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Oasis Iceberg
11
2024
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07
What are the different circulation methods and phase heat exchange processes in closed cooling towers?
The closed cooling tower is an application form of the tubular indirect evaporative cooler.
❶ Three-Part Cycle
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The closed-circuit cooling tower is an application form of the tubular indirect evaporative cooler.
Its working principle can be divided into three cyclical parts—so, what exactly are these three cycles?
2 Primary-side heat exchange cycle:
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When the circulating hot water from the primary side (external loop) flows through the coil of the closed cooling tower, heat transfer occurs in four distinct stages: 1) First, the heat from the hot solution is transferred to the inner surface of the coil via convective heat exchange; 2) Next, the heat conducts through the wall thickness to the outer surface of the coil; 3) Finally, the outer surface of the coil transfers heat to the thin film of water flowing around the outside of the tube—this heat is then carried away by both evaporation and convective heat exchange into the air.
3 Secondary Side Pre-cooling Cycle
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The secondary-side (self-circulating) spray water is drawn from the collection pan at the bottom of the closed cooling tower by a spray centrifugal pump and then delivered to the water-distribution system. From there, it is evenly sprayed onto the heat-dissipating material via specially designed uniform sprinkler heads, facilitating both latent and sensible heat exchange with the air. After preliminary cooling, the water flows into the coil assembly, forming a steady film across the tube surfaces. This film efficiently absorbs the heat transferred from the internal fluid, before finally returning to the collection pan—thus completing an endless循环.
4 Air Circulation
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The fan draws unsaturated air from outside the closed cooling tower into the tower. The airflow passes through coils, heat-dissipating materials, and spray water on the secondary side, where it absorbs both latent and sensible heat. Afterward, the air undergoes unique demisters for effective gas-liquid separation, and finally, the nearly saturated, moist air is discharged back outside the tower.
Through the three-part cycle and four-stage heat exchange described above, the closed cooling tower cools the secondary-side heat-transfer solution to the desired temperature before returning it to the system, ensuring its smooth operation.
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