Application of Twisted Tubes in Heat Exchangers: Principles and Advantages
As a high-efficiency passive heat transfer enhancement technology, twisted tubes significantly improve the overall performance of heat exchangers through their unique geometric structure. This paper systematically describes the structural characteristics and heat transfer enhancement mechanisms of twisted tubes, and analyzes their advantages such as eliminating the need for baffles on the shell side, effectively removing flow dead zones, and suppressing tube bundle vibration. Studies show that the overall heat transfer coefficient of twisted tube heat exchangers can be increased by 30%–50% compared with conventional heat exchangers, showing broad application prospects in chemical engineering, electric power, refrigeration and other fields.
1 Structural Characteristics and Heat Transfer Enhancement Mechanism of Twisted Tubes
1.1 Geometric Structure
A twisted tube is a profiled tube manufactured by twisting a circular tube. Its cross-section is flat (elliptical or nearly elliptical) and rotates continuously along the tube axis. The second end of the tube is twisted at a certain angle around the axis relative to the first end, forming a helical tube wall structure. This special geometry causes periodic changes in both the internal and external flow channels. At present, twisted tubes can be made of copper, titanium, stainless steel (2205, 316, 304) and other materials.
1.2 Heat Transfer Enhancement Mechanism
The heat transfer enhancement mechanism of twisted tubes can be understood from the following aspects:
Secondary flow & Dean vortex effect
When fluid flows through a helical channel, centrifugal force induces secondary flow perpendicular to the main flow direction, forming a pair of counter-rotating Dean vortices. This secondary flow greatly enhances momentum and energy exchange between fluid micro-elements, disrupts boundary layer development, and thus substantially increases the convective heat transfer coefficient.
Periodic disturbance & boundary layer disruption
The continuous rotation of the twisted tube cross-section changes the flow direction constantly, and the boundary layer is repeatedly destroyed and rebuilt in each rotation cycle. Such periodic disturbance effectively thins the laminar sublayer and reduces convective thermal resistance.
Field synergy theory
According to the field synergy principle of convective heat transfer, the structure of twisted tubes improves the synergy between the velocity field and temperature gradient, reducing the included angle between them, thereby achieving higher heat transfer efficiency at the same flow resistance.
2 Performance Advantages of Twisted Tube Heat Exchangers
🔥 Significantly Improved Heat Transfer
Numerous studies indicate that twisted tube heat exchangers are significantly superior to conventional plain tube heat exchangers. In laminar and transitional flow (Re < 3000), the heat transfer coefficient can be 2–3 times higher; under high-Reynolds turbulent conditions, the increase is about 50%. Under identical pressure drop, the overall heat transfer coefficient is improved by 30%–50%.
New configurations such as Spiral Flow Reversers (SFR) and Semicircular Spiral Flow Reversers (SSFR) reach Thermal Performance Ratios of 1.24 and 1.45 at Re 17,207.
⚙️ Simplified Shell-Side & Optimized Flow
Traditional shell-and-tube exchangers use segmental baffles, which cause dead zones and pressure loss. A unique feature of twisted tube exchangers is that adjacent twisted tubes contact each other at the long-axis sides, forming a self-supporting structure, while short-axis sides create gaps, naturally building a network flow channel. This eliminates baffles, flow dead zones, and significantly reduces shell-side pressure drop.
🛡️ Anti-Vibration & Reliability
Due to multi-point contact and mutual restraint between adjacent tubes, the overall rigidity of the twisted tube bundle is enhanced. The uniform shell-side flow avoids vibration induced by periodic vortex shedding. Therefore, twisted tube heat exchangers effectively eliminate the risk of bundle vibration and operate more safely and reliably.
🧼 Anti-Fouling Performance
The special twisted structure causes rotating flow both inside and outside the tubes. The fluid velocity gradient near the wall is large, making it difficult for particulate matter to deposit. Studies show that the cross-twisted design reduces fouling both internally and externally, which is important for fouling-prone fluids.
📦 Compactness & Economy
Twisted tubes allow larger heat transfer area per unit volume, making equipment more compact. Moreover, since baffles and additional supports are not required, the manufacturing process is simplified and material consumption is reduced.
Comparative Performance Data
| Condition / Configuration | Improvement / Characteristic |
|---|---|
| Laminar/transitional flow (Re < 3000) | Heat transfer coefficient 2–3 times higher than plain tubes |
| Turbulent flow (high Re) | ~50% increase in heat transfer coefficient |
| Overall heat transfer coefficient (same ΔP) | 30% – 50% higher |
| SFR (Spiral Flow Reverser) at Re 17,207 | Thermal Performance Ratio (TPR) = 1.24 |
| SSFR (Semicircular SFR) at Re 17,207 | TPR = 1.45 |
| Shell-side structure | No baffles, no flow dead zones, self-supporting |
Anti-Vibration and Flow Field Uniformity
Conventional segmental baffles lead to local eddies and relatively high pressure loss. In contrast, the self-supporting network of twisted tubes eliminates dead zones and dramatically reduces vibration risks. The multi-point contact between tubes enhances bundle stiffness, and the absence of periodic vortex shedding guarantees operational reliability.
Conclusion
Through innovative geometric design, twisted tubes achieve remarkable improvement in heat transfer performance. Their enhancement mechanism mainly comes from twisted-induced secondary flow, periodic boundary layer disruption, and improved synergy between velocity and temperature gradient fields.
Compared with conventional heat exchangers, twisted tube heat exchangers feature higher heat transfer coefficient, baffle-free structure, fewer flow dead zones, excellent anti-vibration performance and compact structure.
Industrial applications show that twisted tube heat exchangers have good applicability and economic benefits in chemical, power, refrigeration and other industries. With the emergence of new configurations and improvement of multi-objective optimization methods, twisted tube technology will play a more important role in energy conservation and emission reduction. Future research should focus on performance prediction under complex working conditions, low-cost manufacturing processes, and long-term operational reliability to promote wider application of this technology.
— Twisted tube technology overview —