Laminar convective heat transfer of Al2O3/water nanofluid through square cross-sectional duct

•Nanofluid in square duct improve inappropriate heat transfer performance.•Square duct wall temperature remarkable decreased using nanofluid.•Nanofluid in square duct increases Nusselt number of base fluid.•Theoretical correlations are not able to predict nanofluid thermal performance.•Using nanofluid be a trick to overcome poor thermal performance of square ducts. The present paper is an experimental study of Al2O3/water nanofluid convective heat transfer through square cross-sectional duct under constant heat flux in laminar flow. The increase of heat transfer coefficient is one of the most important technical aims for industry and researches. Also, the decrease in the pressure drop for systems that generate high fluid pressure drop is very noticeable. Convective heat transfer can be enhanced passively by changing flow geometry and boundary conditions or by improving the thermal conductivity of the working fluid. A square cross section duct has the advantage of lower pressure drop, but it has a lower heat exchange rate than that of a circular duct and it is expected that using of nanofluid as a new heat transfer media may improved the heat transfer performance of this kind of duct. In this study, convective heat transfer coefficients and Nusselt numbers of nanofluid were obtained for different Al2O3 nanoparticles concentrations as well as Peclet numbers. Experiments show that considerable enhancement of heat transfer coefficient is achieved and this enhancement is up to 27.6% at 2.5% volume fraction of nanoparticles comparing to the base fluid (water), also it has been noticed that convective heat transfer coefficient increases with the increment of nanoparticles’ concentration in nanofluid especially at high flow rates. The decrement of wall temperature observed using nanofluid.