Natural convective heat transfer analysis of a vertical tapered inner annulus tube with dual inverted frusto-conical turbulator using CFD

Abstract

Vertical tube heat exchangers play a pivotal role in various industrial processes, where efficient heat transfer is essential for optimal system performance. This research introduces a novel heat exchanger design, the Dual Inverted Frusto-Conical Turbulator Attached Tapered Inner Annulus Tube, aimed at enhancing natural convection in vertical annulus heat exchangers using nano-coolants. Traditional designs often suffer from non-uniform heat transfer due to varying boundary layer thicknesses along the height of the annulus. The proposed design mitigates this by incorporating a tapered inner annulus tube, which has a larger diameter at the bottom and gradually decreases towards the top. This taper reduces wall friction and boundary layer thickness, enhancing thermal diffusivity and improving the heat transfer rate. To further optimize heat transfer, Dual Inverted Frusto-Conical Turbulators are strategically placed around the tapered tube, generating controlled turbulence that minimizes drag and avoids unwanted flow reversals and recirculation. Simulation results show a Nusselt number of 321, a friction factor of 0.023, and a pressure drop of 154 Pa at a Reynolds number of 5000. The design also achieved a thermal conductivity of 0.3 kW/mK, thermal efficiency variation of 0.8658%, and a heat transfer coefficient of 26,000 W/m2K.

Keywords

• Natural convection
• vertical heat exchanger
• turbulator
• annulus heat exchanger
• uncontrolled eddies
• flow reversals