Investigation into a Nanofluid Based Double Tube Heat Exchanger

Abstract

Investigations into heat transfer characteristics of the internal flows have been of prime importance for many engineering applications. This thesis reports an experimental and numerical study on the forced convective heat transfer and flow characteristics of a TiO2-H2O nanofluid (0.05 % and 0.026 % volume concentration). The heat transfer coefficient and friction factor of the TiO2-H2O nanofluid flowing in a horizontal double-tube counter flow heat exchanger, with and without twisted tape inserts under turbulent flow conditions have been investigated experimentally. The twisted tapes of twist ratio 3.2, 4 and 6 have been considered for this purpose. Furthermore, a numerical study has been conducted with different nanoparticles (TiO2, Al2O3 and CuO) with their varying concentration and size under turbulent flow conditions. Numerical investigation is done in ANSYS Fluent 14.5 software. The experimental and numerical investigations have been conducted in Reynolds number range of 5000 to 25000. Experimental results show that the convective heat transfer coefficient of TiO2-H2O nanofluid of 0.05% volumetric concentration is slightly higher than that of the base fluid by 4-6 %. Also, with 0.05% TiO2-H2O nanofluid in a tube with twisted tape of twist ratio 3.2, the heat transfer coefficient is found to increase by 1.45 times the value of the heat transfer coefficient when water is used as a working fluid in a plain tube. Numerically, a comparison is made between single phase and two phase Computational Fluid Dynamics (CFD) models. For the problem under consideration the two phase model (mixture model) gives closer predictions of the convective heat transfer coefficient to the experimental data than the single-phase model. Numerical investigations show that, for 1% volumetric concentration, among the three nanoparticle considered, Al2O3 gives higher enhancement of heat transfer coefficient. Also, at lower volumetric concentrations of nanoparticle, varying the particle size does not cause significant difference in heat transfer coefficient .