What are common cooling tower designs?
Some of the most common cooling tower designs are listed below:
- Natural Draft Cooling Tower
- Induced Draft Cooling Tower
- Forced Draft Cooling Tower
The rest of this article discusses how cooling towers are further classified. You can learn more about this topic in our online Introduction to Cooling Towers video course.
How are cooling towers classified?
Cooling towers can be classified based on several design characteristics. These are:
- Wet or dry.
- Mechanical draft or natural draft.
- Induced, forced or natural draft.
- Counter flow or cross flow.
- Direct or indirect (open or closed circuit).
Let’s have a look at each of these classifications in more detail.
What is the difference between a wet and dry type cooling tower?
A cooling tower that uses liquid as the cooling medium, is a wet cooling tower. A cooling tower that uses air as the cooling medium, is a dry cooling tower. This article focuses upon wet cooling towers as these are the more common types of cooling towers. Wet type cooling towers are easy to identify due to the white plumes of moisture (drift) rising from the towers.
What is the difference between a mechanical draft and natural draft cooling tower?
A cooling tower that uses a fan, or multiple fans, is a mechanical draft cooling tower. Cooling towers utilise axial or centrifugal fans. Axial fans are used for large, medium, and small cooling towers. Centrifugal fans are used for medium and small sized cooling towers, but are less common than axial fans.
A cooling tower that has no fans is a natural draft cooling tower. Natural draft cooling towers rely upon the stack effect to obtain movement of air through the tower. Air is heated by the cooling water, and this causes its density to decrease, the warm air then rises above the cool air due to this density difference. In the tower, this means that the warm air moves upwards through the tower whilst cooler air is drawn in at the base. The cycle is continuous and allows a large volume of air to be used to cool the cooling water. Typically, natural draft cooling towers are only used where the cooling demand is high and constant; thermal power stations for example, often use natural draft cooling towers.
What are induced, forced, and natural draft cooling towers?
A cooling tower that has a fan installed before the heat exchanger, is known as a forced draft cooling tower. A cooling tower that has a fan installed after the heat exchanger, is known as an induced draft cooling tower. Cooling towers without any fans are natural draft cooling towers. Natural draft cooling towers are very large structures that are easy to identify.
What is the difference between a counter flow and cross flow cooling tower?
Counter flow cooling towers force the cooling liquid in the opposite direction to the ambient air. For example, water will flow downwards due to gravity, whilst a fan forces air to flow upwards. The two mediums are thus flowing in opposite directions (180 degrees apart). Cross flow cooling towers force one medium to flow perpendicularly to another, they flow 90 degrees apart relative to each other. For example, air may flow perpendicularly across tubes containing cooling water.
What is the difference between a direct and indirect cooling tower?
Direct and indirect cooling towers are also known as open-circuit and closed-circuit cooling towers respectively. If the cooling medium comes into direct contact with the process medium, the tower is a direct type cooling tower. If the cooling medium does not come into direct contact with the process medium, it is an indirect type cooling tower. For example, water being cooled by air is cooled directly, but water in a pipe that is cooled by air is not cooled directly, because the pipe forms a barrier between the air and water.