This　paper　reports　on　the　results　of　an　experimental　study　on　the　heat　transfer　and　flow　performance　of　multiwalled　carbon　nanotubes　(MWCNT)　in　aqueous　suspensions　flowing　in　multiport　minichannel　flat　tubes　with　smooth/micro-fin　surface　under　a　constant　heat　flux　condition.　The　MWCNT-water　nanofluids　volume　concentrations　are　0.001%,　0.005%,　0.01%,　and　0.1%.　Results　indicate　that　the　friction　factor　and　the　Nusselt　number　of　the　nanofluids　are　higher　than　those　of　water.　The　Nusselt　number　does　not　increase　with　volume　concentration.　The　heat　transfer　of　nanofluids　in　the　micro-fin　tubes　is　higher　than　that　of　nanofluids　in　the　smooth　tube.　However,　the　heat　transfer　enhancement　of　nanofluids　in　the　micro-fin　tubes　is　lower　than　that　of　nanofluids　in　the　smooth　tube.　The　effect　of　micro-fin　spacing　is　more　evident　in　nanofluids　than　in　water.　Nanofluids　with　a　concentration　of　0.01%　flowing　in　the　tube　with　closely　spaced　micro-fin　tube　exhibit　the　optimal　thermal　performance　in　accordance　with　the　performance　evaluation　criterion.　(C)　2016　Elsevier　B.V.　All　rights　reserved.