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Aims and Scope
Editorial Board

1. Numerical simulation of draft tube flow of a bulb turbine

Coelho J. G.¹, Brasil Junior A. C. P.²

1 Federal University of Triângulo Mineiro, Institute of Technological and Exact Sciences, Avenida Doutor Randolfo Borges Junior, 1250 – Uberaba – MG, Brazil.

2 University of Brasilia, Department of Mechanical Engineering, Campus Darcy Ribeiro, Brasilia – DF, Brazil.

Abstract: In this work a numerical study of draft tube of a bulb hydraulic turbine is presented, where a new geometry is proposed. This new proposal of draft tube has the unaffected ratio area, a great reduction in his length and approximately the same efficiency of the draft tube conventionally used. The numerical simulations were obtained in commercial software of calculation of flow (CFX-14), using the turbulence model SST, that allows a description of the field fluid dynamic near to the wall. The simulation strategy has an intention of identifying the stall of the boundary layer precisely limits near to the wall and recirculations in the central part, once those are the great causes of the decrease of efficiency of a draft tube. Finally, it is obtained qualitative and quantitative results about the flow in draft tubes.

Volume 4, Issue 4, 2013, pp.539-548.

2. Optimization of power generation from shrouded wind turbines

Tudor Foote, Ramesh Agarwal

Department of Mechanical Engineering and Materials Science, Washington University in St. Louis, USA.

Abstract: In past several years, several studies have shown that the shrouded wind turbines can generate greater power compared to bare turbines. The objective of this study is to determine the potential of shrouded wind turbines for increased power generation by conducting numerical simulations. An analytical/computational study is performed by employing the well-known commercial Computational Fluid Dynamics (CFD) software FLUENT. An actuator disc model is used to model the turbine. The incompressible Navier-Stokes equations and a two equation realizable k – ε model are employed in the calculations. The power coefficient Cp and generated power are calculated for a large number of cases for horizontal axis wind turbines (HAWT) of various diameters and wind speeds for both bare and shrouded turbines. The design of the shroud is optimized by employing a single objective genetic algorithm; the objective being the maximization of the power coefficient Cp. It was found that the shroud indeed increases the Cp beyond the Betz’s limit significantly and as a result the generated power; this effect is consistent with that found in the recent literature that the shrouded wind-turbines can generate greater power than the bare turbines. The optimized shape of the shroud or diffuser further increases the generated power and Cp.

3. Economics of wastewater treatment in GTL plant using spray technique

G.C. Enyi, G.G. Nasr, M. Burby

University of Salford, Manchester, M5 4WT, United Kingdom.

Abstract: In a Gas-to-liquid (GTL) plant, significant quantities of CO₂ and reaction water are produced and various chemicals are used as intermediate treatment chemicals. The reaction water is contaminated by these chemicals which impair the pH and the related properties of the water. The pH has to be controlled in the effluent treatment unit before the water is re-used or released to the environment. The overall aim of this investigation is to create a novel technique to address the problem of waste water treatment in GTL plants which will assist in the reduction of greenhouse gas (CO₂) emissions into the atmosphere. A laboratory-scale effluent neutralisation unit for pH control utilising gas injectors was designed and built. The unit used the CO₂ produced as a by-product of GTL process as wastewater treatment chemical instead of the conventional Sulphuric acid. The quality of wastewater after treatment with CO₂ met the standards set by the state regulatory agency. The economics of the new process shows a better payout period of 3.6 years for capital investment of $1,645 Million compared to 4.7 years for an existing plant layout with capital investment of $1,900 Million. The effects of increase in plant capacity showed a lower payback back of 2.8 years for plant capacity of 140,000 barrels/day (22258 m³/day), 3.6 years for 34,000 barrels/day and 6.0 years for 12,500 barrels/day (1987 m³/day) plant capacity. The sensitivity analysis using crystal ball simulator with ‘Microsoft Excel’ shows that the annual revenue has the greatest effects on the NPV of the plant than the CAPEX and inflation rate. Apart from the environmental benefits the process generates by reducing CO₂ emissions into the atmosphere, the study also concludes that the replacement of conventional Sulphuric acid (H₂SO₄) unit with CO₂ improves the economics of the plant.

4. Estimation of apparent soil resistivity for two-layer soil structure

M. Nassereddine, J. Rizk, M. Nagrial, A. Hellany

School of Computing, Engineering & Mathematics, University of Western Sydney, Australia.

Abstract: High voltage (HV) earthing design is one of the key elements when it comes to safety compliance of a system. High voltage infrastructure exposes workers and people to unsafe conditions. The soil structure plays a vital role in determining the allowable and actual step/touch voltage. This paper presents vital information when working with two-layer soil structure. It shows the process as to when it is acceptable to use a single layer instead of a two-layer structure. It also discusses the simplification of the soil structure approach depending on the reflection coefficient. It introduces the reflection coefficient K interval which determines if single layer approach is acceptable. Multiple case studies are presented to address the new approach and its accuracy.

5. Comparative evaluation of kinetic, equilibrium and semi-equilibrium models for biomass gasification

Buljit Buragohain¹, Sankar Chakma², Peeush Kumar², Pinakeswar Mahanta^1,3, Vijayanand S. Moholkar^1,2

1 Center for Energy, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam, India.

2 Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam, India.

3 Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati – 781 039, Assam, India.

Abstract: Modeling of biomass gasification has been an active area of research for past two decades. In the published literature, three approaches have been adopted for the modeling of this process, viz. thermodynamic equilibrium, semi-equilibrium and kinetic. In this paper, we have attempted to present a comparative assessment of these three types of models for predicting outcome of the gasification process in a circulating fluidized bed gasifier. Two model biomass, viz. rice husk and wood particles, have been chosen for analysis, with gasification medium being air. Although the trends in molar composition, net yield and LHV of the producer gas predicted by three models are in concurrence, significant quantitative difference is seen in the results. Due to rather slow kinetics of char gasification and tar oxidation, carbon conversion achieved in single pass of biomass through the gasifier, calculated using kinetic model, is quite low, which adversely affects the yield and LHV of the producer gas. Although equilibrium and semi-equilibrium models reveal relative insensitivity of producer gas characteristics towards temperature, the kinetic model shows significant effect of temperature on LHV of the gas at low air ratios. Kinetic models also reveal volume of the gasifier to be an insignificant parameter, as the net yield and LHV of the gas resulting from 6 m and 10 m riser is same. On a whole, the analysis presented in this paper indicates that thermodynamic models are useful tools for quantitative assessment of the gasification process, while kinetic models provide physically more realistic picture.

6. Determination trends and abnormal seasonal wind speed in Iraq

Ahmed F. Hassoon

Department of Atmospheric Sciences, College of Science, AL- Mustansiriyah University, Baghdad, Iraq.

Abstract: Monthly observed wind speed data at four weather stations (Baghdad, Mosul, Basra, Rutba) at 10m above surface were used to explore the temporal variations of the wind speed (1971-2000) in Iraq. There are different methods to analyze wind speed variation data, but the time series are one of the powerful analysis methods to diagnose the seasonal wind speed anomaly. The results show most high abnormal data is found in summer seasons in all the stations of study, where it concentrated at 1975, 1976, 1978,1996-1995, 2000. Rutba station is different where its high deviation about annual average at nearly all the seasons, in this station there are trends in seasonal wind towards decreases in all the seasons, for example in winter it reached to about 0.046m/s.a^-1, while in other stations Mosul and Basra there increases in annual seasonal wind speed trends in seasons spring, summer, autumn where its reached higher value at summer in Basra about 0.0482m/s.a^-1. The second method to determine abnormal annual seasonal wind speed is through comparison seasonal average wind speed, where the average wind speed at the seasons summer and spring in Baghdad and Basra station have very high averages at nearly all years, this cannot see in Mosul and Rutba, in Rutba the seasonal average is intersected with each other, summer and spring is not have greater seasonal average in this station.

7. New solar desalination system using humidification/ dehumidification process

Adel M. Abdel Dayem

Mechanical Engineering Department, College of Engineering and Islamic Architecture, Umm Al-Qura University, 5555 Makah, KSA.

Abstract: An innovative solar desalination system is successfully designed, manufactured and experimentally tested at Makkah, 21.4 ºN. The system consists of 1.15 m² flat-plate collector as a heat source and a desalination unit. The unit is about 400 liter vertical cylindrical insulated tank. It includes storage, evaporator and condenser of hot salt-water that is fed from the collector. The heated water in the collector is raised naturally to the unit bottom at which it is used as storage. A high pressure pump is used to inject the water vertically up through 1-mm three nozzles inside the unit. The hot salt-water is atomized inside the unit where the produced vapor is condensed on the inner surfaces of the unit outer walls to outside. The system was experimentally tested under different weather conditions. It is obtained that the system can produce about 9 liter a day per quadratic meter of collector surface area. By that it can produce about 1.6 liters per kWh of solar energy. Moreover the water temperature has a great effect on the system performance although the scaling possibility is becoming significant. By that way the cost of a liter water production is relatively high and is obtained as 0.5 US$.

8. Estimation and diminution of CO₂ emissions by clean development mechanism option at power sector in Oman

Parmal Singh Solanki¹, Venkateswara Sarma Mallela¹, Chengke Zhou²

1 Caledonian (University) College of Engineering, Muscat, Oman.

2 Glasgow Caledonian University, Glasgow, Scotland, UK.

Abstract: Carbon dioxide (CO₂) is one of the major pollutants among greenhouse gases emitted by fossil fuel based power plants and responsible for environmental tribulations. Therefore diminution of carbon dioxide level by Clean Development Mechanism (CDM) is now serious concern worldwide. This paper evaluates the emission factors of national electric grid in Oman and proposes a wind energy based CDM project to diminish the CO₂ emissions. Estimations show that operating margin emission factors of national grid during five years lies in the range of 0.74 to 0.69 kg CO₂/kWh. Further, proposed CDM project revealed the annual baseline emissions reduction of 45552 ton CO₂ and able to earn the revenue of US$ 61.49 million by certify emission reductions in the first crediting period of project. Paper also critically analyse the opportunities for CDM project, its lucrative aspect, barrier and challenges.

9. Biodegradation of hexavalent chromium (Cr+6) in wastewater using Pseudomonas sp. and Bacillus sp. bacterial strains

Muhammad Qasim

Department of Chemical Engineering, American University of Sharjah, UAE.

Abstract: The recovery of toxic metal compounds is a deep concern in all industries. Hexavalent chromium is particularly worrying because of its toxic influence on human health. In this paper, biodegradation of hexavalent chromium (Cr⁺⁶) present in wastewater has been studied using two different bacterial strains; Pseudomonas sp. and Bacillus sp. A chemostat (with and without recycle of cells) with 10 L liquid culture volume was used to study the substrate and the biomass cell concentrations with time. Also, the degree of substrate conversion was studied by the varying the dilution rate as an independent parameter. The dilution rate (ratio of feed flow rate to the culture volume) was varied by varying the feed volumetric rate from 110-170 mL/h for inlet hexavalent chromium concentrations of 70 mg/dm³. The results show that a chemostat with recycle gives a better performance in terms of substrate conversion than a chemostat without a recycle. Moreover, the degree of substrate conversion decreases as the dilution rate is increased. Also, Bacillus sp. was found to give higher conversions compared to pseudomonas sp.

10. Modelling the drying kinetics of green peas in a solar dryer and under open sun

Sunil¹, Varun², Naveen Sharma³

1 Department of Mechanical Engineering, BRCM CET Bahal, Haryana–127028, India

2 Department of Mechanical Engineering, NIT Hamirpur, (H.P.)–177005, India

3 Department of Mechanical and Industrial Engineering, IITR, (U.K.)–247667, India

Abstract: The drying kinetics of green peas was investigated in an indirect solar dryer and under open sun. The entire drying process took place exclusively in falling rate period. The constant rate period was absent from the drying curves. The rehydration capacity was also determined for peas dried in solar dryer and under open sun. The rehydration capacity of solar dried peas was found higher than open sun dried peas. The drying data obtained from experiments were fitted to eight different mathematical models. The performance of these models was examined by comparing the coefficient of correlation (R²), sum of squares error (SSE), mean squared error (MSE) and root mean square error (RMSE) between observed and predicted values of moisture ratios. Among these models, the thin layer drying model developed by Page showed good agreement with the data obtained from experiments for bottom tray. The Midilli et al. model has shown better fit to the experimental data for top tray and open sun than other models.

11. Effect of dissolved organic matter derived from waste amendments on the mobility of inorganic arsenic (III) in the Egyptian alluvial soil

Mohamed Rashad¹, Faiz F. Assaad², Elsayed A. Shalaby³

1 Land and Water Technologies Department, Arid Lands Cultivation Research Institute, City of Scientific Research and Technological Applications (SRTA-City), New Borg El-Arab, 21934 Alexandria, Egypt.

2 Soils and Water Use Department, National Research Centre, Dokki, Cairo, Egypt.

3 Environmental Studies Department, Institute of Graduate Studies and Research, Alexandria University, Egypt.

Abstract: Dissolved organic matter (DOM) is one of the decisive factors affecting pollutants mobility in soils receiving waste amendments. The aim of this study was to investigate the effects of DOM1 derived from agricultural solid waste (ASW) and DOM2 derived from municipal solid waste (MSW) on the mobility of inorganic arsenic (As) in two alluvial soils from the Nile River Delta. In column experiments, addition of DOM solutions significantly increased As concentration in the effluents. There was no significant difference between the two soils, the obtained results from soil2 columns revealed that DOM2 has stronger capability than DOM1 to facilitate As mobility. The pH of the studied soils is alkaline (8.1) which promoted the dissociation as well as deprotonation of DOM and as a consequence, humic substances in DOM become negatively charged organic anions, leading to their substantial competition with As for the adsorption sites on both soil surfaces. The results emphasized that in alkaline soils there is a risk of groundwater pollution in the long run by arsenic either naturally found in soil or originated at high soil pH when dissolved organic carbon (DOC) released from various organic amendments ASW and/or MSW and leached through soil profile.

12. Investigations on the performance of a double pass, hybrid - type (PV/T) solar air heater

M. Srinivas, S. Jayaraj

Department of Mechanical Engineering, National Institute of Technology, Calicut-673601, India.

Abstract: A solar hybrid energy system having photovoltaic and thermal (PV/T) devices, which produces both thermal and electrical energies simultaneously is considered for analysis. A double pass hybrid solar air (PV/T) heater with slats is designed and fabricated to study its thermal and electrical performance. Air as a heat removing fluid is made to flow through upper and lower channels of the collector. The collector is designed in such a way that the absorber plate is partially covered by solar cells. The raise in temperature of the solar cell is expected to decrease its electrical performance. Thin metallic strips called slats are attached longitudinally at the bottom side of the absorber plate to improve the system performance by increasing the cooling rate of the absorber plate. Thermal and electrical performances of the whole system at varying cooling conditions are presented. An artificial neural network model is used for forecasting the system performance at any desired conditions. The proposed model can be successfully used for evaluating the effect of different operating parameters under different ambient conditions for predicting the overall performance of the system.

13. A two-equation k-omega turbulence model simulation to narrow trench on flat plate

Antar M.M. Abdala, Qun Zheng, Fifi N.M. Elwekeel

College of Power and Energy Engineering, Harbin Engineering University, Harbin 150001, China.

Abstract: In the present work, computational simulations was made using ANSYS CFX to predict the improvements in film cooling performance with narrow trench. Two turbulence models k-ω and k-ε were used. Blowing ratios in the range (0.5:1.8) were investigated. The results compared with experiments at different blowing ratios. Comparison of results with the k-ε model indicates that the k-ω model predicts circulations inside trench equally well at all blowing ratios. Over the surface, at low blowing ratios k-ω and k-ε models in case lateral spreading are under predicted but k-ω model catches experimental data well. At high blowing ratios, all turbulence models were under predicted. Simulations show that k-ω work well near the wall. Simulations show high jet penetration in cross flow for k-ω model than k-ε model. The CFD simulations were also used to gain a better understanding of the mechanisms responsible for improved film cooling performance.

14. An experimental investigation of exhaust emission from agricultural tractors

Rashid Gholami, Hekmat Rabbani, Ali Nejat Lorestani, Payam Javadikia, Farzad Jaliliantabar

Mechanics of Agricultural Machinery Department, Razi University of Kermanshah, Iran.

Abstract: Agricultural machinery is an important source of emission of air pollutant in rural locations. Emissions of a specific tractor engine mainly depend on engine speed. Various driving methods and use of implements with different work capacities can affect the engine load. This study deals with the effects of types of tractors and operation conditions on engine emission. In this study two types of agricultural tractors (MF285 and U650) and some tillage implements such as centrifugal type spreader, boom type sprayer and rotary tiller were employed. Some of the exhausted gases from both tractors in each condition were measured such as, hydrocarbon (HC), carbon monoxide (CO), carbon dioxide (CO₂), oxygen (O₂) and nitrogen oxide (NO). Engine oil temperature was measured at every step for both types of tractors. Difference between steady-state condition and operation conditions was evaluated. The results showed all exhaust gases that measured and engine oil temperature at every operation conditions are higher than steady-state condition. A general conclusion of the work was that, using various implements and employing different types of tractors effect on engine emissions. The results of variance analysis showed all exhausted gases had a significant relationship with types of implements used at 1%. Also, all exhausted gases except CO had a significant relationship with types of tractors. A further conclusion was that NO emission increased as engine oil temperature increased. The final conclusion was about the difference between MF285 and U650; using U650 at operation conditions is better than MF285 in terms of pollution.