Interconnection of a Wind Driven DC Machine with the Power Utilities Grid
Pages 306-313
Maamar Taleb

DOI: http://dx.doi.org/10.6000/1929-6002.2013.02.04.2

Published: 29 November 2013

Abstract: A wind driven DC machine is interconnected with the power utilities grid. The wind driven DC machine is operated in the regenerative mode and that is to guaranty the extraction of the real power from the wind driven generator and inject it into the power grid. This is done through the use of a single phase full wave controlled converter operating in “ an inverter mode of operation”. At any pretended surrounding weather conditions, maximum extraction of power from the renewable energy source (ie. Wind energy source) is targeted. This is done through the realization of a self-adjusted firing angle controller responsible of triggering the semiconductor elements of the controlled converter. An active power filter is shunted with the proposed setup to guaranty the sinusoid quality of the power utilities line current. The overall performance of the proposed system has been simulated in MATLAB/SIMULINK environment. Quite satisfactory and encouraging results have been obtained.

The Impact of Gasfier Stoves Use on Socio-Economic and Environment in Tanzania: The Case of Arusha and Moshi Municipalities
Pages 314-326
Agnes Godfrey Mwakaje

DOI: http://dx.doi.org/10.6000/1929-6002.2013.02.04.3

Published: 29 November 2013

Abstract: This study examined the socio-economic and environmental impact of the adoption of gasfier stoves by households in Arusha and Moshi towns in Tanzania. A total of 55 respondents were selected purposely from the gasfier stoves. For comparative purposes another 55 charcoal users were selected randomly for interview making a total sample of 110. There were also focus group consultations and key informant interviews. Structured and semi-structured questionnaires were used to collect data, which were analysed using the Statistical Package for Social Sciences.

The results show that the respondents who were using gasfier stoves had significant reduction (p=0.001) in the cost of energy for cooking compared to charcoal stove users by spending only T.shs 13,396 per month compared to T.shs 36,932 for charcoal users. The use of gasfier stoves also had a positive impact on the environment. Findings show that by using gasfier stoves 15.4 ha were saved from deforestation per annum and about 365.4.tonnes of carbon were saved for sequestration an act that reduces carbon emissions and global warming.

Nevertheless, despite the impressive performance of gasfier stoves for cooking, the rate of adoption has remained low. The main reason for this was reported to be the high price, poor quality of the pellets and unfriendly usability. The adoption of gasfier stoves could only be enhanced by addressing these constraining factors.

Modeling and Global Sensitivity Analysis of a Solar Powered Air Cooling System Using Liquid Desiccant
Pages 327-339
Hery Tiana Rakotondramiarana, Sambatra Hagatiana Andrianomena, Ando Ludovic Andriamamonjy and Minoson Sendrahasina Rakotomalala

DOI: http://dx.doi.org/10.6000/1929-6002.2013.02.04.4

Published: 29 November 2013

Abstract: Solar energy technology is an option for energy saving in building air conditioning. A theoretical investigation of an open cycle solar air cooling system using aqueous Lithium Chloride solution as liquid desiccant is presented in this paper. The purpose of this work is to analyze the influences of both internal loads and external forcing, on the studied system by developing a computational code related to its mathematical model. The simulation results justify the choice of the system design. Indeed, it was highlighted that the higher is the outdoor temperature; the better is the coefficient of performance (COP) of the system. Furthermore, a global sensitivity analysis of the system model, achieved using Fourier Amplitude Sensitivity Test method, allowed us to identify the most influential factors that were ranked in a decreasing order of their influence degree on the system COP. Hence, key factors to be controlled for improving the system overall performance are specified.

Latent Heat Storage with Phase Change Materials (PCMs)
Pages 340-51
H.L. Zhang, J.Baeyens, J.Degrève and F.Pitié

DOI: http://dx.doi.org/10.6000/1929-6002.2013.02.04.5

Published: 29 November 2013

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.

Role of PVA Flakes in Promoting Self-Degradation of Sodium Metasilicate-Activated Cement under a Hydrothermal Environment at ≥150°C
Pages 352-365
T. Sugama, T. Pyatina and A. Muraca

DOI: http://dx.doi.org/10.6000/1929-6002.2013.02.04.6

Published: 29 November 2013

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.