Photofermentation is one alternative to produce hydrogen sustainably. The photobioreactor design is of crucial importance for an economically feasible operation, and an optimal design should provide uniform velocity and light distribution, low pressure drop, low gas permeability and efficient gas-liquid separation. A glass, stacked tubular bioreactor aimed at satisfying these criteria has been designed for outdoor photofermentative hydrogen production by purple non sulfur bacteria. The design consists of 4 stacked U-tubes (tube diameter 3 cm) and 2 vertical manifolds. The hydrodynamics of the 3-dimensional model of this reactor was solved via COMSOL Multiphysics 4.1. The effects of tube length (1.4, 2.0, 3.8 m), tube pitch (8, 10.5, 13 cm) and volumetric flow rate (25-250 L/h) on the flow distribution were investigated. The glass stacked tubular reactor design results in less ground area and longer life time. This design has been constructed and operated with using Rhodobacter capsulatus YO3 hup(-) and molasses as the carbon source under outdoor conditions. (C) 2016 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.