Numerical investigation of the single phase forced convection heat transfer characteristics of nanofluids flowing in enhanced tubes

Forced convection flows of nano ? uids containing of water with TiO2 nanoparticles in smooth and micro-fin tubes with constant wall temperature are studied numerically in this paper. A single-phase numerical model having two-dimensional equations is solved with either constant heat flux or temperature dependent properties to determine the hydrodynamics and thermal behaviors of the nano ? uid flow by means of a CFD program for the water flow in a smooth tube and several micro-fin tubes having various helix angles (0o,18o). An intensive literature review on the determination of the physical properties (k, µ, ?, Cp) of nanofluids is given in the paper. Artificial neural network (ANN) method is used to determine the most agreeable physical properties of TiO2 nanofluid among correlations. After obtaining the best combination of physical properties of TiO2 nanofluid from ANN analyses, the numerical model is validated by means of a CFD program using the experimental smooth tube data as a case study and it is also solved in the CFD program for several micro-fin tubes as a simulation study. Temperature and velocity distributions are shown in the paper. Besides this, the values of experimental and numerical are compared with each other in terms of friction factors, shear stresses, convective heat transfer coefficients and pressure drops. Moreover, the effect of the presence of micro-fins in the inner surface of the test tube on the heat transfer characteristics is investigated in detail.