Feasibility Study of Heat Transfer Enhancement by Ultrasonic Vibration Under Subcooled Pool Condition

ABSTRACT

In this study, experimental tests were carried out to investigate the feasibility of heat transfer enhancement by ultrasonic vibration under a subcooled pool condition. A commercial stainless-steel heater was utilized along with a water tank, and three ultrasonic transducers were attached underneath the tank bottom to generate ultrasonic vibration with a frequency of 40 kHz and total power of 150 W. For demonstrating the effectiveness, the tests were performed with and without ultrasonic vibration under a constant water temperature of 30°C and pressure of 1 atm. The heights of heater were set at 15, 22, and 33 mm from the tank bottom, and the heat flux was operated from 7800 to 70800 W/m², which covered the regimes of single phase natural convection and subcooled nucleate boiling. Instantaneous signals of temperature and heat flux were recorded during the experiment, and the heat transfer coefficients were determined for each condition. The results show that the heat transfer coefficient can increase up to 3880 W/m²K and the enhancement ratio can reach up to 284% by ultrasonic vibration. Trends of heat transfer increments and enhancement ratios against heat flux and height were presented. This study successfully demonstrated the feasibility of heat transfer enhancement by ultrasonic vibrations.

Nomenclature

A	=	Heat transfer area of the heater, m2
g	=	Gravitational acceleration, m/s2
h	=	Heat transfer coefficient,  W/m2 · K
hu	=	Heat transfer coefficient under ultrasonic vibration,  W/m2 · K
ho	=	Heat transfer coefficient without vibration,  W/m2 · K
(hu − h0)	=	Heat transfer increment, W/m2 · K
H	=	Height from the tank bottom to the heater, mm
i	=	Current, A
L	=	Heater length, m
Nu	=	Nusselt number, dimensionless
q″	=	Heat flux per area, W/m2
Q	=	Electric power, W
Ra	=	Rayleigh number, dimensionless
Th	=	Heater surface temperature, °C
Tl	=	Water temperature, °C
v	=	Voltage, V

Greek symbols

α	=	Thermal diffusivity, m2/s
β	=	Thermal expansion coefficient, K−1
η	=	Heat transfer enhancement ratio, dimensionless
ν	=	Kinematic viscosity, m2/s
Φ	=	Rod diameter, m

Acknowledgments

The authors would like to express their sincere appreciations to the supports from Ministry of Science and Technology, Atomic Energy Commission and Taiwan Power Company of Taiwan.

Additional information

Notes on contributors

Fang-Chin Liu

Fang-Chin Liu is a master student at National Tsing Hua University, Hsinchu, Taiwan, under the supervision of Prof. Shao-Wen Chen. She received the Tai-Power Scholarship for her master study, and she has become a prospective employee of Taiwan Power Company. She is currently working on heat transfer under ultrasonic field.

Shao-Wen Chen

Shao-Wen Chen is an Assistant Professor in the Institute of Nuclear Engineering and Science at National Tsing Hua University (NTHU), Taiwan. He received his B.S. and M.S. from NTHU in 1999 and 2001, respectively. In 2001-2007, he worked in Industrial Technology Research Institute as an engineer. After that, he joined the Nuclear Engineering at Purdue University for a higher degree. In 2012, he received the Ph.D. degree and then continued his work as a post-doctoral research associate at Purdue. Since 2013, he has been at the present position in NTHU. He is currently working on the thermal-fluids topics including two-phase flow, boiling heat transfer, reactor safety and accident analysis.

Jin-Der Lee

Jin-Der Lee is a nuclear scientist at Nuclear Science and Technology Development Center in National Tsing Hua University, Hsinchu, Taiwan. He received his Ph.D. degree in Nuclear Engineering from National Tsing Hua University, Hisnchu, Taiwan, in 2000. His research interests include reactor safety, two-phase flow, boiling heat transfer, and stability analysis.