Analysis of Convective Heat Transfer in Nanofluids Composed of Oxide-Ceramics Particles and Ethylene Glycol Aqueous Solution

For forced-convective flow in a resistive-heated cylindrical channel, the heat transfer coefficients and friction factor of the nanofluids composed of ethylene glycol aqueous solution (50 wt%) and oxide-ceramic nanoparticles, with particle diameter of 200 nm or 300 nm and particle volume concentration of 3.6%, were evaluated under constant heat-flux boundary conditions. The experiments were conducted under turbulent conditions, where the temperature at the entrance of the heated section was 353.15 K. The experimentally measured heat-transfer coefficients of all nanofluids were higher than those of the estimated coefficients obtained from their thermophysical properties. The difference between the experimental and estimated heat transfer coefficients followed the order of the absolute zeta potential value (i.e., the electrostatic repulsive force on the surface of particles) of the nanofluids, which may be owing to the dispersibility of the particles. At the same pumping power, the order of the heat exchange output in the nanofluids was, from largest to smallest, SiO2, ZrO2, Al2O3, and TiO2, which agreed well with the order of the absolute value of their zeta potential.

Automated summary

This study evaluates the heat transfer coefficients and friction factors of nanofluids composed of ethylene glycol aqueous solution and oxide-ceramic nanoparticles in a resistive-heated cylindrical channel. The experimental results show that the measured heat transfer coefficients are higher than the estimated coefficients based on the nanofluids' thermophysical properties. The difference between the experimental and estimated coefficients follows the order of the absolute zeta potential value of the nanofluids, indicating the importance of particle dispersibility. The heat exchange output in the nanofluids is in agreement with the order of their zeta potential values.