This study aims to experimentally investigate the effect of cross-sectional shape and aspect ratio on the heat transfer performance of single-phase flow of Ethanol/Polyalphaolefin nanoemulsion fluid in microchannels manufactured additively with Maraging Steel. An analytical analysis was conducted to establish reasonable criteria to determine sizing and geometry of different cross sections for microchannel heat exchangers with regard to the fluid flow and metal additive manufacturing considerations. While the exterior geometry of the microchannel heat exchangers remains the same, eight different cross sections of channels including: circular, alternately upward/downward semi-circular, alternately upward/downward trapezoidal with three aspect ratios, and rectangular with three aspect ratios, are designed with keeping the channels' wetted perimeters, mass flow rate, and Reynolds number constant for comparison purposes. The microchannel models were then developed in Creo and the prototypes were additively manufactured with Maraging Steel using the Direct Metal Laser Sintering (DMLS) technique to later conduct the experiments to characterize fluid flow and heat transfer performance under uniform wall heat flux boundary conditions within the laminar flow regime.