Experimental study on flow and heat transfer of supercritical carbon dioxide in zigzag channels with bending angle 30° for advanced nuclear systems

Zigzag-channel printed circuit heat exchangers have a wide range of application prospects in Gen-IV nuclear systems related to supercritical carbon dioxide Brayton cycles. Experimental data and empirical correlations are the basis for the design of zigzag-channel printed circuit heat exchangers. In this study, experimental investi-gation on flow and heat transfer of supercritical carbon dioxide in zigzag channels is carried out. The dimensions of the tested zigzag channels are as follows, the channel diameter 1.95 mm, the bending angle 30 degrees, the longi-tudinal pitch 7.24 mm, as well as the radius of the curvature at the bending corner 0.5 mm. The Reynolds number and Prandtl number of supercritical carbon dioxide in the experimental study range between 3201 and 43258 and 1.1-6.0, respectively. Based on the obtained local Fanning friction factors and local Nusselt numbers, the effect of zigzag angle on flow and heat transfer are analyzed. And new flow and heat transfer correlations for the tested zigzag channel are proposed. The predicted values by the new developed correlations agree with the experimental data well. Comparisons between the new developed correlations and the existing correlations developed for printed circuit heat exchangers are conducted. Heat transfer enhancement obviously occurs when comparing with straight channels. Result shows that the heat transfer coefficient in the tested zigzag channels is about twice that predicted by Dittus-Boelter correlation (under cooling condition). The Fanning friction factor in the tested zigzag channel is about seven to ten times that in straight channels within the scope of investigated.