volume-12-Issue 1 (2017)
Latest Articles
A Stable DC Power Supply for Photovoltaic Systems
IJTEE, volume-12, Issue 1 (2017) , PP 67 - 71
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.009
by Hussain A. Attia, Beza Negash Getu, and Nasser A. Hamad from Department of Electrical, Electronics and Communications Engineering, American University of Ras Al Khaimah, Ras Al Khaimah, UAE
Abstract: The use of solar energy as a source of power is becoming not a choice but a necessity due to the unprecedented growth in the demand and consumption of electrical power for various applications. The solar power from the Photovoltaic (PV) systems are currently used as a standalone PV system or integrated with the electric grid. However, the generated DC power from PV systems is not stable due to weather, atmospheric and environmental conditions, which requires the design of a DC power supply to produce a stable and regulated DC voltage output. In this paper, a new design of power supply is presented that provides a stable output voltage (Vout = +12 V, 0 V, -12V) over a significant range of input voltage variations (Vin = +15 V to +50 V) emulating the variation of the output voltage of PV systems. The stabilization of the output voltage reflects the effectiveness of the proposed design for photovoltaic systems applications. The system is simulated using NI-MULTI SIM software. A satisfactory simulation result is obtained showing a strong promise to practically implement using discrete components. read more... read less...
Keywords: PV System, Voltage Variation, Sensing & Protection Circuit, Op-Amp, Zener Diode, DC Supply
Utilizing Reclaimed Asphalt Pavement (RAP) Materials in New Pavements - A Review
IJTEE, volume-12, Issue 1 (2017) , PP 61 - 66
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.008
by Ahmad M. Abu Abdo from Department of Civil & Infrastructure Engineering, American University of Ras Al Khaimah, Ras Al Khaimah, UAE
Abstract: Recently, prices of asphalt pavement materials have been increasing tremendously, which led to attempts to find alternative cheap materials. In addition, more concerns are directed to preserving natural resources and reducing environmental impacts of using virgin asphalt binders, thus more attention is focused on the use of recycled materials in pavement designs. Transportation agencies worldwide are incorporating reclaimed asphalt pavement (RAP) materials in new pavement designs. RAP was used for the first time in 1973, however, with low percentages due to the lack of understanding of its effect on the performance of asphalt mixes. Currently, higher percentages (e.g. >50%) are being utilized to reduce costs and natural resources and make use of demolished old asphalt pavements. The main concern of combining RAP in new asphalt mixes is how it will affect the resistance of these mixes to permanent deformation (rutting), fatigue cracks, and thermal cracks, which are the main distresses that affect the performance of asphalt mixes. Many studies were conducted to evaluate the effects of RAP on asphalt mixes, and all results showed that RAP increased the stiffness of asphalt mixes, thus improving rutting resistance at high temperatures. On the other hand, results were in conflict with regard to fatigue and thermal cracking. Recently, the Department of Public Works and Services at Ras Al Khaimah, UAE started adopting RAP mixes in ongoing projects (e.g. Kadra-Shawka Road) with no clear guidelines, in hope of reducing costs and that these roads would have better performance. To address the concerns of the effects of RAP and to determine the correct RAP percentage for projects in Ras Al Khaimah, this study was initiated and as a first stage, a literature review was conducted and presented in this article. read more... read less...
Keywords: Asphalt Pavements, Reclaimed Asphalt Pavement, Recycling, Rutting, Fatigue Cracking, Thermal Cracking
Waste Heat Recovery from Gas Turbine Flue Gases for Power Generation Enhancement in a Process Plant
IJTEE, volume-12, Issue 1 (2017) , PP 53 - 60
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.007
by Valerie Eveloy, Peter Rodgers, Adesola Olufade, Yuyao Wang, and Ali Al Alili from Department of Mechanical Engineering, the Petroleum Institute, Abu Dhabi, United Arab Emirates
Abstract: To improve on-site power generation capacity and efficiency in process facilities, the thermal coupling of an industrial gas turbine cycle with a bottoming organic Rankine cycle for power plant flue gas waste heat recovery in a processing facility is investigated. Using 1,1,1,3,3-pentafluoropropane (R245fa) as a heat carrier in the Rankine cycle, 5.2 MW of additional electric power is generated, enhancing on-site power generation capacity and energy/exergy efficiency by approximately 23% and 6%, respectively. The overall energy and exergy efficiencies of the waste heat recovery system are estimated at 9% and 24%, respectively. Primary energy savings of approximately 1.3 million standard cubic feet per day (MMSCFD) of natural gas, or net annual operating expenditure savings of 1.6 million USD could be realized with the proposed flue gas waste heat recovery system based on subsidized industrial electricity tariffs in the UAE, with 457 tons of avoided CO2 emissions per year. read more... read less...
Keywords: Organic Rankine Cycle, ORC, Waste Heat, Industrial, Gas Turbine, Exergy
Performance Analysis of a New Waste Heat Recovery System
IJTEE, volume-12, Issue 1 (2017) , PP 47 - 52
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.006
by Saed A. Musmar, Nasim Razavinia, Frank Mucciard, Iskander Tlili from Department of Industrial Engineering, Faculty of Engineering and Technology, University of Jordan, Amman, Jordan Materials and Metallurgical Department, McGill University, Montreal, Canada Mechanical Engineering Department, Engineering College, Majmaah University. Kingdom of Saudi Arabia
Abstract: The overall theme of this research is to capture, concentrate and convert some of the waste heat generated at industrial plants to a valuable form of energy. A new system for heat recovery from low-grade energy has been built and tested based on a modified heat pipe technology. A single heat pipe used in this research was able to extract 2 kW of energy from waste heat of 250 oC. However, a heat pipe can extract 11.5 kW/m2 heat fluxes. The maximum energy extraction by such a system from low grad energy can be up to 3 kW. While a heat pipe regardless of its size can have heat flux up to 16.5 kW/m2 from waste heat flow at 250 oC and 12.3 m/s velocities. Also, the system can extract about 1 kW heat or 6.5 kW/m2 heat flux at temperatures as low as 150 oC. However, the system doesn’t function properly at temperatures lower than 150 oC read more... read less...
Keywords: Waste heat recovery, Latent heat, Heat pipe, Vortex promoters, thermal conveying
Finite Element Analysis with COMSOL Code for Air Flow and Thermal Convection in Sealed Attic Spaces with Experimental Validation
IJTEE, volume-12, Issue 1 (2017) , PP 39 - 46
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.005
by Antonio Campo, and Jaime Sieres from Department of Environmental Engineering, Faculty of Engineering, University of Vermont, Burlington, VT 05405, USA Área de Máquinas y Motores Térmicos, Escuela de Ingeniería Industrial, Universidad de Vigo, Campus Universitario Lagoas-Marcosende, 36310 Vigo, Spain
Abstract: The scope of the present paper is concerned with the numerical prediction of the confined airflow characteristics and thermal convection patterns in sealed attic spaces in roofs with upper inverted V-shapes and horizontally suspended ceilings of conventional houses and buildings. For these isosceles triangular cavities, two relevant cases involve prescribed wall temperatures wherein the bottom base wall is cooled/heated and the upper two inclined walls are symmetrically heated/cooled during the summer and winter seasons. Based on finite element analysis, the COMSOL code is implemented to perform numerical solutions of the two-dimensional system of coupled NavierStokesBoussinesq and energy equations. The computational domain is made coincident with the physical domain to handle potential non-symmetric velocities and non-symmetric temperatures that may occur when exposed to vigorous air flows. The numerical solution via finite elements provides the two velocity fields u (x, y), v (x, y), and the temperature field T (x, y) for the confined air flows. Overall, the target design quantity is the mean wall heat fluxes w q varying with the attic aspect ratio and the temperature difference at two opposing walls. The predicted w q values match the experimental measurements for the two distinct cases related to summer and winter seasons. In the end, comprehensive correlation equations are constructed for the quantification of the mean Nusselt number in terms of the Grashof number and the attic aspect ratio, which could be used in building science research. read more... read less...
Keywords: Sealed Attics of Houses And Buildings, Circulatory Air Flow, Thermal Convection, Finite Element Analysis, COMSOL Code, Experimental Measurements)
Cooling a Solid Disc with Uniform Heat Generation Using Inserts of High Thermal Conductivity within the Constructal Design Platform
IJTEE, volume-12, Issue 1 (2017) , PP 15 - 26
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.003
by F. Sharfi, R. M. Salimpuor, and A. Campo from Department of Mechanical Engineering, Ishafan University of Technology, Ishafan, Iran Department of Mechanical Engineering, The University of Vermont, Burlington, VT 05405, USA
Abstract: In the present study, the problem of cooling a solid disc by way of placing inserts with high thermal conductivity was examined analytically and numerically within the platform of the Constructal Theory. The work was accomplished using a fixed amount of highly conductive material distributed in the form of incomplete inserts from the center (sink). Using Constructal Theory, the magnitudes of the heat resistance in the radial and the branching configurations were calculated analytically. Additionally, to validate the analytical solution, a numerical solution with the Finite Element Method was employed. The one-to-one comparison between the two distinct results reveals a good agreement. In the present case, the length of the inserts was different from the disc radius viz. a new degree of freedom was considered and the solution was remarkably different from the case involving a complete insert. The heat resistance was minimized with respect to the aspect ratio in order to determine the optimal number of inserts as well as the disc radius. It was demonstrated that within a certain range of parameters, the heat conduction performance of incomplete inserts in the solid disc surpasses the heat conduction performance of standard complete inserts. read more... read less...
Keywords: Cooling, Solid Disc, Uniform Heat Generation, Incomplete Inserts, High Thermal Conductivity, Constructal Theory.
Experimental Determination of the Global Mass Transfer Coefficients of the Tropical Woods in order to Deduce the Drying Curves at the Lower Temperature
IJTEE, volume-12, Issue 1 (2017) , PP 9 - 14
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.002
by Merlin Simo-Tagne, Louis Monkam, Romain Rémond, André Zoulalian, Yann Rogaume, Beguidé Bonoma from University of Yaoundé I, Higher Teacher Training College, Applied Physic Laboratory, PO Box 47, Yaoundé, Cameroon Douala Institute of Technology (DIT), PO Box 1623, Douala, Cameroon University of Douala , Energy Laboratory of the Doctorate School of Physics and Engineering Sciences, PO Box 8698, Douala, Cameroon University of Lorraine, LERMAB, ENSTIB, 27 rue Philippe Séguin, PO Box 1041, F-88051 Epinal, France University of Lorraine, LERMAB, Faculty of Sciences and Technologies - Aiguillettes Campus- PO Box 70239 - 54506 Vandoeuvre les Nancy Cedex, Nancy, France
Abstract: We determine the global mass transfer coefficients of five tropical woods (obeche, iroko, loofa, Sapele, and freak) coming from Cameroon. In this effect, drying kinetics using a solar dryer and a conventional dryer is utilized. In addition, the comparison is doing between the values obtained and these coming from Chileans tropical woods and temperate. Thus, when the drying kinetics are between 0.25 to 1.5m/s, dry temperature equal to 33.5°C and wet temperature equal to 25°C, global mass transfer coefficients are between 2x10-5 and 4x10-5 kg/(m2 .s), for the conventional dryer. These values conform to those obtained on the Chilean tropical woods and less than those obtained on the temperate woods. In the case of an indirect solar dryer functioning between October and November 2004 at Yaoundé, this coefficient is lower because the wood thickness is almost 24mm in the case of conventional drying and 50mm in the case of solar drying. read more... read less...
Keywords: Global mass transfer coefficients, Drying kinetics, Tropical woods, Conventional dryer, Solar dryer, Experiment, Modeling, Cameroon.
Building Eco-Cities of the Future: The Example of Masdar City
IJTEE, volume-12, Issue 1 (2017) , PP 1 - 8
Published: 19 Dec 2017
DOI: 10.5383/ijtee.12.01.001
by T. Mezher, G. Dawelbait, I, Tsai, N. Al-Hosany from Masdar Institute of Science and Technology, iSmart Center, Abu Dhabi, UAE Masdar Company, Abu Dhabi, UAE
Abstract: Global warming and increased population growth are putting more pressure on policy decision-makers to adopt more sustainable approaches to planning and designing future cities. This has led to the rise of Eco-Cities that have smart and sustainable infrastructures such as green buildings; intelligent transportation systems; and efficient electricity, water, wastewater, and solid waste networks. In addition, these cities should be less dependent on fossil fuels and ensure healthier life and comfort. This paper gives a brief overview of the sustainable design concept of six Eco-cities from around the world such as Vauban in Germany, BedZed in the UK, Sonoma Mountain in California, Dongtan, and Tianjin in China, and Songdo in Korea. Masdar City is discussed in more detail including the green buildings, intelligent transportation systems, and other important infrastructure systems. This endeavor requires the managing of complex systems which necessitates the coordination and collaboration of all the stakeholders that are involved in designing, constructing, and operating the city. The paper concludes with lessons learned so far from Masdar City read more... read less...
Keywords: Eco-City, Masdar, sustainable Abu Dhabi