An extended surface consisting of studs resistance-welded to
in. tubes was hurriedly conceived for naval economizers during the war. Minor modifications have met the needs of nuclear heat exchangers and modern merchant and fighting ships. Its use in many well-known fleets is first enumerated followed by a discussion of the different requirements of nuclear-power plant. Sixteen different designs of extended surface were tested in clean conditions, some being repeated on wider spacings, staggered and in-line. Each test series is analysed by means of simplified heat-transfer and draught-loss formulae enabling interpolation to design various tube banks. The various surfaces are compared by calculating the characteristic dimensions of heat exchangers with identical performance. Finally the laboratory tests are compared with the trial results of economizers on highly rated boilers.
