Passive　containment　Air-cooling　System　(PAS)　is　an　important　passive　system　of　the　modular　small　nuclear　reactor,　ACP100.　After　a　severe　accident,　the　air　in　the　annular　gap　between　the　steel　shell　and　the　concrete　shell　of　the　containment　is　heated,　forming　buoyancy-driven　mixed　convection　which　removes　decay　heat.　Thus,　the　heat　transfer　of　mixed　convection　in　PAS　is　essential　for　the　safety　of　nuclear　reactor.　However,　there　are　very　less　related　studies　on　this　phenomenon.　In　the　present　study,　experiments　on　the　mixed　convection　of　atmospheric　air　in　a　parallel-plate　channel　with　one-side　heating　for　PAS　were　carried　out.　The　regions　of　Re,　Gr　and　Bo　range　from　1.7　×　104　to　8.8　×　104,　1.0　×　108　to　1.0　×　1010　and　4　×　10−5　to　90,　respectively.　Furthermore,　the　effect　of　the　inclination　angle　on　heat　transfer　was　analyzed　for　the　dome　which　is　an　integral　part　of　PAS.　A　heat　transfer　correlation　was　newly　proposed,　which　can　more　accurately　predict　the　heat　transfer　of　PAS　with　an　error　within　±15%.　In　addition,　the　predicted　values　of　heat　transfer　agree　well　with　other　experimental　data　of　mixed　convection　in　the　rectangular　channel.　The　present　research　puts　forward　a　new　model　for　the　analysis　of　PAS　heat　transfer　performance,　and　has　the　reference　significance　for　the　optimal　design　of　PAS.　©　2022