Heat transfer oil testing and heat transfer oil change standards
October 08, 2022
Heat transfer oil (also known as heat transfer fluid) has a series of physical properties, such as viscosity, vapor pressure, boiling range, initial boiling point, flash point, ignition point, flow point, etc. The viscosity index of the heat transfer oil is directly related to the heat transfer effect. The smaller the viscosity of the heat transfer oil, the faster the flow. Its heat transfer efficiency is higher. The vapor pressure, flash point, and ignition point of the heat transfer oil are factors related to whether the heat transfer oil is easy to volatilize and whether it is easy to catch fire. fire. The initial slip point of heat transfer oil is related to its safety and operating temperature. The higher the initial boiling point, the better its safety and the higher the operating temperature. The flow point of the heat transfer oil is the low temperature that guides the flow of the heat transfer oil, and the heat transfer oil with a low flow point can keep flowing even in the cold north. If the flow point is too high, it will make it difficult to start the heat transfer oil furnace and system. Therefore, the heat transfer oil with a low flow point is easy to use in cold places.
To judge the properties of heat transfer oil, mainly by testing the following seven indicators 1. Viscosity Viscosity is the thinness and fluidity of heat transfer oil under specified conditions. When the mechanical load and speed are the same. The higher the viscosity of the heat transfer oil used, the greater the power loss. Since most of the domestic oil is used in the high temperature heat transfer stage, almost all brands of heat transfer oil have similar viscosity at high temperature. Generally, manufacturers consider this indicator to be scrapped when the viscosity of heat transfer oil changes by ±15%. If the heating medium undergoes oxidative polycondensation reaction, the viscosity will increase significantly. Small viscosity and good pumping performance. Due to overheating, soluble polymer is produced after cracking, and the viscosity will increase sharply; when the viscosity increases, the flow point of the heat transfer oil also increases. The furnace tube is blocked, the hot oil pump cannot be rotated, and the hot oil furnace cannot be heated. At this time, cleaning the hot oil furnace requires a lot of manpower and material resources to clear the hot oil furnace tube, and sometimes the hot oil furnace is scrapped. If there are too many light volatiles, the viscosity will decrease, but the vapor pressure will increase, and the volatility will be large, which will cause the heat transfer oil pump running at high temperature to produce air resistance, resulting in difficult transportation. 2. Acid value The acid value is the total amount of organic acid and inorganic acid in the heat transfer oil, that is, the total amount of potassium hydroxide consumed per gram of heat transfer oil. Organic acids are divided into low molecular organic acids and high molecular organic acids. Low molecular organic acids and inorganic acids are corrosive to metals. Corrosion increases especially in the presence of water molecules. Most of the heat transfer oil is a polymer organic acid, and the polymer organic acid has little corrosion to the equipment. The heat transfer oil has the coking process of induction, adsorption, hardening and shedding in high temperature operation. These processes form a layer of heat-conducting oil coke in the pipeline of the hot-oil furnace, which affects the heat-transfer effect of the hot-oil furnace, and at the same time isolates the contact between the heat-conducting oil and the metal pipe wall, so that these acids cannot corrode the equipment. The value is not significant for the corrosivity of the metal. The degree of deterioration of the oil can be judged by the acid value. When the high temperature heat carrier is above 60°C, it is easily oxidized to form organic acid when it encounters air or water. The value of the value can determine the difficulty and severity of the heat carrier being oxidized by high temperature. 3. Flash point (open) It refers to the low temperature when the mixture of steam and air escaping from the heated oil comes into contact with the flame and flashes instantaneously under specified conditions. The higher the flash point, the smaller the possibility of fire, and the safer the use, but it cannot be understood that the higher the flash point, the more suitable for high temperature. Different brands of heat transfer oil have different flash points, as low as 140°C and as high as 200°C. The heat transfer oil is used in the heating oil furnace of the closed system, so that the three elements of combustion are not available (combustion = fuel + temperature + oxygen), so the heat transfer oil will not burn. If there is leakage in the system, smoke will be emitted first, and flash fire will only occur in case of open fire, and it will not burn if handled in time. It can be seen that the flash point of the heat transfer oil is not an important factor for the waste index of the heat transfer oil. As long as it is mastered well, the heat transfer oil will not burn, and it will not affect the safety of the heat oil furnace. 4. Residual carbon Residual carbon is a mixture of polycyclic aromatic hydrocarbons, colloids and asphaltenes, which is easily decomposed, dehydrogenated and condensed to form residual carbon by strong heat under the condition of insufficient air. The size of the carbon residue can roughly determine the coking tendency of the heat transfer oil in high temperature use. The heat transfer coefficient of coking is very different from that of metal, and the energy consumption increases, so the residual carbon is the main factor affecting the heat transfer oil. 5. Moisture Moisture is an important indicator for the smooth operation of the device. If the moisture in the heat carrier exceeds the standard, it is easy to cause oil boiling during the heating process, and it is easy to accelerate the hydrolysis and oxidation reactions of oil products. It will cause the thermal oil to decompose and fail. The product used in general industrial installations shall not exceed 0.05%, and the domestic electric heater cannot remove moisture. To ensure safety, the index is set to not exceed 0.02%. 6. Pour point Pour point is a quality index representing the low temperature flow properties of oil products. The meaning of this index is: (1) The amount of paraffin wax can be estimated. (2) Instruct the ambient operating temperature 7. Distillation range Distillation range The distillation range of the heat transfer oil is related to the operating temperature of the heat transfer oil. It refers to the range between the low boiling point and the highest boiling point of the oil composition. The larger the range, the wider the boiling range, and low boilers in the oil should be considered. The appropriate amount should be used to ensure that the oil will not be lost too much during the process, and at the same time will not affect the effect and form carbon deposits due to the high viscosity of the oil. It is better for the heat transfer oil to have a narrower distillation range within the specified operating temperature range.
