Heat transfer characteristics of a falling film generator for various configurations of heating tubes in an absorption chiller

A generator is a heart of an absorption refrigeration system. It plays a significant role in the operation cycle by desorbing the water vapor from a lithium bromide (LiBr) solution. The wettability of the solution over the heating tubes has been considered for heat transfer enhancement in a water-LiBr falling film generator. This paper proposes seven types of heating tube bundles modified by surface treatments to improve the wettability. Each heating tube bundle was installed in the falling film generator for each experimental set, and the heat transfer characteristics were observed to evaluate the shell side heat transfer coefficients. Experiments were carried out with the following operating conditions: feed solution temperature (63.5 °C), solution flow rate (4–9 kg/min), feed solution concentration (55–58%), and pressure at the shell side (4.7–6.7 kPa). Hot water was used as a heat source, and the operating parameters were the feed temperature (85–97 °C) and the flow rate (10–28 L per minute). Each heating tube bundle had entirely different heat transfer characteristics, which were distinctly illuminated. The experimental correlations for a shell side heat transfer were developed to estimate the real benefits of using the proposed heating tube bundles. All the obtained empirical correlations were validated within an error limit of around ±20%.