Critical heat flux in a vertical tube at low and medium pressures - Part I. Experimental results

This paper presents experimental CHF data obtained for vertical up flow in an 8 mm I.D. test section, for a wide range of exit qualities (5-75%) and e xit pressures ranging from 5 to 40 bar. The experiments were carried out fo r heated lengths of 0.75, 1, 1.4, 1.8, 2.5 and 3.5 m. A :number of differen t coordinate systems are used to present the experimental results, these in clude CHF as a function of the inlet subcooling, as a function of the outle t thermodynamic quality, and as a function of the boiling length. An analys is of these commonly used representations of the CHF, has shown, that for a ll of the cases studied, the critical heat flux is dependent in some manner on the heated length. This dependence greatly complicates the possibility of obtaining a universal correlation for the critical heat flux at low and medium pressures. (C) 1999 Elsevier Science S.A. All rights reserved.