bluuebunny/crossref_metadata_2025 huggingface dataset:
Fluid Mechanics and Heat Transfer Measurements in Transitional Boundary Layers Conditionally Sampled on Intermittency
Authors: Kim J. , Simon T. W. , Kestoras M.
Published: June 2008

An experimental investigation of transition on a flat-plate boundary layer was performed. Mean and turbulence quantities, including turbulent heat flux, were sampled according to the intermittency function. Such sampling allows segregation of the signal into two types of behavior—laminarlike and turbulentlike. Results show that during transition these two types of behavior cannot be thought of as separate Blasius and fully turbulent profiles, respectively. Thus, simple transition models in which the desired quantity is assumed to be an average, weighted on intermittency, of the laminar and fully turbulent values may not be entirely successful. Deviation of the flow identified as laminarlike from theoretical laminar behavior is due to a slow recovery after the passage of a turbulent spot, while deviation of the flow identified as turbulentlike from fully turbulent characteristics is possibly due to an incomplete establishment of the fully turbulent power spectral distribution. Measurements were taken for two levels of free-stream disturbance—0.32 and 1.79 percent. Turbulent Prandtl numbers for the transitional flow, computed from measured shear stress, turbulent heat flux, and mean velocity and temperature profiles, were less than unity.
Viscous Analysis of Three-Dimensional Rotor Flow Using a Multigrid Method
Authors: Arnone A.
Published: June 2008

A three-dimensional code for rotating blade-row flow analysis has been developed. The space discretization uses a cell-centered scheme with eigenvalue scaling for the artificial dissipation. The computational efficiency of a four-stage Runge–Kutta scheme is enhanced by using variable coefficients, implicit residual smoothing, and a full-multigrid method. An application is presented for the NASA rotor 67 transonic fan. Due to the blade stagger and twist, a zonal, nonperiodic H-type grid is used to minimize the mesh skewness. The calculation is validated by comparing it with experiments in the range from the maximum flow rate to a near-stall condition. A detailed study of the flow structure near peak efficiency and near stall is presented by means of pressure distribution and particle traces inside boundary layers.
Detailed Flow Measurements in a Centrifugal Compressor Vaneless Diffuser
Authors: Pinarbasi A. , Johnson M. W.
Published: June 2008

Hot-wire anemometer measurements have been made in the vaneless diffuser of a 1-m-dia low-speed backswept centrifugal compressor using a phase lock loop technique. Radial, tangential, and axial velocity measurements have been made on eight measurement planes through the diffuser. The flow field at the diffuser entry clearly shows the impeller jet-wake flow pattern and the blade wakes. The passage wake is located on the shroud side of the diffuser and mixes out slowly as the flow moves through the diffuser. The blade wakes, on the other hand, distort and mix out rapidly in the diffuser. Contours of turbulent kinetic energy are also presented on each of the measurement stations, from which the regions of turbulent mixing can be deduced.
Three-Dimensional Time-Marching Inviscid and Viscous Solutions for Unsteady Flows Around Vibrating Blades
Authors: He L. , Denton J. D.
Published: June 2008

A three-dimensional nonlinear time-marching method of solving the thin-layer Navier–Stokes equations in a simplified form has been developed for blade flutter calculations. The discretization of the equations is made using the cell-vertex finite volume scheme in space and the four-stage Runge–Kutta scheme in time. Calculations are carried out in a single-blade-passage domain and the phase-shifted periodic condition is implemented by using the shape correction method. The three-dimensional unsteady Euler solution is obtained at conditions of zero viscosity, and is validated against a well-established three-dimensional semi-analytical method. For viscous solutions, the time-step limitation on the explicit temporal discretization scheme is effectively relaxed by using a time-consistent two-grid time-marching technique. A transonic rotor blade passage flow (with tip-leakage) is calculated using the present three-dimensional unsteady viscous solution method. Calculated steady flow results agree well with the corresponding experiment and with other calculations. Calculated unsteady loadings due to oscillations of the rotor blades reveal some notable three-dimensional viscous flow features. The feasibility of solving the simplified thin-layer Navier–Stokes solver for oscillating blade flows at practical conditions is demonstrated.
A Linearized Euler Analysis of Unsteady Transonic Flows in Turbomachinery
Authors: Hall K. C. , Clark W. S. , Lorence C. B.
Published: June 2008

A computational method for efficiently predicting unsteady transonic flows in two-and three-dimensional cascades is presented. The unsteady flow is modeled using a linearized Euler analysis whereby the unsteady flow field is decomposed into a nonlinear mean flow plus a linear harmonically varying unsteady flow. The equations that govern the perturbation flow, the linearized Euler equations, are linear variable coefficient equations. For transonic flows containing shocks, shock capturing is used to model the shock impulse (the unsteady load due to the harmonic motion of the shock). A conservative Lax–Wendroff scheme is used to obtain a set of linearized finite volume equations that describe the harmonic small disturbance behavior of the flow. Conditions under which such a discretization will correctly predict the shock impulse are investigated. Computational results are presented that demonstrate the accuracy and efficiency of the present method as well as the essential role of unsteady shock impulse loads on the flutter stability of fans.
Measurement of Compressible Flow Pressure Losses in Wye-Junctions
Authors: Abou-Haidar N. I. , Dixon S. L.
Published: June 2008

This paper considers the compressible flow pressure losses in sharp-cornered wye-junctions with symmetric branches under dividing and combining flow conditions. Determination of the additional total pressure losses occurring in flow through several three-leg junctions, using dry air as the working fluid, has been made experimentally. Results covering a wide speed range up to choking are presented for 30, 60, and 90 deg wye-junctions. Separate flow visualization schlieren tests detected the presence of normal shock waves, located at up to one duct diameter downstream of the junction, and therefore confirmed the choking of the flow at the vena contracta. The highest attainable Mach number (M3) of the averaged whole flow was 0.9 for one of the dividing flow geometries and 0.65 for several of the combining flow cases. These values of M3 were the maximum possible and hence represent a limiting condition dictated by choking. In general, the compressible flow loss coefficients, caused by the presence of the wye-junctions, can be expected to be higher for dividing flows and lower for combining flows than would be the case for incompressible flows because of the influence of Mach number, M3.
Calculation of Turbulent Flow for an Enclosed Rotating Cone
Authors: May N. E. , Chew J. W. , James P. W.
Published: June 2008

Prediction of the flow in the cavity between a rotating cone and an outer stationary cone with and without throughflow is considered. A momentum-integral method and a finite difference method for solution of the Reynolds-averaged Navier–Stokes equations with a mixing-length model of turbulence are applied. These two methods have previously been validated for flow between corotating and rotor–stator disk systems, but have not been properly tested for conical systems. Both methods have been evaluated by comparing predictions with the experimental measurements of other workers. There is good agreement for cone half-angles greater than or equal to 60 deg but discrepancies are evident for smaller angles. “Taylor-type” vortices, the existence of which has been postulated by other workers and which are not captured by the present steady, axisymmetric models, may contribute to these discrepancies.
Development of a Transonic Front Stage of an Axial Flow Compressor for Industrial Gas Turbines
Authors: Katoh Y. , Kashiwabara Y. , Ishii H. , Tsuda Y. , Yanagida M.
Published: June 2008

This paper describes the aerodynamic blade design of a highly loaded three-stage compressor, which is a model compressor for the front stage of an industrial gas turbine. Test results are presented that confirm design performance. Some surge and rotating stall measurement results are also discussed. The first stator blade in this test compressor operates in the high subsonic range at the inlet. To reduce the pressure loss due to blade surface shock waves, a shock-free airfoil is designed to replace the first stator blade in an NACA-65 airfoil in a three-stage compressor. Comparison of the performance of both blades shows that the shock-free airfoil blade reduces pressure loss. This paper also presents some experimental results for MCA (multicircular arc) airfoils, which are used for first rotor blades.
Tip Leakage Flow in Linear Compressor Cascade
Authors: Kang S. , Hirsch C.
Published: June 2008

Tip leakage flow in a linear compressor cascade of NACA 65-1810 profiles is investigated, for tip clearance levels of 1.0, 2.0, and 3.25 percent of chord at design and off-design flow conditions. Velocity and pressure data are collected from three transverse sections inside tip clearance and sixteen sections within flow passage. Tip separation vortex influence is identified from the data. Leakage flow mixing is clearly present inside the clearance and has a significant influence on the internal loss.
Numerical Simulations of Unsteady Cascade Flows
Authors: Dorney D. J. , Verdon J. M.
Published: June 2008

A time-accurate Navier–Stokes analysis is needed for understanding the relative importance of nonlinear and viscous effects on the unsteady flows associated with turbomachinery blade vibration and blade-row noise generation. For this purpose an existing multi-blade-row Navier–Stokes analysis has been modified and applied to predict unsteady flows excited by entropic, vortical, and acoustic disturbances through isolated, two-dimensional blade rows. In particular, time-accurate, non-reflecting inflow and outflow conditions have been implemented to allow specification of vortical, entropic, and acoustic excitations at the inlet, and acoustic excitations at the exit, of a cascade. To evaluate the nonlinear analysis, inviscid and viscous numerical simulations were performed for benchmark unsteady flows and the predicted results were compared with analytical and numerical results based on linearized inviscid flow theory. For small-amplitude unsteady excitations, the unsteady pressure responses predicted with the nonlinear analysis show very good agreement, both in the field and along the blade surfaces, with linearized inviscid solutions. Based on a limited range of parametric studies, it was also found that the unsteady responses to inlet vortical and acoustic excitations are linear over a surprisingly wide range of excitation amplitudes, but acoustic excitations from downstream produce responses with significant nonlinear content.
Unsteady Wake Over a Linear Turbine Blade Cascade With Air and CO2 Film Injection: Part I—Effect on Heat Transfer Coefficients
Authors: Ou S. , Han J.-C. , Mehendale A. B. , Lee C. P.
Published: June 2008

The effect of unsteady wake flow and air (D.R. = 1.0) or CO2 (D.R. = 1.52) film injection on blade heat transfer coefficients was experimentally determined. A spoked wheel-type wake generator produced the unsteady wake. Experiments were performed on a five-airfoil linear cascade in a low-speed wind tunnel at the chord Reynolds number of 3 × 105 for the no-wake case and at the wake Strouhal numbers of 0.1 and 0.3. Results from a blade with three rows of film holes in the leading edge region and two rows each on the pressure and suction surfaces show that the Nusselt numbers are much higher than those for the blade without film holes. On a large portion of the blade, the Nusselt numbers “without wake but with film injection” are much higher than for “with wake but no film holes.” An increase in wake Strouhal number causes an increase in pressure surface Nusselt numbers; but the increases are reduced at higher blowing ratios. As blowing ratio increases, the Nusselt numbers for both density ratio injectants (air and CO2) increase over the entire blade except for the transition region where the effect is reversed. Higher density injectant (CO2) produces lower Nusselt numbers on the pressure surface, but the numbers for air and CO2 injections are very close on the suction surface except for the transition region where the numbers for CO2 injection are higher. From this study, one may conclude that the additional increases in Nusselt numbers due to unsteady wake, blowing ratio, and density ratio are only secondary when compared to the dramatic increases in Nusselt numbers only due to film injection over the no film holes case.
An Application of Octant Analysis to Turbulent and Transitional Flow Data
Authors: Volino R. J. , Simon T. W.
Published: June 2008

A technique called “octant analysis” was used to examine the eddy structure of turbulent and transitional heated boundary layers on flat and curved surfaces. The intent was to identify important physical processes that play a role in boundary layer transition on flat and concave surfaces. Octant processsing involves the partitioning of flow signals into octants based on the instantaneous signs of the fluctuating temperature, t′, streamwise velocity, u′, and cross-stream velocity, v′. Each octant is associated with a particular eddy motion. For example, u′ <0, v′>0, t′>0 is associated with an ejection or “burst” of warm fluid away from a heated wall. Within each octant, the contribution to various quantities of interest (such as the turbulent shear stress, −u′v′, or the turbulent heat flux, v′t′) can be computed. By comparing and contrasting the relative contributions from each octant, the importance of particular types of motion can be determined. If the data within each octant are further segregated based on the magnitudes of the fluctuating components so that minor events are eliminated, the relative importance of particular types of motion to the events that are important can also be discussed. In fully developed, turbulent boundary layers along flat plates, trends previously reported in the literature were confirmed. A fundamental difference was observed in the octant distribution between the transitional and fully turbulent boundary layers, however, showing incomplete mixing and a lesser importance of small scales in the transitional boundary layer. Such observations were true on both flat and concave walls. The differences are attributed to incomplete development of the turbulent kinetic energy cascade in transitional flows. The findings have potential application to modeling, suggesting the utility of incorporating multiple length scales in transition models.
A Bypass Transition Model for Boundary Layers
Authors: Johnson M. W.
Published: June 2008

Experimental data for laminar boundary layers developing below a turbulent free stream show that the fluctuation velocities within the boundary layer increase in amplitude until some critical level is reached, which initiates transition. In the near-wall region, a simple model, containing a single empirical parameter, which depends only on the turbulence level and length scale, is derived to predict the development of the velocity fluctuations in laminar boundary layers with favorable, zero, or adverse pressure gradients. A simple bypass transition model, which considers the streamline distortion in the near-wall region brought about by the velocity fluctuations, suggests that transition will commence when the local turbulence level reaches approximately 23 percent. This value is consistent with experimental findings. This critical local turbulence level is used to derive a bypass transition prediction formula, which compares reasonably with start of transition experimental data for a range of pressure gradients (λ θ = −0.01 to 0.01) and turbulence levels (Tu = 0.2 to 5 percent). Further improvement to the model is proposed through prediction of the boundary layer distortion, which occurs due to Reynolds stresses generated within the boundary layer at high free-stream turbulence levels and also through inclusion of the effect of turbulent length scale as well as turbulence level.
Conversion of Solar Radiation Into Electricity in Silicon Solar Cells: A Thermodynamic Assessment
Authors: Osterle J. F. , Swantner S. R.
Published: June 2008

The thermodynamic dissipations in crystalline silicon solar cells are identified and evaluated. The ratio of the exergy of the output electrical power to the exergy of the input solar radiation is the effectiveness of the solar cell. The input exergy is converted to the output exergy (the electrical power delivered) with a series of dissipations. These dissipations are identified and evaluated for crystalline silicon cells in terms of the thickness and certain fundamental properties of the light absorbing silicon semiconductor (in this case a P-type material). It is assumed that the N-type material is very thin and absorbs no radiation. For representative values of these properties and a range of thicknesses, it is found that the dissipations due to transmission and thermalization and in the photogeneration process are dominant. The dissipations due to the dark current and recombination are small.
Effect of the Circulation Number on the Stratification Coefficient for Solar Heating Systems
Authors: Dave Rajesh N.
Published: June 2008

The effect of the circulation number (the number of times the entire storage mass is circulated through the system each day) on the stratification coefficient is investigated. An earlier model ignored the effect of the circulation number, assuming that a large value (a value > 2) did not have any effect. In this paper, an analytical model is developed to consider the effect of low circulation number. This model is combined with the previous model and a general expression for the stratification coefficient is developed that is valid for the entire range of circulation number. The extended analytical model is verified through numerical simulations. The results are valid for liquid-based as well as air heating systems. Clarifications are made regarding the definition of the stratification coefficient by introducing a concept of an instantaneous stratification coefficient.
Transient Dehumidification Characteristics of a Heat Pump in Cooling Mode
Authors: Katipamula Srinivas , O’Neal Dennis L.
Published: June 2008

Much of the seasonal cooling operation of the heat pump occurs at part-load conditions when the unit cycles on and off to meet the cooling load. The seasonal efficiency under part-load conditions of the heat pump is typically estimated from a laboratory measurement of the degradation coefficient (CD). Manufacturers are only required to estimate CD at a single test condition where the indoor coil performs sensible cooling only. The effects of transient dehumidification losses are not accounted in estimating the seasonal efficiency. In hot and humid climates, dehumidification performance of a heat pump is as important as the sensible cooling performance. Therefore, a series of tests were designed to quantify the part-load dehumidification characteristics of a three ton residential air-to-air heat pump. The tests include: cycling rates from 0.8 to 10 cycles per hour (cph), percent on-times of 20, 50, and 80 percent, indoor dry-bulb temperature between 22.2°C and 26.7°C, and indoor relative humidity between 20 to 67 percent. The outdoor conditions and the indoor air flow rate were constant for all test runs. All experiments were performed in psychometric chambers under controlled conditions. The dehumidification process started between 60 to 150 seconds after start-up depending on the test conditions. During start-up, the losses in the latent capacity were greater than the losses in the sensible capacity. The dehumidification response increased with indoor dry-bulb temperature at constant relative humidity and decreased with indoor temperature at constant dew-point temperature.
Analysis of a Two-Stage Linear Fresnel Reflector Solar Concentrator
Authors: Feuermann D. , Gordon J. M.
Published: June 2008

The two-stage linear Fresnel reflector solar concentrator is analyzed via an in-depth study of an installed, nominally 220 KWt system. The concentrator includes: (1) a primary linear Fresnel reflector comprised of curved mirrors and (2) a secondary nonimaging CPC-type trough with a tubular receiver. The principal practical design options for the secondary concentrator are evaluated. Via a computer simulation which includes ray-tracing of the primary reflector, we evaluate the sensitivity of energy output to: concentrator optical errors, system geometry, tracking mode, and the option of using flat versus curved primary mirrors. The two-stage Fresnel concentrator can be considerably less expensive than the corresponding parabolic trough collector, but is found to deliver about one-fourth less yearly energy. However, much of this difference could be eliminated through the use of higher-quality CPC reflectors.
A Comparison of Alternative Approaches for the Synthetic Generation of a Wind Speed Time Series
Authors: Kaminsky F. C. , Kirchhoff R. H. , Syu C. Y. , Manwell J. F.
Published: June 2008

In this paper, alternative approaches for synthetically generating a wind speed time series are discussed. These approaches include: (1) the use of independent values from a specific probability distribution; (2) the use of an algorithm based on the statistical behavior of a one-step Markov chain; (3) the use of an algorithm based on the behavior of a transition probability matrix that describes the next wind speed value statistically as a function of the current wind speed value and the previous wind speed value; (4) the use of Box-Jenkins models; (5) the use of the Shinozuka algorithm; and (6) the use of an embedded Markov chain. The ability of each approach to capture the statistical properties of the desired wind speed time series is discussed. In this context the statistical properties of interest are the probability distribution of the wind speed values, the autocorrelation function of the wind speed values, and the spectral density of the wind speed values.
Global Energy in the Different Spectral Bands at Dhahran, Saudi Arabia
Authors: Elhadidy M. A.
Published: June 2008

Global, spectral isolation data measured every minute over a four-year period at Dhahran (26° 32′ N, 50° 13′ E) Saudi Arabia, using five Schott filters with cutoff at “285, 500, 530, 630, and 695” nm, and ultraviolet radiation sensor, 295–385nm, are analyzed. Monthly averages of the diurnal variations of these bands are presented. The rainfall, dust/sand storm, cloud and air mass effects on the band radiation are also investigated. Comparisons of the yearly average of band radiation measured at Dhahran and those reported in Goldberg and Klein (1977) for Jerusalem (32° N) and Rockville (39° N) are presented. Monthly average band radiation are also presented. The data showed that the ratio of the monthly average of the diurnal band radiations to the total radiation for winter and summer are nearly the same. The data also showed that the rainfall increases the percentage of radiation in the bands 385–500nm, 500–530nm, and 630–690nm, and it decreases the percentage radiation of the band 690–2800nm and that the opposite is true for dust/sand storm effect. The change in the band radiation due to cloud cover is small. The data also showed that the monthly and yearly averages of the radiation in the bands “630–695, and 695–2800” nm are latitude independent. The monthly radiation values at each band over the year are almost constant.
Void Formation in Radial Solidification of Cylinders
Authors: Sulfredge C. D. , Chow L. C. , Tagavi K. A.
Published: June 2008

Experiments were carried out to observe the solidification sequence and void distribution for two different experimental liquids (cyclohexane and butanediol) enclosed in Pyrex tubes. Both liquids exhibited about ten percent volumetric shrinkage during the phase transition from liquid to solid. To evaluate the possibility of regulating void formation by soluble gases, tests were conducted both in the presence and absence of dissolved air. A physical model has been developed which predicts the essential features of the solidification pattern under earth’s gravity field of 1-g for cylindrical geometries and allows extrapolation of the results to outer space conditions of 0-g. Finally, an attempt was made to determine analytically the final void shape which would result from each nucleated bubble in 0-g. Understanding these aspects of the solidification process is vital to development of better thermal energy storage systems for space power applications.
A Simple Device for Monitoring Flow Rates in Thermosyphon Solar Water Heaters
Authors: Bannerot Richard B. , Tu Yi-Wey , Scott Allen , Placke George , Poche´ Tom
Published: June 2008

Direct measurements of fluid flow rates in thermosyphon solar water heaters in the field are difficult. This paper reports on an activity to develop, calibrate, and evaluate a simple device for such measurements. A suitable device should have the following general characteristics: low pressure drop, rugged, inexpensive, simple, nondisruptive, low power requirements, and reasonably accurate. Moderate success has been achieved in satisfying all of these requirements with a hydrogen bubble generator (utilizing the electrolysis of water) in a clear plexiglass tube mounted in a vertical section of the flow line in which the flow is upward. The rate at which the hydrogen bubbles are swept along with the water can be used (when calibrated) to indicate the flow rate.
Appropriate Thermodynamic Performance Measures for Closed Systems for Thermal Energy Storage
Authors: Rosen M. A.
Published: June 2008

Several definitions of energy and exergy efficiency for closed systems for thermal energy storage (TES) are developed and discussed. A simple model is utilized in which heat quantities are transferred at specified temperatures to and from a TES. Efficiency definitions are considered for the overall storage process and for the three component periods which comprise a complete storage process (charging, storing, and discharging). It is found that (1) appropriate forms for both energy and exergy efficiency definitions depend on which quantities are considered to be products and inputs; (2) different efficiency definitions are appropriate in different applications; (3) comparisons of different TES systems can only yield logical results it they are based on a common definition, regardless of whether energy or exergy quantities are considered; and (4) exergy efficiencies are generally more meaningful and illuminating than energy efficiencies for evaluating and comparing TES systems. A realistic, but simplified, illustrative example is presented. The efficiency definitions should prove useful in the development of valid and generally accepted standards for the evaluation and comparison of different TES systems.
Analysis of Catalytically Enhanced Solar Absorption Chemical Reactors: Part II—Predicted Characteristics of a 100 kWchemical Reactor
Authors: Skocypec R. D. , Hogan R. E.
Published: June 2008

The CAtalytically Enhanced Solar Absorption Receiver (CAESAR) is a 100 kWchemecal test reactor currently in operation. This type of high-temperature chemical reactor volumetrically absorbs concentrated solar energy throughout a catalytic porous absorber matrix volume, promoting heterogeneous reactions with fluid-phase reactant species flowing through the absorber. A numerical model of these reactors has been developed to provide guidance in the catalytic matrix design for CAESAR. In the CAESAR reactor, methane is reformed using carbon dioxide and a rhodium catalyst. In addition, the model is being used to evaluate both the reactor performance and test data. This paper presents the thermal and chemical characteristics of the reactor for varying incident solar flux, fluid mass flow, convective heat-transfer coefficient, solar and infrared extinction coefficients, and catalyst loading. Predicted CAESAR performance is based on a prototype absorber and anticipated operating conditions. Model results suggest the mass flux must be proportioned to the incident solar flux radial distribution to prevent unacceptably high local temperatures and to provide a reactor having more uniform exit conditions. Either the catalytic loading or geometric thickness of the absorber should be increased for conversion to approach equilibrium levels. Also, the optical density of the matrix (particularly at the sunlit side of the reactor) should be decreased to distribute solar energy more uniformly in depth and decrease matrix temperatures at the front of the absorber.
One-Dimensional Analysis of Energy Storage in Packed Capsules
Authors: Chen S. L.
Published: June 2008

A one-dimensional porous-medium model to determine the thermal characteristics of energy storage for the utilization of phase change material (PCM) in packed capsules has been developed. Comparisons of this theory with experimental data obtained in the previous work show good agreement. Predictions from the present model have also been compared with the lumped capacitance model which assumes temperature uniformity in the packed capsules and in the coolant flow. The results show that the one-dimensional model has the advantage of predicting the temperature distributions of PCM and coolant. For engineering application, a useful correlation of the overall heat-transfer coefficient for ice-water cool storage in packed capsules has also been presented.
A Four-Parameter Change-Point Model for Predicting Energy Consumption in Commercial Buildings
Authors: Ruch David , Claridge David E.
Published: June 2008

This paper develops a four-parameter change-point model of energy consumption as a function of dry-bulb temperature, along with accompanying error diagnostics for the model’s parameters. The model is a generalization of the widely used three-parameter, or variable-base degree-day method. The model is applied to data from a case study grocery store, is compared to the three-parameter PRISM CO model of the store data, and is shown to provide a statistically better fit to consumption data below about 15°C. This model appears to be useful for diagnosing unexpected energy use in some buildings and should be useful for determining retrofit energy savings from monitored pre-retrofit and post-retrofit data for the class of buildings whose pre-retrofit consumption is fit by a four-parameter linear change-point model.
Air Movement in Buildings Using Computational Fluid Dynamics
Authors: Haghighat F. , Jiang Z. , Wang J. C. Y. , Allard F.
Published: June 2008

This paper presents the development of a three-dimensional numerical model to study the distributions of indoor air velocity, air temperature, contaminant concentration, and ventilation effectiveness in a two-zone enclosure. The numerical model is based on the k–ε two-equation model of turbulence and the SIMPLE algorithm. The false-time step and ADI iteration procedure are employed. The results of the computed velocity and temperature profiles and convective heat transfer by the model are in good agreement with the measurements as well as with the prediction of the PHOENICS code.
Improving the Performance of Floating Solar Pool Covers
Authors: Cole Martin A. , Lowrey Preston
Published: June 2008

Experimental and analytical analyses are presented for the evaluation of heat transfer through floating solar swimming pool covers. Two improved floating solar swimming pool cover designs are proposed and investigated. The results conclusively show that both new cover designs should have significantly better performance than conventional floating solar swimming pool covers.
An Analysis of Methods for Deriving the Constituent Insolation Components From Multipyranometer Array Measurements
Authors: Curtiss Peter
Published: June 2008

A multipyranometer array (MPA) is a static platform of solar sensors designed to “untangle” the beam, diffuse and reflected portions of the total solar radiation. Over the past four years, a series of weather stations located throughout Colorado has used MPA’s to record insolation. This paper compares the beam radiation derived from an MPA with that measured by a nearby tracking pyrheliometer. Three different diffuse sky models as well as uniform and specular foreground reflectance models are used in the analysis. The ability of each model to predict the actual beam radiation is tabulated. Finally, two novel methods for deriving the beam component without the use of sky models are presented, along with a comparison with the conventional models.
A Numerical Investigation of the Natural Convection Heat and Mass Transfer From Uniformly Heated Falling Films in Vertical Channels
Authors: Buck Gregory A. , Wood Byard D.
Published: June 2008

In the design of solar collector/regenerators for use in open-cycle absorption refrigeration (OCAR), the problem of predicting evaporation rates and solution temperatures is of paramount importance in determining overall cycle performance. This transport of heat and mass is dominated by natural convection with buoyant forces primarily generated as a result of film heating by the solar flux, but aided by the evaporation of water (the lighter species) into the rising moist air stream. In order to better understand the mechanism of these combined buoyant interactions, the governing equations for natural convection flow in a vertical channel bounded by a heated falling film (simulating a glazed collector/regenerator) were solved using several different finite difference techniques. Under the assumptions appropriate to solar collector/regenerator falling films, the gas-side problem may be uncoupled from the falling film side, with the interfacial conditions treated as unknown boundary conditions for the gas-side flow which are iteratively determined from the film mass and energy balances. The numerical results were validated against existing experimental and numerical results for simplified boundary conditions. The appropriate nondimensionalization for the falling film boundary condition was established, ostensibly for the first time, and a parametric study for an air-water vapor mixture was conducted. Curve fits to the numerical results were determined for engineering design applications.
Bench-Scale Reactor Tests of Low Temperature, Catalytic Gasification of Wet Industrial Wastes
Authors: Elliott Douglas C. , Baker Eddie G. , Butner R. Scott , Sealock L. John
Published: June 2008

Bench-scale reactor tests are under way at Pacific Northwest Laboratory to develop a low temperature, catalytic gasification system. The system, licensed under the trade name Thermochemical Environmental Energy System (TEES®), is designed for to a wide variety of feedstocks ranging from dilute organics in water to waste sludges from food processing. The current research program is focused on the use of a continuous feed, tubular reactor. The catalyst is nickel metal on an inert support. Typical results show that feedstocks such as solutions of 2 percent para-cresol or 5 percent and 10 percent lactose in water or cheese whey can be processed to >99 percent reduction of chemical oxygen demand (COD) at a rate of up to 2 L/hr. The estimated residence time is less than 5 min at 360°C and 3000 psig, not including 1 to 2 min required in the preheating zone of the reactor. The liquid hourly space velocity has been varied from 1.8 to 2.9 L feedstock/L catalyst/hr depending on the feedstock. The product fuel gas contains 40 percent to 55 percent methane, 35 percent to 50 percent carbon dioxide, and 5 percent to 10 percent hydrogen with as much as 2 percent ethane, but less than 0.1 percent ethylene or carbon monoxide, and small amounts of higher hydrocarbons. The byproduct water stream carries residual organics amounting to less than 500 mg/L COD.
Monolithic and Mechanical Multijunction Space Solar Cells
Authors: Jain R. K. , Flood D. J.
Published: June 2008

High-efficiency, lightweight, radiation-resistant solar cells are essential to meet the large power requirements of future space missions. Single-junction cells are limited in efficiency. Higher cell efficiencies could be realized by developing multijunction, multibandgap solar cells. Monolithic and mechanically stacked tandem solar cells surpassing single-junction cell efficiencies have been fabricated. This article surveys the current status of monolithic and mechanically stacked multibandgap space solar cells, and outlines problems yet to be resolved. The monolithic and mechanically stacked cells each have their own problems related to size, processing, current and voltage matching, weight, and other factors. More information is needed on the effect of temperature and radiation on the cell performance. Proper reference cells and full-spectrum range simulators are also needed to measure efficiencies correctly. Cost issues are not addressed, since two approaches are still in the developmental stage.
Calculation of the Shape Factor From a Small Rectangular Plane to a Triangular Surface Perpendicular to the Rectangular Plane Without a Common Edge
Authors: Noboa H. L. , O’Neal D. , Turner W. D.
Published: June 2008

In developing an analytical model of radiative heat transfer inside attics, the necessity of calculating the shape factor from a small rectangle to a triangular plane may arise. This paper describes a methodology of calculation for such a shape factor from simple relations using shape-factor algebra. The shape factor is calculated using a mirror image of the triangular surface, in such a way that the small rectangular plane is positioned symmetrical between the two triangular surfaces. Numerical results are presented in graphical form.
Interzonal Natural Convective Heat and Mass Flow Through Doorway-Like Apertures in Buildings: Experimental Results
Authors: Said M. N. A. , Barakat S. A. , Whidden E. A.
Published: June 2008

This paper presents the results of full-scale experiments in a realistic building to evaluate natural convective heat and mass transfer through doorway-like apertures under small temperature differentials. The zone-to-zone temperature differences were nominally between 1°C and 2.5°C. Heat transfer correlations, coefficient of discharge, and thermal stratification are reported for air (Pr = 0.71), an enclosure aspect ratio of 0.26, aperture height relative to the enclosure height in the range of 0.75 to 1, and aperture width relative to the enclosure width in the range 0.29 to 0.79. In general, the results extends the validity of previous theoretical and experimental work in the literature to large doorway-like apertures and small temperature differentials across the aperture typical of residential building conditions.
A Change-Point Principal Component Analysis (CP/PCA) Method for Predicting Energy Usage in Commercial Buildings: The PCA Model
Authors: Ruch D. , Chen Lu , Haberl J. S. , Claridge D. E.
Published: June 2008

A new method for predicting daily whole-building electricity usage in a commercial building has been developed. This method utilizes a Principal Component Analysis (PCA) of intercorrelated influencing parameters (e.g., dry-bulb temperature, solar radiation and humidity) to predict electricity consumption in conjunction with a change-point model. This paper describes the PCA procedure and presents the results of its application in conjunction with a change-point regression, to predict whole-building electricity consumption for a commercial grocery store. Comparison of the results with a traditional Multiple Linear Regression (MLR) analysis indicates that a change-point, Principal Component Analysis (CP/PCA) appears to produce a more reliable and physically plausible model than an MLR analysis and offers more insight into the environmental and operational driving forces that influence energy consumption in a commercial building. It is thought that the method will be useful for determining conservation retrofit savings from pre-retrofit and post-retrofit consumption data for commercial buildings. A companion paper presents the development of the four-parameter change-point model and a comparison to the Princeton Scorekeeping Method (PRISM) (Ruch and Claridge, 1991).
Infrared Imaging Results of an Excited Planar Jet
Authors: Farrington R. B.
Published: June 2008

Planar jets are used for many applications including heating, cooling, and ventilation. Generally, a planar jet provides good mixing within an enclosure. In building applications, the jet provides both thermal comfort and adequate indoor air quality. Increased mixing rates may reduce short circuiting of conditioned air, eliminate dead zones within the occupied zone, reduce energy costs, increase occupant comfort, and increase indoor air quality. This article discusses how an infrared imaging system was used to demonstrate how jet excitation affected the spread angle and the jet mixing efficiency. Infrared imaging captures a large number of data points in real time (over 50,000 data points per image) providing significant advantages over single-point measurements. We used a mesh screen with a time constant of approximately 0.3 seconds as a target for the infrared camera to detect temperature variations in the jet. The infrared images show that excitation of the jet caused increased jet spread. Digital data reduction and analysis show changes in jet isotherms and quantify the increased mixing caused by excitation.
Numerical Modeling of Reflux Solar Receivers
Authors: Hogan R. E.
Published: June 2008

Using reflux solar receivers to collect solar energy for dish-Stirling electric power generation systems is presently being investigated by several organizations, including Sandia National Laboratories, Albuquerque, N. Mex. In support of this program, Sandia has developed two numerical models describing the thermal performance of pool-boiler and heat-pipe reflux receivers. Both models are applicable to axisymmetric geometries and they both consider the radiative and convective energy transfer within the receiver cavity, the conductive and convective energy transfer from the receiver housing, and the energy transfer to the receiver working fluid. The primary difference between the models is the level of detail in modeling the heat conduction through the receiver walls. The more detailed model uses a two-dimensional finite control volume method, whereas the simpler model uses a one-dimensional thermal resistance approach. The numerical modeling concepts presented are applicable to conventional tube-type solar receivers, as well as to reflux receivers. Good agreement between the two models is demonstrated by comparing the predicted and measured performance of a pool-boiler reflux receiver being tested at Sandia. For design operating conditions, the receiver thermal efficiencies agree within 1 percent and the average receiver cavity temperature within 1.3 percent. The thermal efficiency and receiver temperatures predicted by the simpler thermal resistance model agree well with experimental data from on-sun tests of the Sandia reflux pool-boiler receiver. An analysis of these comparisons identifies several plausible explanations for the differences between the predicted results and the experimental data.
Photocatalytic Destruction of Chlorinated Solvents in Water With Solar Energy
Authors: Pacheco J. E. , Prairie M. R. , Yellowhorse L.
Published: June 2008

Sandia National Laboratories and the National Renewable Energy Laboratory are developing a photocatalytic process to destroy organic contaminants in water. Tests with common water pollutants have been conducted at Sandia’s Solar Thermal Facility using a near commercial scale, single-axis tracking parabolic trough system with a glass pipe reactor mounted at its focus. Experiments at this scale provide verification of laboratory studies and allow examination of design and operation issues at a real-life scale. The catalyst, titanium dioxide (TiO2), is a harmless material found in paint, cosmetics, and toothpaste. Experiments were conducted to determine the effects of key process parameters on destruction rates of chlorinated organic compounds that are common water pollutants. In this paper, we summarize the engineering-scale results of these experiments and analyses.
Wind Effects on a Stretched Membrane Heliostat
Authors: Bienkiewicz B.
Published: June 2008

Wind effects on stretched membrane heliostat were investigated in a boundary layer wind tunnel. The membrane response was measured at stow and representative operational conditions. It was found that both at the stow and operational conditions the mean response was much higher than the rms response. At stow conditions the largest response occurred near the leading edge of the membrane, while the rms response was the largest at the membrane centerpoint. For the operational conditions, the largest mean and rms responses were found at the membrane centerpoint. The membrane response was significantly reduced by the membrane focusing induced through the internal underpressure.
Regeneration Characteristics of Adsorbent in the Integrated Desiccant/Collector
Authors: Saito Y.
Published: June 2008

This study presents a solar desiccant system using an adsorbent in an “integrated desiccant/solar collector” that uses direct solar energy as a heat source for efficient regeneration of the adsorbent. The objective of this study is to investigate an integrated desiccant/collector in which the adsorbent absorbs solar radiation fully and is heated for regeneration. Another objective is to obtain the regeneration characteristics in the equipment proposed by both experiments and simulations. Throughout this study, silica gel is used as the adsorbent.
A Performance Test Method of Solar Thermosyphon Systems
Authors: Huang B. J. , Du S. C.
Published: June 2008

A method of test for the thermal performance rating of thermosyphon systems is developed in the present study. It is suggested that the overall performance rating of a solar thermosyphon system should include (1) system efficiency test during the energy collecting phase and (2) system cooling loss test during the cooling phase. Both the tests are performed outdoors. The cooling loss test is performed right after the efficiency test. A semi-empirical system efficiency model with a variable (Ti−Ta)/Ht is derived to correlate the daily efficiency test results; while a simple first-order model with a cooling time constant τc is used to evaluate the loss parameter in cooling phase. A method of test is then proposed and an expert system is designed to perform the outdoor tests. It is shown that very good correlation for the system efficiency model is obtained and the system parameters obtained can be used to rate the thermal performance in energy collecting phase; while the thermal performance in cooling phase is rated by examining the time constant τc of the cooling loss model.