An experimental study of an ammonia-water absorption refrigeration cycle using a novel modified horizontal liquid film absorption system

• Autor(a) principal: Narváez Romo, Beethoven
• Data de Publicação: 2020
• Tipo de documento: Tese
• Idioma: eng
• Título da fonte: Biblioteca Digital de Teses e Dissertações da USP
• Texto Completo: https://www.teses.usp.br/teses/disponiveis/3/3150/tde-14012021-102524/
• topic: Absorção; Absorption process; Absorption refrigeration cycle; Ammonia-water; Amônia; Falling film; Filme descendente; Filme horizontal; Heat and mass transfer; Horizontal film; Molhabilidade total; Processo de absorção; Refrigeração; Total wettability; Transferência de calor

The falling film technology has been widely used in different engineering applications, including in the absorption refrigeration cycles (ARC) because it has a huge potential to be used for heat recovery from thermal sources and from solar energy. Open-source literature review shows different studies over the heat and mass transfer (HMT) behavior for both absorption and generation processes, demanding more experimental results in this field. Moreover, the wettability problems are still present in liquid falling film applications. Therefore, the current work deals with an experimental test rig of an ARC for a 1500 W cooling capacity, allowing to study the absorption process in real operational conditions. Furthermore, the present research study the heat and mass transfer absorption process in a novel configuration, using a horizontal liquid film in ammonia-water mixtures. Firstly, a complete literature review on falling film technology focused on the HMT study in sorption processes was carried out, in which both ammonia-water and lithium bromide-water working fluid were analyzed. Based on that review, a HMT mapping for the most common working fluid was obtained by using a modeling of the absorption refrigeration system. Secondly, a modeling of the ammonia-water absorption process using a new proposal of heat and mass exchanger in which the total wettability is guaranteed was developed. A mathematical model based on the overall balance of mass, ammonia species, and energy equations was carried out. Finally, an ammonia-water absorption refrigeration test was projected, built and tested, in which it allowed studying the ARC as a function of several operational parameters such as strong mass flow rate, generation temperature, weak solution temperature, concentrations, and absorption pressure. Moreover, the horizontal modified liquid film absorber was tested in real operational conditions. According to the theoretical studies, a HMT mapping were obtained for those experimental and analytical correlations, obtaining the possible operating range of the Nusselt number and Sherwood number in some typical operational conditions from ARC\'s. The heat and mass transfer coefficients were strongly enhanced as the absorption refrigeration cycle achieved vaporization temperatures below 0 °C for ammonia-water working fluid. Moreover, a parametric study of the ammonia-water absorption process was carried out. Absorber heat rate was improved by using lowest surface temperature and lowest liquid film thickness. Also, studies showed absorption heat rejection decreases as a function of the position into the absorber, whose first plate absorbed about 30% of the total heat of absorption. Based on experimental studies, results showed the operation of the ammonia-water absorption refrigeration cycle, achieving temperatures below 0 °C.