Browsing by Author "Bekker, G. M."

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    Numerical investigation of pressure recovery in an induced draught air-cooled condenser for CSP application.
    (Stellenbosch : Stellenbosch University, 2021-12) Bekker, G. M.; Meyer, C. J.; Van der Spuy, S. J.; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: This study aims to enhance the performance of an induced draught air-cooled condenser (ACC) by increasing the ACC’s air mass flow rate and heat rejection rate. These improvements are achieved through pressure recovery, which is the conversion of the dynamic pressure at the fan outlets into static pressure. Pressure recovery increases the effective static pressure rise of the axial flow fans in the ACC, resulting in a higher operating airflow rate. Consequently, higher heat removal rates are possible. Stator blade rows and diffusers are capable of pressure recovery. Combinations hereof are tested for the axial flow fan featured in the ACC (i.e. the M-fan) through numerical simulation in OpenFOAM. Diffuser lengths of ldif = dF, 0.4dF and 0.2dF are considered, where dF = 7.315 m is the fan diameter. The most promising discharge configurations are selected for a five-by-four induced draught ACC. The ACC is then analysed with and without these appendages under windless and windy conditions. Wind directed along the shorter and longer axes of the ACC is considered at wind speeds of 3, 6 and 9 m/s. Amongst the diffusers of length ldif = dF, an annular diffuser with both walls diverging at 22° from the axial direction recovers the most pressure for the M-fan over a range of flow rates. For the ldif = 0.4dF length, a conical diffuser with an included angle of 2θ = 32° recovers the most pressure. And a conical diffuser with 2θ = 40° yields the highest pressure recoveries for the ldif = 0.2dF length. However, the ldif = dF annular diffuser is deemed impractical for ACC application due to its long length and wide wall angles. Under windless conditions, both conical diffusers increase the mass flow rate through the five-by-four ACC by ∼2.5 %. As a result, the heat transfer rate improves by 2.0 %. The power consumption of the ACC fans also drops by 5.2–5.5 %, increasing the heat-to-power ratio by 12.4–13.1 W/W. In a light breeze of 3 m/s, the increase in mass flow rate due to the diffusers is 1.7–2.0 %; in a moderate breeze of 6 m/s, the increase is 0.9–1.3 %; and in a fresh breeze of 9 m/s, it is 1.0–1.6 %. There is more variation in the thermal performance results of the ACCs featuring the two different diffusers: The shorter diffuser does not improve the heat transfer rate of the ACC as much as the longer diffuser does under windy conditions. At 6 m/s, the ACC with longer diffusers rejects 1.6–2.2 % more heat than the ACC with shorter diffusers. At 9 m/s, the former rejects ∼2.5 % more heat than the latter. This research demonstrates that discharge diffusers can enhance the performance of an induced draught ACC. The diffusers’ pressure recovery increases the mass flow rate through the ACC, aiding its heat rejection capability. From a performance perspective, the ldif = 0.4dF diffuser is recommended. However, practical considerations might render the shorter ldif = 0.2dF diffuser more suitable.