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New flow pattern map for CO2 two-phase flow in horizontal smooth tube.

Number: pap. ID: 504

Author(s) : SAITO Y., WETZEL M., KIND M., et al.

Summary

In this study, we propose an improved flow pattern transition criterion for a horizontal two-phase flow in round tubes. Several flow pattern transition criteria have been derived based on the Kelvin-Helmholtz stability theory to determine the wavy- to annular flow (or intermittent flow) transition. However, some researchers have pointed out that such criteria do not account for the large observational deviations in high pressure conditions occurring at high quality region. The purpose of this study is to develop a new flow pattern map that can be applied for adiabatic two-phase flow of CO2 and CO2-oil mixture at pressures ranging from 1.9 MPa to 4.0 MPa. The experiments involved in our study were performed at the Institute of Thermal Process Engineering, Karlsruhe Institute of Technology in Germany. The experimental equipment involved a test loop consisting of 4 pre-evaporators, a test section, a thermal guard, and a sight glass in a line. The sight glass had an inner diameter of 14 mm and a length of 100 mm. For the flow pattern observations and pressure drop measurements, the quality of the two-phase mixture was controlled only with the first three pre-evaporators in order to obtain a sufficient adiabatic entrance length (L/D > 100) to the test section, where the pressure drop was measured. Two-phase flow images were recorded by a high-speed video camera (Kodak, Motion Coder Analyzer SR1000) at 500 to 1000 fps and the void fraction was approximately estimated from the recorded images by taking into account the effects of refraction through the sight glass. Our experimental results show that the measured void fraction agreed well with that obtained by the Rouhani-Axelsson correlation (1970) for G > 150 kg/m2s. By taking into account the stability theory for a disturbance wave at the high quality region, a new equation was derived for the stratified to nonstratified flow transition. Our modified flow pattern map appeared consistent with the observed results for the CO2 two-phase flow. Moreover, the new equation appears to accurately account for the effect of system pressure on the flow pattern map.

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Pages: 8 p.

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Details

  • Original title: New flow pattern map for CO2 two-phase flow in horizontal smooth tube.
  • Record ID : 30003221
  • Languages: English
  • Source: Proceedings of the 23rd IIR International Congress of Refrigeration: Prague, Czech Republic, August 21-26, 2011. Overarching theme: Refrigeration for Sustainable Development.
  • Publication date: 2011/08/21

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