A　visualization　study　of　boiling　and　condensation　co-existing　phase　change　heat　transfer　in　a　small　confined　space　is　conducted　with　de-ionized　water　as　the　working　medium.　The　confined　space　is　a　closed　chamber　that　consists　of　a　heating　copper　rod　(40　mm　in　diameter)　whose　top　end　is　used　as　boiling　surface,　a　cooling　copper　block　whose　bottom　end　(40　mm　in　diameter)　is　used　as　condensing　surface　and　a　circular　quartz　glass　tube.　The　spacing　between　the　boiling　and　the　condensation　surface　is　33　mm,　water　layer　thickness　in　the　chamber　is　set　at　9　mm,　12　mm,　15　mm,　18　mm,　21　mm　and　24　mm,　respectively.　Experimental　observation　and　results　show　that,　at　the　covered　heat　flux　region　(4.6　x　10(4)　W/m(2)-9.7　x　10(4)　W/m(2))　in　this　paper,　the　boiling　and　condensation　processes　have　strong　interactions　over　each　other　and　there　always　exist　an　optimum　liquid　level　at　which　both　boiling　and　condensation　heat　transfer　coefficients　acquired　their　maximum　values.　Typical　images　and　possible　explanations　for　the　heat　transfer　characteristics　of　different　water　layer　thicknesses　are　presented　and　it　is　disclosed　that　the　heat　transfer　performance　is　strongly　related　to　the　interaction　between　boiling　and　condensation.　Some　peculiar　phenomena　are　reported　of　the　bubble　behavior　and　boiling-condensation　interactions.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.