| Summary: | 碩士 === 國立成功大學 === 機械工程學系 === 87 === Due to the rapid growth of industrial development along with the rapid increase in population density over the past few years in many countries, the demand for fresh water has risen to a record level. Therefore, people are becoming aware of the importance of water resource. It is commonly believed that the seawater desalination may be the most reliable way to provide enough fresh water for the next coming century. Among many seawater desalination methods, MD method embodies the advantages of both the conventional membrane separation and the conventional distillation methods.
Membrane distillation essentially is a process in which two solutions at different temperatures are separated by a microporous-hydrophobic membrane. As a result of the temperature difference, it causes a corresponding vapor pressure difference across the membrane to provide the driving force for the membrane distillation process. The vapor evaporates through the membrane, and condenses on the coolant surface at the other side of the membrane.
This paper is focused on air-gap membrane distillation (AGMD). A single-stage AGMD apparatus is set up to study the heat and mass transfer process. Various kinds of membranes are used to examine the relationship between the permeate and many other important parameters such as feed and cooling temperatures, membrane pore size, porosity etc. After a certain period of operation, the crystallized salts will appear at membrane surface. The detailed structure of membranes before and after long-time tests are examinated by scanning electron microscopy (SEM). The obtained experimental data indicates that the permeate flux decreases sharply if the temperature difference between feed water and cooling water is over 30℃。
|
|---|
