A　hydrodynamics　of　deionized　water　flowing　through　the　micro　heat　sinks　with　cavities　and　ribs　are　investigated　experimentally.　The　Reynolds　number　ranges　from　70　to　320.　Using　micro　particle　image　velocimetry　(Micro-PIV)　and　numerical　simulation,　velocity　and　vector　fields　are　both　obtained.　The　comparative　results　show　that　the　distribution　of　centerline　velocity　changes　periodically,　which　shows　good　agreement　between　simulations　and　experiments.　Moreover,　the　vortices　easily　form　in　the　cavities　zones　if　the　kinetic　energy　and　negative　pressure　gradient　exhaust　along　the　flow　direction.　The　physical　mechanism　of　heat　transfer　enhancement　is　explained　from　the　view　point　of　fluid　flow.　The　main　reasons　can　ascribe　that　the　heat　transfer　area　and　flow　turbulence　increase　due　to　the　existent　of　cavities　and　ribs　under　small　Reynolds　number;　the　secondary　flow　is　helpful　for　mixing　the　cold　and　hot　fluid　in　cavities　zones　as　well　as　the　increased　turbulence　in　ribs　zones　under　high　Reynolds　number.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.