Sarah Kang

Effects of nanofluids containing graphene/graphene-oxide nanosheets on critical heat flux

The superb thermal conduction property of graphene establishes graphene as an excellent material for thermal management. In this paper, we selected graphene/graphene oxide nanosheets as the additives in nanofluids. The authors interestingly found that the highly enhanced critical heat flux (CHF) in the nanofluids containing graphene/graphene-oxide nanosheets (GON) cannot be explained by both the improved surface wettability and the capillarity of the nanoparticles deposition layer. Here we highlights that the GON nanofluid can be exploited to maximize the CHF the most efficiently by building up a characteristically ordered porous surface structure due to its own self-assembly characteristic resulting in a geometrically changed critical instability wavelength.

CRITICAL HEAT FLUX ENHANCEMENT IN FLOW BOILING OF Al₂O₃ AND SiC NANOFLUIDS UNDER LOW PRESSURE AND LOW FLOW CONDITIONS

Critical heat flux (CHF) is the thermal limit of a phenomenon in which a phase change occurs during heating (such as bubbles forming on a metal surface used to heat water), which suddenly decreases the heat transfer efficiency, thus causing localized overheating of the heating surface. The enhancement of CHF can increase the safety margins and allow operation at higher heat fluxes; thus, it can increase the economy. A very interesting characteristic of nanofluids is their ability to significantly enhance the CHF. Nanofluids are nanotechnology-based colloidal dispersions engineered through the stable suspension of nanoparticles. All experiments were performed in round tubes with an inner diameter of 0.01041 m and a length of 0.5 m under low pressure and low flow (LPLF) conditions at a fixed inlet temperature using water, 0.01 vol.% Al2O3/water nanofluid, and SiC/water nanofluid. It was found that the CHF of the nanofluids was enhanced and the CHF of the SiC/water nanofluid was more enhanced than that of the Al2O3/water nanofluid.

Numerical study of in-vessel retention under the gallium–water external reactor vessel cooling system using MARS-LMR

To confirm the feasibility of the gallium–water IVR-ERVCS (in-vessel retention-external reactor vessel cooling system), this paper focuses on the numerical simulation of severe accidents in APR 1400 using MARS-LMR (multidimensional analysis of reactor safety-liquid metal reactor). To analyze the gallium-cooled systems, the properties of liquid gallium were added to the MARS-LMR code used in our previous work. In this system, the generated decay heat is transferred to liquid gallium through the reactor pressure vessel and then removed from the water pool as a heat sink. The numerical analyses results show that the temperature range of the liquid gallium is much lower than its boiling point and confirm the natural convection. Sensitivity studies were also performed by changing several parameters such as the initial temperature of gallium and water pool inventory and their results indicated that the working time of the gallium–water IVR-ERVCS depends on the inventory of the water pool. Because liquid gallium in this system does not have a phase change, unlike water, the gallium–water IVR-ERVCS can provide stable and reliable cooling capability. To solve the limitation due to critical heat flux in IVR-ERVCS and to ensure the sufficient thermal margin, it is confirmed that the gallium–water IVR-ERVCS can be a successful severe accident mitigation strategy in nuclear power plants.