bluuebunny/crossref_metadata_2025 huggingface dataset:
Optimal Control of Solar Heating and Off-Peak Energy Storage Installations
Authors: Winn G. B. , Winn R. C.
Published: January 2010

It is well known that the widespread use of solar heating or cooling systems could lead to an increase in the cost of supply of power by the electric utilities. However, it is also recognized that by using appropriate control strategies in these systems the cost of supply may be reduced relative to that of electric resistance heating systems. Control strategies for solar heating systems and for off-peak heat storage systems have been developed and investigated in terms of utility cost of supply for the year 1990. This paper includes a discussion of results obtained for off-peak storage systems, solar heating systems, and combined solar and off-peak systems for the area served by Public Service Co. of New Mexico.
Performance Benefits of the Direct Generation of Steam in Line-Focus Solar Collectors
Authors: May E. K. , Murphy L. M.
Published: January 2010

The performance benefits of the direct (in situ) generation of steam in the receiver tube of a line-focus solar collector are assessed in this paper. Compared to existing technology using steam-flash or unfired boiler systems, the in situ technique could reduce the delivered cost of steam in excess of 25 percent. The analysis indicates that two-phase flow instabilities, if present, can be readily controlled, and that the possibility of freezing is not an impediment to the use of water in cold climates.
Exergy Analysis for the Performance of Solar Collectors
Authors: Fujiwara M.
Published: January 2010

The optimum control and performance evaluation of solar collectors are analyzed from the standpoint of exergy. The pressure drop inside the collector is introduced to the analysis using the Hottel-Whillier model. By treating the friction process as exergy loss, the optimum operating conditions are presented in a simple statement. The maximum capability of collectors is determined and expressed by a relationship among the collector parameters and the environment in which they operates.
Methodology to Determine Cost and Performance Goals for Active Solar Cooling Systems
Authors: Warren M. L. , Wahlig M.
Published: January 2010

Economic and thermal performance analyses of typical residential and commercial active solar cooling systems are used to determine cost goals for systems to be installed between the years 1986 and 2000. Market penetration for heating, ventilating, and air conditioning systems depends on payback period, which is related to the expected real return on investment. Postulating a market share for solar cooling systems increasing to 20 percent by the year 2000, payback and return on onvestment goals as a function of year of purchase are established. The incremental solar system cost goal must be equal to or less than the 20-year present value of future energy savings, based on thermal performance analysis, at the desired return on investment. Methods for achieving these cost goals and expected solar cooling system costs will be discussed.
The Effects of Temperature Settings on Cycling Rates for Bang-Bang Controllers
Authors: Winn C. B.
Published: January 2010

An analytical method for determining the effects of temperature differentials on cycling rates for a bang-bang controller in a solar collector loop is presented. The method is an extension of previously published numerical results. The collector thermal capacitance is included in the analysis.
Analysis of a Combined Thermal-Photovoltaic Solar System Based on the Spherical Reflector/Tracking Absorber Concentrator
Authors: Bar-Lev A. , Waks S. , Grossman G.
Published: January 2010

The Stationary Reflector/Tracking Absorber (SRTA) solar system, which has been described and used in the past for heat and steam generation, is analyzed with the aim of combining with it photovoltaic (PV) generation. The light concentration function along a finite size absorber is calculated. The areas of the absorber which may be unilluminated during parts of the day are determined. It is shown that for a system to be useful for PV generation, the absorber must turn one side toward the outside perimeter of the reflector while tracking, and its diameter must increase with the distance from the reflector. A special two-section polygonal cone is shown to give an approximately constant light concentration along most of its length, and can therefore be used with an array of solar cells of one type only. Such a design also contributes to an incidence angle of the reflected light rays on the absorber surface that is closer to normal than with a cylindrical shape. It is also shown that the length of a real absorber is always shorter than that of an ideal line absorber of zero radius, and that only about 50 percent of the area should be covered with cells, with the rest to be used for thermal absorption and heat generation only.
Dust Storm Simulation for Accelerated Life Testing of Solar Collector Mirrors
Authors: Bethea R. M. , Collier E. G. , Reichert J. D.
Published: January 2010

A dust storm simulation chamber has been designed based on worst-case conditions to simulate the effects of blowing dust and sand on candidate solar concentrator materials. After evaluation with common glass mirrors, the system was used to simulate field exposure of Carolina glass mirrors in the West Texas environment in terms of loss of reflectivity. System calibration was achieved by comparing actual exposure data over a three-year period to results obtained in the simulation chamber. It was found that a twenty-year service life can be simulated by 80 hrs. exposure in the dust storm chamber. Degradation of the Carolina glass mirrors has been shown to be primarily dependent on momentum transport to and kinetic energy deposition on the mirror surface during dust storms: annual reflectivity losses of 2.4 percent and 1.4 percent may be expected, respectively, from dust storm and the sum of all other effects.
Effects of Friction and Extraction on the Stability of Solar Ponds
Authors: Cha Y. S. , Sha W. T. , Soo S. L.
Published: January 2010

Experimental results were compared to theoretical stability criteria of a salt gradient solar pond. Cellular motion in the nonconvective layer may be caused by instablity. Extension of stability criteria suggests use of stabilizing barriers via friction. Stability of longitudinal extraction assures optimum availability of energy from a solar pond.
Design and Testing of a Plastic Bubble-Film Covered Shallow Solar Pond
Authors: Forbes R. E.
Published: January 2010

A shallow solar pond was designed from inexpensive plastic materials and tested during the summer months. The bag containing the water consisted of a black polyethylene bottom (1.5 mil) covered with a clear polyvinylchloride top (4 mil) and a layer of polyethylene bubble-film on the top of the PVC bag. The bubble-film material is of the type commonly used for protection of breakable goods during shipment. The bubble-film material provided an inexpensive and effective upper glazing for the bag assembly. The bag was insulated from bottom losses by placing it on a 2.22-cm (0.875-in.)-thick layer of polystyrene foam. Tests were performed during May, June, and July 1980. These tests were performed by batch-filling the bag in the morning with a measured quantity of water and measuring the temperature rise of the water during the day. Measurement of water quantity, initial temperature, final temperature, and total incident radiation allowed for calculation of a daily efficiency for the pond. Tests were made for water depths of 5.2 and 10.2 cm (2.05 and 4 in.). Maximum daily efficiencies of up to 63 percent were recorded during the testing. Daily efficiency was determined by dividing the total daily heat collection of the pond by the total radiation incident on the pond for the day. Maximum water temperature of 67°C (152°F) was reached during the testing program. Temperature rise in the pond assembly was typically on the order of 33–39°C (60–70°F) during clear days.
Size Effects in DAWT Innovative Wind Energy System Design
Authors: Foreman K. M.
Published: January 2010

By means of a case study, we examine the effect of size on the estimated weight and cost of an advanced wind energy conversion system, the diffuser-augmented wind turbine (DAWT) concept. Preliminary designs are described for three DAWT sizes (ratings) in each of three construction approaches: all-aluminum, ferrocement, and a hybrid fiberglass reinforced plastics (FRP) diffuser shell on an aluminum frame. Common design criteria are employed in designs for these three materials. Installed cost estimates are generated by professional industrial estimators. Excluding the foundation, it is concluded that for geometrically similar DAWTs the weight-to-power ratio varies approximately as the rotor diameter to the one third power, over a 4 to 1 change in rotor diameter, 2.7–11 m (9–36 ft). Futhermore, because the total direct production cost of these various DAWT units and designs proves to change by about D1.5, the cost-to-power ratio is approximately proportional to D−.5 and the cost/weight ratio varies as D−1/6. Therefore, for the investigated DAWT unit ratings between 5 and 200 kW, the larger units appear increasingly to become more efficient structures with apparently lower specific costs (dollars per kW) for each of three candidate construction approaches.
Experimental Performance Characterization of Line-Focus Collectors
Authors: Lukens L. L.
Published: January 2010

To be able to predict accurately the performance of a specific solar collector in a given environment, its performance must first be characterized over the range of conditions under which the collector is expected to operate. In the present paper, collector performance models are developed for parabolic trough and compound-parabolic type concentrating collectors. Experimental collector performance data from Sandia National Laboratories, Albuquerque, New Mexico and Wyle Laboratories, Huntsville, Alabama are used in a multiple linear regression analysis to identify significant independent variables and refine the collector performance models. The refined collector performance models are used to characterize performance of three different parabolic trough collectors and two different compound-parabolic collectors, with good correlations between modeled and experimental performance.
A TRNSYS/GROCS Simulation of the TECH House I Ground-Coupled Series Solar-Assisted Heat Pump System
Authors: Roeder D. J. , Reid R. L.
Published: January 2010

The series solar-assisted heat pump heating system with ground-coupled storage in The University of Tennessee’s TECH House I in Knoxville, Tennessee, has been modeled using TRNSYS/GROCS and was compared to the experimental performance for the 1980–81 heating season. The simulation results were within 8 percent of the experimental measurements. Both simulation and experimental results showed that ground coupling of thermal storage led to the elimination of electric resistance backup heat and a large reduction in the peak heating demand of the house. Results of a parametric study showed that, in general, a ground-coupled storage tank performs better than a storage tank placed outdoors in the Knoxville area. Application of a next generation heat pump resulted in the most significant impact on the seasonal performance factor. As expected, higher performance collectors and larger collector areas led to higher system seasonal performance. An economic analysis showed that the series solar heat pump system cannot economically compete with the stand-alone heat pump system in the Knoxville area.
Internal Force and Moment Transmission in a Cardan Joint With Manufacturing Tolerances
Authors: Fischer I. S. , Freudenstein F.
Published: January 2010

The literature on the internal forces in Cardan joints, which is sparse, tacitly assumes the vanishing of certain force components. For a joint of ideal proportions the torque transmission has been analyzed, but the force transmission has been only partially developed. In this investigation the displacement analysis and static force and torque analysis of a Cardan joint with manufacturing tolerances has been derived. The forces have been shown to be statically indeterminate by a degree of three. An experiment was undertaken to check on the validity of the assumed vanishing of the abovementioned force components. For the particular joint tests this assumption was not valid. Based on the displacement analysis, which includes the axial sliding at the joints in the presence of manufacturing errors, optimum tolerances can be determined in the design stage. Further experimentation is recommended in order to determine representative magnitudes of the abovementioned axial joint forces in joints of varying constructions and sizes. Together with the static analysis which has been developed in this investigation this will permit the sizing of universal joints in the design stage.
On the Elimination of the Branching Problem in the Synthesis of Spatial Motion Generators with Spheric Joints. Part 2: Application
Authors: Sandor G. N. , Zhuang Xirong
Published: January 2010

The theory for elimination of the branching problem described in Part 1 is applied to the synthesis of spatial motion generators with at least one spheric joint. The techniques are illustrated with numerical examples of the synthesis of an RSSR-SC motion generator mechanism for three and four prescribed finitely separated positions, using methods developed earlier by the authors [2, 3].
Kinematic Structure of Mechanisms for Fixed and Variable-Stroke Axial-Piston Reciprocating Machines
Authors: Freudenstein F. , Maki E. R.
Published: January 2010

The creation of mechanisms according to the separation of kinematic structure and function has been carried out for a class of three-dimensional mechanisms suitable for conversion between rotary and reciprocating motion in axial engines, pumps and compressors. The structural and kinematic classification of such mechanisms has been established and a suitable search specification formulated with its aid. The resulting search has yielded fifty linkage configurations which have been determined to be possible candidates for such motions. These have four links, one degree-of-freedom and incorporate rotary, sliding, cylindrical, ball, and plane joints. Eleven of these linkages show sufficient promise to be considered for additional evaluation. Several of the linkages have a double-frequency motion of the floating link which would be suitable for a swash-plate drive. These linkages appear to be particularly promising because the double-frequency motion would reduce the stroke and swash-plate speed by one-half compared to a conventional swash-plate drive of the same displacement.
Efficient Computation of Band Saw Blade Stresses
Authors: Borchelt J. E. , Ulsoy A. Galip , Papalambros P.
Published: January 2010

The stresses in a band saw blade are difficult to measure, and are known to be significant for band sawing performance. This paper presents an approximate solution method, using the principle of minimum potential energy, for computation of blade stresses in band sawing. The method presented accounts for effects typical of bandsawing such as velocity-dependent blade tension, thermal gradients, and cutting forces. A program based on the method presented is shown to be accurate and computationally efficient when compared to a standard finite element program. This stress analysis program, together with a previous program for blade vibration analysis, can form the modeling basis for design and process optimization studies in band sawing.
Computer-Aided Methods for Development of Transition Sections
Authors: Dhande S. G. , Ramulu P. B.
Published: January 2010

Transition sections are the ducting surfaces used to connect two pipes of dissimilar shapes and sizes. The two pipes to be connected may not be coaxial. In the present paper, an algorithm has been developed so as to obtain the development view of a transition section defined in terms of the geometry of its boundary curves. Also presented in the paper is an algorithm for specifying the coordinates of the vertices of the developed polygon with reference to a coordinate system defined by means of the optimal encasing rectangle of the polygon. Based on the algorithms discussed, two computer programs using a graphics package have been developed. Results of two illustrative examples have been presented and discussed.
Shape Optimal Design of an Engine Connecting Rod
Authors: Yoo Y. M. , Haug E. J. , Choi K. K.
Published: January 2010

Shape optimal design of an engine connecting rod for minimum weight is presented, subject to upper and lower bound constraints on principal stresses. A two-dimensional plane stress model with multiple external loads is used to determine optimum boundary shape and thickness distribution. The variational equations of elasticity, the material derivative idea of continuum mechanics, and an adjoint variable technique are employed to calculate shape design sensitivities of stress. A 20-percent weight reduction is achieved in the neck region of the connecting rod, with reasonable computation cost. The method, combined with a steepest descent optimization method, is shown to be stable and applicable to broad classes of elastic structural shape optimization problems.
Synthesis of Planar Linkages That Contain Guiding Tracks
Authors: Singh Yesh P.
Published: January 2010

In this paper synthesis procedures are developed for planar cam-link mechanisms for exact generation of arbitrary specified motion and arbitrary specified path with coordinated crank rotation specifications. Complex-number loop-closure method is used for determining the position of links and tracks. Equations of the tracks are derived in general and parametric form. Then the envelope theory is used for determining the follower contact points on the tracks. A numerical example, Table 1, is also presented for illustration.
Optimum Design of Internal Strain-Gage Balances: An Example of Three-Dimensional Shape Optimization
Authors: Hou J. W. , Twu S. L.
Published: January 2010

Internal strain-gage balances are often applied to measure the aerodynamic loads acting on the aircraft model in the wind-tunnel test. The balance system consists essentially of one main body and two shoulders elastically interconnected by multibar cages. Designing the cross-sectional geometry of such a multibar cage balance to improve the accuracy of load measurement is an important task for a balance engineer. The study presents an initial attempt to carry out such a design task in a systematic and automated manner. This is achieved by considering two aspects. One is to establish a mathematical model to analyze the stress distribution in the elastic cage and the other is to adopt a three-dimensional shape optimization scheme to design the cross-sectional geometry of the internal strain-gage balance. The design procedure has been completely automated in a computer program. Numerical examples shows that the proposed numerical scheme performs very well.
The Generalized Transmission Error of Spiral Bevel Gears
Authors: Mark W. D.
Published: January 2010

The traditional definition of the transmission error of parallel-axis gear pairs is reviewed and shown to be unsuitable for characterizing the deviation from conjugate action of bevel gear pairs for vibration excitation characterization purposes. This situation is rectified by generalizing the concept of the transmission error of parallel-axis gears to a three-component transmission error for spiral bevel gears of nominal spherical involute design. A general relationship is derived which expresses the contributions to the three-component transmission error from each gear of a meshing spiral bevel pair as a linear transformation of the six coordinates that describe the deviation of the shaft centerline position of each gear of the pair from the position of its rigid perfect involute counterpart.
Toward a More Exact Kinematics of Roller Chain Drives
Authors: Chen C.-K. , Freudenstein F.
Published: January 2010

A kinematic analysis has been developed for the motion of roller chain drives, which is exact for relatively slow-speed chain drives with negligible wear. The results shed new light on chordal or polygonal action, and the associated impact velocity and motion fluctuation of the chain drive. The results have also revealed the existence of a remarkable degree of sensitivity of chain performance with respect to center distance including discontinuities in the motion derivatives. This in turn provides a new opportunity for the optimization of chain drives by optimizing center distance both in the design stage, as well as during installation and maintenance.
Assessment of Generic Solar Thermal Systems for Large Power Applications
Authors: Apley W. J. , Bird S. P.
Published: January 2010

A comparative analysis of generic solar thermal conversion configurations was performed to evaluate and rank the principal concepts under consideration in the DOE Solar Thermal Power Program. Year-long performance simulations were conducted for the 50- to 200-MWe systems using Barstow, California meteorological and insolation data. Multiattributable utility methodology was used to rank the eleven concepts.
A Reciprocating Solar-Heated Engine Utilizing Direct Absorption by Small Particles
Authors: Hull P. G. , Hunt A. J.
Published: January 2010

A new type of reciprocating solar engine utilizing small particles to absorb concentrated sunlight directly within the cylinders is described. The engine operates by drawing an air-particle mixture into the cylinder, compressing the mixture, opening an optical valve to allow concentrated sunlight to enter through a window in the top of the cylinder head, absorbing the solar flux with the particles, and converting the heat trapped by the air-particle mixture into mechanical energy with the downward stroke of piston. It differs from other gas driven heat engines using solar energy in three main respects. First, the radiant flux is deposited directly in the working fluid inside the cylinder; second, the heat is directed to the appropriate cylinder by controlling the solar flux by an optical system; third, the gas is heated during a significant portion of the compression stroke. The thermodynamic efficiency of the engine is calculated using an analytical model and is compared to several other engine cycles of interest.
The Effect of Concentrator Field Layout on the Performance of Point-Focus Distributed Receiver Systems
Authors: Pons R. L. , Dugan A. F.
Published: January 2010

The effect of concentrator field layout on the technical-economic performance of a point-focusing distributed receiver (PFDR) solar thermal power plant is presented. The plant design is based on the small community prototype system currently under development by Ford Aerospace for JPL/DOE; parabolic dish concentrators are employed and small heat engines are used to generate electricity at each dish. The effect of field size, array proportions, dish-to-dish spacing and packing fraction (concentrator-land area ratio) are presented for typical PFDR layouts. Economic analyses are carried out to determine optimum packing fraction as a function of site cost.
Instantaneous Flux Distribution on a Solar Central Receiver
Authors: Vant-Hull L. L.
Published: January 2010

An important aspect in the design of a Solar Central Receiver system is the distribution of the solar flux on the receiver. In this paper, we present information for the Central Receiver Pilot Plant, Solar One, at Barstow, California, on the time variation of the receiver flux during cloud passage, at sunrise and during the day.
The Effects of Unbalanced Flow on the Thermal Performance of Collector Arrays
Authors: Culham R. , Sauer P.
Published: January 2010

This paper details a mathematical model and a computer program that were developed to examine the effects of a flow imbalance on the total solar energy gain of a collector array. The model allows for variation in collector geometry, array geometry, collector flow rate, and collector inlet temperature, as well as fluctuations in ambient temperature and incident solar radiation. The program calculates the collector plate temperature, the heat removal factor, the collector heat loss coefficient, and the solar energy collected. The program is written in the BASIC language. It is iterative and uses the collector plate temperature as its test for convergence. The significance of a flow imbalance is explored by a systematic variation of the above parameters. Results indicate a relatively minor penalty for an unbalanced system, provided none of the rows in the array stagnate.
Weather Sensitivity Analysis of Solar-Assisted Heat Pump Systems
Authors: Ucar M. , Mittur S.
Published: January 2010

In the scientific literature, various weather models have been proposed and used for the simulation of solar thermal systems. The problem of the sensitivity of solar thermal systems to random fluctuations and persistent patterns in weather have been a source of concern and discussion for a long time. A general solution to this problem has proved to be elusive. This paper presents the results of weather sensitivity analyses performed on solar-assisted heat pump systems used in large buildings. The type of systems modeled usually incorporate relatively small collector areas (approximately equal to 5 to 15 percent of the building floor area). A detailed computer program was used for conducting hour-by-hour, zone-by-zone simulations of the buildings and the energy systems. Truncated Fourier series were used to represent weather data. It is concluded that various unusual weather sequences and perturbations do not affect the long-term energy consumption of the building so long as the average value of these variations is constant. Short-term energy consumption was found to be much more sensitive to these variations. It was also found that a uniform change in the average value of the weather functions, does, in fact, substantially influence building energy use.
Performance of the Heat Exchangers of a 100-kW (Gross) OTEC Plant
Authors: Mochida Y. , Kawano S. , Takahata T. , Miyoshi M.
Published: January 2010

A power-generating test of the world’s largest (100-kW gross power) ocean thermal energy conversion (OTEC) demonstration plant was conducted from October through December 1981 in the Republic of Nauru in the central Pacific Ocean. Fluorocarbon-22 was selected as a working fluid. During the power-generating test, a maximum gross power output of 120-kW (31.5-kW net) was achieved. Continuous operation was maintained for ten days. This plant verified the results of various development tests that were conducted by the authors on the heat exchangers. The evaporator is a horizontal, shell-and-tube, pool-boiler with the titanium tubes enhanced by a flame-sprayed, porous copper coating on the outside. The condenser is a vertical shell-and-tube type with the titanium tubes fluted on the outside (working-fluid side). Overall heat transfer coefficients of approximately 4300 and 3000 W/m2K for the evaporator and condenser, respectively, were achieved at the seawater design velocity of 2 m/s.
Prediction of Long-Term Performance of Active Solar Heating Systems Using Daily Hours of Bright Sunshine
Authors: Nguyen C. T. , Galanis N.
Published: January 2010

An algorithm based on daily hours of bright sunshine has been developed and used to evaluate the performance of active solar heating systems for different values of system parameters (collector area and efficiency curves; orientation and inclination; storage capacity; heating load). Comparisons of monthly and annual results with those obtained by other methods using measured values of global horizontal radiation show good results. The results were used to construct charts (for southern Que´bec in this case) which do not require values of solar radiation for the prediction of the system’s performance.
Two-Dimensional Mathematical Model of Evacuated Tubular Solar Collector
Authors: Rahman F. , Al-Zakri A. S. , Rahman M. A. A.
Published: January 2010

Analysis of an evacuated tubular solar collector is presented by developing a two-dimensional performance model. The collector uses a thin flat plate spanning its diameter as its absorbing surface. Energy balances are made on collector plate and tube, each considered as a separate unit. It has been found that a zero capacitance model is quite adequate when hourly meteorological data are used, and hence in this study steady state analysis of the collector is made [1]. The overall loss coefficient has been assumed to be constant for the whole plate. The model also includes optical effects. The emphasis of the investigation is to study the two-dimensional effects in the absorber plate housed in evacuated glass cylinders. Performance curves obtained from the two-dimensional model has been compared with that of HW model. It was found that the HW model overestimates the performance.
Utilization of Solar Energy for Sludge Drying Beds
Authors: El-Ariny A. S. , Miller H. I.
Published: January 2010

The present work is aimed to assess experimentally solar heated sludge drying beds located in the New Orleans, Louisiana metropolitan area with an appropriately sized solar system designed to operate on a fiberglass-covered drying bed. Another open drying bed was left without solar heating for comparative purposes. Five experimental runs were conducted over a one-year period to account for all weather conditions utilizing aerobically digested waste activated sludge. Compared to conventional beds, the solar beds achieved an average reduction of 50 percent in the drying period required to obtain a total solids concentration of 30 percent and an average reduction of 60 percent in the drying period of sludge to reach a total solids concentration of 60 percent. Sludge of total solids content of more than 90 percent was produced in an average period of 20 days under the solar drying process. System energy effects and economic analysis were also discussed.
Proportional Versus On/Off Control: A Detailed Comparison
Authors: Naumann P. , Wolfson R.
Published: January 2010

Through a series of single-day experiments, we have compared in detail the performance of on/off and proportional control strategies for solar hot water systems. The experiments encompass a variety of meteorological conditions, and include start-up with both warm and cool storage tanks. Insolation, tank temperatures, and pump energy use are monitored nearly continuosly throughout the day. Results show a consistent advantage in thermal energy gain for proportional control, especially under conditions of low or variable insolation, although proportional control requires considerably more parasitic pumping energy under these conditions.
Effect of Thermal Buoyancy on the Recirculating Flow in a Solar Pond for Energy Extraction and Heat Rejection
Authors: Cha C. K. , Jaluria Y.
Published: January 2010

An analytical and numerical study is carried out to determine the effect of buoyancy, resulting from temperature differences, on the recirculating flow arising in enclosed regions, such as the surface and storage layers of a salt-gradient solar pond, due to the discharge of fluid into it. The study investigates the time-dependent flow, considering an initially isothermal or thermally stratified fluid region, and the approach to the steady-state circumstance. Various flow configurations and boundary conditions, of particular relevance to energy extraction and heat rejection in solar ponds, are considered. The governing parameters, particularly the buoyancy parameter, are varied to determine the dependence of the flow field on these. Both laminar and turbulent flow are considered and numerical results are obtained for the velocity and temperature fields in the pond. Several interesting features are observed, particularly the strong effect of thermal buoyancy on the flow in the range of physical variables of practical interest and the effect of the flow on the growth and decay of a stable thermal stratification in the enclosed region. The effect of a periodic heat input into the region is studied. The study also considers relevant one-dimensional steady and transient analytical models for the thermal field and results are presented to indicate the range of validity of such simple models. The results obtained are also compared with earlier numerical and experimental studies of this flow circumstance and a fairly good agreement is observed. The relevance of the work to practical solar ponds is also outlined.
Desiccant Cooling System Performance: A Simple Approach
Authors: Epstein M. , Grolmes M. , Davidson K. , Kosar D.
Published: January 2010

A simple algebraic model of wave motion arising in the adiabatic fixed-desiccant bed dehumidification of an air stream is applied to the prediction of the performance potential of a desiccant air conditioning system. The model is used to explain the increase in cooling system performance that has been realized through the use of mixed inert-desiccant material adsorption beds. The response of cooling system performance to changes in external process conditions is examined and conclusions are drawn relative to optimization of system characteristics.
Combined Conduction and Radiation Heat Transfer in Porous Materials Heated by Intense Solar Radiation
Authors: Matthews L. K. , Viskanta R. , Incropera F. P.
Published: January 2010

An analysis is presented to predict the heat transfer characteristics of a plane layer of a semitransparent, high-temperature, porous material which is irradiated by an intense solar flux. A transient, combined conduction and radiation heat transfer model, which is based on a two-flux approximation for the radiation, is used to predict the temperature distribution and heat transfer in the material. Numerical results have been obtained using thermophysical and radiative properties of zirconia as a typical material. The results show that radiation is an important mode of heat transfer, even when the opacity of the material is large (τL > 100). Radiation is the dominant mode of heat transfer in the front third of the material and comparable to conduction toward the back. The semitransparency and high single scattering albedo of the zirconia combine to produce a maximum temperature in the interior of the material.
A Low-Temperature Heat Storage System Utilizing Mixtures of Magnesium Salt Hydrates and Ammonium Nitrate
Authors: Vaccarino C. , Barbaccia A. , Frusteri F. , Galli G. , Maisano G.
Published: January 2010

The heat storage system based on mixtures of salt hydrates and anhydrous salts described in previous articles has been applied to Mg(NO3)2 • 6H2O and MgCl2 • 6H2O (alone or in eutectic mixtures), added with NH4NO3. Calorimetric measurements showed that in the temperature range 25–60° C, Mg(NO3)2 • 6H2O allows a Thermal Energy Storage (TES) capacity of about 56 kcal/kg (equivalent to 86 kcal/liter), which is slightly lower than the values previously recorded with ammonium alum. When the maximum temperature was lowered to 55° and to 50° C, in order to be closer to the peak-efficiency of commercial flat-plate collectors, the best results were obtained, respectively, with Mg(NO3)2 • 6H2O and with the eutectic mixture Mg(NO3)2 • 6H2O – MgCl2 • 6H2O, both added with NH4NO3. The mixtures of the aforementioned magnesium salts and ammonium nitrate do not show any significant efficiency reduction after many thermal cycles, and at the present stage of the research, they may be considered the most suitable for obtaining heat storages in the temperature range of commercial solar collectors.
Research Results for the Tornado Wind Energy System: Analysis and Conclusions
Authors: Jacobs E. W.
Published: January 2010

The Tornado Wind Energy System (TWES) concept utilizes a wind-driven vortex confined by a hollow tower to create a low-pressure core intended to serve as a turbine exhaust reservoir. The turbine inlet flow is provided by a separate ram air supply. Numerous experimental and analytical research efforts have investigated the potential of the TWES as a wind energy conversion system (WECS). The present paper summarizes and analyzes much of the research to date on the TWES. A simplified cost analysis incorporating these research results is also included. Based on these analyses, the TWES does not show any significant promise of improving on either the performance or the cost of energy attainable by conventional WECS. The prospects for achieving either a system power coefficient above 0.20 or a cost of energy less than $0.50/kWh (1979 dollars) appear to be poor.
Catalytic Steam Gasification of Biomass for Methanol and Methane Production
Authors: Mudge L. K. , Baker E. G. , Mitchell D. H. , Brown M. D.
Published: January 2010

The technical and economic feasibility of producing specific gas products by the catalytic gasification of biomass is presented in this paper. Active catalysts were developed for generation of synthesis gases from wood by steam gasification. A trimetallic catalyst, Ni-Co-Mo on silica-alumina doped with 2 wt% Na, was found to retain activity indefinitely for generation of a methanol synthesis gas from wood at 750° C (1380° F) and 100 kPa (1 atm) absolute pressure. Potassium carbonate was an effective catalyst for conversion of wood to synthesis gases and methane-rich gas and should be economically viable. Results of development studies at 1000 kPa (10 atm) absolute pressure are presented.
Analysis of Heat Transfer and Solar Radiation Absorption in an Irradiated Thin, Falling Molten Salt Film
Authors: Webb B. W. , Viskanta R.
Published: January 2010

A study was conducted to investigate the heat transfer characteristics of an irradiated, gravity-driven semitransparent fluid flowing over an opaque substrate. The physical model simulated is prototypical of cavity-type solar central receivers. Both absorption and emission in the fluid were considered, while scattering was neglected. The effects of model parameters such as substrate emissivity, fluid layer opacity, spectral nature of incident radiative flux, flow model, and fluid layer physical thickness were investigated. Results are presented for fluid mixed mean temperature and collector efficiency along the layer length in order to evaluate the performance of such systems.
Cost and Performance Goals for Commercial Active Solar Absorption Cooling Systems
Authors: Warren M. L. , Wahlig M.
Published: January 2010

Economic and thermal performance analysis is used to determine cost goals for typical commercial active solar cooling systems to be installed between the years 1986 and 2000. Market penetration for heating, ventilating, and air conditioning systems depends on payback period, which is related to the expected return on investment. Postulating a market share for solar cooling systems increasing to 20 percent by the year 2000, payback and return on investment goals as a function of year of purchase are established. The incremental solar system cost goals must be equal to or less than the 20-year percent value of future energy savings, based on thermal performance analysis, at the desired return on investment. The methodology is applied to determine the allowable incremental solar system cost for commercial-scale, 25-ton absorption cooling systems based on the thermal performance predicted by recent simulation analysis, Methods for achieving these cost goals and expected solar cooling system costs will be discussed.
Depth Sounding Diagnostic Measurements of Salt Gradient Solar Ponds
Authors: Newell T. A. , Hull J. R.
Published: January 2010

A recording depth sounding instrument has provided several different diagnostic measurements in the 1000 m2 Research Salt Gradient Solar Pond at Argonne National Laboratory. The sounder has been used to locate gradient zone boundaries and layers of debris within the pond. The instrument has also helped to verify that the presence of salt piles in the bottom of the pond has been responsible for automatically maintaining the constant position of the gradient zone lower boundary during the last three years. Subsurface waves have been observed at the bottom of the gradient zone near the pond side walls. The sounding instrument has also proved capable of identifying density driven plumes and turbulent disturbances within the pond.
Construction of a 100 kW Solar Thermal-Electric Experimental Plant
Authors: Boy-Marcotte J. L. , Dancette M. , Bliaux J. , Bacconnet E. , Malherbe J.
Published: January 2010

A focusing collector thermal-electric power plant has been erected in Corsica (France). This plant consists of a field of 1176 m2 fixed mirror concentrators, producing heat at 250° C, a stratification thermal energy storage of about 1250 kWh, two power conversion units of 45 kWe each, with a supersonic turbine expanding a heavy organic working fluid, and two cooling towers of 200 kW each. This full-scale prototype has been built mainly to demonstrate the capability of the distributed collector solar plant concept, in the power range from 50 kWe to 1000 kWe, and the temperature range from 150 to 300° C. This paper describes the conceptual design and the performance of the plant, and discusses problems that were met during construction.
Condensing Heat Transfer Enhancement on Vertical Spiral Double Fin Tubes With Drainage Gutters
Authors: Takazawa H. , Kajikawa T.
Published: January 2010

Spiral double-fin tubes with drainage gutters are proposed for a vertical condenser to achieve high-condensing heat transfer performance for ocean thermal energy conversion application. There aluminum tubes have 5 or 10 spiral primary fins per pitch of spiral drainage fin. The condensation occurs mainly on the 0.8-mm-high primary fins; the 2-mm-high drainage fin collects the condensate from the primary fins, and a vertical drainage gutter removes the condensate from the drainage fin. Thus performance degradation due to accumulation of condensate in the vertical direction is avoided. Experiments were carried out using R-22 (chlorodifluromethane) as the working fluid in a shell using seven aluminum tubes (900 mm in effective length and 20 mm in nominal diameter). The drainage fin pitch, the primary fin pitch, shape of primary fin, and number of drainage gutters per tube were selected as parameters. One of the tubes had a 0.2-mm-thick titanium cladding on the inside (water side). The measured working-fluid-side condensing heat transfer coefficients for these tubes were four to six times those for a smooth tube based on the outer surface area.
Improvement of the Performance of Solar Energy or Waste Heat Utilization Systems by Using Phase-Change Slurry as an Enhanced Heat-Transfer Storage Fluid
Authors: Kasza K. E. , Chen M. M.
Published: January 2010

This paper is concerned with the benefits of using phase-change slurries as enhanced heat-transfer/storage working fluids in solar energy and waste heat utilization systems. Literature is cited to show that a slurry containing a phase-change material as the dispersed phase promises to have much higher heat-transfer coefficients than conventional single-phase working fluids. Because of the latent heat, the phase-change slurry also requires lower pumping rates and smaller storage tanks than single-phase fluids for the same energy content. These benefits are documented by comparisons of temperature drops, pumping rates, pumping powers, and the sizes of storage tanks for a generic energy collection system operating with and without a slurry.
A Comparison of Three Years of Performance for Air-to-Air Parallel Solar Heat Pump System in TECH House IV
Authors: Reid R. L. , Bedinger A. F. G. , McGraw B. A.
Published: January 2010

A parallel solar augmented heat pump system has been experimentally evaluated in TECH House IV for three heating seasons between fall 1979 and spring 1982. Several changes were made in the operation of the system during the three year period. During 1979–1980, the use of on-peak purchased energy was minimized by charging the pebble bin in the off-peak period with a resistance duct heater. This configuration resulted in 83 percent of the purchased energy occurring in the off-peak period but the seasonal performance factor was only 1.61. During 1980–1981, the system was operated in the normal mode without the use of the off-peak heater. The seasonal performance factor then increased to 2.56. During 1981–1982, the mode of operation was the same as 1980–1981, but new outer cover sheets were installed and the inner cover sheet was eliminated resulting in a single glazed collector. The seasonal performance factor for the 1981–1982 season was measured to be 2.11.
Windmill Tip-Speed Ratio Regulation Using an Impedance-Matching Control System
Authors: Hendler J. , Flowers W. , Bell A.
Published: January 2010

A discussion of the approaches to, and benefits of, windmill tip-speed ratio (TSR) control is presented. Rotational speed regulation via load-controlled impedance matching is identified as the most efficient control method. An all-mechanical, self-powered windmill TSR controller using this method is presented with a discussion of its operation and wind tunnel test results. The controller, which is applicable to a variety of windmill/load combinations, also provides for rotor start-up and for shutdown in high winds. A design methodology is presented and used to design a controller for a windmill driving an electrical generator and for the same windmill driving a water pump. These designs are verified with a digital computer simulation using real wind data. The TSR controller regulated windmill speed for efficient operation at all wind speeds, limited only by the power rating of the windmill and load machinery. The simulation results also demonstrate the economic feasibility of the system.
Short-Term Performance of Integral Solar Water Heaters
Authors: Tully N.
Published: January 2010

The 8-hr daily test of solar integral or collector/storage domestic water heaters is considered. For the case of no draw-off, it is shown that a computer simulation gives results closely in agreement with an integral equation which involves the collector parameters, the total insolation and the daily temperation variation, but does not require the actual daily ambient temperature. The relationship of this test to integral unit performance when water is drawn off according to various demand patterns is investigated, and it is shown that the short-term efficiency is typically reduced to two thirds of the daily test result, but can be as low as one third. Thus a simple thermal test such as that specified by the South African Bureau of Standards, and other standards organizations, should at best be regarded as a comparison between various units of similar type, although even there the importance of optical efficiency is overemphasized. Simple tests do not provide a guide to performance in actual service.
An Analytic Model of Stratification for Liquid-Based Solar Systems
Authors: DenBraven K.
Published: January 2010

Accurate modelling of solar air or liquid heating, cooling, or domestic hot water systems with storage generally requires an accounting of the stratification within such storage. Overall system performance may be significantly affected by the storage temperature distribution. Most current stratification models utilize a finite difference scheme for solution to the general equations. An analytic method to determine the temperature distribution has been derived for liquid storage within a solar system. In liquid storage, it is assumed incoming fluid enters at the location with the temperature closest to its own. Hence, the solution requires the possibility of a region within storage where there is no forced flow. In addition, ther may be collector loop flow, load loop flow, or both concurrently. Each of these cases has different boundary conditions, and each must be solved separately. Comparisons of the resulting calculations with system data for the Colorado State University Solar House I show good agreement. This suggests that inclusion of an analytic stratification model within a system simulation may be useful by allowing direct calculation of temperatures in stratified storage.