Critical heat flux for water boiling in channels. Modern state, typical regularities, unsolved problems, and ways for solving them (a review)

Abstract

Some general matters concerned with description of burnout in channels are outlined. Data obtained from experimental investigations on critical heat fluxes (CHF) in different channels, CHF data banks, the main determining parameters, CHF basic dependences, and a system of correction functions are discussed. Two methods for estimating the CHF description errors are analyzed. The influence of operating parameters, transverse sizes of channels, and conditions at their inlet are analyzed. The effects of heat-transfer surface shape and heat supply arrangement are considered for concentric annular channels. The notions of a thermal boundary layer and an elementary thermal cell during burnout in channels with an intricate cross section are defined. New notions for describing CHF in rod assemblies are introduced: bundle effect, thermal misalignment, assembly-section-averaged and local parameters (for an elementary cell), cell-wise CHF analysis in bundles, and standard and nonstandard cells. Possible influence of wall thermophysical properties on CHF in dense assemblies and other effects are considered. Thermal interaction of nonequivalent cells and the effect of heat supply arrangement over the cell perimeter are analyzed. Special attention is paid to description of the effect the heat release nonuniformity along the channels has on CHF. Objectives to be pursued by studies of CHF in channels of different cross-section shapes are formulated.