Numerical analysis and model prediction of flow enhanced heat transfer mechanism in spirally corrugated tubes

The spirally corrugated tube (SCT) has advantages such as bidirectional enhanced heat transfer, which can effectively improve the economic efficiency of heat exchange equipment. However, the influence law of the start value (n) on the flow and heat transfer of the SCT is not clear enough, and it is still necessary to explore how to design and select suitable SCT according to the application working conditions. Therefore, in this study, a numerical simulation of the flow and heat transfer inside the tube of a multi-start SCT with an equivalent inner diameter (D_i = 20 mm) was carried out. The effects of n (n = 1–8), pitch ratio (p/D_i = 1.5–3.0), corrugated depth ratio (e/D_i = 0.05–0.20) and Reynolds number (Re = 5000–30000) on the velocity and temperature distributions on the multi-start SCT were investigated, and comparisons were made with four other types of enhanced tubes (conically corrugated tubes, arc-corrugated tubes, converging–diverging tubes and spirally grooved tubes). The comprehensive performance of the multi-start SCT was evaluated according to the Performance Evaluation Criteria (PEC), and the mechanism of heat transfer enhancement was revealed through the field synergy theory. The results show that the PEC of the SCT is significantly better than that of the other four types of enhanced tubes. As n and e/D_i increase, the PEC first decreases and then increases. as p/D_i increases, the PEC gradually increases. The synergy between the temperature gradient, pressure gradient and velocity of the eight-start SCT is the least affected by Re, and it can maintain a relatively high PEC, with its optimal PEC being 1.764. In addition, a prediction model for the SCT was proposed through linear fitting, and the error between the prediction model and the simulated values is within 15 %, providing guidance for the practical engineering application of the SCT.