Experimental　investigation　of　nucleate　boiling　heat　transfer　of　a　water-based　multi-walled　carbon　nanotubes　(MWCNTs)　nanofluid　in　a　confined　space　is　presented　in　this　study.　First,　the　effects　of　four　different　surfactants　on　the　stability　of　the　nanofluids　were　investigated　and　the　suitable　surfactant　gum　acacia　(GA)　was　selected　for　the　boiling　experiments.　Then,　the　boiling　experiments　of　the　nanofluids　with　various　volume　fractions　(0.005-0.2%)　of　the　MWCNTs　were　conducted　at　a　sub-atmospheric　pressure　of　1　x　10(-3)　Pa　and　the　test　heat　fluxes　are　from　100　to　740　kW/m(2).　Furthermore,　GA　with　four　different　mass　fractions　was　respectively　dissolved　in　the　nanofluids　to　investigate　the　effect　of　the　GA　concentration　on　the　boiling　heat　transfer.　The　effects　of　the　heat　flux,　the　concentrations　of　the　MWCNTs　and　surfactants,　the　bubble　behaviors　and　the　surface　conditions　after　the　boiling　processes　have　been　analyzed.　The　results　show　that　the　MWCNTs　nanofluid　can　enhance　boiling　heat　transfer　as　compared　to　the　base　fluid.　This　is　mainly　caused　by　the　nanoparticles　deposition　on　the　boiling　surface　result　in　increasing　the　surface　roughness　and　reducing　surface　contact　angle.　It　is　also　found　that　addition　of　GA　can　inhibit　the　deposition　of　the　nanoparticles　but　may　reduce　the　boiling　heat　transfer　coefficient　of　the　nanofluids.　According　to　the　experimental　results,　the　maximum　heat　transfer　coefficient　enhancement　ratio　can　reach　40.53%.　It　is　also　noticed　that　the　heat　transfer　enhancement　ratio　decreases　with　increasing　the　heat　flux　at　lower　heat　fluxes　from　100　to　340　kW/m(2)　while　it　increases　with　increasing　the　heat　flux　at　higher　fluxes　from　340　to　740　kW/m(2).　At　the　lower　heat　fluxes,　the　deposition　layer　increases　the　frequency　of　bubble　formation　and　thus　the　boiling　heat　transfer　is　strengthened.　While　at　the　high　heat　fluxes,　the　increasing　heat　flux　may　strengthen　the　capability　of　the　nanoparticles　deposition　and　the　disturbance　of　the　nanoparticles　and　increase　the　enhancement　ratio　of　heat　transfer　coefficient.　(C)　2017　Elsevier　Ltd.　All　rights　reserved.