Heat transfer characteristics of horizontal flow boiling with uniform and non-uniform circumferential heat flux

Abstract

This study assesses effects of the non-uniform circumferential heat flux on horizontal flow boiling of R141b in a stainless-steel tube at ambient system pressure with an inner diameter of 10.92 mm. The main motivation for this are application in Concentrated Solar Power using the Direct Steam Generation process inside horizontal absorber tubes. Experiments were conducted for two mass velocities (50 and 150 kg m−2s−1) and two mean heat fluxes (3.4 and 11.0 kW m−2), with three different heating conditions (uniform, top-concentrated, and bottom-concentrated). The differences in the Onset of Nucleate Boiling between uniform and bottom-concentrated heating are assessed, and the transient behavior of the wall temperatures is investigated. It is found that the heating condition significantly affects the mean heat transfer coefficient in the case of non-annular flow regimes but practically not in annular flow. The circumferential wall temperature gradient is with uniform heating highest for non-annular flow regimes. But with non-uniform heating the circumferential wall temperature gradient is highest for annular flow. The use of empirical correlations for the heat transfer coefficients are evaluated.