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Aims and Scope
Editorial Board

1. Analysis of transport phenomena and electrochemical reactions in a micro PEM fuel cell with serpentine gas flow channels

Maher A.R. Sadiq Al-Baghdadi

Fuel Cell Research Center, International Energy and Environment Foundation, Najaf, P.O.Box 39, Iraq.

Abstract: Micro-fuel cells are considered as promising electrochemical power sources in portable electronic devices. The presence of microelectromechanical system (MEMS) technology makes it possible to manufacture the miniaturized fuel cell systems. The majority of research on micro-scale fuel cells is aimed at micro-power applications. Performance of micro-fuel cells are closely related to many factors, such as designs and operating conditions. CFD modeling and simulation for heat and mass transport in micro PEM fuel cells are being used extensively in researches and industrial applications to gain better understanding of the fundamental processes and to optimize the micro fuel cell designs before building a prototype for engineering application. In this research, full three-dimensional, non-isothermal computational fluid dynamics model of a micro proton exchange membrane (PEM) fuel cell with serpentine gas flow channels has been developed. This comprehensive model accounts for the major transport phenomena such as convective and diffusive heat and mass transfer, electrode kinetics, transport and phase-change mechanism of water, and potential fields in a micro PEM fuel cell. The model explains many interacting, complex electrochemical, and transport phenomena that cannot be studied experimentally.

Volume 5, Issue 2, 2014, pp.139-154.

2. Experimental study on a simplified crossflow turbine

Chiyembekezo S. Kaunda¹, Cuthbert Z. Kimambo², Torbjorn K. Nielsen¹

1 Waterpower Laboratory, Department of Energy and Process Engineering, Norwegian University of Science and Technology, Trondheim 7491, Norway.

2 Department of Mechanical and Industrial Engineering, University of Dar es Salaam, P.O. Box 35091, Dar es Salaam, Tanzania.

Abstract: The main aim of the study is to enhance the design of a Crossflow turbine, as an appropriate technology for small-scale power generation. This study evaluates the performance of a simplified Crossflow turbine at conditions other than the ‘best efficiency point’. It also explores the ‘reaction’ behavior of the Crossflow turbine as well as characterizes the torque transfer in the two stages of the turbine. The experiments were conducted on a physical simplified Crossflow turbine model using the test facilities in the Waterpower Laboratory at the Norwegian University of Science and Technology. The results show that the maximum turbine efficiency is 79%, achieved at a head of 5m and reduced speed of 13.4; making it a low speed turbine. This turbine efficiency compares well with some reported efficiency values. The result also show that the turbine is efficient when it operates with a degree of reaction and this is achieved at large valve openings; validating observations that the Crossflow turbine is not a pure impulse turbine. Performance evaluation outside the best efficiency point shows that the efficiency decreases with increase in head above the best efficiency head. The turbine efficiency is not sensitive to flow variations: except at a head of 3m, at all tested heads, 25% of the flow at best efficiency point still generates efficiency of above 50%. Torque characterization shows that the second stage plays a significant role in torque transfer, especially when at large valve openings. Therefore, design efforts must also look at how the flow inside the runner interior space can be controlled so that the jet enters the second stage with optimum flow angles. The use of strain gauge to characterize the torque produced using momentum principle as employed in this study presents an additional opportunity to analyze the trends in the torque transfer.

3. Inclusion of a simple dynamic inflow model in the blade element momentum theory for wind turbine application

Xiaomin Chen, Ramesh K. Agarwal

Department of Mechanical Engineering & Materials Science, Washington University in St. Louis, Campus Box 1185, One Brookings Drive, St. Louis, Missouri, 63130, USA.

Abstract: It is well established that the power generated by a Horizontal-Axis Wind Turbine (HAWT) is a function of the number of blades B, the tip speed ratio λr (blade tip speed/wind free-stream velocity) and the lift to drag ratio (C_L /C_D) of the airfoil sections of the blade. The previous studies have shown that Blade Element Momentum (BEM) theory is capable of evaluating the steady-state performance of wind turbines, in particular it can provide a reasonably good estimate of generated power at a given wind speed. However in more realistic applications, wind turbine operating conditions change from time to time due to variations in wind velocity and the aerodynamic forces change to new steady-state values after the wake settles to a new equilibrium whenever changes in operating conditions occur. The goal of this paper is to modify the quasi-steady BEM theory by including a simple dynamic inflow model to capture the unsteady behavior of wind turbines on a larger time scale. The output power of the wind turbines is calculated using the improved BEM method incorporating the inflow model. The computations are performed for the original NREL Phase II and Phase III turbines and the Risoe turbine all employing the S809 airfoil section for the turbine blades. It is shown by a simple example that the improved BEM theory is capable of evaluating the wind turbine performance in practical situations where operating conditions often vary in time.

4. MINLP model for simultaneous scheduling and retrofit of refinery preheat train

Zulkafli N. Izyan¹, M. Noryani¹, Abdul H. Dayanasari¹, M. Shuhaimi²

1 Universiti Teknikal Malaysia Melaka, Hang Tuah Jaya, 76100 Durian Tunggal, Melaka, Malaysia.

2 Universiti Teknologi PETRONAS, Bandar Seri Iskandar, 31750 Tronoh, Perak, Malaysia.

Abstract: There is greater awareness today on the depleting fossil energy resources and the growing problem of atmospheric pollution. Engineers are developing practical techniques to ensure energy processes are designed and operated efficiently. Inefficient heat exchangers lead to higher fuel demand and higher carbon emission. This paper presents mixed-integer nonlinear programming (MINLP) model for simultaneous cleaning and retrofit of crude preheat train (CPT) in oil refinery plant. The formulation of the model is generated and coded in General Algebraic Modeling System (GAMS). The model minimizes the cost of energy and the cost of cleaning. The model takes into account the changes in fouling rates throughout time. There are two cases for this study. The cases are online cleaning (Case 1) and simultaneous online cleaning and retrofit (Case 2). The largest energy saving are found in Case 2. The installation of high efficiency heat exchangers improves furnace inlet temperature (FIT) from 215oC to 227oC. Furthermore, Case 2 results in the highest percentage of cost saving by about 59%. The payback period for investment in high efficiency heat exchangers is 5 months. Thus, Case 2 is the most cost effective option for reductions of energy consumption in Crude Distillation Unit (CDU).

5. Optimization of energy required and potential of greenhouse gas emissions reductions for nectarine production using data envelopment analysis approach

Peyman Qasemi-Kordkheili¹, Ashkan Nabavi-Pelesaraei²

1 Department of Agricultural Machinery Engineering and Mechanization, Khuzestan Ramin Agricultural and Natural Resources University, Mollasani, Ahvaz, Iran.

2 Department of Agricultural Machinery Engineering, Faculty of Agriculture, University of Tabriz, Tabriz, Iran.

Abstract: In this study a non-parametric method of Data Envelopment Analysis (DEA) is used to estimate the energy efficiency and greenhouse gas emissions reduction of nectarine orchard holders in Sari region of Iran. Data were collected using a face-to-face questionnaire method from 45 orchardists. The results showed that based on constant returns to scale model, 24.4% of nectarine orchards were efficient, though based on variable returns to scale model it was 26.7%. The average of technical, pure technical and scale efficiency of nectarine orchards were 0.85, 0.99 and 0.86, respectively. By following the recommendations of this study about 1309 MJ ha-1 (3.25%) of total input energy could be saved. From total saved energy, electricity by 24.8% had highest share, followed by diesel fuel by 22.2%, fertilizers by 16.6% and water for irrigation by 11.8%. Also, energy ratio, energy productivity and net energy gained could improve by 3.68%, 2.78% and 9.03%, respectively. The results indicated that the total GHG emission of present and optimum orchards was found to be about 1266 and 1221 kgCO2eq.ha-1, respectively. Moreover, the total GHG emissions can be reduced about 45 kgCO2eq.ha-1in nectarine production by converting inefficient units to efficient ones.

6. Short term pumped storage scheduling using two proposed techniques

M.M. Salama¹, M.M. Elgazar², S.M. Abdelmaksoud¹, H.A. Henry¹

1 Department of Electrical Engineering, Faculty of Engineering (Shoubra), Benha University, Cairo, Egypt.

2 Department of Electrical Engineering, Faculty of Engineering, Azher University, Cairo, Egypt.

Abstract: In this paper, a genetic algorithm and constriction factor based particle swarm optimization technique are proposed for solving the short term pumped storage hydro thermal scheduling problem. The performance efficiency of the proposed techniques is demonstrated on hydrothermal test system comprising of five thermal units and one pumped storage power plant. A wide rang of thermal and hydraulic constraints are taken into consideration such as real power balance constraint, minimum and maximum limits of thermal units and pumped storage power plant, water discharge and water pumping rate limits and reservoir storage volume constraints. The simulation results obtained from the constriction factor based particle swarm optimization technique are compared with the outcomes obtained from the genetic algorithm in terms of cost saving and execution time to reveal the validity and verify the feasibility of the proposed methods. The test results show that the constriction factor based particle swarm optimization technique performs better than genetic algorithm in solving this problem in terms of cost saving and computational time.

7. Modeling and analysis of DFIG in wind energy conversion system

Omer Elfaki Elbashir, Wang Zezhong, Liu Qihui

School of Electrical and Electronics Engineering, North China Electric Power University, Beinong Road, Changping district, Beijing, china.

Abstract: This paper deals with the modeling, analysis, and simulation of a doubly-fed induction generator (DFIG) driven by a wind turbine. The grid connected wind energy conversion system (WECS) is composed of DFIG and two back to back PWM voltage source converters (VSCs) in the rotor circuit. A machine model is derived in an appropriate dq reference frame. The grid voltage oriented vector control is used for the grid side converter (GSC) in order to maintain a constant DC bus voltage, while the stator voltage orientated vector control is adopted in the rotor side converter (RSC) to control the active and reactive powers.

8. Synergistic evaluation of the biomass/coal blends for co-gasification purposes

S Gaqa^1,2, S Mamphweli², D Katwire¹, E Meyer²

1 Chemistry Department,  University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.

2 Institute of Technology, University of Fort Hare, Private Bag X1314, Alice 5700, South Africa.

Abstract: Approximately 95% of electricity in South Africa is generated from coal, which is a fossil fuel that has detrimental environmental impacts. Eskom has started investigating the possibility of co-firing coal with biomass to improve their carbon footprint. However, co-firing  utilizes approximately 80% of water and results in extensive environmental impacts. This research seeks to investigate the possibility of co-gasification of coal and biomass, which is a thermochemical process that uses about a third of the water required by a coal-fired power station, and results in much lower emissions. Thermogravimetric analysis (TGA) was conducted to investigate the existence of a synergy between coal and biomass during gasification.  Various coal/biomass blends were investigated using TGA. The synergistic effect between the two feedstock as determined through TGA allowed the prediction of the gasification characteristics of the blends that most likely gave the highest conversion efficiency. Preliminary results suggested the existence of this synergy.

9. Reliability based performance modelling and evaluation: A case study of heat exchanger

Usman Abubakar^1,2, I. A. Mohammed², Bashar Dan-asabe³, Abubakar Alkali⁴

1 School of Engineering, University of Aberdeen, Aberdeen, AB24 3FX, UK.

2 Chemical Engineering Department, Ahmadu Bello University, Zaria, Nigeria.

3 Shell Chair Office, Department of Mechanical Engineering, Ahmadu Bello University, Zaria, Nigeria.

4 School of Engineering, Robert Gordon University, Aberdeen, AB10 1FR, UK.

Abstract: This paper presents an approach that combines First Order Reliability Method (FORM) with Monte Carlo Simulation (MCS) to solve constrained stochastic optimization problems in a proficient way. Based on FORM/MCS, this paper shows how parametric uncertainties can be characterized, modelled, propagated across the life cycle of an engineering system and then obtain a wide range of performance measures that can support engineers as they seek to improve design/operational robustness, safety and cost efficiency. A case study involving counter flow heat exchanger is performed to illustrate applicability and usefulness of the approach. Impacts of uncertainties on the worth of energy to be recovered by the heat exchanger from waste process fluid are represented through probability distributions, bounds and a number of performance measures. Sensitivity of the performance target, in this case, financial gain, to each of the basic variables is determined, both in magnitude and direction. Two sets of specifications are also considered to demonstrate that the approach can be used to conduct reliability based performance improvement without attracting disproportionate cost.

10. Passive thermal performance increase in cisterns

Najmeh Najafi¹, Arash Alipour², Seyed Mohamad Ali Najafi¹

1 Department of Architecture, Beyza Branch, Islamic Azad University, Beyza, Iran.

2 Mechanical Engineering Department, Yazd University, Yazd, Iran.

Abstract: Cisterns are ancient building having two main tasks. First task is storing water in raining seasons for using in dry seasons and the second task is decreasing water temperature, which happens because of the air flow above water surface and evaporating water. It can be stated that by increasing fluid flow above the surface, evaporating increase so increasing in heat transfer happens and decreasing of water temperature is the result. This paper has investigated fluid flow around and inside cisterns with FLUENT software results. Increasing in air flow demand to the cistern is the primary purpose of this study, by changing main parameters of cistern geometry like increasing or decreasing of doom hale diameter, inlet and outlet of wind catcher, elevation of wind catcher and also wind speed. This study introduces the best geometry for cisterns according to maximum air flow demand and minimum volume. Considering that, there is a direct relation between heat transfer and airflow rate in cisterns, so in this study, the influence of mentioned parameters are investigated to reach optimum design for the best performance of cisterns.