Department of Mechanical and Mechatronic Engineering

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Browsing Department of Mechanical and Mechatronic Engineering by Subject "Actuators -- Disc model"

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    Performance comparison of forced draft and induced draft air-cooled condensers under adverse Crosswind Conditions.
    (Stellenbosch : Stellenbosch University, 2021-12) Louw, D. L.; Meyer, C. J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: n this study numerical models of two 8×8 fan-unit Air-Cooled Condensers (ACCs) were developed using Computational Fluid Dynamics (CFD). The two ACCs investigated were respectively a Forced Draft ACC with A-frame fan- units and an Induced Draft ACC with V-frame fan-units. The performance of the two ACCs was investigated under various adverse crosswind conditions. The numerical models were implemented using the open-source OpenFOAM CFD code and solved in parallel using a computer cluster. The ACCs’ axial flow fans were modeled using an Actuator Disk Model (ADM). The ACCs investigated in this study were configured using two dif- ferent axial flow fans: an eight bladed fan identified as the L-fan, and a nine bladed fan identfied as the N-fan. Comparatively the L-fan has a steeper pressure characteristic and a higher power consumption than the N-fan and was used exclusively at the front and back periphery of the ACCs. The ADM was specifically implemented for the two fans and succesfully validated against experimental results obtained from a BS 848 Type A Facility. A direct comparison of the two ACCs shows that under normal operating conditions the Induced Draft ACC outperforms the Forced Draft ACC both with regards to its volumetric effectiveness and heat transfer effectiveness. The two ACC were then subjected to crosswinds of 3, 6 and 9 m/s from two different directions: primary crosswinds where the L-fan is used at the leading edge, and secondary crosswinds where the N-fan is used at the leading edge. The Forced Draft ACC showed a greater reduction in axial flow fan per- formance under crosswind conditions than the Induced Draft ACC. Under primary crosswinds the L-fan equipped leading edge fan-units were able to mitigate the reduced fan performance better than the N-fan equiped leading edge fan-units under secondary crosswinds. The Induced Draft ACC showed higher heat exchanger inlet air temper- atures under crosswind conditions than the Forced Draft ACC. The Induced Draft ACC’s perpendicular orientation of its V-frame fan-units to secondary crosswinds allowed for greater increases in the inlet air temperatures at its downwind fan-units’ heat exchangers. The Induced Draft ACC’s heat transfer rate to fan power consumption ratio under primary crosswind conditions was higher than that of the Forced Draft ACC under either primary or secondary crosswinds. In contrast the Induced Draft ACC’s heat-to-power ratio under secondary crosswind conditions was worse than that of the Forced Draft ACC under either primary or secondary crosswinds. The mean heat-to-power ratio of the Induced Draft ACC under normal operating conditions was higher than that of the Forced Draft ACC with a ratio of 120.6 W/W compared to 99.4 W/W. However, the mean heat-to- power ratio of the Induced Draft ACC decreased more by 23.3% and 35.6% under 9 m/s primary and secondary crosswinds, while the heat-to-power ratios of the Forced Draft ACC decreased less by 10.8% and 15.4% under the same crosswinds.