Time and Frequency Characteristics of Pressure Fluctuations during Subcooled Nucleate Flow Boiling

ABSTRACT

Time and frequency analyses methods including PDF (Probability Density Function), CDF (Cumulative Probability Function), FFT (Fast Fourier Transform) and PSD (Power Spectral Density) were used to investigate the pressure fluctuation characteristics during subcooled nucleate flow boiling and the effects of various parameters. The experimental conditions were heating currents to a high frequency induction heater of 200–720 A, liquid temperatures of 50–85°C, and flow rates of 0–290 L/h. The CDF and PSD methods were more effective than the PDF and FFT methods for the time-frequency analyses of the pressure fluctuations. Higher heating currents, lower liquid temperatures and lower flow rates result in wider frequency distributions and larger pressure fluctuation amplitudes in the time domain and wider frequency distributions and higher PSD of the pressure fluctuations in the frequency domain. The effects of the operating conditions on the Onset of Nucleate Boiling (ONB) were analyzed qualitatively by correlating the pressure fluctuation signals with visual images obtained from the experiments. A pressure drop occurs at the ONB regardless of the conditions with the pressure drop appearing earlier at higher heating currents and liquid temperatures and lower flow rates.

Acknowledgments

This work was supported by the Tsinghua University Initiative Scientific Research Program (No. 20131089319), and the National Natural Science Foundation of China Science Fund for Creative Research Groups (No. 51621062). The authors thank Dr. Tien Zhang and Prof. Weizheng Zhang for their help with the experiments.

Additional information

Notes on contributors

Xuan Zhang

Xuan Zhang is a Ph.D. candidate in the Department of Thermal Engineering, Tsinghua University, Beijing, China. He received his B.S. from the Beijing Institute of Technology, majoring in thermal and power engineering, and continued his study at Tsinghua University for his Ph.D. degree with Prof. Xiaomin Wu. He is currently working on numerical and experimental studies of boiling heat transfer.

X.M. Wu

Xiaomin Wu is a Professor and Vice Director of the Institute of Engineering Thermophysics, Department of Thermal Engineering, Tsinghua University. She received her B.E. (1985), M.E. (1988) degrees from the Dalian University of Technology, and her Ph.D. (1996) degree from Hiroshima University. Her current interests include enhanced heat transfer and heat exchanger technologies, heat and mass transfer in air conditioning and refrigeration systems, heat transfer enhancement in miniature heat pipes, and the mechanisms and control of frost formation on cold surfaces.