Investigation of convective heat transfer, pressure drop and efficiency of ZnO/water nanofluid in alternating elliptical axis tubes

In this study, for the first time, the heat transfer and the pressure drop of zinc oxide nanoparticles in alternating elliptical axis (AEA) tube have been investigated experimentally. The zinc oxide nanoparticles were at volumetric concentrations 1% and 2%. The base fluid was heat transfer oil and the experiments were conducted at constant wall temperature. Also, the study was done in Reynolds number range of 400- 1900. The experimental results show that the heat transfer, pressure drop and, the efficiency of AEA tubes are higher than the circular tube. The heat transfer rate and pressure drop increase by flattening the tube and adding nanoparticles. To compare the heat transfer and pressure drop simultaneously, an efficiency parameter is defined. This parameter shows how much increase in heat transfer can be obtained for the pressure drop of a circular tube with the same hydraulic diameter as the AEA tube. Using AEA tube with nanoparticles increases heat transfers by up to threefold, and pressure drop by up to twofold, resulting in an overall twofold increase in the efficiency.