[3] added the condition that the particles must be in colloidal suspension.
Choi and his colleagues have carried out experiments on heat transport in systems with CuO nanoparticles in water and Al2O3 particles in ethylene glycol and water.
They found that the particles improve the heat transport by as much as 20%, and they interpreted their result in terms of an improved thermal conductivity k/k0 which they named the effective thermal conductivity [3].