Subcooled heating/boiling process under pool condition is widely seen in present engineering applications such as nuclear spent fuel pool and reactor core under maintenances and/or accident scenarios. In order to understand the heat transfer characteristics and possible enhancement mechanism of using ultrasonic vibration to improve the heat removal performance and safety operating ranges, detail investigations are required. In this study, experimental tests are carried out to investigate the heat transfer performance under pool natural convection and subcooled boiling conditions, and ultrasonic vibration is introduced to evaluate the possible enhancement performance. The commercial stainless-steel circular-rod heaters and ultrasonic vibrators are utilized to generate the heat flux of 4 × 10^3 × 2 × 10^5 W/m^2 and ultrasonic vibration waves with a frequency of 40 kHz and a power of 150W. Experimental tests are divided into two groups: (1) pool natural convection and subcooled boiling tests without vibration (stationary), and (2) pool natural convection and subcooled boiling tests with ultrasonic vibration. These tests are carried out under atmosphere pressure (1atm) with three subcooled pool temperatures. Detailed experimental data such as surface temperature, fluid temperature and heater power are recorded during the tests, and the heat transfer coefficients are analyzed for different operating conditions. Through this study, an experimental database of pool-subcooled heat transfer from single phase natural convection to pool boiling is established, and the heat transfer enhancement performance is identified and determined under with and without ultrasonic vibration conditions. The results shows that the heat transfer enhancement is higher in single phase than in subcooled boiling. The heat transfer augmentation is better in high heat flux condition. This paper can provide clear experimental evidences and better understanding about the influences of ultrasonic waves on heat transfer performance in pool conditions, and the experimental database can be useful for future safety design of reactor core and fuel storage.
