Computational Fluid Dynamics Based Optimal Design of Vertical Axis Marine Current Turbines
Abstract Marine turbines are being increasingly used to harness kinetic energy of water and convert it into other useful forms of energy. Widespread commercial acceptability of these machines depends upon their efficiency. This largely depends upon the geometric features of the marine turbines such as number of blades, shape of blades etc. Researchers have been using experimental facilities to optimise these machines for maximum power generation. With the advent of advanced computational techniques, it has now become possible to numerically simulate the flow of water in the vicinity of marine turbines and monitor their performance output. In this work Computational Fluid Dynamics (CFD) based techniques have been used to analyse the effects of number of blades within the stator and rotor, of an in-house built Vertical Axis Marine Current Turbine (VAMCT), on the performance output of the turbine. Furthermore, an effort has been put forward towards better understanding of the flow structure in the vicinity of the blades during transient interaction between rotor and stator blades. This study provides vital information with regards to the flow sensors’ requirements and placements in order to monitor various blade configurations of a VAMCT in real world. The results of this study show that the torque output from a VAMCT is a strong function of blade configurations and there is a significant degradation in the performance output of marine turbines as the inequality between the number of rotor and stator blades increases. Hence, CFD has the potential to optimise the design of marine turbines and can be used as a potential modelling tool in the near future for on-line health monitoring of such systems.
Performance investigation of self-adjusting blades turbine through experimental study
Abstract In the quest for renewable energy sources and sustainable development, hydrokinetic energy available in marine currents, river currents, water flows and man-made canals should be harnessed. This is particularly true for rural and remote areas, which have access to water but often have poor electricity. The vertical axis current turbine, which is a key hydrokinetic technology, has been greatly improved over the last few years. It has numerous advantages, including independency of flow direction, design simplicity, quiet operation, no required yaw mechanism and low cost. The Savonius hydrokinetic turbine is one of the most important drag-type configurations of a vertical axis current turbine. However, it suffers from negative torque, negative drag force on the returning blades, low efficiency and difficulty interfacing with a generator. This paper proposes a novel drag-based vertical axis current turbine using arms and self-adjusting blades. This novel design was developed based on the framework of a Savonius hydrokinetic turbine. In an effort to decrease the hydrodynamic resistance of the returning blades and increase the total output torque of the turbine, this study aims to investigate the performance characteristics of a novel vertical axis current turbine (hereinafter referred to as “self-adjusting blade turbine”). Experimental tests were conducted in the Universiti Teknologi Malaysia (UTM) at low speed currents to assess the performance characteristics of three configurations of a fixed blade turbine and a self-adjusting blade turbine. The force acting on one blade of the self-adjusting turbine was analysed in detail. The results showed that the arm length and blade angle affected the performance of turbine, and that there was 30.7% increase in performance for the self-adjusting blade turbine compared to the fixed blade turbine.
Production of xylanase by Aspergillus awamori on complex medium in stirred tank and airlift tower loop reactors
Abstract Aspergillus awamori was cultivated on complex medium containing wheat bran as sole carbon source in the precultures as well as in the main cultures in stirred tank and airlift tower loop reactors. The decomposition of the wheat bran particles by α -amylase and xylanase produced by the fungus was investigated by monitoring the enzyme activities, the CO 2 production rate, the concentrations of reducing sugars, glucose, xylose, phosphate and ammonium as well as by applying transmission electron microscopy. By applying synthetic medium in the preculture, the time lag was longer, the growth faster, the xylanase activity higher in the main culture, than by using wheat bran in the preculture. With increasing the stirrer speed the intimate contact between the pellets and the wheat bran was reduced, which caused a decrease of the growth and the xylanase production. By applying ground wheat bran, filamentous mycelium was formed, the growth and the substrate uptake rates increased, but the xylanase production decreased due to the less intimate contact between the fungus and the wheat bran. In the airlift tower loop reactor filamentous mycelium was formed due to the low specific power input. In spite of the high medium viscosity, high xylanase productivity was obtained. With ground wheat bran the particles were completely covered by filamentous mycelium, medium viscosity strongly increased and as consequence the growth and xylanase production decreased.