Nanofluids suppress secondary flow in laminar pipe flow

For the first time it is experimentally shown that free convection in laminar pipe flow with constant heat flux is significantly suppressed by nanoparticles. Moreover, for nanofluid flow with high heating power, an increase above the analytical solution for pure forced convection is lowered by increasing inlet temperature. It is argued that an explanation for the observed effects can only be found if nanofluids are strictly understood as two-phase media. Especially Brownian diffusion is seen as one of the players equalising thermal gradients necessary for thermal instabilities to grow.