bluuebunny/crossref_metadata_2025 huggingface dataset:
Numerical Modeling of Quench Cooling Using Eulerian Two-Fluid Method
Authors: Wang De Ming , Alajbegovic Ales , Su Xuming , Jan James
Published: May 2008

A numerical approach is presented for modeling quenching cooling of solid metal parts. The approach is based on the Eulerian two-fluid model with modifications toward specific needs of boiling heat transfer. Numerical aspects are discussed on handling high phase change rate of boiling, flux formulation in the presence of strong body force, and conjugate heat transfer of solid immersed in a liquid bath. The modeling approach is assessed for a quenching cooling problem with a simple geometry. Comparisons are made between the computed temperature history within the solid and that of measured data using thermocouples. Reasonably well agreement is observed. The study demonstrated that the present modeling approach is able to meet the numerical challenges entailed in quenching cooling and able to predict the quenching cooling phenomena with satisfactory accuracy. Areas for further improvement are also noted.
Study of Seat System Performance Related to Injury of Rear Seated Children and Infants in Rear Impacts
Authors: Saczalski Kenneth J. , Burton Joseph Lawson , Lewis Paul R. , Friedman Keith , Saczalski Todd K.
Published: May 2008

Since 1996 the NHTSA has warned of the airbag deployment injury risk to front seated children and infants, during frontal impact, and they have recommended that children be placed in the rear seating areas of motor vehicles. However, during most rear impacts the adult occupied front seats will collapse into the rear occupant area and, as such, pose another potentially serious injury risk to the rear seated children and infants who are located on rear seats that are not likely to collapse. Also, in the case of higher speed rear impacts, intrusion of the occupant compartment may cause the child to be shoved forward into the rearward collapsing front seat occupant thereby increasing impact forces to the trapped child. This study summarizes the results of more than a dozen actual accident cases involving over 2-dozen rear-seated children, where 7 children received fatal injuries, and the others received injuries ranging from severely disabling to minor injury. Types of injuries include, among others: crushed skulls and brain damage; ruptured hearts; broken and bruised legs; and death by post-crash fires when the children became entrapped behind collapsed front seat systems. Several rear-impact crash tests, utilizing sled-bucks and vehicle-to-vehicle tests, are used to examine the effects of front seat strength and various types of child restraint systems, such as booster seats and child restraint seats (both forward and rearward facing), in relation to injury potential of rear seated children and infants. The tests utilized sedan and minivan type vehicles that were subjected to speed changes ranging from about 20 to 50 kph (12 to 30 mph), with an average G level per speed change of about 9 to 15. The results indicate that children and infants seated behind a collapsing driver seat, even in low severity rear impacts of less than 25 kph, encounter a high risk of serious or fatal injury, whether or not rear intrusion takes place. Children seated in other rear seat positions away from significant front seat collapse, such as behind the stronger “belt-integrated” types of front seats or rearward but in between occupied collapsing front seat positions, are less likely to be as seriously injured.
Scalable Multi-Group Full-Spectrum Correlated-K Distributions for Radiative Transfer Calculations
Authors: Zhang Hongmei , Modest Michael F.
Published: May 2008

A new full-spectrum k-distribution method has been developed, in which spectral locations are sorted into M spectral groups, according to their absorption coefficient dependence on (partial) pressure and temperature. Calculating correlated-k full-spectrum k-distributions for each of the M groups, LBL accuracy can be obtained with M ≤ 32. Database values have been assembled for CO2 mixtures at atmospheric pressure. The method is fully scalable, i.e., spectral groups from the database can be combined to obtain coarser group models (M = 1,2,4,···) for greater numerical efficiency (accompanied by slight loss in accuracy).
Inertial Vibration Damping Control for a Flexible Base Manipulator
Authors: George Lynnane E. , Book Wayne J.
Published: May 2008

A rigid (micro) robot mounted serially to the tip of a long, flexible (macro) manipulator is often used to increase reach capability, but flexibility in the macromanipulator can interfere with positioning accuracy. A rigid manipulator attached to a flexible but unactuated base was used to study a scheme to achieve positioning of the micromanipulator combined with enhanced vibration damping of the base. Inertial interaction forces and torques acting between the robot and its base were modeled and studied to determine how to use them to damp the vibration. One issue is that there are locations in the workspace where the rigid robot loses its ability to create interactions in one or more degrees of freedom. These “inertial singularities” are functions of the rigid robot’s joint variables. A performance index was developed to predict the ability of the rigid robot to damp vibration and will help ensure the robot is operating in joint space configurations favorable for inertial damping. When the performance index is used along with the appropriate choice of feedback gains, the inertia effects, or those directly due to accelerating the robot’s links, have the greatest influence on the interactions. By commanding the robot link’s accelerations out of phase with the base velocity, vibration energy will be removed from the system. This signal is then added to the rigid robot’s position control signal. Simulations of a rigid three degree of freedom anthropomorphic robot mounted on a flexible base were developed and show the effectiveness of the control scheme. In addition, experimental results demonstrating two degree of freedom vibration damping are included.
Investigation of Thin Film Evaporation Limit in Single Screen Mesh Layer
Authors: Wang Y. X. , Peterson G. P.
Published: May 2008

Thin film evaporation heat transfer plays an extremely important role in capillary microstructures of the type used extensively in micro heat pipes, loop heat pipes and high-flux film heat spreaders. Because the formation of the liquid meniscus in the pore cell has a significant effect on the evaporation process occurring at the interface of the liquid meniscus, it is necessary to investigate the mechanisms and limitations of the phase-change phenomena occurring in the thin layer. In the current study, an analytical model, which combines the heat conduction in the wick layer with bubble formation mechanisms in the capillary structure, has been developed to determine the evaporation heat transfer limit. Temperature distribution, superheat, and heat flux distribution in the liquid meniscus area are investigated for a single layer of metal screen mesh. The wire diameter, the space between the wires and the contact conditions between the solid wall and mesh layer is shown to have a significant effect on the evaporation limit and capillary force. Results indicated that evaporation takes place mainly in the thin film region, and the heat transfer coefficient is much higher in this area than in the intrinsic region. The evaporation limit is restrained by the formation of the liquid meniscus, and the higher the capillary pressure, the lower the evaporation heat transfer limit.
A New Perspective for Time Delayed Control Systems With Application to Vibration Suppression
Authors: Sipahi Rifat , Olgac Nejat
Published: May 2008

Most control systems are contaminated with some level of time delay. Whether it appears due to the inherent system dynamics or because of the sensory feedback, the delay has to be resolved regarding the system stability. We explain an unprecedented and fundamental treatment of time delay in a general class of linear time invariant systems (LTI) following a strategy, which we call the ‘Direct Method’. The strengths of the method lie in recognizing two interesting and novel features, which are typical for this class of systems. These features enable a structured strategy to be formed for analyzing the stability of LTI-TDS (Time Delayed Systems). Vibration control settings are not immune from time delay effects. We present a case study on active control of vibration using linear full state feedback. We then apply the Direct Method on this structure to display the stability outlook along the axis of delay. There appears an interesting property, which is related to the determination of the imaginary (i.e. marginally stable) roots of LTI-TDS. We state a general lemma and proof on this point.
Nonlinear Adaptive Vibration Absorber for Linear Uncertain Systems Experiencing Unknown Sinusoidal Disturbances
Authors: Derkhorenian R. , Jalili N. , Dawson D. M.
Published: May 2008

This paper describes the design and implementation of a nonlinear adaptive disturbance rejection approach for single-input-single-output (SISO) linear-time-invariant (LTI) uncertain systems subject to sinusoidal disturbances with unknown amplitude and frequency. The technique requires the construction of a set of stabilizing tuning functions utilizing a state estimate observer in a backstepping fashion to achieve asymptotic disturbance rejection. Utilizing only the system output, a virtual control input is used in place of non-measurable and unknown signals. The performance of the adaptation algorithm is demonstrated through simulations on a two-degree-of-freedom (2DOF) system, representing a mass-spring-damper vibration absorber setting appended on a single DOF (SDOF) primary system with unknown parameter.
Adaptive Backstepping Control of a McKibben Actuator Driving an Inertial Load
Authors: Reutzel William T. , Rahn Christopher D.
Published: May 2008

McKibben artificial muscles are pneumatic linear actuators with high strength-to-weight ratio and natural compliance. The actuator consists of an elastic cylindrical tube within an inelastic braided shall. With a sufficiently shallow braid angle, increasing internal pressure causes the muscle to expand radially and contract longitudinally, providing a large actuation force. When McKibben actuators attach to an inertial load, however, PID position control cannot provide accurate tracking due to excessive vibration. Based on a third-order system model, two adaptive position controllers are developed, proven stable using Lyapunov Theory, and tested experimentally. First, adaptive control with a PID pressure loop yields acceptable sine wave tracking up to 3 Hz. Second, backstepping compensation for the pressure dynamics ensures accurate tracking of a 4 Hz since wave with increased amplitude.
Comparison of Experiments and 1-D Steady-State Model of a Loop Heat Pipe
Authors: Chuang Po-Ya Abel , Cimbala John M. , Brenizer Jack S. , Conroy C. Thomas , El-Ganayni A. A. , Riley David R.
Published: May 2008

A modern, effective, two-phase heat transfer device, a loop heat pipe (LHP), was studied analytically and experimentally. A 1-D steady-state model was developed based on energy balance equations. The mathematical modeling procedures of each component are explained in detail, including a model of the secondary wick in the evaporator. Other models neglect the existence of the secondary wick because the detailed designs of the secondary wick are often proprietary. Three sets of experiments were performed at different elevations. Results of experimental data are compared with 1-D steady-state model predictions. The comparisons show that the model predictions of steady state operating temperatures for both zero elevation and adverse elevation are within 2 percent. It has been clearly demonstrated that the 1-D steady-state model is a useful tool for future LHP study.
Optimization to Limit Vibration of a Hypotrochoidally Driven Machine
Authors: Cook Nathan L. , Book Wayne J.
Published: May 2008

A real-time optimization routine is presented. The routine calculates the “best” coefficients of a fifth-order polynomial trajectory. The trajectory is used to calculate the setpoints given to a servomotor every ten milliseconds to drive a patented hypotrochoidal gear mechanism as part of an industrial food packaging machine (Howard et al, 2000). It is desired to minimize the upward, vertical forces that the gear mechanism exerts on the machine. The optimization routine is shown in simulation to result in a trajectory that can reduce the upward force by 30–40%, without sacrificing the production rate, by explicitly taking into account the hypotrochoidal kinematics of the gear mechanism.
A Reduced-Order Observer Based Piezoelectric Control of Flexible Cartesian (SCARA) Robot Manipulator
Authors: Liu Zeyu , Jalili Nader , Dadfarnia Mohsen , Dawson Darren M.
Published: May 2008

An observer based control strategy is proposed for a flexible Cartesian (SCARA) Robot which is modeled as a flexible cantilever beam with a translational base support. A piezoelectric (PZT) patch actuator is bonded on the top surface of the flexible arm to apply a controlled moment for vibration suppression requirement. Utilizing three measurable quantities (i.e., the base displacement, arm tip deflection and the strain at the root end of the arm), a reduced-order observer is designed to estimate the velocity related variables, which are not measurable. A simple PD controller is selected for the moving base regulation control, while a Lyapunov function candidate based on a very simple energy relationship is utilized for the PZT input voltage to make the closed-loop system energy dissipative and hence stable. In this paper, the PZT input voltage control uses the velocity related signals estimated by the reduced-order observer, which makes the control structure simpler. The feasibility of the controller is validated by the numerical simulations and experimental results.
Structures and Characterization of Organoclay-Epoxy-Vinylester Nanocomposites
Authors: Hussain Farzana , Dean Derrick , Haque Anwarul
Published: May 2008

The field of polymer-clay nanocomposites has attracted considerable attention as a method of enhancing polymer properties and extending their utility. Layered silicates dispersed as a reinforcing phase in a polymer matrix are one of the most important forms of such inorganic-organic nanocomposites, making them the subject of intense research. We have recently prepared several thermoset-based nanocomposites with improved thermal and mechanical properties. This paper is primarily focused in studying the effects of nano clay particles such as montmorillonite on improving mechanical and thermal properties of the polymer matrix composite. Epoxy and vinyl ester nanocomposites were prepared by adding different weight percentages (0.5%, 1%, 2%, 5% and 10%) of montmorillonite nano clay particles to epoxy and vinyl ester matrices. The results show significant improvements in mechanical and thermal properties of the nanostructured materials with low loading of organo silicates. Thermal property measurement includes dynamic mechanical analysis (DMA). Mechanical properties such as flexural strength and flexural modulus of polymer matrix were improved in nano structured materials owing to their unique phase morphology and improved interfacial interactions. Molecular dispersion of the layered silicate within the cross-linked matrix was verified using Wide Angle X-Ray Diffraction (WAXD) and Transmission Electron Microscopy (TEM) revealing the intercalated nanocomposites were formed.
The Anti-Gravity Phenomena in EHD Heat Pipe Model
Authors: Yang Jiaxiang , Wang Jiancai , Chen Chuntian , Yu Changsheng
Published: May 2008

A heat pipe model of electrohydrodynamical (EHD) enhancement heat transfer has been designed and made. The insulating liquid was selected as working fluid and the copper wire whose diameter was 1mm was used as the high voltage electrode. The temperature in the inlet and outlet of both the vaporization section and the condensation section, the saturation vapor pressure inside this model were measured respectively under different applied dc voltage and different tilt angle, that is, the vaporization section was placed higher than the condensation section. The experiment results indicate that the circumfluence between the condensation section and the vaporization section was improved with the increase of the applied dc voltage. Such EHD enhancement heat transfer technology can be practically employed in the heat transfer engineering, and has some reference values for the investigation of heat pipes used in the case of anti-gravity.
Experimental Investigation of a Capillary Pumped Loop Towards Its Integration on a Scientific Microsatellite
Authors: Riehl R. R. , Camargo H. V. R. , Heinen L. , Bazzo E.
Published: May 2008

This paper presents the experimental investigation of a capillary pumped loop (CPL) to be integrated on a scientific microsatellite. Tests in laboratory have been focused on the thermal behavior of a CPL on a reduced scale, using UHMW (Ultra High Molecular Weight) polyethylene as porous structure and anhydrous ammonia as working fluid. The experimental tests have shown that the proposed CPL presents reliable startups when operating on a heat load range between 20 and 50 W, also presenting very short transients when operating on different heat load profiles. Very fast responses of the CPL have been verified for sudden changes on the heat load applied to the capillary evaporator with reduced superheat. The proposed CPL will be part of a payload to be integrated on a Scientific Microsatellite scheduled to be launch in early 2004.
Active Control of Vibrations in Tall Structures Subjected to Earthquake and Wind Disturbances
Authors: Kruck Kevin , Kelkar A. G.
Published: May 2008

This paper presents active control design methodologies for control of tall building structures subjected to earthquake and wind disturbances. In particular, a robust control methodology based on passivity-based design techniques is given and is compared with traditional optimal control design methods such as LQR and LQG. The controller designs are tested in simulation on a multi-storied building structure subjected to an earthquake disturbance using the actual seismic data from the famous 1940 El Centro earthquake of the Imperial Valley in southern California. The comparison of open- and closed-loop responses show the effectiveness of passivity-based control design over LQR and LQG designs.
Development and Design of a Controller for a Two-Dimensional Actively Controlled Toolpost
Authors: Foreman E. P. M. , Al-Jumaily A. M.
Published: May 2008

This paper has a two-fold purpose. The first is to present the development and design of control criteria used for a two-dimensional actively controlled toolpost, whilst the second is to develop a theoretical simulation program to assess the relationships between the controller parameters and the toolholder stiffness. The control scheme provides suitable commands to the actuators to abate vibrations produced at the interface between the tool tip and the workpiece. The toolpost with the proposed controller is used on a Nakamura Tome lathe to machine aluminum samples. A comprehensive series of tests involving machining stock at constant cutting rates for a range of depths of cut and axial feed rates is conducted and demonstrates the effectiveness of the scheme in providing suitable corrective signals to abate vibrations. The results reveal good operation criteria based on setting the controller parameters for better controller performance. However, the theoretical simulation has demonstrated that a PI controller can produce a sufficient control action, which results in a smoother surface. It indicates that a stiffer structure requires larger integral action in order to produce a smoother surface of the workpiece.
Micro-Control Actions of Actuator Patches Laminated on Hemispherical Shells
Authors: Smithmaitrie P. , Tzou H. S.
Published: May 2008

Spherical shell-type structures and components appear in many engineering systems, such as radar domes, pressure vessels, storage tanks, etc. This study is to evaluate the micro-control actions and distributed control effectiveness of segmented actuator patches laminated on hemispheric shells. Mathematical models and governing equations of the hemispheric shells laminated with distributed actuator patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components. Due to difficulties in analytical solution procedures, assumed mode shape functions based on the bending approximation theory are used in the modal control force expressions and analyses. Spatially distributed electromechanical actuation characteristics resulting from various meridional and circumferential actions are evaluated. Distributed control forces, patch sizes, actuator locations, micro-control actions, and normalized control authorities of a free-floating hemispheric shell are analyzed in a case study. Parametric analysis indicates that 1) the control forces and membrane/bending components are mode and location dependent and 2) the meridional/circumferential membrane control actions dominate the overall control effect.
Micro-Actuations and Location Sensitivity of Actuator Patches Laminated on Toroidal Shells
Authors: Tzou H. S. , Chai W. K. , Wang D. W.
Published: May 2008

Toroidal shell structure has been proposed for components of inflatable space structures and telescope etc. Thus, distributed control of toroidal shells becomes a critical issue in precision maneuver, operation, and reliability. The converse effect of piezoelectric materials has made it one of the best candidates for distributed control actuators. The resultant control forces and micro-control actions induced by the distributed actuators depend on applied voltages, geometrical (e.g., spatial segmentation and shape) and material (i.e., various actuator materials) properties of the actuators. The purpose of this analysis is to study the location effects of actuator placement and to evaluate the micro-control actions imposed upon toroidal shell structures. Mathematical models and governing equations of the toroidal shells laminated with distributed actuator patches are presented first, followed by formulations of distributed control forces and micro-control actions including meridional/circumferential membrane and bending control components. Spatially distributed electromechanical microscopic actuation characteristics and control effects resulting from various meridional and circumferential actions are evaluated.
Dynamic Response of Cracked Cylindrical Shells With Internal Pressure
Authors: Vaziri A. , Nayeb-Hashemi H. , Estekanchi H. E.
Published: May 2008

Sub-surface cracks in pipelines with internal pressure may severely affect their dynamic response. The extreme cases of these cracks are when these cracks go through the thickness of the pipes. Dynamic responses of cracked and un-cracked pipes with fixed ends and under various internal pressures were evaluated experimentally and theoretically. In the experimental part, the effects of pipe internal pressure on the resonant frequencies and damping of the pipe were evaluated. In the theoretical part, finite element analyses were performed to find dynamic response of pipes with various crack length and orientation respect to the axis of the pipe. The experimental results showed resonant frequencies of the pipe are little sensitive to the pipe internal pressure. Similar results were obtained from the theoretical investigations. An axial crack had little effect on the pipe resonant frequencies. In contrast, cracks oriented at an angle to the axis of the pipe had a pronounced effect on some of the resonant frequencies of the pipe. This depended on the crack location in a particular mode shapes. For frequencies where the nodal point of the mode shape was located on the crack region, the frequencies were not significantly affected by the presence of the crack in the pipe. Furthermore, it was observed that the pipe internal pressure had little effect on the resonant frequencies of the cracked pipes.
Effect of Bundle Waviness on Compressive Strength and Notch Sensitivity of Non-Crimp Fabric Composites
Authors: Joffe Roberts , Varna Janis
Published: May 2008

Non-Crimp Fabrics (NCF) and vinylester resins seem to give lower compression strength data than similar prepreg-based composites. However, the lower data turned out to be not only material issue, but a problem associated with testing methodology, namely design of test fixtures and specimen configuration. Specimen geometry optimization study led to research concerning notch sensitivity of NCF. Investigations were performed testing specimens with circular center holes and symmetric sharp edge notches. In all cases reduction of compressive strength, corresponding to the net cross-section, due to introduced notches was not observed. Although NCF composites showed rather low compressive strength if compared with similar prepreg materials, they also exhibit almost complete notch insensitivity. This can be explained by irregular and uneven internal structure of NCF composite. Due to complex internal geometry NCF composite fails close to an internal defect, prior to the failure in vicinity of the notch, where stress concentration takes place.
Measurements and Code Comparisons for Advanced Gas Reactor Coolant Channels Containing Spacer Ribs
Authors: McCreery Glenn E. , Foust Thomas D. , McEligot Donald M. , Condie Keith G. , Pink Robert J.
Published: May 2008

Core coolant channels and control rod passages in prismatic gas-cooled nuclear reactors consist of typically hexagonal arrays of circular tubes or annuli containing spacer ribs. A major goal of an ongoing study to characterize the fundamental thermal fluid physics of high temperature flows in gas cooled reactors is to guide code development and assess code capabilities for treating forced convection problems in advanced reactors. Flow through an idealized annular channel containing an array of spacer ribs is examined both experimentally and computationally without complicating thermal phenomena. Laser Dopler Velocimetry (LDV) measurements in a transparent quartz model with index-matching oil flow are obtained in the INEEL’s unique large Matched Index of Refraction (MIR) flow facility to determine the velocity and turbulence fields, and to provide visualization of the flow. Experimental results are compared with numerical computations as a first step to understanding heat transfer enhancement and hindrance by the bluff spacer rib bodies.
A “Boundary Layer” Method of Obtaining an Approximate Solution to the Infinite Fin Problem
Authors: Janna William S. , Hochstein John I.
Published: May 2008

The classical infinite fin problem is considered in this study. First the exact solution is stated in which temperature, heat transfer rate, effectiveness and fin efficiency are all given. Then the boundary layer method is used to obtain alternative solutions in polynomial form. Boundary conditions are written for this method, and applied in various combinations to an assumed temperature profile. First, second, and third order approximate solutions are derived. Temperature profiles obtained from these solutions are compared to that calculated from the exact solution. It is shown that as more terms are included in the assumed profile, the resultant expression better fits the exact solution. Very good agreement between the third order and exact solution was obtained. Also derived from the approximate solutions was a distance along the fin beyond which the temperature difference between the fin and the surroundings is negligible. This arbitrary distance is analogous to the boundary layer thickness for boundary layer flow over a flat plate.
Bifurcation Analysis for Horizontal Longitudinal Fins Under Multi-Boiling Conditions
Authors: Krikkis Rizos N. , Sotirchos Stratis V. , Razelos Panagiotis
Published: May 2008

A numerical bifurcation analysis is carried out in order to determine the solution structure of a fin subject to multi-boiling heat transfer mode. The thermal analysis can no longer performed independently of the working fluid since the heat transfer coefficient is temperature dependent and includes the nucleate, the transition and the film boiling regime where the boiling curve is obtained experimentally for a specific fluid. The heat transfer process is modeled using one-dimensional heat conduction with or without heat transfer from the fin tip. Furthermore, five fin profiles are considered: the constant thickness, the trapezoidal, the triangular, the convex parabolic and the parabolic. The multiplicity structure is obtained in order to determine the different types of bifurcation diagrams, which describe the dependence of a state variable of the system (for instance the fin temperature or the heat dissipation) on a design (CCP) or operation parameter (base TD). Specifically the effects of the base TD, of CCP and of the Biot number are analyzed and presented in several diagrams since it is important to know the behavioral features of the heat rejection mechamism such as the number of the possible steady states and the influence of a change in one or more operating variables to these states. Stability analysis is carried out using the “resonance integral” technique and the Sturm-liouville eigen system analysis.
Experimental Study of Electrohydrodynamic Induction Pumping of a Dielectric Micro Liquid Film in External Horizontal Condensation Process
Authors: Brand K. , Seyed-Yagoobi J.
Published: May 2008

Electrohydrodynamic induction pumping of a dielectric micro condensation film is experimentally investigated in an external horizontal configuration. The pumping and its effect on heat transfer are explored by varying the voltage and frequency of the electric traveling wave, as well as the condensation heat flux. The induced pumping impacts the phase change process, but it provides first and foremost a tool for effective flow management. This is of significant importance in phase-change processes.
Effect of Wall Conduction on Natural Convection in Symmetrically Heated Vertical Parallel Plates With Discrete Heat Sources
Authors: Manca Oronzio , Nardini Sergio , Naso Vincenzo
Published: May 2008

The effect of heat conduction on air natural convection in a vertical channel, symmetrically heated, with flush-mounted strips at the walls, was numerically analyzed. Reference was made to laminar two-dimensional steady-state flow and to full elliptic Navier-Stokes equations on a I-shaped computational domain. Solutions were carried out by means of the FLUENT code. Results are presented in terms of wall temperature profiles, air velocity and temperature profiles in the channel. The wall temperature is affected by the location of the strip on the channel wall and maximum wall temperature is far larger when the heater is located in the upper region of the channel. Heat conduction in the channel wall lowers maximum wall temperature below the heater and the thicker the wall the larger the temperature reduction.
Experiments on Effect of Jet Impingement on Heat Transfer in Annular Channels With Parallel and Counter Flows
Authors: Mhetras S. , Lau S. C.
Published: May 2008

This experimental research examines, for turbulent parallel and counter flows of air through an annular channel, the effects of varying the geometries of the channel and the array of holes along the inner tube on the heat transfer distribution on the inner surface of the outer tube. Each hole array has 5 or 6 inline or staggered circular holes around the circumference of the inner tube at 10 axial stations along the inner tube. Heat transfer experiments are performed for three inner tube diameters, two hole diameters, and Reynolds numbers of 5,000, 12,250 and 30,000, to determine the distribution of the regional average Nusselt numbers along the outer tube, as a result of the jets impinging on its inner surface. Pressure measurements give the overall pressure drops, and the pressure distributions along the inner tube and the annular channel between the inner and outer tubes. The pressure data is needed to determine the mass flow rates of the impinging jets along the inner tube. The jets along the inner tube enhance the regional heat transfer on the inner surface of the outer tube by up to eight times when compared with the heat transfer for fully developed turbulent flow through an annular channel. Heat transfer enhancement is higher for a smaller inner tube and a lower Reynolds number. In the parallel flow case, the heat transfer coefficient on the outer wall of the annular channel is higher near the downstream end of the annular channel, while in the counter flow case, the heat transfer coefficient is higher near the upstream end of the annular channel. For both parallel and counter flows, the heat transfer coefficient is higher in a channel with a larger inner tube. With smaller holes along the inner tube, the heat transfer coefficient along the outer tube is higher and more uniform. Smaller holes, however, cause a higher overall pressure drop across the annular channel, resulting in a lower thermal performance. Increasing the total number of holes lowers the heat transfer, and causes a lower overall pressure drop. The hole mass flow rate increases along the main flow direction in the annular channel for parallel flow, and decreases for counter flow. The variation of the hole mass transfer is smaller for a larger inner tube diameter.
On the Calculation of Coated Fins
Authors: Cortes C. , Diez L. I. , Campo A.
Published: May 2008

Coated fins constitute a new concept in heat transfer enhancement. This type of fin is made from a primary material (the substrate) that usually possesses a low-to-moderate thermal conductivity. To augment the transfer of heat from the primary material to a surrounding fluid, a viable avenue is to coat the substrate with a thin layer of a high conductivity material (the coating). Undoubtedly, the formal model for a two-material fin is complicated because it involves a conjugate system of two heat conduction equations in two space variables. As a simpler alternative, Campo (2001) proposed a simplified quasi one-dimensional model that engages an ordinary differential equation with embedded spatial means of the thermal conductivities of the substrate and the coating. The objective of the present study is to extend the statistically-based ideas for a one material fin to two-material fins of variable thickness. To this end, a system of two heat conduction equations, coupled with the applicable boundary conditions, is solved with the Finite Element Method (FEM). The adequacy of the approximate algebraic route for the estimation of fin efficiencies is tested against the numerically-determined fin efficiencies supplied by the FEM.
Heat Shock Protein 70 Expression Kinetics
Authors: Wang Sihong , Diller Kenneth R. , Aggarwal Shanti J.
Published: May 2008

HSP70 is well known for its major role in cardiac ischemia protection. The purpose of this study was to determine the HSP70 expression kinetics for new protocol design in cardiac surgery, based on HSP70 protection function in clinical applications. Bovine aortic endothelial cells (BAEC) were used in experiments. Cells were heated at 42°C at different time intervals up to 5 hours and subsequently incubated at 37°C for up to 48 hours. Western blot and quantitative protein analysis were performed to measure HSP70 expression. The expression kinetics is a function of thermal stress time as well as poststress time. At least three stages were identified for the kinetics curve: increasing, maximum plateau and decreasing regions. The peak HSP70 concentration is 10 times the basal level for western blot analysis in BAECs. Two hours incubator heating followed by twelve hours post-heating falls in the plateau region. This research result provides information applicable to evaluation of energy sources and heating methods to induce optimal HSP70 expression in a target tissue.
Toward Improved CVTs: Theoretical and Experimental Results
Authors: Brokowski M. E. , Kim Songho , Colgate J. E. , Gillespie R. Brent , Peshkin Michael
Published: May 2008

Revolute-jointed cobots depend on continuously variable transmissions (CVTs). CVTs constrain the speed ratio between two shafts to a particular value within a continuous range. The spherical CVT is well suited to cobots, but like other point contact transmissions, achieving good performance is challenging. We have studied the contact mechanics of the spherical CVT under certain simplifying assumptions. Results of the calculations are compared to experimental measurements of an instrumented CVT. Improved CVT performance may require better control of compliance and contact forces in the CVT. Results for the contact forces under load conditions are shown. We conclude with a discussion of design implications for improved CVTs.
A Tiny Detector Made of a Self-Heated Thermistor for Determining Thermal Conductivity of Biomaterials in Temperature Range 233~313K
Authors: Zhang H. F. , Cheng S. X. , He L. Q. , Zhang A. L. , Zheng Y. , Gao D. Y.
Published: May 2008

In this paper, a new technique, using a tiny thermistor with 0.3~0.5mm in diameter to determine thermal conductivity of biomaterials in wide temperature range, has been developed. Based on steady spherical heat transfer in an infinite homogeneous medium, thermal conductivity of the measured medium can be determined by power applied and temperature rise of the thermistor. Compared with recommended values, maximum measurement errors of standard samples, aqueous glycol and CaCl2 solutions, water and ice, are 5.1% in temperature range 233~313K. The thermal conductivities of rabbit’s liver, kidney, heart and carotid artery in temperature range 233~293K are determined. Error caused by measurement parameters, effects of the finite scale of the measured medium and the decoupler between the thermistor and the medium are analyzed.
Thermostability Studies of Desiccated Murine Spermatozoa Nuclear DNA to Predict the Beneficial Effect of Trehalose in Long Term Storage
Authors: Bhowmick Sankha , Nath Bharat D. , Biggers John D. , Toner Mehmet
Published: May 2008

Long term preservation of mouse sperm in a desiccated state using sugars like trehalose may offer attractive economic benefits in the management of rapidly increasing transgenic mouse strains. The goal of the current study was to evaluate the protective effect of intracellular trehalose on sperm nucleus by predicting the long-term nuclear degradation kinetics of desiccated spermatozoa using an Arrhenius model whose parameters are obtained from high temperature-short time storage studies. B6D2F1 sperm isolated in an EGTA supplemented tris-HCl buffer (with or without 0.5M intracellular trehalose) were convectively dried with inert nitrogen gas in a controlled manner to moisture content >5%. The samples were then vacuum packed and stored at 22, 37, 45, 60 and 90°C for 1, 3 or 7 days. Following rehydration, the sperm sample was assayed for DNA damage using the sperm chromatin structure assay (SCSA). Results indicate significantly (p>0.05) lower DNA degradation for cells dried with intracellular trehalose at 45, 60 and 90°C for 1, 3 or 7 days compared to cells dried without trehalose. Based on a 10% increase in the index of injury, the calculated activation energy and frequency factors were 10.33 kcal/mole and 5.4×105 hr−1 respectively for cells dried in EGTA solution only. The corresponding numbers for cells dried in EGTA solution supplemented with 0.5M trehalose were 5.7 kcal/mole and 43.73 hr−1. Based on these parameters the time required for 10% DNA degradation are 279 and 759 hours for samples desiccated in plain EGTA vs. trehalose supplemented EGTA. These results indicate the beneficial effect of intracellular trehalose for the long-term storage of desiccated sperm.
Heat-Induced Denaturation of Collagenous Tissue: A Comparison of Numerical Simulations With OCT and MRI Data
Authors: Aksan Alptekin , Gmitro Arthur F. , Barton Jennifer K. , Anseth Scott , Arnoczky Steven P. , Fron Damien J. , McGrath John J.
Published: May 2008

Application of sub-ablative levels of heat to collagenous tissues has important therapeutic applications in medicine, such as tissue welding, thermokeratoplasty, skin resurfacing and treatment of joint instability. Sub-ablative heating produces collagen denaturation with desired tissue shrinkage yet detrimental comprises in mechanical properties of the tissue. In this paper, results of preliminary analyses with Optical Coherence Tomography (OCT) and Magnetic Resonance Imaging (MRI) are compared with a numerical model of tissue denaturation.
Estimating Parameters of Thermal Damage From Transient Exposures: Laser Coagulation of Rat Liver
Authors: Pearce John A. , Thomsen Sharon
Published: May 2008

Estimating effective thermal damage process coefficients for the first order kinetic model of damage processes is not difficult when the temperature is held constant for a substantial period. Laser coagulation experiments, however, are of short duration and, because of non uniform beam profiles, exhibit important heat transfer effects: the thermal histories are transient by nature and spatial temperature gradients are significant. An attempt is made to obtain useful estimates of activation energy, E, and collision frequency factor, A, directly from the transient history at the boundary of the zones of white coagulation and red hemorrhagic coagulation in liver in the rat, as identified by histologic studies. The Trial Region Method proves to be effective for transient data, in that a useful estimate of A and E can be obtained even from a single temperature curve. However, the results are very sensitive to small uncertainties in the actual value of Ω for the transient thermal histories to which the method is applied.
Comparison of Temperature Metrics of Heating-Induced Damage
Authors: Wright Neil T.
Published: May 2008

The temperature dependence of the rate of denaturation of Type I collagen due to heating is described well by chemical kinetics via the Arrhenius equation or transition state theory (TST) [1, 2, 3], each of which requires two material parameters. Nevertheless, many have sought to find a single convenient metric, such as one with units of temperature, to describe thermal denaturation of collagen. Comparing the results of studies that measured denaturation and cell death for a variety of biological samples shows that the parameters for either the Arrhenius equation (i.e. activation energy Ea and the frequency factor A) appear correlated over the range of temperatures for which biological materials are tested [4]. It has also been suggested that denaturation is a first-order phase change (i.e., melting) and thus should be characterized by a melting or denaturation temperature Td [5].
Flow and Heat Transfer Study in an Autoclave for Hydrothermal Crystal Growth With a Three-Dimensional Conjugate Heat Transfer Model
Authors: Li Hongmin , Evans Edward A. , Wang G.-X.
Published: May 2008

Numerical modeling becomes an important technique to study hydrothermal crystal growth since experimental measurements in hydrothermal autoclaves are extremely difficult due to the high pressure and high temperature growth conditions. In all existing models for hydrothermal growth, isothermal boundary conditions are assumed, although electric heaters are employed around the outside surface of the thick autoclave wall in practice. In this paper, a conjugate heat transfer model based on an industry size autoclave is developed to investigate the validity of such an assumption. The model includes not only turbulent fluid flow and heat transfer of the solution but also the heat conduction in the thick wall. The outside surfaces of the wall are under constant heat flux conditions, simulating electric resistance heating used in practice. Non-uniformity of the heat flux in the circumferential direction is also introduced in the model. The results indicate that the temperature at the solution/wall interface is far away from uniform. The isothermal wall boundary condition in previous efforts is questionable. Predictions of the isothermal wall model are analyzed. Parametric studies with the conjugate model show that total heat supply rate does not affect vertical uniformity dramatically. Heat loss can be lowered without affecting the flow and temperature fields if heaters are put half diameter or further away from the middle height (baffle) plane.
Transport Phenomena in Two-Phase Micro-Channel Heat Sinks
Authors: Qu Weilin , Mudawar Issam
Published: May 2008

The design and reliable operation of a two-phase micro-channel heat sink require a fundamental understanding of the complex transport phenomena associated with convective boiling in small, parallel coolant passages. This understanding is the primary goal of this paper. This goal is realized by exploring the following aspects of boiling in micro-channels: hydrodynamic instability, two-phase flow patterns, pressure drop, and convective boiling heat transfer. High-speed photographic methods were used to determine dominant flow patterns and explore as well as characterize hydrodynamic instabilities. Two types of dynamic instability were identified, a severe pressure drop oscillation and a mild parallel channel instability, and a simple method is recommended to completely suppress the former. Predictions of three popular two-phase pressure drop models and correlations were compared to micro-channel water data, and only a separated flow (Lockhart-Martinelli) correlation based on the assumption of laminar flow in both phases gave acceptable predictions. Several popular heat transfer correlations were also examined and deemed unsuitable for micro-channel heat sinks because all these correlations are based on turbulent flow assumptions, and do not capture the unique features of micro-channel flow such as abrupt transition to slug flow, hydrodynamic instability, and high droplet entrainment in the annular regime. These findings point to the need for further study of boiling behavior and new predictive tools specifically tailored to micro-channel heat sinks.
An Advanced Multiblock/Multigrid Method for Incompressible Flows and Its Application to EFG Growth of Silicon Tube
Authors: Sun D. , Zhang H.
Published: May 2008

A numerical method for incompressible flow is develped based on the multiblock scheme and implicit conservative block interface treatment and the SIMPLE pressure-correction algorithm using curvilinear finite volume approach. The full approximation scheme-full multigrid (FAS-FMG) is utilized to accelerate the convergence rate. A patch-based multiblock method is used as a smoother in the solution algorithm. The proposed numerical scheme has been tested for several benchmark solutions, including lid-driven cavity, Benard convection and Karman vertex shedding problems. Performance and the convergence characteristics of the multiblock and multigrid method are examined. The proposed method is also applied to an important industrial process, the edge-defined film-fed growth (EFG) of silicon tube, in which the multi-length-scale phenomena is resolved.