Production, Characterization and Application of Meso-, Micro- and Nano-Scaled Surface Structured Devices for Boilers and Heat Exchangers

In this paper we report on the investigations of 48 tubular and 3 planar meso-, micro- and nano-scaled surface structured devices for boilers and heat exchangers made of steel, copper and brass.The tubular structured components are object of protective right in terms of industrial power tube (ip tube). Hexagonal types with sinusoidal structures and roughness values in the order of bts/dHyd = 0.3 used for heating of a fluid by a fluid proved to have a heat transmittance of k = 1737 W · m−2 · K−1 and to be increased by 47 % compared to the corresponding value of a smooth tube k = 1182 W · m−2 · K−1.Dodecahedronal closed structured tubes with smaller roughness of bts/dHyd = 0.1 used for falling film evaporation showed a heat transmittance of k = 5130 W · m−2 · K−1 corresponding to an increase by 19 % depending on the Reynolds number Re between 7100 and 17600.Types of micro-structured tubes with 1000000 straight pins per square centimeter investigated in boiling experiments with Solkatherm SDS 36 at 0.7 bar appeared to have a decreased temperature excursion by 21 %, while there is a 25 % greater boiling resistance at low heat fluxes of about 25 W.Steam condensation experiments were performed using copper tubes fabricated both with meso-scaled structures and 1000 straight pins per square centimeter. At a subcooling temperature of ΔT = 60 K at 1.1 bar the heat flux density proved to be increased by 340 % to a value of k = 420 kW · m−2 · K−1 compared to the conventional component. In addition the formation of droplets with a diameter of 0.003 m was observed. The numerical calculation of the local heat transfer coefficient at the interior wall resulted in a value of αi = 11.4 kW · m−2 · K−1. Micro-scaled tubular devices with 3.3 million crossed pins per square centimeter made of copper were investigated with respect to heterogeneous catalysis of carbon monoxide under oxidizing conditions at 478 K and 1 bar. The achieved yield measured by CO conversion rate was equal to the unit value with a delay time of 17000 s due to an initial oxygen layer at the surface.Prototypic air cooled hot gas coolers were developed, constructed and evaluated, configurated with steel tubes and a small number of conical structures with a roughness of bts/dHyd = 0.01–0.03. By experiments using a biomass gasification test facility the heat transmittance of one cooler model proved to be increased by 22 % to a value of k = 11 W · m−2 · K−1. The corresponding pressure loss was so small that the effectivity of the applied measures to enhance heat transfer had a value of about 10 %. Moreover the formation of deposits on the side of the raw gas was found to be suppressed by 40 % to a fouling rate of 1.1 Mas.-% of the initial freight.Copyright © 2013 by ASME