Title: A numerical investigation of turbulent convective heat transfer of supercritical CO₂ in vertical mini tubes

Authors: Zhenghua Rao; Shengming Liao

Addresses: School of Energy Science and Engineering, Central South University, Changsha, 410083, China ' School of Energy Science and Engineering, Central South University, Changsha, 410083, China

Abstract: This article presents a numerical investigation on the turbulent convective heat transfer of supercritical CO₂ in vertical mini tubes. For buoyancy-aided cases, buoyancy-opposed cases and buoyancy-free cases, the profiles of velocity, temperature and turbulent kinetic energy, as well as heat transfer coefficients and Nusselt numbers inside the tubes with the diameters less than 2 mm, under heating and cooling conditions, are obtained. It is found that the buoyancy is significant near the pseudocritical point due to the sharply varied properties of supercritical CO₂, leading to the variations of the flow pattern, turbulent production and hence heat transfer coefficient in the tube. Detailed explanations to the physics of the complex but interesting transport phenomena are given. Furthermore, the values of the buoyancy parameter Gr_b/Re_b ^2.7 are calculated, and Jackson and Hall's criterion for assessing the buoyancy's influence is examined for cooling flows in mini tubes.

Keywords: carbon dioxide; supercritical CO2; turbulent flow; buoyancy; convective heat transfer; vertical mini tubes; cooling flows; velocity; temperature; turbulent kinetic energy; heat transfer coefficients; Nusselt numbers.

DOI: 10.1504/PCFD.2014.062428

Progress in Computational Fluid Dynamics, An International Journal, 2014 Vol.14 No.3, pp.166 - 176

Published online: 31 Jul 2014 *

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