Flow regime classification and transition of flow boiling through porous channel

A visual experiment was carried out on the flow regimes of the porous channels in the spherical fuel element nuclear reactor. Boiling two-phase flow in porous channels composed of particles with diameters of 4 mm, 6 mm and 8 mm was conducted respectively, and four different flow regimes occur within the experimental parameter range: bubbly flow, bubbly-slug flow, slug flow and slug-annular flow. The effects of mass flux, heat flux and particle diameter on the flow regimes were concluded. Bubbles deform, coalesce and break up more frequently, increase and enlarge with the increase of heat flux. The size and number of the bubbles will decrease with the increase of the mass flux as well as the decrease of particle diameter. At higher mass flux, a higher heat flux is required to bring about the same flow regime that occurs at lower mass flux, with particles of smaller diameter, a higher heat flux is required to bring about the same flow regime as that of particles of larger diameter. The flow regime map and flow regime transitional void fractions were proposed by modifying the Tung/Dhir model.