Some problems for bundle CHF prediction based on CHF measurements in simple flow geometries

A comparison of critical heat flux (CHF) fuel bundles data with CHF data ob tained in simple flow geometries was made. The base for the comparison was primary experimental data obtained in annular, circular, rectangular, trian gular, and dumb-bell shaped channels cooled with water and R-134a. The inve stigated range of flow parameters (pressure, mass flux, and critical qualit y) in R-134a was chosen to be equivalent to modern nuclear reactor water fl ow conditions (p = 7 and 10 MPa, G = 350-5000 kg (m(2) s)(-1), x(cr) = - 0. 1-1). The proper scaling laws were applied to convert the data from water t o R-134a equivalent conditions and vise versa. The effects of flow paramete rs (p, G, x(cr) and the effects of geometric parameters (D, L) were evaluat ed during comparison. The comparison showed that no one simple flow geometr y can be used for accurate and reliable bundle CHF prediction in wide range of flow parameters based on local (critical) conditions approach. The comp arison also showed that the limiting critical quality phenomenon is unique characteristic for each flow geometry which depends on many factors: flow c onditions (pressure and mass flux), geometrical parameters (diameter or sur face curvature, gap size, etc.), flow obstructions (spacers, appendages, tu rbulizers, etc.) and others. (C) 2000 Elsevier Science S.A. All rights rese rved.