bluuebunny/crossref_metadata_2025 huggingface dataset:
A Computational Study of Enhanced Heat Transfer in Laminar Flows of Non-Newtonian Fluids in Corrugated-Plate Channels
Authors: Metwally Hossam M. , Manglik Raj M.
Published: November 2021

The enhanced heat transfer behavior of laminar shear-thinning, power-law fluid flows in sinusoidal corrugated-plate channels is investigated. With duct plates at uniform wall temperature, periodically developed flows are considered for a wide range of channel corrugation aspect ratio (0 ≤ γ ≤ 1), flow rates (10 ≤ Reg ≤ 1500), and pseudo-plastic flow behavior indices (n = 0.5, 0.8, and 1.0). Typical velocity and temperature distributions, along with extended results for isothermal friction factor f and Collburn factor j are presented. The enhanced forced convection is found to be strongly influenced by γ, and the flow field displays two distinct regimes: undisturbed laminar or no swirl, and swirl flow regimes. In the no-swirl regime, behavior similar to that in fully developed straight duct flows with no cross-stream disturbance is obtained. The shear-thinning nature of the fluid, however, decreases f and enhances j. In the swirl regime, flow separation and reattachment in the corrugation troughs generates transverse vortices that grow with Reg and γ. The transition to this regime is also seen to depend on Reg, γ, and n, and in shear-thinning flows, it occurs at a lower Reg. The combined effects of corrugated plate geometry and non-Newtonian fluid rheology produce a heat transfer enhancement, as measured by the factor j/f, of over 3.3 times that in a flat-plate channel depending upon γ, n, and Reg.
Natural Convection From Horizontal Helicoidal Pipes
Authors: Al-Ahmadi Hamed , Fakheri Ahmad
Published: November 2021

Natural convection heat transfer from a horizontal helicoidal pipe is experimentally investigated for different coil-pitches. A modified characteristic length incorporating the tube diameter, the coil diameter, and the coil spacing, is proposed as the relevant scale for defining Nusselt and Rayleigh numbers. Using the proposed characteristic length, it is shown that the Nusselt number for horizontal helicoidal pipes can be determined using the available Nusselt versus Rayleigh number correlation for straight horizontal cylinders with high degree of accuracy over the range of the experimental data.
Two-Stage Non-Regenerative Silica Gel-Water Adsorption Refrigeration Cycle
Authors: Saha B. B. , Alam K. C. A. , Akisawa A. , Kashiwagi T. , Ng K. C. , Chua H. T.
Published: November 2021

Over the past two decades there have been considerable efforts to use adsorption (solid/vapor) for cooling and heat pump applications, but intensified efforts were initiated only since the imposition of international restrictions on the production and use of CFCs (chlorofluorocarbons) and HCFCs (hydrochlorofluorocarbons). Closed-type, conventional adsorption refrigeration and heat pump systems have an increasing market share in Japan. In this paper, a two-stage non-regenerative, silica gel-water adsorption chiller design is outlined. Experimental measurements are performed on a prototype of a 3.5 kW rated cooling capacity adsorption heat pump in order to determine its performance under different operating temperatures (hot, cooling and chilled water). The chiller performance is analyzed in terms of cooling capacity and coefficient of performance (COP). The main innovative feature in the two-stage adsorption chiller is the ability to utilize low-temperature waste heat (∼55°C) as the driving source with a cooling source of 30°C. The technological difficulty inherent in operating a thermally activated cycle with such a small regenerating temperature lift (temperature difference between heat source and heat sink inlets) is overcome by use of a two-stage cycle.
Design, Analysis and Fabrication of a Meso-Scale Centrifugal Compressor
Authors: Laveau A. , Kapat J. S. , Chow L. C. , Enikov E. , Sundaram K. B.
Published: November 2021

A gas or vapor compressor is one of the key components of many engineering systems, such as certain designs of vapor compression refrigeration systems, cryo-coolers, air handlers. For meso-scale systems with linear dimensions of a few centimeters, conventional designs do not work efficiently because of rather large relative tolerances, and hence these meso-scale systems require micro-fabricated components for efficient operation. This paper presents a meso-scale centrifugal compressor fabricated by photo-lithographic techniques.

A preliminary design based on 1-D flow analysis using air as the working fluid shows that a 50 mm diameter centrifugal compressor with a blade height of 200 μm gives a static pressure ratio of 1.12. In this design, the impeller has 10 full blades and 10 splitter blades. Each blade has the NACA profile 9510 with the maximum camber at 50% of the chord. These impeller blades have exit angles 35° with exit flow angles of 60°. A vaned diffuser having 20 equally spaced vanes with the same NACA profile is used to improve compressor efficiency. A 3-D compressible, viscous flow analysis has been done using a commercial finite volume software. The results of this analysis allowed the verification of the flow characteristics inside the meso-scale centrifugal compressor.

The compressor has been fabricated using micro-fabrication techniques. The rotor and the stator are made by etching a silicon wafer by using DRIE (Deep Reactive Ion Etching) technique. A Pyrex wafer is then bonded to the stator for visual access inside the compressor.
A Review of Refrigerant Condensation in Horizontal Micro-Fin Tubes
Authors: Liebenberg Leon , Bergles Arthur E. , Meyer Josua P.
Published: November 2021

This paper reviews currently available experimental evidence and predictive techniques for heat transfer and pressure drop during film condensation in horizontal micro-fin tubes, as used in heat pump systems. The enhanced heat transfer mechanism of condensation using micro-fin tubes is explained, and special attention is paid to the dependence of heat transfer and pressure drop on the geometric parameters of the micro-fin tube. It is shown that most of the existing predictive heat transfer and pressure drop models employ strictly empirical techniques. The difficulty of accurate (analytic) modeling of micro-fin tubes lies in the numerous dimensional variables involved in the tube surface, and these are also reported. Heat transfer and pressure drop correlations for micro-fin tubes are presented for pure single fluids and pure mixtures (i.e. R-12, R-125, R-22, R-134a, R-113, R-407C, R-410A, R-32/R-134a, and R-22/R-502/R-134a). The saturation temperatures vary between 22 to 53°C, the mass fluxes between 84 to 910 kg/(m2s), tube diameters between 5.95 to 14.18mm, the number of fins from 24 to 65, fin heights between 0.1 to 0.25mm, apex angles from 25 to 90°, and helix (spiral) angles from 7 to 30°. Correction techniques are suggested when using refrigerant mixtures. It is shown that the currently available correlations satisfy only limited experimental data for a limited number of refrigerants, and that there is little unanimity over a single correlation. The appraisal of the existing correlations by numerous researchers is presented, and recommendations for design calculations are made.
An Experimental Study on Heat and Mass Transfer in a Helical Absorber Using LiBr+LiI+LiNO3+LiCl Solution
Authors: Yoon Jung-In , Moon Choon-Geun , Kwon Oh-Kyung , Kim Eunpil
Published: November 2021

An experimental study has been performed to investigate the heat and mass transfer performance in a falling film absorber of a domestic small-sized absorption chiller/heater. The components of the chiller/heater were concentrically arranged in a cylindrical form with low temperature generator, an absorber and an evaporator from the center. The arrangement of such a helical-type heat exchanger allows to make the system more compact as compared to a conventional one. As a working fluid, the LiBr+LiI+LiNO3+LiCl solution is used to get improved heat transfer. The heat and mass flux performance of the LiBr+LiI+LiNO3+LiCl solution shows 2 ∼ 5% increase than that of the LiBr solution. When a surfactant in the LiBr+LiI+LiNO3+LiCl solution is used, the performance of heat and mass transfer improves 15 ∼ 20%. This result shows the LiBr+LiI+LiNO3+LiCl solution with a surfactant can be applied to a small-sized absorption chiller/heater.
The Use of Decomposition for the Large Scale Synthesis/Design Optimization of Highly Coupled, Highly Dynamic Energy Systems: Part I—Theory
Authors: Muñoz Jules R. , von Spakovsky Michael R.
Published: November 2021

A general methodology for the decomposed optimization of highly coupled, highly dynamic energy systems is presented. The approach is based on the physical division of the system into units (sub-systems, components or disciplines) subject to functions describing the energy, cost and other couplings between them. Two versions of the approach are proposed. The first approach is called the Local-Global Optimization (LGO) Approach. LGO requires unit optimizations to be carried out with respect to purely local decision variables for various combinations of the functions that connect the units. The results are used to create an Optimum Response Surface (ORS) for the entire problem. The ORS is then searched by a system-level optimizer to find the values of the coupling functions that lead to an optimum system-level solution. The second approach proposed is an iterative version of LGO (ILGO). In this case, the ORS is closely approximated using a linear Taylor series expansion. The partial derivatives resulting from such an approximation are seen to correspond to the marginal costs typically used in the thermoeconomic literature. ILGO effectively and significantly reduces the number of unit optimizations required. The properties used to describe the coupling functions play a critical role in the convergence of ILGO to a global system-level optimum. A discussion of this and its implication for the choice of First or Second-Law based quantities for the optimization of systems is given.
Numerical Prediction of Local Temperature and Current Density in a PEM Fuel Cell
Authors: Shimpalee S. , Dutta S. , Van Zee J. W.
Published: November 2021

The heat generation inside polymer electrolyte membrane (PEM) fuel cells affects fuel cell performance significantly. A numerical model for three-dimensional single fuel cell is developed by including the energy equation and the phase change aspects. A control volume approach is used and source terms for species transport equations, heat generation, and phase change model are introduced to incorporate the coupled flow physics in commercial flow solvers. Details of local current density distribution and temperature profiles are obtained and predictions from this model are compared with previous conclusions. The results reveal that the water evaporation and condensation generated by temperature change in fuel cell control humidity of the membrane and vary the local current density value. Further, the temperature distributions are dependent on the amount of heat generation created by electrical losses and water phase change. The predictions also present that the performance of the fuel cell relies not only on the inlet humidity condition but also on the temperature change inside the fuel cell.
3-D Model of Proton Exchange Membrane Fuel Cells
Authors: Zhou Tianhong , Liu Hongtan
Published: November 2021

A comprehensive three-dimensional model for a proton exchanger membrane (PEM) fuel cell is developed to evaluate the effects of various design and operating parameters on fuel cell performance. The geometrical model includes two distinct flow channels separated by the membrane and electrode assembly (MEA). This model is developed by coupling the governing equations for reactant mass transport and chemical reaction kinetics. To facilitate the numerical solution, the full PEM fuel cell was divided into three coupled domains according to the flow characteristics. The 3-D model has been applied to study species transport, heat transfer, and current density distributions within a fuel cell. The predicated polarization behavior is shown to compare well with experimental data from the literature. The modeling results demonstrate good potential for this computational model to be used in operation simulation as well as design optimization.
A Pseudo-Homogeneous Model for Cathode Catalyst Layer of PEM Fuel Cells
Authors: You Lixin , Liu Hongtan
Published: November 2021

A pseudo-homogeneous model for cathode catalyst layer performance in PEM fuel cells is derived from a basic mass-current balance by the control volume approach. The model considers kinetics of oxygen reduction at the catalyst/electrolyte interface, proton transport through the polymer electrolyte and oxygen diffusion through porous voids. A relaxation method is developed to solve the governing equations, which belong to the two-point boundary problem. The numerical results are compared well with our experimental data. The influences of various parameters such as overpotential, proton conductivity, catalyst layer porosity, and catalyst surface area on the performance of catalyst layer are quantitatively studied. The model can be used to determine important catalyst layer design parameters for different working conditions. From the discussions in this paper, it is possible to design high performance, low cost cathode catalyst layer, and hence, to improve PEM fuel cell performances.
A Passive Portable Water Pasteurization System for Developing Countries: Design, Analysis and Proof-of-Concept Experiments
Authors: Anderson Christianne V. D. R. , Kulacki Francis A.
Published: November 2021

The design, simulation, and testing of a novel portable pasteurization system suitable for the daily needs of four individuals are presented. This is the first self-powered, large-scale portable system developed to kill waterborne pathogens that contaminate current water supplies worldwide. The major components of the system consist of available technology: two evacuated solar collectors, a heat exchanger, two holding tanks, and a thermostatic valve. Flow of contaminated water through these components is permitted only when the temperature specified by the thermostatic valve is reached. Simulation of system performance is obtained via a lumped capacitance, time-dependent analysis with a limited number of input parameters. A prototype pasteurizer was designed and constructed, and proof-of-concept experiments were conducted in Minnesota in May 1998. The system was able to deliver nearly the predicted quantity of pasteurized water, approximately 70 liter/day.
Two Dimensional Simulations of Enhanced Heat Transfer in an Intermittently Grooved Channel
Authors: Greiner M. , Fischer P. F. , Tufo H. M.
Published: November 2021

Two-dimensional Navier-Stokes simulations of heat and momentum transport in an intermittently grooved passage are performed using the spectral element technique for the Reynolds number range 600 ≤ Re ≤ 1800. The computational domain has seven contiguous transverse grooves cut symmetrically into opposite walls, followed by a flat section with the same length. Periodic inflow/outflow boundary conditions are employed. The development and decay of unsteady flow is observed in the grooved and flat sections, respectively. The axial variation of the unsteady component of velocity is compared to the local heat transfer, shear stress and pressure gradient. The results suggest that intermittently grooved passages may offer even higher heat transfer for a given pumping power than the levels observed in fully grooved passages.
On the Optimal Configuration of Three Cylinders in a Row Cooled by a Slot Jet of Air
Authors: Gori F. , Bossi L.
Published: November 2021

The optimal positions of three circular cylinders, cooled by a slot jet of air, are investigated. The diameters of the three cylinders are the same, D = 10 mm, while the slot jet has an height of S = 5 mm. The first cylinder is set up at a distance, H, from the slot exit, H/S = 6, which is the optimum in a one cylinder configuration. The second cylinder is set up at a distance from the first one, L1, with L1/S = 4, which is the optimum when two cylinders are present. The optimal distance of the third cylinder from the second one is L2, such that L2/S = 4, and the mean heat transfer coefficient on the third cylinder is at the maximum value. Local heat transfer coefficients on the surface of the third cylinder varies with L2/S. Measurements of axial velocity and turbulence intensity, in the axial direction, accompany the heat transfer results.
Free Convective Flow in a Two Enclosure Arrangement With a High Aspect Ratio Side Enclosure Joined to a Large Square Enclosure
Authors: Oosthuizen Patrick H.
Published: November 2021

A numerical study of free convective flow in a vertical joined two-enclosure arrangement has been undertaken. In this arrangement, a vertical heated wall kept at a uniform high temperature is contained in a high aspect ratio rectangular side enclosure. This enclosure is separated from a larger square enclosure by a vertical dividing wall which is impermeable but offers no resistance to heat transfer. The vertical wall of the main flow enclosure opposite to the dividing wall is maintained at a uniform lower temperature. All remaining walls in both enclosures are adiabatic. The situation considered is an approximate model of a window exposed to a hot outside environment and covered by a plane blind which in turn is exposed to cooled room. The flow has been assumed to be laminar and two-dimensional and results have been obtained for a Prandtl number of 0.7. The effects of Rayleigh number and the dimensionless width of the side enclosure on the Nusselt number have been investigated. The results show that there is a minimum in the Nusselt number variation with side enclosure width for a fixed Rayleigh number. The effect of Rayleigh number on the conditions under which this minimum occurs and on the value of the minimum Nusselt number has been investigated.
Numerical Modeling of Radiative and Convective Heat Transfer From an Irradiated Complex Window Assembly
Authors: Collins M. , Harrison S. J. , Oosthuizen P. H. , Naylor D.
Published: November 2021

The present numerical study examines the influence of heated, horizontal, and rotateable louvers on the convective and radiative heat transfer from a hot or cold vertical isothermal surface. The system models absorption of solar energy in a Venetian blind adjacent to the indoor surface of a window. Building on previous analyses, a steady, laminar, two-dimensional, conjugate conduction / convection / radiation model of this problem has been developed, and solutions have been obtained using the finite element method. Validation of the model against existing solutions has been undertaken. Results were obtained for two window temperatures (warm and cool compared to ambient), two louver to plate spacings, and three louver angles.

The results clearly demonstrate the effect of the model variables on heat transfer from the plate surface. With few exceptions, steady periodicity along the plate was clearly demonstrated. More importantly, increased independence of the results from the louver angle as louver to plate distance increased was demonstrated.
Mechanically Optimized Orientation of Intracellular Stress Fibers Under Cyclic Stretch
Authors: Yamada Hiroshi , Takemasa Tohru , Yamaguchi Takami
Published: November 2021

To elucidate the orientation of stress fibers in a cultured endothelial cell under cyclic stretch, we hypothesized that a stress fiber aligns so as to minimize the summation of its length change under cyclic stretch, and that there is a limit in the sensitivity of cellular response to the mechanical stimulus. Results from numerical simulations based on the continuum mechanics describe the experimental observations under uniaxial stretch well. They give us an insight to the biological phenomenon of the orientation in stress fibers under biaxial stretch from the viewpoint of mechanical engineering.
Determination of Flow and Heat-Transfer Parameters in Porous Media With Consideration of Density Variation of Working Fluid
Authors: Hsieh W. H. , Wu W. T.
Published: November 2021

An experimental investigation is conducted to determine the flow and heat-transfer parameters of porous media with the consideration of density-variation effect of the working fluid. The permeability (K), inertial coefficient (F), and local convective heat transfer coefficient (hloc) are determined for two types of metal screens at Reynolds numbers ranging from 20 to 400. A single-blow transient technique combined with a compressible non-local-thermal-equilibrium model determines the hloc. The compressible non-local-thermal-equilibrium model is also adopted in a Levenberg-Marquardt optimization technique for deducing the K and F from measured steady-state pressure drops at different flow rates. Results show that the permeability increases with the increase of the porosity. A set of empirical correlations is obtained for calculating the Nusselt number. Results also show that, under the test condition of this study, consideration of the density-variation effect would improve the accuracy in deducing the K, F, and hloc.
A Parametric Study of Phonon Energy Transport in Semiconductor Devices
Authors: Walker D. Greg , Fisher Tim S. , Ralston-Good Jeremy , Schrimpf Ron D.
Published: November 2021

Microscale energy transport typically can not be described by traditional continuum models. This is especially true for semiconductor devices where length and time scales are continually becoming smaller. These conditions tend to place the physics of the energy transport into the non-equilibrium regime. Moments of the Boltzmann equations which describe average quantities of particle physics can be used under these conditions to obtain solutions to the transport problem. Most simulations, using this approach neglect non-equilibrium energy transport through phonon interactions. The goal of this work is to identify parameters crucial to non-equilibrium energy transport in semiconductor devices specifically where phonon interactions are concerned through a systematic variation of parameters. A Gallium Arsenide device that has been examined in previous research will be used as a benchmark for comparisons.
Effects of the Manufacturing Process on the Dimensional Accuracy of Thermoset Composites
Authors: Zhu Qi , Geubelle Philippe H.
Published: November 2021

The warpage of thermoset composite structures during the manufacturing process is a direct consequence of residual stress development. The capability to predict residual stresses is crucial to the manufacture of dimensionally accurate composite structures. This paper is focused on understanding the fundamental issues leading to residual stresses in thermoset polymer composites and their effect on the dimensional accuracy of the manufactured components. Special emphasis is placed on the simulation of autoclave curing and hot pressing. A three-dimensional coupled thermo-chemo-viscoelastic model is developed to simulate the heat transfer, curing, residual stresses and deformation of a composite part during the entire cure cycle. The predicted values of curvature for cross-ply graphite-epoxy laminates agree well with experimental observations. The numerical result indicates that a significant fraction of the residual stress develops before cooldown. Detailed studies are also performed to examine the springforward phenomenon in L-shaped composite parts. The finite element results show that mold design (male vs. female mold), mold thermal expansion, and part thickness all play an important role on the final shape of the parts.
A New Facility for Measurements of Three-Dimensional, Local Subcooled Flow Boiling Heat Flux and Related Critical Heat Flux
Authors: Boyd Ronald D. , Cofie Penrose , Li Qing-Yuan , Ekhlassi Ali
Published: November 2021

In the development of plasma-facing components (PFC) for fusion reactors and high heat flux heat sinks (or components) for electronic applications, the components are usually subjected to a peripherally non-uniform heat flux. Even if the applied heat flux is uniform in the axial direction [which is unlikely], both intuition and recent investigations have clearly shown that both the local heat flux and the eventual critical heat flux (CHF) in this three-dimensional case will differ significantly from similar quantities found in the voluminous body of data for uniformly heated tubes and flow channels. Although this latter case has been used in the past as an estimate for the former case, more study has become necessary to examine the three-dimensional temperature and heat flux distributions and related CHF. Work thus far has shown that the non-uniform peripheral heat flux condition enhances CHF in some cases.

In order to avoid the excess costs associated with using electron- or ion-beams to produce the non-uniform heat flux, a new facility was developed which will allow three-dimensional conjugate heat transfer measurements and two-dimensional local subcooled flow boiling heat flux and related critical heat flux measurements.

The configurations under study consist of: (1) a non-uniformly heated cylindrical-like test section with a circular coolant channel bored through the center, and (2) a monoblock which is a square cross-section parallelepiped with a circular drilled flow channel through the center line along its length. The theoretical or idealization of the cylindrical-like test section would be a circular cylinder with half (−90 degrees to +90 degrees) of its outside boundary subjected to a uniform heat flux and the remaining half insulated. For the monoblock, a uniform heat flux is applied to one of the outside surfaces and the remaining surfaces are insulated. The outside diameter of the cylindrical-like test section is 30.0 mm and its length is 200.0 mm. The monoblock square has lengths 30.0 mm. The inside diameter of the flow channel for both types of test sections is 10.0 mm. Water is the coolant. The inlet water temperature can be set at any level in the range from 26.0 °C to 130.0 °C and the exit pressure can be set at any level in the range from 0.4 MPa to 4.0 MPa. Thermocouples are placed at forty-eight locations inside the solid cylindrical-like or monoblock test section. For each of four axial stations, three thermocouples are embedded at four circumferential locations (0, 45, 135, and 180 degrees, where 0 degrees corresponds to that portion of the axis of symmetry close to the heated surface) in the wall of the test section. Finally, the mass velocity can be set at any level in the range from 0.6 to 10.0 Mg/m2s.
Analysis of RELAP5 Drift-Flux Model for Vertical Subcooled Boiling Flow at Low Pressure Conditions
Authors: Končar Boštjan , Kljenak Ivo , Mavko Borut
Published: November 2021

The RELAP5/MOD3.2.2 Gamma code was assessed against low pressure boiling flow experiments performed by Zeitoun and Shoukri (1997) in a vertical annulus. The predictions of subcooled boiling bubbly flow showed that the present version of the RELAP5 code underestimates the void fraction increase along the flow and strongly overestimates the vapor drift velocity. It is shown that in the calculations, a higher vapor drift velocity causes a lower interphase drag and may be a possible reason for underpredicted void fraction development. A modification is proposed, which introduces the replacement of the EPRI drift-flux formulation, which is currently incorporated in the RELAP5 code, with the Zuber-Findlay (1965) drift-flux model for the experimental low pressure conditions of the vertical bubbly flow regime. The improved experiment predictions with the modified RELAP5 code are presented and analysed.
Percolation Theory Applied to Study the Effect of Shape and Size of the Filler Particles in Thermal Interface Materials
Authors: Devpura Amit , Phelan Patrick E. , Prasher Ravi S.
Published: November 2021

An important aspect in electronic packaging is the heat dissipation. Flip-chip technology is widely being used to increase the rate of heat transfer from the chip. A method to further enhance the thermal conductivity is by the use of a thermal interface material between the device and the heat sink attached to it in the flip-chip technology. Percolation theory holds a key to understanding the behavior of thermal interface materials. Percolation, used widely in electrical engineering, is a physical phenomenon in which the highly conducting particles distributed randomly in the matrix form at least one continuous chain connecting the opposite faces of the matrix. This phenomenon was simulated using the matrix method, to study the effect of different shapes and size of the filler particles. The different shapes considered were spherical, vertical or horizontal rods, and flakes in horizontal or vertical orientation. The effect of the size of these particles was also examined. The results indicate that the composites with particles having the largest side in the direction of heat flow will always have a better conductivity than the particles oriented normal to it. Also, from the results, we can choose the best filler size in the composite if we know the filler concentration we are aiming at.
A Thermal Model for Reburning Fuel Injectors in Glass Furnaces
Authors: Swanson L. W. , Koppang R. R.
Published: November 2021

A quasi-steady multi-mode heat-transfer model for retraining fuel injectors in glass furnaces has been developed that predicts the effect of geometry, furnace heat source and heat sink temperatures, radial and axial injector wall conduction, and coolant flow rate on the injector wall temperature distribution. The model imposes a radiation boundary condition at the outlet tip of the injector, which acts as a heat source. A parametric study has been conducted to investigate effects that the furnace gas temperature, reburning methane fuel and purge-air flow rates, and furnace wall temperature have on the injector wall temperature distribution. For nominal operating conditions, highly nonlinear temperature distributions were observed throughout the injector. Operation with methane as the coolant produced an extremely large temperature gradient near the injector tip that could cause excessive thermal stresses in the injector wall. The results also showed that nominal injector operating conditions should prevent alkali deposition at the injector tip and produce injector/metallic disconnect temperatures well below the initial deformation temperature for stainless steel.
Experiments and Numerical Simulations of Flow Patterns of Water Droplets From Fire-Fighting Helicopters
Authors: Satoh Kohyu , Sagae Kohei , Kuwahara Kunio , Yang K. T.
Published: November 2021

In large forest fires over wide areas, aerial fire fighting with water drop from helicopters has been widely employed in the world. After the large earthquake fires in Japan, possibilities were raised to employ similar fire-fighting technique to city fires. However, forest and city fires were inherently different in nature and require different fire-fighting implementations. Since the city fires are concentrated in extent and isolated, thus requiring more dense water application to extinguish fires. As a result, accurate engineering data on the optimum water application relative to a given fire are critically needed to design fire-fighting strategies. This study describes the experiments carried out in open fields using real-life helicopters, in comparison with the 3-D numerical simulations. Numerical simulations can provide reasonable flow patterns of the water droplets from the helicopters, and can be used as a design tool for implementing the fire-fighting technique for real city fires.
A New Method for Estimating the Effects of Thermal Radiation From Fires on Building Occupants
Authors: Torvi David A. , Hadjisophocleous George V. , Hum Joe
Published: November 2021

A new model for estimating the effects of high thermal radiation heat fluxes on occupants has been developed. This model allows the user to specify the type of clothing worn by typical occupants (e.g., street clothing or protective clothing), percentage of body covered by clothing, and occupant characteristics (e.g., age). Numerical models of heat transfer in fabrics and skin are used to estimate the times required to produce burn damage to bare and clothed skin. These skin burn estimates are used along with occupant characteristics to estimate the time-dependent probability of death from a fire. This paper reviews existing models for estimating the effects of high heat fluxes on occupants, describes the heat transfer models used to make skin burn estimates, and compares the results of the new model with those from existing models.
Effect of Draw Furnace Geometry on High Speed Optical Fiber Manufacturing
Authors: Cheng Xu , Jaluria Yogesh
Published: November 2021

The motivation of manufacturers to pursue higher productivity and low costs in the fabrication of optical fibers requires large diameter silica-based preforms drawn into fiber at very high speed. An optimal design of the draw furnace is particularly desirable to meet the need of high-volume production in the optical fiber industry. This paper investigates optical fiber drawing at high draw speeds in a cylindrincal graphite furnace. A conjugate problem involving the glass and the purge gases is considered. The transport in the two regions is coupled through the boundary conditions at the free glass surface. The zonal method is used to model the radiative heat transfer in the glass. The neck-down profile of the preform at steady state is determined by a force balance, using an iterative numerical scheme. Thermally induced defects are also considered. To emphasize the effects of draw furnace geometry, the diameters of the preform and the fiber are kept fixed at 5 cm and 125 μm, respectively. The length and the diameter of the furnace are changed. For the purposes of comparison, a wide domain of draw speeds, ranging from 5 m/s to 20 m/s, is considered, and the form of the temperature distribution at the furnace surface is kept unchanged. The dependence of the preform/fiber characteristics, such as neckdown profile, velocity distribution and lag, temperature distribution and lag, heat transfer coefficent, defect concentration, and draw tension, on the furnace geometry is determined. Based on these numerical results, an optimal design of the draw furnace can be developed.
Performance Based Evaluation of Bridge Substructure in North Mississippi Using Nonlinear FEM and Field Vibration Measurement
Authors: Mullen Chris L. , Tuladhar Prabin R.
Published: November 2021

Discussion of a Performance - Based Engineering evaluation procedure for an existing interstate highway bridge in north Mississippi. The bridge is in a highly trafficked location near the Memphis Metropolitan area and is reflective of modern design practices in Mississippi.

Results are presented of nonlinear damage response and displacement ductility performance of the reinforced concrete bents and their foundations predicted using static finite element (FE) computations. The model considers the composite action of the concrete and the reinforcing steel materials under axial force, shear, torsion and flexure.

The performance-based evaluation includes three-dimensional computational simulations of the nonlinear bridge system, including substructures and superstructure. The response spectrum dynamic analysis method will also be carried out on the linear elastic three-dimensional model to predict the linear elastic behavior.

Field vibration measurements, including ambient and hammer-impact, were performed to calibrate the models. The computed transfer functions are currently being evaluated to correlate vibration measurements and the Finite element models.
Numerical Evaluation of Advanced Multi-Stage FCC Units
Authors: Chang S. L. , Zhou C. Q. , Lottes S. A. , Petrick M.
Published: November 2021

Conceptual multi-stage fluid catalytic cracking (FCC) units that use several short risers are considered by some refining industries to enhance product yields and product selectivity. A validated computational fluid dynamic (CFD) code was used to evaluate the concept. The code solves conservation equations of FCC flow properties for three phases: gaseous species, oil droplets, and catalyst particles. Phenomenological models were developed to characterize multi-phase interactions, including interfacial drag and heat transfer, droplet vaporization, cracking reactions, and flow turbulence. Parametric and optimization studies were performed to evaluate the impacts of operation/design parameters on the product yields of the conceptual advanced FCC units. The results showed that promising product yields and selectively could be achieved by proper design of stage arrangements and operation parameters.
Introducing the Carangithopter: A Small Piezoelectrically Actuated Swimming Vehicle
Authors: Borgen Michael , Washington Gregory , Kinzel Gary
Published: November 2021

A new type of miniature swimming vehicle is discussed in this study. Propulsion is developed through a posteriorly mounted fin that laterally oscillates in a fish-like manner. The fin is driven by a kinematic mechanism, which is in turn actuated by two high-deflection, curved-beam piezoelectric actuators. Analytical theories relating to individual components of this multidisciplinary system are covered, including discussions of kinematics and fin propulsion. A summary of the generation of static and dynamic actuator models is presented. The physical evolution of an actual swimming vehicle is discussed through the positive and negative aspects of several design iterations. The current vehicle status is presented in detail in terms of its physical design, operation, and controls and is evaluated in terms of speed and maneuverability.
Model Based Simulation of the Active Damping of a Cantilever Plate and Redistribution of Stresses
Authors: Hanagud Sathya V. , Roberts Patrick J.
Published: November 2021

In most structures, fatigue critical areas are associated with regions of high stresses. Sometimes, passive stiffening of structures can displace these high stress regions. Thus, for most applications, active vibration control is preferred. However, the question of whether an active vibration control scheme involving a set of actuators will reduce stresses in the whole structure or create high stress areas in the vicinity of the actuators arises. In previous works, this question has been addressed for cantilever beams which showed that the stresses are reduced by approximately the same order of magnitude as the reduction in vibrations. However, many aerospace structures are constructed of thin walled components whose response to vibration reduction can be very different than that of beams. In this paper, the stresses induced by an active vibration control system, based on the use of an offset piezoceramic stack actuator with acceleration feedback control, are investigated in a plate structure. A 3-D finite element simulation of the closed loop active vibration control system is developed and both the closed loop stresses and vibration amplitude reductions are studied.
State-Switched Absorber for Vibration Control of Point-Excited Beams
Authors: Cunefare Kenneth A.
Published: November 2021

A system that has the capability to make instantaneous changes in its mass, stiffness, or damping may be termed a state-switchable dynamical system. Such a system will display different dynamical responses dependent upon its current state. State-switchable stiffness may be practically obtained through the control of the termination impedance of piezoelectric stiffness elements. If such a switchable stiffness element is incorporated as part of the spring element of a vibration absorber, the change in stiffness causes a change in the resonance frequencies of the system, thereby instantaneously ‘retuning’ the state-switched absorber to a new frequency. In between state switches, the operation of such a device is passive, being fundamentally a passive vibration absorber. This concept has improved performance over classical passive vibration absorbers or dampers, particularly for disturbances with multiple spectral components. This paper considers the application of such a device for the purpose of vibration control on beams subjected to harmonic point-force excitation.
Stability of a Class of Piezoelectric State-Switching Methods
Authors: Kurdila Andrew J. , Clark William W. , Wang Weijian , McDaniel Dwayne E.
Published: November 2021

Experimental and anecdotal evidences have shown that state-switched control strategies for piezoelectric actuators can be advantageous. However, most discussions of the stability of these systems has relied on heuristic, or physically motivated, arguments. In this paper, we show that recent open-circuit/short-circuit state-switching control laws can be viewed as hybrid dynamical systems of Witsenhausen type. Within this framework, the closed-loop stability of OC/SC switching is rigorously established using the method of multiple Lyapunov functions.
Weak Noise Expansion of Moment Lyapunov Exponents of a Two-Dimensional System Under Bounded Noise Excitation
Authors: Xie Wei-Chau
Published: November 2021

The moment Lyapunov exponents of a two-dimensional system under bounded noise parametric excitation are studied in this paper. The method of regular perturbation is applied to obtain weak noise expansions of the moment Lyapunov exponent, Lyapunov exponent, and stability index in terms of the small fluctuation parameter.
The Quadratically-Damped Mathieu Equation and Its Application to Submarine Dynamics
Authors: Rand Richard H. , Ramani Deepak V. , Keith William L. , Cipolla Kimberly M.
Published: November 2021

This work is motivated by naval use of passive towed sonar arrays of hydrophones. We consider the simplest model of a towed mass. The mass is considered to move only in a horizontal direction x perpendicular to the tow direction. The tension in the tow cable is expected to be nonconstant due to turbulence, and is modeled by a sinusoidal forcing function. The resulting differential equations are analyzed for linear stability and nonlinear dynamical effects. In particular we study the nonlinear dynamics of the ODE: x ¨ + ( δ + ϵ cos t ) x + x ˙ | x ˙ | = 0
Adaptive Noise Isolation in Finite Ducts
Authors: Li Yugang , Malatpure Aniket , Rahn Christopher D. , Dawson Darren M.
Published: November 2021

Noise from jet engines, vehicle exhaust systems, and heating, ventilation, and air conditioning systems often involves planar acoustic wave propagation through finite ducts. This paper introduces controllers that use a loudspeaker actuator and two microphone pressure sensors to adaptively decouple adjacent ducts, thereby isolating a quiet duct from bounded disturbances in an adjacent noisy duct. The system model includes a one dimensional displacement-based partial differential equation for planar noise propagation in the two ducts and an ordinary differential equation for the speaker dynamics. Based on Lyapunov theory, Exact Model Knowledge and adaptive isolation controllers exponentially and asymptotically regulate the controlled duct from bounded disturbances in the uncontrolled duct, respectively, while ensuring bounded uncontrolled duct response and control voltage.
In-Situ Measurement and Monitoring of Fiber Preform Permeability for Liquid Composite Molding
Authors: Liang Zhiyong , Zhang Chuck , Wang Ben , Shih Chiang
Published: November 2021

In a liquid composite molding (LCM) process such as resin transfer molding (RTM), quality control depends on an in-situ permeability profile of the fibrous preform taken just before resin injection. However, the conventional permeability measurement method, which uses liquid (oil or resin) as its working fluid, only measures the average preform permeability in an off-line mode. It cannot be used to create an in-situ permeability profile because of fiber pollution, and cannot be used to reveal local permeability variations of preform. This study develops a new permeability characterization method that uses gas flow and pressure profiles to measure preform permeability variation in a closed mold assembly. This method is based upon two research findings: (1) that the air permeability of a preform can be obtained through measuring the pressure profile of gas flow, and (2) that resin permeability is highly correlated with air permeability for the same fiber preform. In this paper, the validity of this method is discussed. Experimental results of gas permeability measurement with defective and defect-free preforms are presented, and quantitative models for correlation of gas permeability versus pressure profile and of gas permeability versus resin permeability are also provided. Finally, the efficacy of the proposed method is illustrated through experimental results.
Representation of Heterogeneous Objects in ISO 10303 (STEP)
Authors: Patil Lalit , Dutta Debasish , Bhatt A. D. , Jurrens K. , Lyons K. , Pratt M. J. , Sriram R. D.
Published: November 2021

Solid modeling of objects forms an important task in design and manufacturing. Recent developments in the field of layered manufacturing have shown potential for the physical realization of heterogeneous (multi-material) objects. Thus, there is a need to represent material information as an integral part of the CAD model data. Information models for the representation of product data are being developed as an international standard called STEP (ISO 10303). However, the current application protocols focus on the representation of homogeneous objects only. This paper proposes an information model to represent heterogeneous objects using the information modeling methodology developed for ISO 10303. This will help in providing a uniform base in the development of heterogeneous solid modeling systems. It will also equip the solid modeler with the ability to integrate with other applications and process planning in the domain of layered manufacturing.
Formulae to Size Axisymmetric Heat Spreaders Above Dielectric Layers
Authors: Hodes Marc
Published: November 2021

The thermal resistance of requisite thin dielectric layers between high power dissipating devices and thermal ground, i.e., the base of a heat sink, is substantial. Thus power devices are frequently mounted on a heat spreader attached to the dielectric layer to reduce this thermal resistance. This paper provides analytically-derived formulae and accompanying dimensionless plots for the thermal resistance between the power device/heat spreader interface and thermal ground as a function of the relevant dimensionless geometric and thermal parameters for the axisymmetric and one-dimensional Cartesian geometries. These formulae/plots can be used to properly size the thickness and footprint of heat spreaders above dielectric layers. The utility of the results is demonstrated by an example.
Optimal Blank Design for the Drawings of Arbitrary Shapes by the Sensitivity Method
Authors: Shim H. B. , Son K. C.
Published: November 2021

The sensitivity method in order to find initial blank shapes which result in desired shapes after deformation has been used in this study.. By assuming the final deformation shape be the drawn cup with uniform trimming allowance at the flange, the corresponding initial blank which gives final shape after deformation has been found. With the aid of a well-known dynamic explicit analysis code PAM-STAMP, shape sensitivity has been obtained. To get the shape sensitivity numerically, a couple of deformation processes have been analyzed. Drawings of trapezoidal cup, oil pan, and Audi front door panel, the benchmark test problem of Numisheet ’99 have been chosen as the examples. At every case the optimal blank shape has been obtained only a few times of modification without predetermined deformation path. With the predicted optimal blank, both computer simulation and experiment are performed. Excellent agreements are recognized between simulation and experiment at every case. Through the investigation the sensitivity method is found to be very effective in the arbitrary shaped drawing process design.