spt29970
Contributor
Let me make clear what I was referring to in the previous post about the claims of Titaniium showing a stunning lack of understanding of the physics of heat transfer.
The various heat loss mechanisms of any body can be broken up into a series of mechanisms, some of which are relevant underwater and some of which are not.
radiation = blackbody radiation into an environment at a different temperature. In a thermos bottle this is important and can be reduced by metal reflectors, which is why an aluminized vacuum flask is better than a non aluminized one. Underwater this is so small as to be completely irrelvant
conduction = Heat loss through materials in direct contact. For diving, this is loss through the suit. The rubber of the neoprene is not a very good insulator. It is the air bubbles in the neoprene which are good insulators and serve to lower the overall conductivity. When the bubbles break over time a wetsuit loses its insulating properties. Similarly when you descend and the bubbles shrink due to pressure, the suit becomes a poorer insulator.
free convection. This is heat loss caused by the fact the heating a fluid causes it to expand. It becomes buoyant and rises, carrying heat along with it. Despite what they teach in the "Encyclopedia of Diving" free convection is actually a very small proportion of your heat loss since it is usually overwhelmed by forced convection.
forced convection. This is heat loss similar to free convection, but here the motion that causes warm fluid near your body to move is not its buoyancy, but by your motion or current. This is one of the reasons that on land you feel a lot colder when the wind blows than when it is still. Another form of forced convection is water that flushes in and our of the suit due to a poor fit or poor seals. The pumping action of gaps and folds cause warm water to exit the suit, only to be replaced by cold water.
The marketing hype of "Titanium" comes from the confusion that metalizing vacuum flasks makes a big difference in cryogenic applications, but for diving, radiation is so tiny that it is completely ignorable. The marketers either don't understand the physics, or they don't care because it "sounds good".
The various heat loss mechanisms of any body can be broken up into a series of mechanisms, some of which are relevant underwater and some of which are not.
radiation = blackbody radiation into an environment at a different temperature. In a thermos bottle this is important and can be reduced by metal reflectors, which is why an aluminized vacuum flask is better than a non aluminized one. Underwater this is so small as to be completely irrelvant
conduction = Heat loss through materials in direct contact. For diving, this is loss through the suit. The rubber of the neoprene is not a very good insulator. It is the air bubbles in the neoprene which are good insulators and serve to lower the overall conductivity. When the bubbles break over time a wetsuit loses its insulating properties. Similarly when you descend and the bubbles shrink due to pressure, the suit becomes a poorer insulator.
free convection. This is heat loss caused by the fact the heating a fluid causes it to expand. It becomes buoyant and rises, carrying heat along with it. Despite what they teach in the "Encyclopedia of Diving" free convection is actually a very small proportion of your heat loss since it is usually overwhelmed by forced convection.
forced convection. This is heat loss similar to free convection, but here the motion that causes warm fluid near your body to move is not its buoyancy, but by your motion or current. This is one of the reasons that on land you feel a lot colder when the wind blows than when it is still. Another form of forced convection is water that flushes in and our of the suit due to a poor fit or poor seals. The pumping action of gaps and folds cause warm water to exit the suit, only to be replaced by cold water.
The marketing hype of "Titanium" comes from the confusion that metalizing vacuum flasks makes a big difference in cryogenic applications, but for diving, radiation is so tiny that it is completely ignorable. The marketers either don't understand the physics, or they don't care because it "sounds good".
