bluuebunny/crossref_metadata_2025 huggingface dataset:
Model-Based Performance Analysis of the Enthalpy Wheel
Authors: Ruan Wei , Qu Ming
Published: October 2010

A mathematic model of an enthalpy wheel has been developed to analyze its performance based on energy and mass balance and heat and mass transfer correlation in the enthalpy wheel. It is a one-dimensional transient model solved by the finite volume method. Both summer and winter conditions were studied to explore the impact on the performance of an enthalpy wheel from various design and operating conditions such as the wheel depth, process air face velocity, isotherm coefficient (C), and the maximum water content. The model result predicted that the total effectiveness of the enthalpy wheel is at range of 50∼75% at typical operation condition. The depth of wheel and the face velocity of process air play an important role in the performance of the enthalpy wheel, compared to the other studied parameters. The increase of the wheel depth from 0.15 meter to 0.3 meter can improve the total effectiveness of the enthalpy wheel from 53% and 58% to 72% and 69% in summer and winter. The increase of process air face velocity from 0.5 m/s to 1.5 m/s reduces the total effectiveness of the enthalpy wheel from 75% to 50%.
Performance of an Absorber With Hydrophobic Membrane Contactor at Aqueous Solution-Water Vapor Interface
Authors: Ali Ahmed Hamza H. , Ahmed Mahmoud
Published: October 2010

In this study, analytical investigation at off-design conditions on performance of a plates-and-frames absorber with hydrophobic microporous membrane contactor at aqueous solution-water vapor interface are carried out. The absorber is a component of a single-effect lithium bromide-water absorption chiller with a hot water thermally driven generator and water-cooled absorber and condenser. Integrating the absorber model with the chiller model is used to evaluate the absorber performance at off-design conditions corresponding to different inlet both driving hot water and cooling water (coolant) temperatures. For the same cooling capacity of the chiller and referring to design point values, the results indicate that, increasing the inlet driving hot water temperature results in an increase in the required absorber size, consequently, a decrease in the absorber performance. While, decreasing the cooling water (coolant) inlet temperature leads to slightly decreases in the required absorber size, consequently, an increase in the absorber performance.
Thermal Conversion Characteristic of Pelletized Jatropha Residue and Glycerol Waste
Authors: Sricharoenchaikul Viboon , Atong Duangduen
Published: October 2010

Adverse environmental effects resulting from fossil fuel usage as well as foreseeable conventional energy depletion lead to the exploration of alternative fuel materials especially the renewable ones. In this work, characterization of synthetic fuel material formed by pelletization of Jatropha residue (physic nut) using glycerol waste as a binder was carried out in order to investigate the feasibility of utilizing these waste materials as another renewable energy source. Both wastes are by products from biodiesel manufacturing process. Synthetic fuel materials of Jatropha residue mixed with 0–50% glycerol waste were formed to length of about 11 mm and diameter of about 13 mm under pressure of 7 MPa in a hydraulic press. Maximum compressive stress (2.52×105 N/m2) of the fuel pellet occurred at 10% glycerol waste. Thermal conversion characteristic of solid fuel was studied by using single particle reactivity testing scheme at temperature of 500–900°C under partial oxidation atmosphere. In general, higher glycerol content in solid fuel as well as oxygen concentration in reacting gas resulted in greater decomposition rate from 0.006–0.110 g/sec. Burning started with a relative short drying phase, followed with a longer pyrolysis time and thereafter the dominated char combustion time which took around 35–57% of total conversion time. The average total conversion time varied from 26 to 288 sec, depended mainly on reaction temperature. Higher glycerol content resulted in char with lower density and higher shrinkage with greater porosity. Greatest changes in pellet diameter, height, and density of 75.6%, 89.2%, and 91.5%, respectively, were exhibited at 5% oxygen atmosphere and 900°C. The results suggested that Jatropha residue mixed with glycerol is suitable for utilization as quality solid fuel.
Solar Refrigerator With Efficient Adsorbent
Authors: Trujeque Bolio Jessica
Published: October 2010

The design a solar-sorption refrigerator to be used in the warm and humid climate of Mexico, the most critical environmental conditions and most demanding climatic zone for cooling technology, requires that the adsorption capacity of the composite sorbent to be characterize. It must be verified that the composite sorbent such as silica gel, calcium chloride and various natural zeolites, with different substances in a gaseous state as sorbate, (water, methanol and ethanol), has hydrogen bonds that can be united and broken easily, measuring the amount of energy required by the sorption-desorption mechanism.
A Two-Phase Model for Solar Thermochemical Water Splitting With FeO/Fe3O4
Authors: Chen Ken S. , Hogan Roy E.
Published: October 2010

A two-phase, multi-dimensional, multi-physics computational model based on the finite-element method is presented for simulating the solar thermochemical water splitting process in which hydrogen gas is produced from steam. The model takes into account heat transfer, gas-phase diffusion and advection of neutral species in open channels and through pores of the porous reactant layer, solid-state transport of charged species, and redox chemical reactions. Preliminary results (temperature distribution, velocity field, and species concentration) computed from the gas-phase transport dominating (i.e., resistance to solid-state transport is taken to be negligible) regime are presented to illustrate the utility of the model. Efforts are underway to improve the present first-generation model by incorporating solid-state transport with more realistic kinetic model, internal radiation, reactant-layer support, and temperature-dependent properties.
The Role of Passive Solar Design on Peak and Annual Heating and Cooling Loads in Office Buildings in Mexico
Authors: Figueroa Ani´bal , Fuentes Victor , Castorena Gloria
Published: October 2010

According to the International Energy Agency in 2006 nearly 36% of the total world energy was consumed by buildings and urbanization. This paper dimensions the effect of passive design corrections on the envelope of a new corporate office building in the temperate climate of Mexico City’s central area. It confirms that these are the most cost effective measures to reduce HVAC peak load, minimize system size and improve performance. It used thermal analysis to evaluate the impact of three corrective strategies: low E double glassing, adjusting shading coefficient (SC) and insulation of walls and ceiling. Results show that if low E double glassed windows are installed, heating requirements are cut by half, while peak cooling load is reduced one fifth. A 50% Shading Coefficient (SC) has also a significant effect, reducing peak cooling load in May an additional 26%.
Cost-Effectiveness of a Photovoltaic-Powered Heat Pump Water Heating System vs. Solar Thermal Water Heating
Authors: Wilson Eric J. H. , Burkhardt John J.
Published: October 2010

The cost-effectiveness of a photovoltaic (PV) powered heat pump water heater (HPWH) system is compared to that of a traditional solar thermal water heating system. HPWH evaporators are most often located inside the conditioned building space, resulting in a year-round cooling effect in the building. This effect is beneficial during the cooling season but detrimental during the heating season. The significance of this cooling effect was evaluated as part of the life cycle cost (LCC) analysis of the PV-powered HPWH system. Four different locations were considered: Boulder, CO; Miami, FL; Chicago, IL; and Seattle, WA. For the solar thermal analysis, both electric resistance and gas-fired auxiliary water heating scenarios were considered. Life cycle costs for the PV-HPWH system were calculated for the case of a PV system dedicated to providing electricity for the HPWH, and for the case of a previously planned residential PV system being increased in size to accommodate the HPWH. This latter case uses a lower, incremental cost of increasing the size of the PV system. The most notable results of the analysis are summarized below: • In general, the solar thermal system is more cost effective than the PV-HPWH system, even using the incremental cost of increasing the size of a planned PV system. • In locations where there are incentives that apply to PV but not solar thermal systems, as in much of Colorado, the PV-HPWH system will be more cost-effective than solar thermal. • The cooling effect of the HPWH evaporator is a net benefit in Miami, FL, but a net penalty in the other three locations. • The PV-HPWH system becomes more cost-effective than solar thermal with gas auxiliary in Miami when the price of natural gas is increased from $1 to $1.50 per therm. • Increasing the price of gas in the other locations does not make the PV-HPWH system compete against solar thermal because the cooling effect penalty also increases with the price of natural gas.
A First Order Thermodynamic and Economic Analysis for Integrating Thermal and Compressed Air Energy Storage for a Dispatchable Wind and Solar Powered System
Authors: Garrison Jared B. , Kapner Mark , Webber Michael E.
Published: October 2010

Wind and solar technologies have experienced rapid market growth recently as a result of the growing interest for implementation of renewable energy. However, the intermittency of wind and solar power is a major obstacle to their broader use. The additional risks of unexpected interruptions and mismatch with demand have hindered the expansion of these two primary renewable resources. The goal of this research is to analyze an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. The proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrated solar thermal power in order to achieve this desired dispatchability. While current CAES facilities use off peak electricity to power their compressors, this system uses power from wind turbines to compress air to high pressure for storage. Also, rather than using natural gas for heating of the compressed air before its expansion through a turbine, which it typical for conventional systems, the system described in this paper replaces the use of natural gas with solar thermal energy and thermal storage. Through a thermodynamic and a levelised lifetime cost analysis we have been able to develop estimates of the power system performance and the cost of energy for this integrated wind-solar-storage system. What we found is that the combination of these components resulted in an efficiency of over 50% for the main power components. We also estimated that the overall system is more expensive per unit of electricity generated than two of the current technologies employed today, namely coal and nuclear, but cheaper than natural gas peaking units. However, this economic analysis, though accurate with regard to the technologies chosen, will not be complete until cost values can be placed on some of the externalities associated with power generation such as fuel cost volatility, national security, and emissions.
A Novel “Wireless On-Off Control” Technique for Household Heat Adjusting and Metering in District Heating System
Authors: Liu Lanbin , Fu Lin , Jiang Yi
Published: October 2010

A large-scale survey and on-site measurements on space heating systems in Beijing has been carried out since 2005. Detailed analysis shows that the improvement of system regulation to adjust the heating demand and to avoid over-heating in building space is the key to reduce the heating energy consumption. It also indicates that combined heat and power (CHP) based district heating network is the most suitable solution for the space heating in Chinese northern cities. Thus, the priority should be in the research and development of new techniques to improve heating system regulation and control. In China, there are three reasons for poor heating system regulation: • the lack of control devices in space heating system, • the complex and inconvenient operation, and • the insufficient motivation because the charging policy is based on the heating areas. Field test results show that 20% to 30% of thermal energy is wasted because of the poor heating system regulation. In order to solve these problems, a novel “wireless on-off control” system for household heat adjusting and metering has been proposed. This technology works in the following way: 1) a calorimeter is installed at each building to measure the total heat consumption of the whole building; 2) an on-off valve is installed for each household and an indoor temperature controller is provided for the occupants. The operation procedure is as follows. First, the desired indoor temperature is set by the users through the indoor temperature controller and wireless signals are sent to the on-off valve. Then the on-off valve detects the real indoor temperature and determines the difference between the real temperature and the set value. After this, the valve calculates the proportion of on-time to off-time in the next step according to the thermal strategies programmed in the valve’ CPU. Then the valve is controlled according to the proportion to maintain the desired indoor temperature; and 3) the heating cost of each household can be allocated according to its heating area and the accumulative open time of the valve. The proposed technique has been applied in fifteen residential communities with the total areas of 1,200,000 m2. The testing results show that: 1) indoor temperatures were accurately controlled within +/− 0.5 °C around the set point, so that the problem of overheating can be avoided; 2) the difference of temperature in different room is less than 1 °C. Therefore, if radiators in each room are designed reasonably, to control the temperature of one room can meet the requirements of the entire user’s apartment; 3) energy consumption in the controlled household was approximately 30% lower than the uncontrolled household with the same building type.
Air-Sand Heat Exchanger for High-Temperature Storage
Authors: Warerkar Shashikant , Schmitz Stefan , Goettsche Joachim , Hoffschmidt Bernhard , Reißel Martin , Tamme Rainer
Published: October 2010

In view of rising energy prices and an increasing share of power generated by renewable energy sources, the importance of energy storage is growing. In the framework of this project a thermal energy storage concept for solar power towers is being developed, in which quartz sand serves as storage medium. Sand is suited due to its properties as high thermal stability, specific heat capacity and low-cost availability. Compared to storages based on ceramic bodies the usage of sand promises to reduce costs of energy storage and thus to reduce the costs of electricity generation. In addition the storage concept could be applicable in steel industry. The central element of the storage concept is an air-sand heat exchanger, which is presently under development. This paper describes simulation results and measurements of the heat exchanger prototype. It includes sand flow behaviour and experience with different porous walls as well as up-scaling options.
A New Type of District Heating System Based on Distributed Absorption Heat Pumps
Authors: Fu Lin , Li Yan
Published: October 2010

This paper presents a new approach to utilize geothermal energy with absorption heat pump in district heating system. The heat pump is driven by the temperature-difference between primary and secondary heating loops. In this method, the low-grade thermal energy can be used in district heating system effectively, as a result, the heating capacity and energy efficiency of district heating system can be improved more than 20%. On one hand, it could relieve the existing dilemma (shortage) of central heat source, as well enhance the delivery capacity of heating network dramatically. On the other hand, heating cost may be reduced remarkably, due to the reduction in both coal consumption of central heat and energy consumption of delivery pump. Firstly, this paper introduces the district heating method based on distributed absorption heat pumps through the analysis on the parameter characteristics of low-grade energy, hot water of primary and secondary heating network, as well as the operation parameters of absorption heat pumps. Secondly, an economic and energy consumption analysis was discussed by comparing the new approach with conventional heating system. Finally, this paper presents several system configurations, discusses the operation strategies in various conditions, and proposes the operation modes for heating season.
Atmospheric Wind Data Collection and Wind Turbine Analysis in UAE
Authors: Janajreh Isam , Qudaih Rana , Talab Ilham , Al Nahari Zaki
Published: October 2010

Wind turbine technology has improved dramatically in the last two decades as demonstrated by their plummeting capital costs ($0.08/KW), the enhanced reliability, and the increased efficiency. Large-scale wind turbines and wind farms provided 94.1GW of electrical grid capacity in 2007, and are expected to reach 160 GW by 2010 according to WWEA. Wind energy is plentiful and sustainable energy source with an estimated potential capacity of 72 TW. In Denmark the inland and offshore implementation of wind energy generation adds 1/5 of their electrical grid capacity. In Germany, it is forecasted to attain 12.5% by early 2010. Offshore wind farms have lower ecological impact due to lack of land mortgage, easier transportation, and low perception of noise issue. In the gulf region, the generated power can fulfill the power needs of UAE’s islands, while the excess capacity can be channeled to the inland grids fulfilling the peak demand. In this work we will investigate the implementation of low-turning moment wind turbines in the UAE, suited for low wind speeds (∼3–5m/s) and that consists of two research components: (i) Collection of wind data, analysis, recommendation for implementation strategies, and using Masdar wind data to assess its characteristics and its fit for wind turbine implementation; (ii) Carry out flow analysis on a downwind, two-bladed, horizontal-axes wind turbine to investigate the flow lift, drag and wake characteristics on the tower blade interaction. The interaction is studied utilizing Arbitrary Lagrangian Eulerian method. Downwind turbines are self-aligned, pass up yaw mechanisms and its needed power, and have fewer moving parts that necessitate regular maintenance. These factors however play in favor of wind turbine that is subjected to low wind speed.
S and T Fellowship Experiences in Washington, D.C.
Authors: Hutzel William J. , Glawe Diana D.
Published: October 2010

The currency of the engineering profession is knowledge. The knowledge gained by an engineer immersed in public policy is commonly undervalued because it is seen as not being applicable to the technical discipline. However, knowledge of the policymaking process is exactly what is needed to understand and communicate technical data in a way that decision-makers can leverage in developing prudent policies. So exposure to policy in effect enables engineers to apply their knowledge for public benefit — the genesis of the engineering discipline. This is only one of the many compelling reasons why interaction between engineers and policymakers should be valued by industry and academia. It was a motivating factor for two faculty members who recently made a temporary transition away from their respective universities to pursue Science and Technology fellowships in Washington, DC. Both individuals had tremendous experiences, professionally and personally, and encourage other engineers to make a similar adventure in Washington, DC one of their career goals.
CHP as an Economically Viable Green Energy Solution for Municipal Wastewater Treatment
Authors: Lami Lianne B. , Craft Jesse D.
Published: October 2010

The environmental and economic impact of a municipal wastewater treatment plant can be reduced through a novel application of CHP technology. By operating a natural-gas fired prime mover to generate electricity and utilizing the rejected heat in the sludge drying process, energy cost savings and both site- and grid-wide emissions reductions can be realized. The design case is the Almeda Sims Wastewater Treatment Plant for the City of Houston. This plant treats the waste, and then dewaters the sludge that results from the process with a large natural-gas fired dryer. The plant handles about 40 tons of sludge per day. The proposed CHP plant would use a natural-gas fired turbine to generate base-load electricity for the facility, and utilize the heat from the turbine exhaust to reduce the natural-gas requirement at the burner tip of the dryers. Utilization of emission-reducing technology on the turbine exhaust and the reduction in natural-gas consumption at the dryer burner tip, as well as reduced electrical draw from the grid, results in a significant reduction in environmental pollutants. Modeling of the proposed system shows a potential for a CHP system efficiency of approximately 76%, compared to 30–35% efficiency of grid-wide power generation equipment. The result is an economically viable green energy solution for any municipality with significant wastewater processing needs.
The Water Quality and Energy Impacts of Biofuels
Authors: Twomey Kelly M. , Stillwell Ashlynn S. , Webber Michael E.
Published: October 2010

Concerns over rising fuel prices, national security, and the environment have led to the Energy Independence and Security Act (EISA) of 2007, which established a mandate for the production of at least 36 billion gallons of biofuels in 2022, up to 15 billion gallons of which can come from traditional first-generation biofuels sources such as corn starch-based ethanol. One consequence of ramped-up biofuels production is the risk of additional soil runoff. This runoff, potentially laden with nitrogen and phosphorus compounds from fertilizers, can detrimentally impact water quality. Consequently, the water treatment sector might require additional energy to remove increased quantities of sediment and run-off from nutrients and pesticides in degraded water bodies downstream of agricultural land. At the same time, the cumulative effects of increased eutrophication in the Mississippi and Atchafalaya River Basins have already negatively impacted much of the aquatic life in the Louisiana-Texas continental shelf. A recent report by U.S. Geological Survey measured nitrogen loading in the Mississippi River basin as high as 7,761 metric tons per day, the highest recorded loading in the past three decades, 52% of which is attributed to loading from corn and soybean crops. Massive algae blooms that thrive in nutrient-rich water deplete the water of oxygen when they die, creating a hypoxic region. This hypoxic region, which currently covers a region the size of New Jersey, is considered to be the second-largest dead zone in the world as of 2007. As a result, the Gulf Hypoxia Action Plan of 2008 was established to reduce nitrogen and phosphorous loading by 45% in order to shrink the hypoxic region to 5,000 square kilometers. Thus, at a time when water quality priorities aim to decrease nitrogen and phosphorous loading in waterways, legislative targets are seeking to increase corn starch-based ethanol production to 15 billion gallons a year, and thereby potentially increase nitrogen loading in this region by 10–34% due to runoff. Consequently, the energy intensity for water treatment may have a two-fold challenge. Because water and wastewater treatment is already responsible for 4% of the nation’s electricity consumption, putting more stringent demands on this sector could put upward pressure on energy consumption. This analysis quantifies the impact that the mandated increase in ethanol production might have on the energy required for water treatment in the United States. It reports results from a first-order top-level analysis of the energy impacts of ethanol. The results indicate that the increased production corn-starch based ethanol in the United States is not likely to increase the energy consumed during surface water treatment, but might cause significant increases in the energy consumed during groundwater treatment.
An Intelligent System for Improving the Efficiency of a PHEV for the EcoCar Challenge
Authors: King Alex , Del Buono Matt , Marolf Jonathan , Dop Michael , Stansbury Richard S.
Published: October 2010

Globally, significant efforts are being made to reduce green-house gases and decrease the demand of fossil fuels. Automotive manufacturers are offering significantly more “green” versions of their popular automobiles in order to combat the negative impact of rising fuel prices. The EcoCar Challenge is a college-level competition primarily sponsored by General Motors and the United States Department of Energy in an effort to provide global awareness of this effort and educate future engineers in the processes and technologies used to construct fuel economic hybrid vehicles. The program consists of 17 teams with a wide variety of hybrid vehicle types. Embry-Riddle Aeronautical University (ERAU) is implementing a plug-in hybrid electric vehicle (PHEV) through the modification of a stock 2009 Saturn Vue as described in [1]. This paper presents the Intelligent Drive Efficiency Assistant (IDEA) system a hardware/software component being added to ERAU’s EcoCar vehicle. The IDEA system uses artificial intelligence techniques to analyze the driving conditions ahead (terrain, traffic, and anticipated torque requirements) to select the best operating mode for the hybrid vehicle. The IDEA system submits its recommendation to a hybrid or supervisory control unit, presented in [2], which does the necessary work to transition the vehicle into that operating mode (so long as it deems the request safe). This preemptive strategy is believed to provide two key benefits. First, through learning algorithms, new control strategies may be developed based on the driving conditions and past experience. Second, by preemptively making recommendations ahead of a driving event such as an uphill climb, or a frequent stop in rush-hour traffic, it is believed that there will be less energy wasted by not waiting until the need arises to start making the transition between hybrid modes. Within this paper, the initial design of the IDEA system is be presented, and the evaluation plan using hardware-in-the-loop and software-in-the-loop simulation is discussed.
Life Cycle Cost for a Solar Heating and Cooling System
Authors: Hang Yin , Qu Ming
Published: October 2010

Solar absorption cooling has been an intriguing research subject since 1970. However, it is not widely applied because the first cost of the system is high, the commercial hot water absorption chiller is not mature, the site demonstration and evaluation are not adequate and the price of conventional fossil energy sources is relatively low. This paper investigates the commercialization potentials of solar absorption cooling and solar heating system by comparing the life cycle cost between it and the conventional electrical chiller cooling and gas-fired boiler heating system. A computational model has been programmed in the Engineering Equation Solver (EES) to analyze the economical performances of the two systems applied to a dedicated building. The model considers the cost of capital, installation, operation and maintenance, the discount rate, the fuel prices, and the inflation rates. The result of the model indicated that given the present fuel cost, the solar absorption cooling and heating system is not as economic as the conventional system especially when its size is small. However, according to the sensitivity analysis carried, the solar absorption cooling and heating system could compete with the conventional cooling and heating system when the electricity price and fuel inflation increase.
Bubbly Silicon: A New Mechanism for Solid Phase Crystallization of Amorphous Silicon
Authors: Anderson Curtis , Cui Lin , Kortshagen Uwe
Published: October 2010

This paper describes the rapid formation of polycrystalline silicon films through seeding with silicon nanocrystals. The incorporation of seed crystals into amorphous silicon films helps to eliminate the crystallization incubation time observed in non-seeded amorphous silicon films. Furthermore, the formation of several tens of nanometer in diameter voids is observed when cubic silicon nanocrystals with around 30 nm in size are embedded in the amorphous films. These voids move through the amorphous film with high velocity, pulling behind them a crystallized “tail.” This mechanism leads to rapid formation of polycrystalline films.
Measurement and Analysis of the Annual Daylighting Performance of a Middle School in North Carolina
Authors: Athalye Rahul , Eckerlin Herbert M.
Published: October 2010

This paper evaluates the measured annual daylighting performance of the Northern Guilford Middle School at Greensboro, North Carolina. A side-daylighting strategy that employs a unique curved interior translucent light-shelf is used in the classrooms. The measured average annual illuminance under clear sky conditions is about 100 foot-candles. However, there is great variation in the space illuminance from season to season. The building occupants react to this variation in ways that cannot be controlled and this ultimately determines how well the design works. Along with the annual measurements, two tests were performed on the side-lit design to determine the effects of individual design elements. The results from these experiments as well as those from the computer modeling of a typical classroom using the side-lit strategy at Northern Guilford are presented in this paper. These results may be extended to any day-lit space with an interior translucent element, located on similar latitude and a comparable solar radiation profile.
Circulation Controlled Airfoil Analysis Through 360 Degrees Angle of Attack
Authors: Graham Henry Z. , Hubbell Meagan , Panther Chad , Wilhelm Jay , Angle Gerald M. , Smith James E.
Published: October 2010

Wind turbines are a source of renewable energy with an endless supply. The most efficient types of wind turbines operate by utilizing the lift force of its blades to create a rotational force. The power capabilities of a wind turbine are tied to the blades’ ability to convert the aerodynamic forces into rotational energy. Vertical axis wind turbines (VAWT), unlike the more common horizontal axis (HAWT) type, do not need to be directed into the wind and can place the transmission and electrical power generation components at the bottom of the turbine shaft, near the ground. Currently VAWTs cannot feather or pitch the blades, in the same fashion as a HAWT, for a lift change to control power generation and/or rotational speed at different or changing wind speeds. A method of increasing the lift of a blade without physically moving the blade is to use circulation control (CC), via a blowing slot over a rounded trailing edge. The CC air flow entrains the air around the blade to create more lift. Adding an actuated valve for the blowing slot allows a CC-VAWT to control the amount of lift generated, as well as the location of the augmentation relative to the wind direction, resulting in augmented power generation. In order to study the performance capabilities of a CC-VAWT, a NACA0018 blade was modified to incorporate circulation control. This modified shape was analyzed using computational fluid dynamics at two Reynolds numbers and a wide range of angles of attack. The lift to drag ratio of the CC-VAWT blade shows benefits at low Reynolds numbers over a NACA0018 blade for post stall angles of attack, but there is a decrease in the lift to drag before stall due to a significant increase in drag of the circulation control models. Further CFD refinement and experimental investigations are recommended to validate the predicted effects circulation control will have on the performance of a VAWT.
Investigation of Reverse Thermosyphoning in an Indirect SDHW System
Authors: Cruickshank Cynthia A. , Harrison Stephen J.
Published: October 2010

Thermal energy storages with thermosyphon natural convection heat exchangers have been used in solar water heating systems as a means of increasing tank stratification and eliminating the need for a second circulation pump. However, if the storage system is not carefully designed, under adverse pressure conditions, reverse thermosyphoning can result in increased thermal losses from the storage and reduced thermal performance of the system. To investigate this phenomenon, tests were conducted on a single tank and multi-tank thermal storage under controlled laboratory conditions. Energy storage rates and temperature profiles were experimentally measured during charge periods, and the effects of reverse thermosyphoning were quantified. A further aspect of this study was to empirically derive performance characteristics and to develop numerical models to predict the performance of the heat exchanger during reverse thermosyphon operation, and to quantify the relative magnitude of these effects on the energy stored during typical day-long charge periods. Results of this study show that the magnitude of the reverse flow rate depends on the pressure drop characteristics of the heat exchange loop, the system temperatures and the geometry of the heat exchanger and storage tank. In addition, the results show that in the case of a multi-tank thermal storage, the carry over of energy to the downstream thermal energy storages depend on the effectiveness of the exchangers used in the system.
Momentum Analytical Model of a Circulation Controlled Vertical Axis Wind Turbine
Authors: Wilhelm Jay P. , Panther Chad , Pertl Franz A. , Smith James E.
Published: October 2010

A possible method for analytically modeling a CC-VAWT (Circulation Controlled Vertical Axis Wind Turbine) is the momentum model, based upon the conservation of momentum principal. This model can consist of a single or multiple stream tubes and/or upwind and downwind partitions. A large number of stream tubes and the addition of the partition can increase the accuracy of the model predictions. The CC-VAWT blade has blowing slots located on the top and bottom trailing edges and have the capability to be site controlled in multiple sections along the span of the blade. The turbine blade, augmented to include circulation control capabilities, replaces the sharp trailing edge of a standard airfoil with a rounded surface located adjacent to the blowing slots. Circulation control (CC), along with a rounded trailing edge, induces the Coanda effect, entraining the flow field near the blowing slots thus preventing or delaying separation. Ultimately, circulation control adds momentum due to the mass flow of air coming out of the blowing slots, but is negligible compared to the momentum of the free stream air passing through the area of the turbine. In order to design for a broader range of operating speeds that will take advantage of circulation control, an analytical model of a CC-VAWT is helpful. The analytical modeling of a CC-VAWT could provide insight into the range of operational speeds in which circulation control is beneficial. The ultimate goal is to increase the range of operating speeds where the turbine produces power. Improvements to low-speed power production and the elimination or reduction of startup assistance could be possible with these modifications. Vertical axis wind turbines are typically rated at a particular ratio of rotational to wind speed operating range. In reality, however, wind speeds are variant and stray from the operating range causing the power production of a wind turbine to suffer. These turbines, unless designed specifically for low speed operation, may require rotational startup assistance. The added lift due to circulation control at low wind speeds, under certain design conditions, will allow the CC-VAWT to produce more power than a conventional VAWT of the same size. Circulation control methods, such as using blowing slots on the trailing edge are modeled as they are applied to a VAWT blade. A preliminary CC-VAWT was modeled using a standard NACA 0018 airfoil, modified to include blowing slots and a rounded trailing edge. This paper describes an analytical momentum model that can be used to predict the preliminary performance of a CC-VAWT.
Heating System Supervisory Control for Residential Energy Conservation
Authors: Woods D’Angelo R. , Hammonds James S.
Published: October 2010

For most households space heating and domestic hot water production constitute the largest portion of energy consumption, which for a typical home space and water heating can comprise over 60% of the total energy usage. Therefore significant energy savings can be accomplished by using energy sources and systems for heating more efficiently. An approach discussed in this work uses system controls to better manage available resources and balance user comfort with efficient use of energy systems. In this work the results of a supervisory control approach applied to residential heating system are presented. The control system is characterized by a supervisory unit that controls the subsystems. The subsystems of this analysis include a thermal source and an energy storage unit. Dynamic thermal system control is demonstrated using a real-time, pseudo-hardware-in-the-loop test bench. The results show the potential reduction of energy consumption through advanced control implementation.
The Effects of Thermal Mass and Phase Change Material on a Buildings’ Thermal Load
Authors: Gilbert Robert B.
Published: October 2010

A finite-difference model is used to simulate the effects of thermal mass and phase change material on thermal transmission through a building’s envelope wall. The exterior temperature is simulated by a sinusoidal function. The inside temperature is held constant. A comparison is given between the effects of thermal mass and phase change material. The maximum reduction in thermal load and required conditions is given for both thermal mass and phase change material. Equations are given for the maximum thermal load reduction as a function of the inside and outside temperature. Equations are also given which treat the thermal mass as a lumped capacitance and the expected error as a function of the amount of thermal mass. The conditions under which the addition of thermal mass and/or phase change material will result in a reduction of thermal load is given.
Comparison of Two-Tank Indirect Thermal Storage Designs for Solar Parabolic Trough Power Plants
Authors: Kopp Joseph , Boehm R. F.
Published: October 2010

The performance of a solar thermal parabolic trough plant with thermal storage is dependent upon the arrangement of the heat exchangers that ultimately transfer energy from the sun into steam. An indirect two-tank molten salt storage system that only transfers heat with the solar field heat transfer fluid is the most commercially acceptable thermal storage design. Annual electricity generation from two differing indirect two-tank molten salt storage designs and a base case with no thermal storage were modeled. Four components were characterized in a quasi-steady state analysis dependent upon key ambient and operational parameters: solar field, storage, heat exchangers, and power block. The parameters for the collector field remained constant for all models and were based on the SEGS VI plant. The results of net power generation favor storage though the design that maximizes annual output depends on whether maximum power generation or power generation during the evening peak demand hours is desired. Additionally, the economic trade offs are discussed for the three arrangements.
Flow Boiling of Isopentane From a Structured-Porous Copper Fin
Authors: Zhao Zenghui , Wirtz R. A.
Published: October 2010

Flow boiling experiments in isopentane assess the utility of porous fin structures consisting of stacked and bonded layers of fine-weave woven copper. Porous fins are horizontally oriented in a vertical channel with flow through the fin. Experiments are conducted over the 1bar to 3bar pressure range with channel Reynolds number ranging from 1,000 to 5,000. The results indicate that these porous fins provide stable boiling with fin-base area heat fluxes ranging to 0.6 MW/m2 at a moderate superheat and channel Reynolds number.
A Parametric Study of Conjugate Heat Transfer of Solar Chimney
Authors: Arce J. , Xaman J. P. , Alvarez G. , Jime´nez M. J. , Heras M. R.
Published: October 2010

Recently, new buildings are being designed considering natural sources such as natural ventilation as a passive technique. Solar chimneys are among those techniques of passive ventilation systems in buildings, to enhance the air quality and some times the thermal comfort. In this work, a numerical study of a solar chimney for forced ventilation is carried out. Also a parametric study varying the ambient air temperature, the solar irradiance and Reynolds number is considered. The dimensions of the solar chimney are 4.0 m high, and 0.35 m deep, the absorber surface of the solar chimney was 0.15 m thick of reinforced concrete. The conservation equations of mass, momentum, energy and two turbulence equations are solved under some simplifications such as: 2-D, incompressible, steady state turbulent air flow and conjugated heat transfer (conduction, forced convection and radiation). k-ω turbulent model was implemented and finite volume technique was applied to solve the conservation equations. In order to guarantee the right performance of the computer code, it was reduced to cases reported in the literature and verified; also, it was validated with an experiment. The variation of ambient temperature, solar irradiance and Reynolds number are analyzed in the parametric study. The heat transfer correlations for total Nusselt number (convective plus radiative) are introduced. From the results, it was found that the heat transfer increases as the Reynolds number increases for the hot surface of the solar chimney.
Numerical Modeling of the Ignition Process of a HCCI Engine With Reduced Chemical Mechanisms
Authors: Prince Juan C. , Ovando Guillermo E. , Prado Ivette , Romo Marco A.
Published: October 2010

A numerical simulation of ignition process for propane/air and heptane/air mixtures are conducted on an homogeneous charge compression ignition (HCCI) engine. The objective of this work is to obtain reduced chemical mechanisms of these fuel mixtures and to test their effectiveness on software based on Finite Element Method (FEM). Reduced mechanisms instead of detailed fuel mechanisms will allow future simulations in 2 and 3 dimensions of HCCI engines without using complex computer equipment. In this investigation, a kinetic chemistry code (CHEMKIN) was used to reduce detailed chemistry mechanisms. This study let reduce a propane mechanism from 46 reactions to 35 reactions. On the other hand, the heptane mechanism was reduced from 55 to 33 reactions. In both cases, the pressure-temperature interval ranks were obtained. Then the FEM based software was used and the reduced chemical kinetics was incorporated to simulate a zero-dimensional HCCI engine. For the numerical model, the mass and energy equations with heat generation due to ignition were included. The results of the numerical simulation on the FEM based software show that temperature and ignition times are equal to the CHEMKIN results, which is widely recognized in the combustion field like reference in process calculation with chemistry reactions.
Generation of Electricity Utilizing Solar Hot Water Collectors and a Tesla Turbine
Authors: Crowell Ryan
Published: October 2010

Threats of climate change and depleted petroleum supplies have prompted the need for eco-conscious alternative energy. This paper introduces a ground-breaking concept for harnessing the sun’s power that is significantly more efficient than existing systems. Solar collectors gather the electromagnetic radiation emitted by the sun and heat a propylene glycol to a high temperature that will then transfer the heat to a working fluid (Care30) through a plate heat exchanger. The Care30 then exits the heat exchanger in a gaseous state, and is passed through a Tesla turbine, which in turn rotates a shaft. The shaft is connected to a generator, which transforms the mechanical energy into electricity. The absorption efficiency of the solar collectors allows for mechanical loses while maintaining the overall efficiency at higher levels than any existing PV based system. Ambient temperatures drastically reduce the effectiveness of flat plate solar collectors, cooling the liquids inside before the heat can be efficiently consumed. In contrast, an evacuated tube collector maintains efficiency during such conditions. The collectors are insulated from ambient temperatures by the vacuum pressure inside the tube. A stainless steel flat plate heat exchanger is used to transfer the heat from the glycol/water solution to the refrigerant, which is sent to the turbine after it has been converted to its gaseous state. The solution also provides freeze protection in colder climates. A heat exchanger then cools the gas, returning it to its liquid state, which completes the cycle for the working fluid. The water used in the heat exchanger is then used as a supplementary heating source for the home, for domestic or radiant heating needs. As it is effective even in environments that compromise the functionality of existing PV systems, the proposed system responds effectively to the need for more efficient alternative energy sources.
Modeling and Experimental Characterization of a Permanent Magnet Linear Alternator for Free-Piston Engine Applications
Authors: Aichlmayr Hans T. , Van Blarigan Peter
Published: October 2010

Sandia National Laboratories is developing a prototype 30kW free-piston internal-combustion-based linear generator for vehicular applications. This paper describes the development and experimental validation of a mathematical model for the permanent magnet linear alternator that will be used by the prototype. A magnetic-flux versus mover-position function is used to correlate individual coil fluxes to the motion of the mover. This function is derived from a finite element electromagnetic simulation of the linear alternator. The mathematical model of the alternator is compared to experiments with prototype hardware driving 0.5–2kW loads; excellent correspondence to measured voltage and current waveforms is found.
Investigation Into the Effects of Reaction Duration on the Isothermal Fast Pyrolysis of Biomass
Authors: Mayor J. Rhett , Williams Alexander
Published: October 2010

Bio-oils were produced within a fast-pyrolysis micro-reactor at 400°C from Loblolly Pine (Pinus Taeda) with varying residence times. This preliminary study has considered two boundary values for the residence time, evaluating the products of the reaction at 20 seconds and 120 seconds. The collected bio-oils were analyzed for their calorific values (LHV) and biomass conversion efficiencies. Heating rates greater than 100°C/s were achieved for the biomass, allowing for isothermal conditions to exist throughout the majority of the reaction despite short residence times. This study shows the effect that reaction duration has on the mass of the bio-oil yield and energy content present for the isothermal fast pyrolysis of Loblolly Pine and evaluates the predictive capabilities of TGA derived Arrhenius coefficients.