Graphite Immersion Plate Heat Exchanger Fins
Graphite’s combination of corrosion resistance and thermal conductivity makes it an excellent material for heat exchangers. While individual graphite sheets display strong anisotropic thermal characteristics (since phonons propagate quickly along the tightly-bound planes, but are slower to travel from one plane to another), the amorphous graphite material used in heat exchangers “averages out” the anisotropic characteristics so that the thermal conductivity is essentially equal in all directions.
A key feature of an immersion plate heater is it’s compact size. While graphite is thermally conductive, it still requires a significant surface area to transfer heat efficiently. The surface area could be increased by make the plate heater very thin, and extend is height and width to fill the tank. This would compromise the strength of the immersion heater and eliminate a key feature, it’s compact size.
Fins and Grooves
To increase the surface area while retaining the compact size, fins or grooves are machined into the sides of the plate heater. The dimensions of the machined features are chosen so that the fins are strong and maintain mechanical integrity while increasing the surface area as much as possible. In practice, properly engineered grooves or fins increase the surface area by 100% over a smooth surface.