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Hydropower is considered as one of the most convenient and popular renewable energy technologies and its capacity is growing rapidly throughout the world. Its rapid deployment also comes up with various environmental issues which cannot be neglected at a glance. Previous studies had imposed questions about its sustainable nature and now it becomes important to think about the sustainability of hydropower projects so that the technology would grow effectively in future. This paper reviews the status of research on environmental assessment of hydropower projects. The factors which affect the environmental impacts associated with hydropower generation are also explored. It is found that environmental impact assessment of hydropower projects must be performed considering all aspects and factors which affects the environmental impacts associated with hydropower projects. Most of the previous studies are focused on the estimation of GHG emissions so it is necessary to give emphasis on other environmental impacts like acidification, land use, energy consumption etc. and also consider biomass decomposition in submerged land. In fact it is not worthy to predict the sustainability of hydropower projects without considering almost all biophysical impacts associated with them. The paper also compares large and small hydro considering all sustainability assessment factors. Small hydropower projects are considered as a good alternative to control the problems associated with large hydropower projects but still many studies found that so many issues are associated with small hydro as well which cannot be neglected completely. Image 1 • Factors that influence the environmental impacts of a hydropower plant are summarized. • Current status of research related to sustainability assessment of hydropower projects is discussed. • Comparison among Large and Small Hydropower in respect of sustainability is provided. • Improvements required in the future research in order to obtain more realistic and useful results are outlined. [ABSTRACT FROM AUTHOR]

Energy saving is a vital element in today's scenario. Earth Air Heat Exchangers (EAHE) is a technique that promotes energy savings. EAHE is a non-conventional technique that uses the earth's underground heat for space cooling/heating. In this article, review of different combinations of EAHEs is presented. The review presents an apprehensible summary of the previous works on EAHE. The review addresses an elaborated description of the analytical and experimental studies on the different combination of EAHE and analyses the results from the thermal performance. It also consider the environmental aspect in the field of energy saving. It is concluded from the summary that the design parameters directly or inversely affect the outlet temperature. The result also shows that the pipe materials does not have much influence on the outlet temperature. In the case of energy saving, EAHE technology saves more energy that can replace the conventional air conditioning systems. Thus, this technology can effectively reduce the greenhouse gases and improve the environment. [ABSTRACT FROM AUTHOR]

Heat transfer enhancement is an important matter of concern for energy conservation and also beneficial from economic point of view. The use of passive devices like twisted tapes, roughness elements, wires inserts etc. are effective methods of heat transfer augmentation. Many research studies on different types of twisted tapes geometries to increase heat transfer rate have been carried out. Also, several correlations were developed to determine heat transfer and friction factor for twisted tape inserts. In the present study, a review on work done in the area of heat transfer augmentation using twisted tapes has been carried out. Previous experimental and numerical studies on various types of twisted tapes (based on the literature survey) were discussed. These studies reveal that the future research in the area of twisted tapes will bring more development in the heat exchanger systems. The optimum shape for twisted tapes can also be developed based on maximisation of heat transfer and minimisation of friction factor regarding fluid used in the system. [ABSTRACT FROM AUTHOR]