Assessment of surfactant-induced Marangoni convection within high-temperature aqueous Lithium-Bromide solution

A common technical practice to boost the transfer performance of falling film absorbers within absorption cycles relies on surfactant additives for triggering the interfacial turbulence known as Marangoni convection. Given the phenomenon complexity and the interdependencies with other phenomena, such as surface wetting, the assessment of the related enhancement is unresolved yet, and data from previous literature are limited to the operative conditions of single effect refrigerators. This work combines numerical simulations and experiments for evaluating the transfer performance enhancement due to Marangoni convection in a wide operative range encompassing refrigeration and heat pump cycles. Falling film transfer coefficients are measured, with and without n-octanol, with LiBr solution temperature between 50 and 120^oC, and specific mass flow rate between 0.011 and 0.11Kg·m^-1s^-1. Consequently, a semi-empirical model estimates the contribution of improved wettability and consequently indicates the portion of the transfer enhancement related to the Marangoni convection.