Two models based on modifications of the capillary representation of a particle bed are proposed in order to evaluate the pressure gradient for the flow of non-Newtonian purely viscous fluids through fixed beds. In the first model, the ideas of flow around particles are considered simultaneously and the bed factor is used as a dynamic characteristic of the bed. In the second one, the tortuosity factor and dynamic specific area are used as bed structure parameters. The validity and accuracy of the models have been tested using an extensive set of experimental data concerning fixed beds of spherical and various shaped non spherical particles. In these experiments, 19 particle-fluid systems were investigated in the range of Reynolds number including creeping and transition flow regimes, power-law fluid behaviour index was ranged between 0.27 and 1. The mean deviation between pressure drop model predictions and the whole set of experimental data is less than 10% for both models presented. The models are efficient even when important wall effect exists.