![]() ![]() Life of the vacuum varies from collector to collector, anywhere from 5 years to 15 years. The inner tube is coated with a thermal absorbent. Typically, the water piping in an ETC is therefore surrounded by two concentric tubes of glass with a vacuum in between that admits heat from the sun (to heat the pipe) but which limits heat loss back to the environment. Since two flat sheets of glass are normally not strong enough to withstand a vacuum, the vacuum is rather created between two concentric tubes. Since heat loss due to convection cannot cross a vacuum, it forms an efficient isolation mechanism to keep heat inside the collector pipes. Bhatia, in Advanced Renewable Energy Systems, 2014 Evacuated tube collectors (ETC)Įvacuated tube collectors are a way in which heat loss to the environment, inherent in flat-plates, has been reduced. In general, ETCs will outperform flat plate collectors in cold climates, because the efficiency of ETCs does not fall off as quickly when the outside air temperatures drop. Overall operating efficiencies of (30–45) % are typical. Heat is then transferred to water flowing through a manifold and the condensed fluid sinks to the bottom of the heat pipe, where the cycle is repeated.Ĭommon applications include residential and commercial water heating, space heating and cooling and industrial process heat. Heat transfer fluid inside the heat pipe vaporises and rises to a condenser located in the top portion of the heat pipe. The right-hand side of Figure 20.2 shows a schematic of an ETC with a heat pipe. This design used a double-walled tube, and water flows directly into the inner tube. ![]() Direct flow designs are also available and are the predominant collector type in China. The double-walled design is better at maintaining vacuum because it does not require a metal-to-glass seal, but the single-walled design captures more light and therefore has better thermal performance. In this design, the air in the entire space inside the tube is evacuated. Left – Credit: NREL/PIX 09501 Right – Illustration by Alfred Hicks/NREL. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |