Development of a prototype demonstration of a direct air-cooled libr-h2o absorption cooling machine

Resumen

The main objective of this thesis is the development of a direct air-cooled single-effect LiBr-H2O absorption machine and intended for small power applications such as residential use, agri-food industry, farms, cellars, etc. The single effect cycle is designed to be integrated with low temperature solar thermal collectors or in systems where it is possible to do waste heat valorisation. However, focusing on the study and development of small thermal capacity systems (5-15kW) involves additional design challenges, especially in air-cooled systems where cooling towers are not used. Furthermore, the study of the behavior of the machine under different outline conditions, the optimal distribution of the standard thermal equipment and the development of competitive adhoc solutions at the manufacturing and cost levels is also faced. The work developed in the thesis has followed the next steps: i) Stationary numerical simulation oriented to the design of the cycle and the components (flooded evaporator, absorber: fin and tube heat exchanger, desorber: coil, condenser : fin and tube heat exchanger, solution exchanger: plate heat exchanger), ii) Development of a dynamic numerical modeling tool to evaluate the overall performance of the LiBr-H20 absorption cycle based on semi-empirical correlations, iii) Study of internal control strategies of the absorption machine to prevent the appearance of phenomena such as crystallization or freezing, and external control strategies (operation of the partial-load absorption machine) using dynamic modelisation (study carried out in a virtual environment), iv) Development of a small capacity direct air-cooled single-effect LiBr-H20 absorption machine, achieving TRL 6, and the construction and start-up of the prototype through solutions that can be directly replicated in the industry. This thesis has been structured in 5 different chapters. The first chapter is an introduction to non-vapor compression systems, with special emphasis on absorption technology (thermally driven machines). At the same time, this chapter presents an exhaustive analysis of the state of the art and the IPR protections which conditionated the design of the machine. The second chapter details the used and/or implemented numerical simulation models for the design and optimization of absorption machines. The modeling is basically divided into 3 sections, depending on the level of detail: i) Thermodynamic model, ii) Use of detailed heat transfer and mass models, iii) Transient lumped model based on semi-empirical correlations. The third chapter focuses on the control and operation strategy of the air-cooled absorption chiller. The scope of this chapter is to give an overview of the state of the art in terms of control strategies, identifying different operating conditions of the machine and detecting the limitations that could constrain the necessary thermal supply to meet cooling demand, avoiding problematic situations such as crystallization or freezing. The performance and behavior study of the absorption chiller is done in conjunction with a complete solar cooling system, including the solar collectors, storage tanks, pumps, etc. The fourth chapter provides a detailed description of the manufacturing and assembly process of the demonstration absorption chiller, altogether with feasibility tests (hydraulic, sensoris, mechanic, electric). This section of the thesis describes the experimental configuration of the components of the machine, the test bench and methodologies developed to achieve the technical objective. Finally, in the chapter of conclusions a summary of all the results reported in the previous chapters is presented. At the same time, future actions at scientific and technological level are also identified, presenting the following steps and providing lines of work that are considered strategic.