Abstract
The problem of thermal protection is explored for two idiosyncratic reactive systems, namely a sacrificial heat-sink material and an intumescent system where a dynamically evolving insulation layer is produced from an initially thin coating. Relatively simple mathematical models of both systems are proposed that encompass the important physical characteristics of each situation and these models are analysed using a mixture of numerical and analytical techniques. Important dimensionless parameter groups are identified and domains of parameter space where thermal performance is particularly good- or particularly bad- are identified.
Highlights
Despite the advances in modelling various important methods of thermal protection, in particular reactive systems such as intumescent coatings or heat sink additives, there has been little investigation into the important engineering parameters that should be optimised for best performance
For small pores it is possible to show that radiation heat transfer rate increases with pore size, suggesting that pore size should be kept as small as possible
If the goal of the thermal protection is maximise failure time of a substrate, it transpires that λtot/(1 − φ) should be as small as possible, where λtot is the total effective thermal conductivity including radiation augmentation
Summary
Despite the advances in modelling various important methods of thermal protection, in particular reactive systems such as intumescent coatings or heat sink additives, there has been little investigation into the important engineering parameters that should be optimised for best performance. Important parameter groups are identified for two important scenarios and their role in thermal protection is analysed Both situations involve the use of a reactive component either as a heat sink or as a means of Materials 2015, 8 producing a porous insulation layer and, as we shall see, the analysis yields interesting insight into the significant dynamics for each case. A simple dynamically evolving insulation layer is analysed where a reaction is assumed to occur in a thin coating that produces a thick insulating layer In this case the rate of heat transfer to the unexposed surface is governed by a balance between the rate at which expansion occurs and the rate at which heat is added to the system
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