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DeclarationBy submitting this dissertation electronically, I declare that the entirety of the work contained therein is my own, original work, that I am the sole author thereof (save to the extent explicitly otherwise stated), that reproduction and publication thereof by Stellenbosch University will not infringe any third party rights and that I have not previously in its entirety or in part submitted it for obtaining any qualification.This dissertation includes four original papers published in peer-reviewed journals, peer-reviewed conference proceedings or books and one unpublished publication. The development and writing of the papers (published and unpublished) were the principle responsibility of myself and, for each of the cases where this is not the case, a declaration is included in the dissertation indicating the nature and extent of the contribution of co-authors. Abstract Performance Characteristics of the Spiky CentralReceiver Air Pre-heater (SCRAP)A combined cycle concentrating solar power (CSP) plant provides significant potential to achieve an efficiency increase and an electricity cost reduction compared to current single-cycle plants. A combined cycle CSP system requires a receiver technology capable of effectively transferring heat from concentrated solar irradiation to a pressurized air stream in a gas turbine. The novel spiky central receiver air pre-heater (SCRAP) technology is proposed to provide such a receiver and overcome barriers experienced by developments to date. The SCRAP receiver is a novel metallic receiver technology aimed at preheating an air stream to about 800 • C, either prior to a combustion chamber or alternatively a cascaded secondary non-metallic receiver system, capable of achieving elevated temperatures. The SCRAP receiver is distinguished in shape and functioning from receiver concepts presented to date for the application in Brayton or combined cycles.The receiver is predicted to perform at solar-thermal efficiencies exceeding 80 %. The geometric design of the receiver achieves a relatively low radiative heat loss, predicted at about 4 % -5 %, whereas the relatively large surface results in vulnerability to convective heat losses. The pressure drop was found to be dependent on the geometries selected but relatively low, compared to existing alternative receiver designs, with system pressure drops below 40 mbar achievable.A ray-tracing analysis showed that the flux impinging on the absorber assemblies is in its spatial distribution dependent on the solar field, more specific, the heliostat size and design. A thermodynamic model was developed to investigate the performance characteristics of the SCRAP receiver. The iii Stellenbosch University https://scholar.sun.ac.za iv ABSTRACT developed thermodynamic computer model was verified against an experimental test setup designed and built at the heat transfer laboratory at Stellenbosch University. Tests with steam heating at nominally 100 • C show good agreement between the experimental results and the modeled predictions, at...

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A conventional impinging jet is effective at transferring a large heat flux. However a significant pressure loss is also experienced by the free jet of a jet impingement heat transfer device due to rapid expansion because it does not incorporate effective pressure recovery. A novel high-flux impingement heat transfer device, called the Tadpole, is developed to improve the heat transfer and pressure loss (performance) characteristics of the conventional impingement domain by incorporating pressure recovery with a diffuser. The Tadpole is scrutinized through an experimental comparison with a conventional jet impinging on the inner wall of a hemisphere under the turbulent flow regime. The Tadpole demonstrates promising capability by exceeding the performance characteristics of the impinging jet by up to 7.3% for the heat transfer coefficient while reducing the pressure loss by 13%. Multiple dimensional degrees of freedom in the Tadpole's flow domain can be manipulated for an enhanced heat transfer coefficient, a reduced total pressure loss or a favourable combination of both metrics. A Computational Fluid Dynamics (CFD) model is developed, the Four-Equation Transition SST turbulence model demonstrates satisfactory experimental validation with a deviation of < 5% for the heat transfer coefficient and < 23% for the total pressure loss. The Tadpole is a promising heat transfer device for high-flux applications and is recommended for further work incorporating design improvements and multidimensional optimization.