Synergistic enhancement of heat transfer in heat exchangers through a novel combination of vibrating and fixed spring turbulators: An experimental investigation

Heat exchangers are often constrained by thermal performance limits, motivating the development of advanced heat transfer enhancement techniques. While vibrating turbulators using strips or string-type oscillators have shown potential, spring-based oscillators remain largely unexplored. This study introduces a novel vibrating spring turbulator and investigates its interaction with a fixed spring turbulator in a double-pipe heat exchanger (DPHX). Experiments were conducted over a Reynolds number (Re) range of 630–7372, varying oscillator diameters (d = 4–6 mm), pitch distances (Pd = 1–3 mm), and fixed spring gaps (1–4 mm). The results show that the vibrating spring turbulator alone boosts heat transfer by up to 3.06 times relative to a smooth tube, achieving a maximum Performance Evaluation Criterion (PEC) of 2.54 at Pd = 1 mm and d = 6 mm. When combined with a fixed spring, a synergistic effect was observed. The optimal configuration—vibrating spring (Pd = 1 mm, d = 6 mm) with a fixed spring gap of 2 mm—yielded a PEC of 2.75, with a 4.27-fold increase in heat transfer and a 3.75-fold increase in pressure loss relative to a plain tube. These findings indicate that spring-based vibrational devices can provide an effective and versatile strategy for enhancing thermal performance, offering a promising approach for designing compact, high-efficiency heat exchangers in industrial applications.