Experimental and numerical investigation of turbulent heat transfer enhancement of an intermediate heat exchanger using corrugated tubes

The intermediate heat exchanger (IHX) in a very-high-temperature gas-cooled reactor (VHTR) can realize a variety of process heat applications including hydrogen production, which is beneficial to the green and sustainable development of global energy. In the present study, three corrugated tubes are adopted to enhance the heat transfer capabilities of the IHX. The flow and heat transfer characteristics of these tubes are comprehensively investigated and compared using experiments and three-dimensional numerical simulations. Air and helium are the working fluid of the experiment and numerical simulation, respectively, with Reynolds number (Re) ranging from 10,000 to 20,000 and Prandtl numbers of 0.70 and 0.66. An innovative corrugation parameter acquisition method is proposed by combing high-precision computed tomography imaging and computer vision techniques. Thermal-hydraulic experiments are conducted and the k-kl-omega transition model is applied and validates well with the experimental data obtained for Nusselt number (Nu) and friction factor (f). By analyzing the flow field, heat flux field and the synergy angle distribution, it is found that corrugation disrupts the boundary layer development, strengthens the turbulent mixing, reduces the temperature gradient in the boundary layer and improves the synergy between the velocity field and the heat flux field, thus enhancing the heat transfer. The effects of corrugation parameters on the thermal-hydraulic performance of the three tubes are also discussed. The transversely corrugated tube with dimensionless height e/d = 0.03, dimensionless pitch p/d = 0.6, and Re = 20,000 produces the maximum Nu obtained, which is about 60% larger than that of a smooth tube. The helically corrugated tube with e/d = 0.03, p/d = 0.6, and Re = 12,000 has the best comprehensive performance, with a performance evaluation criterion of about 1.09. Finally, empirical correlations with geometric parameters (e/d and p/d) and Re are proposed for Nu and f for all three corrugated tubes. (c) 2021 Elsevier Ltd. All rights reserved.