Closed Circuit Cooling Tower

Closed Circuit Cooling Tower

I. Overview

An evaporative cooling tower is a heat exchanger that combines the performance of a standalone water-cooled chiller and a cooling tower (i.e., the water-cooled chiller is directly placed in the cooling tower for water spray evaporation heat exchange). This not only shortens the process but also reduces the scope of thermal pollution.

II. Working Principle

The heat transfer process in an evaporative cooling tower involves the heat from the fluid inside the tubes being conducted through the tube wall to the water flowing outside the tubes, and then from the water to the air. The heat transfer from water to air consists of latent heat transfer during water evaporation and sensible heat transfer due to changes in the sensible heat of the air.

The top of the cooling tower is equipped with an exhaust fan. Air enters through the air inlet at the lower part of the tower (fitted with louvers) and flows over the heat transfer tube bundle. The lower part of the tower is a collection pool (or tank). A pump delivers the cooling water to the water distribution device at the top of the tower, where it is sprayed onto the heat transfer tube bundle through nozzles. The spray water contacts the tube walls and is heated, causing a small portion of the water to evaporate and carry away heat, while the majority of the water flows back to the collection pool (tank) for recirculation. The air flowing over the tube bundle comes into contact with the hot water and carries away the heat from the water. After passing through the upper drift eliminator to remove entrained moisture, the air is discharged into the atmosphere by the fan. During operation, due to evaporation, drift loss, and blowdown of the cooling water, it is necessary to appropriately supplement the water in the pool (tank).

III. Applicable Conditions

In an evaporative cooling tower, since the heat from the fluid inside the tubes is transferred to the air via the water outside the tubes, it is more rational compared to using a water-to-water heat exchanger and a cooling tower separately. Compared to an air-cooled tower, the evaporative cooling tower utilizes the latent heat of evaporation of the water outside the tubes, offering the advantage of requiring less heat transfer area.

Generally, when cooling fluids >100°C, using an air-cooled tower is advantageous; when cooling fluids between 80-60°C, using an evaporative cooling tower is beneficial.

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