This　study　experimentally　investigated　TiO2-water　nanofluid　single-phase　flow　and　heat　transfer　characteristics　in　a　multiport　minichannel　flat　tube　with　a　1.65　mm　hydraulic　diameter.　TiO2　nanoparticles　with　nominal　diameters　of　10,　30,　and　50　nm　were　dispersed　in　water　at　various　volume　concentrations　ranging　from　0.005%　to　1%.　The　friction　factor　and　Nusselt　number　of　the　nanofluids　were　tested　and　compared　with　those　of　the　base　fluid,　the　Reynolds　number　of　which　varied　from　100　to　6100.　Results　indicated　that　friction　factor　and　Nusselt　number　of　the　nanofluids　were　higher　than　those　of　water.　Both　nanofluid　density　and　particle　migration　significantly　affected　friction　factor.　Meanwhile,　a　slightly　earlier　laminar-turbulent　transition　was　found　for　the　nanofluids.　Nu　did　not　increase　with　increasing　volume　concentration　and　decreased　with　increasing　particle　diameter　(4).　The　effects　of　thermal　conductivity,　viscosity,　and　chaotic　movement　of　nanoparticles　on　heat　transfer　were　discussed　in　this　study.　Nanofluids　at　0.01%　concentration　with　d(p)　=　10　nm　exhibited　the　best　performance　on　the　basis　of　the　evaluation　criterion,　which　considered　heat　transfer　enhancement　at　the　consequence　of　increased　friction　factor.　(C)　2014　Elsevier　Ltd.　All　rights　reserved.