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Abstract : Latent Heat Storage with Phase Change Materials (PCMs)
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Abstract: Latent heat thermal energy storage with phase change materials (PCMs) is attractive since providing a high energy density storage due to the phase change by solidification/melting at constant temperature. Relative to sensible heat energy storage systems, latent heat storage with PCMs requires a smaller weight and volume of material for a given amount of captured/stored energy, and has the capacity to store heat of fusion at a constant or nearly constant temperature, thus maintaining a high and constant temperature difference between the heat exchanging surface and the PCMs. The present review paper will summarize the required properties of PCMs, with their respective advantages and disadvantages; the current state of development and manufacturing; the development of PCM applications, including their incorporation into heat exchangers, insertion of a metal matrix into the PCM, the use of PCM dispersed with high conductivity particles. PCM uses will be illustrated through some case-studies. Keywords: Heat storage, Latent heat, Sensible heat, Phase change materials, Encapsulation.Download Full Article |
Abstract : Role of PVA Flakes in Promoting Self-Degradation of Sodium Metasilicate-Activated Cement under a Hydrothermal Environment at ≥150°C
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Abstract: We investigated the effect of flakes of polyvinyl alcohol (PVA) on the self-degradation of sodium metasilicate (SMS)-activated slag/Class C fly ash cement, which is used as temporary sealer for fractures in Enhanced Geothermal System (EGS) wells under a hydrothermal environment at ³150°C and at pressure of 1000 psi. The reactions between PVA and SMS dissolved in an aqueous medium at 85°C led to the formation of a colloidal hydroxylated silicate-cross-linked PVA gel in the cement body. This gel-incorporated cement had a compressive strength >2000 psi, so ensuring that it adequately plugs the fractures. Increasing the hydrothermal temperature to ³150°C triggered the transformation of the gel into a sol. This in-situ gel®sol phase transition played a pivotal role in promoting the cement’s self-degradation because of the extensive spreading of sol in the cement body, and its leaching from the cement. In contrast, when gel was dry heated at ³150°C, the gel®xerogel phase transformation engendered the molecular fragmentation of PVA. This fragmentation yielded polysilicate cross-linked PVA derived from the combination of extended-chain scission, carboxylation and condensation, so that it no longer served as a self-degrading promoter of cement. Keywords: Enhanced Geothermal System, polyvinyl alcohol, cement, sodium metasilicate, lost circulation, temporary sealer.Download Full Article |
Abstract :Biomass Production for Energy in India: Review
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Abstract: This paper presents a general view about biomass production in India and its potential energy for use in differentfields. India has tremendous potential for energy generation through biomass and its residues. Biomass energy is normally produced from firewood, agricultural residues such as bagasse, crop stalks, animal dung and wastes generated from agro-based industries. With the estimated and predicted values, the generating power from the surplus biomass in India was significant and it will continue to be more effective in future. Residue use as a fuel in India is estimated to be 216 Mt as projected value in 2010, recently, around 605 MW of electricity is being produced from biomass firing and 720 MW from cogeneration activities for residue. About 185 Mt (40%) of the dung collected is used as fuel in cook stoves. The potential for biogas production annually is 8750 million m3 from 251 Mt of dung. The amount of fuel-wood consumption during year 2004 was 205 million tonnesused as fuel for traditional cook stoves with low efficiency, 16 Mt used in industrial sector producing 10 PJ, and it was estimated that the production of fuel wood and charcoal increased to the rate of 1.98 per cent per annum. The total quantity of solid wastes generated in larger towns and cities has been estimated at 40 Mt in 2001, and in 2005 the average MSW generation in overall India was approximately 100,000 Mt/day. For the wastewater in India, in 2010, the energy estimated to be around 3929.8 TJ as energy value of CH4. Keywords: Biomass, energy, crop residues, animal manure, fuelwood and municipal solid wastes.Download Full Article |
Abstract :Gasification of High and Low Density Crop Residues
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Abstract: Crop residue constitutes a large fraction of biomass particularly in agricultural based economies like India. The most abundantly generated crop residues are paddy husk, paddy straw, coconut shell, cotton stalk and sugar cane trash. It is estimated that the potential of power generation using crop residue is close to 14 GWe in a country like India. Even though the potential is large, the main drawback with crop residue is that it is sparsely distributed and being of low density causes collection and transportation problem. This drawback could be converted into an advantage by adopting distributed power generation technologies. The distributed power generation would fare well in the power range of few hundred kilowatts and the most appropriate technology would be the biomass gasification technology. Among the biomass gasification technologies, the downdraft technology is ideally suited for power generation. The downdraft technology is proven with solid or woody biomass, whereas there are limitations in terms of acceptance of all types of crop residues. In this paper, performance study of two vastly differing crop residues, namely coconut shell and cotton stalk has been discussed; both the feedstocks have been tested in “post-harvested” condition with minimum amount of pre-processing. The performance with cotton stalk was found to be comparable at part load; however at higher load the gas composition deteriorated due to poor material movement within the reactor. This had implication in terms of maximum power generated. There was loss of power to an extent of 12%. The operational issues with post-harvested cotton stalk has been brought out which are based on detailed measurements. Keywords: Biomass Gasification, Crop Residue, Cotton Stalk, Coconut Shells.Download Full Article |
