Phase　change　heat　transfer　in　micro　heat　sink　was　an　effective　method　to　solve　the　thermal　issues　of　high　heat　flux　micro　devices.　The　geometric　structure　modification　of　the　micro　heat　sink　could　enhance　its　heat　transfer　performance　obviously.　In　this　paper,　a　microchannel　with　triangular　cavities　and　rectangular　fins　(Tri.C-Rec.F)　was　fabricated　for　the　purpose　of　flow　boiling　improvement.　Flow　boiling　experiments　were　carried　out　using　pure　acetone　with　a　fixed　inlet　temperature　of　29　degrees　C　at　four　mass　fluxes　83　kg/(m(2).$),　147　kg/(m(2).$),　324　kg/(m(2).$)　and　442　kg/(m(2).$),　effective　heat　flux　ranging　from　0　to　101　W/cm(2).　The　flow　boiling　characteristics　of　the　microchannel　Tri.C-Rec.F　were　studied　and　compared　with　those　of　the　conventional　rectangular　microchannel　(R).　The　physics　behind　the　flow　boiling　process　and　the　heat　transfer　enhancement　mechanisms　of　the　micro　heat　sink　were　explored.　Experimental　results　indicated　that　the　microchannel　Tri.C-Rec.F　showed　significant　enhanced　heat　transfer,　reduced　onset　of　nucleate　boiling　(ONB),　and　delayed　critical　heat　flux　(CHF)　compared　to　the　microchannel　R　because　of　the　increased　bubble　nucleation　and　the　particular　flow　boiling　phenomena.　Moreover,　the　modified　microchannel　improved　the　flow　boiling　stability　distinctly　for　high　mass　fluxes.　The　continuously　developing　liquid　film　could　enhance　the　liquid　film　evaporation,　maintain　the　liquid　supplement　and　prevent　partial　dryout　effectively.　The　flow　disturbance　effect　of　the　micro　structures　and　the　bubble　breaking　effect　of　the　micro　fins　promoted　bubble　departure　and　mitigated　the　flow　reversal.　The　microchannel　Tri.C-Rec.F　presented　a　remarkable　higher　heat　transfer　coefficient　than　microchannel　R　with　a　maximum　increment　of　300%　and　51.6%　at　G　=　=83　and　442　kg/(m(2).$),　respectively.　The　acceleration,　disturbance　and　separation　effects　of　the　micro　fins　increased　the　pressure　drop,　which　could　be　improved　by　further　structural　optimization.　(C)　2019　Elsevier　Ltd.　All　rights　reserved.