THERMAL SCIENCE

International Scientific Journal

Thermal Science - Online First

Authors of this Paper

External Links

online first only

Visual study on two-phase flow in a horizontal closed-loop oscillating heat pipe

ABSTRACT
Two-phase flow boiling of working fluid within a closed-loop oscillating heat pipe in the horizontal orientation (HCLOHP) was studied visually. The HCLOHP was made of Pyrex glass tubes with an inside and outside diameter of 2 and 7 mm, respectively. The evaporator, adiabatic and condenser of the HCLOHP were 50 mm in length. The internal flow phenomena was carefully investigated for various number of turns, evaporator temperatures and filling ratios of the two working fluids, i.e. distilled water and absolute ethanol. The HCLOHP was installed on cooling and heating copper plates and the two-phase flow patterns were recorded by digital still and video cameras. The rate of heat transferred to the cooling water at the condenser was evaluated. The fluid motion characteristics may be separated into two main conditions viz., the oscillating slug flow and the standstill condition. The thermal performance improved when the number of turns reached the critical value of 10 turns at which the vapor fraction was small and the time fraction of oscillating flow was long. For both working fluids, the time fraction of oscillating flow was longest for 50% filling ratio, which led to the lowest thermal resistances. The wavy vapor-liquid interface which induced the vapor/liquid slug train formation was only found for water. Nucleate boiling followed by oscillating flow was discovered in the evaporator part only at the 50% and 80% filling ratios of water. At these filling ratios the thermal resistance of water tended to be lower than that of ethanol.
KEYWORDS
PAPER SUBMITTED: 2017-05-14
PAPER REVISED: 2017-11-04
PAPER ACCEPTED: 2017-11-09
PUBLISHED ONLINE: 2017-12-03
DOI REFERENCE: https://doi.org/10.2298/TSCI170514232C
REFERENCES
  1. Akachi, H., et al., Pulsating Heat Pipes, Proceedings, 5th International Heat Pipe Symposium, Melbourne, Australia, 1996, pp. 208-217
  2. Lee, W.H., et al., Characteristics of Pressure Oscillation in Self-Excited Oscillating Heat Pipe Based on Experimental Study, Proceedings, 6th International Heat Pipe Symposium, Chiang Mai, Thailand, 2000, pp. 394-403
  3. Qu, W., Ma, T., Experimental Investigation on Flow and Heat Transfer of a Pulsating Heat Pipe, Proceedings, 12th International Heat Pipe Conference, Moscow, Russia, 2002, pp. 226-231
  4. Khandekar, S., et al., Pulsating Heat Pipes: Thermo-Fluidic Characteristics and Comparative Study with Single Phase Thermosyphon, Proceedings, 12th International Heat Transfer Conference, Grenoble, France, 2002, pp. 459-464
  5. Khandekar, S., Groll, M., An Insight into Thermal-Hydrodynamic Coupling in Closed Loop Pulsating Heat Pipes, International Journal of Thermal Sciences, 43 (2004), 1, pp. 13-20
  6. Lin, Y.H., et al., Fabrication of Polydimethylsiloxane (PDMS) Pulsating Heat Pipe, Applied Thermal Engineering, 29 (2009), 2-3, pp. 573-580
  7. Charoensawan, P., et al., Closed Loop Pulsating Heat Pipes-Part A: Parametric Experimental Investigations, Applied Thermal Engineering, 23 (2003), 16, pp. 2009-2020
  8. Khandekar, S., et al., Closed Loop Pulsating Heat Pipes-Part B: Visualization and Semi-Empirical Modeling, Applied Thermal Engineering, 23 (2003), 16, pp. 2021-2033
  9. Charoensawan, P., Terdtoon, P., Thermal Performance of Horizontal Closed-Loop Oscillating Heat Pipes, Applied Thermal Engineering, 28 (2008), 5-6, pp. 460-466
  10. Yang, H., et al., Performance Characteristics of Pulsating Heat Pipes as integral Thermal Spreaders, International Journal of Thermal Sciences, 48 (2009), 4, pp. 815-824
  11. Lips, S., et al., Experimental Evidences of Distinct Heat Transfer Regimes in Pulsating Heat Pipes (PHP), Applied Thermal Engineering, 30 (2010), 8-9, pp. 900-907
  12. Lin, Z., et al., Heat Transfer Characteristics and LED Heat Sink Application of Aluminum Plate Oscillating Heat Pipes, Applied Thermal Engineering, 31 (2011), 14-15, pp. 2221-2229
  13. Kammuang-Lue, N., et al., Effect of Working Fluids and Internal Diameters on Thermal Performance of Vertical and Horizontal Closed-Loop Pulsating Heat Pipes with Multiple Heat Sources, Thermal Science, 20 (2016), 1, pp. 77-87
  14. Tong, B.Y., et al., Closed-Loop Pulsating Heat Pipe, Applied Thermal Engineering, 21 (2001), 18, pp. 1845-1862
  15. Miyazaki, Y., et al., Operating Limit of Oscillating Heat Pipe, Proceedings, 16th International Heat Pipe Conference, Lyon, France, 2012
  16. Qu, W., Ma, H.B., Theoretical Analysis of Startup of a Pulsating Heat Pipe, International Journal of Heat and Mass Transfer, 50 (2007), 11-12, pp. 2309-2316