Experimental and numerical characterization of single-phase pressure drop and heat transfer enhancement in helical corrugated tubes

TL;DR

This study combines experimental and numerical methods to analyze how helical corrugations in tubes influence pressure drop and heat transfer, revealing optimal geometries for enhanced thermal performance across flow regimes.

Contribution

It provides a comprehensive characterization of flow and heat transfer in helical corrugated tubes, including the effects of geometry on transition and performance, validated by experiments and CFD simulations.

Findings

Corrugation induces swirl, reducing the critical Reynolds number for transition.

All corrugated tubes outperform smooth tubes in heat transfer, except at low Re.

The lowest pitch corrugated tube offers the best performance in transitional and turbulent regimes.

Abstract

The internal flow in corrugated tubes of different helical pitch, covering from the laminar to turbulent regime, was studied in order to characterize the three-dimensional flow and the influence of corrugation geometry on pressure drop and convective heat transfer. With water as working fluid and an imposed wall heat flux, ranging from around 4 to 33 kW/m2, a numerical model was developed with a CFD commercial software, where k-omega SST was used to model turbulence. Experimental tests were performed covering Reynolds numbers in the range from around 300 up to 5000, which allowed to identify the transition region and validate the numerical model. The results show that due to the swirl induced by the corrugation, the critical Reynolds number for the start of transition to turbulent flow is reduced. The thermal performance factor, which quantifies the heat transfer enhancement at the expense of pressure drop, was used to compare the corrugated tubes against the reference case of smooth tube. Based on this, all investigated corrugated geometries performed better than the smooth tube, except for low Reynolds numbers (Re<500) in the laminar regime. Overall, the corrugated tube with the lowest pitch showed a clearly better performance for the intermediate range of Reynolds numbers (1000<Re<2300), being an optimal choice for a wider range of operating conditions in the transitional and turbulent flow regimes.