An Eulerian turbulent two phase flow model using kinetic theory ofgranular flows for the particle phase was developed in order to studyevolving upward turbulent gas particle flows in a pipe. Themodel takes the feedback of the particles into account and its resultsagree well with experiments. Simulations show that the pipe length required for particle laden turbulent flow to become fully developed is up to five times longer than an unladen flow. To increase theunderstanding of the dependence of the development length on particlediameter a simple model for the expected development length wasderived. It shows that the development length becomes shorter forincreasing particle diameters, which agrees with simulations up to aparticle diameter of 100 μm. Thereafter the development lengthbecomes longer again for increasing particle diameters because largerparticles need a longer time to adjust to the velocity of the carrierphase.