Search

Erosion of material surface due to collision of solid particles has been a challenge to several fields of engineering. Despite of centuries of investigations and research, the exact phenomenon of erosion of surface by the solid particles has not been fully understood. Increasing number of hydropower plants are being built in the regions where rivers are heavily loaded with sediments. This induces material erosion in hydro turbines, leading to change in flow pattern, losses in efficiency, vibrations and even final breakdown of turbine components. To overcome sediment erosion related failures, development of erosion resistant alloys, coatings of the components, and optimization of hydraulic design of the components, are the important practices. In Francis turbines, erosion causes increase of clearance gap between guide vanes and facing plates and cross flow occurs from this increased gap. This cross flow together with other secondary flows disturbs the velocity profile at the runner inlet. Change in velocity profile at the inlet causes additional erosion damage and other undesired effects in the turbine runner. Most of the past studies in Francis turbine were focused to understand the flow phenomenon inside the turbine components and to analyze their effects on design improvements. There is still a need of further fundamental research to understand the effects of sediment erosion of turbine components on the flow phenomenon, and developing better designs of hydro turbines to minimize those effects. [ABSTRACT FROM AUTHOR]

The low heat transfer rate in a flat plate solar air heater (SAH) is due to the development of a laminar sub-layer near the heated absorber plate. Owing to this, the plate temperature rises substantially, instigating losses and thus reducing the efficiency. Extensive research has been carried out to mitigate this problem, of which passive technique emerged to be a promising solution. The passive method involves the application of fins/turbulators/ribs on the surface where the boundary layer develops so that it breaks the same. Various profiles and configurations of the ribs ranging from transverse to inclined and continuous to discrete have been presented concisely. Correlations on Nusselt number (Nu) and friction factor (f) for different rib configurations have been summarized in order so that it can be accessed for future research. 3-D CFD analysis is carried out to gain insight into the flow pattern of various V-ribbed SAH, and with the help of streamlines and contours, the findings are established. Furthermore, various exergy destruction has been studied in detail for different V-rib configurations, namely– V-rib, multiple V-rib, and multiple V-rib with the gap, and analyzed in detail for prospective studies. Exergetic performance study of these rib configurations indicates that the multiple ribs and the multiple rib-gap combinations enhance exergetic efficiency (η ex) by 12% and 31.6%, respectively, in comparison to V-rib SAH. • A critical review of ribbed solar air heaters (SAHs) is presented. • 3-D CFD analysis is carried out to study the impact of the rib gap on performance. • Energy and exergy analysis of SAH with various V-rib configurations are presented. • Multiple V-ribs with gap shows 31.6% higher exergetic efficiency compared to V-rib. [ABSTRACT FROM AUTHOR]