Material handling is one of the most important parts of industrial processes. In different industries like pharmaceutical industry and process engineering, Pneumatic conveying systems are used to convey the powdery material to the processing devices. However, different factors may affect the operation efficiency of such systems. In order to optimize the design and operation of such systems, careful studies and investigation around the associated gas-particle flow is required. One of the most important aspects of the gas-particle flow, particularly in confined conveying systems, is the effect of bounding walls since the particle-wall collisions are strongly influenced by the wall-friction and wall-roughness of the conveying line. This, in turn, requires an appropriate wall boundary condition in numerical prediction of system operation. In this thesis a new boundary condition for kinetic theory based two-fluid models was developed to account for rough bounding walls. This model is based on the concept of a virtual wall angle proposed by Sommerfeld (Int. J. Multiphase Flow, 905-926, 1992). By considering the average wall-roughness effect for an ensemble of colliding particles, this concept was generalized to be compatible with two fluid models. The model was validated for two different cases (straight duct and pipe bend) and the results revealed good agreement with the experimental study and/or Lagrangian simulation. Finally the developed boundary conditions are applied for the simulation of complex industrial geometries and the results are discussed. The results show that the presented models are capable to optimize the operation of the system.