Membrane distillation

Thermally driven Membrane Distillation (MD) has been identified as a promising approach for desalination or the separation of other aqueous solutions. This thesis presents comprehensive methods for MD process, module and system evaluation. The methods refer to the context of desalination, but their general validity also allows application to related MD separation problems. Extensive experimental and numerical analysis of the fundamental MD phenomenology in coupled heat and mass transfer is performed. The approach includes a comparative discussion on different MD process configurations, known as DCMD, PGMD and AGMD. The role of the key material properties and operational parameters is quantified experimentally and analysed. The results are then transferred to the scale of application, considering full-scale module flow channels. Different DCMD, PGMD and AGMD module prototypes with membrane surface areas of 5 to 15 m² were fabricated and characterised. The performance of the MD modules is comparatively discussed on the basis of key performance parameters such as output capacity, flux, thermal efficiency and thermal as well as electrical energy consumption. Suggestions on material selection are provided. Parametric field studies demonstrate the fundamental thermodynamic limitations imposed for the different MD processes. The technological discussion is followed by an economic evaluation of the different MD concepts in the context of small-scale desalination applications. A comprehensive cost model is suggested for the estimation of water unit costs, to be used as an integral quantitative measure for module and system comparison and as an optimisation criterion. Adapted module design specifications are derived by iterative techno-economic optimisation.