Nanofluids are suspensions of nanosized particles in any base fluid that show significant enhancement of their heat transfer properties at modest nanoparticle concentrations. Due to enhanced thermal properties at low nanoparticle concentration, it is a potential candidate for utilization in nuclear heat transfer applications. In the last decade, there have been few studies which indicate possible advantages of using nanofluids as a coolant in nuclear reactors during normal as well as accidental conditions. In continuation with these studies, the utilization of nanofluids as a viable candidate for emergency core cooling in nuclear reactors is explored in this paper by carrying out experiments in a scaled facility. The experiments carried out mainly focus on quenching behavior of a simulated nuclear fuel rod bundle by using 1% Alumina nanofluid as a coolant in emergency core cooling system (ECCS). In addition, its performance is compared with water. In the experiments, nuclear decay heat (from 1.5% to 2.6% reactor full power) is simulated through electrical heating. The present experiments show that, from heat transfer point of view, alumina nanofluids have a definite advantage over water as coolant for ECCS. Additionally, to assess the suitability of using nanofluids in reactors, their stability was investigated in radiation field. Our tests showed good stability even after very high dose of radiation, indicating the feasibility of their possible use in nuclear reactor heat transfer systems.
In this work, the vapor film thickness below a stagnant Leidenfrost drop at saturation temperature is predicted by performing a balance of the dominant forces acting on the drop. Inclusion of a new momentum force term is proposed. Two assumptions are considered for the radial velocity of vapor at drop–vapor interface. One of them is zero radial velocity at interface and the other is zero shear at interface. The actual scenario is expected to lie between these extremes. This is also supported by the comparison against experimental data on vapor film thickness. The effect of convection in the vapor layer is also modeled and it is shown that the use of ad hoc heat transfer coefficients in the vapor layer to explain difference between experiments and prediction is incorrect. Finally, it is highlighted that accurate prediction of the vapor layer characteristics also requires proper quantification of the shape of the drop–vapor interface.
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