Extended Surface Heat Transfer

(Fins, Heat Sinks, etc.)

Air-Cooled Franklin Engine

The cooling fins on this 1910 4-cylinder, air-cooled Franklin automobile engine run longitudinally along the cylinders, not radially as in more modern air-cooled cylinder designs. Perhaps the Franklin engineers didn’t want to deal with Bessel functions! Photo courtesy of B. Hosticka.

Air-Cooled Radial Aircraft Engine

The Curtiss-Wright R-3350 Turbo-Compound Engine had 5850 ft² (543 m²) of fin surface area to help get rid of waste heat! The silver-colored device at the left is one of the three Power Recovery Turbines (PRT). The exhaust streams from six cylinders were directed to each of the three turbines, which extracted additional energy. Jim Buckel took this photo at the Sun & Fun Museum in Lakeland, Florida. The alternative to air cooling for a reciprocating aircraft engine is liquid cooling. Click here for commentary and photos of the biggest reciprocating aircraft engine every built. It was liquid-cooled.

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Air-Cooled Rotary Aircraft Engine

The fins on the two 80 hp Le Rhone 9C rotary engines powering this French Caudron G.4 World War I light bomber and reconnaissance aircraft are much less dramatic than those on the R-3350 above. They didn’t need to be. In a rotary engine (as opposed to a radial), the crankshaft is stationary and the rest of the engine rotates at the same speed as the propeller! With such high air velocities and resulting convection coefficients, long fins were not needed to dissipate the heat.

Air-Cooled Motorcycle Engine

If you would like to include radiative as well as convective heat transfer in your analysis of the extended surface heat transfer from this 1.45 liter air-cooled engine, note that the fin sides are a black, matte finish, while the fin tips are highly polished and reflective! Looks great!

Bristle-Fin Surface on Condenser Tubes

Bristle fins applied to the outside surface of these condenser tubes greatly increase the surface area exposed to ambient air.

Extended Surface Heat Transfer in Computers

Pentium 3 processor and attached heat sink

Pentium 4 processor (under the aluminum heat sink) with (green) cooling air shroud in place

Pentium 4 with cooling shroud raised to show heat sink and fan drawing air through it.

The Trans-Alaska Pipeline Passive Cooling System

Extended surface heat transfer devices (cooling fins) are very prominent at the condenser end of the heat pipes that are part of the vertical support members along the Trans-Alaska Pipeline. Some 380 miles of pipeline in the north are insulated and buried, a few miles with active refrigeration, most without. Further south, where the heat generated overcoming fluid friction in the pipeline could cause thawing of the permafrost and possible structural damage to the pipeline, the pipeline is elevated on vertical support members. There are two heat pipes for each vertical support member. The heat pipes (actually they are Perkins tubes, a type of thermosyphon, because they use gravity rather than capillary action in a wick for the return flow of the condensate to the evaporator end) are designed so that during the winter they remove as much heat as possible from the area around the base of the VSM’s. During the summer, the working fluid (anhydrous ammonia) sits idle at the bottom of the tube. Essentially the heat pipe acts as a thermal “diode” actively promoting heat transfer upward in the winter and inhibiting downward heat transfer in the summer. The idea is to chill the permafrost so thoroughly during the winter that it will remain solid through the following summer. The winter and summer operation of the heat pipes is shown here in schematic form. More technical details about the TAP may be found at the Alyeska website and more about heat pipes may be found in An Introduction to Heat Pipes: Modeling, Testing and Applications, by G.P. Peterson, Wiley (1994). Recent upgrades in which the ammonia in many pipes has been replaced with carbon dioxide are reported here. This change has been made because of the build-up over time of non-condensable gases at the top end of the pipes, which decrease the area available for condensation .

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The stegosaurus graphic above is from: Farlow, J.O., Thompson, C.V., and Rosner, D.E., “Plates of the Dinosaur Stegosaurus: Forced Convection Heat Loss Fins?” Science, 192, No. 4244, pp. 1123-25, June 1976.

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