In this work, the problem of mathematical modeling of transport phenomena during semi-solid metal processing is investigated from a fundamental approach. The phenomenon of solid phase interaction is modeled by an evolution equation of an internal state variable. The formation of an interconnected network of agglomerated solid fragments at high values of solid fraction is also accounted for, leading to a more realistic prediction of momentum transport in comparison to other standard models reported in the literature. Numerical simulations are performed based on two separate momentum transport models. One of the models essentially neglects solid phase interaction mechanisms, whereas the other one incorporates the associated transport features, in order to capture the implications of solid phase agglomeration in a semi-solid slurry processing. A detailed analysis of the results reveals a profound impact of agglomeration and break-up on the transport phenomena, which need to be effectively captured. (C) 2007 Elsevier Ltd. All rights reserved.