Dissipative particle dynamics investigation of heat transfer mechanisms in Al₂O₃-water nanofluid

The current paper applied dissipative particle dynamics (DPD) approach to investigate the effect of nanoparticles on the heat transfer mechanisms in natural convection using Al₂O₃-water nanofluids. The study investigated in detail the effect of nanoparticle concentration on the random heat flux (i.e., Brownian motion) and the total heat flux. The DPD model considered the viscosity and the thermal conductivity of the Al₂O₃-water nanofluid to be dual function of temperature and volume fraction of nanoparticles. The study covered a wide range of nanoparticles (1% ≤ φ ≤ 7%) and three Rayleigh numbers were considered, which are Ra = 10⁴, Ra = 5 × 10⁴, and Ra = 10⁵. The DPD results predicted an enhancement in heat transfer due to the addition of nanoparticles. However, the results revealed that the relative of enhancement of the total heat flux in the cavity is more effective at low Rayleigh numbers than at high Rayleigh numbers. The regions around the hot wall of the cavity are found to experience the maximum enhancement in heat transfer in the cavity whereas the region adjacent to the cold wall experienced a deterioration in heat transfer due to the addition of nanoparticles. Also, the DPD results revealed that the role of Brownian motion in the vicinity of hot and cold walls was negligible where the ratio of random heat flux to the total heat flux was below 5%. However, this ratio reached a very large value around the center of the cavity and the bottom wall of the cavity, where this value at low Rayleigh number and high volume fraction of nanoparticles exceeded 65%. Moreover, the study revealed that the random heat flux enhances with increase of volume fraction of nanoparticles.