Article ID | Journal | Published Year | Pages | File Type |
---|---|---|---|---|
669174 | International Journal of Thermal Sciences | 2016 | 11 Pages |
Abstract
The present study describes a series of flow boiling experiments with R141b in coiled tubes conducted to investigate the local heat transfer enhancement mechanism of U-bends compared with bubbles growing in horizontal straight tubes. The study focuses on two-phase flows with boiling in U-bends of a vertical upward coiled tube of inner diameter 6 mm at mass fluxes of 120.94, 181.41 and 241.88 kg mâ2 sâ1 and heat fluxes between 6191 and 13 929 W mâ2. The experimental results show that the bubble growth rates in U-bends are 2-4 times faster than those in the downstream horizontal straight tube. The local heat transfer mechanism was analyzed using a transient CFD model with faster bubble growth rates predicted in a U-bend than in a horizontal straight tube. The heterogeneous effects of reheating and thermal non-equilibrium at the tube walls caused by the U-bend structure were found to play critical roles in the two-phase flow and heat transfer, as the main reason for local heat transfer enhancement in bubbly or intermittent flows.
Related Topics
Physical Sciences and Engineering
Chemical Engineering
Fluid Flow and Transfer Processes
Authors
M. Meng, X.F. Peng,