Investigation of Flow through a 2x2 PWR Rod Bundle: Effect of Twisted Tapes


Twisted-tape is one of the most important members of passive heat transfer augmentation techniques for forced convection in many applications. In this paper, a numerical investigation of the heat transfer, pressure drop and secondary flow under the normal operating conditions of the NuScale SMR reactor for sub-channel with and without twisted tape geometry are performed. 3D models for twisted tapes on 2 x 2 rod bundle inside spacer grid fitted was developed. Subsequently, a twisted tapes on 2 x 2 along the entire sub-channel, that spacer grid and the gap between spaces were evaluated through the comparison with no twist tapes and with several twist ratios (p/d = 4.2, 1.7 and 0.85). The results have revealed a strong effect of twist ratios on pressure drop and secondary flow (SF) increases with decreasing twist ratio. Moreover, the Nusselt number (Nu) is increased with Reynolds number (Re) and there is a significant improvement in the Nusselt number when a twisted tape is inserted into the entire sub-channel under the same Reynolds number. For p/d=0.85, heat transfer (Nu) enhancement of 25% and 101% was observed for twisted tapes inside spacer grid and the entire sub-channel respectively. Results showed that the pressure drop with twisted tapes inside spacer grid and the entire sub-channel are influenced by variation of twisted ratio. The highest pressure drop is achieved for the twist ratio of p/d =0.85 which is the lowest twist ratio in this study. Pressure drop showed an almost linear dependence on the twist ratios. Likewise, the secondary flow is observed to be much more pronounced when the entire channel length contained the twisted tape. Interestingly, SF seems to be peaking at the exit point of the spacer grid where the twisted tape ends. SF seems along the entire sub-channel when the entire length contained the tape. The highest SF is achieved for the twisted ratio (p/d =0.85) which is the lowest twist ratio in this study by about SF=.0.16.

Meeting Name

International Topical Meeting on Advances in Thermal Hydraulics, ATH 2018 (2018: Nov. 11-15, Orlando, FL)


Nuclear Engineering and Radiation Science


The first author of this paper was supported by King Abdulaziz City for Science and Technology and would like to express his gratitude for the financial help enabling him to complete this work.

Keywords and Phrases

Drops; Hydraulics; Nusselt number; Pressure drop; Reynolds number; Secondary flow; Small nuclear reactors; Channel length; Linear dependence; Normal operating conditions; Numerical investigations; Passive heat transfer augmentations; Rod bundles; Twist ratios; Twisted tapes; Pressurized water reactors

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Article - Conference proceedings

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© 2018 American Nuclear Society (ANS), All rights reserved.

Publication Date

01 Nov 2018