bluuebunny/crossref_metadata_2025 huggingface dataset:
Photodynamic therapy with intravitreal application of triamcinolone acetonide in age‐related macular degeneration: functional results in 54 patients
Authors: Frimpong‐Boateng Adjoa , Bunse Arnd , Rüfer Florian , Roider Johann
Published: June 2008

Purpose:  This study aimed to investigate the functional results, efficacy and complications after photodynamic therapy (PDT) combined with intravitreal triamcinolone acetonide injection (IVTA) in patients with choroidal neovascularization (CNV) caused by age‐related macular degeneration (AMD).

Methods:  A retrospective analysis of clinical data for 54 patients with CNV resulting from AMD was carried out. All patients had a follow‐up of 12 months. The patients were treated with standardized PDT and IVTA (4 mg) as a first‐line treatment or following PDT failure. Visual acuity (VA), greatest linear diameter (GLD) of the CNV and foveal thickness were evaluated.

Results:  Mean VA at baseline was 0.8 logMAR (0.4–1.4). After 12 months VA improved (> 2 lines) in 20.4% of patients and stabilized (± 2 lines) in 64.8%. There was no statistical significance in VA outcome between patients undergoing first‐line treatment and patients with PDT failure; however, fewer PDT treatments were required to stop CNV activity in patients undergoing first‐line treatment. At 12 months, a reduction in foveal thickness was seen in 67.7% of patients and a reduction in CNV GLD in 32.7%. Complications occurred in 22% of patients and included a transient rise in intraocular pressure, cataract and sterile hypopyon.

Conclusions:  Our analysis shows that fewer PDT treatments were required to stop CNV activity when triamcinolone was used as first‐line treatment. We can thus conclude that PDT combines synergistically with IVTA and the combination may lead to a cost reduction compared with PDT therapy alone. The overall complication rate of 22% is high and must be compared with complication rates caused by new intravitreal anti‐VEGF (vascular endothelial growth factor) drugs in combination with PDT.
Efficacy and safety of one intravitreal injection of bevacizumab in diabetic macular oedema
Authors: Fang Xiaoyun , Sakaguchi Hirokazu , Gomi Fumi , Oshima Yusuke , Sawa Miki , Tsujikawa Motokazu , Ikuno Yasushi , Kamei Motohiro , Kusaka Shunji , Tano Yasuo
Published: June 2008

Purpose:  To assess the efficacy, duration of effect and safety of one intravitreal injection of bevacizumab in diabetic macular oedema (DMO).

Methods:  Bevacizumab (1 mg/0.04 ml) was injected intravitreally into eyes with DMO (29 with and nine without previous treatments). Best corrected visual acuity (BCVA), intraocular pressure and central retinal thickness (CRT) were measured; slit‐lamp examination, macular biomicroscopy, optical coherence tomography and fluorescein angiography were performed before and at 2–4, 8 and 12 weeks post‐injection. Best corrected VA and CRT were analysed in both groups.

Results:  In the non‐pretreated group, mean BCVA improved from 0.76 ± 0.33 (baseline) to 0.57 ± 0.30 and 0.54 ± 0.27 at 2–4 weeks and 8 weeks post‐injection, respectively (p = 0.02, p = 0.014, paired t‐test). Mean CRT decreased from 632.4 ± 196.0 μm (baseline) to 392.3 ± 113.6 μm and 370.4 ± 141.7 μm at the same time‐points, respectively (p = 0.01, p = 0.01). There was no difference in BCVA or CRT at 12 weeks. In the pretreated group, mean BCVA improved from 0.62 ± 0.30 (baseline) to 0.53 ± 0.33 at 2–4 weeks post‐injection (p = 0.01), and mean CRT decreased from 583.9 ± 180.7 μm (baseline) to 404.1 ± 197.9 μm at 2–4 weeks post‐injection (p < 0.001). Mean BCVA was unchanged at 8 weeks and 12 weeks post‐injection, although mean CRT remained lower at 8 weeks (p = 0.004). No ocular or systemic side‐effects developed during follow‐up.

Conclusions:  One intravitreal injection of bevacizumab for DMO seems to be effective and safe in both eyes that have been treated previously and eyes that have not. The therapeutic effect is temporary and repeat treatment may be needed.
Distributed Shape Optimization of Compliant Mechanisms Using Intrinsic Functions
Authors: Lan Chao-Chieh , Cheng Yung-Jen
Published: June 2008

A compliant mechanism transmits motion and force by deformation of its flexible members. It has no relative moving parts and thus involves no wear, lubrication, noise, or backlash. Compliant mechanisms aim to maximize flexibility while maintaining sufficient stiffness so that satisfactory output motion may be achieved. When designing compliant mechanisms, the resulting shapes sometimes lead to rigid-body type linkages where compliance and rotation is lumped at a few flexural pivots. These flexural pivots are prone to stress concentration and thus limit compliant mechanisms to applications that only require small-deflected motion. To overcome this problem, a systematic design method is presented to synthesize the shape of a compliant mechanism so that compliance is distributed more uniformly over the mechanism. With a selected topology and load conditions, this method characterizes the free geometric shape of a compliant segment by its rotation and thickness functions. These two are referred as intrinsic functions and they describe the shape continuously within the segment so there is no abrupt change in geometry. Optimization problems can be conveniently formulated with cusps and intersecting loops naturally circumvented. To facilitate the optimization process, a numerical algorithm based on the generalized shooting method will be presented to solve for the deflected shape. Illustrative examples will demonstrate that through the proposed design method, compliant mechanisms with distributed compliance will lessen stress concentration so they are more robust and have a larger deflected range. It is expected that the method can be applied to design compliant mechanisms for a wide variety of applications.
Biological Modeling and Evolution Based Synthesis of Metamorphic Mechanisms
Authors: Zhang Liping , Wang Delun , Dai Jian S.
Published: June 2008

A methodology for synthesis and configuration design of metamorphic mechanisms is developed in this paper based on biological modeling and genetic evolution with biological building blocks. The goal is to conceive an appropriate source-metamorphic-mechanism configuration when the multiple phases of kinematic functions are given. The key enabler is the way of developing genetic evolution in modeling and design by capturing the metamorphic configuration characteristics. With the unique characteristic of achieving multiple working-phase functions in a mechanism, the metamorphic mechanism possesses two features: one, the ametabolic feature referring to the specified working phases that can be accomplished by a number of traditional mechanisms; two, the metamorphic feature occurring in transition between different working phases, resulting in change of topology of the mechanism. Based on this transition between phases, the concept of mechanism evolution is for the first time introduced in this paper based on biological building blocks in the form of metamorphic cells and associated intrinsic elements as the metamorphic gene. This leads to development of cell evolution and genetic aggregation with mechanism decomposition and evolutionary operation based on mapping from the source-metamorphic mechanism to multiphase working configurations. Examples are given to demonstrate the concept and principles.
Design and Prototyping of a New Balancing Mechanism for Spatial
Parallel Manipulators
Authors: Baradat C. , Arakelian V. , Briot S. , Guegan S.
Published: June 2008

This paper proposes a new solution to the problem of torque minimization of spatial parallel manipulators. The suggested approach involves connecting a secondary mechanical system to the initial structure, which generates a vertical force applied to the manipulator platform. Two versions of the added force are considered: constant and variable. The conditions for optimization are formulated by the minimization of the root-mean-square values of the input torques. The positioning errors of the unbalanced and balanced parallel manipulators are provided. It is shown that the elastic deformations of the manipulator structure, which are due to the payload, change the altitude and the inclination of the platform. A significant reduction of these errors is achieved by using the balancing mechanism. The efficiency of the suggested solution is illustrated by numerical simulations and experimental verifications. The prototype of the suggested balancing mechanism for the Delta robot is also presented.
Heat Transport Capability in an Oscillating Heat Pipe
Authors: Ma H. B. , Borgmeyer B. , Cheng P. , Zhang Y.
Published: June 2008

A mathematical model predicting the oscillating motion in an oscillating heat pipe is developed. The model considers the vapor bubble as the gas spring for the oscillating motions including effects of operating temperature, nonlinear vapor bulk modulus, and temperature difference between the evaporator and the condenser. Combining the oscillating motion predicted by the model, a mathematical model predicting the temperature difference between the evaporator and the condenser is developed including the effects of the forced convection heat transfer due to the oscillating motion, the confined evaporating heat transfer in the evaporating section, and the thin film condensation in the condensing section. In order to verify the mathematical model, an experimental investigation was conducted on a copper oscillating heat pipe with eight turns. Experimental results indicate that there exists an onset power input for the excitation of oscillating motions in an oscillating heat pipe, i.e., when the input power or the temperature difference from the evaporating section to the condensing section was higher than this onset value the oscillating motion started, resulting in an enhancement of the heat transfer in the oscillating heat pipe. Results of the combined theoretical and experimental investigation will assist in optimizing the heat transfer performance and provide a better understanding of heat transfer mechanisms occurring in the oscillating heat pipe.
Exergy Analysis of Condensation of a Binary Mixture With One Noncondensable Component in a Shell and Tube Condenser
Authors: Haseli Y. , Dincer I. , Naterer G. F.
Published: June 2008

The exergy (second-law) efficiency is formulated for a condensation process in a shell and one-path tube exchanger for a fixed control volume. The exergy efficiency ηex is expressed as a function of the inlet and outlet temperatures and mass flow rates of the streams. This analysis is utilized to assess the trend of local exergy efficiency along the condensation path and evaluate its value for the entire condenser, i.e., overall exergy efficiency. The numerical results for an industrial condenser, with a steam-air mixture and cooling water as working fluids, indicate that ηex is significantly affected by the inlet cooling water and environment temperatures. Further investigation shows that other performance parameters, such as the upstream mixture temperature, air mass flow rate, and ratio of cooling water mass flow rate to upstream steam mass flow rate, do not have considerable effects on ηex. The investigations involve a dimensionless ratio of the temperature difference of the cooling water and environment to the temperature difference of condensation and the environment. Numerical results for various operational conditions enable us to accurately correlate both the local and overall exergy efficiency as linear functions of dimensionless temperature.
Hybrid Full-Spectrum Correlated k-Distribution Method for Radiative Transfer in Nonhomogeneous Gas Mixtures
Authors: Pal Gopalendu , Modest Michael F. , Wang Liangyu
Published: June 2008

The full-spectrum k-distribution (FSK) approach is a promising model for radiative transfer calculations in participating media. FSK achieves line-by-line (LBL) accuracy for homogeneous media at a tiny fraction of LBL’s high computational cost. However, inhomogeneities in gas temperature, total pressure, and component-gas mole fractions change the spectral distribution of the absorption coefficient and can cause inaccuracies in the FSK approach. In this paper, a new hybrid FSK method is proposed that combines the advantages of the multigroup FSK (MGFSK) method for temperature inhomogeneities in a single gas species and the multiscale FSK (MSFSCK) method for concentration inhomogeneities in gas mixtures. In this new hybrid method, the absorption coefficients of each gas species in the mixture are divided into M spectral groups depending on their temperature dependence. Accurate MGFSK databases are constructed for combustion gases, such as CO2 and H2O. This paper includes a detailed mathematical development of the new method, method of database construction, and sample heat transfer calculations for 1D inhomogeneous gas mixtures with step changes in temperature and species mole fractions. Performance and accuracy are compared to LBL and plain FSK calculations. The new method achieves high accuracy in radiative heat transfer calculations in participating media containing extreme inhomogeneities in both temperature and mole fractions using as few as M=2 spectral groups for each gas species, accompanied by several orders of magnitude lower computational expense as compared to LBL solutions.
Heat Transfer in a Two-Pass Rectangular Channel (AR=1:4) Under High Rotation Numbers
Authors: Liu Yao-Hsien , Huh Michael , Han Je-Chin , Chopra Sanjay
Published: June 2008

This paper experimentally investigated the rotational effects on heat transfer in a two-pass rectangular channel (AR=1:4), which is applicable to the channel near the leading edge of the gas turbine blade. The test channel has radially outward flow in the first passage through a redirected sharp-bend entrance and radially inward flow in the second passage after a 180deg sharp turn. In the first passage, rotation effects on heat transfer are reduced by the redirected sharp-bend entrance. In the second passage, under rotating conditions, both leading and trailing surfaces experienced heat transfer enhancements above the stationary case. Rotation greatly increased heat transfer enhancement in the tip region up to a maximum Nu ratio (Nu∕Nus) of 2.4. The objective of the current study is to perform an extended parametric study of the low rotation number (0–0.3) and low buoyancy parameter (0–0.2) achieved previously. By varying the Reynolds numbers (10,000–40,000), the rotational speeds (0–400rpm), and the density ratios (inlet density ratio=0.10–0.16), the increased range of the rotation number and buoyancy parameter reached in this study are 0–0.67 and 0–2.0, respectively. The higher rotation number and buoyancy parameter have been correlated very well to predict the rotational heat transfer in the two-pass, 1:4 aspect ratio flow channel.
Heat Transfer Enhancement in Combined Convection Around a Horizontal Cylinder Using Nanofluids
Authors: Abu-Nada E. , Ziyad K. , Saleh M. , Ali Y.
Published: June 2008

Heat transfer enhancement in combined convection around a rotating horizontal cylinder using nanofluids is presented. The transport equations are solved numerically using a second-order finite volume scheme. Water-based nanofluid containing various volume fractions of different types of nanoparticles is used. The nanoparticles used are Cu, Ag, Al2O3, and TiO2. In the region outside the plume, the Nusselt number increases by increasing the volume fraction of nanoparticles. However, in the plume region, the effect of the volume fraction of nanoparticles on the Nusselt number is less pronounced.
Friction Numbers and Viscous Dissipation Heating for Laminar Flows of Water in Microtubes
Authors: El-Genk Mohamed S. , Yang In-Hwan
Published: June 2008

The friction numbers for laminar flows of water in microtubes, determined from the temperature rise due to the viscous dissipation heating assuming a velocity slip, show a strong dependence on the diameter and aspect ratio. The calculated values compare well with those determined from experimental data for water flows in glass and diffused silica microtubes (16–101μm in diameter D and aspect ratios L∕D=499–1479). With a slip, the friction number almost exponentially decreases as D decreases and, to a lesser extent, as L∕D increases. For D>400μm, the friction number approaches the theoretical Hagen–Poiseuille for macrotubes (64) when L∕D>∼1500, but higher values at smaller L∕D. The developed semiempirical analytical expression for calculating the friction number is in good agreement with the numerical and experimental results. The results suggest the presence of a velocity slip in the experiments and the plausible presence of a thin nanolayer at the walls of the microtubes. For D>200μm, this layer, if exists, is estimated to be ∼18.9nm, but increases to ∼21.5nm for D<200μm, when R¯e=800 and L∕D=1479.
An Indicator Response Surface Method for Simulation-Based Reliability Analysis
Authors: Zou Tong , Mourelatos Zissimos P. , Mahadevan Sankaran , Tu Jian
Published: June 2008

An accurate and efficient Monte Carlo simulation method is presented for limit-state-based reliability analysis at both component and system levels, using a response surface approximation of the failure indicator function. The cross-validated moving least squares method is used to construct the response surface of the indicator function, based on an optimum symmetric Latin hypercube sampling technique. The proposed method can handle problems with complicated limit state(s). Also, it can easily handle implicit, highly nonlinear limit-state functions, with variables of any statistical distributions and correlations. The method appears to be particularly efficient for multiple limit state and multiple design point problems. Three structural reliability examples are used to highlight its superior accuracy and efficiency over traditional reliability methods.
A Decomposed Gradient-Based Approach for Generalized Platform Selection and Variant Design in Product Family Optimization
Authors: Khajavirad Aida , Michalek Jeremy J.
Published: June 2008

A core challenge in product family optimization is to jointly determine (1) the optimal selection of components to be shared across product variants and (2) the optimal values for design variables that define those components. Each of these subtasks depends on the other; however, due to the combinatorial nature and high computational cost of the joint problem, prior methods have forgone optimality of the full problem by fixing the platform a priori, restricting the platform configuration to all-or-none component sharing, or optimizing the joint problem in multiple stages. In this paper, we address these restrictions by (1) introducing an extended metric to account for generalized commonality, (2) relaxing the metric to the continuous space to enable gradient-based optimization, and (3) proposing a decomposed single-stage method for optimizing the joint problem. The approach is demonstrated on a family of ten bathroom scales. Results indicate that generalized commonality dramatically improves the quality of optimal solutions, and the decomposed single-stage approach offers substantial improvement in scalability and tractability of the joint problem, providing a practical tool for optimizing families consisting of many variants.
Burmester and Allievi: A Theory and Its Application for Mechanism Design at the End of 19th Century
Authors: Ceccarelli Marco , Koetsier Teun
Published: June 2008

The second half of 19th century can be considered as the Golden Age of TMM for the achieved theoretical and practical results that led to enhancements of machinery during the second Industrial Revolution. Burmester and Allievi can be considered as significant examples of that time for their personalities and careers as well as for their work on kinematics of mechanisms. In this paper, a survey is presented on their curricula and main scientific works on mechanism design with the aim also to stress similarities and differences in the life of kinematicians and in developments in mechanism design at the end of 19th century.
Representation of Topological Changes in Metamorphic Mechanisms With Matrices of the Same Dimension
Authors: Lan Z. H. , Du R.
Published: June 2008

This short paper introduces a new adjacency matrix to represent the topological changes of metamorphic mechanisms. An element “−1” is introduced to indicate the frozen kinematic pairs, which gives an easy way to represent the transformation and the dimension of the adjacency matrix is kept unchanged after the transformation. In this way, the information of the original mechanism is preserved and all possible changes of the mechanism can be derived according to the adjacency matrix. A demonstration example is included.
Numerical Heat Transfer Optimization in Modular Systems of Y-Shaped Fins
Authors: Lorenzini Giulio , Moretti Simone
Published: June 2008

This paper analyses the heat exchange behavior in systems characterized by Y-shaped fins through a numerical approach based on a CFD software. Starting from individual Y profiles, as optimized in a previous work in relation to the dimensionless conductance and to the performance parameter of efficiency, it has been here investigated the advantage of a modular use of profiles. The analysis has been performed by superimposing some dimensional constraints to make immediately comparable the results obtained in the different configurations faced. Each module considered has a number of fins depending on the angle α between the two arms of the Y profile. This number depends therefore also on the horizontal width occupied by the whole system and it is upperly limited by the value allocated to the best performing individual fin. The results showed a significant increase of the dimensionless conductance and therefore of the exchanged thermal power for those multifin configurations with low values of α. This result validates the new optimization criterion proposed.
Experimental Study on Fundamental Phenomena of Boiling Using Heat Transfer Surfaces With Well-Defined Cavities Created by MEMS (Effect of Spacing Between Cavities)
Authors: Sato Takato , Koizumi Yasuo , Ohtake Hiroyasu
Published: June 2008

Pool nucleate boiling heat transfer experiments were performed for water using heat transfer surfaces having unified cavities. Cylindrical holes of 10μm in diameter and 40μm in depth were formed on a mirror-finished silicon wafer of 0.525mm in thickness using Microelectromechanical systems technology. The test heat transfer surface was heated by a semiconductor laser beam. Experiments were conducted in the range of up to 4.54×104W∕m2. The temperature of the back side of the heat transfer surface was measured by a radiation thermometer. When the spacing between cavities was S∕Lc<0.8, the horizontal and declining coalescence of bubbles on the neighboring cavities were dominant. Strong thermal and bubble coalescence interactions between nucleation sites were observed in this situation. This vigorous bubble coalescence created strong convection. The heat carried by this convection accounted for a large part of the heat transfer. As the cavity interval became wide, S∕Lc≥1.2, the horizontal and the declining coalescence of the bubbles ceased. The coalescence was limited to the vertical or no coalescence. The thermal and bubble coalescence interactions between the nucleation sites became quite low, to the extent of being negligible. The bubbles themselves were key in carrying heat away from the heat transfer surface.
A Multiscale Model of Thermal Contact Resistance Between Rough Surfaces
Authors: Jackson Robert L. , Bhavnani Sushil H. , Ferguson Timothy P.
Published: June 2008

A new multiscale model of thermal contact resistance (TCR) between real rough surfaces is presented, which builds on Archard’s multiscale description of surface roughness. The objective of this work is to construct the new model and use it to evaluate the effects of scale dependent surface features and properties on TCR. The model includes many details affecting TCR and is also fairly easy to implement. Multiscale fractal based models often oversimplify the contact mechanics by assuming that the surfaces are self-affine, the contact area is simply a geometrical truncation of the surfaces, and the pressure is a constant value independent of geometry and material properties. Concern has grown over the effectiveness of frequently used statistical rough surface contact models due to the inadequacies in capturing the true multiscale nature of surfaces (i.e., surfaces have multiple scales of surface features). The model developed in this paper incorporates several variables, including scale dependent yield strength and scale dependent spreading resistance to develop a new model that can be used to evaluate TCR. The results suggest that scale dependent mechanical properties are more influential than scale dependent thermal properties. When compared to an existing TCR model, this very inclusive model shows the same qualitative trend. Results also show the significance of capturing multiscale roughness when addressing the thermal contact resistance problem.
Efficiency and
Effectiveness of Heat Exchanger Series
Authors: Fakheri Ahmad
Published: June 2008

The concept of heat exchanger efficiency is extended to the heat exchanger networks. General expressions that can be used for determining the overall efficiency and effectiveness of heat exchangers connected in series regardless of the heat exchanger type have been presented. A simple, accurate, approximate algebraic expression is provided for determining the efficiency of the heat exchanger. The approach presented is far more general compared to the traditional approaches, providing the designer the flexibility to select the efficiency of the individual heat exchangers, the overall system efficiency, the number of heat exchangers, as well as the type of heat exchanger to select, by utilizing a single equation. An expression is derived for determining the minimum number of shells, as a convenient alternative for the traditional methods currently in use.
Size Effect on the Thermal Conductivity of Thin Metallic Films Investigated by Scanning Joule Expansion Microscopy
Authors: Gurrum Siva P. , King William P. , Joshi Yogendra K. , Ramakrishna Koneru
Published: June 2008

A technique to extract in-plane thermal conductivity of thin metallic films whose thickness is comparable to electron mean free path is described. Microscale constrictions were fabricated into gold films of thicknesses 43nm and 131nm. A sinusoidal voltage excitation across the constriction results in a local temperature rise. An existing technique known as scanning joule expansion microscopy, measures the corresponding periodic thermomechanical expansion with a 10nm resolution and determines the local temperature gradient near the constriction. A three-dimensional finite-element simulation of the frequency-domain heat transfer fits the in-plane thermal conductivity to the measured data, finding thermal conductivities of 82±7.7W∕mK for the 43nm film and 162±16.7W∕mK for the 131nm film, at a heating frequencies of 100kHz and 90kHz, respectively. These values are significantly smaller than the bulk thermal conductivity value of 318W∕mK for gold, showing the electron size effect due to the metal-dielectric interface and grain boundary scattering. The obtained values are close to the thermal conductivity values, which are derived from electrical conductivity measurements after using the Wiedemann–Franz law. Because the technique does not require suspended metal bridges, it captures true metal-dielectric interface scattering characteristics. The technique can be extended to other films that can carry current and result in Joule heating, such as doped single crystal or polycrystalline semiconductors.
Steady State Performance of a Single Phase Natural Circulation Loop With End Heat Exchangers
Authors: Rao N. M. , Maiti B. , Das P. K.
Published: June 2008

In the present investigation, the steady state performance of a rectangular single phase natural circulation loop (NCL) with end heat exchangers is studied. One-dimensional governing equations are considered in developing the mathematical model. Analytical expressions are derived for the circulation rate and temperature profile. However, the individual performance parameters are to be computed iteratively as the equations are strongly coupled. A suitable iterative procedure is given to evaluate the important loop parameters such as steady state flow rate, and riser and downcomer temperatures. Few special cases are discussed where analytical expressions for circulation rate and temperature distribution can be obtained directly without any iterative procedure. It is also shown that both the hot and cold end heat exchangers should have equal conductance (UA) for maximization of circulation rate. This feature of NCL is identical with heat power cycle and can be explained in light of equipartition principle.
Solar Dynamic Modules for Space Station Freedom: The Relationship Between Fine-Pointing Control and Thermal Loading of the Aperture Plate: Part II—Results
Authors: Kerslake T. W. , Quinn R. D.
Published: June 2008

The analytical approaches developed in a companion paper (Part I) were used to quantify the relationship between fine-pointing control and thermal loading of the aperture plate. Dynamic simulations of Space Station Freedom configured with solar dynamic (SD) power modules were performed. The structure was subjected to shuttle docking disturbances, while being controlled with a “natural” vibration and tracking control approach. Three control cases were investigated for the purpose of investigating the relationship between actuator effort, SD pointing, and thermal loading on the receiver aperture plate. Transient one-dimensional heat transfer analyses were performed to conservatively predict temperatures of the multilayered receiver aperture plate assembly and thermal stresses in its shield layer. Results indicate that the proposed aperture plate is tolerant of concentrated flux impingement during short-lived structural disturbances. Pointing requirements may be loosened and the required control torques lessened from that previously specified. Downsizing and simplifying the joint drive system should result in a considerable savings in mass.
Calculation of Hourly Output of a Solar Still
Authors: Sharma V. B. , Mullick S. C.
Published: June 2008

An approximate method for calculation of the hourly output of a solar still over a 24-hour cycle has been studied. The hourly performance of a solar still is predicted given the values of the insolation, ambient temperature, wind heat-transfer coefficient, water depth, and the heat-transfer coefficient through base and sides. The proposed method does not require graphical constructions and does not assume constant heat-transfer coefficients as in the previous methods. The possibility of using the values of the heat-transfer coefficients for the preceding time interval in the heat balance equations is examined. In fact, two variants of the basic method of calculation are examined. The hourly rate of evaporation is obtained. The results are compared to those obtained by numerical solution of the complete set of heat balance equations. The errors from the approximate method in prediction of the 24-hour output are within ±1.5 percent of the values from the numerical solution using the heat balance equations. The range of variables covered is 5 to 15 cms in water depth, 0 to 3 W/m2K in a heat-transfer coefficient through base and sides, and 5 to 40 W/m2K in a wind heat-transfer coefficient.
Second-Law Efficiency of an Energy Storage-Removal Cycle in a Phase-Change Material Shell-and-Tube Heat Exchanger
Authors: Charach Ch.
Published: June 2008

This communication extends the thermodynamic analysis of latent heat storage in a shell-and-tube heat exchanger, developed recently, to the complete heat storage-removal cycle. Conditions for the cyclic operation of this system are formulated within the quasi-steady approximation for the axisymmetric two-dimensional conduction-controlled phase change. Explicit expressions for the overall number of entropy generation units that account for heat transfer and pressure drop irreversibilities are derived. Optimization of this figure of merit with respect to the freezing point of the phase-change material and with respect to the number of heat transfer units is analyzed. When the frictional irreversibilities of the heat removal stage are negligible, the results of these studies are in agreement with those developed recently by De Lucia and Bejan (1991) for a one-dimensional latent heat storage system.
On the Accurate Determination of Reaction Rate Constants in Batch-Type Solar Photocatalytic Oxidation Facilities
Authors: Klausner J. F. , Martin A. R. , Goswami D. Y. , Schanze K. S.
Published: June 2008

A rigorous analysis is presented which allows for the accurate determination of reaction rate constants in batch-type photocatalytic oxidation facilities as well as any other batch-type chemical process where the reaction kinetics are known. Experimental verification of the model is accomplished using an indoor facility which utilizes an ultraviolet (UV) lamp source for the destruction of 4-chlorophenol (4CP). It has been observed that the first-order reaction rate constant increases by about 50 percent with an order of magnitude increase in flow rate. Using the present analysis, it is demonstrated that the approximate method of determining rate constants (the product of the apparent rate constant and the ratio of the reactor volume to the total system volume) is useful over a surprisingly wide range of operating conditions.
Generalized Analytical Equation for the Top Heat Loss Factor of a Flat-Plate Solar Collector With N Glass Covers
Authors: Samdarshi S. K. , Mullick S. C.
Published: June 2008

A generalized analytical equation for the top heat loss factor of a flat-plate collector with one or more glass covers has been developed. The maximum computational errors resulting from the use of the analytical equation with several simplifications are ± 5 percent compared to numerical solution of the set of heat balance equations. The analytical equation is considerably more accurate than the available semi-empirical equations over the entire range of variables covered. An additional advantage of the proposed technique over the semi-empirical equations is that results can be obtained for different values of sky temperature, using any given correlation for convective heat transfer in the air gap spacings, and for any given values of fluid (air in the present case) properties.
Hydrodynamic Instability of Solar Thermosyphon Water Heaters
Authors: Du S. C. , Huang B. J. , Yen R. H.
Published: June 2008

The flow instability of a solar thermosyphon water heater is studied analytically. A system dynamics model is derived by means of a one-dimensional approach and a linear perturbation method. The characteristic equation is obtained and the Nyquist criterion is used to examine the flow stability. The parameter M is a dimensionless parameter of system stability. The stability maps are plotted in terms of 14 parameters. The occurrence of hydrodynamic instability is determined by comparing the stability curves and the designed values of M. Flow instability is shown not to occur in most of solar water heaters commercially available, because the loop friction is relatively high in the design and because solar irradiation in field operation is still not high enough to cause flow instability.
Performance of Nonconcentrating Solar Photocatalytic Oxidation Reactors: Part II—Shallow Pond Configuration
Authors: Wyness P. , Klausner J. F. , Goswami D. Y. , Schanze K. S.
Published: June 2008

A solar photocatalytic oxidation facility has been fabricated in which the destruction of 4-chlorophenol (4CP) is tested in three adjacent shallow pond reactors. Each of the reactors has depths of 5.1, 10.2, and 15.3 cm (2, 4, and 6 in.), respectively. It is found that 4CP is successfully oxidized with the photocatalyst, titanium dioxide (TiO2), suspended in a slurry or adhered to a fiberglass mesh. The pond reactors, however, perform better with the slurry. It has also been found that the first-order rate constant for oxidation of 4CP increases with decreasing initial concentration. For the same incident ultraviolet (UV) intensity, catalyst loading, and initial solute concentration, the oxidation rate of 4CP is invariant provided the aperture to volume ratio is fixed. It has been determined that the 4CP solution contains sufficient dissolved oxygen to support the photocatalytic oxidation process. Direct evidence is provided to demonstrate that the utilization of photons in the photocatalytic process becomes less efficient as the number of incident photons on the catalyst increases.
Photochemistry of Aqueous Solutions of Dicyanomercury(II) and Potassium Tetracyanomercurate(II)
Authors: Rader W. Scott , Solujic Ljiljana , Milosavljevic E. B. , Hendrix J. L. , Nelson J. H.
Published: June 2008

Photochemically induced reactions of dicyanomercury(II) and potassium tetracyanomercurate(II) in alkaline aqueous solutions were investigated in detail. The studies were conducted in the presence or absence of a titanium(IV) oxide semiconductor photocatalyst utilizing sunlight as the irradiation source. It was established that the cyanide ion liberated from the thermodynamically stable mercury-cyano species can be photocatalytically oxidized via cyanate and nitrite to nitrate. In addition, the process removes over 99 mol% of mercury from the solution. In the absence of the photocatalyst, no photoproducts were detected and mercury remained in solution. The results obtained may have ramifications for the use of solar power for the efficient treatment of large quantities of precious metals mill tailings wastes containing various cyanide species. In addition, in order to follow the fate of cyanide in these experiments, a novel gas-diffusion flow injection analysis system for the determination of cyanide from the thermodynamically stable mercury-cyano complexes was utilized.
Operation of Large-Scale Pumps and Valves in Molten Salt
Authors: Smith D. C. , Rush E. E. , Matthews C. W. , Chavez J. M. , Bator P. A.
Published: June 2008

The molten salt pump and valve (P&V) test loops at Sandia National Laboratories (SNL) National Solar Thermal Test Facility (NSTTF) operated between Jan. 1988 and Oct. 1990. The purpose of the P&V test was to demonstrate the performance, reliability, and service life of full-scale hot and cold salt pumps and valves for use in commercial central receiver solar power plants. The P&V test hardware consists of two pumped loops; the “Hot Loop” to simulate the hot (565°C) side of the receiver and the “Cold Loop” to simulate the receiver’s cold (285°C) side. Each loop contains a pump and five valves sized to be representative of a conceptual 60-MWe commercial solar power plant design. The hot loop accumulated over 6700 hours of operation and the cold loop over 2500 hours of operation. This project has demonstrated that standard commercial scale pump and valve designs will work in molten salt. The test also exposed some pitfalls that must be avoided in specifying such equipment. Although certainly not all of the pitfalls were discovered, careful design and specification should result in reliable or at least workable equipment.
Experimental Study on the Aerodynamic Performance of a Savonius Rotor
Authors: Fujisawa Nobuyuki , Gotoh Futoshi
Published: June 2008

The aerodynamic performance of a Savonius rotor has been studied by measuring the pressure distributions on the blade surfaces at various rotor angles and tip-speed ratios. It is found that the pressure distributions on the rotating rotor differ remarkably from those on the still rotor especially on the convex side of the advancing blade, where a low pressure region is formed by the moving wall effect of the blade. The torque and power performances, evaluated by integrating the pressure, are in close agreement with those by the direct torque measurement. The drag and side force performance is also studied.
Unintended Stalling of the USW 56-100 During Optimum Pitch Control Operation
Authors: McNerney G.
Published: June 2008

The U.S. Windpower 56-100 is a three-bladed, free yaw wind turbine, using full span blade pitch control for power regulation. It is theoretically possible to increase the energy capture of the 56-100 by adjusting the blade angle to the optimum pitch angle on a continuing basis at below rated speeds. This concept was field tested on the 56-100, but it was found that the optimum pitch control logic opens a pathway for the 56-100 to fall into stall operation when the winds are above the rated wind speed. The 56-100 then operates as a stall-regulated wind turbine with an overall reduction of energy capture and an increase in system loads.
Pressure Setpoint Control of Adjustable Speed Fans
Authors: Lorenzetti D. M. , Norford L. K.
Published: June 2008

In a variable air volume (VAV) ventilation system equipped with an adjustable-speed supply fan, the fan speed typically is controlled based on the pressure measured at some location in the duct. The pressure setpoint can be fixed at a value chosen to meet maximum flow requirements, or, for greater energy efficiency, can be continuously minimized to provide for only the current flow rate. This paper describes one such pressure reset strategy, presenting energy consumption and pressure setpoint data measured in a pair of mixed-use university buildings. Fan power is modeled as a function of duct pressure, flow, and air temperature, and the model is fit to measured data. The results are used to estimate savings due to the pressure reset scheme. Savings estimates also are derived directly from measured performance of several fans under both pressure reset and fixed pressure mode control.
Thermal Storage in the Walls of a Solar House
Authors: Turner R. H. , Liu Geng , Cengel Y. A. , Harris C. P.
Published: June 2008

Residential winter thermal energy storage features water encapsulated into 3-in. (7.6-cm) diameter plastic pipes, mounted into conventional stud wall cavities of a house. With an air solar collector, solar-heated air can be passed through the stud cavities, heating the water. During the discharge mode, this water loses its heat directly to the house, and the radiating walls allow the residents to feel warm even at lower interior air temperatures. Empirical and theoretical component performance data are reported for the waterfall thermal energy storage unit. The interaction between a large air-heating solar collector and the waterfall thermal energy storage is considered for the winter heating mode. The collector-storage thermal integration analysis is detailed for a charging flow rate of 40 cfm per cavity. A simpler but reasonably accurate integration analysis is illustrated for 10 cfm cavity flow rate. Performance parameters indicate that the waterfall thermal energy storage approach is very compatible with a solar air heater.
Experimental Study of a Forced Convection Solar Collector/Regenerator for Open-Cycle Absorption Cooling
Authors: Yang Ru , Wang Pai-Lu
Published: June 2008

This paper presents an experimental study of the performance of a forced convection glazed solar collector/regenerator (C/R) operated under the meteorological conditions of Kaohsiung, Taiwan. The C/R is the key component of an open-cycle absorption solar cooling system because its performance directly indicates the system performance. The present results show that the counterflow case can improve the C/R efficiency when inlet solution concentration is low. The effects of individual parameter on the C/R performance are analyzed. Dimensionless heat and mass transfer coefficients are given.
Design of a Multiple-Lamp Large-Scale Solar Simulator
Authors: Kenny S. P. , Davidson J. H.
Published: June 2008

A simple solution to the conflicting constraints of providing uniformity and collimation of irradiance in multiple-lamp solar simulators is proposed. As proof of concept, irradiance measurements obtained in a simulator comprised of 28 1-kW mercury-iodide gas discharge lamps and capable of irradiating a 1.22 m-by-2.44 m collector plane are given. The design is based on preventing a portion of the light from each bulb from reaching the collector plane. Light blockage is achieved by placing a “shadow board” 1.02 m from and parallel to the plane of the lamps. Lamps are arranged in an hexagonal pattern with 4 columns of 7 lamps at a lamp-to-lamp spacing and column-to-column spacing of 0.45 m. Lamp-to-collector plane distance is 3.05 m. The design is determined from measurements of the spatial distribution of radiant energy from a single lamp. Irradiance from an array of lamps is then simulated. Measurements of irradiance in the full-scale simulator confirm that uniformity and collimation conform to the American Society of Heating, Refrigerating and Air Conditioning Engineers’ standard. Average irradiance is 1080 W/m2. Maximum irradiance is 1190 W/m2 and minimum irradiance is 980 W/m2. Every point on the plane of the collector receives 100 percent of radiant energy from an area on the lamp array contained within a subtended angle of 20 deg.
Experimental Setup of a Laser Diagnostics System for a High-Temperature Solar Receiver/Reactor
Authors: Steinfeld A. , Bombach R. , Haueter P. , Hemmerling B. , Kreutner W. , Thompson G. , Wuillemin D.
Published: June 2008

A solar receiver/reactor has been designed specifically to study high-temperature gas phase chemical reactions using a laser based metrology. It is a cavity-type receiver, lined with stabilized ZrO2, and operated at temperatures up to 2000 K. The gas temperature is measured in situ using the coherent anti-Stokes Raman spectroscopy (CARS) of N2. Optical access for the CARS measurement is accomplished via two side windows, each subtending a 118-mrad cone angle at the center of the cavity, providing enough clearance for the input laser beams and the output signal carrying the temperature information. Two endothermic processes were used for the initial evaluation of this method: the NH3 dissociation into N2 and H2, and the CO2-reforming of CH4 into synthesis gas. The process flow was directly exposed to high solar fluxes in addition to infrared radiation emitted by the hot reactor walls. The laser-based metrology performed satisfactorily in spite of the presence of the intense radiation field. This paper describes in detail the technical aspects of the experimental setup, presents examples of spectra and temperature measurements, and discusses practical problems encountered during experimentation.
Forced Convective Heat Transfer in Cross-Corrugated Solar Air Heaters
Authors: Piao Y. , Hauptmann E. G. , Iqbal M.
Published: June 2008

Forced convective heat transfer in a cross-corrugated channel solar air heater has been studied experimentally using air as a working fluid. The channel was formed by two transversely positioned corrugated sheets and two flat thermally insulated side walls. One corrugated sheet was heated by a radiant heater, while the other was thermally insulated. The fluid velocity and temperature, and the wall temperature and the local heat flux across the heated corrugated sheet were measured for a variety of operating flow rates. Experimental results for the channel geometry have yielded the correlation Nu=0.0743(Re)0.76. This heat-transfer coefficient is about 2.8 times that of a smooth flat channel. The experiments showed that local heat transfer rate was smaller on the valley of the corrugation than that on the peak. The ratio of the local heat transfer rates on the two locations was related to the Reynolds number.