微孔膜的可压缩性及参数变化对膜蒸馏跨膜传质速率的影响

Compaction of microporous membrane and its influence on the mass flux of membrane distillation

针对两种聚四氟乙烯膜在膜两侧压差为10～100kPa范围内进行了气体渗透实验,结果表明:实验用膜具有一定的可压缩性,随膜两侧压差的增大,膜孔径r减小,而膜孔隙率与有效厚度的比值ε/τδ是增大的,且其变化幅度随膜厚度的增大而增大.通过求解数学模型方程得到了不同膜参数时直接接触式膜蒸馏和真空膜蒸馏跨膜传质速率的预测值,与相同条件下的膜蒸馏实验测定的传质速率进行对比,结果表明:由膜的可压缩性带来的膜参数变化能够使跨膜传质速率有所增长.采用相近压差下气体渗透实验测定的膜参数能够较准确地预测膜蒸馏的跨膜传质速率.

Two pieces of microporous polythtrafluoroethylene membranes of different parameters were employed to observe their compaction and its influence on membrane distillation. The gas permeation （GP） experiments were conducted with the pressure difference between the two sides of the membrane ranging from 10 to 100 kPa, and it was found that with the increase of pressure difference, the employed membranes show smaller membrane pore size and larger ε／τδ values. This reveals the compaction effect of the employed membranes. The mass fluxes for direct contact membrane distillation （DCMD） and vacuum membrane distillation （VMD） were obtained by solving the model equations of these two processes using different membrane parameters and by means of experiments respectively. And the results indicate that the changes in membrane parameters caused by compaction can result in enhanced mass flux for MD process. It is concluded that, for predicting mass flux of MD process, parameters should be obtained from the GP experiment conducted under the same pressure difference as that of MD process.