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Aims and Scope
Editorial Board

1. Effect of channel geometrical configuration on the pressure distribution and stress failure in a running PEM fuel cell

Maher A.R. Sadiq Al-Baghdadi

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

Abstract: Proton Exchange membrane (PEM) fuel cells are still undergoing intense development, and the combination of new and optimized materials, improved product development, novel architectures, more efficient transport processes, and design optimization and integration are expected to lead to major gains in performance, efficiency, durability, reliability, manufacturability and cost-effectiveness. PEM fuel cell assembly pressure is known to cause large strains in the cell components. All components compression occurs during the assembly process of the cell, but also during fuel cell operation due to membrane swelling when absorbs water and cell materials expansion due to heat generating in catalyst layers. Additionally, the repetitive channel-rib pattern of the bipolar plates results in a highly inhomogeneous compressive load, so that while large strains are produced under the rib, the region under the channels remains approximately at its initial uncompressed state. This leads to significant spatial variations in GDL thickness and porosity distributions, as well as in electrical and thermal bulk conductivities and contact resistances (both at the ribe-GDL and membrane-GDL interfaces). These changes affect the rates of mass, charge, and heat transport through the GDL, thus impacting fuel cell performance and lifetime. In this study, computational fluid dynamics (CFD) model of a PEM fuel cell has been developed to simulate the pressure distribution inside the cell, which are occurring during fuel cell assembly (bolt assembling), and membrane swelling and cell materials expansion during fuel cell running due to the changes of temperature and relative humidity. The PEM fuel cell model simulated includes the following components; two bi-polar plates, two GDLs, and, an MEA (membrane plus two CLs). This model is used to study and analyse the effect of channel geometrical configuration on the mechanical behaviour of the PEM fuel cell components. The analysis helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell durability under various conditions. The model is shown to be able to understand the effect of pressure distribution inside the cell on the performance and durability that have limited experimental data.

Volume 8, Issue 2, 2017, pp.105-126.

2. Improvements of mixing process in a rapidly tubular flame burner

Yoldoss Chouari¹, Wassim Kriaa¹, Hatem Mhiri¹, Philippe Bournot²

1 UTTPI, National Engineering School of Monastir (ENIM), Av. Ibn El Jazzar, 5019 Monastir, Tunisia.

2 IUSTI, UMRCNRS 6595, 5 rue Enrico Fermi,Technopôle de Château-Gombert, 13013 Marseille, France.

Abstract: A three-dimensional simulation of a steady non-reactive mixing process in a rapidly mixed type tubular flame burner is carried out in order to examine the effects of the injectors’ number (N= 2, 3, 4 and 6), the swirl number (Sw=0.46, 0.68, 1.05 and 1.83) and the injector arrangements (3-3 and 4-2). The mixing process is investigated by focusing on the following criterions: Particles trajectory, Central reverse zone (CRZ) and mixing layer thickness. The particles are tracked using a Lagrangian Discrete Phase Model (DPM). The numerical solutions are validated by comparing with previous experimental results. It is pertinent to note that the model predicts properly the flow field and the mixing in a rapidly tubular flame. The obtained results have generally shown, that for the same swirl number and same average axial velocity, the increase of injectors’ number generates a larger reverse flow and decreases the mixing layer thickness. It is also shown that a high swirl number and same distribution of the injectors’ number could significantly promote the mixing in rapidly tubular flame.

3. Estimating the effect of a phase change material on the performance of a photovoltaic unit using a five parameter model approach

Panagiotis Kladisios, Athina Stegou-Sagia

Laboratory of Heat Transfer and Thermal Processes, School of Mechanical Engineering, National Technical University of Athens, 9 Iroon Polytechniou Str., Zografou 15780, Greece.

Abstract: Photovoltaic modules operate under a large range of conditions. This, combined with the fact that manufacturers provide electrical parameters at specific conditions (STC, Standard Test Conditions) renders the prediction of a PV module’s power efficiency very difficult. The most common model for calculating the electric characteristics and, consequently, the generated power of a photovoltaic unit under real transient conditions is the five-parameter model. It is noteworthy that this model demands a relatively small amount of data that are normally available from the manufacturer. The purpose of this paper is to determine the actual benefit in the power efficiency of a photovoltaic unit that has its cell temperature reduced using a phase change material. All approaches of the five-parameter model involve simulating the solar cell, photovoltaic module or photovoltaic array with an one-diode equivalent electrical circuit. The operation of such a circuit is defined by a characteristic I-V equation which contains five parameters: the photocurrent I0, the reverse saturation current Il, the series resistance Rs, the parallel resistance Rp and, depending on the approach, either the diode’s ideality factor m or the modified ideality factor α. For every pair of cell temperature T and solar radiation G, a new characteristic I-V is in effect and, therefore, the above parameters must be calculated anew using correlations between reference and non-reference values of the parameters.

4. Feasibility study and design of an ocean wave power generation station integrated with a decommissioned offshore oil platform in UK waters

Ulugbek Azimov, Martin Birkett

Department of Mechanical and Construction Engineering, University of Northumbria, Newcastle, NE1 8ST, UK.

Abstract: Wave energy exploits the movement of the wind across the surface of the sea to provide an inexhaustible, carbon-free energy source for electricity generation. This can potentially provide a significant contribution to electricity generation supply in the UK, meeting up to 20% of the UK’s electricity demand. This represents 30-50 MW capacity of electrical energy by 2020, and potentially 27 GW by 2050 as technology within the industry develops and matures. Studies show that developing marine energy resources in the UK can save 60 metric tons of carbon dioxide by 2025 and aid in the UK meeting 20-20-20 renewable energy objectives. In this paper the design of a wave power station integrated with a decommissioned offshore oil platform is proposed. This approach provides ideal conditions for the exploitation of wave energy for electricity generation. It not only saves the cost of decommissioning but also provides the offshore oil platform with new life, generating electrical energy from an inexhaustible source. The objective of this work was to conduct an extensive feasibility study to develop a proof of concept design for wave energy generation integrated with an offshore oil platform.

5. Optimization of parameters of heating system with low-temperature water panels by changes of entropy

АndriyRedko, ArtemCherednik, NatanLantsberg, NataliiaKulikova, AlexandrRedko

Department of Heat and Gas supply, Ventilation and the Use of Thermal Waste Energy, Sanitary-Technical Faculty, Kharkiv National University of Construction and Architecture, Street Sumskaya, 40, 61002, Kharkov, Ukraine.

Abstract: The results of a numerical study of the radiant heat-exchange processes of water ceiling panels of industrial premises heating systems are presented. Numerical simulation and parameters optimization of panel system using the method of LPτ-search on the condition of minimum entropy generation has been completed. The influence of the design parameters of the panels, the conditions of their accommodation and regime operation parameters is studied. The minimum entropy production in the system has been taken as one of the optimization criteria. Estimation of non-uniformity of the temperature field of the surface panels and non-uniformity of radiation intensity has been carried out. The energy performance indicators of the system efficiency are estimated.

6. Numerical investigation of a micro-heat exchanger with various channel geometries

Viorel Ionescu

Department of Physics and Electronics, Ovidius University, Constanta, 900527, Romania.

Abstract: The Micro-Electro-Mechanical System (MEMS) based heat exchangers had become popular recently in many practical applications. For example, MEMS heat exchangers can be used as a cooling system for micro-chips squeezed into smaller and smaller spaces, with very little place for heat to escape. Therefore, the improvement of their heat transfer characteristics is a key issue for the development of micro-scale integrated systems. In this paper, it was implemented a basic unit model for a micro-heat exchanger using commercial Finite Element Method (FEM) package Comsol Multiphysics (version 5.0). Thermal performance for this model having four different fluid channel geometries: circular, rhombic, square and octagonal was investigated in terms of temperature gradient, total internal energy and total enthalpy distributions along the hot and cold channels.

7. Forecasting of photovoltaic power at hourly intervals with artificial neural networks under fluctuating weather conditions

Stamatia Dimopoulou^1,2, Alice Oppermann^1,2, Ekkehard Boggasch¹, Andreas Rausch²

1 Faculty of Supply Engineering, Ostfalia University of Applied Sciences, Salzdahlumer Str. 46-48, 38302 Wolfenbüttel, Germany.

2 Faculty of Mathematics, Computer Science and Mechanical Engineering, TU Clausthal, Julius-Albert-Str. 4, 38678 Clausthal-Zellerfeld, Germany.

Abstract: The requirement of the in advance knowledge of the future photovoltaic (PV) production in the domestic field for a better allocation of the on-site PV generation to the local load demand and the available storage facilities is more and more emerging. In this study two different methods were applied so as to forecast the next hour PV power using artificial neural networks (ANN). In the first case the weather parameters of solar irradiance and ambient temperature were predicted, the output was fed to the developed model of the PV installation and the next hour PV power was computed. In the second case it was attempted to predict directly the PV power. The performance of the applied ANNs was compared with the respective outcomes from the persistence models. In each case the applied ANN outperforms the persistence model. In addition, during the evaluation phase the extracted annual energy results were compared with the respective registered data from the installed meters. Again in both cases the results approximated the reality, though in the first case the difficulty in identification and representation of malfunctions in operation of the PV plants due to snow accumulation on the panels caused minor deviations.