The　effect　of　geometric　parameters　on　water　flow　and　heat　transfer　characteristics　in　microchannel　heat　sink　with　triangular　reentrant　cavities　is　numerically　investigated.　A　three-dimensional　laminar　flow　model,　consisting　of　Navier　Stokes　equations　and　energy　conservation　equation,　with　the　conjugate　heat　transfer　between　the　silicon　base　and　water　taken　into　consideration　is　solved　numerically.　In　order　to　find　the　optimum　geometric　parameters,　four　variables,　representing　the　distance　and　geometry　of　the　triangular　reentrant　cavity,　are　designed.　It　is　found　that　the　vortices　in　the　triangular　reentrant　cavities　lead　to　chaotic　advection　and　can　greatly　enhance　the　convective　fluid　mixing.　The　thermal　and　hydraulic　boundary　layers　are　interrupted　and　the　repeated　developing　flow　enhances　heat　transfer　in　the　constant　cross-section　segment.　Furthermore,　the　effects　of　the　four　design　variables　on　heat　transfer　augmentation　and　pressure　drop　penalty　are　investigated　depending　on　different　Reynolds　numbers　by　using　the　simulated　annealing　method.　Based　on　the　thermal　enhancement　factor　performance　maps,　the　optimal　geometric　parameters　are　obtained　in　principle.　Crown　Copyright　(C)　2010　Published　by　Elsevier　Ltd.　All　rights　reserved.