Fin-fan Heat Exchanger
A fin-fan (finned) is a type of heat exchanger that forces air over a set of coils to cool the process. It is also referred to as an air cooled heat exchanger. Fin-fan heat exchangers are generally used where a process system generates heat which must be removed, but for which there is no local use. An example is the radiator in your car. Air is forced over a bundle of finned tubes which dissipates heat generated by the engine.
Typically, an air-cooled exchanger consists of a finned-tube bundle with rectangular box headers on both ends of the tubes. These headers can be configured to make the exchanger to be of a single pass type or multi-pass. Cooling air is forced over the bundles by one or more fans. Usually, the air blows upwards through the horizontal tube bundle. The fans can be either forced or induced draft, depending on whether the air is pushed or pulled through the tube bundle. The space between the fan and the tube bundle is enclosed by a plenum chamber which forces the air across the bundles. The whole assembly is usually mounted on legs to facilitate air movement.
The fans are usually driven by electric motors. The speed of the fans are reduced by either V-belts, gearing or variable frequency drives. The fin-fan may have louvers on the outlet of the fan to direct air over or away from the tube bundles and to control the efficiency of the process.
Fin-Fan Controls
Typically each fin fan has a vibration switch to detect an imbalance in the mechanical unit and shut it down before it causes damage to the tubes or the support structure. Fan motors may be shut down independently or throttled if vibration becomes too high.
Temperature and pressure is usually monitored upstream and downstream of the fan to ensure the process is functioning properly. By measuring the differential pressure across the fin-fan, maintenance concerns can be addressed. For example, if the differential pressure is too high, the tubes may be plugged.
Fin-Fan Design Considerations
Air-cooled heat exchangers should be located so that the hot air emitted is not a hazard or an inconvenience to personnel or has an adverse affect on the operation of adjacent equipment.
Air-cooled heat exchangers should be at least 50ft (15m) horizontally from fired heaters, to minimize the possibility of circulation (and recirculation) of hot air.
Consider the possibility of failure of exchanger tubes releasing more combustible fluid into a fire. Be certain to leave enough paths of egress in the event of a catastrophic tube failure to allow safe exit.
Tags: Heat Exchanger