In situ synthesis of ammonia by catalytic hydrolysis of urea in the presence of aluminium oxide for safe use of ammonia in power plants for flue gas conditioning

BACKGROUND: Ammonia is applied to increase the efficiency of an electrostatic precipitator for fly ash removal from a flue gas stream from a boiler using fossil fuel. In the present work, the hydrolysis of urea to generate ammonia for flue gas conditioning, with the help of aluminium oxide catalyst, has been studied. RESULTS: The effect of temperature, catalyst and initial concentration on the conversion was studied. Conversion was found to increase exponentially with temperature. Addition of catalyst resulted in an increase in conversion. Experiments were conducted with different doses of catalyst, and the optimum dosage of catalyst for a particular feed concentration was determined. A decrease in conversion was observed when the initial concentration of ammonia was increased. CONCLUSION: A study of reaction kinetics showed the effect of reaction time on conversion of urea to ammonia. The catalytic hydrolysis of urea, using aluminium oxide behaved as a first‐order reaction; the rate constant at different temperatures was found, and the activation energy determined. Copyright © 2011 Society of Chemical Industry     

Challenges left in the area of in-vessel melt retention

The in-vessel melt retention becomes an important safety objective for the present or future middle power nuclear plants, so care has to be taken in the evaluation of the various phenomena related to ensuring the feasibility of this objective. Since the prediction of the relevant phenomena has to be performed for the prototypical accident conditions, the applicability of the measured data or of the correlations derived from these measurements have to be established and the uncertainties determined. In this context, most uncertainties are introduced by the non-prototypicalities in the experiments. The paper describes the major findings from the OECD RASPLAV project and discusses the remaining challenges left in the area of in-vessel molten corium coolability.     

Clinical utility of human polymerized hemoglobin as a blood substitute after acute trauma and urgent surgery

We have previously documented the safety of 1 unit (50 gram) of human polymerized hemoglobin (Poly SFH-P) in healthy volunteers. This report describes the first patient trial to assess the therapeutic benefit of Poly SFH-P in acute blood loss. Thirty-nine patients received 1 (n = 14), 2 (n = 2), 3 (n = 15), or 6 (n = 8) units of Poly SFH-P instead of red cells as part of their blood replacement after trauma and urgent surgery. There were no safety issues related to the infusion of Poly SFH-P. The plasma hemoglobin concentration ([Hb]) after the infusion of 6 units (300 gram) of Poly SFH-P was 4.8 +/- 0.8 g/dL (mean +/- SD). Although the red cell [Hb] fell to 2.9 +/- 1.2 g/dL, the total [Hb] was maintained at 7.5 +/- 1.2 g/dL. Poly SFH-P maintained total [Hb], despite the marked fall in red cell [Hb] due to blood loss. The utilization of O2 (extraction ratio) was 27 +/- 16% from the red cells and 37 +/- 13% from the Poly SFH-P. Twenty-three patients (59%) avoided allogeneic transfusions during the first 24 hours after blood loss. Poly SFH-P effectively loads and unloads O2 and maintains total hemoglobin in lieu of red cells after acute blood loss, thereby reducing allogeneic transfusions. Poly SFH-P seems to be a clinically useful blood substitute.     

Effect of fluid Prandtl number on heat transfer characteristics in internally heated liquid pools with Rayleigh numbers up to 10

This paper presents an analysis of effects of the fluid Prandtl number (Pr) on natural convection heat transfer in volumetrically heated liquid pools. Experimental and computational studies performed in the past are reviewed, with particular emphasis on the analysis of Pr number effects. As a practical exercise, numerical analysis is performed for two-dimensional square, semicircular and elliptical enclosures, and for three-dimensional semicircular and hemispherical cavities, to investigate the physics of the effect of the Pr number on heat transfer in internally heated liquid pools with Rayleigh numbers up to 10¹². It was found that the fluid Prandtl number has a small effect on heat transfer in the convection-dominated regions (near the top surface and side walls) of the enclosures. The decrease of the Pr number leads to the decrease of the top and side wall Nusselt (Nu) numbers. The effects of the Pr number on the Nu number at the bottom surface of the enclosures are found to be significant and they become larger with increasing Rayleigh numbers. Two physical mechanisms, i.e. thermal diffusivity and kinematic viscosity phenomena, have been proposed to explain the fluid Prandtl number effects. Calculational results have been used to quantify the significance and the area of influence for each mechanism. Also, strong dependence on the geometry (curvilinearity) of the downward cooled pool surface has been found.     

Multi-material gate poly-crystalline thin film transistors: Modeling and simulation for an improved gate transport efficiency

In this work, a two-dimensional potential distribution formulation is presented for multi-material gate poly-crystalline silicon thin film transistors. The developed formulation incorporates the effects due to traps and grain-boundaries. In short-channel devices, short-channel effects and drain-induced barrier lowering (DIBL) effect exists, and are accounted for in the analysis. The work aims at the reduction of DIBL effect and grain-boundary effects i.e. to reduce the potential barriers generated in the channel by employing gate-engineered structures. A study of work-functions and electrode lengths of multi-material gate electrode is done to suppress the potential barriers, hot electron effect and to improve the carrier transport efficiency. Green's function approach is adopted for the two-dimensional potential solution. The results obtained show a good agreement with simulated results, thus, demonstrating the validity of our model.     

A warm standby redundant system with correlated failures and repairs

This paper presents the analysis of a two-unit warm standby system assuming a bivariate exponential density for the joint distribution of failure and repair times of the units. Investigations regarding the stochastic behaviour and important reliability characteristics of the system have been made and earlier results have been verified as particular cases. A few graphs have also been provided to support the theoretical results.     

Ultrafast All-Optical Synchronous Multiple Access Fiber Networks

Two synchronous multiple access schemes, TDMA and CDMA, are proposed for fiber optic networks using optical signal processing. Network synchronization is achieved by using a central modelocked laser which also serves as the source for each station. The data are converted into a high-bandwidth optical signal using electrooptic modulators. The accessing schemes use optical fiber delay lines. The feasibility of these schemes is discussed.     

Underground coal gasification: A new clean coal utilization technique for India

Energy demand of India is continuously increasing. Coal is the major fossil fuel in India and continues to play a pivotal role in the energy sector. India has relatively large reserves of coal (253 billion tonnes) compared to crude oil (728 million tonnes) and natural gas (686 billion cubic meters). Coal meets about 60% of the commercial energy needs and about 70% of the electricity produced in India comes from coal, and therefore there is a need for technologies for utilization of coals efficiently and cleanly. UCG offers many advantages over the conventional mining and gasification process. UCG is a well proven technology. Due to the site-specific nature of the process, possibility of land subsidence and surrounding aquifer water contamination, this technology is still in a developing stage in India. Potential for UCG in India is studied by comparing the properties of Indian coals with the properties of coal that are utilized by various UCG trials. The essential issues are elaborated for starting UCG in India based on the reported information from the successful field trials conducted all over the world. Indian industries are in the process of initiating pilot studies of UCG at various sites. This study will help to motivate both applied and theoretical research work on UCG sites in India and after detailed analysis it will provide basic data to interested industries.     

Emissivity of substrate supported films

Results of experimental measurements of emissivity carried out on cobalt oxide and nickel sulphide films deposited on aluminum substrates are reported in this paper. Experimental results supported the general behaviour of variation of emissivity with film thickness as reported theoretically. The theoretical model is based on the interaction and attenuation of the emitted wavelengths from the substrate and film materials.     

Effect of the dielectric-substrate interface on charge accumulation from vacuum ultraviolet irradiation of low-k porous organosilicate dielectrics

We compare the effect of various dielectric-substrate interfaces on charge accumulation during vacuum ultraviolet irradiation of capped low-k porous organosilicates to find that more charges are trapped in a dielectric stack deposited on silicon compared with the same stack deposited on copper. Insertion of a 5-nm interfacial thermal oxide layer further increases the amount of trapped charges in the dielectric. The difference between the photoemission and injection currents determines the number of charges trapped in the dielectric as a result of irradiation. Fewer charges are trapped when the injection current increases.