(An) experiment study of counter-current flow limitation and re-flooding heat transfer phenomenon of nano-fluids

Abstract

The first part of this study was investigated on Reflooding heat transfer phenomenon of nanofluids. A reflooding (quenching) phenomenon is important for analysis of the reflood phase associated with the emergency cooling in water-cooled nuclear reactor core under a loss of coolant accident and the reflood is happened when water refills the reactor vessel and quenches the fuel rod at the time of the severe accident in nuclear power plant. In the first part, we have observed a quenching phenomenon of a hot vertical tube during a reflood using waterbased nanofluids as a coolant, instead of water. The result shown that there quench speeds of nanofluids were faster compare to water. It was shown too that the nanofluids were more hydrophilic since the shifting of cooling time to the left. The minimum heat flux found higher on nanofluids case compare to water. The effect of roughness on nanocoated surface had shown that there more cavity distribution which creates more heterogeneous nucleation bubbles. Theoretical reasoning of the reflooding mechanism and phenomenon was explored. The second part of this study was investigated on the Flooding (CCFL) of air-water and air-nanofluids. Flooding (CCFL) is determined as the point at which the relative velocities of two fluids results in a change in the directions of a portion of the liquid phase. In the nuclear reactor system counter current flow limit (CCFL) or flooding is an interesting phenomenon since it could prevents the emergency coolant injected by the emergency core cooling system (ECCS) from entering the core region. In the second part of this study, experiments have been conducted on countercurrent flow of air-water and air-nanofluids in a tube. In particular, the effects of nanofluids to the flooding behavior were investigated. The experimental investigation has been carried by injecting from the top 0.001 Vol%, 0.01 Vol.%, and 0.1Vol.% CNT nanofluids and $Al_2O_3$ nanofluids to a transparent tube with a diameter of 25mm and high of 1 meter

meanwhile we were injecting air from the bottom of tube. The result showed a slightly enhanced of a flooding air flow rate in the case of air-nanofluids compare to that of air-purewater. It was evident that the fluids properties are effect to the counter-current flow limitations. According to the visual observation it could concluded that the mechanism of the enhancement is due to the wave entrainment.