bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Determination of Pressure Loss Through Porous Membranes
Authors: Anderson Gary A. , Kommareddy Anil , Gu Zhengrong , Puetz Anderson Joanne , Gent Stephen P.
Published: October 2014

Air with carbon dioxide is bubbled through Photobioreactors (PBRs) to add carbon dioxide to the reactor medium, remove oxygen, and mix the medium. Most PBR systems use various types of spargers/diffusers that consist of straight or curved tubes with perforation in them to inject air into the PBR reactor volume. A possible novel approach to introducing air into the PBR reactor volume is to use a plenum under the PBR reactor volume in conjunction with a porous membrane that separates the air in the plenum from the liquid medium in the reactor volume. The resistance offered by the porous membrane and the liquid in the reactor volume to air flow needs to be established so that power requirements to provide the desired air flow through the PBR can be determined. Four types of porous membranes were tested: 1)Sintered High Density Polyethylene HDPE 1.59 mm thick with 15–45 μm pore size, 2) Sintered HDPE 0.79 mm thick with 20μm pore size, 3) Genpore black plastic sheet with 45 μm pore size, and 4) Porex 7896 HDPE with pore size of 35 μm). Specimens were tested in a 76.2 mm inside diameter reactor with a depth of 304.8mm and a 76.2 mm plenum depth. Water was used as the reactor medium and the depth was varied between 0 and 228.6 mm. Results showed that the Porex 7896 membrane had little resistance to air flow when the water depth was 0.0mm (1–22 Pa), 1–200 Pa for the Genpore plastic sheet, 1200–1400Pa for the Porex with 20μm pores, and 1100–2500 Pa for the Porex with the 15–45 μm pore sizes for superficial air velocities between 0.00345 m/s to 0.0242 m/s. Water depth was then increased to 228.6 mm in 25.4 mm increments and tested with the same air flow rates. The addition of water significantly increased the resistance to air flow for all membranes (highest being 4200 Pa). Least square correlations for the membranes using water depth and superficial air velocity indicate that resistance to air flow of the membranes was linear with superficial velocity but parabolic with water depth.
Empirically Driven Computer Simulations of Solar Thermal Systems for Space Heating and Domestic Hot Water
Authors: Robbins Curtis , Goldade Travis , Hoekman S. Kent , Jacobson Roger , Turner Robert
Published: October 2014

The Desert Research Institute (DRI) has developed a Renewable Energy Deployment and Display Facility (REDD) which utilizes solar and wind to create a net zero energy residence for research, education, and outreach. The facility is a demonstration of the integration of many renewable energy technologies into a residential setting such that technology developers can show proof-of-concept, students and trade workers can get hands-on experience, and public organizations can see renewable energy components implemented into a residential setting. A major technological aspect of the facility is the use of solar thermal energy to provide space heating, Domestic Hot Water (DHW), and solar cooling. Data are monitored from three separate solar thermal systems, each with their own hot water storage, to evaluate optimized utilization of solar thermal energy into residential applications.

The three solar thermal systems differ in their working fluids. System 1 uses a conventional mixture of glycol and water in 200 ft2 of ground mounted collector area, System 2 uses DHW in 210 ft2 of roof mounted collector area, and System 3 uses air in a 578 ft2 collector built into the roof. Each system is configured to be used for space heating and DHW. Systems 1 and 2 are built into the HVAC system of the 1200 ft2 house, and System 3 is built into the HVAC system of the 600 ft2 detached workshop. Data collected from each system provide the basis for year-long energy and economic simulations using TRNSYS for comparison. The results from the simulations are used to demonstrate the effectiveness of site-built solar air collectors, which have the advantage of using conventional materials, and avoid the issues of liquid collectors associated with boiling and freezing. This paper describes the experimental setup of the solar thermal systems, how the data are used as inputs to the computer simulations, and the configuration of the computer simulations.

The REDD Facility, as well as the use of TRNSYS will continue to be used by DRI researchers to investigate not only the most feasible integration of components for a solar thermal residential system, but also as a tool to properly size and implement solar thermal systems.
Optimization of a D-CHP System Based on Monthly Power-to-Heat Ratio
Authors: Knizley Alta , Mago Pedro J. , Tobermann James
Published: October 2014

In this paper, a combined heat and power (CHP) system utilizing two power generation units operating simultaneously with differing operational strategies (D-CHP) is analyzed on the basis of operational cost savings. An operating cost optimization metric, based on the facility monthly power-to-heat-ratio (PHR), is presented. The PHR is defined as the ratio between the electric load and the thermal load required by the facility. Previous work in this field has suggested that D-CHP system performance may be improved by limiting operation of the system to months in which the PHR is relatively low. The focus of this paper is to illustrate how the facility PHR can be used to determine the potential of a D-CHP system to reduce operational cost. This paper analyzed the relationship between the PHR and the operational cost savings of six different benchmark buildings, including buildings that are traditionally poor candidates for CHP or D-CHP systems, due to high cost of operation as compared with conventional systems with separate heating and power (SHP). Achieving operational costs savings through optimal operation based on monthly PHR for these building types can enhance the practical implementation potential of D-CHP and CHP systems.
Lead-Bismuth Eutectic as a High Temperature Heat-Transport Fluid for Thermal Solar Power
Authors: Frazer D. , Cionea C. , Popovic M. , Aussat Y. , Gubser A. J. , Hosemann P.
Published: October 2014

In order to increase the thermal efficiency and produce process heat for hydrogen production, the operating temperature of the heat-transfer fluid in thermal solar plants needs to increase, but to increase the operating temperature, new heat-transport liquids need to be evaluated. Liquid metals have been proposed as heat-transport fluids because of the large temperature ranges over which they remain liquid. One of the most studied liquid metals for non-solar applications has been lead-bismuth eutectic alloy (LBE), for the nuclear industry. The main challenge with using LBE as a coolant is that the major constituents of structural steels have high solubility in LBE. In this work, the challenges of using LBE as a high temperature heat-transport fluid are discussed, as well as initial results of high-temperature static corrosion tests of structural steels to evaluate their potential use in a thermal solar power plant.
Ammonia and Gasoline Fuel Blends for Internal Combustion Engines
Authors: Haputhanthri Shehan Omantha , Maxwell Timothy Taylor , Fleming John , Austin Chad
Published: October 2014

Ammonia, when blended with hydro carbon fuels, can be used as a composite fuel to power existing IC engines. Such blends, similar to ethanol and gasoline fuel blends, can be used to commercialize ammonia as an alternative fuel. Feasibility of developing ammonia gasoline liquid fuel blends and the use of ethanol as an emulsifier to enhance the solubility of ammonia in gasoline were studied using a small thermostated vapor liquid equilibrium (VLE) high pressure cell in this research. A larger VLE cell was used to develop identified fuel blends in sufficient quantities for engine dynamo-meter tests. A engine dynamometer equipped with a 2.4L gasoline engine was used to benchmark performance of ammonia fuel blends against standard fuels. Solubility test results proved that ethanol free gasoline is capable of dissolving 4.5% of ammonia on volume basis (23 g/l on mass basis) at 50 psi [344.7 kPa] pressure and 286.65 K temperature in liquid phase. Solubility levels are increased with the use of ethanol. Gasoline with 30% ethanol can retain 18% of ammonia in the liquid phase by volume basis (105 g/l by mass basis) at the same pressure and temperature. Dynamometer results show the ability of new composite fuel blends to produce the same amount of torque and power in the lower rpm limits. At higher rpm levels ammonia rich fuels result in an increased torque and power. Thus it can be concluded that hydrogen energy can be stored as ammonia-gasoline fuel blends and recovered back successfully without any strenuous modification to the existing infrastructure and end user equipment or behavior.
Advanced Low Pressure Cycle for Concentrated Solar Power Generation
Authors: Garg Pardeep , Krishna Sriram Hebbalguppe , Kumar Pramod , Conboy Thomas , Ho Clifford
Published: October 2014

Turbine inlet pressures of ∼ 300 bar in case of CO2 based cycles call for redesigning the cycle in such a way that the optimum high side pressures are restricted to the discharge pressure limits imposed by currently available commercial compressors (∼150 bar) for distributed power generation. This leads to a cycle which is a combination of a transcritical condensing and a subcritical cycle with an intercooler and a bifurcation system in it. Using a realistic thermodynamic model, it is predicted that the cycle with the working fluid as a non-flammable mixture of 48.5 % propane and rest CO2 delivers ∼37.2 % efficiency at 873 K with a high and a low side pressure of 150 and 26 bar respectively. This is in contrast to the best efficiency of ∼36.1 % offered by a transcritical condensing cycle with the same working fluid at a high side pressure of ∼ 300 bar.
Design of a Concentrator With a Rectangular Flat Focus and Operation With a Suspension Reactor for Experiments in the Field of Photocatalytic Water Splitting
Authors: Wullenkord Michael , Jung Christian , Sattler Christian
Published: October 2014

Photocatalytic water splitting is a potential route for future carbon-free production of hydrogen. However catalysts still need to be enhanced in order to reach acceptable solar-to-fuel efficiency. In the context of the project HyCats funded by the Federal Ministry of Education and Research of Germany a high performance test facility for the evaluation of the activity of photocatalysts under practical conditions was established. It mainly consists of a solar concentrator and a planar receiver reactor. A modified linear Fresnel concentrator configuration was chosen based on ray tracing simulation results and improved concerning the number of different facets and the tolerance of tracking errors. It meets the major demand of a homogeneous irradiance distribution on the surface of the reactor. The SoCRatus (Solar Concentrator with a Rectangular Flat Focus) is a 2-axis solar concentrator with a geometrical concentration ratio of 20.2 and an aperture area of 8.8 m2. The tracking accuracy is better than 0.1° respecting both the solar azimuth and altitude angle. Its 22 highly UV/Vis-reflective flat aluminum mirror facets reflect the sunlight resulting in a rectangular focus with a nominal width of 100 mm and a nominal length of 2500 mm. The reactor is placed in the focal plane at a distance of 2500 mm from the mounting plane of the facets and allows concentrated solar radiation to penetrate suspensions of water, electrolytes and photocatalyst particles flowing through it. Corresponding to a maximum angle of incidence of 36.6° the Quartz window reflects not more than 5% of the incoming radiation and assures only marginal absorption, particularly in the UV-part of the sun’s spectrum. The material of the receiver body is PTFE (polytetrafluoroethylene) providing reflection coefficients above 90% concerning wavelengths of UV-A and UV-B. The design of the reactor features two parallel reaction chambers, offering the possibility to test two separate suspensions at the same irradiation conditions. A pump transports the tempered suspension to the reactor. The geometry of the reactor inlet and outlet minimizes critical regions with inadequate flow caused by vortices. Any evolved gases are separated from the suspension in a tank together with nitrogen introduced in the piping upstream and are analyzed by micro chromatographs. Numerous devices are installed in order to control and monitor the reaction conditions. First experiments have been carried out using methanol as a sacrificial reagent.
Estimating CO2 Emissions Reductions With EnergyPlus for an Office Building in Salt Lake City
Authors: Lucich Stephen M. , Smith Amanda D.
Published: October 2014

This research estimates the achievable CO2 emissions reductions for a medium sized office building located in Salt Lake City, Utah. Four strategies that required minor retrofits or changes to a building’s operational controls were considered: automatic window shading, changes in window construction, lighting intensity, and temperature setpoint adjustment. Since 70% of energy consumed by the building sector is for heating, cooling and lighting, the methods introduced were targeted to reduce these sources of demand. The model building used was selected from the U.S. DOE’s commercial reference buildings. The simulations were run using the DOE’s EnergyPlus building energy modeling software and a TMY3 weather data file for Salt Lake City. The effect of these possible building changes on energy consumption and the CO2 emissions resulting from the production of this energy were examined. The impact of the automatic window shade was the lowest of the strategies considered with a 1% reduction in GHG emissions. This is likely the result of a low solar irradiation area to building volume ratio and should be explored for smaller residential and commercial buildings. Window construction was more promising with GHG emissions reductions between 2% and 6%. Lighting strategies and altered temperature set points demonstrated GHG emissions reduction of up to 15%. This research establishes a technique to evaluate building emissions reductions with respect to location, building construction, and operation.
Computer-Based Management of Mirror-Washing in Utility-Scale Solar Thermal Plants
Authors: Alon Lital , Ravikovich Gregory , Mandelbrod Matan , Eilat Udi , Schop Zafrir , Tamari Dror
Published: October 2014

BrightSource solar power plants consist of fields of tens of thousands of mirrors, spread across kilometers of open areas. These huge mirrors are in constant motion, reflecting the sun’s rays on to the solar thermal collector. Maintaining high reflectivity of the mirrors is essential for the solar field’s performance, a task that becomes complex when expanded to encompass the solar field’s features. The solution for mirror cleaning must be efficient, cost-effective, time-saving, and easy to maintain for dozens of years.

BrightSource has designed and constructed a system of GPS-based mirror washing machines (MWMs) that are controlled and managed by end-to-end software. The system generates optimized cleaning tasks, positions the mirrors, and efficiently controls the navigation and state of the MWMs with their 25-meter-long extendable cranes. All of these actions together provide an optimal mirror cleaning solution.

This article describes the BrightSource cleaning control technology, for example, in the Ivanpah project, the world’s largest solar thermal facility. The Ivanpah solar field includes 173,500 heliostats divided among three solar fields. Each heliostat holds two mirrors of approximately 2.5 × 3.5 meters, all of which require periodic cleaning.

Specifically, this article addresses issues such as the following:

• The mirror washing machine (MWM) types: truck and tractor-based, and their differing usage in the solar field

• Designation and choice of the cleaning area

• Estimation of the stopping points in the designated area, and association of the mirrors to clean from each stopping point

• Cleaning time optimization: stopping point density, order in which to clean heliostats, and heliostat position during cleaning

• Heliostat positioning: opening clear corridors through which the MWM can travel, and setting heliostats in cleaning orientations

• Receiving and responding to callback messages from the MWMs, such as cleaning progress and machine faults

• Working in the real world: resources shared with the power plant, and recovery from system faults
Time Instant Optimization of a Heliostat Field Using a Heuristic Algorithm
Authors: Atif Maimoon , Al-Sulaiman Fahad A.
Published: October 2014

Solar central receiver systems are viewed as one of the most promising concentrated solar power (CSP) technologies for power production, in which solar radiation is concentrated through large mirrors (heliostats) onto a central receiver. This is due to the fact that very high temperatures can be reached at the receiver and thus higher thermal efficiency can be achieved compared with other CSP technologies. Heliostat field layout optimization is an essential task for any solar central receiver system.

In this paper, a heuristic algorithm, i.e. the differential evolution (DE), was employed to perform efficient optimization of the conventional radial staggered heliostat field layout using MATLAB. The model calculates all the required optical performance parameters at every step of the optimization process for each heliostat and consequently more reliable results are obtained as compared with many other optimization methods. Two cases were considered: one with single variable optimization and the other with multi-variable optimization. For the first case, the azimuthal spacing between the adjacent heliostats or the radial distance between the rows of heliostats were optimized independently and for the second case both of these variables were optimized simultaneously. Both cases were examined for high sun altitude angle and low altitude angle and a comparison study was performed between them to check their effect on the heliostat field efficiency. Finally, it was noted that varying the radial distance between the rows of the heliostats yields slightly better efficiency as compared with when optimizing the azimuthal spacing.
Development of High Temperature, Corrosion Resistant Sensors for Concentrating Solar Power Systems
Authors: Usrey Michael W. , Liu Yiping , Anderson Mark , Lubbers Jon , Knowles Brady , Harsh Kevin , Pilant Evan
Published: October 2014

Solar power is a sustainable resource which can reduce the power generated by fossil fuels, lowering greenhouse gas emissions and increasing energy independence. The U.S. Department of Energy’s SunShot Initiative has set goals to increase the efficiency of concentrating solar power (CSP) systems. One SunShot effort to help CSP systems exceed 50% efficiency is to make use of high-temperature heat transfer fluids (HTFs) and thermal energy storage (TES) fluids that can increase the temperature of the power cycle up to 1300°C.

Sporian has successfully developed high-temperature operable pressure, temperature, thermal flux, strain, and flow sensors for gas path measurements in high-temperature turbine engines. These sensors are based on a combination of polymer derived ceramic (PDC) sensors, advanced high-temperature packaging, and integrated electronics. The overall objective is the beneficial application of these sensors to CSP systems.

Through collaboration with CSP industry stakeholders, Sporian has established a full picture of operational, interface, and usage requirements for trough, tower, and dish CSP architectures. In general, sensors should have accurate measurement, good reliability, reasonable cost, and ease of replacement or repair. Sensors in contact with hot salt HTF and TES fluids will experience temperature cycling on a daily basis, and parts of the system may be drained routinely. Some of the major challenges to high-temperature CSP implementation include molten salt corrosion and flow erosion of the sensors. Potential high-temperature sensor types that have been identified as of interest for CSP HTF/TES applications include temperature, pressure, flow, and level sensors.

Candidate solar salts include nitrate, carbonate, and chloride, with different application temperatures ranging from 550°C-900°C. Functional ceramics were soaked for 500 hours in molten nitrate, carbonate, and chloride salts, showing excellent corrosion resistance in chloride salts and good resistance in nitrate salts. The demonstration of functional ceramics in relevant HTFs laid the foundation for full prototype sensor and packaging demonstration.

Sporian has developed a packaging approach for ceramic-based sensors in various harsh gaseous environments at temperatures up to 1400°C, but several aspects of that packaging are not compatible with corrosive and electrically conductive HTFs. In addition to consulting published literature, a 300 hour soak test in molten chloride salt allowed the authors to identify suitable structural metals and ceramics.

Based on discussions with stakeholders, molten salt corrosion testing and room-temperature water flow testing, suitable for CSP sensor/packaging concepts were identified for future development, and initial prototypes have been built and tested.
REopt: A Platform for Energy System Integration and Optimization
Authors: Simpkins T. , Cutler D. , Anderson K. , Olis D. , Elgqvist E. , Callahan M. , Walker A.
Published: October 2014

REopt is an energy planning platform offering concurrent, multiple technology integration and optimization capabilities to help clients meet their cost savings and energy performance goals. The REopt platform provides techno-economic decision support analysis throughout the energy planning process, from agency-level screening and macro planning to project development to energy asset operation. REopt employs an integrated approach to optimizing the energy costs of a site by considering electricity and thermal consumption, resource availability, complex tariff structures including time-of-use, demand and export rates, incentives, net metering, and interconnection limits. Formulated as a mixed integer linear program, REopt recommends an optimally sized mix of conventional and renewable energy, and energy storage technologies; estimates the net present value associated with implementing those technologies; and provides the cost-optimal dispatch strategy for operating them at maximum economic efficiency. The REopt platform can be customized to address a variety of energy optimization scenarios including policy, microgrid, and operational energy applications. This paper presents the REopt techno-economic model along with two examples of recently completed analysis projects.
High Temperature Durability of Solid Particles for Use in Particle Heating Concentrator Solar Power Systems
Authors: Knott R. C. , Sadowski D. L. , Jeter S. M. , Abdel-Khalik S. I. , Al-Ansary H. A. , El-Leathy Abdelrahman
Published: October 2014

Using solid particulates as a heat absorption and transfer medium in solar concentrated systems is a solution for collecting and storing thermal energy. Solid particulates, such as sand, are relatively inexpensive and are much less corrosive and expensive to maintain than molten salts. Small particles may be stored easily, and can be used as a heat transfer medium for use with a suitable heat exchanger. Despite their anticipated low cost, excessive degradation of the particulates requiring replenishment or disrupting operation could impair the overall economics. Consequently, the durability of the particulates should be verified. Responding to this need, this study examines the durability of solid particulates as a heat transfer medium in a closed cycle for concentrated solar power central receiver systems. Specifically, this study analyzes the combination of attrition and sintering of sand with varying temperatures. Attrition is the reduction of a particle’s mass and sintering is a process of fusing two or more particles together to form a larger agglomerate. In a closed cycle, particularly for a concentrated solar power tower, a particle will experience typical temperatures from 600°C to 1000°C. The increase in temperature may change the physical characteristics of the particles and along with any impurities may promote lower softening point bonding. Thus, it is important to investigate particle durability at high temperatures.

The experimental procedure used in this investigation involves heating and abrading particulates of a known mass and size distribution to temperatures between 600°C and 1000°C, and also at 25°C to observe attrition only. The testing is conducted using a specially designed experimental apparatus described below. The heated particulates are contained in a metal cylinder. Inside the cylinder is another cylinder made of a porous silicon carbide foam. As the temperature is held constant, the particulate sample is rotated 180 degrees around a horizontal axis every 15 seconds from a low position to a higher position so that the particulates fall and abrade against each other. This process is repeated for a known number of cycles (many thousands). Then the resulting particulate size distribution is measured to determine the amount of attrition and sintering occurred during the experiment. The particulates tested are various types of sand with varying mean diameters and composition, along with a ceramic particulate similar to hydraulic fracturing proppants. Sample composition, sample size distribution, and temperature will be used to establish parameters for rates of attrition and sintering. These rates will be used to predict the behavior of particulates in a concentrated solar power tower closed cycle.
The Effect of a Thermotropic Material on the Optical Efficiency and Stagnation Temperature of a Polymer Flat Plate Solar Collector
Authors: Gladen Adam C. , Davidson Jane H. , Mantell Susan C.
Published: October 2014

Solar hot water and space heating systems constructed of commodity polymers have the potential to significantly reduce the initial cost of solar thermal systems. However, a polymer absorber must be prevented from exceeding its maximum service temperature during stagnation. Here we consider the addition of a thermotropic material to the surface of the absorber. The thermotropic layer provides passive overheat protection by switching from high transmittance during normal operation to high reflectance if the temperature of the absorber becomes too high. In this paper, a one dimensional model of a glazed, flat-plate collector with a polymer absorber and thermotropic material is used to determine the effects of the optical properties of a thermotropic material on optical efficiency and stagnation temperature of the collector. A key result is identification of the reflectance in the translucent state required to provide overheat protection for potential polymer absorber materials. For example, the reflectance of a thermotropic material in the translucent state should be greater than or equal to 51% for a polypropylene absorber which has a maximum service temperature of 115 °C.
Roof Cover Impact on Cooling Energy Use of Office Buildings
Authors: Krarti Moncef
Published: October 2014

This paper analyzes the impact of roof covers on office building energy use for representative US climate zones. In particular, the study presented in the paper investigates the potential annual cooling energy use savings that roof covers could provide using whole-building simulation analysis to evaluate the performance of a 2-story office building in five US locations. Three parameters of the roof covers including their size, height, and transmittance, are considered in the analysis. The simulation results indicate that while roof covers had similar affects on buildings in all climate zones, their impact in reducing cooling energy usage is different and is more pronounced in cooler climates. Specifically, roof covers could potentially achieve cooling energy savings of up to: 25% in Houston, 33% in Atlanta, 31% in Nashville, 38% in Chicago, and 41% in Madison. Based on the detailed simulation analysis results, a simplified calculation model is developed to help the estimation of cooling energy savings as a function of the roof cover size, height, and transmittance.
Evaluation of the Energy Efficiency Effectiveness of Cool Roofs for Residential Applications
Authors: Krarti Moncef
Published: October 2014

This study determines the effects of cool roofs on a home’s energy use, specifically on heating and cooling energy end-uses. Representative cities were chosen for several ASHRAE US climate zones. A series of parametric simulations in EnergyPlus was carried out to assess the performance of cool roofs for selected prototypical residential building models using detailed simulation analysis. The simulation results are then correlated for each climate zone type to give an approximation of the best roof color per climate. The results are given based on total energy used as well as energy cost based on national average electricity and natural gas residential rates. This method allows builders and homeowners the choice between the most cost effective roofing type, and the most energy efficient in the case that they are not the same.

Overall, it was found that in hot climates, it is more efficient to have a white roof, while a black roof benefits cooler climates. In mild and mixed climates, the effect of roof color was found rather are different for energy use and energy cost. Therefore the choice is determined by the owner’s requirements. In the cooler and milder climate zones, the analysis shows that the cost excess or savings is fairly small; usually under $10 difference per year. Hotter climates also have a relatively small effect, but more so than the cooler climates, with Phoenix especially showing a savings of $48.60 per year when a white roof is used over a black roof. Energy changes as low as only 4% in the as-built construction style, or as high as nearly 100% change in upgraded envelope cases were found. The study further finds that both the lack of an attic, and high efficiency envelopes increases the magnitude of the percent change in energy requirements.
Evaluation of Solar Optical Modeling Tools for Modeling Complex Receiver Geometries
Authors: Yellowhair Julius , Christian Joshua M. , Ho Clifford K.
Published: October 2014

Solar optical modeling tools are valuable for modeling and predicting the performance of solar technology systems. Four optical modeling tools were evaluated using the National Solar Thermal Test Facility heliostat field combined with flat plate receiver geometry as a benchmark. The four optical modeling tools evaluated were DELSOL, HELIOS, SolTrace, and Tonatiuh. All are available for free from their respective developers. DELSOL and HELIOS both use a convolution of the sunshape and optical errors for rapid calculation of flux profiles on the receiver surfaces. SolTrace and Tonatiuh use ray-tracing methods to determine reflected solar rays on the receiver surfaces and construct flux profiles. We found the ray-tracing tools, although slower in computation speed, to be more flexible for modeling complex receiver geometries, whereas DELSOL and HELIOS were limited to standard receiver geometries. We provide an example of using SolTrace for modeling non-conventional receiver geometries. We also list the strengths and deficiencies of the tools to show tool preference depending on the modeling and design needs.
Experimental and Numerical Studies of Air Curtains for Falling Particle Receivers
Authors: Ho Clifford K. , Christian Joshua M. , Moya Adam C. , Taylor Josh , Ray Daniel , Kelton John
Published: October 2014

The use of an air curtain blowing across the aperture of a falling-particle receiver has been proposed to mitigate convective heat losses and to protect the flow of particles from external winds. This paper presents experimental and numerical studies that evaluate the impact of an air curtain on the performance of a falling particle receiver. Unheated experimental studies were performed to evaluate the impact of various factors (particle size, particle mass flow rate, particle release location, air-curtain flow rate, and external wind) on particle flow, stability, and loss through the aperture. Numerical simulations were performed to evaluate the impact of an air curtain on the thermal efficiency of a falling particle receiver at different operating temperatures. Results showed that the air curtain reduced particle loss when particles were released near the aperture in the presence of external wind, but the presence of the air curtain did not generally improve the flow characteristics and loss of the particles for other scenarios. Numerical results showed that the presence of an air curtain could reduce the convective heat losses, but only at higher temperatures (>600°C) when buoyant hot air leaving the aperture was significant.
Carbon Particle Generation and Lab-Scale Small Particle Heat Exchange Receiver Experimentation and Modeling
Authors: Frederickson Lee , Leoni Mario , Miller Fletcher
Published: October 2014

Central receivers being installed in recent commercial CSP plants are liquid-cooled and power a steam turbine in a Rankine cycle. San Diego State University’s (SDSU) Combustion and Solar Energy Laboratory has built and is testing a lab-scale Small Particle Heat Exchange Receiver (SPHER). The SPHER is an air-cooled central receiver that is designed to power a gas turbine in a Brayton cycle. The SPHER uses carbon nanoparticles suspended in air as an absorption medium. The carbon nanoparticles should oxidize by the outlet of the SPHER, which is currently designed to operate at 5 bar absolute with an exit gas temperature above 1000°C.

Carbon particles are generated from hydrocarbon pyrolysis in the carbon particle generator (CPG). The particles are mixed at the outlet of the CPG with dilution air and the mixture is sent to the SPHER. As the gas-particle mixture flows through the SPHER, radiation entering the SPHER from the solar simulator is absorbed by the carbon particles, which transfer heat to the gas suspension and eventually oxidize, resulting in a clear gas stream at the outlet.

Particle mass loading is measured using a laser opacity measurement combined with a Mie calculation, while particle size distribution is determined by scanning electron microscopy and a diesel particulate scatterometer prior to entering the SPHER. In predicting the performance of the system, computer models have been set up in CHEMKIN-PRO for the CPG and in ANSYS Fluent for the SPHER, which is coupled with VeGaS ray trace code for the solar simulator.

Initial experimentation has resulted in temperatures above 850°C with around a 50K temperature difference when particles are present in the air flow. The CPG computer model has been used to estimate performance trends while the SPHER computer model has been run for conditions to match those expected from future experimentation.
Oxidation Rate Analysis of Carbon Nanoparticles for a Small Particle Heat Exchange Receiver
Authors: Leoni Mario , Frederickson Lee , Miller Fletcher
Published: October 2014

A new experimental set-up has been introduced at San Diego State University’s Combustion and Solar Energy Lab to study the thermal oxidation characteristics of in-situ generated carbon particles in air at high pressure. The study is part of a project developing a Small Particle Heat Exchange Receiver (SPHER) utilizing concentrated solar power to run a Brayton cycle. The oxidation data obtained will further be used in different existing and planned computer models in order to accurately predict reactor temperatures and flow behavior in the SPHER.

The carbon black particles were produced by thermal decomposition of natural gas at 1250 °C and a pressure of 5.65 bar (82 psi). Particles were analyzed using a Diesel Particle Scatterometer (DPS) and scanning electron microscopy (SEM) and found to have a 310 nm average diameter. The size distribution and the complex index of refraction were measured and the data were used to calculate the specific extinction cross section γ of the spherical particles. The oxidation rate was determined using 2 extinction tubes and a tube furnace and the values were compared to literature. The activation energy of the carbon particles was determined to be 295.02 kJ/mole which is higher than in comparable studies. However, the oxidation of carbon particles bigger than 100 nm is hardly studied and almost no previous data is available at these conditions.
Condensation Heat Transfer on a Partially Hydrophobic Surface
Authors: Vanga Ramana Saketh , Kim Sunwoo
Published: October 2014

Renewable energy systems operated by a thermal energy resource such as geothermal power plants and solar thermal power systems are demanding improvement in their condensation performance [Kutscher & Costenaro, 2009]. While their energy resources are naturally obtained at almost no cost, heat rejecting components become relatively expensive to maintain and operate. In this research, a heterogeneous condensing surface is proposed to enhance the condensation heat transfer coefficient in vapor-to-liquid heat exchangers. On its surface, parallel stripes with hydrophobic feature and ones without it alternate. The effect of the partially hydrophobic condensing surface on the dropwise condensation heat transfer of saturated steam on the flat plate copper surface is experimentally investigated. A vertical flat plat condenser is constructed to evaluate the performance of the heterogeneous condensing surface in comparison with a plain copper sample and a homogeneous hydrophobic-treated copper sample. Experimental results show that condensation heat transfer of steam on the homogeneous hydrophobic-treated sample is superior to that on the plain copper surface despite the fact that both the surfaces stably promote dropwise condensation. The heat transfer coefficients for the heterogeneous surface at lower subcooling temperatures, when its stripes situate horizontally, are as high as the heat transfer coefficients for the homogeneous hydrophobic-treated surface. The enhancement for the horizontal heterogeneous sample over the plain copper sample is approximately 100%. The heat transfer coefficient for the heterogeneous sample with its stripes being vertical at 4 K subcooling is 25% greater than that of the plain copper sample. Higher heat transfer coefficients are observed at lower subcooling temperatures for all the samples. The results and observations of this project suggest that the heterogeneous surface has the potential to enhance the heat transfer coefficients.
Waste Heat Recovery From Generators in the Deployed Army
Authors: Tamm Gunnar , Klosky J. Ledlie , Baxter Jacob , Grant Luke , Melnick Isaac , Young Jacob
Published: October 2014

Electrical power generation in austere settings, such as combat zones, places a heavy burden on the US Army; high costs in both dollars and lives lost require that every drop of fuel be used effectively and efficiently. In remote locations such as combat outposts (COPs) and small forward operating bases (FOBs) in Afghanistan, electrical power derived from the Army’s standard Advanced Medium Mobile Power Sources (AMMPS) generator is even used to heat water for showers and heat living spaces. This heating requires conversion of thermal energy to mechanical energy, which is then converted to electrical energy and back to heat. Thus, a significant fuel savings could be realized through the more efficient production of heat. A combined heat and power system is proposed; efficiency is increased by routing the generator exhaust through simple ducting to a standard gas hot water heater to produce hot water with waste heat. With funding from the U.S. Army Rapid Equipping Force, cadets and faculty at the United States Military Academy designed, built and tested a system for under $1,000 in parts which was readily coupled to a 5 kW AMMPS generator to produce hot shower water. Results indicate a possible fuel savings of 1500–2000 gallons per year, 20–35% increased fuel utility, and the ability to provide 10–20 five gallon showers during every 5 hours of operation of each 5 kW generator. At a fuel cost of $20–50 per gallon in the deployed environment, and considering the large inventory of deployed generators, the payback for the Army could be tremendous.
Energy Security Analysis for West Point Training Camps
Authors: Leemans Adam , Baker Martin , Tamm Gunnar , Andrews Daniel , Johnson Elsa , Hickey Brendan , Martins Nathaniel
Published: October 2014

The United States Military Academy has been charged with reaching Net Zero Energy consumption by 2020. Feasibility assessments to this point have neglected the field facilities used for military training, which are remote locations susceptible to power loss and subject to a higher rate structure for electricity than the rest of the installation. An energy security analysis methodology is described and applied to the training camps at West Point. This began with identifying the mission of the camps and critical power needs based on discussions with the customer, the Director of Cadet Military Training. Details of power and energy usage along with supply and delivery cost structure were provided by the utility and the facility Energy Manager. Conventional and renewable resource potentials were assessed to meet the load profile within financial constraints and funding opportunities unique to a federal government agency. The final recommendation is to incorporate three different technologies: a 50 kW photovoltaic solar system installed through a power purchase agreement, two small scale hydropower systems totaling 30 kW, and a lake based cooling system to provide air conditioning. The installation of these three systems would move the installation closer to the Net Zero Energy goal and lower the energy requirements to provide cooling. Altogether the proposed project would pay back in 16 years with an expected lifespan of 20–30 years. Batteries, generators, and pumped hydro were also examined as possible energy storage options and to shave the peak electrical load. However, the lack of on peak/off peak pricing made these options less viable. These recommendations will increase West Point’s energy security, progress towards the Net Zero Energy goal, and provide cost savings over current utility expenditures.
Multivariate Control and Override of a Two-Step Homogeneous Base-Catalyzed Transesterification Process
Authors: Coronado Horacio Pinzón , Escobar Porto Andrea , Sanjuan Marco E.
Published: October 2014

The most common technology used in biodiesel production is the transesterification of vegetable oils and animal fats. Transesterification (also called alcoholysis) is the reaction of fat oil with an alcohol to form esters and glycerol, in presence of catalyst to improve the reaction rate and yield. Although process industry has established long ago that continuous processes are more cost-effective than batch processing, there is still a substantial number of batch processing biodiesel plants in the world. One of the challenges in switching to a continuous process is the simultaneous control requirement of throughput (flow), temperature, and biodiesel concentration.

In the present work, a two-step homogeneous base-catalyzed transesterification process for a continuous biodiesel production plant is studied. The most relevant variables are: reaction temperature, ratio of alcohol to vegetable oil, amount of catalyst, mixing intensity (RPM), catalyst and vegetable oil used. The objective was to design a control strategy incorporating three key loops, overrides, and decoupling based on multivariate control analysis. The designed control strategy is described and simulation-based performance test results are shown.
Industrial Facilities Overhead Energy Estimation
Authors: Bawaneh Khaled , Overcash Michael , Twomey Janet
Published: October 2014

In this study, two important techniques for estimating the nonprocess energy in industrial and manufacturing buildings were examined. The building energy data for two industrial facilities were collected and analyzed. The building nonprocess energy includes lighting, heating, cooling, and ventilation. The power intensity (W/ft2) for each energy type use was estimated using two methods and then analyzed. This nonprocess energy needs to be clearly defined to allow more quantitative improvements. Previous analysis of industrial energy use often expressed nonprocess energy as a percentage of total energy but without clear values of actual nonprocess energy. This information is a low value since the actual nonprocess energy is then dominated by the dominator which is unspecified. The research in this paper has further contributed to the life cycle assessment of products by estimating nonprocess energy which can then be added to the process energy to obtain a complete energy profile of product manufacturing.
Effectiveness Model of Cooling Coil Unit Based on Parameters Identification
Authors: Hou Zhijian , Qu Ming , Wang Zhirui
Published: October 2014

The performance of cooling coil unit (CCU) can directly influence the performance of ventilating and air conditioning (HVAC) system. In this paper, a dynamic CCU model was obtained by identifying the unknown parameters of existed effectiveness model. Five different conditions information is used to identify five model parameters by an optimal method. Unlike existed effectiveness model, the identified model can be simply determined by flow rate of chilled water, the temperature and humidity of return air and temperature of supply chilled water without requiring geometric specifications, which is very convenient in real engineering application. It was validated by five different experiment conditions on a CCU. The experiment results show that the identified model has a high accuracy despite changing the temperature and volume of chilled water.
Flow Resistance Coefficient Identification of Chilled Water System Based on Multi-Objective Optimization and Experiment Validation
Authors: Hou Zhijian , Qu Ming , Wang Zhirui
Published: October 2014

Hydraulic resistance coefficient (HRC) is a fundamental parameter that characterizes the hydraulic state of a water pipeline and significantly determines the efficiency of the water-transport process. To estimate HRC and diagnose hydraulic process fault in building air conditioning system, a novel method called multi-objective optimization (MBO) strategy was developed in the research effort. MBO is concerned with mathematical optimization problems involving more than one objective function to be optimized simultaneously. In this paper, first, the basic principle of the approach is presented. Then several experiments are conducted to identify the HRC in a real air conditioning system. And the water flow rate of each air handling terminal unit is estimated by the flow rate of primary pipe and identified HRC. The experiment results show that the model can accurately estimate HRCs. The HRCs of each pipe and terminal unit were obtained by the flow rate and the pressure difference of primary pipe without requiring geometric specifications, which is very convenient in real engineering application.
High-performance transparent, all-oxide nonvolatile charge trap memory transistor using In-Ga-Zn-O channel and ZnO trap layer
Authors: Bak Jun Yong , Yoon Sung Min
Published: October 2014

A transparent, nonvolatile all-oxide charge-trap memory transistor (Ox-CTMT) was fabricated with a bottom-gate structure on a glass substrate. A wide memory window of 7.7 V was achieved when the amplitude and duration of program voltage pulses were set as ±20 V and 100 ms, respectively. The values of saturation mobility and subthreshold swing were 0.43 cm2 V−1 s−1 and 0.46 V/dec, respectively. Thanks to the unique band structure of the n-type ZnO oxide semiconductor, the fabricated Ox-CTMT exhibited a memory margin of more than four orders of magnitude for on and off states even after a lapse of 10 000 s.