Experimental study on heat transfer of nanofluids in a vertical tube at supercritical pressures

Regenerative cooling system at supercritical conditions can accommodate high heat fluxes effectively in aerospace applications. The potential of nanofluids as regenerative coolants at supercritical pressures was evaluated in this work. Experiments were carried out to study the heat transfer characteristics of Al2O3-kerosene nanofluids flowing upward in a vertical minitube at supercritical pressures. Parametric effects of mass flow rate, heat flux, pressure and particle content on the heat transfer performance are presented. Results show that increasing the mass flow rate or pressure enhances heat transfer, while higher heat fluxes lead to poorer heat transfer performance. Nanofluids tend to deteriorate heat transfer at supercritical pressures because deposition of the nanoparticles smoothens the wall roughness and presents an additional thermal resistance. As the particle content increases, the heat transfer performance becomes worse. Based on the experimental data, a heat transfer correlation was established for Al2O3-kerosene nanofluids at supercritical pressures and the correlation shows good predictive ability.