scholarly journals Thermal Analysis of Direct Liquid-Immersed Solar Receiver for High Concentrating Photovoltaic System

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Xinyue Han ◽  
Qian Wang ◽  
Jun Zheng ◽  
Jian Qu
Keyword(s):  
Solar Cells ◽  
Conversion Efficiency ◽  
Flow Rate ◽  
Triple Junction ◽  
Concentration Factor ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Dense Array ◽  
Wide Range ◽  
Solar Receiver

Concentrator solar cells that operate at high solar concentration level must be cooled. In this paper, direct liquid immersion cooling of triple-junction solar cells (InGaP/InGaAs/Ge) is proposed as a heat dissipation solution for dense-array high concentrating photovoltaic (HCPV) systems. The advantages of triple-junction CPV cells immersed in a circulating dielectric liquid and dish HCPV technology are integrated into a CPV system to improve the system electrical conversion efficiency. An analytical model for the direct liquid-immersed solar receiver with triple-junction CPV cells is presented. The main outputs of the model are the components temperatures of the receiver and the system electrical efficiency. The influence of concentration factor, mass flow rate, and inlet liquid temperature on the operating temperature of the triple-junction CPV cells and the system electrical conversion efficiency are discussed. It is shown that the system electrical conversion efficiency is very high for a wide range of operating conditions. The three operating parameters have a major effect on the operating temperature of the triple-junction CPV cells and, by extension, system output power. The flow rate selection should match concentration factor to keep the triple-junction CPV cells temperature lower and increase the electrical conversion efficiency of the dense-array HCPV system.

scholarly journals Experimental Investigation and Modeling of Inertance Tubes

2005 ◽  
Vol 127 (5) ◽  
pp. 1029-1037 ◽  
Author(s):  
L. O. Schunk ◽  
G. F. Nellis ◽  
J. M. Pfotenhauer
Keyword(s):  
Mass Flow Rate ◽  
Mass Flow ◽  
Flow Rate ◽  
Acoustic Power ◽  
Operating Conditions ◽  
Thermodynamic Efficiency ◽  
Pulse Tube ◽  
Design Charts ◽  
Wide Range ◽  
Pulse Tube Refrigerators

Growing interest in larger scale pulse tubes has focused attention on optimizing their thermodynamic efficiency. For Stirling-type pulse tubes, the performance is governed by the phase difference between the pressure and mass flow, a characteristic that can be conveniently adjusted through the use of inertance tubes. In this paper we present a model in which the inertance tube is divided into a large number of increments; each increment is represented by a resistance, compliance, and inertance. This model can include local variations along the inertance tube and is capable of predicting pressure, mass flow rate, and the phase between these quantities at any location in the inertance tube as well as in the attached reservoir. The model is verified through careful comparison with those quantities that can be easily and reliably measured; these include the pressure variations along the length of the inertance tube and the mass flow rate into the reservoir. These experimental quantities are shown to be in good agreement with the model’s predictions over a wide range of operating conditions. Design charts are subsequently generated using the model and are presented for various operating conditions in order to facilitate the design of inertance tubes for pulse tube refrigerators. These design charts enable the pulse tube designer to select an inertance tube geometry that achieves a desired phase shift for a given level of acoustic power.

Subsynchronous Vibration Patterns Under Reduced Oil Supply Flow Rates

2017 ◽  
Author(s):  
B. R. Nichols ◽  
R. L. Fittro ◽  
C. P. Goyne
Keyword(s):  
Flow Rate ◽  
High Speed ◽  
Operating Conditions ◽  
System Stability ◽  
Supporting Evidence ◽  
Test Rig ◽  
Flow Rates ◽  
Oil Supply ◽  
Bending Mode ◽  
Wide Range

Many high-speed, rotating machines across a wide range of industrial applications depend on fluid film bearings to provide both static support of the rotor and to introduce stabilizing damping forces into the system through a developed hydrodynamic film wedge. Reduced oil supply flow rate to the bearings can cause cavitation, or a lack of a fully developed film layer, at the leading edge of the bearing pads. Reducing oil flow has the well-documented effects of higher bearing operating temperatures and decreased power losses due to shear forces. While machine efficiency may be improved with reduced lubricant flow, little experimental data on its effects on system stability and performance can be found in the literature. This study looks at overall system performance of a test rig operating under reduced oil supply flow rates by observing steady-state bearing performance indicators and baseline vibrational response of the shaft. The test rig used in this study was designed to be dynamically similar to a high-speed industrial compressor. It consists of a 1.55 m long, flexible rotor supported by two tilting pad bearings with a nominal diameter of 70 mm and a span of 1.2 m. The first bending mode is located at approximately 5,000 rpm. The tiling-pad bearings consist of five pads in a vintage, flooded bearing housing with a length to diameter ratio of 0.75, preload of 0.3, and a load-between-pad configuration. Tests were conducted over a number of operating speeds, ranging from 8,000 to 12,000 rpm, and bearing loads, while systematically reducing the oil supply flow rates provided to the bearings under each condition. For nearly all operating conditions, a low amplitude, broadband subsynchronous vibration pattern was observed in the frequency domain from approximately 0–75 Hz. When the test rig was operated at running speeds above its first bending mode, a distinctive subsynchronous peak emerged from the broadband pattern at approximately half of the running speed and at the first bending mode of the shaft. This vibration signature is often considered a classic sign of rotordynamic instability attributed to oil whip and shaft whirl phenomena. For low and moderate load conditions, the amplitude of this 0.5x subsynchronous peak increased with decreasing oil supply flow rate at all operating speeds. Under the high load condition, the subsynchronous peak was largely attenuated. A discussion on the possible sources of this subsynchronous vibration including self-excited instability and pad flutter forced vibration is provided with supporting evidence from thermoelastohydrodynamic (TEHD) bearing modeling results. Implications of reduced oil supply flow rate on system stability and operational limits are also discussed.

Incident-angle-controlled semitransparent colored perovskite solar cells with improved efficiency exploiting a multilayer dielectric mirror

Nanoscale ◽  
2017 ◽  
Vol 9 (37) ◽  
pp. 13983-13989 ◽  
Author(s):  
Kyu-Tae Lee ◽  
Ji-Yun Jang ◽  
Sang Jin Park ◽  
Song Ah Ok ◽  
Hui Joon Park
Keyword(s):  
Solar Cells ◽  
Visible Light ◽  
Power Conversion Efficiency ◽  
Conversion Efficiency ◽  
Incident Angle ◽  
Power Conversion ◽  
Perovskite Solar Cells ◽  
Dielectric Mirror ◽  
Wide Range ◽  
Multilayer Dielectric

See-through colored perovskite solar cells that exploit a dielectric mirror are demonstrated. The dielectric mirror strongly reflects a wide range of visible light back to a photoactive layer for efficient light-harvesting, yielding 10.12% power conversion efficiency, with iridescent semitransparent colors.

Modelling of Partially Wetting Liquid Film Using an Enhanced Thin Film Model for Aero-Engine Bearing Chamber Applications

2020 ◽  
Author(s):  
K. Singh ◽  
M. Sharabi ◽  
R. Jefferson-Loveday ◽  
S. Ambrose ◽  
C. Eastwick ◽  
...  
Keyword(s):  
Thin Film ◽  
Contact Angle ◽  
Film Thickness ◽  
Liquid Film ◽  
Flow Rate ◽  
Operating Conditions ◽  
Film Model ◽  
Thin Film Model ◽  
Wide Range ◽  
Aero Engine

Abstract In the case of aero-engine, thin lubricating film servers dual purpose of lubrication and cooling. Prediction of dry patches or lubricant starved region in bearing or bearing chambers are required for safe operation of these components. In the present work thin liquid film flow is numerically investigated using the framework of the Eulerian thin film model (ETFM) for conditions which exhibit partial wetting phenomenon. This model includes a parameter that requires adjustment to account for the dynamic contact angle. Two different experimental data sets have been used for comparisons against simulations, which cover a wide range of operating conditions including varying the flow rate, inclination angle, contact angle, and liquid-gas surface tension coefficient. A new expression for the model parameter has been proposed and calibrated based on the simulated cases. This is employed to predict film thickness on a bearing chamber which is subjected to a complex multiphase flow. From this study, it is observed that the proposed approach shows good quantitative comparisons of the film thickness of flow down an inclined plate and for the representative bearing chamber. A comparison of model predictions with and without wetting and drying capabilities is also presented on the bearing chamber for shaft speed in the range of 2,500 RPM to 10,000 RPM and flow rate in the range of 0.5 liter per minute (LPM) to 2.5 LPM.

scholarly journals Flux-Reducing Tendency of Pd-Based Membranes Employed in Butane Dehydrogenation Processes

Membranes ◽  
2020 ◽  
Vol 10 (10) ◽  
pp. 291 ◽  
Author(s):  
Thijs A. Peters ◽  
Marit Stange ◽  
Rune Bredesen
Keyword(s):  
Competitive Adsorption ◽  
Prolonged Exposure ◽  
Hydrogen Permeation ◽  
State Of The Art ◽  
Operating Temperature ◽  
Operating Conditions ◽  
Maximum Temperature ◽  
Hydrogen Flux ◽  
Membrane Performance ◽  
Wide Range

We report on the effect of butane and butylene on hydrogen permeation through thin state-of-the-art Pd–Ag alloy membranes. A wide range of operating conditions, such as temperature (200–450 °C) and H2/butylene (or butane) ratio (0.5–3), on the flux-reducing tendency were investigated. In addition, the behavior of membrane performance during prolonged exposure to butylene was evaluated. In the presence of butane, the flux-reducing tendency was found to be limited up to the maximum temperature investigated, 450 °C. Compared to butane, the flux-reducing tendency in the presence of butylene was severe. At 400 °C and 20% butylene, the flux decreases by ~85% after 3 h of exposure but depends on temperature and the H2/butylene ratio. In terms of operating temperature, an optimal performance was found at 250–300 °C with respect to obtaining the highest absolute hydrogen flux in the presence of butylene. At lower temperatures, the competitive adsorption of butylene over hydrogen accounts for a large initial flux penalty.

scholarly journals A Computationally Efficient Multidiode Model for Optimizing the Front Grid of Multijunction Solar Cells under Concentration

2020 ◽  
Vol 2020 ◽  
pp. 1-10
Author(s):  
Chris H. van de Stadt ◽  
Pilar Espinet Gonzalez ◽  
Harry A. Atwater ◽  
Rebecca Saive
Keyword(s):  
Solar Cells ◽  
Operating Conditions ◽  
Design Parameters ◽  
Computationally Efficient ◽  
Fast Determination ◽  
Wide Range ◽  
Multijunction Solar Cells ◽  
Efficiency Increase ◽  
Light Concentration

We have developed a computationally efficient simulation model for the optimization of redirecting electrical front contacts for multijunction solar cells under concentration, and we present its validation by comparison with experimental literature results. The model allows for fast determination of the maximum achievable efficiency under a wide range of operating conditions and design parameters such as the contact finger redirecting capability, period and width of the fingers, the light concentration, and the metal and emitter sheet resistivity. At the example of a state-of-the-art four-junction concentrator solar cell, we apply our model to determine ideal operating conditions for front contacts with different light redirection capabilities. We find a 7% relative efficiency increase when enhancing the redirecting capabilities from 0% to 100%.

A high efficiency solution processed polymer inverted triple-junction solar cell exhibiting a power conversion efficiency of 11.83%

2015 ◽  
Vol 8 (1) ◽  
pp. 303-316 ◽  
Author(s):  
Abd. Rashid bin Mohd Yusoff ◽  
Dongcheon Kim ◽  
Hyeong Pil Kim ◽  
Fabio Kurt Shneider ◽  
Wilson Jose da Silva ◽  
...  
Keyword(s):  
Solar Cells ◽  
Solar Cell ◽  
Power Conversion Efficiency ◽  
Conversion Efficiency ◽  
Triple Junction ◽  
High Efficiency ◽  
Open Circuit Voltage ◽  
Power Conversion ◽  
Open Circuit ◽  
Tandem Solar Cells

We propose that 1 + 1 + 1 triple-junction solar cells can provide an increased efficiency, as well as a higher open circuit voltage, compared to tandem solar cells.

scholarly journals Systematic derivation of a surface polarisation model for planar perovskite solar cells

2018 ◽  
Vol 30 (3) ◽  
pp. 427-457 ◽  
Author(s):  
N. E. COURTIER ◽  
J. M. FOSTER ◽  
S. E. J. O'KANE ◽  
A. B. WALKER ◽  
G. RICHARDSON
Keyword(s):  
Solar Cells ◽  
Numerical Solutions ◽  
Perovskite Solar Cells ◽  
Practical Interest ◽  
Operating Conditions ◽  
Asymptotic Approach ◽  
Perovskite Layer ◽  
Current Voltage ◽  
Wide Range ◽  
Vacancy Density

Increasing evidence suggests that the presence of mobile ions in perovskite solar cells (PSCs) can cause a current–voltage curve hysteresis. Steady state and transient current–voltage characteristics of a planar metal halide CH3NH3PbI3PSC are analysed with a drift-diffusion model that accounts for both charge transport and ion vacancy motion. The high ion vacancy density within the perovskite layer gives rise to narrow Debye layers (typical width ~2 nm), adjacent to the interfaces with the transport layers, over which large drops in the electric potential occur and in which significant charge is stored. Large disparities between (I) the width of the Debye layers and that of the perovskite layer (~600 nm) and (II) the ion vacancy density and the charge carrier densities motivate an asymptotic approach to solving the model, while the stiffness of the equations renders standard solution methods unreliable. We derive a simplifiedsurface polarisationmodel in which the slow ion dynamics are replaced by interfacial (non-linear) capacitances at the perovskite interfaces. Favourable comparison is made between the results of the asymptotic approach and numerical solutions for a realistic cell over a wide range of operating conditions of practical interest.

scholarly journals A Database for Urdu Text Detection and Recognition in Natural Scene Images

2020 ◽  
Vol 39 (1) ◽  
pp. 47-54
Author(s):  
Mehwish Leghari ◽  
Mukhtiar Ahmad Memon ◽  
Mehjabeen Leghari ◽  
Akhtar Hussain Jalbani
Keyword(s):  
Quantum Dots ◽  
Solar Cells ◽  
Band Gap ◽  
Conversion Efficiency ◽  
Silicon Quantum Dots ◽  
Simulation Efficiency ◽  
Wide Range ◽  
Cell Conversion ◽  
Pv Cell ◽  
Generation Cost

Conventional solar cells are not economical and are recently too expensive to the manufacturers for extensive-scale electricity generation. Cost and efficiency is most vital factor in the accomplishment of any solar technology. In order to improve the conversion efficiency, the major research in third generation photovoltaic (PV) cells is directed toward retaining more sunlight using nanotechnology. Advancement in nanotechnology solar cell via quantum dots (QDs) could reduce the cost of PV cell and additionally enhance cell conversion efficiency. Silicon quantum dots (Si-QDs) are semiconductor nano crystals of nanometers dimension whose electron-holes are confined in all three spatial dimensions. Quantum dots have discrete electronic states. Quantum dots have capacity to change band gap with the adjustment in size of quantum dot. As the quantum dots size fluctuates over a wide range that demonstrates the variety of band gap so it will assimilate or discharge light. In this paper, the generic mathematical models of PV cell are adopted and then I-V and P-V characteristic curves are obtained from selected parameters using MATLAB software. The essential parameters are taken from datasheets. I-V and P-V characteristics curves are obtained for selected model. Silicon quantum dots have the tunable band gap that is added to conventional PV cell and obtain the I-V and P-V curves. After simulation, efficiency and power of Conventional PV cell to quantum dots based PV cell is compared. The property of quantum dots is used in extending the band gap of solar cells and increasing the maximum proportion of incident sunlight absorbed, hence improving efficiency.

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