Dahiru U. Lawal

Flux Prediction in Direct Contact Membrane Distillation

Membrane distillation (MD) is a potential mean of water desalination. MD is a thermally driven desalination technology that has been employed in four basic configurations. One of these configuration is Direct Contact Membrane Distillation (DCMD). In DCMD, both hot and cold solution is maintained in direct contact with micro porous hydrophobic membrane material. Heat and mass transfer analysis was performed on DCMD. Based on Kinetic theory of gas, the performance of different models of membrane permeability (coefficient) was investigated under different DCMD operating parameters (feed temperature, coolant temperature and feed flow rate). Knudsen number provides the guideline in identifying the type of model of mass transfer to be considered under any given experimental conditions. Results revealed that for a given pore size under the same simulation and experimental conditions, Transition (Knudsen- Molecular diffusion) type of flow model predictions is in good agreement with the experimental results. Hence the best model to be consider for flux prediction in DCMD. The effect of membrane pore size was also studied. Results showed that permeate flux increases with increase in pore size up to the critical pore condition where the flux prediction remain constant (unchanged).

Performance of Air Gap Membrane Distillation Unit for Water Desalination

Due to water scarcity in the Arabic gulf region, water desalination technologies are considered extremely important. The present work represents a fundamental study on the effect of basic operating and design variables on the flux of an air gap membrane distillation (AGMD) unit for water desalination. The flat sheet, channeled air gap membrane distillation module was designed and manufactured locally. The effect of feed flow rate, feed temperature, coolant water temperature, the air gap width, and the water salinity on the module flux are investigated. Analytical model for heat and mass transfer is used to predict the flux and the model results are compared to the experimental ones. Results showed that the technique has good potential to be used for water desalination. The permeate flux is increased by increasing feed flow rate, feed temperature, decreasing the air gap width, decreasing coolant temperature, and decreasing salinity of feed water. For a given feed flow rate, the width of the air gap and the feed water temperature are found to be the most effective parameters in increasing the distillate flux. Predicting the permeate flux with analytical models for heat and mass transfer showed good agreement with experimental results.Copyright