothermal bodies. Excellent agreement between the results of the present numerical simulation and available experimental results is observed in the whole laminar flow range 0≤RaA≤108. However, that is why the laminar natural convection from sphere and cylinder with L/D = 1 and a few other shapes turned out to be the same, some of the bodies show better natural convection behavior with specific shapes. In addition, Convexity has small effect on the Nu number for low laminar range of RaA number besides, in convex bodies, removing the sharp edges helps to increase natural convection heat transfer. Finally, it is worth to mention that this numerical simulation reveals that it has the capability to be used as a tool to predict the behavior of flow and heat transfer around isothermal convex / concave bodies.
A Parametric Study of Multi-Stage Chemical Looping Combustion for CO2 Capture Power Plant
Authors: Hassan Bilal , Shamim Tariq , Ghoniem Ahmed F.
Published: July 2013

A thermodynamic model and parametric analysis of a natural gas fired power plant with carbon dioxide (CO2) capture using multi-stage chemical looping combustion (CLC) are presented. CLC is an innovative concept and an attractive option to capture CO2 with a significantly lower energy penalty than other carbon-capture technologies. The principal idea behind CLC is to split the combustion process into two separate steps (redox reactions) carried out in two separate reactors: an oxidation reaction and a reduction reaction, by introducing suitable metal oxide which acts as an oxygen-carrier that circulates between the two reactors.

In this study, an Aspen Plus model was developed by employing the conservation of mass and energy for all the components of the CLC system. In the analysis, equilibrium based thermodynamic reactions with no oxygen-carrier deactivation were considered. The model was employed to investigate the effect of various key operating parameters such as air, fuel and oxygen carrier (OC) mass flow rates, operating pressure, and waste heat recovery on the performance of a natural gas fired power plant with multi-stage CLC. Results of these parameters on the plant efficiency are presented. The analysis shows efficiency gain of more than 6% over that of conventional power plant with CO2 capture technologies when CLC is integrated with the power plant.
Comparative Experimental and Computational Studies for Annular Condensing and Boiling Flows in Millimeter Scale Horizontal Ducts
Authors: Narain A. , Kivisalu M. , Naik R. , Gorgitrattanagul N. , Mitra S. , Hasan M. M.
Published: July 2013

This paper describes experimental approaches for ensuring high heat-flux annular flow boiling and flow condensation under conditions for which shear and pressure forces dominate buoyancy effects. The paper also describes fundamental predictive tools for such flows. For annular flows, the liquid phase flows in the form of a wavy film (often micro-meter scale thin) that continuously irrigates the heat-exchange surface inside millimeter scale ducts. Controlled attainments of these annular flow configurations (which experience only second order effects of surface-tension forces) are essential to integration of functional boilers and condensers for certain space-based as well as micro-scale thermal systems. The experiments deal with flow condensation of FC-72 in a 2 mm gap horizontal channel of 1 m length and flow boiling of FC-72 in a 1.6 mm gap horizontal channel of 0.74 m length. For both boiling and condensing flow experiments, annularity of the respective flows is ensured by choice of an appropriate rate of through flow of vapor that does not actively participate in phase-change and has a flow rate which lies within a well defined range. The through flow of vapor is shown to ensure stability, annularity (by effectively suppressing nucleation in the case of flow boiling), and predictability. This fact is demonstrated by relevant flow visualization videos whose schematic and still pictures are included here. Two sets of annular condensing flow simulation results (one based on a full computational fluid dynamics based steady/unsteady simulations and another based on a quasi 1-D steady simulations) are compared against experimental heat-flux measurements obtained for annular shear driven condensing flows of FC-72 vapor. For quasi-steady annular boiling, only the quasi 1-D steady simulations approach is used for comparisons with experimental heat load measurements.

The reasonableness of the proposed 1-D predictive engineering tool, with proper understanding of its scope and limitations, enables one to generate useful results for more sophisticated simulations. Furthermore the tool readily yields results/estimates for other working fluids, channel dimensions, and flow conditions.
CFD Assisted Control System Design for Chip Cooling
Authors: Zhang R. , Zhang C. , Jiang J.
Published: July 2013

In this paper, a computational fluid dynamics (CFD) assisted control system design methodology has been described in detail. The entire design and evaluation procedure has been illustrated through a feedback control system synthesis for a CPU chip cooling system. The design methodology starts with a full-scale CFD simulation of the nonlinear dynamic process to generate the input and output databases of the process. Using this data set, linear dynamic models around specified operating points are obtained using system identification techniques. Based on these models, one can design appropriate control systems to meet the required closed-loop control system specifications. To illustrate the effectiveness of this technique, it has been used to design a controller for a PC chip cooling system. In particular, the coupling issues between ‘real-time’ dynamic controllers with non real-time CFD simulation have been resolved. A physical experimental test bench based on a cooling system of a Pentium III CPU has been constructed. The feedback linear control systems designed by the proposed CFD approach have been evaluated experimentally for six CPU load conditions.
A Comparative Study of NOx Computation Methods Coupled to Quasi-Dimensional Models in SI Engines
Authors: Aithal S. M.
Published: July 2013

Quasi-dimensional models are widely used in the design, development and analyses of automotive engines. Various phenomenological and empirical relations are used in these models to reduce the computational load compared to multi-dimensional models. These quasi-dimensional models have also been used to calculate NOx, soot and HCs using various reduced chemistry/simplified models. The extended Zeldovich mechanism is widely used for finite-rate NOx computations in these quasi-dimensional models. However, there are several simplifying assumptions in the rate equation used for the NOx computations. This paper compares the traditional method of finite-rate NOx computations with full finite-rate chemistry without the simplifying assumptions used in the former method. NOx formation in a stationary engine is studied using a single zone and two-zone (burned and unburned zone) using a 6-reaction, 7-species model. A detailed comparison of the two methods of NO computation is presented. Analyses of the temporal variation of NO predicted using these two approaches is also presented.
PR30C-LE Locomotive With DOC and Urea Based SCR: Field Trial and Emissions Testing After 1,500 and 3,000 Hours of Operation
Authors: Osborne Dustin T. , Biagini Doug , Holmes Harold , Fritz Steven G. , Jaczola Michael , Iden Michael E.
Published: July 2013

This paper details part two of the demonstration of a 2,240 kW (3,005 HP) PR30C-LE locomotive with exhaust aftertreatment containing diesel oxidation catalysts (DOC) and urea-based selective catalytic reduction (SCR). The PR30C-LE is a remanufactured and repowered, six-axle, diesel-electric, line-haul locomotive. Program objectives were to measure emission levels of the locomotive and record locomotive and aftertreatment operations during a 12 month revenue service field trial. Phase 1 of the program involved engine baseline emissions testing as well as emissions testing with the aftertreatment at the beginning of its useful life, or the 0-hour condition. Results from Phase 1 showed engine-out emission levels were within U.S. EPA Locomotive Tier 2 limits. With aftertreatment at beginning of useful life, hydrocarbons (HC), carbon monoxide (CO), and oxides of nitrogen (NOx) were below Tier 4 limits, and particulate matter (PM) was below Tier 3 limits.

Phase 2 consisted of a 12 month revenue service field trial and additional emissions testing completed at the midpoint and end of the field trial. On-board GPS data, aftertreatment NOx sensor data, and various locomotive operating parameters were logged continuously during the field trial. The field trial data suggests the impact SCR technology has on locomotive NOx emissions is driven primarily by locomotive utilization and loading factor. Overall the field trial included 3,082 hours of operation and PRLX3004 generated approximately 572 MW-hours of work over the 12 month period. Emission test results at the 1,500-hour and 3,000-hour conditions showed very little change from 0-hour test results. Emission levels remained below Tier 4 limits for HC, CO, and NOx, and below the Tier 3 limit for PM. Phase 2 test results suggest there was no significant degradation in emissions performance during the field trial, and no major issues with the locomotive and aftertreatment were detected. In total there are currently five PR30C-LE locomotives in operation within California and Arizona. Together they have completed a cumulative 30,800 hours of revenue service through June 2012 without report of a major issue.
Achieving Low Emissions From a Biogas Fueled SI Engine Using a Catalytic Converter
Authors: Tadrous Mark , Wallace James S.
Published: July 2013

Utilization of biogas is attractive from a greenhouse gas standpoint since it is carbon neutral due to the use of renewable resources. One source of biogas is anaerobic digestors. The biogas produced could be used to power IC engine-generator sets to produce electric power and heat on farms and in rural and northern communities. Use of local energy sources is particularly attractive in remote regions where liquid fuels must be shipped in via difficult terrain. Whatever the fuel, the engine must meet stringent exhaust emission standards. Biogas is typically used in spark ignition engines, where stoichiometric engine operation coupled to a three-way catalyst is a proven technology for achieving low emissions. An appropriate three-way catalyst was selected on the basis of tests with natural gas. A flow mixing system was used to create simulated biogas mixtures consisting of varying concentrations of methane, carbon dioxide, hydrogen and nitrogen. The effectiveness of the catalyst in achieving low emissions when the engine was fueled by the various simulated biogas mixtures was assessed.
Technology Review in IC Engine Applications
Authors: Scheer Anthony , Etemad Shahrokh
Published: July 2013

When a company designs an engine, mandates by the federal government regarding fuel efficiency, safety and emissions must be met. Consumers demand power, reliability, and creature comforts of the vehicles they choose to purchase. Car manufacturers must meet all of these needs and desires as well as maintain profitability.

The present paper reviews the application of recent advances in IC engines. It covers the four specific areas of (a) Electronic Applications (b) Air Flow Management (c) Fuel Injection / Combustion and (d) Loss Reduction technologies to address the needs of engine performance enhancement. Finally it provides a future direction of the technology for IC engine applications.