Experimental investigation on heat transfer of n-decane-ZnO nanofluids in a horizontal tube under supercritical pressure

Abstract

Kerosene-based nanofluid is the potential cryogenic propellant for regenerative cooling system applied in scramjet. The heat transfer characteristics of n-decane with ZnO nanoparticle have been experimentally investigated in a horizontal tube. The flowing nanofluids are pressurized to a supercritical pressure of 3 MPa and heated at non-cracking temperature range under two different heating power. The experimental volume flow rate is fixed at 0.5 ml/s. Results indicate that the test section could be divided into subcritical zone, pseudo-critical zone and supercritical zone. ZnO nanoparticles mainly influence the heat transfer by changing the fluids thermo-physical properties, rather than influencing flow pattern, at pseudo-critical and supercritical zones. At pseudo-critical zone, ZnO nanoparticles modify initial position of pseudo-boiling and enlarge ranges by weakening the pseudo-boiling effect. Compared to n-decane, nanoparticles postpone the temperature of Nu number increasing to the maximum and weaken the heat transfer deterioration. At supercritical zone, the addition of ZnO nanoparticles could further enhance heat transfer. Under supercritical pressure, 0.2 wt% n-decane-ZnO effectively enhanced heat transfer and the Nu increased more than 20%. Based on the experimental results, heat transfer correlations of nanofluids under supercritical pressure are obtained and the calculated values match experimental results well with a reasonable deviation.