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Effects of internal diameter and working fluid on internal flow patterns of closed-end oscillating heat pipes at critical state.

Author(s) : SAKULCHANGSATJATAI P., TEWATA A., TERDTOON P.

Summary

This paper presents the experimental study of the effect of internal diameter and working fluid on the internal flow patterns of a closed-end oscillating heat pipe (CEOHP) operating at critical state. A set of CEOHPs was made of Pyrex glass capillary tubes. The number of turn and lengths of the evaporator, adiabatic and condenser sections of all the CEOHPs were set at 5 and 50 mm, respectively. The CEOHPs were set to operate in vertical orientation under bottom heat mode. Two internal diameters, 1.5 and 2.0 mm, and two working fluids, R123 and a one-to-one by volume mixed solution of water and ethanol, were selected as studied parameters. From the results obtained, it can be concluded as follows. At critical state the flow pattern in a smaller internal diameter CEOHP tended to be a combination of annular and churn flows while in a larger internal diameter CEOHP the flow pattern tended to be mainly churn flow. Thicker liquid film observed in a larger internal diameter CEOHP lead to higher critical heat flux transfer. In respect to the working fluid, the data suggested that the working fluid did not clearly affect the flow pattern inside the CEOHP at critical state. The main flow pattern at critical state of both working fluids were annular and churn flows for smaller internal diameter and churn flow for larger diameter. In all cases, the critical state of the CEOHP was caused by flooding and intermittent dryout, which resulted in a decrease of the critical heat flux. The experimental results are in agreement with Katpradit et al. (2005), who established the assumption based on the flooding limit.

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Pages: ICR07-B2-1459

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Details

  • Original title: Effects of internal diameter and working fluid on internal flow patterns of closed-end oscillating heat pipes at critical state.
  • Record ID : 2008-0098
  • Languages: English
  • Source: ICR 2007. Refrigeration Creates the Future. Proceedings of the 22nd IIR International Congress of Refrigeration.
  • Publication date: 2007/08/21

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