In industrial sectors like petrochemicals and power generation, air coolers function as giant "industrial radiators," using airflow to cool high-temperature process fluids. They are key equipment known for their efficiency and water-saving benefits. However, when ambient temperatures plummet, these systems designed for cooling face serious challenges—internal fluids can congeal, clog, or even freeze due to excessive cooling, posing a shutdown risk. How do engineers design a "winter coat" for these massive, cold-sensitive units?

The Challenge: Extreme Temperature Swings and Freezing Risk

In northern China, the temperature difference between summer and winter can be as high as 60-70°C. This drastic change, combined with uneven heat load distribution among tube rows and the potential presence of non-condensable gases, makes equipment that runs well in warmer seasons highly susceptible to "illness" in severe cold. Fluids with high viscosity and high freezing points, like certain oils, are particularly at risk.

The Strategy: A Multi-Pronged Approach for "Cold Protection"

To ensure safe, reliable, and economical operation of air coolers in low-temperature environments, engineers employ a combination of strategies. The core goal is precise control of the cooling degree to prevent localized overcooling.

• Refined Preliminary Design:​ The design stage is crucial. Selecting the right number of tube rows for different fluids (e.g., 6 rows for lubricating oil) is recommended. Even more critical is setting the design approach temperature (ΔT) between the fluid and air. A smaller ΔT allows for fewer tube rows, while a larger ΔT necessitates a more conservative design with more rows to prevent end freezing.

• Dynamic Operation Control & Structural Optimization:

  • Even Flow Distribution:​ Special piping layouts (like Π-shaped connections) and multiple inlets ensure hot fluid is evenly distributed to each fin tube, preventing local freezing due to low flow.

  • Controlled "Breathing":​ Equipping fans with automatic variable-pitch blades and louvers allows reducing the forced airflow in cold weather, effectively "turning down the fan."

  • The Right "Sweater":​ For easily congealing fluids, high-fin tubes are avoided. Instead, bare pipes or large-diameter tubes with low fin density are used to reduce heat transfer efficiency appropriately.

  • Bottom "Heating Pad":​ Steam tracing coils installed below the tube bundle act as an emergency "heating pad," used only during startup, shutdown, or idle periods to prevent residual fluid from solidifying.

  • Seasonal Flow Direction:​ A clever seasonal strategy is employed. Parallel flow in winter​ lets the hottest fluid meet the coldest air first, minimizing freezing risk at the critical inlet. Counter-flow is used in summer​ for higher efficiency. While parallel flow sacrifices some efficiency, it ensures winter safety.

  • Staged Condensation for Steam:​ For steam condensers, a main and auxiliary condenser in series provides "staged condensation." Steam velocity and tube length are carefully controlled to prevent condensate from becoming supercooled and freezing at the outlet.

  • Precise Wall Temperature Calculation:​ Ensuring the tube wall temperature​ always remains above the fluid's freezing point​ under all conditions is the fundamental design rule to prevent freezing.

Conclusion

Selecting and operating air coolers in cold environments is not a simple purchase but a systematic engineering task integrating design, specification, and operational control. It combines material science, structural design, automation, and process knowledge. Through this array of combined measures, modern air coolers operate reliably in freezing conditions, safeguarding production lines as robust guardians that can both "dissipate heat" and "protect themselves" in the winter chill.