Numerical simulation of heat transfer of turbulent flow for non-Newtonian nano fluid in a coiled double pipe heat exchanger

In this research, the thermal and hydrodynamic behavior of a non-Newtonian nanofluid turbulent flow in the counterflow arrangement in a double pipe helical heat exchanger is numerically simulated. A solution of carboxymethyl cellulose powder in water with a mass percentage of 0.1% with a nanoparticle of aluminum oxide as a working fluid has been used. The CFD commercial software Fluent was used to solve the governing equations while the turbulent flow was simulated using k-ε turbulent model; the results were in a good agreement with experimental data. The effect of important parameters such as curvature, Reynolds number and volume percentage of aluminum oxide nanoparticles on the heat transfer has been investigated. The results show that as the curvature ratio increases in constant Dean (Dn) numbers, the Nu number and the coefficient of friction increases. The addition of nanoparticles of aluminum oxide to the base fluid for the flow with the constant Reynolds and Dn number increases the heat transfer and increases the pressure drop in the helically coiled tubes. The centrifugal force generated by the curvature of the coiled tube results in a secondary flow in the heat exchanger so that the heat transfer and pressure drop increased up to 35% and 30%, respectively, compared to the straight tubes. The effect of heat transfer enhancement methods on the hydrodynamic index has also been studied, so that in the helical coils, the amount of hydrodynamic index increased with decreasing curvature ratio and increasing the volume concentration of nanoparticles.