Performance evaluation and fouling behavior of a submerged vacuum membrane distillation system for desalination

Because of its potential for high permeate flux, vacuum membrane distillation (VMD) holds great promise for the desalination of water. However, high heat-transfer and mass-transfer resistances limit performance and encourage membrane fouling, making practical deployment difficult. In the present work, a submerged VMD module configuration is provided , in which the membrane module is submerged in the saline feed stream. To reduce temperature and concentration polarization, mechanical agitation is also applied. When agitation is introduced, comparative measurements show a ~30% increase in permeate flux compared to when it is not. This suggests that produced turbulence around hollow-fiber membranes greatly lowers temperature-polarization resistance. By operating at a vacuum pressure of 3000 Pa, which is securely below the liquid entrance pressure of around 1.2 bar, the system validates the integrity of the membrane and permits the measurement of permeability. The impacts of feed temperature were further investigated. The module obtained a permeate flux of 10.92 kg h⁻¹ m⁻² at 70 °C, and both model-based and experimental results emphasize feed temperature as a key factor influencing performance. These results show that agitation and module immersion are efficient ways to lower fouling risk and transfer resistances in VMD, providing a feasible path to increased desalination efficiency and accurate membrane characterization.