Liquid-vapor　phase　change　heat　transfer　on　nanoporous　membranes　in　facing　horizontal　upwards,　downwards　and　vertically　was　investigated.　Anodic　aluminum　oxide　(AAO)　membranes　were　as　the　nanoporous　substrates.　Water　was　supplied　through　nanoporous　membranes　by　pressure　difference.　Heat　transfer　characteristics　and　temperature　instability　were　analyzed　and　compared　among　three　orientations.　Results　showed　that　negative　slope　and　＇special　points＇　appeared　on　boiling　curves.　The　interaction　between　liquid　film　thickness　and　heat　transfer　coefficient　(HTC)　was　proposed　and　verified　to　be　the　main　mechanism　that　leading　to　this　phenomenon.　Because　the　rapid　replenishment　of　liquid　and　removal　of　heated　liquid　under　gravity,　horizontal　downward　surface　always　had　the　best　heat　transfer　performance　which　exhibited　maximal　enhancement　of　HTC　was　170%　and　70%　at　heat　flux　of　39　W/cm2　over　horizontal　upward　and　vertical　surfaces.　Temperature　instability　in　horizontal　downward　and　vertical　surfaces　had　the　similar　trend　and　became　more　pronounced　at　higher　heat　fluxes.　In　horizontal　upward　surface,　temperature　was　stable　at　the　heat　flux　range　of　40　55　W/cm2　and　＇thin　film　evaporation＇　was　realized.　In　addition,　the　maximum　heat　flux　was　calculated　by　liquid　transport　limit　and　kinetic　theory　limit　for　evaporation　and　a　comprehensive　understanding　was　established.　©　2020　Elsevier　Ltd