The heat transfer oil is partially added and replaced gradually during use, and the service life is generally relatively long. According to the German heating system safety technical standard (DN4754), the qualified heat transfer oil should be used at the highest temperature for at least one year. Selection of heat transfer oil Select the product according to the use temperature limit The so-called use temperature limit of the heat transfer oil refers to the upper and lower temperature limits that are directly related to the efficient and safe operation of the heat transfer system. The evaporability and safety of the heat transfer oil flash point opening meets the standard index requirements, the initial boiling point is not lower than its maximum use temperature, the distillation range is relatively narrow, and the spontaneous ignition point is high. The refined depth of the heat transfer oil is a light yellow transparent liquid, with good storage stability, and does not change color or precipitate after exposure to light. The residual carbon is not more than 0.1%, and the sulfur content is not more than 0.2%. The low-temperature fluidity of the heat transfer oil is based on the user's area and the ambient temperature of the equipment, and the appropriate low-temperature performance is selected. The heat transfer performance of heat transfer oil has lower viscosity, higher density, higher specific heat capacity and thermal conductivity.
Quality monitoring of heat transfer oil in use The main purpose of regular inspection during operation is to understand the changes in the internal quality of the heat transfer oil, and from this, discover the problems of the system design, operation, management and the conduction oil itself, and correct it in time to extend its service life. ① The change of distillation range indicates the change of relative molecular mass. In recent years, gas chromatography has been used in foreign countries. Compared with the distillation range of new oil, the content of high boiling point substances and low boiling point substances is used to indicate the degree of cracking and polymerization of heat transfer oil. . ②The change of viscosity can explain the change of relative molecular mass and molecular structure. Cracking lowers the viscosity, while polymerization and oxidation increase the viscosity. These changes have little effect on the viscosity in the high-temperature range, but may have a greater impact on the low-temperature viscosity. Therefore, for cold regions and operating processes with cooling, the low-temperature viscosity increase should be taken seriously.
③The change of acid value can judge the aging degree of the oil. The increase in acid value is usually caused by the oxidation of the oil, which mainly occurs in the expansion tank system without nitrogen sealing. However, when aging to a certain extent, the soluble organic acid may further polymerize to form polymer oxides, and the acid value may decrease at this time. Therefore, attention should be paid to judging the aging degree of oil from the changing trend of acid value.
④ Carbon residue is the residue left by the evaporation and pyrolysis of the heat transfer oil in operation. During operation, the carbon residue column has a rising trend over time, which can explain the tendency of polymer deposit formation and the degree of aging.
Generally, the above indicators are used to comprehensively judge the deterioration of oil.
