With the growing energy needs, a conscious effort has been made to use non-conventional energy sources to generate clean energy efficiently. Solar energy has always been popular among humanity. Using solar energy in heating applications is one of the most prominent ways to extract solar power. Various developments have been made to augment solar water heating system (SWHS) performance. Each modified design of SWHS has its advantages and disadvantages. Broadly, solar water heaters are categorized into two types: Flat plate solar collectors (FPSCs) and evacuated tube solar collectors (ETSCs). Earlier studies show that evacuated tube SWHS are more efficient than flat plate SWHS. Extensive research is going on the design modification of evacuated tube SWHS to enhance their efficiency. Firstly, the present review article briefly introduced the numerous types of solar collectors and their range of operation. The current work reviews various techniques used for heat transfer enhancement in SWHS, their advantages, and the region of applications. The article concentrates on research involving the usage of energy storage medium, nanomaterials, reflecting surfaces, and hybrid techniques for performance augmentation of ETSCs.

The primary issues in the Himalayan Rivers are sediment and cavitation degradation of the hydroelectric power turbine components. During the monsoon season, heavy material is transported by streams in hilly areas like the Himalayas through regular rainfalls, glacial and sub-glacial hydrological activity, and other factors. The severe erosion of hydraulic turbines caused by silt abrasion in these areas requires hydropower facilities to be regularly shut down for maintenance, affecting the plant's overall efficiency. This article provides an in-depth examination of the challenges that can lead to cavitation, silt erosion, and a decrease in the efficiency of various hydroelectric turbines, and it demands attention on the design, manufacture, operation, and maintenance of the turbines. This study's main objective is to critically evaluate earlier theoretical, experimental, and numerical evaluation-based studies (on cavitation and silt erosion) that are provided and addressed throughout the study. As a part of this study, various strategies for mitigating the effects of these problems and elongating the time that turbine may be utilized before they must be replaced have been provided.

Heat transfer in water with the help of solar energy is an effective way to harness renewable energy and reduce reliance on non-renewable sources of energy. The utilization of turbulent promoters is an efficient solution to ameliorate the performance of heat exchangers (HE). The current work summarizes the experimental and numerical behaviour of HE reported in the literature, including the thermal examinations of HT and fluid flow characteristics with various turbulent promoters and tube arrangements. This article reviews multiple studies in which different twisted tape (TT) geometry enhances the HT rate in various HE tubes. The current work also compares the thermal performance (η) of TT configurations in HE tubes using correlations developed by different investigators. Maximum heat transfer and minimum friction factor concerning fluid utilized in the system may also produce the optimal form for twisted tapes.