TY - JOUR
T1 - LDA measurements of coherent flow structures and cross-flow across the gap of a compound channel with two half-rods
AU - Bertocchi, F.
AU - Rohde, M.
AU - Kloosterman, J. L.
PY - 2018
Y1 - 2018
N2 - The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work investigates the flow between two curved surfaces, representing the gap between two adjacent fuel rods. The aim is to investigate the presence of the aforementioned structures and to provide, as partners in the EU SESAME project, an experimental benchmark for numerical validation to reproduce the thermal hydraulics of Gen-IV LMFRs. The work investigates also the applicability of Fluorinated Ethylene Propylene (FEP) as Refractive Index Matching (RIM) material for optical measurements. The experiments are conducted on two half-rods of 15 mm diameter opposing each other inside a Perspex box with Laser Doppler Anemometry (LDA). Different channel Reynolds numbers between Re = 600 and Re = 30,000 are considered for each P/D (pitch-to-diameter ratio). For high Re, the stream wise velocity root mean square vrms between the two half rods is higher near the walls, similar to common channel flow. As Re decreases, however, an additional central peak in vrms appears at the gap centre, away from the walls. The peak becomes clearer at lower P/D ratios and it also occurs at higher flow rates. Periodical behaviour of the span wise velocity across the gap is revealed by the frequency spectrum and the frequency varies with P/D and decreases with Re. The study of the stream wise velocity component reveals that the structures become longer with decreasing Re. As Re increases, these structures are carried along the flow closer to the gap centre, whereas at low flow rates they are spread over a wider region. This becomes even clearer with smaller gaps.
AB - The enhancement of heat transfer from fuel rods to coolant of a Liquid Metal Fast Reactor (LMFR) decreases the fuel temperature and, thus, improves the safety margin of the reactor. One of the mechanisms that increases heat transfer consists of large coherent structures that can occur across the gap between adjacent rods. This work investigates the flow between two curved surfaces, representing the gap between two adjacent fuel rods. The aim is to investigate the presence of the aforementioned structures and to provide, as partners in the EU SESAME project, an experimental benchmark for numerical validation to reproduce the thermal hydraulics of Gen-IV LMFRs. The work investigates also the applicability of Fluorinated Ethylene Propylene (FEP) as Refractive Index Matching (RIM) material for optical measurements. The experiments are conducted on two half-rods of 15 mm diameter opposing each other inside a Perspex box with Laser Doppler Anemometry (LDA). Different channel Reynolds numbers between Re = 600 and Re = 30,000 are considered for each P/D (pitch-to-diameter ratio). For high Re, the stream wise velocity root mean square vrms between the two half rods is higher near the walls, similar to common channel flow. As Re decreases, however, an additional central peak in vrms appears at the gap centre, away from the walls. The peak becomes clearer at lower P/D ratios and it also occurs at higher flow rates. Periodical behaviour of the span wise velocity across the gap is revealed by the frequency spectrum and the frequency varies with P/D and decreases with Re. The study of the stream wise velocity component reveals that the structures become longer with decreasing Re. As Re increases, these structures are carried along the flow closer to the gap centre, whereas at low flow rates they are spread over a wider region. This becomes even clearer with smaller gaps.
KW - Coherent structures
KW - Cross-flow
KW - Laser Doppler Anemometry
KW - Rod bundle
UR - http://www.scopus.com/inward/record.url?scp=85032937789&partnerID=8YFLogxK
UR - http://resolver.tudelft.nl/uuid:e810d4f3-c4dd-46f6-b305-59e83001cd3c
U2 - 10.1016/j.nucengdes.2017.10.023
DO - 10.1016/j.nucengdes.2017.10.023
M3 - Article
AN - SCOPUS:85032937789
SN - 0029-5493
VL - 326
SP - 17
EP - 30
JO - Nuclear Engineering and Design
JF - Nuclear Engineering and Design
ER -