bluuebunny/crossref_metadata_2025 huggingface dataset:
Some Aspects of Particle Agglomeration in Simulated Slurry Fuels
Authors: Choudhury P. Roy
Published: March 2022

A series of experiments and analyses with JP-10 slurries, prepared with inert particles ranging in size from 0.3 μm to 2 μm, have been performed to study the influence of particle size, mass loading and droplet diameter on particle agglomeration in a slurry fuel. Particle mass loadings of 20% and 50% in droplets ranging in size from 100 μm to 3000 μm were studied analytically. Inert SiC and Al2O3 particles were chosen to avoid the complexities associated with reacting solids. Similarly, slurries were prepared without any chemical additives which could decompose. The choice of non-stabilized slurry with inert particles was made in order to isolate the problem under study, and not to cloud the issue of particle agglomeration due to burning particles and secondary reactions involving chemical stabilizers. Scanning Electron Microscopic (SEM) studies of the residues from burning and also evaporating droplets suggest that instead of using the usual very small particles (1 μm or smaller), intermediate size particles (∼ 3 μm) should be used in preparing the slurries. Intermediate size particles are affected neither by any interacting forces nor by chemical cementation caused by fuel decomposition at the particle surface heated by flame radiation. Therefore, the intermediate size particles are expected to minimize particle agglomeration. Analysis corroborates the fact that fuel decomposition is negligible at the surface of small particles. Also the solid mass loading between 20% and 50% seems to have a very small effect on fuel decomposition at the particle surface.

Because of increased mass and heat transfer rates in a flow field, analysis predicts a lower degree of fuel decomposition when droplets are exposed to flow.
Particle Temperature Response to Transient Thermal Perturbations in a Dilute Suspension Including Radiation Heat Transfer
Authors: Coimbra C. F. M. , Edwards D. K. , Rangel R. H.
Published: March 2022

The thermal response of particles subjected to time-dependent temperature perturbations in the surrounding medium, including radiation heat transfer, is studied. The continuous medium containing the dispersion of particles is assumed to be weakly participating, having a small but non-zero absorption coefficient. The particles in suspension are either in Stokes flow or stationary, so that the mechanisms of heat transfer between the particles and the continuous phase are of diffusive and radiative nature only. The general solution for the temperature response of the particles to time-dependent perturbations in the continuous phase is derived. The method used to derive the general solution consists of including the radiative effects in an integro-differential equation that describes the temperature history of the particles. A fractional-differential operator is then applied to the radiation-diffusion equation. The resulting equation is solved exactly by the method of variation of parameters for the temperature potential between the particles and the medium. Linear and harmonic perturbations are analyzed and discussed.
The Influence of Fuel Feed Unsteadiness and Spatial Nonuniformity on Spray Diffusion Flames
Authors: Greenberg J. B.
Published: March 2022

A mathematical model is formulated to describe the fluctuations of spray diffusion flames brought on by fuel feed unsteadiness and spatial nonuniformity. The spray is modelled using the sectional approach. An analytic solution is developed and utilized for computing the dynamics of the flame envelope under various operating conditions, such as liquid fuel volatility and droplet size, expressed through a vaporization Damkohler number. Calculated data reveal the way in which the underlying alternate waves of liquid and gaseous fuel lead to flame growth, collapse and distortion. This behaviour influences the temperature field temporally and spatially, and produces regions that are periodically hotter and colder. The ramifications of these results on combustion efficiency and pollutant production are discussed.
Transfer Process in Multisolid Two-Chamber Recirculated Reactor
Authors: Goldman Y. , Shavit A. , Dayan Y.
Published: March 2022

Prepyrolysis of coal as a precursor to its utilization in a power plant or gas turbine is experimentally investigated. The pyrolyzer, 800 mm in diameter and 1500 mm in height, consists of two concentric chambers. Coarse char particles, used like inert medium (“sand” in the sequel). The char is heated in the outer chamber by an external source of heat, such as hot gases. The inner chamber is used for the pyrolysis process of fine coal powder (50 micron), that is fed into it. The heat required for the endothermic pyrolysis process is supplied by the circulating char. Cold tests conducted on the apparatus indicate that the parameters most influencing solid circulation between the chambers are: the aerosol nature of the flow, the sand seals area, and the superficial velocity. The tests show that the intensive recirculation process exists only under very limited range of flow conditions. Outside this range of conditions, sand “bridges” are formed at the seals preventing proper operation. These bridges can be destroyed by strong fluidization at the inner chamber wall. Results of cold and hot tests, including parametric study of the pyrolzer performance, will be presented. The feasibility of the suggested scheme for mild gasification, of a precursor to its combustion in a power plant, will be discussed.
Measurements of Fully-Developed Augmented Convection in a Symmetrically Grooved Channel
Authors: Wirtz R. A. , Huang Feng , Greiner Miles
Published: March 2022

Measurements of fully-developed augmented convection and pressure drop of air flow in an isothermal, symmetrically grooved channel are reported for channel Reynolds numbers ranging from 800 to 5,000. Grooves, oriented transverse to the flow, are of triangular shape with dimensions that are comparable to the hydraulic diameter of the channel. The grooved section is designed to excite instabilities in the flow leading to increased mixing at sub-transitional Reynolds numbers.

Local heat transfer measurements are made using a holographic interferometer. Interferograms, representative of the cross-span-average temperature of the air in the channel, are analyzed to produce data records of the air temperature distribution and the local heat flux along the grooved walls. Heat flux distributions are spatially averaged to produce a correlation of fully-developed Colburn j-factor for this surface configuration. A performance evaluation of the grooved surface applied to a simple heat exchanger shows that it provides thermal performance which is comparable to other surfaces commonly employed in compact heat exchangers.
Turbulent Heat Transfer in a Steam Turbine Bypass Pipe Flow
Authors: Amano R. S. , Draxler G. R. , Golembiewski J. M.
Published: March 2022

The main goal of this study is to investigate the evaporation process of a coolant (water droplets) which is injected through spray nozzles mounted on a steam turbine bypass pipeline in a co-generator system. The study includes several important factors: (1) the effects of elbows on the flow pattern and evaporation process of the water particles; (2) heat transfer that affects the steam temperature and also the evaporation rates; and (3) the effects of insertion of a perforated plate in the flow path on the evaporation process.

Modeling of the high-pressure turbulent steam flow was based on a non-staggered finite volume method in 3-D, turbulent, compressible, two-phase dispersed flow formulations. Computations were performed by separating the entire pipeline system into four sections, each of which was generated in a 3-D grid system for more efficient computations by maintaining a sufficiently large number of meshes for each section. Flow calculations were made in each region separately by patching the end conditions from one pipe to the inlet conditions of the next one.

Through this research, numerous data have been acquired and analyzed for heat transfer mechanisms of the cooling water droplets in the pipeline system. The accuracy of the computations were validated by comparing them with theoretical models, and were shown to be quite reliable.
Measurement of Thermal Gradients and Fluctuations Using Liquid Crystals
Authors: Mukherjee D. K. , Prasad V. , Tan H.
Published: March 2022

The experimental and image processing technique presented here seeks to provide time accurate information on local temperature and gradient fluctuations. Thermochromic liquid crystals (TLC) are used to map instantaneous two dimensional temperature fields. The color response of the liquid crystals is tracked by a CCD camera. A synchronization circuit is designed to correlate the perceived color of two different bands of TLC with the thermocouple measured temperature. An XI1 based algorithm is then used to extract quantitative information from the transient video images. Results on a rotational flowfield are presented to show the utility of the technique.
Consecutive-Photo Method to Measure Vapor Volume Flow Rate During Boiling From a Wire Immersed in Saturated Liquid
Authors: Ammerman C. N. , You S. M.
Published: March 2022

A photographic measurement technique is developed to quantify the vapor volume flow rate departing from a wire during boiling. The vapor flow rate is determined by measuring the volume of bubbles after departure from the boiling surface in consecutive frames of high-speed video. The measurement technique is more accurate and easier to implement than a previously developed photographic/laser Doppler anemometry (LDA) method. Use of the high-speed camera in place of a standard video camera eliminates the requirement for LDA-acquired bubble velocity measurements. The consecutive-photo method requires relatively few video images to be analyzed to obtain steady-state vapor volume flow rates. The volumetric flow rate data are used to calculate the latent heat transfer and, indirectly, sensible heat transfer which comprise the nucleate boiling heat flux. The measurement technique is applied to a 75-μm platinum wire immersed in saturated FC-72.
High Temperature Heat Flux Calibration
Authors: Langley Lawrence W.
Published: March 2022

Today heat flux sensors are available with temperature ratings up to 800°C. In many situations these sensors do not have to be cooled at all, and therefore do not produce aerodynamic or thermal disturbances. However, the variation of their sensitivity with temperature can be an important source of error.

The High Temperature Heat Flux Calibration System described here is designed to perform calibrations of heat flux sensors at ambient temperatures up to 816°C and heat fluxes up to 341 watts/cm2. The response of the sensor being calibrated is compared with that of a reference sensor, with the two sensors located on opposite sides of a thin heated flat plate.

Calibrations with this system are performed in a vacuum of about 1 torr, effectively eliminating convective heat transfer and heated flat plate oxidation. A controlled temperature heated stage is provided for the sensor on test, and a constant temperature cooled stage for the reference sensor. The heated flat plate is powered by direct current, and shielded from the sensors during warm-up by a bifurcated water-cooled graphite shutter. After the temperature of the heated flat plate has stabilized, the shutter is opened. This exposes the sensor on test and the reference sensor simultaneously to steep wavefronts of heat flux. After a few seconds the shutter is closed again and power to the heated flat plate is cut off.

All functions of the calibration system are performed under control of Labview® software. After mounting the sensor to be tested, the operator enters a list of desired temperatures and heat fluxes. Tests are then performed automatically in the sequence which will utilize the resources of the system most efficiently. At the end of the test sequence, calculations are performed and a report of calibration results is generated and printed. During the test the operator may monitor system functions and intervene at any point if desired.

Problems encountered in the design of this system and typical results of calibrations performed during its development will be presented.
Free and Mixed Convection in a Doubly Layered Porous Medium
Authors: Jendoubi S. , Kulacki F. A.
Published: March 2022

Convection in a horizontal, doubly layered porous medium has been investigated numerically. Both natural and mixed convection are considered for steady state heating from above. For natural convection, the effects of Rayleigh number on the Nusselt number are investigated. For mixed convection where a uniform flow enters at the side wall, the effects of both Rayleigh number and Peclet number are studied. The effects of the thickness of one layer as well as the length of the heated zone are also examined. Further, the permeability and the thermal conductivity ratios of the lower layer to the upper layer are varied from 0.1 to 100.0 and from 0.2 to 5.0, respectively.
Transient Temperature Measurements in a Simulated RTCVD Reactor
Authors: Horton J. F. , Peterson J. E.
Published: March 2022

Instantaneous transient gas temperatures were measured in a simulated rapid thermal chemical vapor deposition (RTCVD) reactor. The gas flow consists of an axisymmetric jet impinging on a heated wafer. The jet momentum is opposed by buoyancy from the heated surface. Temperatures were found non-invasively by laser induced Rayleigh light scattering (RLS). A RLS diagnostic system measures temperature by sensing intensity of light scattered from a control volume. Intensity is related to gas molecular number density, and thus temperature can be found from the ideal gas law. The RLS system was calibrated first with measurements in the potential core of a heated jet, and then in the RTCVD test section operating at ambient temperature but reduced pressure. In both cases, the measured intensity of Rayleigh scattered light had low uncertainty. Measured molecular number density corresponded well with that theoretically predicted from the ideal gas law. Transient temperature measurements were then recorded at several radial locations above the wafer surface as it was heated from ambient temperature to 200°C. Operating conditions consisted of Reynolds number Re, = 60, maximum Grashof number GrH = 4.4 × 106, and maximum mixed convection parameter GrH/Rei2 = 1200. Uncertainty of mean transient temperature was ±2°, while temperature fluctuations were large (T′ ∼ 50°C). Both flow visualization and temperature measurements showed that the flow field consisted of buoyancy dominated recirculations, and was highly three dimensional.
Application of Transient Radiative Transfer Equation to Oceanographic Lidar
Authors: Mitra Kunal , Kumar Sunil
Published: March 2022

This paper examines the formulation of the different methods of solving the one-dimensional transient radiative transfer equation for ocean remote sensing. This work is particularly helpful in determining school of fishes inside the ocean for commercial purpose. In this technique a pulsed laser is focused into the ocean, and the time-dependent back-scattered flux is measured at different depths inside the ocean. A large number of parameters such as the spatial and temporal variability of optical properties inside the ocean, ocean depth, type of ocean water, presence of biological matters, etc. can significantly affect the radiative transport through oceans. But since the emphasis of the work is on the scattering phenomenon, important parameters associated with it, namely the scattering albedo and scattering phase function distribution, are considered in detail in this paper.
Analytical Solutions for Inverse Radiative Transfer Optical Property Estimation
Authors: McCormick N. J.
Published: March 2022

An overview is given of analytical algorithms for estimating the optical properties of a homogeneous slab or a homogeneous optically-thin, convex-shaped medium.
Microgasketing and Room Temperature Wafer Joining for Liquid-Filled MEMS Devices
Authors: Simon Jonathan , Huang Long-Sun , Sridharan Balaji , Kim Chang-Jin
Published: March 2022

A closed liquid reservoir in typical fluidic microdevices contain liquid volumes ranging from μl to ml. A new approach for liquid filling and sealing of multiple microdevices with a volume less than 1 nl is presented. A Teflon microgasketing technique combined with a room temperature curing UV epoxy adhesive is used to isolate liquid inside each lithographically defined area and permanently seal the device all in a batch fashion. The technique has been applied to successfully package an array of liquid-filled mercury microrelays, each of extremely small volume (< nl). To ensure good penetration of the adhesive throughout the entire die of many microdevices, a method for adhesive distribution using wicking microchannels has been developed. The microgasketing technique is further combined with electroplated microriveting, another low-temperature wafer joining method, to provide sealing to the microriveting technique. Microgasketing is a quite general technique, as it can be combined with most low-temperature wafer joining methods and the reservoir area could contain liquid or gas and can be of a wide range of volumes and shapes.
A Novel Dual-Axial AFM Cantilever With Independent Piezoresistive Sensors for Simultaneous Detection of Lateral and Vertical Forces
Authors: Chui Benjamin W. , Kenny Thomas W. , Mamin H. Jonathon , Terris Bruce D. , Rugar Daniel
Published: March 2022

This paper describes a novel dual-axial AFM cantilever with independent piezoresistive sensors for simultaneous detection of lateral and vertical forces. The cantilever consists of a flat, triangular probe with a vertical direction of compliance, implanted with a piezoresistive layer to form a vertical deflection sensor. This probe is connected to the base by tall, narrow “ribs” that give the structure lateral compliance. Embedded on the side-walls of some of the ribs are a second set of piezoresistors that form a lateral deflection sensor. A special ion implant at approximately 45 degrees to the vertical is used to create the piezoresistive sensors and electrical connections. Both the vertical and the lateral deflection sensors exhibit measured piezoresistive sensitivities ΔR/R on the order of 5 × 10−7 per Å. The cantilever was successfully used to obtain AFM images of a known sample, yielding correlated z-signal and x-signal images of the sample topography.
A Microstructure for the In Situ Determination of Residual Strain
Authors: Pan Chi Shiang , Hsu Wensyang
Published: March 2022

A new strain sensor with a compact structure has been designed, demonstrated, and characterized. The strain sensor composes of a pair of adjacent cantilever beams with different lengths connected by a short tip beam. Residual strain causes two beams to deflect and to magnify the deflection into optically measurable displacement of the tip beam. The analytical model to relate the measured displacement to residual strain has been derived, and its results are then verified by finite element modeling. The strain sensor does not need correction factor for the strain-displacement relation. The relation of the displacement and residual strain is linear, and the displacement is independent of both Young’s modulus and the thickness of the film. All three properties are not found simultaneously in previously reported strain sensors. Based on the same strain with the same calibrated displacement, our structural size can be smaller than other strain sensors. The strain sensor has been fabricated and demonstrated by using a wet SiO2 film, and undoped LPCVD polysilicon films without post annealing.
Nodal Simulation of Suspended MEMS With Multiple Degrees of Freedom
Authors: Vandemeer Jan E. , Kranz Michael S. , Fedder Gary K.
Published: March 2022

A mixed-domain schematic representation compatible with node-based behavioral simulators is developed for rapid design of suspended microelectromechanical systems (MEMS). Hierarchical models of several basic microelectromechanical elements are created. The components are interconnected to represent both devices and more complex systems. Using beams, masses, and electrostatic actuators as the fundamental building blocks, a nodal simulation of complete in-plane motion of a crab-leg resonator demonstrates the design approach. Electrical properties are included in the component models, enabling electrical and electromechanical signal analysis to be performed. This work is part of an continuing project that eventually will provide full six DOF models for a broad class of MEMS.
A Triangular Frequency-Tuning Comb Array
Authors: Lee Ki Bang , Cho Young-Ho
Published: March 2022

We present a new post-fabrication frequency-tuning method for laterally driven electrostatic microresonators using the DC-biased electrostatic tuning-comb structures arranged in a triangular shape. The tuning-comb structures adjust the resonant frequency of the microresonator using the linear electrostatic force, generated by the tuning-combs of linearly varied finger-length. The electrostatic tuning force and the associated frequency change, caused by the DC-biased triangular tuning-comb array, have been derived in terms of the tuning voltage A set of frequency-tunable microresonators has been designed and fabricated by the four-mask surface-micromachining process. The resonant frequency of the microfabricated microresonator has been measured at the reduced pressure of 1 torr in order to eliminate the air damping effect. The resonant frequency reduction of 80Hz is obtained for a tuning voltage increase of 20V. Possible source of the discrepancy between the theoretical estimates and experimental results has been discussed.
Boiling Heat Transfer From a Micro Heater
Authors: Hijikata Kunio , Yamamoto Norihiko , Takagi Shu
Published: March 2022

Heat transfer from a micro heater is investigated experimentally and numerically. The micro heaters made of Indium Tin Oxide (ITO) are set on a glass substrate immersed in FX3250 coolant. Two different sizes (50μm, 100μm) of heaters are used in the experiments to analyze the size effect. The effect of the surface deposited layer by Al2O3 is also investigated with changing the thickness of the layer. All the experiments are performed in both subcooled and saturated boiling. The boiling curves of different conditions are obtained and compared. The results show that there exists an optimum thickness of deposited layer for heat transfer enhancement. They also show that the present heat transfer process is quite different from that of usual boiling. The phenomena are dominated by heat conduction in the substrate and large portion of the generated heat is transferred to the liquid and then vapor bubble through the substrate around a heater. Further, a photograph of a liquid microlayer under a vapor bubble is taken and the relation between an unsteady bubble behavior and local temperature fluctuations is analyzed.
Two-Phase Flow in Microchannels
Authors: Stanley Roger S. , Barron Randall F. , Ameel Tim A.
Published: March 2022

As the field of microfluidics continues to grow, it is becoming increasingly important to understand the mechanisms involved with heat transfer in two-phase flow through microgeometries. This importance is reiterated by the increasing number of applications which use phase change as the principal mechanism to conduct or remove heat. The purpose of this study was to investigate fluid mechanic and heat transfer characteristics of two-phase two-component flow in rectangular microchannels. Experiments were conducted using rectangular aluminum channels with hydraulic diameters ranging between 56 μm and 256 μm and aspect ratios which varied from 0.5 to 1.5. Both single- and two-phase tests yielded excellent correlations of the friction factor. Reynolds number and the combination of Reynolds number and Prandtl number were the dominant parameters in the prediction of pressure drop and heat transfer rate, respectively. The pressure drop predictions, based on available semi-empirical relations for two-phase flows, were shown to substantially over predict the measured pressure drop.

Other findings showed that for single-phase flow, the transition from laminar to turbulent regimes of the friction factor was suppressed as the channel hydraulic diameter decreased. Two-phase friction factor data indicated a definite transition from laminar to turbulent regimes at a Reynolds number of 3,000 for all channel configurations tested. It is believed that the transition was due to the intense pressure fluctuations associated with two-phase flows. In both single- and two-phase experiments, Nusselt number data exhibited a trend similar to the macroscale turbulent regime correlations; however, the data were somewhat less than the macroscale predictions. In contrast to the friction factor data, both single- and two-phase Nusselt number data suggested no change in flow regimes occurred.
Nanoscale Thermometry Using Scanning Joule Expansion Microscopy
Authors: Majumdar Arun , Varesi John
Published: March 2022

This paper introduces scanning Joule expansion microscopy (SJEM), which is a new thermal imaging technique with lateral resolution in the range of 10–50 nm. Based on the atomic force microscope (AFM), SJEM measures the thermal expansion of Joule heated elements with a vertical resolution of 1 pm, and provides an expansion map of the scanned sample. Sub-micron metal interconnect lines as well as 50 nm-sized single grains of an indium tin oxide resistor were imaged using SJEM. Since the local expansion signal is a convolution of local material properties, sample height, as well as temperature rise, extraction of the thermal image requires deconvolution. By coating the sample with a uniformly thick polymer film, this was experimentally achieved resulting in direct measurement of the sample temperature distribution. A detailed thermal analysis of the metal wire and the substrate showed that the predicted temperature distribution was in good agreement with the measurements of the polymer-coated sample. However, the frequency response of the expansion signal agreed with theoretical predictions only below 30 kHz, suggesting that cantilever dynamics may play a significant role at higher frequencies. The major advantage of SJEM over previously developed sub-micron thermal imaging techniques is that it eliminates the need to nanofabricate specialized probes and requires only a standard AFM and simple electronics.
Molecular Dynamics Simulation of Ice Crystal Growth From a Surface Containing Adsorbed Antifreeze Protein
Authors: Grandum Svein , Kobayashi Yasunori , Yabe Akira , Matsumoto Sohei , Takemura Fumio , Nakagomi Kazuya , Frivik Per-Erling
Published: March 2022

In order to develop advanced low temperature storage systems based on slurry ice, resistant to recrystallization, Antifreeze Protein (AFP) has been introduced as an effective additive. In this paper, the mechanism of crystal growth when AFPs are adsorbing to the surface of ice has been investigated by Molecular Dynamics simulation. Liquid water molecules were located above the adsorption plane, containing a simplified model of the AFP and the growth potential, corresponding to a supercooling of approximately 40 K was applied. Growth was not easily occurring close to the AFP but at sites where the molecules easily could generate at least two hydrogen bonds to the crystal lattice. This resulted in a curved ice surface, similar to the previously observations using a Scanning Tunneling Microscope.
The Effects of Transverse Acceleration-Induced Body Forces on the Capillary Limit of Helically-Grooved Heat Pipes
Authors: Thomas Scott K. , Klasing Kevin S. , Yerkes Kirk L.
Published: March 2022

A helically-grooved copper heat pipe with ethanol as the working fluid has been fabricated and tested on a centrifuge table. The heat pipe was bent to match the radius of curvature of the table so that uniform transverse (perpendicular to the axis of the heat pipe) body force fields could be applied along the entire length of the pipe. The steady-state performance of the curved heat pipe under transverse body force fields was determined by varying the heat input (Qin = 25 to 250 W) and centrifuge table velocity (radial acceleration |a→r| = 0 to 10-g). The thermal resistance decreased with increasing heat input until dryout was reached. As dryout commenced, the thermal resistance increased. Due to the geometry of the helical grooves, the capillary limit increased by a factor of five when the radial acceleration increased from |a→r| = 0 to 6.0-g. This important result was verified by a mathematical model of the heat pipe system, wherein the capillary limit of each groove was calculated in terms of centrifuge table angular velocity, the geometry of the heat pipe and the grooves (including helix pitch), and temperature-dependent working fluid properties.
Parametric Analysis of Laminar Forced Convective Cooling of Heated Obstacle Arrays
Authors: Young Timothy J.
Published: March 2022

An extensive parametric analysis has been performed to fully investigate the fundamental aspects of laminar convective cooling of an array of heated obstacles within a channel. The analysis employs the finite element method to solve the Navier-Stokes equations for the fluid flow and fully accounts for conjugate conduction within the solid obstacles. The influences of parametric changes in the obstacle thermal conductivity, fluid coolant flow rate, and input heating method are examined to establish important fundamental effects and provide practical results. The dependence of the streamlines, isotherms, and local Nusselt numbers on the governing parameters is documented. It was found that increases in the obstacle thermal conductivity improve the internal obstacle heat flow through reduced temperature gradients with large values of the solid thermal conductivity (ksolid/kfluid ≥ 100) effectively isothermalizing the obstacles. Differences between two methods typically used to model the waste heat production in electronic devices, surface flux and volumetric heating, were found to only manifest themselves within the obstacle with only small changes in Nusselt numbers.
Propane Fueled AMTEC Auxiliary Electric Power Systems for Remote Site Deployment
Authors: Mital Rahul , Hendricks Terry J. , Svedberg Robert C. , Sievers Robert K.
Published: March 2022

A 60 Watt(e) Alkali Metal Thermal to Electric Converter (AMTEC) auxiliary electric power supply (AEPS) is being designed and built to provide reliable electrical power for stand-alone operation in remote sites. This unit is designed to bum propane, although any fossil fuel can be used with the properly designed burner.

The system provides 60 Watt(e) power at overall system efficiencies between 11–14% from 12 AMTEC multi-tube cells, each with a nominal power output of 7 watts at 3.5 volts. These efficiencies are 3–4 times higher than existing power conversion systems and represent $6–7 million per year in reduced fueling costs, depending on the number of systems deployed. It is the modular capability of the AMTEC which allows the system to maintain this high conversion efficiency even at the low power level. The cells can be connected to provide either 12 or 24 volt DC operation without the need for a DC/DC converter.

This paper presents results from the first non-adiabatic AMTEC cell SINDA/FLUINT model integrated with a combustion system and a recuperator. Parametric studies were performed using this system model to identify performance sensitivities of the most crucial parameters for the system design. Results indicate that the system efficiency is primarily limited by the heat transfer from the flame to the hot end of the cells and from the cold end of the cells to the environment. This heat transfer is a function of the heat transfer coefficients and the surface area available. Results also indicate that as high as 15% of the total energy may be lost through the insulation unless reduced by optimizing the system design. Maximum cell/system efficiencies, maximum system power output and optimum voltage/current conditions have been determined using this model.
150 Watt Portable Thermophotovoltaic Power Supply
Authors: Becker Frederick E. , Doyle Edward F. , Shukla Kailash C.
Published: March 2022

Thermophotovoltaic (TPV) energy conversion, which uses photovoltaic (PV) cells to directly convert radiant thermal energy into electric power, has a number of important advantages for portable power generation in military applications. Since TPV is a direct energy conversion technology with no moving parts in the energy conversion system, it has the potential to provide quiet, reliable, maintenance-free electric power for thousands of hours. These systems also have the potential to be as efficient as small portable engine generators, operate on military logistic fuels, and start and operate in sub-freezing environments.

A 150 Watt thermophotovoltaic (TPV) power module has been designed, built, and tested. The technical approach taken in the design focused on optimizing the integrated performance of the primary subsystems in order to yield high energy conversion efficiency and cost effectiveness. An important aspect of the approach is the use of a narrow band fibrous emitter radiating to a bandgap matched photovoltaic array to minimize thermal and optical recuperation requirements, as well as the non-recoverable heat losses. For the prototype system, fibrous ytterbia emitters radiating in a narrow band centered at 980 nm are matched with high efficiency silicon photoconverters. The integrated system includes a dielectric stack filter for optical energy recovery and a ceramic recuperator for thermal energy recovery.

The prototype TPV system uses a rapid mix distributed fuel delivery system with controlled feeding of the fuel and heated air into a flame at the surface of the emitter. This makes it possible to operate at air preheat temperatures well above the auto-ignition temperature of the fuel thereby substantially increasing the system efficiency. The system has been operated with air preheat temperatures up to 1367 K and has produced a uniform narrow band radiation over the surface of the emitter with this approach.

The design of the system is described and test data for the system and some of the key components are presented. The results from a system model, which show the impact of various parameters on system performance, are also discussed.
The Relationship of Optimum Heat Exchanger Allocation and Minimum Entropy Generation for Refrigeration Cycles
Authors: Klein S. A. , Reindl D. T.
Published: March 2022

This paper investigates the effect of heat exchanger allocation on overall system performance using both reverse Carnot and vapor compression refrigeration cycle models to calculate system performance and entropy generation rate. The algebraically simple constraints applied in previous studies are shown to be justifiable. The vapor compression model considers non-ideal compressor performance, compressor volumetric efficiency, refrigerant properties, and throttling in addition to mechanistic heat exchanger models. The results support the conclusions of previous studies in that maximum performance is observed when the condenser and evaporator sizes are approximately equal. However, it is found that minimizing the entropy generation rate does not always result in the same design as maximizing the system performance. This conclusion opens to question the utility of minimizing entropy generation rate as a general technique for optimizing the design of refrigeration cycles.
Optimization of a Simplified Vapor Adsorption Cycle
Authors: Ramotowski M. , Shamsundar N.
Published: March 2022

An analysis is performed to find the optimum coefficient of performance of three models of a vapor adsorption heat pump, namely, a basic cycle with no regeneration, a cycle with cocurrent-flow regenerative heating, and a cycle with countercurrent-flow regenerative heating. Nonlinear optimization techniques are employed to find the best operating conditions within a range of temperatures. The results for the three model cycles are computed for the water and Zeolite-NaX pair and compared to those for an equivalent 3-T Carnot device. The usefulness of thermodynamic cycle optimization as a preliminary step to performing more detailed thermal analyses is discussed.
Thermodynamics of Insulated Pressure Vessels for Vehicular Hydrogen Storage
Authors: Aceves Salvador M. , Berry Gene D.
Published: March 2022

This paper studies the application of insulated pressure vessels for hydrogen-fueled light-duty vehicles. Insulated pressure vessels can store liquid hydrogen (LH2); low-temperature (80 K) compressed hydrogen (CH2); or ambient-temperature CH2. In this analysis, hydrogen temperatures, pressures and venting losses are calculated for insulated pressure vessels fueled with LH2 or with low-temperature CH2, and the results are compared to those obtained in low-pressure LH2 tanks. Hydrogen losses are calculated as a function of daily driving distance during normal operation; as a function of time during long periods of vehicle inactivity; and as a function of initial vessel temperature during fueling. The number of days before any venting losses occur is also calculated as a function of the daily driving distance.

The results show that insulated pressure vessels have packaging characteristics comparable to those of conventional, low-pressure LH2 tanks (low weight and volume), with greatly improved dormancy and much lower boil-off. Insulated pressure vessels used in a 17 km/1 (40 mpg) car do not lose any hydrogen when the car is driven at least 15 km/day in average. Since almost all cars are driven for longer distances, most cars would never lose any hydrogen. Losses during long periods of parking are also relatively small. Due to their high-pressure capacity, these vessels would retain about a third of their full charge even after a very long dormancy, so that the owner would not risk running out of fuel. If an insulated pressure vessel reaches ambient temperature, it can be cooled down very effectively by fueling it with LH2 with no losses during fueling. The vessel has good thermal performance even when thermally insulated with inexpensive microsphere insulation. In addition, the insulated pressure vessels greatly ease fuel availability and infrastructure requirements, since it would be compatible with both compressed and cryogenic hydrogen refueling.
Getting the Most Out of Geothermal Energy: Economics of Power Generation, Heating, and Cooling
Authors: Kanoglu Mehmet , Çengel Yunus A.
Published: March 2022

Geothermal energy is mostly used for electric power generation, and there is the perception that power generation is the best use of high temperature geothermal energy since electricity is a more valuable commodity than heat, and the price of electrical energy is about 4 times the price of heat energy. However, the conversion efficiencies of geothermal power plants are typically about 10%, and thus the generation of 1 unit of electricity requires the consumption of about 10 units of geothermal energy.

Also, the temperature of the geothermal fluid leaving the heat exchanger of a binary power plant can be as high as 100°C, which is very suitable for low-temperature uses such as space heating and preheating of process water, but is unsuitable for economical power generation, and is discarded. So it is no surprise that the electricity generated by a geothermal power plant is only about one-fifteenth of the heat that can be harvested and sold to prospective users for space, water, and process heating. As a result, the revenues from a geothermal site can be increased by 4 times by selling geothermal heat directly instead of producing and selling electricity. Therefore, for a specified geothermal resource, an initial investment of up to 4 times (even more, depending on the relative prices of electricity and natural gas) can be justified if the geothermal heat plant (including the circulation loop) is to be built at that site instead of a geothermal power plant.

Typical coefficient of performance of heat driven absorption cooling systems is about 0.7, and the revenues from a geothermal resource can be increased by 2.5 times by using high-temperature geothermal energy for cooling. Of course a good compromise is to use the portion of geothermal energy above 115°C for power generation, the portion between 115°C and 90°C for cooling, and the remaining part for heating.
An Approach of Exergoeconomic Analysis of Thermal Systems
Authors: Kim Si-Moon , Oh Si-Doek , Kwon Yong-Ho , Kwak Ho-Young
Published: March 2022

A new approach of the combination of exergetic and economic analysis for the complex energy system has been proposed, that is, a general exergy and the corresponding cost balance equation which can be applied to any component of thermal system have been formulated. One of distinct features of this method is that the exergy of a material stream is decomposed into thermal, mechanical and chemical exergy flows and entropy production flow and that a unit cost exergy is assigned to each disaggregated exergy in the streams at any state. This methodology permits to obtain a set of equations w.r.t. the unit cost of various exergies by applying the cost balance equation to each component of the system and junctions. The monetary evaluation of various exergy (thermal, mechanical, etc) costs as well as the production cost of electricity of the thermal system are possible by solving the set of equations. The proposed exergy costing method has been applied to a 1000kW gas turbine cogeneration system. It turns out that the production cost calculated is same as that estimated from the overall cost balance equation, which is concluded as a reasonable result. Also the exergy costing method proposed provides some information on decision about the design and operation of the cogeneration system.
Using an Exergy Analysis to Design a Heat Exchanger for Low Temperature Waste Heat Recovery
Authors: Al-Ragom Fatouh Abdul Aziz , Daly Michael , Kowalski Gregory J. , Zenouzi Mansour
Published: March 2022

A numerical analysis of a heat pipe heat exchanger is described and coupled to an exergy analysis in order to determine the best configuration for a waste heat recovery application. One advantage of the heat pipe heat exchanger configuration is the high velocity flow that it can produce as compared to a conventional heat exchanger design. The heat pipe heat exchanger analysis includes sonic flow limitations and two-phase flow conditions. Results for the temperature, pressure and quality distributions in the flow directions are given. The second law efficiency is calculated using the results from the numerical model. The conventional heat exchanger design has the largest second law efficiency of the examined cases. The problem also illustrates the use of the exergy analysis as a design tool.
Hat Cycle Exergetic Analysis and Thermoeconomic Evaluation of Fuel Costs
Authors: Gallo Waldyr L. R. , Llagostera Jorge , Walter Arnaldo C. S.
Published: March 2022

The need of advanced and high performance power cycles is becoming an ever increasing social demand, to reduce environmental impacts as well as to get a better use of natural resources in power generation.

The HAT cycle is one of these advanced cycles being considered for use in the next years. This cycle is gas-turbine based, comprises a recuperator and uses water to recover low temperature energy from compressor intercooler, aftercooler and from exhaust gases. However, this cycle requires high-quality water consumption. Consequently, some concerns about water use and costs are being discussed.

This work presents an exergetic analysis of the HAT cycle, for different total pressure-ratio on compressor train. The effect of pressure ratio over the water use is also shown. The turbine inlet temperature was kept fixed, to simulate the same technological level on blade cooling and metal alloys. All sub-systems are analyzed from irreversibility viewpoint.

An exergy-based thermoeconomic evaluation is made, regarding only fuel and water costs and their impacts on power cost. This methodology can highlight not only the final electric power cost (result that could be also achieved by conventional economic analysis), but also the internal costs of each stream and sub-system of the plant. The complete exergoeconomic analysis of the HAT cycle will depend on reliable economic data, as investment costs of each sub-system, operation and maintenance costs and the operational profile of the plant (base or peak load, yearly operation hours), as well as financial conditions.
Numerical Simulation of a Closed Solar Regenerator
Authors: Valencia Hans F. , Metghalchi Hameed
Published: March 2022

Many attempts have been made to use solar energy in absorption refrigeration systems. In all these systems an important component is the regenerator, in which the weak solution is reconcentrated. Among the regenerators found in the literature, open regenerators have received much attention because of their simplicity. However, problems with solution contamination, and low performance under humid climates have pointed towards alternative regenerators. It has been shown that covering the regenerator with glass solves these problems permanently. Still, an analysis of the energy and mass transfer processes occurring inside the regenerator has not been fully presented. In this paper, a one-dimensional theoretical simulation of a closed solar regenerator is developed. The theoretical model is constructed by combining three energy balances and three mass balances on infinitesimally thin slices of the solar regenerator, the solution, and the solution-vapor interface. These balances yield three independent ordinary differential equations in the three dependent variables: solution temperature, glass (condensed water) temperature and solution mass flow rate. Solutions to the differential equations have been obtained numerically and the performance of a typical aqueous solution is presented.
A Lumped-Parameter Method for the Computation of the Temperature of Hot Combustion Gases Flowing Inside Chimneys
Authors: Cortés C. , Campo A. , Correas L.
Published: March 2022

This paper addresses the practical calculation of the thermal performance of industrial chimneys by means of recent results in forced convection heat transfer. The temperature decay of the combustion gases is a result of heat transfer processes involving both internal forced convection and external heat transfer to the surroundings, and the analysis of the problem is scarcely treated in the energy- and environmental-related literature. Thermal design and performance estimations of chimneys are therefore based on engineering rules of thumb dictated by experience.

The aim of this paper is to introduce rigorous heat transfer results into the subject, but from a framework accessible to design engineers. To this end, a 1-D lumped model of this kind of situations is used (Campo and Lacoa, 1994). Although largely simplified, the model provided adequate estimates of the mean bulk temperatures when compared with those computed with a 2-D distributed model (Campo and Lacoa, 1995), thus satisfying the requirements of simplicity and accuracy for the present purpose. The paper describes the design criteria for thermal calculation of industrial chimneys, the application of the 1-D lumped model through the use of standard heat transfer correlations, and several examples. The sequence of calculations is easy to accomplish and it is explained in such a way that it can be directly employed by engineers engaged in thermal design of tall chimneys.