Analysis of Swirl Flow by Tube Inserts for CFD Study

Abstract

The petroleum and petrochemical industries continually seek mechanical methods to improve heat transfer in shell-and-tube heat exchangers. Tube bundle inserts are popular mechanical devices that help improve performance. The increase in the tubeside heat transfer coefficient by the insert allows for a decrease in required shellside flow length, assuming single tube pass. The flow length reduction allows for designing higher velocities and subsequent shellside shear rates, to help reduce crude oil fouling potential. This work presents some of HTRI’s ongoing experimental measurements and preliminary Computational Fluid Dynamics (CFD) simulations. CFD visualization of swirl flow dynamics and heat transfer inside the augmented tube provides insight on complex flow physics, which is misunderstood. Heat Transfer Research, Inc. (HTRI) collected experimental data for in-tube single-phase flow using twisted tape inserts in the Tubeside Single-Phase Unit (TSPU) situated in the Research and Technology Center (RTC). Our data will be used to calibrate ANSYS FLUENT CFD simulations of a tube with a twisted tape swirl insert. We first performed plain tube simulations and compared the heat transfer results with open literature measurements, for validation. We will modify the CFD tube model to have a swirl flow insert, and compare numerical results against open literature experimental data of diabatic single-phase swirl flow. In future, we will compute heat transfer (heating and cooling) and pressure drop for tube insert configurations at laminar and turbulent Reynolds numbers from 3000 to 500000. The range of tubeside Reynolds numbers required the use of the laminar, transition, and Realizable k-epsilon turbulence models with scalable wall functions. This study describes some of the mechanisms behind turbulent swirl flow augmentation inside a tube, as well as the limitations of conventional in-tube heat transfer correlations applied to swirl flow inserts.