Experimental study on heat transfer and flow characteristics inside helically corrugated tubes in intermediate heat exchangers

The intermediate heat exchanger (IHX) in very-high-temperature gas-cooled reactors (VHTRs) is essential for process heat applications, serving as the primary component for thermal energy transfer in the intermediate loop. This study experimentally investigated the heat transfer and flow characteristics of a smooth circular tube and eight helically corrugated tubes (HCTs) with varying structural parameters, using air as working fluid, under turbulent conditions spanning Reynolds number from 7000 to 22000. The results indicate that HCTs significantly enhance convection heat transfer within the tube but also lead to increased flow resistance. The Nu and f of the HCTs increase with higher dimensionless corrugation height e/d, and decrease with larger dimensionless corrugation pitch p/d. Based on the experimental data, empirical correlations were developed in the form of power and dimensionless roughness functions, both demonstrating good agreement with the measurements. The maximum errors of the power correlations for Nu and f were ±11.24 % and ±15.89 %, respectively, while the maximum errors for the dimensionless roughness function correlations for resistance and heat transfer were ±15.67 % and ±15.17 %.