The　characteristics　of　fluid　flow　and　mass　transfer　in　a　novel　micromixer　with　gaps　and　baffles　are　studied　numerically　and　experimentally.　Based　on　the　principles　of　multiple　vortices,　abrupt　contraction/expansion　and　twice　split/recombine,　the　effects　of　gaps　and　baffles　are　investigated　considering　both　mixing　performance　and　pressure　drop　at　Reynolds　numbers　ranging　from　0.1　to　60.　The　mixing　efficiency　of　the　novel　micromixer　is　found　to　be　as　high　as　over　94%　at　extremely　low　(Re　=　0.1)　or　high　Reynolds　number　(Re　＞=　40).　The　mechanism　of　mass　transfer　enhancement　in　the　novel　micromixer　is　analyzed　by　the　field　synergy　principle.　It　is　found　that　the　novel　micromixer　is　helpful　to　mass　transfer　enhancement　which　can　be　attributed　to　a　good　synergy　between　the　velocity　field　and　the　concentration　field.　It　is　shown　that　the　field　synergy　principle　provides　an　alternative　way　to　evaluate　the　performance　of　micromixers.　In　addition,　the　influence　of　the　different　locations　of　gaps　and　baffles　on　the　mixing　performance　is　analyzed.　The　comprehensive　performance　of　micromixers　is　investigated　by　the　field　synergy　principle　and　the　ratio　of　the　mixing　index　to　the　pressure　drop　(MI/PD).　The　merits　of　rapid　mixing,　low　energy　consumption　and　short　mixing　length　make　the　novel　micromixer　more　promising　in　microfluidic　application.　(C)　2015　Elsevier　Ltd.　All　rights　reserved.