Patent ID: 6854487

Claim:
A multiple spaced-apart wall fluid conduit enclosing a hollow interior for the flow of a fluid therein, comprising: a metal first conduit wall having a radially inner first surface enclosing the hollow interior and a radially outer second surface; and, a metal second conduit wall spaced apart radially outwardly from the first conduit wall and having a radially inner third surface spaced apart radially in juxtaposition with the outer second surface of the first wall to define a gap therebetween, wherein: the first conduit wall includes on the outer second surface a single layer first low emissivity metal coating, and the second conduit wall includes on the inner third surface a single layer second low emissivity metal coating; the first and second low emissivity coatings each having a coating emissivity of less than 0.2 and a coating thickness at least sufficient to provide the coating emissivity.