A good understanding of the details of hydrodynamic and heat transport conditions and their impact on temperature polarisation and pressure drops is essential for optimum design of membrane distillation (MD) modules. To this end, the present work reports on initial progress in the development of a tool for 3D simulation of spacer-filled MD channels based on the open source CFD code library OpenFOAM. The paper discusses a number of modelling and implementation aspects including model geometry and computational domain, choice of boundary conditions, and discretisation schemes. The results pertaining to the effect of three different spacer types on the fluid dynamics and heat transfer inside the channel are presented and discussed in order to highlight the impact of spacer geometrical features on temperature polarisation and pressure drop. Of the three spacer types considered, the 3-layer spacer with the wall-adjacent filament layers aligned with the flow direction was found to cause the lowest pressure drop while producing a robust symmetrical temperature profile. The 2-layer flow aligned square spacer was found to be the least desirable design, producing asymmetric temperature and velocity profiles and high pressure drops. (c) 2012 Elsevier B.V. All rights reserved.