(A) study on the CHF enhancement mechanism related with surface effect by additives첨가제에 의한 표면효과와 연관된 임계열유속 증진 메커니즘에 대한 연구

Abstract

Critical heat flux (CHF) is one of the key issues in heat transfer system. It is directly related to effi-ciency and safety of the system. At the CHF point, a sudden increase of heat transfer surface temperature or a deterioration of heat transfer rate is shown, and it sets a limit in designing and operating the boiling heat transfer equipment in various power industries such as nuclear, fusion and fossil power plants. Therefore, a CHF enhancement can increase the safety margin and allow more efficient operation of a power plant due to higher operating heat flux. There are many methods for the CHF enhancement, and use of nanoparticles among them has been intensively studied in recent years. In this study, additives are tested for the CHF enhancement. The additives are boric acid and TSP which are used in present nuclear power plants, Al2O3 and CNT nanoparticles. The experiments with down-ward facing and vertical positions of the test heater showed the CHF enhancement effects with additives. Surface condition changes were observed and they were considered as reasons of the CHF enhancement effects. With wire heater experiments, relationships between CHF and boiling time & additive concentrations were shown and boiling processes with additives were also shown. The effects of the heater size and material (SS304 and SA508) on CHF were also tested. As a result of the experiments, semi-empirical model was de-velopment.