Mist/steam cooling in a 180-degree tube bend

An experimental study on mist/steam cooling in a highly heated horizontal 1 80-deg tube bend has been performed. The mist/steam mixture is obtained by blending fine water droplets (3 similar to 15 microns) with the saturated s team at 1.5 bar. The test section consists of a thin wall (similar to0.9 mm ), welded, circular, stainless steel 180-deg tube (20-mm inside diameter) w ith a straight section downstream of the curved section, and is heated dire ctly by a DC power supply. The experiment was conducted with steam Reynolds numbers ranging from 10,000 to 35,000, wall superheat up to 300 degreesC, and droplet to steam mass ratio at about 1 similar to2 percent. The results show that the heat transfer performance of steam can be significantly impr oved by adding mist into the main flow. The highest enhancement occurs at a location about 45-deg downstream of the inlet of the test section. General ly, only a small number of droplets can survive the 180-deg turn and be pre sent in the downstream straight section, as observed by a phase Doppler par ticle analyzer (PDPA) system. The overall cooling enhancement of the mist/s team flow ranges from 40 percent to 300 percent. It increases as the main s team flow increases, bur decreases as the wall heat flux increases.