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《International Journal of Heat and Mass Transfer》2007,50(1-2):67-74
In the present study, a new lattice thermal conductivity model for a thin-film semiconductor is proposed. This model is considered, compared to the existing models, to be more mathematically consistent in the sense that the heat flow is contributed solely by the low-dimensional phonons, and the spatial confinement effects not only on the phonon group and phase velocities but also on the Debye temperature are taken into consideration. To count the boundary scattering effect, an analytical or empirical boundary scattering rate is suggested and added to the total scattering rate via the Mattiessen’s rule. It is found this newly proposed model predicts as well as the existing models and reasonably well with the experimental data. 相似文献
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《Applied Thermal Engineering》2007,27(11-12):2044-2050
A pilot experimental solar chimney power setup consisted of an air collector 10 m in diameter and an 8 m tall chimney has been built. The temperature distribution in the solar chimney power setup was measured. Temperature difference between the collector outlet and the ambient usually can reach 24.1 °C, which generates the driving force of airflow in the setup. This is the greenhouse effect produced in the solar collector. It is found that air temperature inversion appears in the latter chimney after sunrise both on a cool day and on a warm day. Air temperature inversion is formed by the increase of solar radiation from the minimum and clears up some time later when the absorber bed is heated to an enough high temperature to make airflow break through the temperature inversion layer and flow through the chimney outlet. 相似文献
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Thin film solar cells are promising for large-scale commercial applications due to their low manufacturing costs. However, a major problem with thin film technology is material nonuniformity associated with the fabrication of large area films. We are developing a technology for fabricating high-efficiency solar cells based on semiconductor nanostructures that will eliminate the problem of spatial nonuniformity while retaining the low-cost advantage of thin film manufacturing. The technology is based on electrochemical synthesis of semiconductor nanostructures on a preformed template and is flexible in the choice of semiconductor and substrate materials. 相似文献
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Suren A. GevorgyanMikkel Jørgensen Frederik C. KrebsKristian O. Sylvester-Hvid 《Solar Energy Materials & Solar Cells》2011,95(5):1389-1397
A controlled atmosphere setup designed for long-term degradation studies of organic solar cells under illumination is presented. The setup was designed with ease-of-use and compactness in mind and allows for multiple solar cells distributed on four glass substrates to be studied in four different chambers with temperature and atmosphere control. The four chambers are situated at close proximity in the setup thereby allowing the solar cells to be subjected to as uniform an illumination distribution as possible for the given solar simulator employed. The cell substrates serve as the front window and present a tight seal. Hence no illumination correction needs to be performed due to transmission and reflection losses as otherwise seen with test chambers employing a window as a seal. The solar cells in each chamber are continuously and individually electrically monitored under biased conditions by means of a computer controlled multiplexer and source meter. The dimensions of the setup allow it to pass through a mid-size load lock in most common glove box systems allowing for mounting of tested samples under inert conditions.As a demonstration of the applicability of the chamber design, a degradation study of standard P3HT:PCBM solar cells was performed under four different environmental conditions. 相似文献
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《Applied Thermal Engineering》2000,20(14):1297-1314
Polymers have been proven to be high potential low-cost materials for the design and mass production not only for ordinary solar water heaters but also for very simple large size, modular solar collectors, suitable for easy erection of large solar heating plants. Their major drawback for solar–thermal conversion applications is their low thermal conductivity, which prohibits their use unless an appropriate absorber design is employed. The low thermal conductivity of polymers has imposed the need of a particular absorber design, which is basically composed of a pair of dark, closely spaced parallel plates at the top of which solar radiation is absorbed, forming a thin channel for the flow of the heat transfer fluid. The aim of the present work is to investigate the particular limitations of this polymer plate absorber design, for a wide range of collector loss and convective heat transfer coefficients between heat transfer fluid and absorber plate. The aim is also to calculate the particular collector efficiency factors and conditions under which the associated collector performance parameters should be modified to account for the finite absorber plate conductance. This conductance was proven to be another decisive absorber design parameter, improper selection of which may probably lead to strong deterioration of the collector efficiency. 相似文献
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This paper shows that rapidly formed emitters in less than 6 min in the hot zone of a conveyor belt furnace or in 3 min in an rapid thermal processing (RTP) system, in conjunction with a screen-printed (SP) RTP Al-BSF and passivating oxide formed simultaneously in 2 min can produce very simple high-efficiency n+-p-p+ cells with no surface texturing, point contacts, or selective emitter. It is shown for the first time that an 80 Ω/□ emitter and SP Al-back surface field (BSF) formed in a high throughput belt furnace produced 19% FZ cells and greater than 17% CZ cells with photolithography (PL) contacts. Using PL contacts, we also achieved 19% efficient cells on FZ, >18% on MCZ, and 17% boron-doped CZ by emitter and SP Al-BSF formation in <10 min in a single wafer RTP system. Finally, manufacturable cells with 45 Ω/□ emitter and SP Al-BSF and Ag contacts formed in the conveyor belt furnace gave 17% efficient cells on FZ silicon. Compared to the PL cells, the SP cell gave 2% lower efficiency along with a decrease in Jsc and fill factor. This loss in performance is attributed to a combination of the poor blue response, higher series resistance and higher contact shading in the SP devices 相似文献
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S. Noël A. Slaoui S. Peters H. Lautenschlager R. Schindler J. C. Muller 《Solar Energy Materials & Solar Cells》2001,65(1-4)
Rapid thermal processing is opening new possibilities for a low-cost and environmentally safe silicon solar cell production, keeping the process time at high temperature in the order of 1 min, due to enhanced diffusion and oxidation mechanisms. Controlling the surface concentration of the junction is one of the major parameters, in order to obtain suitable front surface recombination velocities. Simultaneous diffusion of phosphorus and aluminum is used to realize emitter and back surface field in a single high-temperature step, with optimized gettering effect. Controlling the mentioned parameters on industrial 1 Ω cm Cz material lead in 17.5% efficient solar cells on a surface of 25 cm2. All results are discussed in terms of process temperature, dopant source concentration and effective process time, below 1 min including high heating and cooling rates. 相似文献
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Juan-Cheng Yang Feng-Chen Li Wen-Wu Zhou Yu-Rong He Bao-Cheng Jiang 《International Journal of Heat and Mass Transfer》2012,55(11-12):3160-3166
Viscoelastic-fluid-based nanofluids with dispersion of copper (Cu) nanoparticles in viscoelastic surfactant solution (aqueous solution of cetyltrimethylammonium chloride/sodium salicylate) were prepared. A comparative study of thermal conductivity and viscosity between viscoelastic-fluid-based Cu nanofluids and distilled water based nanofluids was then performed experimentally. Different concentrations of viscoelastic base fluid and volume fraction of Cu nanoparticles were matched in order to check their influences on fluid’s thermal conductivity and viscosity. The experimental results show that the viscoelastic-fluid-based Cu nanofluids have a higher thermal conductivity than viscoelastic base fluid, and its thermal conductivity increases with increasing temperature and increasing particle volume fraction. Furthermore, the viscoelastic-fluid-based Cu nanofluid shows a non-Newtonian behavior in its viscosity, and the viscosity increases with the increase of Cu nanoparticle concentration and decrease of temperature. 相似文献
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《International Journal of Heat and Mass Transfer》2007,50(23-24):4767-4779
Experiments on removing high heat fluxes from GaN-on-SiC semiconductor dies using microchannel coolers are described. The dies contain an AlGaN/GaN heterostructure operated as a direct current resistor, providing a localized heat source. The active dimensions of the heat source are sized to represent the spatially-averaged heat flux that would appear in microwave power amplifiers. A wide variety of microchannel materials and configurations are investigated, allowing a comparison of performance and the resulting GaN temperatures. Silicon and AlN microchannel coolers exhibit good performance at lower power densities (1000–1200 W/cm2 over 3 × 5 mm2 to 2 × 5 mm2 active areas). Polycrystalline chemical vapor deposited (CVD) SiC microchannel coolers are found to be extremely promising for higher power densities (3000–4000 W/cm2 over 1.2 × 5 mm2 active areas with 120 °C GaN temperature). A hybrid microchannel cooler consisting of low-cost CVD diamond on polycrystalline CVD SiC exhibits moderately better performance (20–30%) than polycrystalline CVD SiC alone. 相似文献
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ZnO nanowires and structures that combine nanowires and nanoparticles were used as the wide band gap semiconducting photoelectrode in dye-sensitized solar cells (DSSCs). The nanowires provide a direct path from the point of photogeneration to the conducting substrate and offer alternative semiconductor network morphologies to those possible with sintered nanoparticles. Growing nanowires with dendrite-like branched structure greatly enhances their surface area, leading to improved light harvesting and overall efficiencies. Hybrid cells based on a combination of nanowires and nanoparticles can be tailored to take advantage of both the high surface area provided by the nanoparticles and the improved electron transport along a nanowire network. Solar cells made from branched nanowires showed photocurrents of 1.6 mA/cm2, internal quantum efficiencies of 70%, and overall efficiencies of 0.5%. Solar cells made from appropriate hybrid morphologies show photocurrents of 3 mA/cm2 and overall efficiencies of 1.1%, while both the nanowire and hybrid cells show larger open circuit voltages than nanoparticle cells. 相似文献
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The pilot project of a multistage solar thermal water desalination system has been developed, and experimental investigations
have been carried out. This paper presents the results of the testing of the system under laboratory conditions. The results
show that the productivity of the developed system is two times higher than that of the conventional solar distillers of the
greenhouse type.
The text was submitted by the authors in English. 相似文献
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在微电子领域中,随着元器件的体积微小化,要求导热材料具备体积小、高导热的特点。高分子导热复合材料能很好的解决器件在不同的工作环境中仍能保持正常的散热问题。以环氧树脂(EP)为基体,石墨烯粉末(GP)和多壁碳纳米管(MWCNTs)为导热填料,采用溶剂和超声分散法,制备出石墨烯/碳纳米管/环氧树脂复合材料。实验采用瞬态电热技术测量其导热系数,结果显示,石墨烯与碳纳米管协同作为导热填料时,复合材料导热性优于单独添加导热填料(GP或MWCNTs),且随着GP所占比例的增大复合材料的导热系数越大。当GP和MWCNTs比例分别为0.7%和0.3%时,复合材料导热系数为0.940 W/(m·K),相比于纯EP导热系数提高了286.83%。 相似文献