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Analysis of Post-Dryout Heat Transfer in Heated Channels with Spacers
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.ORCID iD: 0000-0001-5595-1952
KTH, School of Engineering Sciences (SCI), Physics, Reactor Technology.
2006 (English)In: Proceedings of the 13th International Heat Transfer Conference, 2006Conference paper (Refereed)
Abstract [en]

Post-dryout heat transfer plays an important role in safe and economical operations of Light Water Reactors (LWR). This type of heat transfer is avoided under normal operational conditions of nuclear reactors; however, it may occur in emergency situations. To estimate the risk of clad damages due to increase of temperature associated with the occurrence of post-dryout, it is necessary to properly model heat transfer conditions in such situations. Present paper contains results of measurements performed in a high-pressure thermal hydraulic loop at the Reactor Technology Division, Royal Institute of Technology, Stockholm, Sweden. Post-dryout heat transfer was investigated in an annular test section with inner and outer diameters equal to 10 and 21.1 mm, respectively, and heated length equal to 3650 mm. Seven spacers with typical BWR design were located along the test section to keep the heated rod at the centre of the heated tube. Surface temperatures of both inner and outer wall were measured by several thermocouples installed at various locations along the test section. Distributions of wall temperatures were measured for mass flux in a range from 500 to 2000 kg m-2 s-1, inlet subcooling 10 and 40 K, wall heat flux from 480 to 1380 kW m-2 and pressure 7 MPa. The experiments revealed that spacers have a very strong influence on post-dryout heat transfer and very effectively reduce the heated wall temperatures just downstream of their locations. Only for very high powers the dryout patches could cover the whole distance between two neighbouring spacers. Under moderate powers such dryout patches were limited to a close distance to the downstream spacer, where the influence of the upstream spacer already vanished. The influence of various parameters on heat transfer downstream of spacer was investigated. It was concluded that heat transfer enhancement due to spacers is largely under-predicted for flows with relatively low quality. For such flows the effect of droplets impinging heated walls is significant and must properly be taken into account. Clearly, more work is needed to improve the over-all predictability of post-dryout heat transfer in heated channels with spacers.

Place, publisher, year, edition, pages
National Category
Energy Engineering
Research subject
SRA - Energy
URN: urn:nbn:se:kth:diva-80429OAI: diva2:496322
IHTC-13. Sydney, Australia. 13-18 August 2006
QC 20120529Available from: 2012-02-09 Created: 2012-02-09 Last updated: 2012-05-29Bibliographically approved

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