Enhancing heat transfer in processing systems using swirl tube technology

Abstract

This thesis elucidates the fundamental principles underlying the improvement of the thermal performance of a heat-transfer unit through the introduction of a swirl flow generated by a 4-lobed swirl tube. This research conducts a comprehensive literature review on thermal enhancement methods, investigation techniques, and undertakes two sets of numerical and experimental studies involving a 4-lobed swirl tube in a heat exchanger and a solar water heater.
The literature review classifies and systematically analyzes diverse thermal enhancement methods for tube flows. It also summarises commonly-employed numerical and experimental techniques for investigating these methods, facilitating researchers' method-selection process. Moreover, it compiles the Nusselt number and friction factor correlations relevant to the enhancement methods, which is of great value to the scientific and industrial communities. It is concluded that some thermal enhancement methods, such as the twisted tape method, are often accompanied by a significant amount of pressure drop, potentially nullifying the energy gain from heat transfer enhancement.
Numerical studies on the 4-lobed swirl tube explore and evaluate the thermal performance of different tube configurations. The regularly-spaced 4-lobed swirl tube is proposed as a means to achieve higher heat-transfer enhancement with a moderate pressure drop. A double-pipe heat-exchanger experiment is carried out, and the 3D-printing method is adopted to fabricate 4-lobed swirl tubes with different geometries. The thermal enhancement capability of the 4-lobed swirl tube is verified. Among all configurations, the 4-lobed swirl tube with a pitch-to-diameter ratio of 4 exhibits the highest overall performance, with values ranging from 1.12 to 1.09.
The thermal enhancement effect of the regularly-spaced 4-lobed swirl tube in a simplified solar water heater (SWH) is numerically investigated. The regularly-spaced lobed tube demonstrates superior thermal performance compared to the regularly-spaced twisted- tape tube. Based on the previous findings, a solar water heater equipped with regularly-spaced 4-lobed swirl tubes is constructed and compared with a circular SWH. The swirl-tube-equipped SWH shows greater efficiency in turbulent-flow regions. However, in laminar-flow regions, the efficiency of these configurations decreases. The solar water heater with inserted swirl tubes shows approximately a 3% higher efficiency than the circular one, highlighting the potential of this method in real-world applications.

Date of Award	15 Jul 2025
Original language	English
Awarding Institution	University of Nottingham
Supervisor	Nick Miles (Supervisor), Philip Hall (Supervisor) & Zheng Wang (Supervisor)