Passive heat transfer augmentation in conduits by surface modification: a review

The purpose of this study is to review the common passive enhancement techniques with an emphasis on surface modification approaches used for heat transfer enhancement in heat exchangers. The common passive enhancement techniques are discussed, and surface modification approaches are further analyzed. Furthermore, some of the techniques used to generate surface alteration are explored along with the experimental and numerical methods used to study them. Different numerical models used for the calculations are also compared, and the validity of using such numerical models is reviewed. The available earlier work conducted on conduit internal surface grooving is summarized of their contributions to heat transfer enhancement, and the associated pressure loss penalties are discussed. In addition to the surface grooving, the influence of operating fluid is also explored, both as a passive enhancement technique and as a contributing factor in heat transfer enhancement to the surface alteration. It can be concluded that surface alteration of internal conduit provides different level of improvements which highly depend on the geometrical pattern and dimension of the surface along with the surface parameter, namely the depth, width, pitch and inclination angle. Further, the angle parameter and surface continuity provide the dominant factor for the improvement owing to enhanced fluid mixing and reduced stationary flow sites as evident from the numerical study. Finally, the way forward for future research is discussed which emphasizes on the need to provide a generalized condition for surface alteration where all correlating parameters can be assembled to produce a unified model. This serves as valuable tool for engineers towards applying this passive method for thermal management solution.