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Aims and Scope
Editorial Board

1. Modeling optimizes PEM fuel cell durability using three-dimensional multi-phase computational fluid dynamics model

Maher A.R. Sadiq Al-Baghdadi

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

Abstract: Damage mechanisms in a proton exchange membrane (PEM) fuel cell are accelerated by mechanical stresses arising during fuel cell assembly (bolt assembling), and the stresses arise during fuel cell running, because it consists of the materials with different thermal expansion and swelling coefficients. Therefore, in order to acquire a complete understanding of the damage mechanisms in the membrane and gas diffusion layers, mechanical response under steady-state hygro-thermal stresses should be studied under real cell operating conditions and in real cell geometry (three-dimensional). In this work, full three-dimensional, non-isothermal computational fluid dynamics model of a PEM fuel cell has been developed to simulate the hygro and thermal stresses in PEM fuel cell, which are occurring during the cell operation due to the changes of temperature and relative humidity. A unique feature of the present model is to incorporate the effect of hygro and thermal stresses into actual three-dimensional fuel cell model. The mechanical behaviour of the membrane, catalyst layers, and gas diffusion layers during the operation of a unit cell has been studied and investigated. The model is shown to be able to understand the many interacting, complex electrochemical, transport phenomena, and stresses distribution that have limited experimental data. The results show that the non-uniform distribution of stresses, caused by the temperature gradient in the cell, induces localized bending stresses, which can contribute to delaminating between the membrane and the gas diffusion layers. These results may explain the occurrence of cracks and pinholes in the membrane during regular cell operation. This model is used to study the effect of operating, design, and material parameters on fuel cell hygro-thermal stresses in polymer membrane, catalyst layers, and gas diffusion layers. Detailed analyses of the fuel cell durability under various operating conditions have been conducted and examined. The analysis helped identifying critical parameters and shed insight into the physical mechanisms leading to a fuel cell durability under various operating conditions. Optimization study of a PEM fuel cell durability has been performed. To achieve long cell life, the results show that the cell must be operate at lower cell operating temperature, higher cell operating pressure, higher stoichiometric flow ratio, and must have higher GDL porosity, higher GDL thermal conductivity, higher membrane thermal conductivity, narrower gases channels, thicker gas diffusion layers, and thinner membrane. In these optimum conditions, the maximum deformation (displacement) reduction by about 50% than the base case operating conditions.

Volume 1, Issue 3, 2010, pp.375-398.

2. Simulation of the thermal borehole resistance in groundwater filled borehole heat exchanger using CFD technique

A-M. Gustafsson¹, L. Westerlund²

1 Department of Civil, Mining and Environmental Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden.

2 Department of Applied Physics and Mechanical Engineering, Luleå University of Technology, SE-971 87 Luleå, Sweden.

Abstract: The thermal borehole resistance in a groundwater-filled borehole heat exchanger (BHE) is affected of both conductive and convective heat transfer through the borehole water. To calculate this heat transport, different models are required compared to calculation of only conductive heat transfer in a back-filled BHE. In this paper some modelling approximations for groundwater-filled, single U-pipe BHEs were investigated using a 3D CFD model. The purpose is to find approximations that enable to construct a fast, simple model including the convective heat transfer that may be used in thermal response test analyses and BHE design programs. Both total heat transfer calculations (including convective and conductive heat transport) and only conductive heat transfer calculations were performed for comparison purposes. The approximations that are investigated are the choice of boundary condition at the U-pipe wall and using a single pipe in the middle of the borehole instead of the U-pipe. For the total heat transfer case, it is shown that the choice of boundary condition hardly affects the calculated borehole thermal resistance. For the only conductive heat transfer case, the choice of boundary condition at the pipe wall gives large differences in the result. It is also shown that using an annulus model (single pipe in the middle of the borehole) results in similar heat transfer as the U-pipe model provided that the equivalent radius is chosen appropriately. This approximation can radically decrease the number of calculation cells needed.

3. Effect of unsaturated fatty acid esters of biodiesel fuels on combustion, performance and emission characteristics of a DI diesel engine

A. Gopinath¹, Sukumar Puhan², G. Nagarajan³

1 Product Development, Ashok Leyland Technical Centre, Chennai, Tamilnadu, India.

2 Department of Mechanical Engineering, Veltech Engineering College, Chennai, Tamilnadu, India.

3 Internal Combustion Engineering Division, Department of Mechanical Engineering, College of Engineering, Anna University Chennai, Tamilnadu, India.

Abstract: Many studies have reported that exhaust from biodiesel fuel gives higher oxides of nitrogen or lower, while HC and smoke emissions are significantly lower than that of diesel fuel. Possible explanations are: the physical properties and fatty acid composition of biodiesel affecting the spray and the mixture formation with reduced heat losses. The aim of this present investigation is to study the effect of unsaturated fatty acid composition of biodiesel on combustion, performance and emissions characteristics of a diesel engine. For this experiment thirteen different biodiesel fuels with different fatty acid compositions were selected. The performance and emissions tests on a single cylinder DI diesel engine were conducted using same biodiesel fuels. The results showed that biodiesel having more unsaturated fatty acids emit more oxides of nitrogen and exhibit lower thermal efficiency compared to biodiesel having more saturated acids. No significant differences in HC and smoke emissions among the biodiesel fuels were noticed. Thermal efficiency and NOX emission of saturated biodiesel is comparatively better than other biodiesel. Combustion analysis results show that high unsaturated fatty acid biodiesel has longer premixed combustion and high peak pressure compared to that of high saturated fatty acid biodiesel.

4. Hydrodynamic and performance of low power turbines: conception, modelling and experimental tests

Mariana. Simão, Helena M. Ramos

Civil Engineering Department and CEHIDRO, Instituto Superior Técnico, Technical University of Lisbon, Av. Rovisco Pais, 1049-001, Lisbon, Portugal.

Abstract: The present work comprises a research about hydraulic machines with the aim of optimization and the selection of adequate turbines of low power for exploitation of an available energy still unexplored in water supply systems based on analyses of 3D hydrodynamic flows and on characteristic curves which lead to the best efficiency point. The analysis is carried out based on non-dimensional parameters (i.e., discharge, head, efficiency, runner speed and mechanical power) in order to be possible comparisons. Mathematical models based on the physical principles, associated to the development of volumetric and rotordynamic machines, are developed. New turbines are suggested, which are based on similar theory among turbo machines based on applications in hydraulic systems with guarantee discharge and available head. The hydrodynamic fluid mechanical analysis requires the use of complex advanced models (CFD) which apply the equations of Navier-Stokes by using mathematical models of conservation laws, for the study of the turbulent flow behaviour. To determine the correlation between the flow velocity and pressure fields, the k-? model, is used in this research. Many turbines are evaluated (i.e., positive displacement (PD), pump as turbine (PAT), propeller with volute at inlet, four and five blades tubular propellers) and sensitivity analyses, to the best configurations, as well as comparisons between performance curves and experimental tests. Results are presented with the appropriate range variation for each turbine type and application..

5. Energy and exergy analysis of particle dispersed latent heat storage system

S. Jegadheeswaran, S. D. Pohekar

Mechanical Engineering, Tolani Maritime Institute, Induri, Pune 410 507, India.

Abstract: Latent heat thermal storage (LHTS) system has been attractive over the years as an effective energy storage and retrieval device especially in solar thermal applications. However, the performance of LHTS systems is limited by the poor thermal conductivity of phase change materials (PCMs) employed. A numerical study is carried out to investigate the performance enhancement of a LHTS unit of shell and tube configuration due to the dispersion of high conductivity particles in the PCM during charging process (melting). Temperature based governing equations have been formulated and solved numerically following an alternate iteration between the temperature and thermal resistance. Exergy based performance evaluation is taken as a main aspect. The numerical results are presented for several mass flow rates and inlet temperatures of heat transfer fluid (HTF). The results indicate a significant improvement in the performance of the LHTS unit when high conductivity particles are dispersed.

6. Experimental study of operation performance of a low power thermoelectric cooling dehumidifier

Wang Huajun, Qi Chengying

School of Energy and Environment Engineering, Hebei University of Technology, Tianjin, China.

Abstract: The present work was performed to apply thermoelectric technology to a low power dehumidifying device as an alternative to the conventional vapor-compression refrigeration systems. The experimental prototype of a small-scale thermoelectric dehumidifier (TED) with rectangular cooling fins was built and its operation performance was studied experimentally. The results showed that the TED experienced two typical thermodynamic processes including the cooling dehumidification and the isothermal dehumidification, where the latter was dominated. It was found that there existed a peak during the variation of the average coefficient of performance (COP) as a function of the input power of the thermoelectric module. Under the present experimental conditions, the COP of the TED reached the maximum of 0.32 and the corresponding dehumidifying rate was 0.0097 g/min, when the input power was kept at 6.0 W. The rapid elimination of condensed liquid-drops on the cooling fins amounted on the thermoelectric module is a major approach to improving the operation performance of the TED.

7. Hydromagnetic convective flow past a vertical porous plate through a porous medium with suction and heat source

S.S.Das¹, U.K.Tripathy², J.K.Das³

1 Department of Physics, KBDAV College, Nirakarpur, Khurda-752 019 (Orissa), India.

2 Department of Physics, B S College, Daspalla, Nayagarh-752 078 (Orissa), India.

3 Department of Physics, Stewart Science College, Mission Road, Cuttack-753 001 (Orissa), India.

Abstract: This paper theoretically analyzes the unsteady hydromagnetic free convective flow of a viscous incompressible electrically conducting fluid past an infinite vertical porous plate through a porous medium in presence of constant suction and heat source. Approximate solutions are obtained for velocity field, temperature field, skin friction and rate of heat transfer using multi-parameter perturbation technique. The effects of the flow parameters on the flow field are analyzed with the aid of figures and tables. The problem has some relevance in the geophysical and astrophysical studies.

8. Thermoeconomic optimization of the steam power plant

Reşat Selbaş¹, Hilmi Yazıcı², Arzu Şencan¹

1 Department of Mechanical Education, Technical Education Faculty, Süleyman Demirel University, 32260,  Isparta, Turkey.

2 Department of Mechanical Education, Technical Education Faculty, Pamukkale University, Denizli, Turkey.

Abstract: In this study, thermoeconomic optimization of the steam power plant with Levelized-cost method was carried out. Aim of thermoeconomy is to minimize exergy cost. With this aim, the first law and the second law of thermodynamics to each component of system were performed. Irreversibility and exergy values were obtained. Economic analysis by using exergy values was carried out. Unit electric cost for each component of system was calculated. Optimum design and operating conditions for minimum exergy cost were obtained.

9. Matlab / simulink based study of photovoltaic cells / modules / array and their experimental verification

Savita Nema, R.K.Nema, Gayatri Agnihotri

Department of Electrical Engineering, Maulana Azad National Institute of Technology, Bhopal, India.

Abstract: A Matlab-Simulink based simulation study of PV cell/PV module/PV array is carried out and presented in this paper. The simulation model makes use of basic circuit equations of PV solar cell based on its behaviour as diode and comprehensive behavioural study is performed under varying conditions of solar insolation, temperature, varying diode model parameters, series and shunt resistance etc. The study is helpful in outlining the principle and intricacies of PV cell/modules and may be used to verify the impact of different topologies and control techniques on the performance of different types of PV systems. The PV module/Array performance is immensely marred by shading effect and its P-V characteristics exhibit multiple maxima. The Matlab/simulink based study therefore also points out significance of locating maximum power point for a given Module/Array. An experimental verification is also carried out in the lab by developing a PC based data acquisition system, which is also briefly discussed.

10. Which is a better transportation fuel – butanol or ethanol ?

Kenneth R. Szulczyk

Department of Economics, Orbita 3, Suleyman Demirel University, Almaty, 050043 Kazakhstan.

Abstract: This article examines butanol and ethanol as transportation fuels for gasoline-powered engines. This paper examines two aspects. First, the fuel properties of butanol and ethanol are examined and compared to each other. Consequently, butanol overcomes three deficiencies of ethanol. Butanol has a higher energy content, butanol-gasoline blends do not separate in the presence of water, and butanol can be blended with gasoline in any percentage, all the way up to 100%. Second, a review of the fermentation technology is examined for both butanol and ethanol production. Both butanol and ethanol can be fermented from the same feedstocks, which include the sugar and starch crops and lignocellulosic fermentation from wood and crop residues, and fast-growing energy crops like hybrid poplar, switchgrass, and willow. Furthermore, the capital and facilities used to produce ethanol can be switched to butanol fermentation with minimal costs. Thus, society is able to transition away from ethanol and begin to produce butanol with minimal capital and infrastructure costs. Unfortunately, the main drawback to butanol fermentation is its low chemical yield. Until researchers discover or engineer new microorganisms that handle higher butanol concentrations, butanol may not be adapted as an alternative fuel.

11. Solar radiation models - review

M. Jamil Ahmad, G.N. Tiwari

Center for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi-16, India.

Abstract: In the design and study of solar energy, information on solar radiation and its components at a given location is very essential. Solar radiation data are required by solar engineers, architects, agriculturists and hydrologists for many applications such as solar heating, cooking, drying and interior illumination of buildings. For this purpose, in the past, several empirical correlations have been developed in order to estimate the solar radiation around the world. The main objective of this study is to review the global solar radiation models available in the literature. There are several formulae which relate global radiation to other climatic parameters such as sunshine hours, relative humidity and maximum temperature. The most commonly used parameter for estimating global solar radiation is sunshine duration. Sunshine duration can be easily and reliably measured and data are widely available.

12. Auction design for the allocation of carbon emission allowances: uniform or discriminatory price ?

Rong-Gang Cong^1,2,4, Yi-Ming Wei^2,3

1 Institute of Policy and Management, Chinese Academy of Sciences, Beijing, 100080, China.

2 Center for Energy and Environmental Policy Research, Beijing Institute of Technology, Beijing, 100081, China.

3 School of Management and Economics, Beijing Institute of Technology, Beijing, 100081, China.

4 Graduate School of the Chinese Academy of Sciences, Beijing 100080, China.

Abstract: Only four states used auction in Phase (2005-2007) of the European Union Emission Trading System, of which four used a uniform-price sealed auction format. Here we discuss whether the auction should adopt a uniform-price or discriminatory-price format using an agent-based carbon allowances auction model established for the purpose. The main conclusions are as follows: (1) when carbon allowances are relatively scarce, the government should use a discriminatory-price auction; when carbon allowances are relatively abundant, the government should use a uniform-price auction. (2) Uncertainty of the generating cost reduces the ability of an auction to know bidders’ private values, which will reduce the government’s revenue and reduce auction efficiency. (3) Compared with the discriminatory-price auction, the uniform-price auction can prevent large bidders from obtaining excessive profits. (4) The uniform-price auction is relatively insensitive to market structure. However, a monopoly market is more likely to develop under the discriminatory-price auction format. The results of the model have some policy implications for designing carbon market mechanisms in the future.

13. Study of ground-reflected component and its contribution in diffuse solar radiation incident on inclined surfaces over India

A. K. Katiyar, Chanchal Kumar Panday

Department of Applied Sciences & Humanities, Institute of Engineering & Technology, U.P.T.U., Lucknow, India.

Abstract: To define the diffuse radiation incident on an inclined plane of any orientation and of any tilt angle, we need to know sky diffuse radiation as well as ground-reflected radiation. Here we made a study of ground-reflected component of radiation on inclined surfaces with varying inclination angles for Lucknow (Latitude 26.750, Longitude 80.850), Mumbai (Latitude 19.120 N, Longitude 72.850 E), Calcutta (Latitude 22.650 N, Longitude 88.350 E), and Pune (Latitude 18.530 N, Longitude 73.910 E) cities of India using isotropic and anisotropic models. We have calculated the data for entire year using these models for all considered stations and obtained the percentage contributions in diffuse radiations. It is found that anisotropic model predict lower values than isotropic and contribution of ground-reflected component in diffuse radiation for isotropic model is more than anisotropic.