ABSTRACT
A natural circulation system operates on the basis of natural laws like gravity and buoyancy. Although natural circulation can be of use in several heat removal applications due to its simplicity in design, elimination of hazards related to pumps, better flow distribution, cost reduction, etc. the potential threat of flow instabilities still eludes for its wide applications. Although addition of local losses may suppress instabilities, however, it is accompanied by significant flow reduction which is detrimental to the natural circulation heat removal capability. In present work, we have demonstrated experimentally, with the use of nanofluids, not only the flow instabilities are suppressed but also the natural circulation flow rate is enhanced.
In this paper, we present the stability behaviour of a boiling two-phase natural circulation loop with Al2O3 nanofluids. For this, experiments were conducted in a natural circulation loop at different operating powers, pressures, and water levels in the steam drum using water alone and 1% Al2O3 nanofluid. The test results revealed that (i) in case of nanofluids, boiling occurs earlier than in case of water alone, (ii) natural circulation flow rates were found to be higher than that of water and interestingly (iii) the amplitudes of the boiling induced Type I instabilities are found to be significantly reduced with the use of nanofluids.
