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In this study, the performance of using radiant barrier in inclined roof was numerically investigated by using the COMSOL Multiphysics software package. A roof was simulated as two parallel plates with an air gap in between for enhancing ventilation through convection heat transfer. The simulated results were validated using a published experimental work. Results suggest that a maximum of 89% reduction in the heat gain through the roof for a heated channel with a uniform heat flux of 650 W/m2 was possible. Moreover, the roof inclination angle reduces the heatgain through the roof up to 41.5% for an inclined angle of 75 degrees. Variable heat variation effect was considered in a case study to account for ambient temperature and solar heat flux intensity variation from hour to hour throughout the day. This effect will have a direct impact on the heat transfer through the roof. Using radiant barrier helps reduce the amount of heat transfer through the roof up to 28.2% when 75-degree inclined roof is used. [ABSTRACT FROM AUTHOR]

Film boiling is an important phenomenon in the evaluation of an emergency core cooling system following a hypothetical loss of coolant accident in a nuclear reactor. This study investigates the effects of liquid subcooling, surface oxidation, and surface materials on the minimum film-boiling temperature . Quenching experiments were performed using stainless steel and zirconium (Zr) test samples. The samples were heated to a temperature well above then plunged vertically in various degrees of liquid subcooling pools. A visualization study using a high-speed camera was conducted to capture the quenching behavior. Additionally, surface characterization analyses including X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy were performed to quantify the surface conditions. Results indicate that liquid subcooling has a strong influence on . The visualization study shows a very thin vapor formation around the test sample for higher subcooling pools which explains the enhancement in the heat transfer. It is observed from the surface characterization analyses that the variations in the surface condition of the stainless steel and Zr causes the vapor bubbles to depart differently in the nucleate boiling regime. Furthermore, the effect of surface oxidation is clearly noticeable in the Zr test sample compared to the stainless steel test sample due to the oxidation kinematic of each substrate material. It is found that the substrate thermophysical properties have a significant impact on . Comparing the bare substrates shows that for the same degrees of liquid subcooling pool, the value of for the Zr sample is ∼30°C to 60°C higher compared to the stainless steel sample. Moreover, increasing the degrees of liquid subcooling contributes to a significant increase in that varies between ∼50°C and 70°C for both samples. [ABSTRACT FROM AUTHOR]