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Operating limit of heat transport in two-phase thermosyphon with connecting pipe (heated surface temperature fluctuation and flow pattern)
Authors:Toshiaki Inoue  Masanori Monde
Affiliation:1. Department of Mechanical Engineering, Kurume Institute of Technology, 2228 Kamitsu, Kurume, Fukuoka 830-0052, Japan;2. Department of Mechanical Engineering, Saga University, 1 Honjo, Saga 840-8502, Japan;1. Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India;2. Department of Mechanical Engineering, Indian Institute of Technology Kharagpur, Kharagpur 721302, India;1. Centre for Research in Material Science and Thermal Management, School of Mechanical Sciences, Karunya University, Coimbatore 641114, India;2. Department of Mechanical Engineering, Sri Ramakrishna Engineering College, Coimbatore, India;1. Homi Bhabha National Institute, Mumbai, Maharashtra 400 094, India;2. Bhabha Atomic Research Centre, Mumbai, Maharashtra 400 085, India
Abstract:An experiment on heat transport phenomena has been carried out in a two-phase thermosyphon with an adiabatic connecting pipe using water as the working fluid at atmospheric pressure. The thermosyphon has an upper liquid chamber and a lower vapor chamber, which are connected with an adiabatic pipe. A horizontal upward-facing heated surface is installed in the bottom of the lower vapor chamber.The size of the connecting pipe is an inner diameter Dp = 2, 3, 4, 5, 6 and 8 mm and a length L = 250, 500 and 1000 mm. As the heat is supplied into the thermosyphon, the temperature of heated surface starts fluctuating at a heat flux at which unstable vapor–liquid counter current flow is generated in the connecting pipe. Bubbles at the upper end of the connecting pipe were photographed when the temperature fluctuation started. It was found that the heat flux at the onset of the temperature fluctuation increases with an increase in Dp and then can be predicted well by Eq. (1), which was derived based on the flooding velocity presented by Wallis G.B. Wallis, One dimensional two-phase flow, McGraw Hill, New York, 1969], with Cw = 0.7 for Dp = 5, 6 and 8 mm. Furthermore, we clarified that the cause of this fluctuation comes from the inlet effect of the connecting pipe and we demonstrated this finding using a bell mouth, which was installed at either the bottom end or both ends of the connecting pipe.
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