Performance Analysis of Horizontal Axis Wind Turbine using Variable Blade Pitch Control Mechanism

This work investigates the performance of a horizontal axis wind turbine (HAWT) with variable blade pitch control mechanism. The control mechanism is a simple mechanical Watt governor design, which was developed to regulate the blade pitch angle of the HAWT depending on wind speed magnitude. The HAWT model with the control mechanism was tested for performance in a wind tunnel. Response of the control mechanism in terms of blade pitch angle, rotor speed and generator power output were analyzed based on regulated predetermined wind speeds. The result shows a gradual increase in rotor speed and a proportional increase in generator power output between cut-in wind speed of 2.5m/s and rated wind speed of 6 m/s. These parameters were kept constant at 100 RPM and 50 Watts as observed due to the steady response of the control mechanism. The steadiness lasted up to a cut-out wind speed of 9 m/s. The control mechanism subsequently shutdown the turbine at the cut-out wind speed to protect the turbine against wind speeds higher than 9 m/s. The performance test predicts that the variable blade pitch control mechanism was able to regulate and bring about the require control of HAWT model. The mechanism allows the turbine to only operate between 2.5 and 9 m/s at blade pitch angle between 82 and 90 degrees from the axis of wind flow and change in governor height between 0 to 8 mm

Combustion Modeling of a Fixed Bed Downdraft Biomass Gasifier Using Computational Fluid Dynamics Design

Thermochemical conversion of biomass in a gasifier for the production of syngas provides the enabling technology for efficient biomass resource utilization. Gasification is a complex process involving the interactions of numerous parameters, hence CFD tool is usually utilized to numerically optimize the design and operation of the gasifier reactor for improved performance. The gasification of multiple biomass usually requires a complex set of facilities for experimental set up in order to determine the optimum operating conditions for maximum gas yield. When this is not available, it can pose a bottle-neck to process development and optimization.  In this study, the GAMBIT and FLUENT were used to model and simulate the gasifier reactor with emphasis on the combustion and gasification (reduction) zones in order to maximize the thermal output of the combustor by an optimization of biomass fuel types. Model validation was achieved by showing a close agreement between numerical and experimental results within the same configuration, particularly to show the effect of temperature on the gasification of Fixed Bed Downdraft gasifier. The fraction of initial moisture content, air flow rate, temperature of the pyrolysis zone, and chemical composition of the biomass were the required input data for the model to predict the gasification temperature. Computations were carried out for rice husk, saw dust and corn cobs as gasifier fuels, whereby air was used as the oxidizing agent. The porosity and oxidizer velocity were varied between 0.1 – 0.5 and 5 – 15 m/s respectively. The predicted results compared with experimental data showed good agreement. The simulated temperature gradient also indicated that rich fuel combustion zone was greater for rice husk - corn cobs, an indication that improved gasification and pyrolysis were present

Enhanced Impingement Jet Cooling of Gas Turbine Wall Heat Transfer using CFD CHT Code: Influence of Wall Thermal Gradient with Fin and Dimple Obst

Gas turbine (GT) jet cooling using the regenerative or impingement jet backside cooling system is applicable to low NOx GT combustors and was investigated in the present work. The impingement heat transfer investigated is for the techniques where all the combustion air is used for wall cooling prior to passing through the flame stabiliser. Ten rows of impingement holes were modelled and are for four different types of obstacles: rectangular-pin in co- and cross-flows, circular pin-fin in cross-flow and dimple in direct-flow configurations, arranged in the impingement jet air flow direction. Conjugate heat transfer (CHT) and computational fluid dynamics (CFD) techniques were combined and applied in the computational analysis. Only the two obstacles in rectangular shape: co- and cross-flow configurations were validated against experimental results, as the other two has no experimental data available, but similar CFD methodology was applied. The impingement jet cooling enhancing obstacles were aligned transverse to the direction of the impingement jet cross-flow on the target surface and were equally spaced on the centre-line between each row of jet holes transverse to the cross-flow. Also, one heat transfer obstacle was used per impingement jet air flow in order to see the level of heat transfer augmentation of each one.  The CFD calculations were carried out for an air mass flux G of 1.08, 1.48 and 1.94 kg/sm2bar, hence for each obstacle grid geometry, three computations were conducted and therefore a total of twelve different computations for this investigation. These high mass flux used, are only applicable to the regenerative combustor wall cooling applications. Validation of the CFD predictions with the experimental data indicates good agreement for impingement gap flow pressure loss (ΔP/P) and the surface average heat transfer coefficient (HTC), h. Other predictions were also carried out and were for locally average X2 HTC, hole exit pressure loss, turbulence kinetic energy (TKE), flow-maldistribution, Nusselt number (Nu) and normalized temperature, T* or thermal gradient. It was concluded here that the rectangular-pin obstacles have the highest exit hole and impingement gap pressure loss, but with low heat transfer as a result of higher flow-maldistribution. Dimple obstacle has the lowest heat transfer, but is because most of the heat is taken away (or sucked in) by the dimple pot. The main effect of the obstacles was to increase the heat transfer to the impingement jet surface, but the dimple surface was predicted to have a very poor performance, with significantly reduced target wall heat transfer and thermal gradient

Modification, Development and Design Experimental Investigation of an Updraft Biomass Gasifier Stove with Sawdust as Fuel

This work presents the development of an updraft biomass gasifier stove which has been shown to apply the use of biomass fuels for the production of combustible gases. The updraft biomass gasifier stove designed was modified in order to ease the disposal of ashes, which is subsequently constructed using locally available material resources. The gasifier applies the principles of updraft producer gas flows, whereby the stove utilizes rice husk as it useable fuel. The modified gasifier stove was experimentally tested using rice husk as fuel, which was selected based on its availability as is usually classified as a wasteful product: hence the need for its utilization in order to combat environmental effects. Tests were conducted based on loading capacities of the rice husks: 5, 10, 15 and 18 kg respectively and were evaluated accordingly. The gasifier stove performance depends on these loading capacities and the highest was for the 18 kg value, as it gave the highest time of stable flame production of 150.0 min. Furthermore, the 5 kg recorded the least time of stable flame production, implying that the higher the loading capacity the higher the time of stable flame production

NOx Emission in Iron and Steel Production: A Review of Control Measures for Safe and Eco-Friendly Environment

Iron and steel manufacturing involved preparation of raw materials through processes such as sintering, pelletizing and coke making. During these processes, pollutants such as Sulphur (iv) oxides (SO2) Carbon II oxides (CO), Nitrogen oxides (NOX), Volatile organic compounds (VOC) and Particulate matter (PM) etc. are emitted. The present work is aimed at describing some mitigation technologies of controlling emissions in iron and steel production. The processes involved in the production of iron and steel using Blast Furnace (BF) and Basic Oxygen Furnace (BOF) has been described. The mitigation technologies of controlling emissions were analyzed and discussed with environmental impacts based on the economical and technical factors. In this work, the data presented is based on existing reviews. The combination of low NOX burner (LNB) and Selective catalytic reduction (SCR) is capable of reducing emission for up to 90% and above. Emissions of other pollutants into the atmosphere as a result of ammonia slip, formation of acids and other gases are harmful to the environment and causes damage to the SCR systems. Installation and operation cost are the major impacts of the SCR technology in the process of iron and steel production

Investigating the Suitability of Selected Structural Material for the Blade of an Horizontal Axis Wind Turbine

This work presents a comparative analysis on the structural material of a blade used for the horizontal axis wind turbine, which was based on previously developed blade geometry. Two blades of the same parameter: 0.25 m chord lengths at 8 o angle of attack, but different structural materials were compared. This to identify an optimized blade structural material in terms of locally available, strength, cost effectiveness and environmental safety that will be suitable for Maiduguri’s weather condition. The ultimate flap - and edge - wise deflections and load conditions under minimum blade mass (6.8 kg) are determined. These investigations were carried out in two stages: predictions of the aerodynamic analysis using Computational Fluid Dynamics (CFD) code (ANSYS Fluent CFD commercial tool) with Blade Element Momentum (BEM) theory, Finite Element Method (FEM) coded in MATLAB software for the structural analysis and experimental evaluations for the purpose of validation of predicted data obtained. These were employed in order to provide sufficient conclusions of the aerodynamic and structural data that will provide better performance of the blade. These data are expected to handle the design variables meant for the optimization of the blade based on the selected structural material. The blades of each material were divided into 15 elements along the blade span with each element assumed to have uniform cross sectional area. Pressure distribution within the computational domain and around the airfoil section in two dimensions (2D) was predicted. The validated results of the load to deflection showed good agreement and that each of the blade material were based on the structural strength. From the result obtained, it shows that the aluminium blade structure material has good reliability with better performance. These were significant between the maximum strength and the minimum blade mass for aerodynamic loadings, hence better blade structure than that developed from beach wood and most suitable under an ultimate wind speed of 30 m/s

Conjugate Heat Transfer Computational Fluid Dynamic Predictions of Impingement Heat Transfer: The Influence of Hole Pitch to Diameter Ratio X/D at Constant Impingement Gap Z

Conjugate heat transfer (CHT) computational fluid dynamic (CFD) predictions were carried out for a 10 × 10 square array of impingement holes, for a range of pitch to diameter ratio X/D from 1.9 to 11.0 at a constant impingement gap Z of 10 mm and pitch X of 15.24 mm. The variation of X/D changes the impingement wall pressure loss for the same coolant mass flow rate and also changes the interaction with the impingement gap cross-flow. The experimental technique to determine the surface averaged heat transfer used the lumped capacity method with Nimonic-75 metal walls with imbedded thermocouples and a step change in the hot wall cooling to determine the heat transfer coefficient h from the transient cooling of the metal wall. The test wall was electrically heated to about 80  °C and then transiently cooled by the impingement flow and the lumped capacitance method was used to measure the locally surface average heat transfer coefficient. The predictions and measurements were carried out at an impingement jet mass flux of 1.93 kg/s m2 bar, which is a typical coolant flow rate for regenerative impingement cooling of low NOx gas turbine combustor walls. The computations were conducted for a fixed hot side temperature of 353 K that was imposed at the hot face of the target wall. The wall temperatures as a function of distance along the gap were computed together with the impingement gap aerodynamics. Surface average heat transfer coefficient h and pressure loss predictions were in good agreement with the experimental measurements. However, there was less good agreement for the axial variation of the local surface averaged h for lower values of X/D. The surface averaged heat transfer to the impingement jet wall was also computed and shown to be roughly 70% of target wall impingement heat transfer