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Centrifugal compressors have always been under the monopoly of foreign companies. The prices are exorbitant because we don’t have our own brands or manufacturing capabilities in our country. Large state-owned enterprises rely on imports from abroad; there are no domestic brands in this area. In terms of coolers, China does not have companies that are capable of producing high-quality ones. Through years of effort, we are now able to replace imported cooler brands. 1.1 Operating conditions: Ambient temperature: -5°C to 40°C. 1.2 Main technical parameters of the air compressor: Sequence, Parameter, Unit, Rated operating point value. 1. Exhaust pressure, MPa (G): 0.85. 2. Exhaust flow rate, m³/min: 250. 3. Number of compression stages: 3. 4. Compression medium: Air. 5. Design relative humidity: %60. 6. Inlet temperature of cooling water, °C: ≤ 32. 7. Pressure of cooling water supply, MPa: 0.2–0.27. 8. Exhaust temperature (with after-cooling), °C: ≤ 42. 9. Cooling water consumption (with after-cooling), m³/h: 142. 1.3 Requirements: 1. The compressed air volume must be 250–260 cubic meters per minute. 2. Cooling efficiency: The cooler must ensure that the temperature and pressure remain within normal limits, i.e., the temperature of the gas after passing through the cooler should be no more than +12°C above the temperature of the cooling water (the exact temperature depends on the operating environment and whether the quality of the cooling water meets the manufacturer’s specifications). After passing through the cooler, the temperature of normal gas should be between 35-42°C. If this temperature is too high (the cooler is unable to lower the gas temperature), it will directly cause surging in the unit, preventing it from operating properly; in severe cases, this can lead to more serious failures. (Temperature and pressure are merely parameters that indicate the cooling efficiency of the cooler; therefore, they have only alarm values and no shutdown values. When there is an alarm related to temperature or pressure, it serves as a reminder that we need to check the cooling water system. There is no direct connection between these values and surge phenomena.) 3. Corrosion resistance: There are always some corrosive gases in the air, and after compression, these gases form acidic substances upon cooling; hence, materials with good corrosion resistance are very important. 4. Flow capacity: When a large volume of gas passes through the cooler, there is a loss of pressure; if this loss is significant, it means the resistance within the cooler increases. Such an increase in resistance will directly affect the surge behavior of the unit! (1) Tube bundle type: Straight tube type (2) Requirements for tube bundle and fin materials: Red copper (with anti-corrosion treatment) ； The core plates of the inter-stage coolers are all made of stainless steel: 1Cr18Ni9Ti ； (3) Design operating temperature: 95 degrees ； (4) Design working pressure: 7 bar for stages 1 and 2; minimum pressure: -0.8 bar; maximum pressure: 10 bar for stages 1 and 2 ； Level 3 operating pressure: 10 bar; maximum pressure: 10 bar for levels 1 and 2 ； Operating pressure at level 3: 10 bar, maximum pressure: 16 bar ； (5) The test pressure shall be not less than 25 bar; (6) The temperature and pressure at the cooler outlet shall be below 12 degrees