A　visualization　study　of　boiling　and　condensation　co-existing　phase　change　heat　transfer　in　small　and　closed　spaces　with　a　boiling　surface　of　enhanced　structures　is　experimentally　investigated.　The　enhanced　structure　is　fin　arrays　(1.4　x　1.4　x　1.4　mm)　that　directly　manufactured　on　the　top　end　of　the　copper　rod　(40　mm　in　diameter)　which　is　used　as　the　boiling　surface　of　the　confined　space.　A　cooling　copper　block　whose　bottom　end　(40　mm　in　diameter)　is　used　as　condensation　surface　of　the　confined　space　and　a　circular　quartz　glass　tube　is　used　as　the　side　wall　to　observe　the　phenomenon.　The　spacing　between　the　base　of　the　fins　and　the　condensation　surface　is　33　mm.　Liquid　level　(the　water　layer　thickness　in　the　chamber)　is　set　at　9　mm,　18　mm,　and　24　mm,　respectively.　Experimental　results　and　observation　show　that　within　the　covered　heat　flux　region　(4.6　x　10(4)-9.7　x　10(4)　W/m(2))　in　this　paper,　boiling　heat　transfer　is　depressed　while　condensation　heat　transfer　is　enhanced　as　the　increase　of　the　liquid　level.　Typical　images　and　possible　explanations　for　the　heat　transfer　characteristics　of　different　liquid　levels　and　heat　fluxes　are　presented.　Isolated　bubble　regime　and　mushroom　cloud　as　well　as　bubble　coalescence　are　also　found.　The　comparison　between　plain　surface　and　enhanced　surface　shows　that　boiling　heat　transfer　is　significantly　enhanced　by　the　fin　arrays.　The　heat　transfer　resistance　analysis　of　the　confined　space　is　also　performed　and　it　is　disclosed　that　the　heat　transfer　resistance　of　the　condensation　surface　is　the　largest　part　of　the　overall　heat　transfer　resistance.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.