This　study　investigated　the　vapor　condensation　characteristics　in　an　inclined　pipe　under　natural　convection　conditions　experimentally　and　numerically.　The　inclined　blind-end　concentric　pipe　had　an　inner　diameter　of　134　mm　and　a　length　of　680　mm,　which　is　cooled　by　cooling　water.　The　experimental　pressure　range　was　0.2-0.6　MPa,　and　the　dimensionless　mass　number　range　was　0.44　to　202.　The　fog　formation　phenomenon　was　observed　in　the　experiment.　An　empirical　correlation　with　a　broad　range　of　dimensionless　mass　numbers　was　developed　based　on　the　experimental　results　to　predict　the　heat　transfer　coefficient　(HTC).　When　the　air　mass　fraction　was　large　and　the　HTC　was　low,　the　effect　of　fog　formation　on　the　HTC　had　to　be　considered.　In　the　numerical　simulation,　this　study　aimed　to　develop　an　HTC　prediction　model　with　broader　applicability.　Based　on　the　diffusion　boundary　layer　theory,　this　study　improved　Peterson＇s　model　by　adding　fog　effect　and　wave　effect.　The　model　showed　high　adaptability　to　this　experiment　and　other　experiments　in　the　natural　convection　condensation　database.　The　improved　model　performed　significantly　better,　with　96%　of　the　data　falling　within　an　error　zone　of　30%.　The　wide　range　of　dimensionless　mass　number　test　data　might　complement　the　natural　convection　condensation　experimental　database.　(c)　2021　Elsevier　Ltd.　All　rights　reserved.