• Energy Research

In this paper, pool boiling of ethanol at atmospheric pressure was analyzed. The enhanced surfaces were made of copper, on which grooves with a depth ranging from 0.2 to 0.5 mm were milled in parallel. The widths of the microchannels and the distances between them were 0.2 mm, 0.3 mm and 0.4 mm, respectively. The highest heat transfer coefficient, 90.3 kW/m2K, was obtained for the surface with a microchannel depth of 0.5 mm and a width of 0.2 mm. The maximum heat flux was 1035 kW/m2. For the analyzed surfaces, the maximum heat flux increase of two and a half times was obtained, while the heat transfer coefficient increased three-fold in relation to the smooth surface. In the given range of heat flux 21.2–1035 kW/m2, the impact of geometric parameters on the heat transfer process was presented. The diameters of the departing bubbles were determined experimentally with the use of a high-speed camera. A simplified model was proposed to determine the diameter of the departure bubble for the studied surfaces.

Environmental pollution, energy supply and security of supply have become major issues across the world due to climate change, limited energy sources, energy price volatility and energy supply constraints. Energy availability, energy efficiency and the replacement of fossil fuels by renewable energy sources are key factors in the global development of sustainable energy. In many countries with limited fossil fuel resources, the sustainable development of renewable energy sources is an important tool in reducing dependence on imported fuels. Some alternative energy sources, such as wind, solar, tidal and hydropower, seem almost inexhaustible. With the exception of tidal energy, all of these sources have been used extensively and for a long time. This article examines the improvement of energy security and the government’s actions to promote the use of renewable energy sources, focusing on increasing energy efficiency and reducing energy intensity and dependence on energy imports in Lithuania. In addition, the article provides the state of renewable energy sources in Lithuania, aspects of sustainability and future development directions and perspectives.