Applied Mechanics and Materials Vols. 110-116

Abstract: The overall performance of any solar energy project largely depends upon the available solar radiations, inclination and orientation of solar collectors. Presented in this paper is the analytical study on optimum tilt angles and lifetime differential savings for a distributed 200 kW grid connected mono-crystalline solar PV system operating at Khatkar Kalan, Punjab, India. The optimum tilt angles for monthly, seasonally and yearly basis is carried out by searching the values of tilt angle for which electric power output is maximum for a particular day or a specific period using energy conversion model. The results reveal that the yearly optimum tilt angle for the SPV plant at Khatkar Kalan is 36° which is 4.58° higher than the latitude angle. The power output from the array increases with increase in angle of tilt for winter months whereas the trend is reverse for the summer months. In winter months the maximum power output is achieved for the array surface with a tilt of angle 13° - 23° higher than the local latitude while for summer months the maximum power output is achieved at 16° lower than the latitude angle. The optimum tilt angles maximizing monthly power output for south facing surface shows that the monthly optimum tilt angle varies from 15° to 55°. Also the parametric analysis for some influential factors such as latitude of location and reflectivity of ground surface is explored.

Abstract: The presence of hand could alter the energy absorbed in the human head. Hence, a study of the interaction between mobile device antennas and human head in the presence of metallic hand worn jewellery on human hand with different holding ways is investigated. A finite-difference time domain (FDTD) method has been performed by considering an internal PIFA antenna as the radiating source mounted at the top of a commercial clamshell phone positioned nearer the ear. With the introduction of hand-worn jewellery in variation parameters, there were perceptible effects on SAR variation in the human head. SAR distribution in the SAM head was found decreases due to different hand positions. Therefore, the head and in particular the hand may further impairment radiation performance of a mobile device.

Abstract: Flue gas emissions and particle size distribution were investigated during combustion experiments of wood, forest residue and mixtures of these two. The combustion experiments were carried out in a grate fired multi-fuel reactor with and without air staging at stable operation conditions and constant temperature of 850 °C. The overall excess air ratio was held at 1.6, and the primary excess air ratio was 0.8 during air staged experiments. NOx emissions are reduced by air staging. Fly ash particle concentration of forest residues in the flue gas is lower than wood. Aerosols number increased in the staged experiments for fuel blends.

Abstract: Multiple processor cores are built within a chip by advanced VLSI technology. With the decreasing prices, multi-core processors are widely deployed in both server and desktop systems. The workload of multi-threaded applications could be separated to different cores by multiple threads, such that application threads can run concurrently to maximize overall execution speed of the applications. Moreover, for the green trend of computing nowadays, most of modern multi-core processors have a functionality of dynamic frequency turning. The power-level tuning techniques are based on Dynamic Voltage and Frequency Scaling (DVFS). In order to evaluate the performance of various power-saving approaches, an appropriate technique to measure the power consumption of multi-core processors is important. However, most of approaches estimate CPU power consumption only from CMOS power consumption data and CPU frequency. These approaches only estimate the dynamic power consumption of multi-core processors, the static power consumption is not be included. In this study, a hardware approach for the power consumption measurement of multi-core processors is proposed. Thus the power consumption of a CPU could be measured precisely, and the performance of CPU power-saving approaches can be evaluated well.

Abstract: Combined cycle power generation plants are becoming popular to generate power at higher efficiencies with reduced greenhouse gas emissions. In the present work the effect of steam injection in the gas turbine combustion chamber on the performance of a natural gas fired combined cycle power plant is investigated. For a particular combined cycle power generation configuration, the effect of steam injection on the performance is conducted based on first law of thermodynamics. The steam injection influences the work output and efficiencies of gas turbine, steam turbine and combined cycle power generation unit.

Abstract: The aeroacoustic field generated by incompressible airflow over a two-dimensional open cavity is investigated. The main objective of this study is to determine the role of nonlinearity on this phenomenon. To this end the cavity aeroacoustics is investigated with both linearised and nonlinear approaches. Both free-air and confined cavity geometries are investigated and it is shown that nonlinearity does not affect the aeroacoustic field much. The solutions are verified for grid and computational domain independency. It is concluded from this study that nonlinear aeroacoustic phenomena are very weak in external incompressible flows and low-cost linearised formulations can easily be applied in such cases.

Abstract: Unsteady Reynolds-Averaged Navier-Stokes computations are presented for the flow over a pure plunging aerofoil and a plunging wing. The implicit RANS solver used for obtaining time-accurate solution is based on implicit finite volume nodal point spatial discretization scheme with dual time stepping. Baldwin and Lomax turbulence model has been used for the turbulence closure. The results are obtained in the form of aerodynamic coefficients, thrust coefficient and propulsion efficiency for two different cases over the aerofoil and wing and are compared with available literature.

Abstract: There are hundreds models of reticulated structures including the squared reticulated cylindrical shells. It is considered as comprising of a number of circumferential and longitudinal rods. Analytical governing equation for natural frequencies has been derived for this type of structures and to verify the validity of solutions, Finite Element Method (FEM) is used. The comparison of results demonstrate close agreement between analytical and FE solutions. Also a comparison is preformed between a reticulated and equivalent solid hollow cylinder shell. The equivalent solid hollow cylinder has equal weight, length and outer diameter with the squared reticulated cylindrical shell. This comparison shows that the natural frequencies of squared reticulated shells are lower than the hollow solid cylinders.

Abstract: Flow-induced corrosion is one of the most prevalent tube damage mechanisms in steam generators of power plants. In this study, tube failure of a steam generator in Fars Combined Cycle Power Plant is evaluated. In addition to analysis of the measured tube thicknesses and the failure statistics data, computational fluid dynamic (CFD) methods are used to simulate flow distribution inside and outside of the tubes in one header of the low pressure circuit of the plant steam generator. The results show that regarding the created two-phase flow pattern inside the tubes, the droplet impingement erosion is the main source of tube failures in the bending areas where the extrados surface of the tubes are partially prone to the droplets. The results are useful for modifying the design of the steam generator from different viewpoints such as, optimal design for appropriate configuration of downcomer, header and footer and tube bending. Also, selecting suitable material for the steam generator tubes and implementation of protective coating in risky areas would benefit from the present results.

Abstract: 2D Large Eddy Simulation turbulence model coupled with Ffowcs-Williams-Hawkins model and Boundary Element Method is used to perform a study of the effect of the Reynolds number on the broadband noise emitted due to the incompressible fluid structure interaction. The method is then used to calculate the broadband noise emitted by the aerodynamic flow over different shape bodies having same cross-sectional area with the intent to know the most suitable cross sectional geometry of the fuel manifolds in the aircraft engine afterburner in terms of minimum noise emission. The results obtained suggests that a 5dB benefit in sound emission could be obtained by the halving the diameter of the circular cross-section used for the fuel manifolds, to make them elliptical keeping cross sectional area constant.