bluuebunny/crossref_metadata_2025 huggingface dataset:
Periodic Temperature Field and its Application to Thermophysical Property Measurement
Authors: Haji-Sheikh A. , Hong Y. S. , You S. M. , Beck J. V.
Published: July 2023

The frequency domain provides an interesting alternative platform for measuring thermophysical properties. The resulting measurement technique produces reasonably accurate thermophysical data from imprecise surface information. Having a periodic heat flux input at one surface, the thermal diffusivity is obtainable if temperature produces a measurable periodic effect at another surface. The analysis shows that only the phase shift is necessary to produce needed information while the boundary conditions can affect the experimental results. The feasibility of implementing this method is tested near room temperature using two different materials: Delrin and 304 stainless steel. The experiments yield accurate thermal conductivity and thermal diffusivity data for both materials but the data for Delrin exhibit smaller errors. Before performing experiments, a sensitivity analysis is carried out to determine the best range of frequencies for an experimental investigation.
Numerical Algorithms for Parameter Estimation
Authors: Zhuang Xinglai , Zhu Jianping
Published: July 2023

In this paper, we will discuss a numerical algorithm for estimating the unknown thermal conductivity coefficient in the heat equation using the temperature measurement at some points inside the domain. The algorithm has the following features:

• Efficient calculation of sensitivity coefficients. With the perturbation method discussed in this paper, the sensitivity coefficients can be calculated efficiently without repeated simulations or solving the adjoint equation.

• Accurate treatment of the measurements at different time steps. We have developed a method to consider the effect of measurements at all time steps more accurately.

• Adaptive regularization process. Instead of using a fixed constant as the regularization coefficient, we have developed a strategy to modify the regularization parameter dynamically during the solution process.

Numerical results will also be discussed in the paper to demonstrate the implementation of the algorithm and improvement in accuracy.
Local and Instantaneous Heat Transfer Characteristics of Arrays of Pulsating Jets
Authors: Sheriff H. S. , Zumbrunnen D. A.
Published: July 2023

Recent investigations of impinging jets have revealed that pulsations in the incident flow can be an effective technique for modifying convective heat transfer characteristics. While these studies focused on single impinging jets, industrial applications of impinging jets usually involve arrays of jets. When so configured, inter-jet interaction becomes a major consideration in achieving uniform and high heat transfer. To explore the effects of flow pulsations on the heat transfer performance of jet arrays, an experimental investigation has been performed of instantaneous and time-averaged convective heat transfer to a square, in-line array of circular air jets. The flow pulsation frequency was varied from 10 Hz to 65 Hz which corresponded to Strouhal numbers based on the nozzle diameter and velocity from 0.004 to 0.028. The pulse magnitude, which was defined as the ratio of the root mean square of the pulsating component of flow velocity to the mean flow velocity, was varied from 10% to 60%. Dual sensor hot film anemometry was used to document the jet flow-field. Instantaneous and time-averaged convective heat transfer was documented using a heat flux microsensor. An ensemble averaging technique was used to separate the pulsating component of flow velocity from the turbulent component and thereby assess the effect of flow pulsation on turbulence intensity. Instantaneous and time-averaged convective heat transfer conditions are documented as a function of pulse magnitude and pulse frequency within an unit cell of the array.
Heat Transfer From an Obliquely Impinging Circular Air Jet to a Flat Plate
Authors: Yan Xiaojun , Saniei Nader
Published: July 2023

A series of experiments was conducted for the measurement of local convective heat transfer coefficients for an obliquely impinging circular air jet to a flat plate. In the experiments, the oblique angles selected were 90°, 75°, 60° and 45° with 90° being a vertical jet. Two different Reynolds numbers of 10,000 and 23,000 were considered for the purpose of comparison with previous data available in the literature. Another parameter varied in the measurements was the dimensionless jet-to-plate distance, L/D. Four values of L/D(2, 4, 7 and 10) were considered in the experiments.

The experiments were conducted using the pre-heated-wall transient liquid crystal technique. Liquid crystal color changes were recorded with a video system. Local convective heat transfer coefficients were obtained through the surface transient temperatures which were related to the recorded color information.

Detailed local heat transfer coefficients were presented and discussed in relation to the asymmetric wall jet upon impingement of the jet flow. Results of experiments show that, for a given flow situation the point of maximum heat transfer shifts away from the geometrical impingement point toward the compression side of the wall jet on the axis of symmetry. The shift is more pronounced with a smaller oblique angle (larger jet inclination) and a smaller jet-to-plate distance. Comparisons of experimental results with existing heat transfer data for both obliquely impinging jets and vertical impinging jets are made. The effect of oblique angles on heat transfer was assessed.
Capacitance Probes for Measurement of Liquid Film Thickness
Authors: Chen X. , Butler T. , Brill J. P.
Published: July 2023

Liquid film thickness measurement is very important in multiphase science and technology. A capacitance probe is presented in this paper, including its basic principle, geometrical design, electronic circuit, and experimental tests in measuring film thickness during gas-liquid two-phase flow. This method is based on the difference between the dielectric constants of the gas and liquid phases. A ratio-arm bridge circuit is used to convert the capacitance of the fluids between twin parallel plates into voltage. The voltage output from the capacitance probe exhibits an excellent linear relationship with the liquid film thickness. Experiments have shown that the parallel-probe capacitance method is very suitable to gas-hydrocarbon liquid system.
An Experimental Study of Gas-Liquid Slug Flow in Vertical and Inclined Tubes Using High Speed Motion Analyzer
Authors: Xia Guodong , Zhou Fangde , Hu Mingsheng
Published: July 2023

Experimental investigation was carried out for gas-liquid slug flow in vertical and inclined tubes. The non-invasive measurements of the gas-liquid slug flow were taken by using the EKTAPRO 1000 High Speed Motion Analyzer. The present paper has obtained the information on the velocity of the Taylor bubble, the size distribution of the dispersed bubbles in the liquid slugs and some characteritics of the liquid film around the Taylor bubble. The experimental results are in good agreement with the available data.
Boiling and Condensation Heat Transfer Correlations for Refrigerant-Oil Mixture Flows Inside Augmented Tubes
Authors: Usmani G. I. , Ravigururajan T. S.
Published: July 2023

General correlations to predict boiling and condensation heat-transfer-coefficient are proposed. Data analyzed include 134a condensation and evaporation of refrigerants such as R-22, R-12, R-113, and R-134a. Wide ranges of mass flux, heat flux, pressure, and vapor velocities are covered. Both low-fin tubes and the micro-fin tubes are considered. For boiling correlation more than 975 data points from four experimental studies are correlated and for condensation more than 525 data points from three experimental studies are correlated. The efforts resulted in the development of simple correlations for predicting the heat-transfer-coefficients during condensation and evaporation inside augmented tubes.

The results show that the boiling heat-transfer-coefficients decreased with increasing oil concentration and vapor quality, and increased with tube enhancement severity factor. Increasing mass flux, however, diminished the adverse effect of oil on the heat-transfer-coefficient. During condensation, the presence of oil diminished the heat-transfer performance of a micro-fin tube. The heat-transfer-coefficient decreased with increasing oil concentration used, and also with increasing severity factor.
A Fluid Dynamics Study of a Circulating Fluidized Bed With Secondary Air Injection
Authors: Pécora Araí A. B. , Goldstein Leonardo
Published: July 2023

This paper presents an experimental study on the fluid dynamics of a circulating fluidized bed with secondary air injection. The experiments were run in a 4 m high, 100 mm internal diameter riser system. The solid material was 200–920 μm diameter sand. The gas temperature at the beginning of the riser was around 200°C and the superficial gas velocity varied in the 2.5–9.5 m/s range. The data obtained made possible to suggest correlations for the pressure drop in a cyclone and in a recirculating L-valve, which are necessary to study the system pressure balance. The pressure profiles in the loop of the circulating fluidized system show the secondary air injection influence.
Overall and Average Local Heat Transfer From a Horizontal Cylinder in a Gas-Fluidized Bed With an Opposing Oscillatory Flow
Authors: Pence Deborah V. , Beasley Donald E.
Published: July 2023

The Pulsed Atmospheric Fluidized Bed Combustor (PAFBC), a hybrid combustor concept that couples a pulsed combustor with an atmospheric bubbling fluidized bed, has technical advantages in energy efficiency and emissions. The present study examines fundamental aspects of heat transfer in this hybrid combustor by measuring the effect of an opposing oscillatory flow on the overall and time-averaged local heat transfer in a laboratory scale bubbling gas-fluidized bed. This opposing secondary flow consisted of a steady mean component and an oscillating component thereby modeling the flow in the tailpipe of a pulsed combustor.

Data were acquired for a monodisperse distribution of particles with a mean diameter of 345 μm and total fluidization ratios ranging from 1.1 through 2.7. Overall and time-averaged local heat flux measurements from the surface of a submerged horizontal cylinder show that heat transfer characteristics are significantly altered by an opposing oscillatory flow. Increases in overall heat transfer on the order of 12% were identified for operating conditions with low primary’ and secondary flow rates and low pulse frequencies. These enhancements were identified to be a consequence of significant localized enhancements. The fundamental trends and magnitude of the particle Nusselt number are effectively characterized by a modified form of the Strouhal number.
Interfacial Shear Modelling in Two-Phase Annular Flow
Authors: Kumar Ranganathan , Edwards David P.
Published: July 2023

A new interfacial shear stress model called the law of the interface model, based on the law of the wall approach in turbulent flows, has been developed and locally applied in a fully developed, adiabatic, two-phase annular flow in a duct. Numerical results have been obtained using this model in conjunction with other models available in the literature that are required for the closure of the continuity and momentum equations. These results have been compared with droplet velocity data (using laser Doppler velocimetry and hot film anemometry), void fraction data (using gamma densitometry) and pressure drop data obtained in a R-134A refrigerant test facility. Droplet velocity results match the experimental data well, however, the prediction of the void fraction is less accurate. The poor prediction of void fraction, especially for the low void fraction cases, appears to be due to the lack of a good mechanistic model for entrainment.
Temperature Measurements via Narrow Line Laser Absorption of Carbon Dioxide
Authors: Wooldridge Margaret S.
Published: July 2023

Theoretical development for temperature measurements via narrow line, infrared absorption of carbon dioxide (CO2) is presented. The proposed technique is based on rapid-scanning of two adjacent absorption line shapes. Spectroscopic considerations for sensitivity to temperature measurements are discussed. Several line pairs are evaluated, and the R(58) and R(60) transitions of the (00°1) ← (00°0) band are suggested for use in high temperature measurements for combustion systems.
The Effect of Specimen Geometry on Fatigue Crack Growth Behavior in Metal Matrix Composite
Authors: Sallam H. E. M. , Nayeb-Hashemi H.
Published: July 2023

An elastic-plastic two-dimensional finite element model was utilized to simulate the effect of the specimen geometry, i.e. type of specimen and the presence of the notch, on the crack tip deformation, CTD, and stresses and strains distributions around the crack tip in both the plane stress and the plane strain conditions. It was found that, the values of T-stresses and strains near the crack tip were significantly affected by the specimen type and the presence of the notch in both plane stress and plane strain conditions, i.e. thin and thick specimens. However, the analyses show that the presence of notch has a little effect on plastic zone size and shape and crack tip opening displacement, CTOD. The present results were employed to explain the main parameters controlling the fatigue crack growth, FCG, behavior in metal matrix composites, MMCs.
Recent Advances in Finite Element Method for Stochastic Structures
Authors: Elishakoff Isaac , Ren Yongjian
Published: July 2023

Extensive motivation to do an additional work in the finite element method in stochastic problems (FEMSP) is discussed. The qualitative comparison of FEMSP with the state of the art of the deterministic FEM is given. These observations and thoughts are then realized in several manners. We first present the exact inverse FEMSP, which however can not serve as a general tool for stochastic analysis of complex structures. The new variational principles for stochastic beams, for the mean response function, as well as response’s auto-correlation function are formulated and the FEM based on the variational principles is presented. Finally, a general non-perturbative FEM for stochastic probelms is developed, based on the element-level flexibility. It is concluded that much work needs to be done in order FEMSP to be at the level compared to that of the deterministic FEM. The advantage of the main methods presented here over the conventional ones lies in their non-perturbaxional nature. Numerical examples are presented.
Natural Convection Within a Horizontal Circular Cylinder
Authors: Chopin Therese R.
Published: July 2023

Natural convection is modeled in an infinitely long horizontal circular cylinder which is heated from below and cooled from above. This combination of thermal boundary conditions produces an unstable flow which must be modeled with a transient algorithm. The buoyancy-driven flow is studied for three different values of the Rayleigh number, Ra = 5(103), 5(104), and 5(105). The problem is modeled and solved using the finite element based code ANSYS/FLOTRAN™ computational fluid dynamics (CFD) program. Results include temperature and streamline contours.
A Generalized Model for Determining the Thermal Response to a Nuclear Waste Repository
Authors: Jendoubi S. , Kulacki F. A.
Published: July 2023

A generalized integral method for determining unsteady, one-dimensional heat conduction in multi-layer systems with arbitrary thermophysical properties has been developed. Temperature distributions within each sublayer are represented with approximating polynomials, and the source of heat can exist at any location in the system. The recurrence relations between coefficients of temperature profiles are generalized so that any number of sublayers can be handled. Although the model is a general one, it has been applied to temperature independent thermal properties in this study to illustrate the efficiency of the computations. The model is exercised for the stratigraphy of the proposed National High Level Nuclear Waste Repository at Yucca Mountain, Nevada. Results indicate that the model provides a powerful tool for both bounding the coupled thermal and hydrologic performance of the repository and assessing thermal uncertainties over both short and long time scales of repository operations.
The Complex Structure of Propagating Spray Flames
Authors: Kalma A. , Greenberg J. B.
Published: July 2023

The time evolution of a propagating laminar planar pre-mixed multisize spray flame has been investigated numerically. Special attention was focused on the influence of the spray multisizedness (polydispersity) on the structure of the resulting flame. For sprays having identical initial Sauter mean diameters, but different size distributions, both the flame structure and its propagation rate can be significantly altered. The ramifications of flame sensitivity to the spray’s characteristics on modeling and possible control of toxic emissions is discussed.
Thermal Oxidation of Chloro-Hydrocarbon Materials: Prediction and Measurement
Authors: Smith J. D. , Cope R. F. , Van Dell R. D.
Published: July 2023

Efficient thermal oxidation (> 99.99% conversion) utilizes high temperatures associated with “simple” diffusion flames to convert chloro-hydrocarbons (RCls) into H2O, CO2, and HCl. To optimize this process, it is necessary to understand the physical phenomena occurring inside the diffusion flame. This understanding is culminated in advanced combustion models. Although these models may help identify important factors, a more balanced research approach has been used to support industrial thermal oxidation units. Besides modeling, fundamental laboratory experiments coupled with full-scale plant experiments are also essential. Laboratory measurements focus on specific phenomena while plant experiments include the coupled effects of all of the governing subprocesses. This balanced approach leads to a better understanding of thermal oxidation which leads to more efficient operation.
Air Staging and Swirl-Assisted Mixing and Combustion of Methane and Air
Authors: Krass Brady J. , Puri Ishwar K.
Published: July 2023

Two-stage combustors offer an effective method for the suppression of combustion-generated pollutants. The imposition of swirl on the fuel and/or oxidizer flows causes recirculation which enhances mixing that in turn reduces NOx (i.e., total nitrogen oxide) formation. We investigate the characteristics of a burner that allows for both good mixing through swirl, and staging. Temperature measurements establish the presence of separate rich and lean zones during staging. Relative uniformity of the temperature profiles, and small magnitudes of temperature fluctuations are characteristic of the burner exit. In the burner product can be either dispersed (with no radial swirl-type structure) or concentrated into separate lean and rich regions. High speed video images confirm the swirling of the inner rich flame. The swirl allows interaction of the primary region with the secondary zone, and shears the secondary fuel jets causing further turbulence and vorticity that enhances mixing and prevents hot spots. Under conditions favoring unmixedness, product distribution occurs on relatively thin flamelet sheets that curve and wrinkle due to vorticity. In general, lower fractions of secondary air are beneficial from the perspective of mixing and homogeneity. The emission index of NOx, i.e., EINOx values correlate with the relative fractions of primary air. Fluid dynamical effects supersede those related to stoichiometry in the burner. The maximum EINOx value is lower than typical EINOx values for jet-type nonpremixed flames. Therefore, we conclude that we have successfully designed and characterized a low-NOx burner.
An Investigation of Methane-Air Nonpremixed Combustion in a Rapid-Mixing Burner
Authors: Bunnell Russell K. , Krass Brady J. , Puri Ishwar K.
Published: July 2023

An experimental analysis was performed on a rapid-mixing burner in which the mixing of methane and air occurs in discrete vortex structures prior to burning. Air is distributed by large vortex structures, and burning of fuel-air are mixtures occurs in smaller eddies. The burner design was evaluated by utilizing various visualization and diagnostic techniques. The advantages and disadvantages of each are discussed. High speed video is employed to evaluate fickering phenomena. Mixing induced by vortex structures is visualized by means of scattering across a laser light sheet. Velocity measurements made with a laser Doppler velocimeter confirm flow divergence and high kinetic energy at the flow edges through which the vortex structures transit. Temperature measurements made with a fast response thermocouple reveal a well-mixed combustion zone. The flame flickers in a manner similar to that occuring in isothermal helium plumes. Therefore, the results present sufficient evidence that a rapid-mixing burner has been successfully devised using radial fuel injection and a noncircular duct cross-section.
Four-Component Numerical Simulation Model of Radiative Convective Interactions in Large-Scale Oxygen-Hydrogen Turbulent Fire Balls
Authors: Surzhikov Sergey T.
Published: July 2023

Two-dimensional radiative gas dynamics model for numerical simulation of oxygen-hydrogen fire ball which may be generated by an explosion of a launch vehicle with cryogenic (LO2-LH2) fuel components is presented.

The following physical-chemical processes are taken into account in the numerical model:

- an effective chemical reaction between the gaseous components (O2-H2) of the propellant,

- turbulent mixing and diffusion of the components,

- radiative heat transfer.

The results of numerical investigations of the following problems are presented:

- the influence of radiative heat transfer on fire ball gas dynamics during the first 13 sec after explosion,

- the effect of the fuel gaseous components afterburning on fire ball gas dynamics,

- the effect of turbulence on fire ball gas dynamics (in a framework of algebraic model of turbulent mixing).
Benchmark Problem: Natural Convection Within a Horizontal Circular Cylinder
Authors: Huang H.-W. , Heinrich J. C.
Published: July 2023

Two-dimensional buoyancy-driven flow inside a horizontal circular cylinder is modeled using the finite element method. Incompressibility is imposed via the penalty function approximation and convective stability is maintained through the use of a Petrov-Galerkin method. Results are presented for Rayleigh numbers 5 × 103 ≤ Ra ≤ 5 × 107 and unit Prandtl number.
Effect of Controlled Material Variations on the Farfield Sound Radiation From Composite Beams
Authors: Slaughter Julie C. , Mann J. Adin , Adams Dan O.
Published: July 2023

The effects of the geometry and material make-up of a patch embedded in a carbon/epoxy beam were investigated. A tapered carbon/epoxy patch and a square-edged carbon/epoxy patch were each embedded in beams. Patches of Syncore (a syntactic foam core) and Syncore embedded with pultruded carbon rods were also embedded in beams. The radiated sound power per unit length was computed from the measured surface vibration of the beams. A model based on Hamilton’s Principle was used to generate data for comparison with the experimental data. Results from the model are promising but more development is needed.
Damping in Brake Rotor Materials With Different Microstructures
Authors: Yang S. , Gibson R. F. , Li D. , Hecht R. L.
Published: July 2023

Flexural damping factors and flexural moduli of gray cast iron used for making automotive brake rotors and drums were measured from room temperature up to 700°C. The experiments were realized by the half power bandwidth method and the impulse-frequency response technique. Measurements were conducted on samples with different graphite flake morphologies and different Type A graphite flake sizes. The goal of this research was to study damping behavior and the influence on damping behavior of different morphologies, in order to ascertain that the optimized cast iron microstructure for suppressing brake noise and vibration is used for brake components.
Ultrasonic Characterization of Composite Material Stiffness Properties Using Genetic Algorithms
Authors: Balasubramaniam Krishnan , Rao Navin S.
Published: July 2023

In this paper, efforts on the ultrasonic measurements of material stiffness properties of fiber reinforced composites such as graphite-epoxy and glass-epoxy employing inverse methods based on Genetic Algorithms using noise-free oblique incidence data will be discussed. Phase velocity data as a function of the angle of refraction in non-symmetry planes for orthotropic uni-directional composite laminates were used as the input to the genetic algorithm. Optimal parameters were chosen from the sensitivity analysis of the stiffness constants using a direct approach. The inversion using this novel technique was extremely promising in computing the material properties from the ultrasonic phase velocity data. Advantages and disadvantages of such genetic search methods over conventional stiffness reconstruction techniques are also discussed.
Optimization of Composites Through Ultrasonic Characterization
Authors: Gérard A. , Raju P. K.
Published: July 2023

Composites offer the structural designer a wide choice of properties, geometries and characteristics. Various fibers, matrix materials,’ reinforcement geometries and processing histories may be combined to provide a composite with properties that range from isotropic, low strength and low stiffness materials to highly anisotropic, high strength, and high stiffness materials. These options offer additional variables to the designer that can be used to optimize the configuration of the material and structure simultaneously. This process is presented schematically in Fig. 1. Figure 1. shows a typical design cycle for a composite component.
Application of a Thick Beam Frequency Solution Library to the Rapid Identification of Elastic Constants of Thick Orthotropic Rectangular Plates
Authors: Zheng Zhiyang , Ayorinde Emmanuel O. , Gibson Ronald F.
Published: July 2023

The Rayleigh method is used to solve the forward problem of obtaining transverse vibration modal data of the thick beam, where through-the-thickness shear and rotary inertia are significant, for provided elastic constants. The vibration of the rectangular plate is then synthesized from those of beam’s in the plate’s main coordinate directions. In this paper, the forward beam solutions are taken from a pre-computed library, thus drastically economizing CPU time, since the process of elastic identification involves repeated trial solutions of the plate forward problem. An optimization scheme based on the difference between experimental and predicted frequencies is applied for the inverse problem, using the library values.
Linear Stability Analysis of a Planar Slurry Sheet With Gas Flow
Authors: Parthasarathy R. N.
Published: July 2023

A study of the break-up of planar slurry sheets subjected to gas flow was conducted using linear spatial stability analysis. Two models of slurry behavior were considered: (i) a dilute slurry with negligible particle-particle interactions, and (ii) a dense slurry displaying viscoelastic behavior. The gas was treated as inviscid. Dispersion relations were obtained relating the wave growth rates to the frequency and other variables. The wave characteristics were determined by numerical solution of the governing dispersion relations for a variety of conditions. It was found that the presence of particles decreased the disturbance growth rate without affecting the dominant wavenumber, in the case of a dilute slurry. For viscoelastic fluids, the Deborah number played an important role in the wave growth. In all cases, the gas velocity acted as a destabilizing agent.
Corner Singularities and High Weissenberg Number Asymptotics for Viscoelastic Fluids
Authors: Renardy Michael
Published: July 2023

Recent work on corner singularities in viscoelastic flows has shown that, in contrast to the Newtonian case, sharp boundary layers occur near the wall. These boundary layers can be viewed as a special instance of a more general phenomenon, which also occurs in other high Weissenberg number flows. This lecture reviews the derivation of boundary layer equations and their application, in particular to corner flow.
Collective Phenomena in Foam Motion Through Channels of Variable Cross Section and Porous Media
Authors: Bazilevsky Alexander , Kornev Konstantin , Rozhkov Aleksey
Published: July 2023

The flow of foam in a channel with regularly varying square cross-section was investigated both experimentally and theoretically. Observations show a new characteristic feature of foam motion: the forward lamellae of foam filling a wide “pore” of the channel create for themselves an effective liquid channel. The cross-sectional area of the effective channel is of an order of the throat area of original channel. Once the effective channel is formed, the following lamellae are free to pass through it. A simple theoretical model and some estimates of the yield pressure drop are presented.
High-Frequency Rheology of Fine Suspensions
Authors: Buyevich Yuri A.
Published: July 2023

In this paper, mean viscous stresses and interphase interaction in an essentially unsteady suspension flow are analyzed on the basis of a previously developed self-consistent rheological model. Fine suspensions prove to be dispersive media in the sense that the rheological properties they exhibited in monochromatic flows are frequency-dependent. Consequently, at any given moment, viscous stresses and the interphase interaction force depend on how flow kinematic characteristics had evolved up to that point. Viscous stresses and interphase interaction also feature three main relaxation processes, and the corresponding relaxation times remain approximately invariant throughout the whole frequency range. Our model is also applied to two problems of considerable practical concern. In the first problem, a shear wave penetrates into a suspension from an adjoining solid block. In the second problem, a pressure wave originates by impact of a heavy body upon the free surface of the suspension.
Thermal Radiation and the Thermal Management of Micro-Devices via Gaseous Flows
Authors: Baker J.
Published: July 2023

The impact of thermal radiation on heat and momentum transfer characteristics in gaseous micro-flows is explored. A model problem is formulated which incorporates a radiative source term in the energy equation and couples the momentum and energy equations through the use of Sutherland’s model for viscosity. The optically thin approximation is used to model the contribution of thermal radiation. Maxwell/Smoluchowski boundary conditions are applied at the solid-gas interfacial boundaries. Numerical results for flow fields with Knudsen numbers in the slip flow regime are presented. Comparisons are made between results with and without thermal radiation and with results from previously published analytical expressions. A parametric study is examined to determine the impact of various dimensionless quantities on flow field characteristics in micro-channel flows. Skin friction coefficients and Stanton numbers are also presented and discussed. Conclusions as to the importance of thermal radiation in effectively predicting micro-flow behavior are drawn.
Shortening the Defrost Cycle Time With Active Enhancement Within the Suction-Line Accumulator of an Air-Source Heat Pump
Authors: Nutter Darin W. , O’Neal Dennis L.
Published: July 2023

The heating seasonal performance factor (HSPF) of an air-source heat pump is degraded by the defrost cycle. Electric resistance heat was added to the refrigerant through the use of a 750-watt immersion heater inserted at the base of the suction-line accumulator and by heating the accumulator shell via a 900-watt electric band heater attached to the outside of the accumulator. The electric resistance heat and its hot metal surface was used as an active enhancement technique to increase the rate of refrigerant boiling during the initial few minutes of the reverse-cycle defrost. The unit was fully instrumented and equipped with two possible expansion devices: a short-tube orifice and a thermal expansion valve (TXV), for cooling / defrost mode operation and a TXV for the heating mode.

Tests were run in psychrometric rooms that maintained outdoor conditions at 1.7°C dry bulb and 80% relative humidity and indoor conditions at 21.1°C dry bulb. Overall performance characteristics of particular interest were integrated COP, cycle time, defrost cycle time, along with other instantaneous comparisons of power, refrigerant flow rate, temperatures and pressures. Tests with a 1.8 mm diameter orifice defrost mode expansion device and the immersion heater enhancement showed the best system improvement. This test had a 3.1% increase in integrated cyclic COP and a 11% reduction of the defrost cycle time. The reduced cycle time came primarily as a result of a 1.0 minute reduction (31%) of the outdoor coil post-melt (draining) time.
Performance Prediction of a Sub-Slab Heat Exchanger for Geothermal Heat Pumps
Authors: Nielson Eric , Braven Karen Den
Published: July 2023

A large portion of the installation cost of a ground-coupled heat pump system is for the excavation necessary for ground coil placement. One possible method of reducing this cost is to place the ground coils beneath the slab floor of the building. This configuration of ground coil placement has not been specifically addressed in previous research. Freezing of the soil must be avoided in such a system. To simulate the temperature response of the surrounding soil to heat pump operation, a computer model was developed which incorporates line source theory in the form of a system of rings. The fluid temperature change along the length of the coil was used to determine the distribution of the ground load throughout the ring system. The model includes an adiabatic upper boundary, seasonal soil temperature variation, and thermal interference throughout the system. This model was used to explore the effects of pipe spacing and flow direction on soil temperature response under various load conditions. Using these results, the minimum soil temperature over a season was predicted. Based on these results, design recommendations for ground coil installation are provided based on available area, soil type, heat extraction rate, depth of coil beneath the slab floor, and depth of slab floor below grade. These include recommendations for spacing between pipe loops, flow direction, and a method to determine whether this type of system is feasible for installation in a particular location.
Impact of Return Air Leakage on Air Conditioner Performance in Humid Climates
Authors: O’Neal Dennis L. , Rodriguez Angel , Davis Michael , Kondepudi Sekhar
Published: July 2023

An experimental study was conducted to quantify the effect of return air leakage from hot/humid attic spaces on the performance of a residential air conditioner. Tests were conducted in psychrometric facilities where temperatures and humidities could be controlled closely.

Return air leakage from hot attic spaces was simulated by assuming adiabatic mixing of the indoor air at normal conditions with the attic air at high temperatures. Effective capacity and Coefficient of Performance both decreased with increased return air leakage. However, power consumption was relatively constant for all variables except outdoor temperature, which meant that for the same power consumption, the unit delivered much lower performance when there was return air leakage. The increase in sensible heat ratio (SHR) with increasing leakage showed one of the most detrimental effects of return air leakage on performance.
On the Evolution of the Definition of Entropy From Clausius to Today
Authors: Gyftopoulos Elias P.
Published: July 2023

Carnot analyzed an engine operating between two reservoirs. Through a peculiar mode of reasoning, he found the correct optimum shaft work performed during a cyclic change of state of the engine. Clausius justified Carnot’s result by enunciating two laws of thermodynamics, and introducing the concept of entropy as a ratio of heat and temperature of a thermodynamic equilibrium state.

By appropriate algebraic manipulations, in this paper we express Carnot’s optimum shaft work in terms of available energies or exergies of the end states of the reservoirs, and Clausius’ entropy in terms of energy and available energy.

Next, we consider the optimum shaft work performed during a cyclic change of state of an engine operating between a reservoir, and a system with fixed-amounts of constituents, and fixed-volume but variable temperature. We express the optimum shaft work in terms of the available energies of the end states, and Clausius’ entropy in terms of energy and available energy. Formally, the entropy expression is identical to that found for the Carnot engine except for the difference in end states.

Finally, we consider the optimum shaft work performed during a cyclic change of state of an engine operating between system A initially in any state A, (thermodynamic equilibrium or not) and reservoir R. We call this optimum generalized available energy with respect to R, and use it together with energy to define an entropy of any state A,. Again we observe that the expression for entropy is formally identical to the two given earlier except for the difference in end states.
A Graphical Simulator for Teaching Design in a Thermodynamics Course
Authors: Nichols D. , Metghalchi M.
Published: July 2023

A thermodynamic cycle simulation package has been developed for the desktop computer. The package has been written completely in C++, to make it easy to maintain and to improve. The program is based on objects modeling each component used in a vapor power cycle. The package uses a graphical front end for creating cycles using a selection of icons for the different cycle components. The user is required to enter the minimal amount of data to define the operating conditions. The package will calculate the properties of the fluid at all states of the cycle and then determines the performance of the plant. The package can be used in teaching design of any thermodynamic cycle such as refrigeration, heat pump and gas turbine cycle, in addition to steam power plant. Although, currently only steam properties are provided.
Improvements of a Molten Carbonate Fuel Cell Power Plant via Exergy Analysis
Authors: Braun R. J. , Gaggioli R. A. , Dunbar W. R.
Published: July 2023

A proposed molten carbonate fuel cell power plant design, intended for commercial production by the end of the 1990’s and developed under the auspices of the U.S. Department of Energy and the Gas Research Institute, has been analyzed with exergy analysis. The commercial production units, targeted for dispersed power generation markets, are based on an existing demonstration molten carbonate fuel cell power plant design which entered the start-up phase in early 1996. Exergy analysis of the commercial plant design shows the overall, second-law system efficiency to be 53 percent. The principal inefficiency, 17 percent of the total, lies in the catalytic combustor. Another major inefficiency is the stack loss, 14 percent. Heat transfer accounts for approximately 6% of the loss. System reconfigurations, incorporating a steam cycle with reheat (System I) and a gas turbine cycle (System II), both with revised heat exchanger networks, for significant improvement are proposed and evaluated. The second-law system efficiency is raised to 66% in System I and to 70% for System II.
Thermoeconomic Analysis of Steam Turbines: An Approach to Marginal Cost Allocation
Authors: Royo Javier , Zaleta Alejandro , Valero Antonio
Published: July 2023

One of the main problems arising with the thermoeconomic optimization of energy plants, is marginal cost allocation in components containing a flow bifurcation. A typical example is a cogeneration steam turbine. The analysis of the marginal cost allocation of this type of turbine is rigourously studied in this paper.

Structural Theory (Valero et al., 1992; 1993) takes under consideration that marginal cost assessment depends on the marginal consumptions of the inlet flow for each outlet energy flow. Supposing that the behaviour of the turbine would not be affected by the quantity of mass flowing in the process, these marginal consumptions could easily be calculated (Royo and Valero, 1995). Nevertheless, the calculation of marginal consumptions under this supposition is only an initial approach to the problem.

The accurate values of marginal consumptions (and therefore of marginal cost) may be calculated if one knows the actual behaviour of the steam turbine. This is the process followed in this paper to obtain the values of the marginal consumptions of several cogeneration steam turbines. The analysis offers a complete knowledge of the marginal consumptions for different steam turbine characteristics that work under on-design and off-design conditions.

The results obtained are compared with respect to the above initial approach. It is shown that the errors appearing when assessing marginal costs in this way could be relatively important. Nonetheless, a series of correction terms is proposed, by means of which it is possible to considerably decrease these errors.
Precision Motion Control of a Magnetic Suspension System Using a Robust Nonlinear Compensation Scheme
Authors: Mittal Samir , Menq Chia-Hsiang
Published: July 2023

The article presents a robust nonlinear compensation algorithm for realizing large travel in magnetic suspension systems suffering from parameter variations, and external disturbance forces. A geometric feedback linearization technique that utilizes the complete nonlinear description of the electromagnetic field distribution is employed to obtain large travel. Robustness to uncertainties in the feedback linearized system is achieved through the development of a discrete time delay control based compensation algorithm. In comparison to previous developments, the new scheme removes the constraints of triangularity conditions in compensation of unmatched uncertainties. The performance of this algorithm is experimentally investigated on a magnetic suspension system. In each of the experiments, the controller is designed using the approximate nonlinear model of the system which is significantly different from the actual plant model. For a fixed set of gains, the robust nonlinear controller accurately stabilizes the system for a large range of ball positions. In trajectory tracking performance evaluation, the controller provides tracking accuracies that are of the same order of magnitude as the accuracy of the position sensor. Finally, when the suspended ball is impressed with an external disturbance force, the controller provides adequate model regulation and rejection of disturbance forces, demonstrating high stiffness control. The experimental results therefore, verify the consistent performance of the algorithm in realizing large travel inspite of parameter variations and external disturbances.
Implementation of Sensory Feedback and Trajectory Tracking in Active Telemanipulation Systems
Authors: Ephanov Anton V. , Hurmuzlu Yildirim
Published: July 2023

This paper presents an approach to the implementation of sensory feedback in a robotic telemanipulation system. The system considered here consists of kinematically similar master-slave robotic manipulators. We propose a control scheme whereby the slave tracks the motion commanded by the human operator through the master mechanism. The scheme also accommodates, in a unified manner, different sources of sensory feedback. These include combined effects of the interaction with unknown environments and changes in structural properties of the slave manipulator due to additional unknown loads. The control algorithm is based on continuously sliding variable structure control, which is a nonlinear and highly robust control scheme. Due to the robustness of the scheme, the need for a priori information about the environment and the load is minimal. This information can be passed on to the system in the form of upper bounds of the interaction forces and additional loads. Experimental studies with a Pneumatic Haptic Interface (PHI) system were conducted to evaluate the performance of the proposed scheme.
Calibration of Closed Loop Controllers for Setting Impedances in Force-Reflecting Systems
Authors: Jayachandran Vijay , Rahman Tariq , Salganicoff Marcos , Heredia Edwin , Harwin William
Published: July 2023

This paper discusses a new method of impedance control that has been successfully implemented on the master robot of a teleoperation system. The method involves calibrating the robot to quantify the effect of adjustable controller parameters on the impedances along its different axes. The empirical equations relating end-effector impedance to the controller’s feedback gains are obtained by performing system identification tests along individual axes of the robot. With these equations, online control of end-effector stiffness and damping is possible without having to monitor joint torques or solving complex algorithms. Hard contact conditions and compliant interfaces have been effectively demonstrated on a telemanipulation test-bed using appropriate combinations of stiffness and damping settings obtained by this method. Since the method is general in nature and can be used for finding possible relations between controllable parameters and quantifiable output behaviour of a system, it can be extended to calibrating and controlling impedances in poorly modeled robot-actuator systems. A limitation of this method is that the actuator being modeled must have very little friction.
Robot Impedance Synthesis Based on Logic Task Description and Progressive Learning
Authors: Yang Boo-Ho , Doubleday Rolland L. , Asada Haruhiko H.
Published: July 2023

A new approach to the synthesis of robot impedance for force-guided assembly is presented in this paper. An optimal impedance is generated based on the combination of logic task description and learning. First, desired behavior of a robot system for performing a given task is described at a logic level. A simple logic branch control using a quasi-static force-to-motion map is created based on the logic description of desired robot behavior. A new learning method, called “Progressive Learning,” is then applied to this logic branch control in order to create a dynamic control, i.e. impedance control, for performing the task quickly and dynamically. Starting with a simple logic description about the robot behavior, the system can develop a fully dynamic impedance control by progressively learning the process dynamics. The problem is formulated in the context of high-speed insertion, and the major theoretical results are verified through simulation.
Expanded Asymmetric Stability Bounds With First-Order Lyapunov Robustness Method
Authors: Lee Jae-Cheon , Misawa Eduardo A. , Reid Karl N.
Published: July 2023

The problem of stability robustness in linear time-invariant system with structured parameteric uncertainties is considered. A new technique that estimates stability boundaries is proposed. It assumes asymmetric stability bounds and is derived using the Gao’s method and the first-order Lyapunov method. It is shown that new proposed method can inherit the optimal Lyapunov function property proposed by Olas. Two examples illustrate the new method. It is shown that it is simple to apply and significantly improves the estimates of stability boundaries for interval linear dynamic systems.
Robust Stabilizing Control of Stable Interval Plants: A Time Domain Approach
Authors: Zhang Yu M. , Kovacevic Radovan
Published: July 2023

A time-domain algorithm is proposed to control stable interval plants. The closed-loop control actions are determined based on the interval ranges of the model parameters and feedback. Robust stability and robust steady-state performance can be guaranteed if the negative feedback condition is satisfied despite possible open-loop overshooting, delay, and nonminimum phase of the stable interval plants. Simulation and closed-loop control examples are given to illustrate the performance.