Against the backdrop of increasingly severe global energy shortages and carbon emission reduction pressures, traditional shell-and-tube condensers struggle to meet the urgent demand for highly efficient and compact heat exchange equipment in modern engineering due to their low heat transfer efficiency and large size. Addressing this bottleneck, improving the efficiency of heat exchange equipment has become a key pathway to reducing energy consumption.

A study systematically investigated the condensation heat transfer performance of horizontal double-sided enhanced tubes 1 (E1 2 and E2 3). The research employed the environmentally friendly refrigerant R134a under typical operating conditions with a saturation temperature of 40°C, conducting a systematic comparison between a smooth tube and two types of enhanced tubes featuring external serrated fins and internal spiral micro-ribs.

The results not only validated the significant advantages of double-sided enhanced structures in improving heat transfer efficiency but also provided critical engineering insights for condenser design optimization, directly addressing the industry's urgent need for high-efficiency and energy-saving technologies.

The results demonstrated that the enhanced surfaces significantly increased the effective heat exchange area and facilitated rapid drainage of the condensate, enabling the condensation heat transfer coefficients of the E1 and E2 tubes to reach 11-14 times that of the smooth tube. This markedly reduced the condenser volume and material consumption.

Further research revealed that increasing the cooling water velocity under a constant heat load could further amplify the advantages of the enhanced tubes, though the rate of improvement slowed as the velocity increased. When the external heat flux exceeded approximately 94 W*m⁻², the E1 tube, with its larger fin height, exhibited more significant performance degradation due to thickened condensate film, while the E2 tube, with its relatively smaller fin height, demonstrated superior robustness under high-load conditions.

Thus, for applications targeting low to medium heat flux densities and pursuing extreme compactness, the E1 enhanced tube with a larger heat exchange area can be prioritized. In scenarios with highly fluctuating thermal loads or high heat flux densities, the E2 tube, with its more robust geometric parameters, offers higher long-term operational reliability.

This study provides direct guidance for the structural optimization and material selection of next-generation high-efficiency condensers and lays an experimental foundation for the coupled design of environmentally friendly refrigerants and complex enhanced surfaces.

1. Horizontal double-sided enhanced tube : A copper tube with special processing on both its outer and inner walls, designed to make condensation faster and more efficient. It is called "double-sided enhanced" because it features "external serrations and internal grooves," and it is referred to as "horizontal" because the tube is placed horizontally.
2. E1 tube : The outer wall has 150 serrated fins, each 0.8 mm high and spaced 0.57 mm apart; the inner wall is engraved with 75 spiral micro-ribs, each 0.26 mm high and at a 40° angle.
3. E2 tube : The outer wall fins are slightly shorter (0.79 mm), more densely spaced (0.55 mm), and fewer in number (100); the inner wall has spiral ribs that are taller (0.42 mm) and at a larger angle (45°), but only 38 in total.