VOLUME 8, ISSUE 3, 2017 |
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Cover |
Aims and Scope |
Volume 8, Issue 3, 2017, pp.i-viii. | Download Full Text (PDF) |
1. Mathematical model and numerical simulation of porous media gas-water fluid- solid coupling with considering gas adsorption |
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Huajun Wang^{1}, Xueli Wang^{1}, Lufei Feng^{1}, Feng Liu ^{2}, Siyuan Zhao^{1} |
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1 School of Energy and Environment Engineering, Hebei University of Technology, Tianjin 300401, P. R. China. 2 Institute of Hydrogeology and Environment Geology, Chinese Academy of Geological Sciences, Shijiazhuang 050061, P. R. China. |
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Abstract: In order to understand the complex interaction between gas-water two-phase seepage and stress field with gas adsorption, a mathematical model of gas-water fluid-solid coupling for rock-coal porous media was established based on the stress equation, mass conservation equation, Darcy's law and gas adsorption mass equation. Using the COMSOL software with self-defined function codes, the simulation of seepage in rock-coal porous media with random-generated pore structures was carried out. The results indicate that the pressure of closed pores is larger than that of connected pores in saturated rock-coal porous media, and gas is difficult to get through the reservoir. As the pressure of pores increases, the volumetric strain increases, while the weighting of the adsorption strain decreases, appearing a weak influence on the matrix deformation in rock-coal. Under the present simulation conditions, the difference of magnitude between the volumetric strain and the adsorption strain is about 103, where the adsorption strain has a less influence on permeability, and permeability increases as volume strain increases, which conforms to exponent law. |
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Volume 8, Issue 3, 2017, pp.209-218. |
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2. An optimization model for distribution system planning integrated photovoltaic |
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V. V. Thang |
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Department of Electric Power Systems, Thai Nguyen University of Technology (TNUT), Vietnam. |
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Abstract: A two-stage model for the optimal planning of distribution systems with the presence of photovoltaic generation system (PV) is presented in this paper. The proposed model can determine the optimal sizing and timeframe of the equipment (feeders and transformer substations) in distribution systems. Therefore, the optimal displacement, sizing, technology and installation period of PV are also determined. The objective function is minimizing the life cycle costs of the planning project. The technical constraints are used to guarantee the operability of the distribution system including AC power flow, feeder and substation upgrading section, limited of nodal voltage and PV capacity. The binary variables are also employed in the model to represent the cost function of the equipment as well as the investment and upgrade decisions. The algorithm is programmed in GAMS environment. The feasibility and effectiveness of the proposed model are examined in a 7-bus test system. |
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Volume 8, Issue 3, 2017, pp.219-228. | Download Full Text Article (PDF) | |
3. Using the transformer oil-based nanofluid for cooling of power distribution transformer |
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Mushtaq Ismael Hasan |
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Mechanical Engineering Department, College of Engineering, Thi-Qar University, Iraq. |
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Abstract: Thermal behavior of electrical distribution transformer has been numerically studied with the effect of surrounding air temperature. 250 KVA distribution transformer is chosen as a study model and studied in temperature range cover the weather conditions of hot places. Transformer oil-based nanofluids were used as a cooling medium instead of pure transformer oil. Four types of solid particles (Cu, Al2O3, TiO2 and SiC) were used to compose nanofluids with volume fractions (1%, 3%, 5%, 7%, and 9%). In addition to its good thermal characteristics the nanoparticles lead also to increase the dielectric of oil and increase the breakdown voltage. Results obtained show that, using of transformer oil-based nanofluids as a cooling medium instead of pure transformer oil lead to improve the cooling performance of transformer by reducing the temperature of transformer and as a consequence increasing the protection of the transformer against the breakdown. Also increasing the nanoparticles volume fraction in nanofluid cause extra decrease in transformer temperature. Among all of the selected nanofluids the SiC-Oil nanofluid give lower transformer temperature. |
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Volume 8, Issue 3, 2017, pp.229-238. | Download Full Text Article (PDF) | |
4. Experimental and numerical investigation of temperature distribution through shell and helical coil tube heat exchanger using Lab VIEW as a data acquisition program.Part I: Model validation |
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Vinous M. Hameed, Ahmed R. Al-Khafaji |
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Mechanical Engineering Department, College of Engineering, Al-Nahrain University, Baghdad, Iraq. |
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Abstract: Water-water shell and helical coil tube heat exchanger was used in this study. The shell was made from perplex material of length 1000mm and 150mm diameter. The coil tube was made of Cu material; it’s formed in coil shape with length of 800mm and inner diameter of 90mm. The helical coil pitch is (32.7) mm. Hot and cold water tanks with heater for each side were used to reach the required water temperature for shell and helical coil tube at (35 and 65)oC respectively. Different mass flow rates had been selected in shell and tube sides (6, 8, 10, 12 L/min for each side). The data of the rig recorded by using data acquisition computer with prepared a Lab VIEW program which is built specially for this case study. A numerical analysis had done by using ANSYS-Fluent V.16 to predict the results of what had done experimentally. A very good matching of the experimental results with numerical analyses was found in this research. |
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Volume 8, Issue 3, 2017, pp.239-252. | Download Full Text Article (PDF) | |
5. Experimental and numerical investigation of temperature distribution through shell and helical coil tube heat exchanger using Lab VIEW as a data acquisition program. Part II: Parametric investigation |
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Vinous M. Hameed, Ahmed R. Al-Khafaji |
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Mechanical Engineering Department, College of Engineering, Al-Nahrain University, Baghdad, Iraq. |
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Abstract: An experimental and numerical study had been done on shell and helical tube heat exchanger. The perplex tube of 1000 mm length, 150 mm diameter and 2 mm thickness was used as shell. The helical tube was made of Cu material. Its diameter is 12.7 mm and 0.1 mm thickness. The working fluid was water for both shell and tube sides. The experimental rig consist of two water tanks to supply the cold water to the shell (35^{o}C) and hot water to the tube (65^{o}C). Eight thermocouples type K were installed at the inlet and out let of each sides and the other are distributed along the shell length. Two rotameters were used to measure the flow rate of hot and cold water. The Numerical analysis was done by using SNSYS-Fluent V.16 to predict the results of what had done experimentally. The main keys of this study were coil pitch and mass flow rate of water for both sides. Where the helical coil pitch was changed in each case. The first case the helical coil pitch was 52.7 mm, in the second case the pitch was changed to 42.7mm. In the last case (case 3) the pitch distance was 32.7mm. The results compared with case 0 (straight tube). And the mass flow rat were (6, 8, 10 and 12) L/min for both sides shell and tube. The results show that an enhancement in the performance of heat exchanger with the decrease of helical coil tube pitch due to the secondary flow increase. Also the mass flow rate decrease causes an enhancement in the performance of the heat exchanger due to the contact time increase. |
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Volume 8, Issue 3, 2017, pp.253-270. | Download Full Text Article (PDF) | |
6. Finite-time thermodynamic analysis for endoreversible Lenoir cycle coupled to constant-temperature heat reservoirs |
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Xun Shen^{1,2,3}, Lingen Chen^{1,2,3}, Yanlin Ge^{1,2,3}, Fengrui Sun^{1,2,3} |
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1 Institute of Thermal Science and Power Engineering, Naval University of Engineering, Wuhan 430033, China. 2 Military Key Laboratory for Naval Ship Power Engineering, Naval University of Engineering, Wuhan 430033, China. 3 College of Power Engineering, Naval University of Engineering, Wuhan 430033, China. |
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Abstract: A thermodynamic model of a steady-flow endoreversible Lenoir heat engine cycle (a “three point” cycle) coupled to constant-temperature heat reservoirs is established in this paper by using finite time thermodynamic theory. The cycle consists of one isochoric heating branch, one adiabatic expansion branch and one isobaric cooling branch. The analytical formulae about power output and thermal efficiency of the cycle are derived. The optimal performance of the cycle is obtained with the fixed total thermal conductance of heat exchangers. Moreover, the effects of the heat reservoir temperature ratio and the total thermal conductance of heat exchangers on the general and optimal performances are analyzed. The results show that the power and efficiency performance curve of the cycle is a fixed “point” with constant thermal conductance of hot- and cold-side heat exchangers, and there exist optimal thermal conductance distributions, which lead to maximum power and maximum efficiency, respectively, with changeable thermal conductances of hot- and cold-side heat exchangers. Both the power and efficiency will be enhanced with the increase of thermal conductance ratio between high- and low-temperature heat reservoirs, or the total thermal conductance of heat exchangers. |
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Volume 8, Issue 3, 2017, pp.271-278. | Download Full Text Article (PDF) | |
7. Constructal design of elliptic tubes cooled by natural convection |
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Ahmed Waheed Mustafa, Jaafar Ahmed Zahi |
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College of Engineering, Mechanical Engineering Department, Al-Nahrain University, Baghdad, Iraq. |
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Abstract: The optimal spacing between elliptic tubes cooled by free convection is studied experimentally and numerically. A row of isothermal elliptic tubes are installed in a fixed volume and the spacing between them is selected according to the constructal theory (Bejan's theory). In this theory the spacing between the tubes is chosen such that the heat transfer density is maximized. A finite volume method is employed to solve the governing equations; SIMPLE algorithm with collocated grid is utilized for coupling between velocity and pressure. For the numerical study, the range of Rayleigh number is (103 ≤ Ra ≤ 105), the range of the axis ratio of the tubes is (0 ≤ e ≤ 0.5), and the working fluid is air (Pr =0.71). Eexperimental study is also carried out in order to demonstrate the existence of the optimal spacing. The experimental Rayleigh number is (3.5 * 104) and the axis ratio of the elliptic tube is (e =0.25).The numerical results show that the optimal spacing decreases as Rayleigh number increases for all axis ratios, and the maximum density of heat transfer increases as the Raleigh number increases for all axis ratios and the highest value occurs at axis ratio (e =0) (flat plate) while the lowest value occurs at (e =0.5) (circular tube). The results also show that the optimal spacing is unchanged with the axis ratio at constant Rayleigh number. The agreement between the experimental and numerical heat transfer density is qualitative. |
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Volume 8, Issue 3, 2017, pp.279-290. | Download Full Text Article (PDF) | |