Masters Degrees (Mechanical and Mechatronic Engineering)

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Browsing Masters Degrees (Mechanical and Mechatronic Engineering) by Author "Afeltra, MF"

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    The development of a recuperator for a solar hybrid micro gas turbine system.
    (Stellenbosch : Stellenbosch University, 2023-03) Afeltra, MF; Van der Spuy, SJ; Hoffmann, JE; Stellenbosch University. Faculty of Engineering. Dept. of Mechanical and Mechatronic Engineering.
    ENGLISH ABSTRACT: Concentrated solar power (CSP) provides a dispatchable form of electricity due to its energy storage capabilities and adds flexibility to the power network. CSP coupled with a micro gas turbine (MGT), creates a suitable technology for supplying low-carbon electricity to off-grid regions. The solar hybrid micro gas turbine (SHMGT) has the capability of replacing diesel generators, thus reducing operating costs and fuel consumption. For these reasons, Stellenbosch University is involved in the research of SHMGTs. The thermal efficiency of the current MGT system is relatively low and a method of improving this performance metric is through the implementation of a recuperator. Using a recuperator will reduce the combustion chamber’s heating requirement, reducing the fuel required to maintain combustion. Due to its simplicity and cost-effectiveness, a clamped-plate style recuperator design was selected. A significant challenge in the design of the recuperator was the balance of the thermal-hydraulic design constraints, namely the heat transfer effectiveness and the allowable pressure drop. The design was adapted to fall within the project budget by sacrificing effectiveness for pressure drop. With leakage in the system after two successive rounds of sealing the recuperator with two different high-temperature sealants, the design was concluded to be leak inherent. A different method of sealing was proposed with the use of a high-temperature gasket. Experimentation of the recuperator revealed that the MGT system could not self-sustain. This was partly due to an unexpectedly significant pressure drop over the recuperator. This was attributed to flow maldistribution within the headers, which was indicated by the thermal degradation on the recuperator when operated above the limit of 650 ◦C. An improved header design was therefore proposed. The switch-over method used to couple the MGT system was also found to be non-ideal for recuperated operation. It was found that the SHMGT combustion chamber was not suited to high temperature inlet flows due to the accompanying significant induced pressure drop. The recuperator’s effectiveness was obtained in a decoupled state of operation and was verified analytically to be in the range of 0.74 to 0.77. A validated Flownex model of the MGT system was produced, in which the recuperator was included. A case study was performed in Flownex, where the power turbine and accompanying compressor were replaced with the same turbocharger as the gas generator. It was found that the system’s power output and thermal efficiency were doubled with this replacement.