The paper shows three-dimensional CFD modeling of two-phase (water-sand) slurry flows through 53.2mm diameter horizontal pipe for mixture velocity range of 1.8-3.1m/s and overall volumetric concentration range of 15-45% with four grain sizes viz. 0.18, 0.29, 0.55, and 2.4 mm. Eulerian model with RNG k-epsilon turbulence closure is adopted to analyze the monodispersed sand particles of varying granular diameters and density 2650 kg/m(3). Effects of grain size on various slurry flow parameters have been studied. The simulated local solid concentration values are found to be in good agreement with experimental results at solid concentrations and velocities for smaller grain sizes viz. 0.18 and 0.29 mm. Deviations between these values are recorded in the lower half of the cross-section just near the wall for bigger grain sizes viz. 0.55 and 2.4 mm only. Pressure drop per meter increases with increase volumetric concentration for all grain sizes. The same at any particular volumetric concentration increases with increase in grain size. This increase is approximately 3 to 6 times for 2.4 mm grain as compared to 0.18 mm grain. Qualitative aspects of this analysis have also been presented in the paper.