Insulation: The Reduction of ‘A’ and ‘B’ Heat In-flows
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All heat inflows are reduced as far as possible by using the correct insulations.
This chapter is concerned with identifying all the A and B heat inflows, and how these can be reduced individually, or collectively, with suitable insulations.
The first type, suitable for large tanks, is the gas-purged insulations such as perlite powder, fibreglass, plastic foams and rock wool. It is important that gas purged insulations totally fill the insulation space between inner and outer containers, with no holes or gaps. Any unfilled space will allow strong convection cells of purge gas to thermally short circuit the insulation. Ingress of water must also be excluded, because the water will freeze to ice, which has a high k value compared with the insulation.
The second type, suitable for smaller tanks, is evacuated insulations. The latest versions are composed of multi-layer reflective insulation MLI with extremely low k values, provided the vacuum is maintained.
KeywordsBoundary Layer Flow Plastic Foam Cryogenic System Heat Inflow Insulation Space
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