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Aims and Scope
Editorial Board

1. Greece beyond the horizon of the era of transition: Archimedean screw hydropower development terra incognita

Alkistis Stergiopoulou^1,2, Vassilios Stergiopoulos³, Efrossini Kalkani¹

1 National Technical University of Athens, Department of Water Resources and Environmental Engineering, School of Civil Engineering, 15780 Athens, Greece.

2 University of Natural Resources and Life Sciences, Institute for Water Management, Hydrology and  Hydraulic Engineering, Muthgasse 18, A-1190 Vienna, Austria.

3 School of Pedagogical and Technological Education, Department of Civil Engineering Educators, ASPETE Campus, Eirini Station, N.Heraklio, 14121 Athens, Greece.

Abstract: The main aim of this paper is to prove, according to our inventory that, beyond the horizon of the era of transition and economic crisis of nowadays, Greece is a real “Archimedean Screw Hydropower Development Terra Incognita”, a country generously blessed with water, having an important hydropower potential. This inventory shows that the unexploited small hydropower capacity of Greece, including Archimedean possibilities, is approximately 3.500MW. The significant untapped small hydrodynamic potential demonstrates the important role of Pindos Mountain Range, controlling the annual rainfall difference between the North-Western and the Eastern Greece. The climatic and topographic conditions in Greece favor the development of many small Archimedean screw hydropower stations, harnessing the potential of a large number of small and big watercourses crossing mainland of the country. Pleiades of very promising Archimedean small hydro screw plants, having inclined and horizontal axis hydrodynamic rotors, could be installed following two hydro development axis (spears).

Volume 6, Issue 6, 2015, pp.527-536.

2. Optimal fundamental characteristic of a quantum harmonic oscillator Carnot refrigerator with multi-irreversibilities

Xiaowei Liu^1,2,3, Lingen Chen^1,2,3, Feng Wu^1,2,3,4, Fengrui Sun^1,2,3

1 Institute of Thermal Science and Power Engineering, Naval University of Engineering, Wuhan 430033.

2 Military Key Laboratory for Naval Ship Power Engineering, Naval University of Engineering, Wuhan 430033.

3 College of Power Engineering, Naval University of Engineering, Wuhan 430033.

4 School of Science, Wuhan Institute of Technology, Wuhan 430074, P. R. China.

Abstract: The optimal performance of an irreversible quantum Carnot refrigerator with working medium consisting of many non-interacting harmonic oscillators is investigated in this paper. The quantum refrigerator cycle is composed of two isothermal processes and two irreversible adiabatic processes, and the irreversibilities of heat resistance, internal friction and bypass heat leakage are considered. By using the quantum master equation, semi-group approach and finite time thermodynamics (FTT), this paper derives the cooling load and coefficient of performance (COP) of the quantum refrigeration cycle and provides detailed numerical examples. At high temperature limit, the cooling load versus COP characteristic curves are plotted, and effects of internal friction and bypass heat leakage on the optimal performance of the quantum refrigerator are discussed. Three special cases, i.e., endoreversible, frictionless and without bypass heat leakage, are discussed in brief.

3. Experimental and numerical investigation to evaluate the performance of triangular finned tube heat exchanger

Vinous M. Hameed, Bashar Muslem Essa

Mechanical Engineering Department, College of Engineering, Al-Nahrain University, Baghdad, Iraq.

Abstract: Experimental and numerical investigation has been performed in this work to evaluate the performance for triangular finned tube heat exchanger. Experimental work included designing and manufacturing of shaped triangular fins from copper material of (10mm) length, (10mm) height, (1mm) thickness, (22 mm) distance between every two fins shaped and (15mm) pitch between each two of fins which are install on the straight copper tube of (2m) length having (20mm) inner diameter and (22mm) outer diameter. The inner tube is inserted inside the Perspex tube of (54mm) inner diameter and (60mm) outer diameter. Cold Air and hot water are used as working fluids in the shell side and tube side, respectively. Air at various mass flow rates (0.001875 to 0.003133) kg/sec flows through annuli and water at Reynold's numbers ranging from (10376.9 to 23348.03) flows through the inner tube. Performance of (smooth and finned) tube heat exchanger was investigated experimentally. Experimental results showed that the enhancement of heat dissipation for triangular finned tube is (3.252 to4.502) times than that of smooth tube respectively. Numerical simulation has been carried out on present heat exchanger to analyze flow field and heat transfer using COMSOL computational fluid dynamic (CFD) package model. The comparison between experimental work and numerical results showed good agreement.

4. Improvement of outdoor thermal comfort for a residential development in Singapore

Souradeep Gupta, Prashant Anand, Shashwat

Department of Building, National University of Singapore, Singapore.

Abstract: With more urbanization in an island country of limited land area like Singapore, Urban heat island (UHI) is becoming a widely recognized phenomenon which is causing outdoor thermal discomfort to pedestrians and also causes high energy consumption by buildings. For a prospective residential development in Singapore, computational fluid dynamics simulation and temperature mapping have been conducted to highlight the urban parameters that should be considered to mitigate the adverse effects of UHI effect. Simulation shows higher day time and night time temperature at zones with exposed wall surfaces and pavements due to high sky view factor and higher storage of heat. Creation of more openness on ground and planting trees in such exposed spaces shows reduction in maximum temperature during day by about 2.2 ºC with increase in wind velocity as well. Improvement of outdoor thermal comfort from warm to neutral has been obtained with improved orientation of buildings and introduction of urban greenery.

5. Experimental study of the performance of tubular solar still in Najaf city

Salman H. Hammadi¹, Dhafer Manea H. Al-Shamkhee², Hussein Ali Jabar¹

1 Mechanical Engineering Department, College of Engineering, Basrah University, Ministry of Higher Education & Scientific Research, Basrah, Iraq.

2 Alternative and Renewable Energy Research Unit, Technical Engineering College/Najaf, Al-Furat.
Al-Awsat Technical University, Foundation of Technical Education, Ministry of Higher Education & Scientific Research, Najaf, Iraq.

Abstract: A tubular solar still (TSS) was designed, fabricated and tested in Najaf city, Iraq conditions. The trough was made of polycarbonate material black color of a rectangular shape (0.0972 m2 Area) its painted black to increase its absorptivity. The tube cover made of Pyrex glass (0.6 m) length, (0.24 m) outer diameter and (0.01 m) thickness. Number of experiments was conducted to observe the behavioral variation inside the still. The experimental study studied the effect of solar radiation, basin depth and direction of TSS on the productivity of solar still and temperature distribution inside the still for Najaf city condition for period (February to August) in 2015. The result show the maximum productivity in north-south direction and the productivity increase with decreasing the depth of water in basin.

6. Stepped spillway optimization through numerical and physical modeling

Hamed Sarkardeh¹, Morteza Marosi², Raza Roshan²

1 Department of Engineering, Hakim Sabzevari University, Sabzevar, Iran.

2 Hydraulic Structures Division, Water Research Institute (WRI), Hakymia, Tehran, Iran.

Abstract: The spillway is among the most important structures of a dam. It is importance for the spillway to be designed properly and passes flood flow safely with more energy dissipation. The zone which ogee spillway crest and stepped chute profile are joined with each other is important in design view. In the present study, a physical model as well as a numerical model was employed on a case study of stepped spillway to modify the transitional zone and improve flow pattern over the spillway. Many alternatives were examined and optimized. Finally, the performance of the selected alternative was checked for different flow conditions, air entrainment and energy dissipation. To simulate the turbulence phenomenon, RNG model and for free surface VOF model was selected in the numerical model. Results of the numerical and physical models were compared and good agreement concluded in flow conditions and energy dissipation.

7. Effect of the fins configuration on natural convection heat transfer experimentally and numerically

Ahmed F. Khudheyer, Zaid Hameed Hasan

Mechanical engineering department, college of engineering, Al-Nahrain University, Baghdad, Iraq.

Abstract: The cooling of the electronic systems, electrical systems, and CPU of the computer is very important; therefore this study is prepared to improve this aims. In this study, natural convection heat transfer from rectangular fins with five different figures (continuous fins, 1-interrupted fins, 4-interrupted fins, inclined fins and v-fins) are investigated at different heat flux values (175, 350, 525, 700 and 875 Watt per square meter).The effect of base to ambient temperature difference for continuous fins, 1-interrupted fins, 4-interrupted fins, inclined fins and V-fins were determined. All types of the fins are made with different geometries by using CNC machine and wire cut machine, but it have some dimensions in common such as fins thickness (5)mm, fins height (18)mm, space between the fins (10)mm, and the volume of the base plat of heat sink (300*95*2)mm. The heat sink base plate was heated by an attached maximum electric heater 2225 W/m² with an identical size with the base plate of the heat sink, which could supply a specific heat flux. The steady-state temperature of the base plate was measured by eleven copper-constantan (K-type) thermocouples inserted into different grooves in the base plate and glued with thermal tape and epoxy to ensure good thermal contact. The mathematical model of the base plate and fins are solved numerically using COMSOL (5.0) after describing the mesh model using the COMSOL (5.0) and assuming the properties of air variation with film temperature. After finding the numerical result, the validation between experimental and numerical results has been verified. Good agreement has been found between the experimental and CFD results. Empirical correlations for the overall Nusselt number versus average Rayleigh number for these configurations are obtained and compared to other correlations sited in the literature. The range of Rayleigh number, Nusselt number and base plate temperature are, (1.7e7 - 12.5e7), (37 – 83) and (25.6 – 81.34) respectively.