Finned Tube----Air Cooled Heat Exchanger
1.0 Introduction to Air Cooled Heat Exchanger
This kind of heat exchanger are used in petrochemical and refineries to utilize the atmospheric air to cool the hydrocarbon, process and utility fluids by means of indirect heat transfer from fluid (within the tube) to be cooled by air being circulated by means of forces / induced draft fan. In order to increase the heat transfer area, fins are also attached to the periphery of tubes. These heat exchangers are generally designed, inspected and tested as per API661 standard.
These exchangers are similar to the radiator of a motor car. The air cooled heat exchangers are mainly used where the heat load is very high and conventional heat exchanger becomes extremely big with large water requirement. By using air cooled heat exchanger, water requirement reduces drastically and cooling tower size comes down. The air coolers are of very large size as the heat transfer co-efficient with air is very low. Due to the large size, they are mounted on top of the pipe rack to save space.
2.0 Types of Air Cooled Heat Exchanger
There are three types of air cooled heat exchanger:
a) Forces Draft
b) Induced Draft
c) Natural Draft (used for applications like transformer oil cooling)
The outline sketch and components are as identified in figure 1A & B.
3.0 Definitions used for Air Cooled Heat Exchanger
The general terms used for air cooled heat exchangers are defined below:
a) Bank
A bank is one or more bays including one or more items arranged on a continuous structure.
b) Bare tube surface
Total area of the outside surface of the tubes in sq. meter.
c) Bay
A bay is one or more tube bundles serviced by two or more fans and that include structure, plenum and other attendant equipment.
d) Finned Surface
The finned surface of a tube is the total area of the outside surface of fins exposed to air.
e) Forced Draft exchanger
This is the one designed with the tube bundles located in the discharge side of the fan.
f) Induced Draft exchanger
This is the one designed with the tube bundles located on the suction side of the fan.
g) Tube bundle
This is an assembly of headers, tubes and frames.