How many circulation modes and stage heat exchange are there in closed cooling towers?

The closed cooling tower is an application of a tubular indirect evaporative cooler. Its working principle can be divided into three parts of circulation.

1. Primary side heat exchange cycle
When the circulating hot water on the primary side (external circulation) flows through the coil of the closed cooling tower, it is divided into 4 links for heat transfer:
1) First, the heat of the hot solution is transferred to the inner surface of the coil according to convection heat transfer;
2) Heat is transferred to the outer surface of the coil through the wall thickness;
3) Convection heat is transferred from the outer surface of the coil to the water film outside the tube;
4) Finally, from the water film to the air through evaporation and convection heat transfer.

2. Secondary side precooling cycle
The secondary side (self-circulation) spray water is pumped from the water collection tray at the bottom of the closed cooling tower to the water distribution system by the spray centrifugal water pump. After being sprayed on the heat sink through the common sprinkler head, it exchanges latent heat and sensible heat with the air, and flows to the coil group after pre-cooling, forming a stable water film on the surface of the tube. It absorbs the heat transferred by the material in the tube, and finally returns to the water pan, and the cycle continues.

3. Air circulation
The fan draws unsaturated air outside the closed cooling tower into the tower. The airflow passes through the coil, the heat sink and the spray water on the secondary side to exchange latent heat and sensible heat to absorb heat, and then passes through the common water retainer to separate gas and liquid, and finally discharges the nearly saturated moist air out of the tower.

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