The reduction of blood damage is still a big challenge in blood-carrying medical devices. In-vitro experiments are performed to investigate the damage-causing effects, but due to the opaqueness of blood cells, only near-wall flows can be observed. Thus, several transparent blood models to visualize the rheologic behavior of blood have been proposed and examined. Nevertheless, two-phase blood models with added particles still represent the properties of blood inadequately or are very expensive and complex to produce. In this in-vitro study, the viscosity, the flow behavior and the cell deformation of human red blood cells (RBCs) have been compared to a novel, easy-to-produce, two-phase blood model fluid with deformable alginate microspheres. The comparison has been performed in a cone-plate rheometer, a straight and a hyperbolic converging microchannel. The viscosity of the blood model fluid with a particle fraction of 30 % showed a shear-thinning behavior, comparable to that of blood at room and human body temperature within shear rates from 7 s-1 to 2000 s-1. The alginate microspheres were deformable in an extensional flow and formed a cell free layer (CFL) comparable to that of blood in a straight microchannel. The experiments showed a good optical accessibility of the two-phase flow with traceable movements of individual microspheres in the center of the microchannel. It could be shown that our proposed blood model fluid is a promising tool for the analysis of two-phase flows in complex flow geometries.