bluuebunny/crossref_metadata_2025 huggingface dataset:
Experimental Data on a Solar-Powered Ice Maker Using Activated Carbon and Methanol Adsorption Pair
Authors: Pons M. , Grenier Ph.
Published: November 2009

The solar-powered ice maker has been described in a previous article [1]. The present article draws conclusions from experiments conducted on this prototype. Some specific effects appear: the end of desorption is delayed, a chimney effect takes place between collectors, and heat transfers within the collectors are pointed out. The experimental heat balances of each component are analyzed. First, the effective thermal loss coefficients of collectors are calculated in every configuration; their efficiencies lies betweeen 30 and 40 percent. But the nightly cooling is not as efficient as expected. Secondly, the heat transfer coefficient of condensers is very low. Thirdly, the evaporator is efficient and variations of evaporated flow-rate are presented. Supercooling is observed. Finally, the measured Net Solar C.O.P. is 0.12 when Qi is 22 MJ/m2 (a nice summer day in Paris) and 0.10 when Qi is 19 MJ/m2. In conclusion, major improvements are proposed.
Monthly-Averaged Cooling Load Calculations—Residential and Small Commercial Buildings
Authors: Bida M. , Kreider J. F.
Published: November 2009

A simplifed design method for estimating the sensible component of the cooling load of skin dominated buildings suitable for use on programmable calculators or microcomputers is developed. The method uses monthly averaged meteorological data to predict long term energy requirements for cooling using a semi-analytical model. Existing concepts such as variable base degree days and the monthly averaged solar utilizability are applied to the cooling problem. New solar utilizability correlations for multiple aperture solar collectors are used in conjunction with the variable base degree-day method to predict the sensible component of the cooling load for low mass structures. The effect of thermal mass present within the building is then incorporated through the use of an empirical model developed in this work. The method predicts annual cooling loads with an average error of 10 percent with respect to an hourly simulation computer program.
Accurate Correlation of Wind Turbine Response With Wind Speed Using a New Characterization of Turbulent Wind
Authors: Connell J. R. , George R. L.
Published: November 2009

The turbulence encountered by a point on a rotating wind turbine blade has characteristics that in some important respects are different from those measured by a stationary anemometer. The conventional one-peaked continuous spectrum becomes, broadly, a two-peaked spectrum that in addition contains a set of narrowband spikes of turbulence energy, one centered on the frequency of rotor rotation and the others centered on multiples of that frequency. The rotational sampling effect on wind spectra is quantified using measurements of wind velocity by anemometers on stationary crosswind circular arrays. Characteristics of fluctuating wind are compared to measured fluctuations of bending moments of the rotor blades and power output fluctuations of a horizontal-axis wind turbine at the same site. The wind characteristics and the correlations between wind fluctuations and wind turbine fluctuations provide a basis for improving turbine design, siting, and control.
Application of a Monte Carlo Optimization Technique to a Cluster of Wind Turbines
Authors: Crosby P. A.
Published: November 2009

An optimization process based on Monte Carlo sampling of the variables of the objective function is developed. The technique is applied to a grouping of wind turbine generators. The permissible dimensions of the wind turbines and the range of spacing between adjacent machines allows a search for a maximum profit over a wide mix of system configurations. The computer program for the optimization algorithm finds cluster configurations for maximum profit with a high degree of certainty for the relatively simple cost and design constraints used in the model.
Application of Exergy Concept to the Analysis of Optimum Operating Conditions of Solar Heat Collectors
Authors: Suzuki A. , Okamura H. , Oshida I.
Published: November 2009

A linear model was developed to obtain the relationships between the characteristic temperatures of the solar heat collector (e.g., the fluid outlet temperature) and the heat capacitance rate of the heat transfer medium. Combining these relationships and the exergy concept, we derived the optimum operating conditions in a general form to satisfy the requirements for the optimum outlet temperature. The optimum operating conditions can be used as a criterion when an appropriate collector type must be chosen for any particular solar application system. To confirm the analytical results, experiments were carried out with a simple flat-plate type solar collector. Good agreement could be obtained between the theoretical values and the experimental results.
Ultra-Fast Biomass Pyrolysis in a High-Temperature (2200° C), Fluid-Wall Reactor
Authors: Corella J. , Monzon A. , Santamaria J. , Gonza´lez-Can˜ibano J.
Published: November 2009

The pyrolysis of pine sawdust has been carried out in a High-Temperature Fluid-Wall Reactor. This unit has been specially designed to withstand working temperatures of up to 2200° C. The biomass is fed to the top of the reactor after sieving to the appropriate size, at a rate of 1.0 to 1.8 kg/min. The feed falls and, at the same time is very quickly heated by radiation to the reaction temperature. The estimated heating rate is on the order of 106° C/s for reactant surfaces. The fluid-wall, produced by a nitrogen flow through the 30 cm diameter porous reactor core, prevents both reactants and products from reaching the reactor wall. The product distribution at the reactor exit has been determined for different operating conditions. The influence of reactor temperature, biomass feed rate, and biomass particle size on the product distribution and on the heating value of the exit gas has been investigated.
Double-Diffusive Fluxes in a Salt Gradient Solar Pond
Authors: Atkinson J. F. , Adams E. Eric , Harleman D. R. F.
Published: November 2009

The possible influence of double-diffusive stratification on the vertical transport of salt and heat in a mixed-layer simulation model for a salt gradient solar pond is examined. The study is concerned primarily with the interfacial fluxes across the boundary between the gradient zone and upper convecting zone of solar ponds, though the arguments presented should be applicable to other “diffusive” interfaces as well. In the absence of mechanical stirring in the upper convecting zone (e.g., by wind), double diffusive instabilities could govern the vertical flux of heat and salt by adjusting interfacial gradients of temperature and salinity which control transport by molecular diffusion. Because these gradients are generally too sharp to be resolved by numerical models, the fluxes can either be modeled directly or be parameterized by grid-dependent “effective diffusivities.” It is shown that when mechanical stirring is present in the mixed layer, double-diffusive instabilities will not be allowed to grow in the interfacial boundary layer region. Thus, double-diffusive fluxes become important only in the absence of stirring and, in effect, provide a lower bound to the fluxes that would be expected across the interface.
Second Law Analysis of Solid Desiccant Rotary Dehumidifiers
Authors: Van den Bulck E. , Klein S. A. , Mitchell J. W.
Published: November 2009

This paper presents a second law analysis of solid desiccant rotary dehumidifiers. The equations for entropy generation for adiabatic flow of humid air over a solid desiccant are developed. The generation of entropy during operation of a rotary dehumidifier with infinite transfer coefficients is investigated and the various sources of irreversibility are identified and quantified. As they pass through the dehumidifier, both the process and regeneration air streams acquire nonuniform outlet states, and mixing both of these air streams to deliver homogeneous outlet streams is irreversible. Transfer of mass and energy between the regeneration air stream and the desiccant matrix occurs across finite differences in vapor pressure and temperature and these transfer processes generate entropy. The second law efficiency of the dehumidifier is given as a function of operating conditions and the effect of finite transfer coefficients for an actual dehumidifier is discussed. It is shown that operating the rotary dehumidifier at conditions that minimize regeneration energy also yields a local maximum for the second law efficiency.
Mixed Laminar Convection in Trombe Wall Channels
Authors: Chaturvedi S. K. , Mohieldin T. O. , Huang G. C.
Published: November 2009

The two-dimensional, steady, combined forced and natural convection in a vertical channel is investigated for the laminar regime. To simulate the Trombe wall channel geometry properly, horizontal inlet and exit segments have been added to the vertical channel. The vertical walls of the channel are maintained at constant but different temperatures while the horizontal walls are insulated. A finite difference method using up-wind differencing for the nonlinear convective terms, and central differencing for the second order derivatives, is employed to solve the governing differential equations for the mass, momentum, and energy balances. The solution is obtained for stream function, vorticity, and temperature as the dependent variables by an iterative technique known as successive substitution with overrelaxation. The flow and temperature patterns in the channel are obtained for Reynolds numbers and Grashof numbers ranging from 25 to 100 and 10,000 to 1,000,000, respectively. Both local and overall heat transfer coefficients are computed for the channel aspect ratio varying from 5 to 15. For a given value of Grashof number, as the Reynolds number is increased, the flow patterns in the vertical channel exhibit a change from natural convection like flow patterns in which a large recirculating region is formed in the vertical part of the channel, to a forced flow type pattern. This is also the case with isotherms. The size of the recirculating region in the channel increases with increasing value of Gr/Re2. At low Reynolds number, the stream function, and isotherms are qualitatively similar to those reported for the natural convection in rectangular slots.
The Design and Testing of a Molten Salt Steam Generator for Solar Application
Authors: Allman W. A. , Smith D. C. , Kakarala C. R.
Published: November 2009

This paper describes the design and testing of the Steam Generator Subsystem (SGS) for the Molten Salt Electric Experiment at Sandia Laboratories in Albuquerque, New Mexico. The Molten Salt Electric Experiment (MSEE) has been established at the Department of Energy’s five megawatt thermal Solar Central Receiver Test Facility, to demonstrate the feasibility of the molten salt central receiver concept. The experiment is capable of generating 0.75 megawatts of electric power from solar energy, with the capability of storing seven megawatt-hours of thermal energy. The steam generator subsystem transfers sensible heat from the solar-heated molten nitrate salt to produce steam to drive a conventional turbine. This paper discusses the design requirements dictated by the steam generator application and also reviews the process conditions. Details of each of the SGS components are given, featuring the aspects of the design and performance unique to the solar application. The paper concludes with a summary of the test results confirming the overall design of the subsystem.
Experiments and Analysis on the Molten Salt Direct Absorption Receiver Concept
Authors: Bohn M. S. , Wang K. Y.
Published: November 2009

This paper presents results of experiments on the Direct Absorption Receiver (DAR) concept using molten salt as the working fluid. The DAR concept may result in a solar central receiver that costs 50 percent less than the current tube receiver and has significantly lower operational and maintenance costs. These experiments were aimed at determining whether the DAR concept is technically feasible and were carried out at the Advanced Components Test Facility, Atlanta, GA. Results are based on several days of operating with solar flux ranging up to 50 W/cm2 and also on a numerical model that is capable of predicting the thermal performance of the DAR salt film. Issues relating to thermal efficiency, absorber-to-salt heat transfer, and salt film stability are addressed.
Parameter Estimation in Buildings: Methods for Dynamic Analysis of Measured Energy Use
Authors: Rabl A.
Published: November 2009

Dynamic analysis of energy data can help improve the efficiency of buildings in several ways: evaluation of proposed modifications of a building or its operation (e.g., changes in thermostate setpoints); verification of performance on the basis of short-term measurements (corrected for weather); diagnostics and optimal control of HVAC equipment (real-time comparison of actual and predicted performance can be a powerful diagnostic tool). For this purpose one would like a simple building model whose parameters can readily be adjusted by a statistical fit to the data. This paper reviews the available methods: thermal networks, modal analysis, differential equations, ARMA (autoregressive moving average) models, Fourier series, and calibrated computer simulations. The basic models can be applied in several ways, differing in choice of dependent variable, number of coefficients, statistical criterion, time step, finite differencing scheme, and implementation as linear or nonlinear algorithm. The relation between the various approaches is examined. It is shown how the results of each of these methods can be presented in a standardized format that maximizes their physical interpretation, in terms of time constants and admittances (including heat loss coefficient and solar aperture). A general proof is given that the effective heat capacity equals the heat loss coefficient multiplied by a sum of time constants. The methods are tested with data from an office building. Special attention is focused on difficulties, due to air exchange or solar gains, that are likely to arise in practice.
A Fundamental Equation for Exergy Balance on Solar Collectors
Authors: Suzuki Akio
Published: November 2009

This paper presents the exergy balance equation on a solar collector which acts as the fundamental and principal expression for the solar thermal design. The equation fully explains the exergy loss processes and can be used to derive the approximate optimum operating condition for solar collectors. Furthermore, using the equation, it can be shown that two different collectors, an evacuated tubular collector and a flat-plate collector, have both nearly equal capabilities in exergy gain despite large differences in technological efforts and expenses to produce them. In addition, ways for improvement for a solar collector are also discussed here briefly.
Thermally Regenerative Hydrogen/Oxygen Fuel Cell Power Cycles
Authors: Morehouse J. H.
Published: November 2009

Two thermodynamic power cycles are analytically examined for future engineering feasibility. These power cycles use a hydrogen-oxygen fuel cell for electrical energy production and use the thermal dissociation of water for regeneration of the hydrogen and oxygen. The first cycle uses a thermal energy input at over 2000K to thermally dissociate the water. The second cycle dissociates the water using an electrolyzer operating at high temperature (1300K) which receives both thermal and electrical energy as inputs. The results show that while the processes and devices of the 2000K thermal system exceed current technology limits, the high temperature electrolyzer system appears to be a state-of-the-art technology development, with the requirements for very high electrolyzer and fuel cell efficiencies seen as determining the feasibility of this system.
Transmittance of Distilled Water and Sodium-Chloride-Water Solutions
Authors: Kanayama K. , Baba H.
Published: November 2009

The spectral transmittance of pure water and salt water solutions of various concentrations, which are important for the thermal calculation of a solar pond, is measured experimentally for specimen thickness of 1 to 100 mm by means of an autorecording spectro-radiometer inside an air-conditioned room. On the basis of the measured spectral transmittance, the total transmittance of pure and salty waters to 3 m of water depth is calculated as a ratio of the total radiation energy over all wavelengths arriving at any depth from the water surface of the solar pond to the solar radiation incident upon the water surface with various air masses. According to Nielsens’ four-partition method, the effective absorption coefficient is calculated for each wavelength band. Lastly, the transmission properties obtained for pure water, i.e., spectral and total transmittances, absorption wavelength band, and effective absorption coefficient, are compared with past results, and those for salty water with various concentrations are compiled as basic data for the use of solar energy by a solar pond.
Performance Analysis of an Air Drier for a Liquid Dehumidifier Solar
Air Conditioning System
Authors: Queiroz A. G. , Orlando A. F. , Saboya F. E. M.
Published: November 2009

A model was developed for calculating the operating conditions of a non-adiabatic liquid dehumidifier used in solar air conditioning systems. In the experimental facility used for obtaining the data, air and triethylene glycol circulate countercurrently outside staggered copper tubes which are the filling of an absorption tower. Water flows inside the copper tubes, thus cooling the whole system and increasing the mass transfer potential for drying air. The methodology for calculating the mass transfer coefficient is based on the Merkel integral approach, taking into account the lowering of the water vapor pressure in equilibrium with the water glycol solution.
Mixing Depth of a Submerged, Horizontally Injected Buoyant Jet
Authors: Johnstone H. W. , Zangrando F.
Published: November 2009

Tests in the laboratory were conducted to determine the effective mixing depth of turbulent buoyant fluid injected horizontally into an initially unstratified environment through a radial, deeply submerged diffuser. The diffuser was moved slowly during the experiments, at a rate much smaller than the entrainment and mixing process. The effective mixing depth is defined as the relative position between the initial injector level and the lowest position of the resulting mixed layer over which the injected fluid is deposited. Results have applications to discharge of contaminants and heat into large reservoirs (sewage disposal, power plants, OTEC systems) and establishment of a stratified region as is required for operation of salt gradient solar ponds. A functional dependence between mixing depth, scaled by the injector slot size, and injector Froude number was found. Dependence on submergence was not found for the large submergence values tested; dependence on diffuser radius was not investigated. The laboratory data compare well with results obtained in a reservoir of 3355 m2 surface area and indicate a strong dependence of effective mixing depth on the Froude number.
Heat Exchanger Theory Applied to the Design of Water- and Air-Heating Flat-Plate Solar Collectors
Authors: Kowalski Gregory J. , Foster Arthur R.
Published: November 2009

A general method for the design of flat-plate solar collectors based on solar collector theory has been developed. It can be applied to both liquid- and air-heating solar collectors. The solar collector efficiency is determined by the product of the effectiveness (ε) and the insolation use factor (IUF). The effectiveness describes the heat transfer characteristics of the collector and is shown to be a function of a solar number of transfer units (SNTU) and a parameter ψ. For an air-heating collector, the ψ parameter equals the collector efficiency factor, while for a liquid-heating collector it must account for the difference between the plate and tube heat transfer areas. The effectiveness and SNTU parameters are similar to the effectiveness and NTU parameters used in heat exchanger design methods. The IUF is a measure of the operating conditions of the collector. It represents the difference between the transmittance-absorptance product and the ratio of the minimum heat loss to the insolation on the exterior cover. The relationship between the effectiveness and the SNTU parameter is general for all nonconcentrating collectors. One advantage of this method over the traditional Hottel-Whillier method is that it separates the heat transfer characteristics of the solar collector from its optical properties and the operating conditions.
Influence of Reynolds Number on Performance Modeling of Horizontal
Axis Wind Rotors
Authors: Musial W. D. , Cromack D. E.
Published: November 2009

This paper investigates the influence of Reynolds number on performance modeling of horizontal axis wind rotors. A procedure for accounting for Reynolds number effects on airfoil section models was developed and implemented for NACA 0012 and NACA 4415 profiles; both of these models is valid through angles of attack up to 90 deg and for Reynolds numbers ranging from 4 × 104 to 3 × 106. These models were incorporated into both a lifting line computer code, LL200R, adapted for this report. This enabled greater certainty to be obtained in evaluating theoretical performance codes with respect to actual data, as well as providing a means by which a parametric analysis of the relative effects of Re changes on rotor performance to be performed. The use of low Reynolds number section data was found to significantly lower the predicted values of power coefficient, particularly at off-design tip-speed-ratios. For symmetrical airfoils, this effect on performance was only significant for low tip-speed-ratios, while cambered airfoils were affected more uniformly at all operating conditions. Changes in performance were induced by parametric variations of wind speed, rotor scale, and rotor generating mode using the Reynolds number dependent section models. Results show that wind speed variations are more significant for smaller rotors at lower wind-speeds, and section models represented at only a single Reynolds number are more suitable for the analysis of constant RPM rotors.
Heat Transfer Analysis of a Finned Solar Air Heater
Authors: Issacci F. , Zvirin Y. , Grossman G.
Published: November 2009

A theoretical method is presented for the investigation of a reflective fin solar air heater. The heat transfer processes include radiation in both the solar and IR spectra, mixed convection (forced and natural) in the air and conduction in the fins. The governing equations have been solved numerically to obtain the velocity and temperature fields in the developing and developed flow regions. The efficiency of the finned structure is then calculated, and the results of a parametric study are shown. It has been found that natural convection effects are significant and strong buoyancy leads to separation and reversed flow. The efficiency increases with lower surface emissivity and lower thermal conductivity of the fins.
Cost Drivers for Solar Thermal Central Receiver Power Plants
Authors: Brown D. R.
Published: November 2009

Studies completed at the Pacific Northwest Laboratory have allowed an in-depth examination of costs for solar thermal central receiver power plants. Central receiver concepts were evaluated for plant power ratings ranging from 0.5 to 100 MWe, and plant capacity factors ranging from 0.25 to 0.60. The large number of plant configurations considered necessitated the development of cost estimating models. Cost models were developed for concentrator, receiver, transport, storage, energy conversion, balance of plant, and O&M components. This paper presents a detailed discussion of costs for solar thermal central receiver power plants. Principal subcomponents and cost drivers are identified for each component. The impact of alternative design choices on cost and the tradeoffs involved between different working fluids are addressed. Cost uncertainties are examined qualitatively for each component. Finally, equations are presented for making preliminary estimates of direct capital and annual O&M costs for solar thermal central receiver systems.
Heat Pump Ground Coil Analysis With Thermal Interference
Authors: Mei V. C.
Published: November 2009

When two horizontal ground coils are buried in the same trench, one on top of the other, the total energy exchange between coils and ground increases drastically over that of a single coil for the same trench length. However, because of the thermal interference between the two coils, the overall performance of the two-coil trench is very difficult to determine. Traditionally this type of problem is handled by the line source mirror-image approach. However, in applying the line source approach, the strength of the source is not known precisely and must be estimated. Most designers will estimate this value very conservatively in order to be on the safe side, and this will result in a longer coil than is actually needed. This paper provides a detailed mathematical model to describe the operation of the two-coil system that can calculate more realistically the performance of the ground coils, which in turn could make the ground coil heat pump system more economically competitive with other heating and cooling systems. The effect of thermal interference is clearly shown in the calculated soil temperature profile. The effect of fluid inlet positions, from upper or lower coils, is also studied. The comparison of measured and calculated daily energy absorbed from the ground indicated a maximum error of 27 percent, with the average error at less than 12 percent, calculated values are on the conservative side. This model is better than the line source approach for calculating the performance of two coils in the same trench. It can be used for design purposes, or used to check such coil designs by other methods.
Thermal Performance Representation and Testing of Air Solar Collectors
Authors: Bernier M. A. , Plett E. G.
Published: November 2009

The thermal performance of a plate-type air collector was evaluated experimentally. Tests were performed at the two ASHRAE Standard 93-1986 recommended flowrates and at a variety of inlet gage pressures to cover the three possible cases of collector leakage (inward, outward, inward-outward). These tests show that the thermal performance of air collectors depends on flowrate and inlet gage pressure (or the associated leakage rate). If the collector is used at an inlet gage pressure near atmospheric pressure as is often the case in the no-storage type of systems, then it is recommended to test the collector at an inlet gage pressure of zero. For collectors operating at various inlet gage pressures it is suggested to test them at three inlet gage pressures. As for the test flowrate, the present work confirmed the results of other studies and emphasizes the need to test the collectors at the design flowrate. Three methods of thermal performance representation were used and compared: One method bases the efficiency on the inlet flowrate, another on the outlet flowrate, and the third involves an overall enthalpy balance. When plotted in the classic way, that is, η vs. (Ti − Ta)/G the three methods exhibit significant differences, especially for the inward leakage case. An uncertainty analysis on the data obtained for this study indicates that for the inward leakage case, unacceptable uncertainties occur at high values of (Ti − Ta)/G.
Analysis of a Wood-Fueled Trimburner System for Use in a Combined-Cycle, Wood-Fired Power Plant
Authors: Stephenson J. D. , Reistad G. M.
Published: November 2009

This paper investigates the use of wood to fuel a trimburner incorporated in a combined-cycle, wood-fired power plant. The trimburner is designed to boost the temperature of the air stream entering the gas turbine. Wood conversion processes capable of producing a clean synthetic fuel were investigated since direct wood combustion products are too “dirty” to be allowed to pass through the turbine blading. Of the three wood conversion processes considered (pyrolysis, gasification, methanol production), gasification was selected as the most applicable process for the trimburner concept. Three wood-fired trimburner systems employing an up-draft gasifier design were developed and simulated. These subsystems differ in the way the producer gas, formed in the gasifier, was compressed to the trimburner operating pressure. The effects of changing system variables, such as wood moisture content and gasifier air/fuel equivalence ratio, on the performance of the subsystems and the overall system were evaluated. It was determined that the most efficient operation of all the trimburner subsystems occurred at the lowest allowable operating gasifier equivalence ratio, about 0.275. Increasing the wood moisture content from 15 percent to 50 percent decreased the efficiency of the overall system about 3 percentage points, regardless of the specific trimburner system. At the usual wood moisture content of 50 percent, the best trimburner system, operating at the optimum equivalence ratio, increased the overall system performance about 8 percent (1.7 percentage points) relative to the equivalent metallic heat exchanger based system with no trimburner. The system that used air from the gas turbine compressor in a pressurized gasifier exhibited slightly superior performance (approximately 0.5 percentage points) relative to the system using the other trimburner designs. However, this performance superiority must be tempered since the pressurized gasifier system is more sensitive to the efficiency of the heat exchanger used to recover energy from the dirty producer gas.
Performance of a Solar Desiccant Cooling System
Authors: Lo¨f George O. G. , Cler Gerald , Brisbane Thomas
Published: November 2009

A solar desiccant cooling system was operated at the Solar Energy Applications Laboratory, Colorado State University, throughout the 1986 summer. The system comprises an American Solar King fresh air heating/desiccant evaporative cooling unit, a Sunmaster evacuated tube solar collector, hot water solar storage tank, auxiliary electric boiler, controls, and accessories. The cooling unit is operated in the ventilation mode, fresh air being dried in a rotating desiccant matrix, and cooled by heat exchange and evaporative cooling. Return air is used as a cooling medium in a rotating heat exchange matrix, heated by solar energy in a heat exchange coil, and discarded through the rotating desiccant bed. The solar-driven system provided over 90 percent of the seasonal cooling requirements in an experimental, residence type building at average COP levels of 1.0 and solar collection efficiencies of 50 percent when supplied with solar heated water at temperatures of 50 to 65° C. Detailed operating results, including total and average solar cooling provided, coefficients of performance, and overall solar cooling performance ratios are presented.
An Investigation of a Residential Solar System Coupled to a Radiant Panel Ceiling
Authors: Zhang Z. , Pate M. , Nelson R.
Published: November 2009

An experimental study of a solar-radiant heating system was performed at Iowa State University’s Energy Research House (ERH). The ERH was constructed with copper tubes embedded in the plaster ceilings, thus providing a unqiue radiant heating system. In addition, 24 water-glycol, flat-plate solar collectors were mounted on the south side of the residence. The present study uses the solar collectors to heat a storage tank via a submerged copper tube coil. Hot water from the storage tank is then circulated through a heat exchanger, which heats the water flowing through the radiant ceiling. This paper contains a description of the solar-radiant system and an interpretation of the data that were measured during a series of transient experiments. In addition, the performance of the flat-plate solar collectors and the water storage tank were evaluated. The characteristics of a solar-to-radiant heat exchanger were also investigated. The thermal behavior of the radiant ceiling and the room enclosures were observed, and the heat transfer from the ceiling by radiation and convection was estimated. The overall heating system was also evaluated using the thermal performances of the individual components. The results of this study verify that it is feasible to use a solar system coupled to a low-temperature radiant-panel heating system for space heating. A sample performance evaluation is also presented.
A Comparison of Predicted Wind Turbine Blade Loads to Test Measurements
Authors: Wright A. D. , Thresher R. W.
Published: November 2009

The accurate prediction of wind turbine blade loads and response is important in predicting the fatigue life of wind machines. At the SERI Wind Energy Research Center, a rotor code called FLAP (Force and Loads Analysis Program) is currently being validated by comparing predicted results to machine measurements. The FLAP code has been modified to allow the teetering degree of freedom. This paper describes these modifications and comparisons of predicted blade bending moments to test measurements. Wind tunnel data for a 1/20th scale model will be used to compare FLAP predictions for the cyclic flap-bending moments at the 33 percent spanwise station for three different wind speeds. The comparisons will be made for both rigid and teetering hubs. Currently, the FLAP code accounts for deterministic excitations such as wind shear, tower shadow, gravity, and prescribed yawing motions. Conclusions will be made regarding the code’s accuracy in predicting the cyclic bending moments.
Inexpensive Performance Monitoring of Solar Domestic Water Heating Systems
Authors: Clausing A. M.
Published: November 2009

Performance monitoring is essential in order to conclusively demonstrate the cost effectiveness of a solar heating system. Unfortunately, this “last step” is an aspect which has received little engineering consideration. The monitoring programs in progress typically use instrumentation which is much too expensive and complex for use by individual operators of domestic water heating systems. Hence, few systems are monitored, and the average owner knows little about the performance characteristics of his system. Even malfunctions go undetected. An inexpensive performance monitoring system is described in this paper. It could probably be mass-produced for under 15 dollars or built by the typical homeowner for under 30 dollars. The monitor indicates the instantaneous solar fraction. Overall system performance can be improved with this monitor, since it enables the user to correlate load with the availability of solar heated water. Methodology, performance parameters, and some performance data are presented.
Solar Powered Solid Adsorption Cold Store
Authors: Grenier Ph. , Guilleminot J. J. , Meunier F. , Pons M.
Published: November 2009

Experimental results obtained on a 12 m3 solar-powered solid-adsorption cold store are presented. These results are compared to the predictions of a simplified model. On the basis of this model, performance of a similar installation under various conditions (location, orientation) and other technological possibilities are given.
Autonomous Wind-Generated Electricity for Induction Motors
Authors: Vosper Fred C. , Clark R. Nolan
Published: November 2009

A wind turbine with variable-voltage, variable-frequency electrical output was used to power resistive loads and induction motors in an autonomous system. The AC system was selected because AC motors, in multiple kilowatt sizes, can be more practical than DC motors. A wind turbine which produces electricity has a lower overall efficiency than a system producing mechanical power but offers more flexibility in adapting to varying loads and in locating the wind turbine near the load. A permanent magnet alternator designed to operate with a rotor speed from 70 to 150 r/min was first operated in the laboratory. The frequency of the output varied from 30 to 65 Hz, while the voltage changed from 85 to 218 V, resulting in voltage to frequency ratios (V/f) from 2.6 to 3.3 with various loads. The alternator, with a maximum rated output of 9 kW, provided power to resistive load or induction motor loads. The tests revealed that standard three-phase, 240 V, 60 Hz, AC induction motors will operate with an input of 85 V and 30 Hz. A motor temperature rise of 40° C above ambient was not exceeded when power was supplied by the alternator to a 7.6 kW motor. System efficiencies were nearly equivalent to those obtained with utility power, even though the V/f was below that calculated from the motor’s nameplate. The wind energy conversion system (WECS) was then operated in wind-speeds of 3.5 m/s or greater. This WECS was capable of providing power to satisfactorily operate induction motors in an autonomous system.
Seasonal Storage of Thermal Energy—Swedish Experience
Authors: Gabrielsson Erik
Published: November 2009

Sweden reacted to the oil crises of the 1970s by initiating a comprehensive programme of research into, and development of, alternative energy sources. One of the problem areas in this connection is that of energy storage. This paper describes documented Swedish experience of seasonal thermal energy stores, concerned with such aspects as heat balances, heat losses, water sealing, stratification and temperature fields in heat stores and their surroundings. The paper concludes with mention of a number of design guidelines developed from Swedish R&D experience.
Measurement of Fenestration Net Energy Performance: Considerations Leading to Development of the Mobile Window Thermal Test (MoWitt) Facility
Authors: Klems J. H.
Published: November 2009

We present a detailed consideration of the energy flows entering a building space and the effect of random measurement errors on determining fenestration performance. Estimates of error magnitudes are made for a passive test cell; we show that a more accurate test facility is needed for reliable measurements on fenestration systems with thermal resistance 2–10 times that of single glazing or with shading coefficients less than 0.7. A test facility of this type, built at Lawrence Berkeley Laboratory, is described. The effect of random errors in this facility is discussed and computer calculations of its performance are presented. The discussion shows that, for any measurement facility, random errors are most serious in nighttime measurements, and systematic errors are most important in daytime measurements. It is concluded that, for this facility, errors from both sources should be small.
The Effects of Radiation Properties of Surfaces and Coatings on the Performance of Solar Collectors
Authors: Tal-Tarlo I. , Zvirin Y.
Published: November 2009

The present work suggests a more complete method for predicting the performance of solar collectors at intermediate temperatures, taking into account absorptance of the solar short-wave radiation in the glass covers and transmittance through them of the IR long wave radiation from the plate and other surfaces. The governing equations for energy balances of the shield and outer cover were developed, using a ray tracing method and radiation characteristics of slabs and coatings. The equations were solved numerically for the shield and cover temperatures, Tg and Tc, and then the net energy, Qnet, was found. Other heat fluxes were also obtained, to understand better the influence of each parameter on the performance. A parametric study has been carried out to study the effects of various coatings: heat mirrors (reflecting IR radiation) and anti-reflective for solar radiation. The influences of collector pressure, concentration, double glazing, and selective coatings on the absorbing plate have also been investigated. An important conclusion from the results is that there is no configuration of coatings which yields higher efficiencies over the whole temperature range. An “optimal” collector must be designed according to the intended consumer temperature.
Control Strategies for Multistage Solar Collector Systems
Authors: Saltiel C.
Published: November 2009

A comparative study of the yearly performance of multistage solar collector systems, (comprised of more than one collector type) with a single on/off flow control strategy for all the collectors and separate on/off controls for each collector stage, is performed. Detailed numerical simulations under a range of climatic conditions showed that there is little advantage in using individual collector controls over a single on/off control strategy when the systems operate at low collector thresholds, but differences in system performance can be quite significant at high threshold values. In addition, the choice of the single control strategy (i.e., which collector the strategy is based on) at low thresholds is not critical in terms of system performance.
Gradient Layer Entrainment Correlation for a Salt Gradient Solar Pond With Storage Layer Recirculation
Authors: Munoz D. R. , Zangrando F. , Viskanta R. , Incropera F. P.
Published: November 2009

Experiments were performed in a large tank to determine the effects of combined mixing, due to bottom heating and a horizontal recirculation, on the entrainment of salt stratified fluid. Entrainment rate data obtained for large Richardson numbers were used with existing data for smaller Richardson numbers to develop a single term correlation for the range 102 < Ri < 104. The appropriate velocity and length scales for the combined mixing experiments were the convective velocity, the square root of the jet kinematic momentum flux divided by the distance from the discharge diffuser to the interface, and the height of the mixed layer.
An Improved Technique for Computing the Top Heat Loss Factor of a Flat-Plate Collector With a Single Glazing
Authors: Mullick S. C. , Samdarshi S. K.
Published: November 2009

A different approach to evaluate the top heat loss factor of a flat plate solar collector with a single glass cover is proposed. The equation for the heat loss factor in the analytical form is employed instead of the semi-empirical form hitherto employed for solar collectors. The glass cover temperature is, however, estimated by an empirical relation. (This relation replaces the empirical relation for the factor f of the earlier work). Values of the top heat loss factor calculated by this simple technique are within 3 percent (maximum error) of those obtained by iterative solution of the heat balance equations. There is an improvement in accuracy by a factor greater than five over the current semi-empirical equations. The range of variables covered is 50° C to 150° C in absorber plate temperature, 0.1 to 0.95 in absorber coating emittance, and 5 W/m2C to 45 W/m2C in wind heat-transfer coefficient. The effect of variation in air properties with temperature has been taken into account.
A Review of Test Results on Solar Thermal Power Modules With Dish-Mounted Stirling and Brayton Cycle Engines
Authors: Jaffe Leonard D.
Published: November 2009

This paper presents results of development tests of various solar thermal parabolic dish modules and assemblies that used dish-mounted Brayton or Stirling cycle engines for production of electric power. These tests indicate that early modules achieve net efficiencies up to 29 percent in converting sunlight to electricity, as delivered to the grid. Various equipment deficiencies were observed and a number of malfunctions occurred. The performance measurements, as well as the malfunctions and other test experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.
A Review of Test Results on Parabolic Dish Solar Thermal Power Modules With Dish-Mounted Rankine Engines and for Production of Process Steam
Authors: Jaffe Leonard D.
Published: November 2009

This paper presents results of development testing of various solar thermal parabolic dish modules and assemblies. Most of the tests were at modules and assemblies that used a dish-mounted, organic Rankine cycle turbine for production of electric power. Some tests were also run on equipment for production of process steam or for production of electricity using dish-mounted reciprocating steam engines. These tests indicate that early modules achieve efficiencies of about 18 percent in converting sunlight to electricity (excluding the inverter but including parasitics). A number of malfunctions occurred. The performance measurements, as well as the malfunctions and other operating experience, provided information that should be of value in developing systems with improved performance and reduced maintenance.
Verified Accurate Performance Simulation Model of Direct Thermosyphon Solar Energy Water Heaters
Authors: Hobson P. A. , Norton B.
Published: November 2009

A detailed analysis of the heat transfers and fluid flows within direct thermosyphonic solar energy water heaters has been undertaken. The collector energy equations were cast in a two-dimensional form in order that the heat transfer and thermal capacitance effects can be simulated accurately at the small flow rates encountered commonly in these buoyancy-driven systems. The use of an appropriate nonisothermal friction factor correlation when calculating energy losses in the collector’s riser pipes, produced predicted flow rates which were corroborated to within 2 percent by the values measured under steady flow conditions. For the laminar flow rates and the store configuration investigated, relaxation of the thermocline was shown to be dominated by axial conduction in the store walls. An indoor test facility, monitored and controlled by a microcomputer, enabled “real” operating conditions to be simulated. The predicted responses of the system to identical conditions showed good agreement with the corresponding experimental observations, the predicted heat delivery being within 2.8 percent of that measured.
An Experimental Study of Free Convection in Compound Parabolic Concentrator (CPC) Cavities
Authors: Chew T. C. , Wijeysundera N. E. , Tay A. O.
Published: November 2009

An experimental study of the free convection heat transfer between the cylindrical absorber and the flat top of a compound parabolic concentrator (CPC) is described. Results are obtained for a range of absorber temperatures and four CPC cavity heights. For similar conditions of operating temperature, the heat transfer from a cylinder in free air is about 30 to 50 percent higher than in a CPC cavity. Two correlations for Nusselt and Grashof numbers have been obtained using the equivalent length and the cavity height as the characteristic length of the system.
Analytical Determination of Soil Thermal Conductivity and Diffusivity
Authors: Ingersoll J. G.
Published: November 2009

A simple model has been developed that can be used to calculate the soil thermal conductivity and diffusivity on the basis of the following factors: soil porosity; soil water content; conductivity, specific heat, and density of the constituents of soil, i.e., solid matter, water, and air. The model assumes that the void space in soil can be presented by a combination of plane fissures, whose direction is either parallel to the heat flow or perpendicular to it. A coefficient introduced to account for this combination in the two directions can be estimated from measured data as a function of the soil water content. Moreover, it is assumed that air and moisture conduct heat across the fissures in parallel. It is found that soil conductivity and diffusivity increase relatively rapidly with a few percent addition of moisture to entirely dry soil. For instance, assuming a typical soil porosity of 40 percent we conclude that the ratio of soil diffusivities of saturated to dry soil is about four, while that of soild with 2.5 percent moisture content to dry soil is a little over two. That is to say, a small moisture addition to dry soil brings the diffusivity half way to its saturation value. Since soil always contains small amounts of moisture, this finding explains the fact that measured seasonal temperature damping factors in extreme humid and extreme arid climates differ by less than a factor of two even though the moisture content of the respective soils may differ by more than an order of magnitude.