FATE OF MERCURY IN THE ARCTIC Michael Evan ... - COGCI

Fate of Mercury in the Arctic 36
Based on experience gained at Barrow, the heating mantles lost too much heat, so further
improvement was made at NERI to the heating mantles prior to the Station Nord, 2002 campaign.
The improvements are specifically: an extra layer of insulation, an extra hard shell for
enhanced wind protection, silicone sealant to protect against water or melted snow and insulated
end caps to warm from the inlet onwards. The original heating mantle assembly was placed inside a
larger PVC pipe, allowing 5 cm spacing between sidewalls, giving an overall diameter of
approximately 9.6 cm. The space between the two shells was then filled with self-expanding
polyurethane foam thermal insulation. Upon drying, the insulation was cut, so that top and bottom
end caps will fit snugly. The inside of the top and bottom caps are filled with foam cut to fit the
inlet and outlet of the denuder. The heating mantle is sealed at each end with silicone, so that it is
watertight. Other shells than PVC may be used, for example, metal tubing. This work chose
thermally rated PVC since it was cost efficient.
The result is a self-regulating heating mantle capable of producing the heating required for an
efficient active coating temperature of 50 o C in the Arctic spring.
page 53.
The improved heating mantles are seen on the tower in the photo from Station Nord: Figure 5.,
Once the air in the heating cap is heated and the denuder is heated to equilibrium, there is no
heating gradient directly across the mantle wall to the denuder, as there is in heating mantles that
employs direct application of heating tape to the denuder walls, since the airspace functions as an
insulator, thus avoiding uneven heating and activation of the denuder coating, or over heating the
coating.
However, there is certainly a gradient and therefore expansion of air, as an air parcel travels
through the denuder and becomes warmer. This is a source of experimental error that we