Dong Won Lee

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.

MHD Analysis and Preparation of an Experiment for Developing the Korean Test Blanket Module

To develop a Korean (KO) test blanket module (TBM) for an International Thermonuclear Experimental Reactor (ITER), particularly for a liquid breeder type, a currently developed conventional code, CFX, with an electromagnetic module for analyzing the magnetohydrodynamics (MHD) effect of the liquid breeder under a high magnetic field is numerically validated using a theoretical equation and previous experimental data. From a comparison with the previous data, the code shows its capability to simulate the MHD effect very well. The KO TBM was then analyzed using the code for comparing the velocities and pressure drops when there was a high magnetic field of the ITER condition (5 T) and when there was not. From the analysis, the pressure drop increased from 0.008337 to 486.8 Pa, and the flow became more uniform in the upward region but concentrated in a corner or inlet manifold, which provided the idea to modify the manifold design. Since the pressure drop by the MHD effect will be tested with the constructed experimental loop for the liquid breeder, a preliminary analysis was performed using the installed test section and magnet, which can produce a magnetic field of up to 2.2 T.

MHD analysis and preparation of an experiment for developing the Korean Test Blanket Module

To develop a Korean (KO) test blanket module (TBM) for an International Thermonuclear Experimental Reactor (ITER), particularly for a liquid breeder type, a currently developed conventional code, CFX, with an electromagnetic module for analyzing the magnetohydrodynamics (MHD) effect of the liquid breeder under a high magnetic field is numerically validated using a theoretical equation and previous experimental data. From a comparison with the previous data, the code shows its capability to simulate the MHD effect very well. The KO TBM was then analyzed using the code for comparing the velocities and pressure drops when there was a high magnetic field of the ITER condition (5 T) and when there was not. From the analysis, the pressure drop increased from 0.008337 to 486.8 Pa, and the flow became more uniform in the upward region but concentrated in a corner or inlet manifold, which provided the idea to modify the manifold design. Since the pressure drop by the MHD effect will be tested with the constructed experimental loop for the liquid breeder, a preliminary analysis was performed using the installed test section and magnet, which can produce a magnetic field of up to 2.2 T.

Design and analysis of a high temperature and pressure he supplying system

In order to examine design and manufacturing techniques of the Korean Helium Cooled Molten Lithium (HCML) Test Blanket Module (TBM) for International Thermonuclear Experimental Reactor (ITER), we constructed a scale downed high temperature and high pressure helium supplying system which was linked with KoHLT-2 (Korea Heat Load Test-2). The main components for the helium supplying system (such as a circulator, a pre-heater and a heat exchanger) were designed and manufactured base on analyses of commercial CFD code, ANSYS-CFX V11. A trial operation is scheduled up to the design pressure (9 MPa), temperature (500 °C) and helium mass flow rate (0.5 kg/s). In the near future, the system with heat load test facilities is utilized to test various mock-ups and to validate code with the test data.