The correlations were presented to calculate the Nusselt numbers in terms of Rayleigh numbers in these studies, which are in the condition of infinite space. Studies of the steady state free convection heat transfer from horizontal isothermal cylinders with low Rayleigh numbers were presented, such as Sadeghipour and Asheghi (1994) and Tokanai et al. There are some researches focused on the heat transfer of the tube bundle and the single tube under different conditions, respectively. The natural convective heat transfer characteristics of the tube bundles are very different from a single rod. The disturbance and the pre-heating effects of the lower tube will enhance and weaken the heat transfer ability of the upper tube bundles, respectively. When the temperature of cooling water is low, the flow in the tube bundles is single-phase natural convection. Therefore, the natural convection heat transfer of the fuel assembly in the carrier is different from the natural convection in an infinite space or in enclosure. This would result to a weakened heat exchange. However, the fuel assembly is located in the carrier in the transfer tube, which is a semi-closed rectangular cavity. The core of the cooling problem of the fuel assembly in the transfer channel is the natural convection heat transfer of the horizontal rod bundle. The fuel assembly usually employs an arrangement of 17 × 17. It is a key factor affecting the cladding temperature of the fuel assembly. The natural convection in the cross section is more complicated compared with the longitudinal flow along the transfer tube. The flow of cooling water in the cross section of the fuel assembly in the transfer tube is shown in Figure 1B. In the previous analysis, the flow field in the transfer tube can be decomposed into two directions: longitudinal flow along the transfer tube and crosswise flow in the cross section of the transfer tube, respectively ( Xi-dao et al., 2018). The water flows back to the pool through the upper part of the tube. The cooling water is heated in the fuel assembly and then flows out of the assembly through the top holes of the carrier due to the buoyancy. The water flows into the fuel assembly through the circular holes on both sides of the carrier. The cold water from the pool flows from the lower part of the tube to the fuel assembly. The driving force of natural circulation in the transfer tube comes from the density difference of hot and cold fluids.
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |