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A project report submitted to the Faculty of Engineering, University of the Witwatersrand, Johannesburg, in partial fulfilment of the requirements for the degree of Master of Science in Engineering. / This project is a part of a research programme by Eskom to develop power station rotary regenerative air heaters that are more compatible with South African coal properties. Large costs are involved in the replacement of air heater surfaces due to the erosion caused by the abrasive South African coal ash. The performance of an air heater L governed by numerous parameters, some of which (such as erosion) are unpredictable. A laborar: 'v testing facility which can produce a real-situation environment for air heater research is not only impractical but also expensive. Hence it has been decided to generate a computer simulation model of a power station air heater. The various alternatives for the improvement of existing air heaters will be assessed using this computer model. Extensive information regarding the influence of various parameters such as thermal performance, erosion, flow resistance, corrosion, etc. is necessary as input to the simulation model. Various test facilities have been commissioned to obtain this information. This project is an experimental study on the thermal performance of the regenerative air heater heating elements using a thermal test facility situated at the Eskom Technology Research and Investigations centre in Johannesburg. The facility uses the single-blow transient technique to establish the heat transfer coefficients of various air heater heating elements. Ten different types of heating elements were tested and the results were analysed .. These test results and recommendations give useful indications for power station application even before the final simulation model is available. The primary objective of this project was to find the heat transfer coefficient and also to make correlations between Colburn j factor, Fanning friction factor and Reynolds number. Packs were tested for various air tlow rates, ranging from Reynolds number 1200 to 6000. The test results were analysed and the correlations were made. A detailed uncertainty analysis was done and found that the results are showing less than 7 % error which is acceptable. The consistency of the test results was tested by a repeatability test and the results were quite satisfactory. The single blow method used in this project considered the longitudinal conduction within the material and it can accommodate any arbitrary inlet fluid temperature history. A comparative study of the various packs was done and traced certain trends. The high density packs gave better heat transfer and high pressure drop. The packs with alternate corrugated and flat plates had lower heat transfer performance, due to the fact that the tlat plates do not create such turbulence to the flow to reduce the boundary layer thickness to enhance the heat transfer. In short the flat plates only add weight to the pack, making it heavier than other packs. Based on the correlations and trends obtained from the analysis, some recommendations are also made. A further modification of the test facility was recommended to include a wider range of flow from very low Reynolds number to very high. This is necessary to find whether the packs with flat plates really perform better for highly turbulent tlow. The non - adiabatic nature of the side wall has to be considered for better reliability of the results. Some other recommendations are made to make the testing of packs more convenient. / Andrew Chakane 2018

A dissertation presented in fulfilment of the requirements for the Degree of Master of Science in Engineering DECEMBER 1982 / Although transpiration cooling has been demonstrated to keep the metal surface temperatures, in a gar turbine, below that at which oxidation occurs even though the hot gas temperatures are in excess of the metals melting temperature, few experimental studies have been conducted on the heat transfer aspects of transpiration cooling. Especially the effect blowing has on a turbulent boundary layer that has developed over a porous surface that is heated by the mainstream. Many studies have involved the blowing or suction oi the boundary layer through heated porous plates. Trans. an cooling was exper cntally investigated by making use of an existing wind tunnel which was modified so as to simulate the heat transfer phenomenon resulting from blowing coolant through a porous wall into a heated mainstream. The existing wind tunnel was designed and commissioned by Krieg (13) who considered the momentum transfer aspects of transpiration cooling. The solution of the momentum equation by Krieg forms the basis from which this investigation was developed, the original solution procedure being put forward by Cebeci and Smith (7). Krieg developed a generalised two-dimensional finite-differunce compute* program to solve the incompressible momentum equations describing a blown boundary layer. This program was further developed as part of this effort to solve the compressible momentum and neigy equations so as to account for the heat transfer in the blown boundary layer. The program is used to predict the experimental results obtained from the literature as well is those ottained during the nine experimental runs on the wind tunnel. Freestream flow velocities varied from 4,^5 m/s to 14,95 m/s with correspoi ;.ng temperatures of 44,95°C and 33,00eC respectively. The blowing fr tion F, was varied from 0,0059 to a maximum of , temperature of 40°C. The numerically calculated profiles and tho: » obi lined expurim ntally, as well as one set presented by another researcher, compared well. Finally, recommendations for future studies have been suggested.

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