The Solar Transmittance of Some Convection Suppression Devices for Solar Energy Applications: An Experimental Study

1982 ◽  
Vol 104 (3) ◽  
pp. 251-256 ◽  
Author(s):  
J. G. Symons
Keyword(s):  
Experimental Studies ◽  
Diffuse Radiation ◽  
Azimuth Angle ◽  
Test Facility ◽  
Integrating Sphere ◽  
Angle Of Incidence ◽  
Correlation Equations ◽  
Energy Applications ◽  
Radiation Properties ◽  
Extensive Information

The solar transmittance of seven convection suppression devices (CDSs) has been measured as a function of both angle of incidence and azimuth angle using a large integrating sphere test facility. The CSD designs tested include a honeycomb and various slat geometries made from FEP Teflon1 film, and a tubular glass honeycomb. All FEP Teflon CSDs tested had solar transmittances not less than 0.94 for angles of incidence up to 45 deg, whereas for the glass tubular CSD, the solar transmittance was not less than 0.87 over the same range. The results for FEP Teflon CSDs compare well with previous theoretical and experimental studies of similar CSDs. Empirical solar transmittance correlation equations have been derived, based on a simple CSD solar transmittance model, and they match the measured performance of the CSDs to within 2 percent. The transmittance, reflectance, and absorptance of each CSD to isotropic diffuse radiation have been determined. The radiation properties data presented provides extensive information on some alternative CSD designs, some of which have not been analysed previously.

Improved Accuracy Models For Hourly Diffuse Solar Radiation

2005 ◽  
Vol 128 (1) ◽  
pp. 104-117 ◽  
Author(s):  
T. Muneer ◽  
S. Munawwar
Keyword(s):  
Solar Radiation ◽  
Regression Models ◽  
Global Radiation ◽  
Diffuse Radiation ◽  
Evaluation Procedure ◽  
Accuracy Score ◽  
Error Statistics ◽  
Diffuse Solar Radiation ◽  
Energy Applications ◽  
Extensive Evaluation

Solar energy applications require readily available, site-oriented, and long-term solar data. However, the frequent unavailability of diffuse irradiation, in contrast to its need, has led to the evolution of various regression models to predict it from the more commonly available data. Estimating the diffuse component from global radiation is one such technique. The present work focuses on improvement in the accuracy of the models for predicting horizontal diffuse irradiation using hourly solar radiation database from nine sites across the globe. The influence of sunshine fraction, cloud cover, and air mass on estimation of diffuse radiation is investigated. Inclusion of these along with hourly clearness index, leads to the development of a series of models for each site. Estimated values of hourly diffuse radiation are compared with measured values in terms of error statistics and indicators like, R2, mean bias deviation, root mean square deviation, skewness, and kurtosis. A new method called “the accuracy score system” is devised to assess the effect on accuracy with subsequent addition of each parameter and increase in complexity of equation. After an extensive evaluation procedure, extricate but adequate models are recommended as optimum for each of the nine sites. These models were found to be site dependent but the model types were fairly consistent for neighboring stations or locations with similar climates. Also, this study reveals a significant improvement from the conventional k-kt regression models to the presently proposed models.

Fractal and Non-Fractal Surfaces in Ion Sputtering

1995 ◽  
Vol 407 ◽  
Author(s):  
A.-L. Barabási ◽  
R. Cuerno
Keyword(s):  
Nonlinear Equation ◽  
Penetration Depth ◽  
Experimental Studies ◽  
Ion Bombardment ◽  
Physical Parameters ◽  
Angle Of Incidence ◽  
Ion Sputtering ◽  
Scaling Properties ◽  
Fractal Surfaces ◽  
Experimental Parameters

ABSTRACTRecently a number of experimental studies focusing on the scaling properties of surfaces eroded by ion bombardment provided apparently contradictory results. A number of experiments report the observation of self-affine fractal surfaces, while others provide evidence about the development of a non-fractal periodic ripple structure. To explain these discrepancies, here we derive a stochastic nonlinear equation that describes the evolution and scaling properties of surfaces eroded by ion bombardment. The coefficients appearing in the equation can be calculated explicitly in terms of the physical parameters characterizing the sputtering process. We find that transitions may take place between various scaling behaviors when experimental parameters, such as the angle of incidence of the incoming ions or their average penetration depth, are varied.

scholarly journals Thermal-Hydraulic Studies on the Shell-and-Tube Heat Exchanger with Minijets

Energies ◽  
2019 ◽  
Vol 12 (17) ◽  
pp. 3276 ◽  
Author(s):  
Jan Wajs ◽  
Michał Bajor ◽  
Dariusz Mikielewicz
Keyword(s):  
Heat Transfer ◽  
Heat Exchanger ◽  
Waste Heat ◽  
Experimental Studies ◽  
Convection Heat Transfer ◽  
Test Facility ◽  
Experimental Investigations ◽  
Transfer Coefficients ◽  
Tube Heat Exchanger ◽  
Shell And Tube

In this paper a patented design of a heat exchanger with minijets, with a cylindrical construction is presented. It is followed by the results of its systematic experimental investigations in the single-phase convection heat transfer mode. Based on these results, validation of selected correlations (coming from the literature) describing the Nusselt number was carried out. An assessment of the heat exchange intensification level in the described heat exchanger was done through the comparison with a shell-and-tube exchanger of a classical design. The thermal-hydraulic characteristics of both units were the subjects of comparison. They were constructed for the identical thermal conditions, i.e., volumetric flow rates of the working media and the media temperatures at the inlets to the heat exchanger. The experimental studies of both heat exchangers were conducted on the same test facility. An increase in the heat transfer coefficients values for the minijets heat exchanger was observed in comparison with the reference one, whereas the generated minijets caused greater hydraulic resistance. Experimentally confirmed intensification of heat transfer on the air side, makes the proposed minijets heat exchanger application more attractive, for the waste heat utilization systems from gas sources.

Experimental and Numerical Investigation of Fuel–Air Mixing in a Radial Swirler Slot of a Dry Low Emission Gas Turbine Combustor

2015 ◽  
Vol 138 (6) ◽  
Author(s):  
Festus Eghe Agbonzikilo ◽  
Ieuan Owen ◽  
Jill Stewart ◽  
Suresh Kumar Sadasivuni ◽  
Mike Riley ◽  
...  
Keyword(s):  
Experimental Data ◽  
Large Scale ◽  
Experimental Studies ◽  
Flux Ratio ◽  
Turbulence Models ◽  
Test Facility ◽  
Combustion System ◽  
Fuel Gas ◽  
Low Emission ◽  
Air Mixing

This paper presents the results of an investigation in which the fuel/air mixing process in a single slot within the radial swirler of a dry low emission (DLE) combustion system is explored using air/air mixing. Experimental studies have been carried out on an atmospheric test facility in which the test domain is a large-scale representation of a swirler slot from a Siemens proprietary DLE combustion system. Hot air with a temperature of 300 °C is supplied to the slot, while the injected fuel gas is simulated using air jets with temperatures of about 25 °C. Temperature has been used as a scalar to measure the mixing of the jets with the cross-flow. The mixture temperatures were measured using thermocouples while Pitot probes were used to obtain local velocity measurements. The experimental data have been used to validate a computational fluid dynamics (CFD) mixing model. Numerical simulations were carried out using CFD software ansys-cfx. Due to the complex three-dimensional flow structure inside the swirler slot, different Reynolds-averaged Navier–Stokes (RANS) turbulence models were tested. The shear stress transport (SST) turbulence model was observed to give best agreement with the experimental data. The momentum flux ratio between the main air flow and the injected fuel jet, and the aerodynamics inside the slot were both identified by this study as major factors in determining the mixing characteristics. It has been shown that mixing in the swirler can be significantly improved by exploiting the aerodynamic characteristics of the flow inside the slot. The validated CFD model provides a tool which will be used in future studies to explore fuel/air mixing at engine conditions.

scholarly journals Design of a Concentrator With a Rectangular Flat Focus and Operation With a Suspension Reactor for Experiments in the Field of Photocatalytic Water Splitting

2014 ◽  
Author(s):  
Michael Wullenkord ◽  
Christian Jung ◽  
Christian Sattler
Keyword(s):  
Water Splitting ◽  
High Performance ◽  
Performance Test ◽  
Test Facility ◽  
Angle Of Incidence ◽  
Solar Concentrator ◽  
Tracking Accuracy ◽  
Photocatalytic Water Splitting ◽  
Maximum Angle ◽  
Production Of Hydrogen

Photocatalytic water splitting is a potential route for future carbon-free production of hydrogen. However catalysts still need to be enhanced in order to reach acceptable solar-to-fuel efficiency. In the context of the project HyCats funded by the Federal Ministry of Education and Research of Germany a high performance test facility for the evaluation of the activity of photocatalysts under practical conditions was established. It mainly consists of a solar concentrator and a planar receiver reactor. A modified linear Fresnel concentrator configuration was chosen based on ray tracing simulation results and improved concerning the number of different facets and the tolerance of tracking errors. It meets the major demand of a homogeneous irradiance distribution on the surface of the reactor. The SoCRatus (Solar Concentrator with a Rectangular Flat Focus) is a 2-axis solar concentrator with a geometrical concentration ratio of 20.2 and an aperture area of 8.8 m2. The tracking accuracy is better than 0.1° respecting both the solar azimuth and altitude angle. Its 22 highly UV/Vis-reflective flat aluminum mirror facets reflect the sunlight resulting in a rectangular focus with a nominal width of 100 mm and a nominal length of 2500 mm. The reactor is placed in the focal plane at a distance of 2500 mm from the mounting plane of the facets and allows concentrated solar radiation to penetrate suspensions of water, electrolytes and photocatalyst particles flowing through it. Corresponding to a maximum angle of incidence of 36.6° the Quartz window reflects not more than 5% of the incoming radiation and assures only marginal absorption, particularly in the UV-part of the sun’s spectrum. The material of the receiver body is PTFE (polytetrafluoroethylene) providing reflection coefficients above 90% concerning wavelengths of UV-A and UV-B. The design of the reactor features two parallel reaction chambers, offering the possibility to test two separate suspensions at the same irradiation conditions. A pump transports the tempered suspension to the reactor. The geometry of the reactor inlet and outlet minimizes critical regions with inadequate flow caused by vortices. Any evolved gases are separated from the suspension in a tank together with nitrogen introduced in the piping upstream and are analyzed by micro chromatographs. Numerous devices are installed in order to control and monitor the reaction conditions. First experiments have been carried out using methanol as a sacrificial reagent.

The Experimental Studies of Improving the Aerodynamic Performance of a Turbine Exhaust System

2014 ◽  
Vol 137 (1) ◽  
Author(s):  
Stephen Guillot ◽  
Wing F. Ng ◽  
Hans D. Hamm ◽  
Ulrich E. Stang ◽  
Kevin T. Lowe
Keyword(s):  
Reynolds Number ◽  
Mach Number ◽  
Experimental Studies ◽  
Experimental Result ◽  
Test Facility ◽  
Test Rig ◽  
Blow Down ◽  
Recovery Coefficient ◽  
Scale Test ◽  
Turbine Exhaust

Analysis and testing were conducted to optimize an axial diffuser–collector gas turbine exhaust. Two subsonic wind tunnel facilities were designed and built to support this program. A 1/12th scale test rig enabled rapid and efficient evaluation of multiple geometries. This test facility was designed to run continuously at an inlet Mach number of 0.41 and an inlet hydraulic diameter-based Reynolds number of 3.4 × 105. A 1/4th geometric scale test rig was designed and built to validate the data in the 1/12th scale rig. This blow-down rig facilitated testing at a nominally equivalent inlet Mach number, while the Reynolds number was matched to realistic engine conditions via back pressure. Multihole pneumatic pressure probes, particle image velocimetry (PIV), and surface oil flow visualization were deployed in conjunction with computational tools to explore physics-based alterations to the exhaust geometry. The design modifications resulted in a substantial increase in the overall pressure recovery coefficient of +0.07 (experimental result) above the baseline geometry. The optimized performance, first measured at 1/12th scale and obtained using computational fluid dynamics (CFD) was validated at the full scale Reynolds number.

Experimental Study on the Static and Dynamic Characteristics of Screw Grooved Seals

1988 ◽  
Vol 110 (3) ◽  
pp. 326-331 ◽  
Author(s):  
H. Kanki ◽  
T. Kawakami
Keyword(s):  
Dynamic Characteristics ◽  
Load Capacity ◽  
Experimental Studies ◽  
Test Method ◽  
Test Facility ◽  
Test Results ◽  
Heavy Duty ◽  
Static And Dynamic Characteristics ◽  
Basic Characteristics ◽  
Annular Seals

Screw grooved annular seals are used in many heavy duty pumps such as boiler feed pumps. These annular seals have a significant effect on rotordynamic characteristics of the pumps. Studies on the dynamic characteristics of plain and circumferentially grooved annular seals have been published by many researchers. However, published works on screw grooved seals are few, and pump designers have not fully recognized the basic characteristics of screw grooved seals. Extensive experimental studies have been conducted for determining the basic characteristics of screw grooved seals. The leakage characteristics, load capacity, and dynamic characteristics for rotordynamic analysis were determined by using a specially designed test facility and test method. The test results were compared to the results of plain seals [3] and the basic differences were extracted for effective application of screw grooved seals.

Fourier Transform Reflectance Spectrometry between 8000 cm−1 (1.25 μm) and 800 cm−1 (12.5 μm) Using an Integrating Sphere

1983 ◽  
Vol 37 (1) ◽  
pp. 32-38 ◽  
Author(s):  
W. Richter
Keyword(s):  
Fourier Transform ◽  
Integrating Sphere ◽  
Angle Of Incidence ◽  
Spectral Measurements ◽  
Hemispherical Reflectance ◽  
Infrared Spectral ◽  
High Purity Silicon ◽  
Silicon And Germanium ◽  
Main Components ◽  
Absolute Reflectance

Spectral measurements of the directional hemispherical reflectance of samples exhibiting variant reflection behavior were performed in the near and mid infrared spectral region using the integrating sphere method. The main components of the experimental setup were a sphere with a diffuse gold coating and a commercial Fourier transform spectrometer for the spectral analysis of the radiation incident on and reflected by the sample which is located in the center of the sphere. The capability of the device to measure absolute reflectances was tested with polished slices of high purity silicon and germanium, the reflectances of which can be calculated from the refractive indices. Agreement between the measured and calculated values was found to be within 0.01. Diffuse reflectance standards are not yet available in the infrared. The uncertainty of absolute reflectance measurements is estimated to be ±0.02. Several examples of chemical and technical applications are presented. A relatively low spectral resolution, 16 cm−1, was used to keep the measurement times short, within the range of a few minutes, thereby minimizing signal drifts. Higher resolution, sometimes necessary for special purposes in chemical analysis, can be attained by longer measurement times. No extensive sample preparation and adjustment is necessary besides the choice of the desired angle of incidence.

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