bluuebunny/crossref_metadata_2025_split huggingface dataset:
Two-Phase Flow in Microchannels
Authors: Stanley Roger S. , Barron Randall F. , Ameel Tim A. 
Published: March 2022

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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

Abstract
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.