The application of solar light-to-heat conversion, that is, the direct use of solar heat, is the oldest, most direct, and most common form of solar thermal utilization. According to the historical records of mankind, the sun in the Western Zhou Dynasty (11th century BC) made fire; the ancient Greek scientist Archimedes (3rd century BC) used focused sunlight to burn down an attack on the port of Silasius in eastern Sicily. A Roman fleet; and more than a thousand years ago, the record of “cutting ice into a circle” by Zhang Hua of the Jin Dynasty of China, “Cut the ice into a circle, lift it to the sun, and take the shadow of Ai to get the fire”; all are solar energy Examples of light and heat utilization. Photothermal utilization is mainly the application of solar radiation in the long-wavelength infrared and far-infrared part of the energy. In the 1890s, a French chemistry teacher used a black metal container for the first time, filled it with water and placed it under the sun, using solar radiation to heat the water in the container. As low-temperature hot water for daily use. This is the first recorded device for humans to use solar radiation energy to purposefully heat low-temperature hot water. This measure seems simple but has epoch-making significance! This kind of water heater is inexpensive and has the disadvantage that it does not keep warm. After sunset The hot water temperature quickly dissipates and cannot be used in winter or rainy days. However, due to the simple structure, similar products are still used in some remote rural areas until now. The earliest solar water heater that appeared in China in the 1960s was a hot water bottle made of waterproof plastic. In the early 1970s, people put a flat box-shaped shallow pool metal container with a black heat-absorbing film layer in a container with an oblique corrugated glass cover, and a thermal insulation material was placed on the outer side of the container to make it Practical value of “shallow pool boring solar water heater”. The heat collection effect of this simple water heater is improved due to the addition of a heat-preserving shell. However, in general, this AC water heater still has problems such as poor heat exchange performance, low efficiency, short life, and unclean water quality.
In the mid-1970s, commercial “dual-tube dry solar water heaters” were introduced in Beijing and Tianjin, China. This kind of simple water heater integrates storage and storage, simple structure, low price: the disadvantage is that the heat preservation and heat collection effects are relatively poor, and the daily water production is also small. The hot water cannot be used for overnight insulation and storage, and can only meet specific rural areas. The seasonal needs of summer and autumn have not formed much market value.
In 1975, the American Owens-Illinois (Owens-linois) company, based on the production of the thermos flask invented by Dewar in 1893, elongated its extension tube and developed a solar collector tube with all-glass vacuum tubes. This type of heat collector is composed of two coaxial thin-walled high-strength glass tubes of different diameters. First, the outer layer of the inner tube is coated with a high-efficiency selective heat absorption layer by a vacuum coating process, which serves as a solar energy absorption The heating body collects sunlight to heat the inner tube to store water, and vacuum is used between the inner and outer tubes to reduce the convective heat loss between the two tubes, and the heat-collecting inner tube is insulated to form a piece Heat collection and heat preservation and storage are combined into one, and the functions of the inner and outer tubes are complementary to each other. The closed end of the round head is used as the free end of thermal expansion, and the open end is used as a common channel for swallowing and spitting out hot and cold water. The single-hole cecal-shaped all-glass vacuum tube collector has a tight structure and can resist mild frost and consumption. With few metal materials, after the mass automated mechanized production line is put into production, the products have unique competitive advantages of stable quality, low price, convenient installation and strong interchangeability.