This study focuses on the vortex and heat transfer characteristics within channels formed by helically serrated finned tube bundles, aiming to reveal how different structural parameters synergistically influence flow resistance, heat transfer intensity, and vortex shedding behavior. The goal is to provide a theoretical basis for designing high-efficiency, low-resistance, and long-life heat exchange equipment. Helically serrated fins are widely used in air-cooled heat exchangers, chimneys, and industrial waste heat recovery systems due to their high finning ratio, lightweight structure, and vibration suppression.

However, previous studies have mostly focused on macroscopic heat transfer and pressure drop data, lacking a systematic understanding of the relationship between internal vortex evolution and local heat load distribution. This makes it difficult to balance high heat transfer performance and structural safety during design.

To address this, the present study constructs a three-dimensional periodic channel model, selecting transverse tube pitch, longitudinal tube pitch, and fin spacing as key variables, covering the commonly used Reynolds number range from 10,000 to 50,000. The SST k-ω turbulence model, validated by experiments, is employed on a 1.2 million structured grid to perform unsteady large-eddy simulations, simultaneously capturing instantaneous velocity, vorticity, and temperature fields.

Typical structures such as Kármán vortex streets and horseshoe vortices are identified using the Q-criterion, and area-averaged time integration is used to obtain the Nusselt number, Euler number, and Strouhal number, transforming "invisible" vortices into quantifiable and comparable performance indicators.

The results show that reducing the transverse tube pitch increases flow velocity and significantly enhances vortex shedding frequency, improving heat transfer by more than 30% but doubling the flow resistance. Increasing the longitudinal tube pitch allows vortices to fully develop and reattach, enhancing heat transfer by nearly 50% with limited increase in resistance. Larger fin spacing reduces blockage, increases vortex intensity, and yet decreases pressure drop, presenting a favorable trend of "the sparser, the less resistance, the sparser, the better heat transfer."

Further comparison between local vortex structures and surface heat flux reveals that vortex shedding regions exhibit uniform temperature gradients and high local Nusselt numbers, whereas regions without vortices show high-temperature "hot spots," which can induce thermal stress concentration and early fatigue in the fins.

This finding directly explains the root cause of local cracks and deformation observed in field tube bundles and provides a criterion for subsequent safety assessment. Based on 216 sets of orthogonal simulation data, the study proposes dimensionless correlations for Nu, Eu, and St in terms of Re and the three geometric parameters, with deviations within 10%, which can be directly embedded in engineering selection software for rapid performance prediction. The specific forms are as follows:

The outcomes not only fill the gap in the "vortex-heat" coupling mechanism of helically serrated fins but also provide a multi-objective optimization path of "enhancing heat transfer, reducing resistance, and ensuring safety" for applications such as air-cooled islands in thermal power plants, petrochemical air coolers, and traction transformer cooling in high-speed trains.

Designers can fine-tune the transverse pitch for high heat transfer, use longitudinal pitch to suppress resistance peaks, and alternately arrange fin spacing to eliminate local overheating, achieving minimum life-cycle costs. Under the dual-carbon background, this research has significant potential for reducing cooling system energy consumption and improving industrial waste heat recovery efficiency.

In the future, it can be extended to different tooth profiles, variable-section fins, and mixed working fluids, continuously promoting the development of high-efficiency thermal management technologies.