Shell-Side Flow Field in a Doughnut and Disk Baffle Shell Tube Heat Exchanger

Abstract

Shell Tube Heat Exchangers (STHXs) are widely employed across many industrial applications, including oil coolers, steam generators in nuclear power plants and the chemical industry. One less well-understood variation utilises alternating doughnut and disk baffles, which offers a superior heat transfer-to-pressure drop ratio over conventional single segmental baffles. Often, authors involved in STHX research are only interested in the shell-side total pressure loss or average heat transfer coefficient across a compartment or the entire STHX, without trying to gain a fundamental understanding of the complex flow field. The authors of this paper aim to overcome this shortcoming by employing an innovative mechatronic test facility to obtain detailed shell-side pressure measurements within a doughnut and disk baffle STHX for Reynolds numbers of 5,402 and 19,454. A comparable STHX was simulated for the high-flow rate case using Computational Fluid Dynamics (CFD), which verified that there is inherent flow unsteadiness. Some of the key findings include: (1) the axial momentum of the fluid resulted in significant flow bias towards the rear baffle in every compartment, (2) the circumferential pressure coefficient profile is strongly dependent on the ratio between transverse-to-axial velocity, where regions with a considerable value behave somewhat similarly to external flow around a 2D cylinder, and (3) the separation regions behind the doughnut baffles grew in size, whereas they shrank behind the disk baffles due to the adverse and favourable pressure gradients, respectively, as a result of the radial flow directions.