Two-phase flow and heat transfer characteristics of tetra-n-butyl ammonium bromide clathrate hydrate slurry in horizontal 90° elbow pipe and U-pipe

Abstract

Tetra-n-butyl ammonium bromide (TBAB) clathrate hydrate slurry (CHS) is commonly used as a cold storage medium and secondary refrigerant in the secondary-loop refrigeration. In the present study, the solid–liquid two-phase flow and heat transfer characteristics of TBAB CHS in horizontal 90° elbow pipe and U-pipe were numerically investigated using Eulerian–Eulerian multiphase model coupled with the interphase heat and mass transfer model. In order to validate the numerical models, the numerical pressure drops and wall temperatures as well as heat transfer coefficients were compared with the experimental evidences. After the model validation, the numerical models were firstly adopted to investigate the isothermal flow characteristics of TBAB CHS in the horizontal 90° elbow pipe and U-pipe. The numerical results showed that the primary flow was accelerated near the inner wall of the bending section and a secondary flow caused by the centrifugal force occurred on the cross-section of bending section, which made the solid particles agglomerate to the outer wall of the bending section. Meanwhile, vortex flow occurred beyond 45° of the bending section of 90° elbow pipe due to the boundary layer separation. Thereafter, the flow and heat transfer characteristics of TBAB CHS in horizontal 90° elbow pipe and U-pipe were also numerically investigated at inlet velocity of 1.0m/s and inlet solid volume fraction of 10.0vol%. The solid volume fraction distribution and local heat transfer coefficient were obtained, which indicated that the solid particles were melted more easily in the vortex region of the 90° elbow pipe and the inner side of U-pipe, resulting from the heat transfer enhancement by the secondary flow.