Nanoparticles Found in Superheated Steam: a Quantitative Analysis of Possible Heterogeneous Condensation Nuclei
Abstrakt
The number of nanoparticles available as nucleation sites for heterogeneous nucleation of droplets in the steam turbine is an important parameter for the modelling of the non-equilibrium condensation process. In this paper, measurements of particles of sizes down to 3 nm are reported.
Superheated steam was sampled at Power Plant Prunéřov II using a special sampling device avoiding sample condensation. Samples were taken at two pressure and temperature levels: 0.133 MPa, 174 oC and 0.27 MPa, 250 oC.
The number of particles was determined as 1.5 x 109 per kg of steam at the lower pressure and as 2.5 x 109 at the higher pressure. A diffusion battery was used to determine the size distribution of particles instead of the previously used scanning mobility particle sizer.
The size distribution was obtained by deconvolution of particle concentrations obtained for various numbers of screens. Compared to the scanning mobility particle sizer results, the diffusion battery revealed a smaller geometric mean particle size.