bluuebunny/crossref_metadata_2025 huggingface dataset:
Turbulent Natural Convection Along a Vertical Backward-Facing Step
Authors: Yuan X. , Chen T. S. , Armaly B. F.
Published: July 2023

Flow separation with reattachment occurs in many flows of practical interest. In this paper a two-equation turbulence model by Ince and Launder (1989) with Yap correction and a four-equation turbulence model by Abe et al. (1995) are utilized to predict turbulent natural convection along a vertical backward-facing step. Numerical computations were performed for a Prandtl number of 0.7 for three step heights (1.1, 2.2 and 4.4 cm) and with a temperature difference of 30°C between the heated plates and the free stream. Results are presented for mean flow velocity and temperature distributions, turbulence kinetic energy and its dissipation rate, turbulent heat flux, intensity of turbulent temperature variance and its dissipation rate, local Nusselt number, and reattachment length. A comparison between the predicted results from the two turbulence models shows that the differences in the maximum Nusselt number and in the reattachment length range, respectively, from 4% to 24% and 10% to 2% as the step height increases from 1.1 to 4.4 cm.
Effects of Bubble Motion on Chord Length Measured by Double-Needle Conductance Probe
Authors: Monji Hideaki , Matsui Goichi
Published: July 2023

This study deals with effects of bubble motion on average chord length of bubbles measured by a double-needle type conductance probe system. So far, known estimation methods for bubble size are restricted to only a spherical bubble. For the estimation of deformed bubble size, the rocking motion of a bubble should be considered. Furthermore, in order to obtain the value of bubble size near the wall, the relation between the size and average chord length of bubbles should be derived taking both the restricted bubble motion and the probe position into account. The results show that taking the rocking motion of a bubble into account, the bubble size is estimated accurately for an oblate spheroidal bubble, and that the restriction of the bubble motion by the wall induces the peak in the chord length distribution, even if the bubble size is uniform.
Flow Boiling Inside Enhanced Heat Transfer Tubes
Authors: Xiang G. M. , Hu H. Y. , Peng X. F. , Wang B. X.
Published: July 2023

A tube with longitudinal microchannels on inside wall was developed to enhance flow boiling heat transfer. The experimental investigation was conducted to identify the flow boiling heat transfer performance of liquid through the enhanced tubes. The flow boiling heat transfer in the enhanced tubes is greatly intensified, especially for the fully-developed nucleate boiling regime. The heat transfer coefficient in microchanneled tubes with smaller diameter is increased with a magnitude of 170% compared with the identical smooth tubes. The geometric configuration of microchannels and tubes would have significant effect of the flow boiling inside microchanneled tubes. The heat transfer performance of the microchanneled tubes is as good as or even better than that of other existing enhanced tubes.
Mixed Convective Heat Transfer for Fluid Flowing Through Annular Porous Medium
Authors: Wang B. X. , Du J. H. , Peng X. F.
Published: July 2023

The study of the transport phenomena in porous media provides the fundamentals for various branches of science and engineering. We have reported currently on our researches on the fluid flow and convective heat transfer in porous media. The entrance and non-Darcy’s effects on the forced and mixed convective heat transfer were studied experimentally for air, water and transformer-oil flowing through a vertical annulus packed with porous media beads of different sizes. The results are reported and discussed here briefly.
Experimental Study on Flow Rate Measurement by Using Cross-Correlation of Temperature Fluctuations
Authors: Sun Xiaodong , Dai Zhenxi , Weng Yihao , Xu Jijun
Published: July 2023

The applicability of cross-correlation method based on fluid temperature fluctuations to flow rate measurement under steady flow condition is investigated with experiments by using an on-line, digital instrument developed by the authors. The thermocouple transducer design, the signal data pre-processing system and the correlator design with chip microprocessor 8031 are described. The experimental results show that the intrinsic temperature fluctuations existing naturally in flowing fluid are adequate to be detected. The method is proved to be a reliable and accurate one of flow rate measurement in turbulent flow. In laminar flow, the measurement is not so satisfactory.
Numerical Study of Flow in Gas-Stirred Ladle Systems With and Without Throughflow
Authors: Park Hee-Jin , Yang Wen-Jei
Published: July 2023

Two turbulent models, the conventional k-ε and Reynolds Stress models, are employed to simulate turbulent recirculating two-phase flow generated by air injection to a ladle with or without throughflow. A Lagrangian-Eulerian scheme for two phases is computed numerically. It is shown that the k-ε model, while overpredicting turbulent kinetic energy, underpredicts the mean velocity of the Reynolds Stress model. It is also disclosed that the dispersion rate of a plume is more dependent on the bubble flow-rate than on the bubble size. The location of the air injection nozzle is varied for the throughflow case. It is shown that the k-ε model is not suitable for predicting highly swirling flow, even though it yields results which are in agreement with measurements in less swirling flow. It is also revealed that air injection from the left bottom nozzle is more effective in reducing the zone of zero turbulent kinetic energy which results in poor mixing.
A Numerical Simulation of the Solidification Process of a Binary Mixture in a V-Shaped Enclosure
Authors: Jones W. K. , DeZego S. E. , Dong Z. F. , Ebadian M. A.
Published: July 2023

A numerical study of the solidification process in a V-shaped sump has been conducted for a binary mixture. This geometry is of particular interest as it simulates the limiting cases of the physical domain of the molten metal in the direct chill (DC) continuous casting process. Solutions were obtained by solving a two-phase set of conservation equations of mass, momentum, energy, and species in a polar coordinate system. The necessary interfacial terms for the two-phase model are discussed. A non-uniform grid, biased at the point discontinuity, was chosen for the calculations to improve the stability of the numerical procedure. The binary mixture studied was a eutectic forming aluminum-copper (Al-Cu) alloy. Two limiting cases of sump angle (8° and 16°) were simulated to gain insight into the influence of geometric effects on the final cast properties. The effects of melt convection and solid movement are also discussed as contributing factors to the segregation patterns. The results of the study showed the angle of the enclosure greatly affected the developing negative segregation bands in the mushy region. Furthermore, the original negative-segregated mushy zone gradually developed into a positively-segregated region throughout the solid area.
Experimental Investigation of a Bubbly Flow by Means of an Image Analysis Technique
Authors: Schmidl William D. , Hassan Yassin A. , Ortiz-Villafuerte Javier
Published: July 2023

Particle Image Velocimetry (PIV) is a non-intrusive measurement technique, which can be used to study the structure of various fluid flows. PIV is used to measure the time varying full field velocity data of a particle-seeded flow field within either a two-dimensional plane or three-dimensional volume. PIV is a very efficient measurement technique since it can obtain both qualitative and quantitative spatial information about the flow field being studied. This information can be further processed into information such as vorticity and pathlines. Other flow measurement techniques (Laser Doppler Velocimetry, Hot Wire Anemometry, etc..) only provide quantitative information at a single point.

PIV can be used to study turbulence structures if a sufficient amount of data can be acquired and analyzed, and it can also be extended to study two-phase flows if both phases can be distinguished. In this study, the flow structure around a bubble rising in a pipe filled with water was studied in three-dimensions. The velocity of the rising bubble and the velocity field of the surrounding water was measured. Then the turbulence intensities and Reynolds stresses were calculated from the experimental data.
Heat Transfer Characteristics for Some Coolant Additives Used for Water Cooled Engines
Authors: Abou-Ziyan Hosny Z. , Helali Abdel-Hamid B.
Published: July 2023

Engine coolants contain certain additives to prevent engine overheating or coolant freezing in cold environments. Coolants, also, contain corrosion and rust inhibitors, among other additives. As most engines are using engine cooling solutions; it is of interest to evaluate the effect of engine coolants on the boiling heat transfer coefficient. This has its direct impact on radiator size and environment.

This paper describes the apparatus and the measurement techniques. Also, it presents the obtained boiling heat transfer results at different parameters. Three types of engine coolants and their mixtures in distilled water are evaluated, under sub-cooled and saturated boiling conditions. A profound effect of the presence of additives in the coolant, on heat transfer, was clear since changes of heat transfer for different coolants were likely to occur. The results showed that up to 180% improvement of boiling heat transfer coefficient is experienced with some types of coolants. However, at certain concentrations other coolants provide deterioration or no enhancement in the boiling heat transfer characteristics. This investigation proved that there are limitations, which are to be taken into consideration, for the composition of engine coolants in different environments. In warm climates, ethylene glycol should be kept at the minimum concentration required for desolving other components, whereas borax is beneficial to the enhancement of the heat transfer characteristics.
Studies of Artificial Cracks at Simulated Rocket Motor Liners by the Frozen Stress Method
Authors: Smith C. W. , Finlayson E. F. , Liu C. T.
Published: July 2023

Two types of bimaterial specimens, one consisting of two photoelastic materials with different critical temperatures (Type A) and one consisting of a photoelastic material with and without aluminum powder (the powder added to alter the modulus of elasticity without changing the critical temperature (Type B)) are constructed by bonding two halves of the dissimilar materials together. Each type of specimen contains an artificial edge crack along the bond line and loaded normal to the bond line. After evaluating the two specimen types by measuring the variation of the Mode I stress intensity distribution through the specimen thickness, Type B was selected as a superior model and its features studied in detail.
Modeling and Simulation of Crack Initiation and Growth in Particulate Composites
Authors: Kwon Y. W. , Lee J. H. , Liu C. T.
Published: July 2023

A micro/macromechanical approach was used to model and simulate crack initiation and crack propagation in particulate composite structures. The approach used both the micromechanical and macromechanical analyses in tandem. The micromechanical analysis was based on a simplified micromechanical model and damage mechanics at the micro-level, and the macromechanical analysis utilized the finite element method. In using these methods, crack initiation and growth in a general shape of composite structure were investigated with an efficient computational effort. It was assumed that a crack initiates and/or propagates when localized damage is saturated. As a result, the crack length was assumed to be the size of the saturated damage zone. Matrix crack initiation and propagation at circular notch tips were simulated using this approach. Modeling and simulation were also conducted for cases of non-uniform particle distribution in particulate composite structures. Predicted results showed a good agreement with the experimental data.
The Computation of the Time Dependent Natural Convection Flow in a Horizontal Cylinder Heated From Below
Authors: Nagai Hiroaki , Emery A. F.
Published: July 2023

The time dependent natural convection in a horizontal cylinder heated from below is computed using the stream function/vorticity approach. The flow is characterized by a rapid development to a quasi-static state and then the occurrence of a periodic oscillation. The time of onset of the oscillations, their period, and their magnitudes are functions of the grid and time increments. It is found that a grid independent solution cannot be obtained by using finite differences and we speculate that this is true for other computational methods. If the grid is sufficiently fine and the time step is sufficiently small, fine and small being related to the Rayleigh number, it is possible to extrapolate to zero grid and time increments. The extrapolation is linear in time, but not in space.
Destruction of Hazardous Military Wastes Using Plasma Arc Technology
Authors: Kanaras Louis , Qazi Mahmood
Published: July 2023

A Plasma Arc Technology (PAT) system treats hazardous wastes in a furnace, at temperatures of 2000° C, or higher, using a plasma torch. The organic components vaporize, decompose or oxidize. The off-gases consist of hydrogen, carbon monoxide, carbon dioxide and nitric oxides. A wet air scrubber is used to remove most of these gases. The scrubber water is treated and recycled. Metal-bearing solids are melted or vaporized. The solids are usually recovered as molten metal, or as non-leachable vitrified slag, suitable for disposal in a landfill.

A Plasma Arc Centrifugal Treatment system was used to evaluate this technology for destruction of the four military hazardous wastes listed below:

1. Sludge from Longhorn Army Ammunition Plant, TX;

2. Blast media from Letterkenny Army Depot, PA;

3. Medical incineration ash from Aberdeen Proving Ground, MD; and

4. Contaminated soil from open burning/open detonation ground at Picatinny Arsenal, NJ.

The evaluation, Phase 1 of a two-phase program, includes determining the process capability of PAT for the ultimate destruction of hazardous components; verifying the suitability of the resulting slag for regular landfill disposal; identifying potential hazards associated with the process emissions; and developing qualified cost estimates for the future utilization of the process on large scale operations.

Process variables such as feed rate, composition of off-gases, run duration, percentage of oxygen used in the secondary chamber, and chamber temperature are controlled. Material balance, destruction and removal efficiency (DRE), air emission quality, wastewater quality, and suitability of slag for landfill are determined. The results from these test runs and analyses are presented in this paper.

In Phase 2, four new candidate waste streams were selected, and are listed below:

1. Waste paint from a U.S. Navy facility;

2. Garnet blast media from a U.S. Air Force Base;

3. Simulated oil-contaminated sorbent, used by Tri-Services and private industry; and

4. Mendocino soil spiked with surrogate chemical warfare materials.

Phase 2 testing begins in May 1996, and the results will be available in July 1996.

The ultimate success of PAT for destroying hazardous wastes depends on achieving a slag that is non-leachable and meets Resource Conservation and Recovery Act (RCRA) requirements, and off-gases and scrubber water that meet Clean Air and Clean Water Act standards.

Preliminary results of Phase 1 show that all slags passed Toxicity Characteristics Leaching Procedure (TCLP) tests, for land disposal requirements; air quality meets California standards, and scrubber water can be treated and recycled.
Application of the Three Phase AC Plasma Generator for Drug Destruction
Authors: Polovtsev Igor S.
Published: July 2023

Experiments for gas destruction with the help of the new three phase AC plasma generator were performed. Advantages of the new type plasma generator were studied. It was shown that this generator can be successfully used for destruction of hazardous wastes. Tests methane, freon and malathion were performed. Results of the tests show complete destruction of the injected gases.
Groundwater Removal Near Heat Dissipating Waste Packages
Authors: Manteufel Randall D.
Published: July 2023

The thermohydrologic environment of heat-dissipating nuclear waste packages in a subsurface repository is affected by ventilation of the facility prior to permanent closure. Heat dissipated by the waste will raise the temperature of host rock and vaporize groundwater. Ventilation will remove some heat and water vapor from the subsurface, creating a desiccated region surrounding the waste packages. The resulting hot, dry environment will tend to favorably extend the containment time of the waste. This work evaluates the transient temperature field near emplacement drifts and predicts the extent of rock dryout and removal of groundwater. For two hypothetical ventilation schemes with 30-yr-old fuel and repository loading of 40 metric tons of uranium (MTU) per acre, about 4 to 5 m of rock surrounding the drifts are predicted to be dried during the pre-closure period.
Destruction of Ammonia and Acetic Acid by Hydrothermal Oxidation
Authors: Lee Albert , Saulters Oral S. , Connon Corinne S. , Castillo Harlen G.
Published: July 2023

This investigation demonstrates that both ammonia and acetic acid, which are refractory intermediates in metabolic waste destruction by hydrothermal oxidation, are more effectively oxidized with hydrogen peroxide than oxygen at lower temperatures. Our results highlight the differences between the two oxidants and offer an explanation of the disparities presented in the literature regarding the similarities and dissimilarities of peroxide and oxygen in hydrothermal systems. Furthermore, evidence is presented that shows acetic acid and ammonia may be destroyed better in combination than separately.
Numerical Prediction of Low Frequency Combustion Instability in a Model Ramjet Combustor
Authors: Shang H. M. , Chen Y. S. , Shih M. S. , Farmer R. C.
Published: July 2023

A numerical analysis has been conducted for low-frequency combustion instability in a model ramjet combustor. The facility is two-dimensional, and is comprised of a long inlet duct, a dump combustor chamber, and an exhaust nozzle. The experiments observed that the combustor pressure oscillation under the particular operating condition did not have much cycle-to-cycle variation. The main resonant frequency occurs at about 65 Hz for this case. In the numerical analysis, a time accurate Computational Fluid Dynamics (CFD) code with a pressure-correction algorithm is used, and the combustion process was modeled with a single step chemistry model and a modified eddy breakup model. A high-order upwind scheme with flux limiter is used for convection terms. The convergence of the linear algebraic equations is accelerated through a preconditioned conjugate gradient matrix solver. The numerical predictions show that the flame oscillates in the combustion chamber at the calculation condition and are justified by the experimental schlieren photographs. The numerical analyses correctly predict the chamber pressure oscillation and the unstable combustion mode. However, the pressure oscillation frequency is over predicted compared with the experimental data. The discrepancy can be explained by the simplified turbulence and combustion model used in this study, and the uncertainty of the inlet boundary conditions.
Numerical Simulation of Spark Ignition and Flame Propagation
Authors: Bokka V. K. , Matthews R. D. , Ezekoye O. A. , Davis G. C.
Published: July 2023

A theoretical model to simulate spark ignition and subsequent flame propagation is presented. The model incorporates physical models of the breakdown process, which include effects of the blast wave generated during breakdown and chemical kinetics of fuel combustion. The energy and species equations are solved using a control volume method. A three step mechanism is used to simulate chemical kinetics for fuel combustion and nitrogen chemistry. Plasma ionization is included and its composition is calculated by assuming local thermal equilibrium using statistical thermodynamics and molecular theory. The effects of power input, spark energy, and mixture equivalence ratio on the kernel growth and flame propagation are obtained and compared with experimental and computational results available in the literature.
Improved Damping and Stiffness in Composite Structures Using Geometric Fiber Wave Patterns
Authors: Pratt William F. , Rotz Christopher A. , Jensen C. Greg
Published: July 2023

The use of continuous wave geometric patterns in carbon fiber reinforced plastics for improved structural damping is investigated. This method uses viscoelastic materials that are co-cured with and embedded between fiber layers having continuous wave-like patterns to improve both damping and stiffness in the structure. The result is a practical and more production worthy method of structural damping.
Toughening, Strengthening and Densification Approaches Applied to Carbon/Carbon Composites
Authors: Gajiwala H. M. , Vaidya U. K. , Sodah S. , Jeelani S.
Published: July 2023

The current study is directed towards development of high performance, toughened, strengthened and easily processable carbon/carbon (C/C) composites. These composites were developed through a hybridized matrix approach involving conventional resole-type resin precursor used in conjunction with an in-house synthesized processable polyimide resin. Plain weave graphite fabric layers were impregnated with a resole-type phenolic resin and thermo-oxidatively stable, high carbon yield polyimide resin by the hand lay-up technique. The resultant composite was subjected to two successive cycles of carbonization followed by densification, to obtain a C/C composite. At each stage of the process, the composite was subjected to quantitative ultrasonic velocity measurements using longitudinal dry coupling transducers to characterize the elastic constants in three directions. Destructive interlaminar shear strength (ILSS) testing was done at various stages of processing to determine the failure modes and mechanisms that lead to toughening and strengthening.
Free Bending Vibrations of Partially Stiffened, Stepped-Thickness, Bonded Composite Plates and Panels
Authors: Yuceoglu U. , Özerciyes V.
Published: July 2023

The present study is primarily concerned with the free bending or transverse vibrations of a multi-layer, partially stiffened, bonded composite plate system. Here, the two-layer plate system is composed of two dissimilar, orthotropic plates of different lengths but of the same width and in-between very thin adhesive layer. Thus, a two-layer, partially stiffened, stepped-thickness, bonded composite plate system is created. In the dynamic equations, the influence of the thickness shear deformations and the rotatory moments of inertia of plates are taken into account in the sense of the Mindlin Plate Theory. The normal and shear strains and the corresponding stresses in the relatively very thin adhesive layer are included in the formulation. They are the coupling terms of the upper stiffening plate and the lower base plate. The composite plates are to be simply supported at two opposite edges. However, at the other two opposite edges, the boundary conditions may be arbitrary. The solution technique is a combination of a “Modified Version of the Transfer Matrix Method” and the classical “Levy’s Method“. The natural frequencies and the typical mode shapes of the stepped-thickness and partially stiffened, bonded composite plate system of dissimilar members are presented. It is shown that, in some cases, the deflection shapes of the upper stiffening plate and the lower base plate corresponding to the same mode of the composite system are significantly different. Also, the influence of some of the characteristic parameters on the natural frequencies are plotted and presented.
Laminar Convective Heat Transfer for a Bingham Plastic in a Circular Pipe: The Graetz Problem Extended
Authors: Min Taegee , Yoo Jung Y. , Choi Haecheon
Published: July 2023

Thermally fully developed and thermally developing laminar flows of a Bingham plastic in a circular pipe with uniform heat flux have been studied analytically. For thermally fully developed flow, the Nusselt numbers and temperature profiles are presented in terms of the yield stress and Brinkman number. The solution to the Graetz problem has been obtained by using the method of separation of variables, where the resulting eigenvalue problem is solved approximately by using the method of weighted residuals. The effects of the yield stress, Peclet and Brinkman numbers on the Nusselt number are discussed.
The Motion of Bubbles in Non-Newtonian Fluids
Authors: De Kee D. , Rodrigue D. , Fong C. F. Chan Man
Published: July 2023

The drag and the rise velocity of a spherical bubble rising freely and slowly in an inelastic Carreau fluid are calculated by a perturbation method. Measurements of the rise velocity of gas bubbles in several Newtonian and non-Newtonian fluids are reported. The transition from the Stokes to the Hadamard-Rybczynski regimes has been observed and in the case of viscoelastic fluids a jump discontinuity in the velocity has also been recorded. An equation is proposed to predict the volume at which the jump discontinuity occurs and the prediction is in good agreement with the experimental data.
Bubble-Collision Effects on Nonlinear Void Fraction Waves in Bubbly Liquids
Authors: Delassade Xavier A.
Published: July 2023

The concept of dispersed two-phase flow via the theory of micrmorphic fluids is briefly presented. Balance laws for each phase are given. For the isothermal case, a summary of the constitutive relations expressing the contribution of the collisional forces and other interactions concludes the derivation of the dynamic equations.

For finite amplitude disturbances, nonlinear effects are considered. A balance is made in order to determine the dominant effects of the many terms in the equations of motion. Over a long timescale, the collisional bubble-bubble couplings are shown to be purely dispersive. Weakly nonlinear waves propagate according to the Benney equation or the fifth order Korteweg-de Vries equation, both with perturbation terms which can be either amplifying or dissipative Burgers perturbation terms, depending on the level of description and the sign of a coefficient.

A brief discussion of some of the current issues and their implications is given.
Displacement of a Fluid by Another in Tubes
Authors: Siginer Dennis A. , Bakhtiyarov Sayavur
Published: July 2023

The displacement of Newtonian fluids by non-Newtonian fluids in a horizontal cylindrical tube has been investigated both theoretically and experimentally. Theoretical expressions for the breakthrough time, a function of the constitutive constants of the fluids and of the flow parameters and geometry, are derived when the displacing fluids are either of the inelastic viscous or viscoelastic type. The dynamics of the displacement process is studied experimentally using the photometry method and an oil field spacer fluid and glycerol/water mixtures as the displacing and displaced fluids, respectively. The ratio of the zero shear viscosities of the displacing and displaced fluids plays a crucial role both when the displacing fluid is characterized by a viscoelastic and viscoinelastic structure. The density ratio of the displacing and displaced fluids is close to one in our experiments as it may be in most field operations. We show that characterization of this type of spacer fluid by a viscoelastic model at moderate pressure gradients will not lead to good predictions of the breakthrough time when the viscosity of the displaced crude is much smaller than that of the displacing spacer fluid, that is, for high values of the zero shear viscosity ratios which may be desirable for high efficiency displacement processes.
Do Molten Polyolefins Reptate in Large Amplitude Oscillatory Shear?
Authors: Giacomin A. J. , Jeyaseelan R. S.
Published: July 2023

The linear relaxation spectrum predicted by reptation theory cannot accurately describe melt behavior in mild deformations. Replacing the linear spectrum with a generalized Maxwell model, one can assess how well reptation theory predicts large departures from linear viscoelasticity. In this way, three systems are studied in large amplitude oscillatory shear: a nearly monodisperse unbranched melt, a polydisperse unbranched melt, and a polydisperse branched system. Surprisingly, only the nonlinearities exhibited by the polydisperse branched system are reasonably predicted by reptation theory in oscillatory shear.
Acoustic Enhancement of the Rate of Heat Transfer Over a Flat Plate: An Experimental Investigation
Authors: Preston John M. , Johnson William S.
Published: July 2023

Increasing the rate of heat transfer can improve product quality and lower energy cost for many energy systems and pulsating fluid flow has been used to increase the rate of heat transfer in some situations. Specifically, sound waves below the audible limit, termed infrasound, have been used to increase the rate of heat transfer from small diameter, wire rods. This study examined the effects of infrasound on the rate of heat transfer from a flat plate.

A standing sound wave is formed in the neck of a Helmholtz resonator and may be enhanced by producing sound waves at the resonant frequency at or near the neck of the resonator. In this study a standing wave of infrasound was produced in a rectangular channel by two loudspeakers driven sinusoidally by a function generator at the resonant frequency of the system. The top of the channel was formed by a copper plate maintained at a constant temperature. Thermocouples placed along the center line of the channel measured the temperature of the air inside the channel and heat flux gauges mounted on the inside surface of the copper plate were used to measured the local rate of heat transfer from the plate to the air inside the channel Air flow inside the channel was produced by a centrifugal blower and varied by an inlet damper.

The use of infrasound increased the rate of heat transfer by approximately an order of magnitude when compared to natural convection Infrasonic enhancement of the rate of heat transfer over a two-dimensional region in forced convection was more effective in the laminar flow regime, for Reynolds numbers based on the hydraulic diameter between zero and 10,000. Typically for laminar flow, infrasound increased the rate of heat transfer up to five times the rate of heat transfer without infrasound. For turbulent air flow; however, the increase of the rate of heat transfer was almost negligible. The effect of infrasound on the rate of heat transfer was shown to depend on the air velocity inside the channel, the hydraulic diameter of the channel and the sound pressure level inside the channel. The temperature of the copper plate over the limited range tested did not significantly affect the heat transfer coefficient. It should be noted that the speakers were limited to a maximum sound pressure level of 121 dB, while infrasonic generators are capable of producing sound pressure levels over 170 dB.
Methods of Simulating Fouling Effect in Water-Cooled Condenser With a Sub-Cooler
Authors: Li Shan S.
Published: July 2023

The fouling on heat exchanger surfaces produces an additional thermal resistance Rf. It tends to reduce chiller capacity and increase power consumption. A method is needed to simulate the fouling phenomenon and to test new and fouling-free chillers for performance under simulated condition of the field fouling.

The fouling effect results in a penalty in the form of an additional temperature approach, ΔTa, between the hot and cool sides of a heat exchanger. If assuming single phase or simple two-phase (no sub-cooling) flow and some other conditions, this ΔTa can be rigorously derived by using LMTD method. ARI-550/92 Standard provides one form of the formulation.

When a sub-cooler is combined with a condenser, the temperature profile along the length of the heat exchanger becomes strongly non-linear. Simply using the above method will generate false information if the sub-cooling and the fouling are large. An analysis using piece-wise LMTD method should be utilized to calculate ΔTa. Because of the complexity of the pipe lines and couplings between water and refrigerant sides, this calculation requires iteration algorithm which is not convenient to use.

Present work proposes an approximate formulation. The flow circuit was simplified with the heat duties equivalent to the original circuit. This approximation provides very good accuracy in ΔTa calculation.
Parametric Study of Heat Transfer Enhancement in the Reciprocating Regenerative Magnetic Heat Pump
Authors: Chen D. T. , Murphy R. W. , Mei V. C. , Chen F. C.
Published: July 2023

The heat transfer enhancement parametric study of the gadolinium cores in reciprocating magnetic heat pumps has been studied numerically. The main objective of this study is to enhance the heat transfer rate from the gadolinium core to the regenerative fluid. The optimization of the core includes optimizing the volume of the core and the ratio of the effective heat transfer area to the volume. The total volume represents the total amount of heat generated from the core; the effective surface area to the volume ratio reflects the actual quantity of heat transferred from the core to the surrounding fluid. Both parameters have to be optimized to fit their particular applications. In general, the more core volume, the more heat will be generated; and the more surface area, the more heat will be transferred to the fluid. However, in reciprocating regenerative magnetic heat pumping applications, these two factors have to be adjusted well to allow the core to generate two extremely hot and cold regions in the top and bottom end of the regenerator fluid column, respectively. The result of this numerical study shows that porosity of the gadolinium core in the range 0.36–0.40 and area-to-volume ratio in the range 500–600 are two design criteria for designing a better gadolinium core for reciprocating heat pump application. In addition, the optimal operating conditions based on the regenerator tube’s moving speeds (or Reynolds numbers) have also been studied. According to the current investigation, Reynolds number 60–120 is the optimal operating range for running a well-designed gadolinium core. The flow’s thermal mixing has been controlled by using the technique of variable flow rate, which, according to the current study, can increase the maximum temperature span as much as 5 K.
Feasibility Analysis of a Vortex Generator for Absorption Heat Pumps
Authors: Fineblum Solomon S.
Published: July 2023

Significant thermal resources in the form of low temperature industrial waste heat, between 211 to 528 trillion kJ (200 and 500 trillion BTU’s) per annum, have the potential to drive absorption heat pumps. The proposed vortex generator permits a practical heat pump to operate efficiently with as much as 20 to 30°C below the boiling temperature of water (70–80°C (158–176°F)). Energy flows and auxiliary power requirements are computed. The system is shown to operate with relatively low temperature waste heat with higher specific capacity than conventional systems.
Exergy Analysis of Sodium Tripolyphosphate Manufacture
Authors: Atanasova Lubka G. , Rasheva Dimitrina A.
Published: July 2023

Sodium tripolyphosphate finds wide application in different branches of industry and medicine. It is used in big amounts for softening of water and as a component of different detergent compositions.

Using exergy method for thermodynamic analysis an evaluation of energy effectively of an installation for sodium tripolyphosphate production was done. Material, heat and exergy balances of the whole system and its separate parts were made. The exergy coefficients of efficiency, internal and external exergy losses are calculated.

It was found that-the exergy efficiency of the investigated system is low. The exergy efficiency coefficient is 6.75 %. The high exergy losses are due to poor utilization of heat of flue gas, obtained from natural gas.
Efficiency Analysis of a Process Design Integrating Cogeneration and District Energy
Authors: Rosen M. A. , Le M. N.
Published: July 2023

An efficiency analysis, accounting for both energy and exergy considerations, is reported of a design for cogeneration-based district energy proposed for the city of Edmonton, Canada, by the utility Edmonton Power. The original concept using central electric chillers, as well as two variations (one considering single-effect and the other double-effect absorption chillers), are examined. The energy- and exergy-based results differ markedly (e.g., overall energy efficiencies are shown to vary for the three configurations considered from 83 to 94%, and exergy efficiencies from 28 to 29%). For the overall processes, as well as individual subprocesses and selected combinations of subprocesses, the exergy efficiencies are generally found to be more meaningful and indicative of system behaviour than the energy efficiencies.
Influence of Trailer Tandem-Axle Versus Tridem-Axle on Pavement Damage and Dynamic Performance
Authors: Fekpe Edward S. K. , El-Gindy Moustafa
Published: July 2023

This paper reports a study on the effect of a semitrailer’s axle arrangements, tandem-axle versus tridem-axle, on dynamic performance and pavement damage potential of tractor semitrailers. Generally, dynamic performance properties of both tandem and tridem axles tend to deteriorate with increasing axle spread and maximum axle weight limit. Friction demand in particular is sensitive to tridem axle spread. There are maximum spreads and weight limits for both tridem and tandem axles to satisfy the dynamic performance measures. Tridem axle spreads between 2.4m and 3.6m and weight limits less than or equal to 27000kg satisfy the current dynamic performance criteria. Tandem axle spread less than 2.4m and weight less than 20000kg exhibit adequate dynamic performance properties. In the transportation of dense commodities, it is operationally more efficient to use semitrailers with a tridem axle than one with a tandem axle for gross vehicle weights less than 48,000 kg (i.e. tridem axle spread around 3.6m and maximum weight of about 25000 kg). Relative to the tandem axle, operational performance is greatly improved with the tridem trailer axle.
Stability of a Flexible Wheelset for High Speed Rail Vehicles With Constant and Varying Parameters
Authors: Lieh Junghsen , Yin Jie
Published: July 2023

The stability of an elastic wheelset coupled with a torsional spring and a torsional damper is presented in this paper. With flexible elements between two wheels, the advantages of both rigid and independently rotating wheel (IRW) systems may be obtained. Previous studies indicated that the flexible elements will affect the vehicle dynamic behavior and an optimal parameters may improve the system performance. However, those studies were limited to constant wheel/rail geometry as the wheelset rolls along the track. In this paper, it is intended to determine the critical speed regions thus to reduce the potential for hunting. The critical velocity of constant and time-varying models is presented. The variation in conicity is assumed to be periodic thus the Floquet stability concept may be employed. The computation of the state-transition matrix is based on a Runge-Kutta algorithm.
Wide-Range Surface Roughness Measuring System
Authors: Shiraishi M. , Aoshima S.
Published: July 2023

A wide-range surface roughness measuring system based on a laser beam has been developed. This method consists of two measuring approaches: a laser speckle method for smooth roughness and a light scattering method for rougher surfaces. When a measured roughness value exceeds about 1.0 μm Ra, the measuring principle automatically changes from the speckle approach to the light scattering approach. The experimental results with on-machine measurements indicate the accuracy of 0.04 μm to 0.5 μm for smooth surfaces and 2.0 μm to 5.0 μm for rougher surfaces.
H
∞ Based Robust Multivariable Linear Control of Weld Pool Shape
Authors: Zhang Y. M. , Yao Y. X. , Li L. , Kovacevic R.
Published: July 2023

In order to achieve the desired weld penetration and grain structure, the weld pool shape must be controlled. In this paper, the weld pool shape is specified by the length and width of the weld pool. Its feedback is provided by a realtime vision system. Due to unavoidable variations during welding, the process uncertainty is substantial. In order to develop a robust control system, the H∞ approach is used. Simulation and experimentation showed that the performance of the developed H∞ control system is quite satisfactory.
Performance Evaluation of Modular Real-Time Controllers
Authors: Zhou Lei , Washburn Michael J. , Shin Kang G. , Rundensteiner Elke A.
Published: July 2023

With the progress in the research and development of open-architecture control systems, traditionally-monolithic controllers need to be modularized. Modularization is necessary in order to take advantage of newly available hardware and software components and to reduce controller development and maintenance costs. The resulting modular controllers rely more on the underlying support services, such as the POSIX timer and operating system scheduler. The behavior of an underlying real-time operating system can have a significant impact on an open and modular controller. In this paper, we investigate such an impact by empirically evaluating the performance of our prototype modular controllers in the University of Michigan Open-Architecture Controller testbed. A modular software architecture allows for flexibility in running real-time control applications. For example, a controller may consist of several cooperative periodic real-time tasks, each of which runs as a separate computer process and controls a particular machine axis. However, we observe that real-time operating systems exhibit significant unpredictability. In particular, the timing uniformity of tasks suffers when multiple tasks run as separate computer processes. This indicates a need for approaches to improve controller performance. One strategy we propose is to minimize operating system activities, e.g., by disabling unnecessary peripheral devices. However, we find that some major sources of unpredictability are essential system software modules. Another strategy is to combine tasks with similar periods into a composite task. We conducted experiments to measure performance before and after restructuring software and found that combining tasks with similar periods is a more desirable approach.
Optimal Feedforward Control for High Speed and High Precision Digital Motion Systems
Authors: Guo Lin , Tomizuka Masayoshi
Published: July 2023

A feedforward controller which respects the underlying hybrid nature of digital control systems, i.e. continuous-time plant and discrete-time feedback loop, is proposed for high speed/high precision motion systems. The feedforward controller combines the shift(q) and the delta (δ) operators such that uncancellable discrete-time zeros caused by sampling the continuous-time plant at high rates, which make the mathematical inverse unstable, are handled in a natural way. The controller is optimized by tuning two parameters in a pre-filter of the feedforward controller. The optimization problem is generalized to an H∞ problem. Convex minimization techniques are used to find the solution to the optimization problem. Experiments are carried out on a Matsuura Vertical Machining Center. The performance of the proposed optimal hybrid feedforward controller is compared with that of the zero phase error tracking controller. Some improvements have been observed from the experimental results.
Stable User-Specific Haptic Rendering of the Virtual Wall
Authors: Gillespie R. Brent , Cutkosky Mark R.
Published: July 2023

Efficient control algorithms are developed to implement stiff virtual walls without chatter. An analysis of the complete coupled system comprising controller, interface device, and user’s finger underlies the design of a wall algorithm, thus each virtual wall is tailored to a specific user impedance. The finger is modeled as a static second order impedance with justification drawn from empirical studies of limb dynamics available in the literature and from observations of the disparity in time scales between contact instability and volitional control. Compensation is incorporated for the destabilizing effects of the zero order hold using either model based prediction or design in the digital domain. The destabilizing effects of asynchronous wall on/off switching times and sampling times are tracked by a special watchdog while deadbeat control is used to periodically eliminate these effects. Extensions are discussed, including on-the-fly system identification of the user impedance.
Force Shading for Haptic Shape Perception
Authors: Morgenbesser Hugh B. , Srinivasan Mandayam A.
Published: July 2023

This paper proposes a novel haptic rendering algorithm and describes a perceptual experiment that demonstrates its effectiveness in causing humans to perceive shapes during manual interactions with virtual environments. The algorithm, called “Force Shading” (analogous to Phong Shading for visual displays), refers to a controlled variation in the direction of the force vector displayed by the haptic renderer for the purpose of creating the illusion of a non-flat shape on a nominally flat surface. Experiments on shape perception were done on 5 subjects using the Phantom as the haptic interface device. In these experiments, subjects manually explored the haptic display of various virtual polyhedral approximations of a circular cylindrical bump, with or without force shading. They then indicated the perceived shape by selecting one from a menu of shapes displayed on a computer monitor. Without force shading, the subjects accurately identified the polyhedral nature of the virtual bumps. With force shading, however, the subjects identified the polyhedral approximations as feeling closer to that of a smooth cylinder. The higher the number of polygons, the higher was the percentage of trials in which the shape was identified with a smooth cylinder.
Touching Multiresolution Curves
Authors: Pai Dinesh K. , Reissell L.-M.
Published: July 2023

We describe a multiresolution representation of parametric curves that is well suited to haptic interaction. Our approach has been implemented on an embedded controller for the Pantograph haptic device, and has been used for haptic exploration of boundary curves obtained from images. The resolution of the representation can be dynamically adapted to the task and hardware limitations.

Specifically, we use wavelet multiresolution, using biorthogonal wavelets with good approximation properties. In addition to the multiresolution representation, we maintain a hierarchy of error bounding boxes at each resolution level that is then used for fast, “anytime” collision detection.