Paper presented to the 10th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Florida, 14-16 July 2014.
Nanofluids are generally found to exhibit better thermophysical
properties and heat transfer capabilities than the corresponding
base fluids. Experimental and theoretical investigations on the
forced and free convection behavior have reported superior heat
transfer capability of nanofluids, except in a few cases. Studies
on natural/free convective heat transfer in nanofluids have
shown negative impacts when investigations were performed
on a vertical column of the fluid. The absence of a pumping
system makes natural circulation loops silent and also saves the
energy for pumping the fluid. Since the thermosyphon loop
resembles a forced circulation loop except for the absence of a
pump, a nanofluid can be expected to yield enhanced heat
transfer, compared to the base fluid. The present work captures
the heat transfer performance of oxide nanofluids in a
rectangular thermosyphon loop. The density gradient created by
the temperature gradient between the heating and cooling
sections, assisted by gravity, constitute the driving force in the
loop. The temperature of the fluid at the inlet and exit of the
heating sections and, on the pipe surface along the heating
section is measured. The effect of the external heat input,
concentration of nanofluids and average temperature of the
cooling section on the heat transfer are investigated. The results
have shown that the Al2O3 nanofluids have enhanced heat
transfer characteristics as compared to water in rectangular
thermosyphon loops.
