Numerical assessment of hydrodynamic and thermal performance in innovative pyramidal internally corrugated tubes

This study numerically evaluates the thermo-hydraulic performance of circular tubes equipped with raised pyramidal protrusions on the inner wall, using a steady-state simulation with the standard k – ε turbulence model. These surface modifications serve a dual purpose: they expand the heat transfer area and induce near-wall flow disturbances, thereby enhancing convective heat transfer. Geometric parameterization was conducted through a systematic evaluation of protrusion dimensional ratios, enabling quantification of their effects on both thermal enhancement and hydraulic resistance. Results indicate that optimal thermal performance is achieved with larger relative pyramid lengths, smaller widths, and lower heights. The Nusselt number displays periodic variations, with peak values at the tops and bottoms of the pyramidal structures and minimum values at the “waist"—the midpoint between these extremes. Specifically, at a relative length of 0.53, width of 0.77, and height of 0.089, the pyramidal corrugated tube achieves a mean Nusselt number 2.15 times greater than that of a smooth tube. Moreover, with a relative length of 0.26, width of 0.32, and height of 0.089, the pitch-wise peak of the circumferentially averaged Nusselt number is 3.5 times higher than its smooth counterpart. The proposed correlations relate mean Nusselt number and friction factor to Reynold number and key geometric parameters, with deviations within 7–10 % over the stated ranges. These findings provide actionable guidance for the design and retrofit of tubular heat exchangers—including shell-and-tube and double-pipe configurations—used across industrial services.