A Printed Circuit Heat Exchanger (PCHE) is considered as a promising candidate for the use of an intermediate heat exchanger (IHX) in High Temperature Gas-cooled Reactors (HTGRs), since PCHEs offer high effectiveness and a compact size. It has been reported that the use of binary mixture gas can increase the thermal efficiency and reduce the turbo-machinery size in HTGRs. We performed experiments and numerical analysis on the PCHE using a mixture gas with Helium (He) and CO2. We suggested the procedure to develop the correlations of Fanning factor and Nusselt number for PCHE channel geometry through introducing the concept of the local pitch-averaged correlations. A Computational Fluid Dynamics (CFDs) code, FLUENT, was validated against the current Mixture-Water test data and used to get the local pitch-averaged correlations to develop the local pitch-averaged correlations of Fanning factor and the Nusselt number. Using the local pitch-averaged correlations based on the He-He, the He-Water, and the Mixture-Water test data, we proposed the single Fanning factor correlation and the single Nusselt number correlation. (C) 2013 Elsevier Inc. All rights reserved.