HIGHLIGHTS• Experimental investigation of transitional flow regime in tubes with twisted tapes.• Results based on heat transfer coefficients and pressure drops.• Transitional flow regime was influenced by variation in twist ratios.• Variation in heat fluxes influenced the transitional flow regime.• Transition is earlier as the twist ratios and heat fluxes reduced. ABSTRACTThe purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in the transitional flow regime of twisted tape inserts in a circular tube.Experiments were conducted in a circular tube with an internal diameter of 19.0 mm and a length of 5.27 m, and twisted tape inserts with twist ratios of 3, 4 and 5. A square-edged geometry was used at the tube inlet and it was experimentally operated with water flowing through it while the tube was heated with a constant heat flux. The experiments were conducted at three different heat fluxes of 2, 3 and 4 kW/m 2 . The experimental set-up was operated between Reynolds numbers of 400 and 11 400, and the Prandtl numbers varied between 2.9 and 6.7. Two methods were used to identify the transition points of the different heat fluxes and twist ratios. The first method used the standard deviation of the temperature measurements, and the second method used three linear curve fits on a log-log scale. The curve fits made it possible for correlations to 1 be developed for the non-dimensionalised heat transfer coefficients and friction factors, which took twist ratio, heat flux and Reynolds number into consideration. For the same heat flux, it was found that the Colburn j-factors increased as the twist ratios decreased, and transition started earlier. When the twist ratio was kept constant and the heat flux was varied, higher heat fluxes delayed the transition from laminar to transitional flow. The friction factors were found to increase as the twist ratio decreased. When both the twist ratio and the Reynolds number were kept constant, an increase in heat flux was found to decrease the friction factor.

The purpose of this study was to experimentally investigate the heat transfer and pressure drop characteristics in a smooth circular tube with alternating clockwise and counter clockwise twisted tape (CCCTT) inserts. The CCCTT inserts were fabricated from copper plate strips with a length, width and thickness of 450 mm, 18 mm and 1 mm respectively. The strips were twisted to obtain a twist ratio of 5 and 12 strips were joined longitudinally so that a clockwise direction twisted tape insert was connected to a counter clockwise direction twisted tape. The assembling was at connection angles of 0°, 30° and 60°, to form CCCTT inserts with an overall length of 5.27 m. The CCCTT inserts were placed in a smooth circular copper tube with an inner diameter of 19 mm. Water was used as the test fluid and experiments were conducted at constant heat fluxes of 1.35, 2, 3 and 4 kW/m 2 between Reynolds numbers of 300 and 11 404. This covered the laminar, transitional and turbulent flow regimes. Specific attention was given to the identification of the transitional flow regime with the CCCTT inserts and the influence of the connection angle and heat flux on the transitional flow regime. It was found that both the start and the end of the transitional flow regime were influenced by the connection angle and the heat flux. When different connection angles were compared it was found that an increase in connection angle enhanced the heat transfer in the transitional flow regime. An increase in heat flux significantly enhanced the heat transfer in the laminar flow regime and delayed transition. Heat transfer and pressure drop correlations were developed to predict the experimental data in the laminar, transitional and turbulent regimes as a function Reynolds number, modified Grashof number and connection angle.

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Renewable energy has become an essential component for the survival of human beings. This is because conventional energy supply is limited, nearing its limits, and or destroying our environment. The complete transition to renewable energy is a major approach to achieving sustainable and clean energy distribution progress in this ever-changing and demanding world. This research work investigates the knowledge of renewable energy among the youth and their understanding of sustainable energy prosperity towards meeting the future generation's energy needs. To achieve this, a set of questionnaires was developed to identify their knowledge of various renewable energy resources, energy aspects, applications, and the extent to which the current syllabus provides a well-developed background. They were administered to high school students in KwaZulu-Natal, Durban. The main findings of this investigation reveal that the students were most familiar with solar energy, which could be due to the increasing availability of solar panels across the nation. However, a lack of awareness and little understanding of geothermal energy was noted among the high school students. This indicates a poor future for its development. Furthermore, 86% of the students agreed that conventional energy sources would likely still be relied upon by a significant portion of the global population to meet daily energy needs. Therefore, the government must take swift action to address these issues, by promoting the deployment of renewable energy sources in schools.

A major focus of existing literature on energy conservation is the modelling and quantification of energy savings and the corresponding carbon dioxide emissions from lightings. While many studies have established theoretical frameworks concerning these issues, very little documentation exists relating to energy savings and emission levels in students' hostels. This paper considers the lighting efficiency improvement of four University of Lagos halls of residence for the purpose of quantifying energy saving and the minimization of carbon dioxide that can be made. Compact fluorescent lamps are considered alternatives to the current primary usage of conventional fluorescent and incandescent bulbs. The existing electricity consumption data obtained from energy audit are used in combination with conversion factors to estimate the annual CO 2 contributed to the atmosphere by lighting in each of the buildings. The result of the study shows that over 45% reduction in carbon dioxide emission can be achieved. There is a lot individuals can do to reduce the emissions, for example, using energy saving appliances, turning off appliances when not in use, less use of fossil fuels, are simple measures that can be adopted to reduce annual carbon footprint, improve economic growth, enhance environment, health and save the planet.