Numerical investigation of nanofluid heat transfer in helically coiled tubes using the four-equation model

- Laminar, steady state flow in helically coiled tubes is studied numerically.
- Convective heat transfer of nanofluids are investigated with four-equation model.
- Brownian and thermophoresis are considered as nanoparticle/base-fluid slip mechanisms.
- The results are better matched with experimental results than homogenous model.

Helical coils and nanofluids are among efficient methods for heat transfer augmentation. The present study numerically investigates convective heat transfer with nanofluids in helically coiled tubes. Two boundary conditions are applied to the coil walls; constant temperature and constant heat flux. Heat transfer in nanofluids are mainly investigated using either the homogeneous model or the two-phase model. However, in the present numerical solution, the four-equation model is applied, using slip mechanisms for the base fluid and nanoparticles. Considering that the proposed model is simplified compared to the two-phase model, it can be regarded as an efficient model for numerical solution of heat transfer in nanofluids. Governing equations are solved in the non-dimensional form using the projection algorithm of finite difference method. Water/CuO with a 0.2% volume fraction and water/Ag with a 0.03% volume fraction are examined for validation of numerical results in case of constant temperature and constant heat flux boundary conditions, respectively. The obtained results show a better agreement of this model with respect to experimental data, compared to the homogeneous model.

Laminar, steady state, incompressible viscous flow for two different nanofluid in two different boundary conditions was studied through helical coil with a general two component nonhomogeneous equilibrium model developed by Buongiorno considering the effects of Brownian diffusion and thermophoresis which have been identified as the two most important nanoparticles/base-fluid mechanisms.128