Despite extensive Google time, it's proven difficult to uncover information to help determine the ideal tradeoff between insulation cost, thickness, and effectiveness. In this application, insulation is needed that will handle temperatures as high as 80°C, and a temperature differential as high as 110°C.

Heat loss occurs via a combination of conduction, convection, evaporation, and radiation. Radiation loss can be minimized through the use of surfaces with high reflectivity / low emissivity with adjoining air spaces. Air spaces, however, allow convective loss. Most insulation consists of material with many small air spaces - foam or fiberglass fall into this category.

Space constraints impose an upper limit of approximately 12" insulation thickness. Given this limitation, what is the most cost-effective approach? Alternating layers of aluminum foil and fiberglass? Foil faced polyisocyanurate insulation board? With air spaces between? Of what size?

In order to answer these questions, A test rig was developed. It consists of a one gallon paint can instrumented with calibrated thermistors. The paint can is insulated with various materials and insulation designs and filled with boiling water. The controller is set up to log thermocouple data, and the temperature drop is measured over time.

Questions:

• What materials can withstand the temperatures involved without degrading? (Note: epoxy dipped bead thermistors would appear to not be members of this group)
• How important is evaporation control? Would an oil layer reduce evaporative heat loss?
• What is the optimum air gap between low emissivity surfaces to reduce radiation loss without creating excessive convection loss?
• Would a layer of floating plastic balls reduce heat loss?