An experimental study on the heat transfer performance characteristics of horizontal tube falling film absorbers for single-stage absorption heat transformer

The absorber is one of the most important components in the LiBr-water absorption heat transformer (AHT) because it has the largest heat transfer area, and its performance significantly influences the overall system efficiency. Nevertheless, studies on absorbers used at the high-pressure level have not progressed. In this study, the horizontal tube falling film absorbers were constructed by introducing three types of heat transfer tubes (copper bare, copper-nickel bare, copper-nickel floral). The combined effects of the tube structure and material on the heat transfer performance of the absorber were experimentally investigated under the operating conditions of the single-stage AHTs. The experimental results showed that the film Reynolds number of 50 was optimal for the absorbers used in this study. At that point, the overall heat transfer coefficients of the copper bare tube, the copper-nickel bare tube, and the copper-nickel floral tube were 1,484, 1,448, and 1,299 W/m² K, respectively. In addition, the heat transfer performance of the bare-type tubes was superior to that of the floral tube, except the under the low film Reynolds number. The empirical correlations of the Nusselt number for three types of heat transfer tubes were derived based on the experimental results and were predicted the data within the standard errors of 3.79–5.57 %.