Ice as pipe insulation???

Dr Koolaide

OK so this is a problem me and some co-workers have been discussing. We have refrigeration pipelines that are about 15°F. It is very hot and humid here (assume about 90°F and 75% humidity) so condensation often forms on the pipes and freezes. Thinking of it as a pure heat transfer problem (like you would typically do in an undergraduate heat transfer class) I would guess the ice would offer a miniscule amount of "insulation". However, I could also see looking at it as a part of the equilibrium with the air and it not actually changing anything from a heat transfer perspective.

Any thoughts? Suggestions?

FYI: The thermal conductivity of ice is about 2.3 W/m*K and insulation is typically about 0.04 W/m*K

pa5tabear

Yes, I'm guessing it would offer insulation. The outside layer of the ice will be at 32 F, so it should slow down the heat transfer rate.

Assuming the temperatures and ice thickness are constant, this would be a fairly simple heat transfer problem.

If there were no ice, you would be concerned only with convection of air. This could be either natural or forced convection (is the air flowing quickly?).

In the ice case, you will have to take a logarithmic average to calculate an "overall" heat transfer coefficient.

You could calculate the heat transfer rates in each if you knew the air "velocity", or if it's just calm air.

NascentOxygen

Ice can be an unwelcome insulator on pipes. The "old fashioned" domestic fridges had bare coils visible at the top of the fridge space. Over a period of a few weeks these became covered with ice (humidity that had sublimed) and this layer of ice hindered the flow of cold from the coils, leaving the fridge contents warmer despite making the compressor work even harder. The fridge had to be turned off and the ice melted off the coils periodically or it would become a solid mass of ice compromising the fridge's operation.

Of course, ice still sublimes onto the coldest surfaces in today's fridges, but the problem is handled with automatic defrost and better door seals.