Absorbent solution film flowing over a cooled horizontal tube is a common configuration for absorption-type chiller units. Here a physical model is presented to analyse the absorption phenomena on the basis of various interactions between the parameters and boundary conditions involved in actual situations. The boundary layer assumptions are used for the transport of momentum, energy, and species in an assumed laminar flowing film. The results by the finite-difference method for a water-LiBr solution are discussed with the aid of contour lines and profiles for various conditions. The results show that (1) for larger flow rates, the heat transfer coefficient improves with the increase of tube diameter, whereas for smaller flow rates, the heat transfer coefficient is large, and (2) an optimum flow rate for a particular tube size can be estimated on the basis of flow rate and total mass flux relation.

KEYWORDS: Absorption refrigeration, vapours, tubes, horizontal, models, lithium bromide, flow rate, calculating.