Extended Surface Heat Transfer  (Fins, Heat Sinks, etc.)

Air-Cooled Franklin Engine

The cooling fins on the 1910 4-cylinder, air-cooled Franklin automobile engine seen here run longitudinally along the cylinders:

More modern air-cooled aircraft engine designs use fin configurations that would be described as radial:

Perhaps the Franklin engineers didn’t want to deal with Bessel functions!  Franklin photo courtesy of B. Hosticka.

Air-Cooled Radial Aircraft Engine

The Curtiss-Wright R-3350 Turbo-Compound Engine seen here 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 from six cylinders was directed to each of the three turbines.  The latter extracted additional energy from the exhaust.

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.

Heat Sink in Rolls-Royce AE 3007 Turbofan Bypass Duct. 

 

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.   You might find such a configuration in your backyard.

Extended Surface Heat Transfer in Automobile Cabin Air Heater 

By my estimate there is some 160 times as much surface area on the air side as there is on the liquid side (inside of the pipes).

 

Extended Surface Heat Transfer in LED Light Bulbs

LED bulbs are not supposed to be operated at elevated temperatures as in a closed chandelier. This one has fins integrated into its structure:

 

 

Extended Surface Heat Transfer in Computers

 

 

It took computer engineers a while to catch up with the technologies used in air-cooled aircraft engines of nearly a century ago.   In particular, air would just as soon bypass the heat sink, so you must force it to take the path you want by providing “cowling.”

The Trans-Alaska Pipeline Passive Cooling System

Extended surface heat transfer devices (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 TAP).

Some 380 miles of pipeline in the north are insulated and buried.  A few miles have active refrigeration; most do not.  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.  It is there that you see the aluminum fins.

 

Vertical Support Members/Heat Pipes

There are two heat pipes for each vertical support member. These heat pipes 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.  (Note that these heat pipes are actually Perkins tubes, a type of thermosiphon.  They use gravity rather than capillary action for the return flow of the condensate to the evaporator end.)

The  Alyeska website shows more technical details about the TAP.    In addition, An Introduction to Heat Pipes: Modeling, Testing and Applications, by G.P. Peterson, Wiley (1994) includes much more about heat pipes, including Perkins tubes.  Recent upgrades to the TAP include replacing the ammonia in many pipes with carbon dioxide. 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.  The TAP became operational in 1977.

Reference

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.