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Step 1: Change in boiling point. The variation in the boiling point of heat transfer oil indicates changes in the molecular weight of the heat transfer fluid. A recent new type of gas chromatography method used abroad involves comparing the boiling range of new oil with that of heat transfer oil after it has been in use; they use the levels of high-boiling and low-boiling compounds to determine the degree of cracking and polymerization that has occurred in the heat transfer fluid. Step 2: Char content. The so-called char content refers to the amount of char remaining after the heat transfer fluid has been evaporated and cracked. By observing changes in this char content, we can determine the tendency for the formation of polymeric carbon deposits as well as the degree of aging. Step 3: Change in the acid value of the heat transfer oil. Changes in the acid value occur mainly in systems where the expansion tank is not sealed with nitrogen, and such changes indicate the degree of aging of the heat transfer fluid. When aging reaches a certain extent, soluble organic acids further polymerize to form high-molecular-weight oxidation products, and the acid value may decrease at this point. Therefore, the degree of change in acid value is also an important criterion for assessing the quality of heat transfer oil. Step 4: Change in flash point. The flash point is a key safety indicator for assessing the quality of heat transfer oils; it indicates the likelihood of the formation of volatile substances and flammable gases. Step 5: Changes in adhesion. The changes in adhesion indicate variations in the molecular mass and structure of the heat transfer fluid. If the heat transfer oil undergoes cracking, its viscosity will decrease, while the viscosity due to polymerization and oxidation will increase. For users in low-temperature working environments, we should pay attention to the viscosity of heat transfer oil. Note: For users abroad, they sometimes use insoluble substances such as propylene or pentane to polymerize and produce resin-like materials. This allows it to detect whether there are any insoluble substances present in the heat transfer oil. For more inquiries and technical support regarding heat transfer oil, please visit Schultz Heat Transfer Oil’s official website at www.shschultz.com