Analysis of flow structure of liquid metal pulsating cross flow in-line tube bundles with various pitch-to-diameter ratio

Abstract

In order to further improve the efficiency and safety of tube bundle heat exchangers, liquid metal cross flow tube bundles under pulsating inlet flow conditions are investigated in this paper. The simulation study is carried out using the k-kl-ω turbulence model, which has been validated by previous experimental data, for in-line tube bundles with different arrangements. The numerical studies were carried out for pulsating velocity amplitude of 0.5, frequency of 10, and Re of 20,000 with transverse and streamwise pitch-to-diameter ratios of 1.5, 1.65, and 1.8. The analysis of the circumferential pressure drop factor of the tube bundle reveals that the pulsating flow excites the secondary flow at the back side of the bundle, which strengthens the local flow field, while the increase in global pressure drop is more pronounced at a smaller pitch ratio. Enlarged figure of the local time-averaged flow field show the differential flow behaviors at different pitch ratios, further revealing the obvious asymmetric characteristics of the secondary flow. The local secondary flow time-averaged results show that the first three columns of secondary flow are enhanced more than three times as much as in normal flow. Finally, the time series of secondary flow is analyzed by using power spectral density, continuous wavelet transform, and combined with Gaussian multimodal decomposition to reveal the representative secondary flow change characteristics at the back side of the tube in the first three columns. Finally, the distribution map of vortex structure features under the simulation parameters of this paper is given.