Membrane　distillation　(MD)　is　a　promising　desalination　technology　that　may　help　to　resolve　the　fresh　water　shortage.　Hydrophobic　flat-sheet　polyvinylidene　fluoride　(PVDF)　membranes　were　used　for　desalination　by　direct　contact　MD　(DCMD)　and　vacuum　MD　(VMD)　processes.　The　effect　of　the　operating　conditions,　such　as　the　feed　temperature,　flow　velocity　on　both　the　hot　and　cold　sides　and　the　concentration　of　the　feed　solution　were　investigated.　During　the　DCMD　processing　of　a　35　g/L　aqueous　NaCl　solution,　with　a　hot　side　temperature　of　73　degrees　C　and　a　cold　distillate　water　temperature　of　25　degrees　C,　the　permeate　flux　was　as　high　as　18.9　kg/m(2)　h　with　a　NaCl　rejection　of　99.8%.　A　permeate　flux　of　22.4　kg/m(2)　h　and　a　NaCl　rejection　of　99.9%　were　attained　during　the　VMD　process　at　the　same　feed　temperature　and　a　downstream　pressure　of　31.5　kPa.　Furthermore,　there　was　hardly　any　wetting　during　6　h　desalination　test.　A　dusty　gas　model　was　used　to　successfully　predict　the　permeating　flux　in　both　the　DCMD　and　VMD　processes,　and　the　mass　transfer　mechanisms　through　the　membrane　were　determined.　Comparison　of　the　flux　and　the　thermal　efficiency　in　the　DCMD　and　VMD　processes　under　the　same　conditions　demonstrated　that　this　type　of　thin　flat-sheet　membrane,　which　had　a　high　surface　hydrophobicity　and　a　sponge-like　cross-section,　was　more　suitable　for　use　in　the　VMD　process　than　in　the　DCMD　process.　(C)　2012　Elsevier　Ltd.　All　rights　reserved.