 heat flow composit slab heat flow composit slab paper present solut heat flow problem composit wall heat transfer condit typic uncool rocket engin wall analyt express form fourier sum temperatur distribut composit wall consist inner refractori medium outer metal medium newtonian heat transfer medium neglig heat transfer second medium exterior express base plane parallel composit slab repres model thin cylindr wall thick-to-radiu ratio exceed 0 2 gener composit slab simplifi limit case thin refractori shield thick shield medium thick refractori shield thin shield medium 