A frost spot is observed on a 1 million capacity LNG tank with a double wall containment tank that has a 5-inch thick perlite insulation between the inner and outer tanks. We want to know the thickness of the frost spot and then determine the metal temperature beneath the ice spot. Ambient temperatures in this region range from 30°F to 95°F. No ice formation is noticed on a hot day. Also, we see that sun rays hit the frost spot directly. Do we have to consider irradiance?
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Jim Grant Forum Moderator 118 Posts
Re: Whats Causing The Frost Spot?6 February 2009 at 1:29pmThe frost spot will occur most likely at the vapor/liquid interface where evaporation is taking place inside the vessel. The pressure inside the vessel will determine the saturation temperature and ice will only form when the saturation temperature is significantly below 32°F, especially if there is 5 inches of perlite insulation. If the insulation has gotten wet before then it can be worse than no insulation at all and the frost spots may persist where the insulation has been damaged/wet. Solar radiation effects must be taken into account when determining the energy balance for the tank.