Heat and Mass Transfer Characteristics According to the Shape of the Absorber Heat Transfer Tube for Absorption Chiller

This study examined heat and mass transfer characteristics of absorber heat transfer tubes for absorption chillers. The experiments were conducted using bare and end-cross as the absorber heat transfer tube for the absorption chiller. The variables chosen for the experiment were the inlet conditions of the LiBr aqueous solution and the cooling water. The results showed that with an increase in Reynolds number of cooling water and film Reynolds number, the heat transfer rate, overall heat transfer coefficient, and outside heat transfer coefficient increased. Furthermore, it was observed that as the LiBr solution concentration increased, the overall heat transfer coefficient and the outside heat transfer coefficient also increased, while the overall heat transfer coefficient tended to decrease when the cooling water inlet temperature increased. At a film Reynolds number of 30, the outside heat transfer coefficients of the bare and end-cross tubes were determined to be 1.061 and 1.537 kW/m²-K, respectively, and the performance of the end-cross was improved by 44.86%. In the absorber, the mass transfer coefficient increased until the film Reynolds number was 30, after which it was confirmed that the increase was mostly lower or zero. We propose experimental correlations of Nusselt number for bare and end-cross tubes, which yield a ±20% error band.