Browsing by Author "Engelbrecht, Ruan Aldrich"
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- ItemNumerical Investigation of fan performance in a forced-draft air-cooled heat exchanger.(Stellenbosch : Stellenbosch University, 2018-12) Engelbrecht, Ruan Aldrich; Meyer, Chris J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.ENGLISH ABSTRACT: This study aims to develop an accurate and reliable numerical model of an Air-Cooled Condenser (ACC) using Computational Fluid Dynamics (CFD). Simplified methods for modelling the axial ow fan and heat exchanger are used to limit the complexity of the computations. The actuator disk and extended actuator disk model is presented and validated using two fans with different physical characteristics. The A-fan is an axial flow fan commonly used in industrial cooling applications and the B2a-fan is an axial ow fan developed at Stellenbosch University. The heat exchanger model is based on the A-frame heat exchanger typically used in ACCs. Validation is performed with respect to heat exchanger mechanical losses and heat transfer. The operating point of each combined fan and heat exchanger unit is determined analytically and numerically under ideal operating conditions. The results are validated by comparing the kinetic energy recovery coeficient to an experimental design from literature. A numerical recovery coeficient of 0.527 was measured compared to 0.553 measured experimentally. The axial ow fan, heat exchanger and ACC model are successfully validated. A 30 fan ACC bank in a 6x5 configuration is analysed with regard to performance under cross-wind conditions using three different fan configurations. The ACC is subjected to four different wind speeds along five directions. Comparisons are drawn between the volumetric, thermal and overall performance using the heat-to-power ratio. The so-called A-fan ACC, B2a-fan ACC and Combined ACC are considered. Major findings indicate that the performance of an ACC decreases with increasing cross-wind speed. Superior overall performance is measured for the B2a-fan ACC resulting from a 19 % increase in performance to the A-fans on the upstream periphery. Higher thermal performance is also measured as well as 6-10 % lower power consumption than the A-fan ACC and Combined ACC. The A-fan ACC exhibits the highest sensitivity to increasing cross-wind speeds along with the highest power consumption. Heat-to-power performance is measured 9-10 % lower than the B2a-fan ACC and 7 % lower than the Combined ACC as a result. A comparative study between the 6x5 and 3x10 ACC layout is also presented. Wind directions leads to volumetric, thermal and overall performance differences up to 23 % for the A-fan ACC in 3x10 layout for a constant wind speed. The 6x5 layout measured differences up to 5 %. The 3x10 layout is therefore considered to exhibit a higher sensitivity to wind direction. This is attributed to the asymmetrical nature of the configuration. The A-fan ACC in 3x10 layout consumes 9.70 % more power compared to the 6x5 layout. The B2a-fan ACC consumes 6.95 % more power with similar power consumption measured for the Combined ACC. An on-site measurement methodology for determining the fan volumetric ow rate using the measured fan power consumption and resultant blade loading along with the characteristic curves to determine the flow rate is presented. This is discussed, analysed and applied to the 30 fan ACC under cross-wind conditions. Differences in predicted volumetric ow rate up to 6.45 %, measured to the numerical results, are noted for fans not subjected to distorted inflow. Predictions for upstream periphery fans shows poor correlation with differences up to 22.81 % measured. The results do indicate that the use of the blade loading for fans subject to distorted in flow gives more accurate results for flow rate predictions compared to the power consumption.