A TUBE AND USE OF SAID TUBE

摘要

A metallic tube for heating a medium or subject outside thereof or inside it by transfer of heat energy through walls of the tube, in which heat is absorbed or emitted at least to a substantial degree by radiation on one or both of the inner and outer surfaces of the tube, is of a material forming a layer of essentially AI2O3 on the surfaces thereof when heated to at least approximately 75O0C. At least one of the external and the internal surface of the tube is coated by one of a metal, metal alloy and metal compound, which after oxidation forms a layer having an emissivity coefficient exceeding 0.7, or by a layer essentially consisting of a metal oxide which has an emissivity coefficient exceeding 0.7.