Manifold Microchannels have been proven to enhance thermal management in different fields, such as electronic cooling, dry cooling, and high temperature heat exchangers. Manifold-microchannels use a system of manifolds to divide a microgrooved surface into a system of manifolds, thereby reducing pressure drop and increasing heat transfer by utilizing the developing flow regime. Because of this, design of a manifold-microchannel heat exchanger requires the design of the manifold and microchannel. In some situations, a sequential design approach, where one first designs the microchannel and then the manifold — is sufficient to meet the requirements of the problem statements. The more demanding requirements of contemporary applications require manifold microchannel design to evolve and become more complex. In particular, reducing the volume and pitch of the manifold has become necessary. Reducing the volume of the manifold results in a higher flow maldistribution, and the ability to predict how maldistribution affects heat transfer rate is critical. Similarly, reducing the pitch of the manifold increases the effect of axial conduction in the solid, and understanding the effect on heat transfer is important. To those ends, this work shows a porous medium approach for single-phase flow in manifold microchannel, which allows to predict pressure drop, maldistribution, axial conduction, and heat transfer rate with a much smaller computational demand when compared to a full 3D simulation, while guaranteeing very similar results.