With　the　rapid　development　of　large　data　center,　the　required　power　consumption　increases　sharply.　The　thermal　management　of　that　accounts　for　about　33%　of　energy　consumption.　Single　phase　liquid　convection　heat　transfer　of　microchannel　heat　sink　has　been　thought　as　one　of　the　most　promising　methods.　For　energy　efficient　cooling,　optimized　microchannel　structures　is　one　important　approach.　Hence,　the　novel　offset　zigzag　microchannnel　is　proposed　and　optimized　for　inlet　Reynolds　number　ranging　from　200-800　in　this　paper.　The　heat　sink　is　composed　of　30　parallel　channels,　and　basic　structure　parameters　of　rectangular　channel　are　width　of　0.1　mm,　depth　of　0.3　mm,　length　of　5　mm　and　pitch　of　0.2　mm.　The　numerical　model　considers　entrance　effect,　viscous　heating　and　the　temperature-dependent　thermal-physical　properties.　In　order　to　study　the　influence　of　geometry　on　flow　and　heat　transfer　characteristics,　two　non-dimensional　variables　are　defined,　such　as　the　length　ratio　of　zigzag　length　to　channel　length　(alpha)　and　the　length　ratio　of　zigzag　expansion　to　zigzag　length　(gamma).　Results　indicate　the　zigzag　channel　can　effectively　prevent　the　rise　of　heat　surface　temperature　along　the　flow　direction　and　increase　the　minimum　temperature,　which　improves　the　temperature　distribution　uniformity.　Under　Re-in　=　650　and　alpha　=　0.04,　the　minimum　temperature　increases　from　309.9　K　to　310.1　K　and　maximum　temperature　decreases　from　324.02　K　to　318.91　K.　For　0.04　＜=　alpha　＜　0.1　and　alpha　＜　0.04　of　Re-in　＜　500,　the　thermal　characteristic　is　enhanced　and　the　flow　resistance　also　is　reduced.　Compared　with　rectangle　channel,　the　maximum　temperature　and　pressure　drop　of　zigzag　channel　with　alpha　=　0.04　of　Re-in　=　650　are　also　reduced　from　324.02　K　to　318.76　K　and　29.81　kPa　to　26.75　kPa,　respectively.　It　can　be　interpreted　that　with　the　decrease　of　alpha,　the　porosity　and　convection　heat　transfer　areas　are　increased　and　turbulence　intensity　of　fluid　flow　is　enhanced.　The　smaller　gamma　is　more　favorable　for　the　enhancement　of　heat　transfer　except　for　gamma　=　0　due　to　the　fluid　stagnation　at　the　bottom　of　zigzag　cavity.　However,　compared　with　rectangular　microchannel,　heat　transfer　is　enhanced　for　all　cases　and　flow　resistance　is　decreased　besides　gamma　=　0.1　of　Re-in　＞　500.　For　gamma　=　0　of　Re-in　=　650,　the　maximum　temperature　and　pressure　drop　are　reduced　from　324.02　K　to　318.01　K　and　298.81　kPa　to　27.91　kPa,　respectively.　The　overall　thermal　performance　is　measured　with　total　thermal　resistance　vs　pumping　power.　The　best　performance　of　offset　zigzag　microchannel　is　found　at　alpha　=　0.04　and　gamma　=　0.1.　For　Re-in　=　800,　the　maximum　temperature　of　heat　surface　is　decreased　5.65　K,　the　minimum　increased　0.36　K,　and　pumping　power　is　decreased　1.4%.　And　thermal　resistance　is　reduced　by　17.4%　at　the　P-p　=　0.167　W.　(C)　2016　Elsevier　Ltd.　All　rights　reserved.