Effect of three-orifice baffles orientation on the flow and thermal-hydraulic performance: experimental analysis for net and oscillatory flows

J. Muñoz-Cámara; D. Crespí-Llorens; J. P. Solano; P. G. Vicente

doi:10.1016/j.applthermaleng.2023.121566

paper

Effect of three-orifice baffles orientation on the flow and thermal-hydraulic performance: experimental analysis for net and oscillatory flows

arXiv:2412.15682 · doi:10.1016/j.applthermaleng.2023.121566

Abstract

Three-orifice baffles equally spaced along a circular tube are investigated as a means for heat transfer enhancement under net, oscillatory and compound flows. An unprecedented, systematic analysis of the relative orientation of consecutive baffles -- aligned or opposed -- is accomplished to assess the changes induced on the flow structure and their impact on the thermal-hydraulic performance. The results cover the Nusselt number, the net and oscillatory friction factors and the instantaneous velocity fields using PIV in an experimental campaign with a 32 mm tube diameter. The study is conducted in the range of net Reynolds numbers $50 < R e_{n} < 1000$ and oscillatory Reynolds numbers $0 < R e_{osc} < 750$ , for a dimensionless amplitude $x_{0} / D = 0.5$ and $P r = 65$ . In absence of oscillatory flow, opposed baffles advance the transition to turbulence from $R e_{n} = 100$ to $50$ , increasing the net friction factor (40 %) for $R e_{n} > 50$ and the Nusselt number (maximum of 27 %) for $R e_{n} < 150$ . When an oscillatory flow is applied, augmentations caused by opposed baffles are only observed for $R e_{n} < 150$ and $R e_{osc} < 150$ . Above $R e_{n}$ , $R e_{osc} > 150$ , opposed baffles are not recommended for the promotion of heat transfer, owing to friction penalties. However, the chaotic mixing and lack of short-circuiting between baffles observed with flow velocimetry over a wide range of operational conditions point out the interest of this configuration to achieve plug flow.

20 pages, 16 figures