Numerical investigation of thermal-hydraulic characteristics in cross-flow heat exchangers with different twisted oval tubes

Abstract

This study presents a new strategy to strengthen the flow and thermal performance of gas-liquid tube bundle heat exchangers by combining oval tubes with variable-direction twist method. The effects of twist direction, twist angle and flow velocity on the overall performance were investigated. The variable-direction twisted oval tube enhances the mixing degree of the main stream and the tail vortex, thereby improving the thermal performance and reducing the pressure drop. Both heat transfer coefficient and pressure drop increase with the increase of twist angle, and the overall performance is negatively correlated. Twist period has little effect on overall performance. Convective heat transfer coefficient of the variable-direction twisted oval tube with a twist angle of 120° is increased by 5.8%–10.2%, pressure drop is reduced by 5.0%–7.8% and overall performance is increased by 7.4%–10.7%, as compared circular tube bundle. The proposed variable-direction twisted oval tube realizes the synergistic enhancement of thermal-hydraulic performance, and can directly replace the traditional circular tube. The work of this paper provides technical guidance for improving the processing technology of twisted oval tube and developing new heat exchangers.

Keywords

• Waste heat recovery
• Twisted-oval tubes
• tube bundle
• Thermal performance enhancement
• Cross flow