Air cooled oil coolers or heat exchangers, also known by various names in the industry viz. Plate Fin Oil Coolers, Fan Cooled Oil Coolers, Fin Fan Oilcoolers, Air Blast Oil Coolers, D cup Coolers, Air Oil Coolers, Fin Coolers etc. In these a draft of ambient air is used to remove heat from a fluid, usually oil. However thermic fluids, coolants, water glycol solutions are also commonly cooled using this type of oil coolers. Typically these consist of a fan, a heat exchanger, an outer structure and also some instrumentation like temperature gauge, temperature & pressure switches.
The heat exchanger design uses a number of rectangular tubes. These rectangular tubes are made by brazing together Aluminum alloy plates (also known as separator plates), sidebars & inside bars. The oil to be cooled flows in through an inlet header and is then distributed through these rectangular tubes.
Enclosed inside these rectangular tubes are fins called internal fins. The heat is transferred from the oil to these fins. Internal fins play a very important role in the heat dissipation process. For one there is larger surface area available for heat transfer and secondly the fins cause turbulence in the oil thereby resulting in greater transfer of heat from the oil to the internal fins. The heat is then conducted from the internal fins to the plates. Between each pair of plates are external fins and the heat is in turn transferred from the plates to the external fins by conduction. A draft of cool ambient air is forced through the external fins carrying away the heat.
The external fins also serve a dual purpose of creating turbulence in the air flow and providing a larger surface area, thereby resulting in greater heat transfer. This type of heat exchangers are often categorized as compact heat exchanger to emphasize their relatively high heat transfer surface area to volume ratio. The plate-fin heat exchangers are widely used in many industries, for their compact size and lightweight properties and their ability to facilitate heat transfer even when the temperature difference between the hot fluid and the cool fluid is small. The internal & external fins besides providing an extended surface area for heat transfer also serve to increase the structural integrity of the heat exchanger and allow it to withstand higher pressures & pressure fluctuations. The oil cooled in the rectangular tubes then collects in the outlet header and exits the heat exchanger.