Experimental and numerical investigation of flow and heat transfer characteristics of Chinese ink nanofluid in built-in rotor tube

Abstract

For increasing the heat transfer efficiency of the tubular heat exchanger, Chinese ink (CI) nanofluid was applied in the built-rotor tube, and the effects of the mass fraction of CI and structures of the rotors were investigated through experiments and numerical simulations. The experimental results indicated that the heat transfer performance improved with an increase in the nanofluid mass fraction and that the nanofluid in the built-in rotor tube produced a better heat transfer enhancement effect than that in a plain tube (PT). The Nu of 0.1% CI nanofluid in the PT increased by 11.12%–13.69%, whereas that in the built-in rotor tube increased by 17.57%–18.94%. The flow pattern and temperature distribution in the tube were studied via numerical simulations. The addition of rotors can make the flow pattern change from an axial flow to a three-dimensional spiral flow. This flow pattern reduces the thickness of the laminar sublayer and the temperature of the medium near the wall, as well as the synergy angle in the tube, which makes nanofluid with good thermophysical properties have a better heat transfer enhancement effect in the built-in rotor tube than in the PT.