Miscelaneous Notes NOTE 1-If the preceding pages have made sense, you have probably realized the primary advantage of the two phase thermosyphon over the single phase thermosyphon. It’s like this-It requires an appreciable amount of heat transfer to bring a substance (such as the working fluid) through a phase change. Consequently, the use of a two phase process is much more efficient in removing heat from the ground. Said in another way, the single phase heat transfer process removes the heat required to change the fluid temperature, but “misses out” on the opportunity to remove the heat required to initiate a phase change. It’s as simple as that. NOTE 2-Some materials utilized as a working fluid have been propane, ammonia, freon, butane, and carbon dioxide. NOTE 3-When selecting a working fluid special attention must be paid to the toxicity, flammability, and overall health hazard it presents. The very misadventures of a pipe buried beneath a road in Alaska presents the opportunity for pipe rupture and the release of the fluid into the environment. Propane is flammable. Freon is toxic to all living things. The engineer must consider health hazards first and foremost when choosing a fluid. NOTE 4-Carbon dioxide appears to be a desirable and effective working fluid. NOTE 5-In some circumstances the fluid may react chemically with the thermosyphon tube material in such a way that a gas is produced. The undesirable effects of this gas would be to accumulate in the top of the tube (near the cooling fins) in a pocket of stagnation. This undesirable gas would be lighter than the vaporized working fluid and thus would disrupt or totally stop the heat flow process. This must be considered in the fluid selection. NOTE 6-Thermosyphons are not just used to stabilize road embankments. They have been used successfully to protect concrete building foundations, telephone poles, and other engineering ground protrusions. Proceed to a thermosyphon photo gallery