Lattice Boltzmann simulation of MHD mixed convection in a two‐sided lid‐driven square cavity

In this paper the effects of a magnetic field on mixed convection flow in a two‐sided lid‐driven cavity have been analyzed by the lattice Boltzmann method (LBM). The Hartmann number varied from Ha = 0 to 100. The study has been conducted for different Richardson numbers (Ri) from 0.01 to 100 while the direction of the magnetic field was investigated in the x‐direction. Consequences demonstrate that the heat transfer augments with an increment of the Richardson number for different Hartmann numbers for two cases. The heat transfer declines with the growth of the magnetic field for various Richardson numbers for two cases. The difference between the values of heat transfer for the two cases at variant parameters is negligible but the trend of fluid flow for the two cases is multifarious. © 2011 Wiley Periodicals, Inc. Heat Trans Asian Res; Published online in Wiley Online Library ( wileyonlinelibrary.com/journal/htj ). DOI 10.1002/htj.20402     

Multi-user Quantum Cryptography on Optical Networks

Abstract

Quantum cryptography has been shown to be an effective technology for the secure distribution of keys on point-to-point optical links. We show how the existing techniques can be extended to allow multi-user secure key distribution on optical networks. We demonstrate that using network configurations typical of those found in passive optical network architectures any of the current quantum key distribution protocols can be adapted to implement secure key distribution from any user to any other user. An important feature of these adapted protocols is that the broadcaster, or service provider on the network, does not have to be trusted by the two users who wish to establish a key.     

Polycrystalline Silicon-Film™ Thin-film Solar Cells: Advanced Products

Thin-film polycrystalline silicon has the potential to achieve the cost reduction and performance improvement necessary for large-scale electricity markets. Reduced cost is achieved by capitalizing on the benefits of thin films grown on low-cost, large-area substrates. Improved efficiency is realized, in spite of reduced material quality, by incorporating enhanced optical absorption and back-surface passivation. The cornerstone of AstroPower's thin-film solar cell technology is the Silicon-Film™ process: a method for the manufacture of solar cell-quality, polycrystalline films of silicon on a variety of low-cost, supporting substrates. Three thin-film solar cell designs, based on this technology, are currently under development. This paper presents the key design features of these three products and briefly reviews the current status of the development of the key technologies that comprise the advanced thin-film solar cell products.     

Two dimensional transport characteristics of surface stabilized zero-valent iron nanoparticles in porous media

Zero-valent iron nanoparticles (INP) were synthesized and stabilized using poly acrylic acid (PAA) to yield stabilized INP (S-INP). A two-dimensional physical model was used to study the fate and transport of the INP and S-INP in porous media under saturated, steady-state flow conditions. Transport data for a nonreactive tracer, INP, and S-INP were collected under similar flow conditions. The results show that unstabilized INP cannot be transported into groundwater systems. On the other hand, the S-INP can be transported like a tracer without significant retardation. However, the S-INP plume migrated downward as it moved horizontally in the physical model, indicating that small density gradients have significant influence on two-dimensional transport. The variable-density groundwater flow model SEAWAT was used to model the observed density-driven transport patterns. This is the first time a two-dimensional transport data set is reported for demonstrating the multidimensional transport characteristics of nanoparticles. The data shows the importance of density effects, which cannot be fully discerned using one-dimensional, column experiments. Finally, we also demonstrate that the numerical model SEAWAT can be used to predict the density-driven transport characteristics of S-INP in groundwater aquifers.     

On‐line learning: A quality experience

The paper outlines the strategy being developed for the growth of electronic books within the UK academic community and provides a broad analysis of the e‐book industry and critical factors. The role of the JISC E‐Books Working Group is described and an overview given of its programme of activities.     

Defect passivation on cast-mono crystalline screen-printed cells

Cast-mono crystalline silicon wafers contain crystallographic defects, which can severely impact the electrical performance of solar cells. This paper demonstrates that applying hydrogenation processes at moderate temperatures to finished screen print cells can passivate dislocation clusters within the cast-mono crystalline silicon wafers far better than the hydrogenation received during standard commercial firing conditions. Efficiency enhancements of up to 2% absolute are demonstrated on wafers with high dislocation densities. The impact of illumination to manipulate the charge state of hydrogen during annealing is investigated and found to not be significant on the wafers used in this study. This finding is contrary to a previous study on similar wafers that concluded increased H^– or H⁰ from laser illumination was responsible for the further passivation of positively charged dangling bonds within the dislocation clusters.     

New low-cost storage in air conditioning

This paper describes the development of a new low-cost phase-change material packaging concept for air conditioning systems.

The realization of the promise of storage assisted air conditioning for saving oil and money is dependent upon the successful development of a low-cost storage subsystem and the adoption of time-of-day electricity rates. Time-of-day rates are currently under consideration or have been adopted in 27 different states and consideration of these rates has been required by federal legislation.

The adoption of this low-cost thermal energy storage technology for storage assisted air conditioning and other storage assisted heat pump applications has the potential of saving 100 million barrels of oil over the next ten years and 12 million barrels of oil per year by 1985. These savings would accrue from a change in the summer air conditioning peak electricity load from oil and gas-fired peak electrical generators to the base load electrical generators fired by coal, nuclear and hydroelectric.

This low-cost air conditioning storage concept is based on hydrated salt phase change material, specifically a mixture based on sodium sulphate decahydrate and a new low-cost packaging technology which uses a film laminate as the phase change material mixture's package and heat exchanger.

In this paper. the relative economics of various technological options for air conditioning storage are compared. It is demonstrated that this economic analysis leads to the necessity to develop a low-cost film package and heat exchanger. An analysis of savings to homeowners based on current and planned off-peak rates is included. Since this is the first product developed utilizing this new low-cost material as a packaging film, it is anticipated that major improvements in both cost and performance specifically related to individual systems will be developed and implemented over the next ten years, with significant improvements coming in the next several years.     

Orthophosphate concentrations in the River Thames: reductions in the past decade

Ten years ago plans were made to reduce the phosphorus load from sewage-treatment works' effluents into the River Thames. This was driven by the EC Urban Wastewater Treatment Directive in relation to sensitive areas (eutrophic). Modelling work identified the most significant loads to tackle first. Phosphorus removal had been commissioned at 36 works by 2003. The orthophosphate load to the River Thames from these works has reduced from 5755 to 688 kg P/day. The impact of the improvement programme on the quality of the river was assessed by comparing pre- and post-investment data. Orthophosphate concentrations in the river have reduced from between about 0.5 and 2 mg P/L to 0.2 and 0.4 mg P/L. These observations match the model predictions. Chlorophyll a concentrations in the river have also reduced. This was unexpected given that the orthophosphate concentrations still exceed the values thought to be limiting for algal growth.