At present, the vacuum tubes that are mass-produced and applied in China can generally be divided into two categories: glass heat-absorbing body vacuum tubes and metal heat-absorbing body vacuum tubes. Among them, the so-called glass endothermic vacuum tube is also called all-glass vacuum tube, or double-layer glass vacuum tube. This type of vacuum tube is generally composed of two glass tubes with different diameters: first, the inner tube and the outer layer of the inner tube after being melted and sealed at one end are vacuum-coated and selected. The end of the inner tube and the outer tube are respectively melted and sealed, and the spring bracket with getter is assembled, and then the two tube orifices at one end of the open tube mouth are reserved for annular sealing: Immediately, the annular space between the two tubes is evacuated through the air extraction pipe reserved in advance at the end of the outer tube, and finally the outer tube is melted and sealed to reserve the air extraction nozzle, thereby completing the production and processing of the entire glass vacuum tube. The all-glass evacuated tube collector produced by large-scale mechanization according to this mature process has become the mainstream product of solar water heaters in mainland China today.
The all-glass vacuum tube solves the problem of convection heat loss between the heat collector tube and the heat preservation tube by vacuuming between the inner and outer tubes, but it turns itself into a tube that cannot carry out effective convective circulation. The single-hole cecal tube for heat exchange has been invented for several decades since the invention of the vacuum tube. The all-glass vacuum tube has a single-hole cecal-like inefficient heat exchange dilemma. There are long-standing problems such as pipe blasting, dead water area at the bottom of the water tank, difficulty in realizing collection and storage separation of the system, and inconvenience for building-integrated installation. In fact, the above-mentioned series of congenital defects existing in all-glass vacuum tube products have attracted people’s attention from the very beginning. In order to solve the problem of convective circulation heat transfer of all-glass vacuum tubes, solar energy experts from various countries have also thought of many solutions; More solar energy experts have researched and developed the glass inner tube into a U-shaped (metal) tube type vacuum tube; a metal sleeve type vacuum tube with concentric working fluid in and out: or a glass three-sleeve vacuum tube (also known as a tube-in-tube vacuum tube). ); and straight-through vacuum tubes that open both ends of the inner and outer tubes at the same time, also known as bottomless vacuum tubes, double-opening vacuum tubes, etc.; this series is to improve the heat transfer performance of single-hole cecal-shaped vacuum tubes in convection circulation, and New glass vacuum tubes developed; or glass-metal vacuum tubes. Theoretically speaking, although the defects in the convective circulation heat transfer of the vacuum tube have been improved to varying degrees, and the efficiency of the convective circulation heat transfer of the vacuum tube has been improved to varying degrees, it has also led to a series of glass outer tubes and metal inner tubes. Due to the incompatibility of materials, melting points and expansion coefficients between the tubes, the technical difficulties of sealing the inner and outer tubes of the vacuum tube are generated. At the same time, it is also derived that the processing and assembly process is complex, the material consumption is large, the yield is low, and the production cost is high. Increase in magnitude: and the problem of sealing and product reliability reduction is even greater or even worth the loss. Perhaps it is precisely because of the long-term existence of this series of intractable cross-century drawbacks of vacuum tubes; therefore, although the American Owens-Illinois Company (Owens-Illinois) in 1975, on the basis of the thermos liner invented by Dewar in 1893, first developed the The double-glazed vacuum tube (also known as the “Sydney tube”), but it has always been regarded as a semi-finished product that is not technically perfect in European and American countries, so it has not received more attention and large-scale production applications. .
After years of experimental research, Kunming Nankai Energy Research Institute applies the basic theory of heat transfer and the technical means of modern fluid mechanics, as well as modern mathematical and physical methods and computer simulation experiments, without changing the existing vacuum tube appearance geometry and production process. After years of hard work, we finally found a technical means to realize the natural circulation heat exchange mechanism of the fluid medium (air or water flow) in the single-hole cecal tubular vacuum tube, which can greatly improve the efficiency of the natural circulation light-heat conversion of the vacuum tube. And on this basis, a set of assembly components that can simply divide the fluid (air or water flow) in the vacuum tube is successfully designed, and the system integration of the natural circulation heat transfer function of a single vacuum tube is realized at a higher level. Every ordinary all-glass vacuum tube can be easily converted into a collector water heater or an air collector with independent natural circulation heat exchange function at low cost. It fundamentally solves the historical problem of natural circulation heat exchange of all-glass vacuum tube temperature difference, effectively improves the photothermal conversion efficiency of the vacuum tube system, reduces the operating temperature of the vacuum tube circulation heat exchange, and reduces the radiation heat loss of the vacuum tube. The photothermal conversion efficiency of the vacuum tube is improved by more than tens of percentage points, which greatly improves the heat energy output and quality of the vacuum tube system at the operating temperature. Due to this innovative invention, it overcomes the disadvantages of vacuum tube stagnant water and high temperature scaling, reduces the probability of fouling and scaling in the inner tube and the occurrence of tube explosion; thus eliminates the dead water area of the water tank; prolongs the service life of the vacuum tube; and realizes the vacuum tube no matter Whether it is installed vertically or horizontally, it can realize the separation of storage and storage in the usual sense, as well as the technical difficulties of low-level concealed installation of large thermal insulation and heat storage facilities (or main water tanks). Installation created the conditions. In addition, new functions of forced circulation of vacuum tubes and constant temperature replenishment (release) of water have been expanded, as well as wider thermal energy applications in the field of solar drying. In order to further promote the technological upgrading and transformation of China’s annual output of more than 400 million vacuum tube products, it has laid a solid technical foundation for the improvement of China’s solar thermal utilization technology level. It also makes a new historic contribution to solving the problem of overcapacity of vacuum tubes in China, promoting the consumption of excess products, making up for the shortcomings of solar drying technology, and promoting the development and application of new technologies for solar thermal utilization in my country at a higher level. This high-tech project has obtained a number of utility model and invention patents authorized by the State Intellectual Property Office.
The advantages and beneficial effects of the invention are: due to the selection of new thermoplastic materials and new processes that are non-toxic, environmentally friendly, heat-insulating, heat-aging and weather-resistant, the vacuum tube is designed and manufactured according to the requirements of standardization, modularization and serialization. The cover, the shunt and the corresponding assembly components: thus developing a complete set of all-glass vacuum tubes that have achieved large-scale industrial production in China, without any adjustment or modification of the appearance geometry and production process. In this way, it is possible to realize the technological transformation of system integration and innovation of single-hole cecal-shaped all-glass vacuum tubes: thereby greatly improving the thermal efficiency and the heat yield of the vacuum tube system. Moreover, there are other long-existing drawbacks of all-glass vacuum tube solar hot water series products: high tube temperature, large heat loss, easy scaling, easy tube explosion, difficult sewage discharge, dead water area in the water tank, difficult to achieve a single system integration, and meet the longitudinal requirements. , the building-integrated installation of various forms of horizontal collection and storage separation, etc. At the same time, it has been effectively overcome and fundamentally improved, and it has fundamentally solved the cross-century technical problems that countries have been unable to overcome since the advent of the all-glass vacuum tube for decades.
The successful research and development and patented products of new technology of vacuum tube natural circulation system integration: the industrial development and application of vacuum tube set-water heater and vacuum tube solar air collector assembly components, will definitely promote the technological progress and upgrading of vacuum tube series products, especially for the new The promotion and application of a new generation of building-integrated vacuum tube products and new vacuum tube drying technologies has opened up a new way, making it possible for China’s vacuum tubes to go global in great strides. It has also laid a solid technical foundation.