The nonsteady-state gas-particle flows in pipelines are considered. Chaotically moving particles are described as granular gas characterized by granular temperature. Ibis temperature dissipates because of partially inelastic particle collisions with the wall, with each other and also because of the particle viscous friction with gas. The energy losses on a microscale are translated into the pressure losses on a macroscale. The model developed is validated for both steady-state and nonsteady-state regimes by comparing calculated pressure losses with experimental data. A detailed numerical study of the nonsteady-state flows shows that the pipe wall roughness is a major parameter affecting the pressure drop. Flow regimes for different particle elastic properties, particle sizes, and solids loading are studied.