In this paper, an additively manufactured heat exchanger featuring semi-circular minichannels fabricated using selective laser melting technique has been investigated experimentally and numerically. Thermohydraulic performance was characterized under balanced mass flow rate conditions (1.11–4.44 kg/h) using a Nitrogen–Nitrogen open-loop test facility. The experimentally measured fanning friction factor and Nusselt number were consistently higher than values predicted by smooth-channel theoretical correlations due to additively manufactured induced surface roughness. Surface profilometry revealed average roughness values of 8.11 μm in the channel region and 4.70 μm in header regions. Numerical models (laminar, realizable k-\(\epsilon\), and transition SST) underpredicted Fanning friction factor and Nusselt number relative to experiments, with the Transition SST model providing the closest agreement with respective average percentage difference of 66.6 and 51.7%. Empirical correction factors (\(\:{\beta\:}_{f}\) and \(\:{\beta\:}_{Nu}\)) were developed to reconcile simulations with measurements, improving predictive accuracy. The equivalent sand-grain roughness approach was evaluated using Filonenko, Blasius, Halland, Dittus-Boelter, and Gnielinski correlations. A single relative roughness value could not simultaneously match Fanning friction factor and Nusselt number; therefore, independent roughness parameters of 16\(\:{R}_{a}\) (momentum-related) and 4.5\(\:{R}_{a}\) (heat-transfer-related) are proposed. Numerical flow visualization demonstrated multiple jets and flow recirculation regimes in converging outlet headers, causing mild flow maldistribution and localized variations in heat transfer. The study establishes a validated framework to predict additively manufactured minichannel heat exchanger performance, accounting for surface roughness effects, and provides correlation tools for its design optimization.
