It’s important to reiterate that we use the term Logical Thinking to describe the logical examination of the complex issues that surround insulant performance at very low or cryogenic temperatures - a different approach than simply examining and comparing numbers advertised in datasheets, which are often measured at ambient conditions. In this 3-part series, we will also offer some lessons learned that can help a buyer or engineer improve the likelihood of an apples-to-apples comparison, otherwise made difficult by:
It may be helpful to glance over the first page of Part 1 since we strive to avoid including redundant information in this Part 2. In this second installment, we wrap up a few points on thermal conductivity (arguably the most important physical property of an insulant) by discussing interesting aspects of heat transfer, thermal conductivity across radial versus linear geometries, reasons for and impact of discontinuities in temperature and lambda gradients, and the importance of due diligence.
Heat transfer, for instance, is complex, and we discuss that mathematical modeling is likely problematic, and an empirical approach (lab measurement) is the optimal approach. The radial dimension section makes an important point that calculating lambda using radial geometry creates a better lambda yet is illusionary since it has nothing to do with the inherent properties on the insulant. Next, we venture into an exercise on logically thinking about the linearity/non-linearity of thermal gradients across the insulation system and extrapolated to the lambda gradients. You may find this short quiz interesting!
The conclusion is that decision-makers who have more understanding of the physics of the heat transfer across insulation could ask better questions of their suppliers and improve decision-making not only on insulation selection but also installation.
The third and final installment will delve deeper into physical properties such as water absorption, water vapor transmission, and strength as cryogenic temperatures are approached.
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Don’t forget to view INSULATION PERFORMANCE AT CRYOGENIC/COLD TEMPERATURES: Logical Thinking - Part 2.