MECHANICAL DRAFT
Mechanical draft towers uses fans (one or more) to move large quantities of air through the tower. They are two different classes:
The counterflow tower occupies less floor space than a crossflow tower but is taller for a given capacity. The principle advantages of the crossflow tower are the low pressure drop in relation to its capacity and lower fan power requirement leading to lower energy costs.
All mechanical towers must be located so that the discharge air diffuses freely without recirculation through the tower, and so that air intakes are not restricted. Cooling towers should be located as near as possible to the refrigeration systems they serve, but should never be located below them so as to allow the condenser water to drain out of the system through the tower basin when the system is shut down.
FORCED DRAFT
The forced draft tower, shown in the picture, has the fan, basin, and piping located within the tower structure. In this model, the fan is located at the base. There are no louvered exterior walls. Instead, the structural steel or wood framing is covered with paneling made of aluminum, galvanized steel, or asbestos cement boards.
During
operation, the fan forces air at a low velocity horizontally through
the packing and then vertically against the downward flow of the water
that occurs on either side of the fan. The drift eliminators located at
the top of the tower remove water entrained in the air. Vibration and
noise are minimal since the rotating equipment is built on a solid
foundation. The fans handle mostly dry air, greatly reducing erosion and
water condensation problems.
INDUCED DRAFT
The induced draft tower show in the following picture has one or more fans, located at the top of the tower, that draw air upwards against the downward flow of water passing around the wooden decking or packing. Since the airflow is counter to the water flow, the coolest water at the bottom is in contact with the driest air while the warmest water at the top is in contact with the moist air, resulting in increased heat transfer efficiency.
Mechanical draft towers uses fans (one or more) to move large quantities of air through the tower. They are two different classes:
- Forced draft cooling towers
- Induced draft cooling towers
The counterflow tower occupies less floor space than a crossflow tower but is taller for a given capacity. The principle advantages of the crossflow tower are the low pressure drop in relation to its capacity and lower fan power requirement leading to lower energy costs.
All mechanical towers must be located so that the discharge air diffuses freely without recirculation through the tower, and so that air intakes are not restricted. Cooling towers should be located as near as possible to the refrigeration systems they serve, but should never be located below them so as to allow the condenser water to drain out of the system through the tower basin when the system is shut down.
FORCED DRAFT
The forced draft tower, shown in the picture, has the fan, basin, and piping located within the tower structure. In this model, the fan is located at the base. There are no louvered exterior walls. Instead, the structural steel or wood framing is covered with paneling made of aluminum, galvanized steel, or asbestos cement boards.
INDUCED DRAFT
The induced draft tower show in the following picture has one or more fans, located at the top of the tower, that draw air upwards against the downward flow of water passing around the wooden decking or packing. Since the airflow is counter to the water flow, the coolest water at the bottom is in contact with the driest air while the warmest water at the top is in contact with the moist air, resulting in increased heat transfer efficiency.
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