The Trans-Alaska Pipeline
How They Work
Calculations & Examples
Review of Design and Effectiveness

How They Work

The heat pipes along TAPS, also known as thermosiphons, work as freezers for the ground, without requiring a power source. They operator purely off temperature differential between the air and ground the are buried in. Filled with anhydrous ammonia, the heat pipes remove heat from ground in the winter, effectively super-freezing it, which prevents it from thawing during the warmer summer months. The following diagram explains the general process taking place within a heat pipe.

As seen in the above image, the heat from the ground warms the working fluid (anhydrous ammonia) which then vaporizes and rises to the top of the heat pipe, where the cooling fins remove the heat to the surrounding air and the ammonia condenses, falling back to the bottom of the tube, where the cycle repeats. This heat transfer will only work when the air is colder than the ground. During summer, when the air is warmer than the ground, the ammonia sits in liquid form at the bottom of the tube and nothing happens. If the heat pipe didn't effectively super-freeze the ground during the past winter, risk exists for the ground supporting the VSM to melt, which can lead to shifting of the pipeline. To see the physics behind this heat transfer, click here.