No abstract

Large-scale cooling system fans often operate under distorted inlet air flow conditions due to the presence of other fans and the prevalent wind conditions. Strain gauge measurements have been used to determine the blade loading as a result of the unsteady aerodynamic forces. However, these measurements are of the blade’s response to the aerodynamic forces and include the deformation as a result of the first natural frequency being excited. When considering the dominant first natural frequency and bending mode of the fan blade, one can approximate the fan blade as a cantilever beam that acts as a single degree-of-freedom system. The response of a single degree-of-freedom system can be calculated analytically for any excitation if the system’s properties are known. The current investigation focuses on using these equations to create an algorithm that can be applied to the measured response of a fan blade to then extract the aerodynamic forces exciting it. This is performed by using a simple non-linear, least-squares optimization algorithm to fit a complex Fourier series to the response and using the coefficients of each harmonic term to determine the Fourier series representing the excitation function. The algorithm was first tested by applying it to the response of a finite element cantilever beam representing a simplified model of the fan blade. Good results were obtained for a variety of excitation forces and as such the algorithm was then applied to the measured response of a full-scale fan blade. The full-scale blade was excited with a shaker where the forcing function could be accurately controlled. Once validated, the algorithm was applied to a set of strain gauge measurements that were recorded at a full-scale fan while in operation. The reconstructed aerodynamic loading showed increased forces when the blade passed beneath the fan bridge as well as when it approached the windward side of the casing.

South Africa’s coal-fired power stations use super heated steam to drive generator turbines. In arid regions, air-cooled condensers (ACCs) are used to condense the process steam. These ACCs consists of an array of over 200 axial flow fans, each driven by a motor via a reduction gearbox. Distorted fan inlet air flow conditions cause transient blade loading, which results in variations in output shaft bending and torque. A measurement project was conducted where the input and output shaft of such a gearbox were instrumented with strain gauges and wireless bridge amplifiers. Gearbox shaft speed and vibration were also measured. Torsional and bending strains were measured for a variety of operational conditions, where correlations were seen between gearbox loading and wind conditions. The input side experienced no unexpected loads from the motor or changing wind conditions, whereas output shaft loading was influenced by the latter. Digital filters were applied to identify specific bending components, such as the influence of fan hub misalignment and dynamic blade loading. Reverse loading of the gearbox was measured during the fan stop period, and vibration analysis revealed torsional and gearbox vibrations. This investigation documented reliable full scale ACC gearbox loads.

No abstract

This study attempts to show the effectiveness of using coconut fibre as a loss circulation material in drilling operation. The research incorporated a practical approach. Laboratory experiments was conducted to design drilling muds with the desired loss circulation materials. Their rheological properties and permeability plugging ability was ascertained and compared to determine the most effective loss circulation material blend. To formulate the loss circulation materials, the coconut fibre was processed and particle sizing distribution was conducted on the processed coconut fibre. The coconut fibre was separated into coarse sizes (3350, 2360, 1700 and 1180) and medium be sizes (850 and 425). The distinction between the formulated muds is the loss circulation material combination in them. The three drilling muds had medium-coarse coconut fibre ratio of 60:40, 40:60 and 30:70. The rheological properties of each drilling mud was determined to show suitability of use as a drilling fluid. Experimental results showed similar rheological properties for each mud and they are all suitable for use. The PPT test and ES test were conducted on the mud samples as well. These experiments were conducted at a desired temperature of 200°C and filter press pressure of 1500psi. The thickness of the produced mud cake was measured. By comparing the amount of unrecovered fluid (fluid loss), the least fluid loss was observed in the mud with medium-coarse coconut fiber combination of 60:40