The main reason for the performance decline of the centrifugal unit (1)
After the unit runs for a long time, there will be phenomena such as failure to operate at full load, surge, low evaporation temperature, high condensation temperature, and high motor current, which will cause its cooling capacity to decline. The main reasons for the performance degradation of the unit are the changes in the chemical and thermal properties of the refrigerant, the deterioration of the lubricating oil, the excessive thermal resistance of the heat exchange surface, the poor system sealing, and the mutual penetration of the refrigerant system and the water system.
The refrigerants used in centrifugal refrigeration units mainly include R11, R134a, R123, etc. The performance changes of refrigerants can be explained from three aspects: refrigerant and water, refrigerant and lubricating oil, refrigerant and metal and non-metal. Refrigerant and water, in the refrigeration system with Freon as the refrigerant, when the refrigeration temperature is below 0 ℃, the free water will freeze and block the throttling channel, and cause insufficient liquid supply in the system and decrease the cooling capacity of the unit; in addition, After the water is dissolved in the refrigerant, water decomposition will occur, and acidic substances will be generated, corroding metal materials, and reducing the electrical insulation performance of the winding. The solubility of refrigerant and lubricating oil is different from that of refrigerant and lubricating oil, and they are roughly miscible or insoluble. When mutually dissolved, the lubricating oil can penetrate into the various parts of the compressor along with the refrigerant to form good lubrication conditions and extend the operating life of the unit, but the mutual solubility will reduce the viscosity of the lubricating oil and increase the evaporation temperature of the unit under the same pressure. ; When insoluble, the refrigerant and lubricating oil are easy to separate, but the oil film formed on the heat transfer surface and the inner surface of the unit will reduce the heat transfer coefficient. When refrigerant and metal and non-metal halogenated hydrocarbons contain water, they will be hydrolyzed to form acidic substances and corrosive to metals. Therefore, the mixture of water-containing refrigerant and lubricating oil can dissolve copper and form copper plating. The copper plating phenomenon will affect the sealing condition of moving parts, damage the bearings and then affect the overall sealing performance of the negative pressure unit, so that outside air enters the inside of the unit, resulting in abnormal conditions such as excessive condensation pressure; at the same time, halogenated hydrocarbons are also a good one. Organic solvents will make polymer materials (such as natural rubber, resin, etc.) soft, swell or generate bubbles.
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