Étude numérique et expérimentale d’un cycle combiné de production de froid et d’électricité basé sur la technologie à absorption NH3/H2O

In view of increasing global energy demand and concern for the environment, one particular concern is the increasing demand for cooling, which is expected to triple from 2016 until 2050 due to climate change and increasing population. In this context, absorption systems, which have been a relatively niche technology so far, are well suited to the recovery of low temperature energy for the production of cooling. Research has focused on improving the performance of heat driven cooling systems by merging them with power cycles. Hence, system performance is increased by producing power and cooling simultaneously. Additionally, a combined absorption system producing refrigeration and electricity could be better adapted to the whole range of energy demand, from only power to only refrigeration modes with intermediate operation modes producing different ratios of the two useful products.The work carried out in the present PhD thesis regards the experimental and numerical investigation of an absorption-based combined cooling and power production cycle using low temperature heat (80-150 °C). The architecture is that of a single stage ammonia-water absorption chiller to which a power production line, including a turbine for the production of electricity, is integrated in parallel to the cooling production line.The present document presents first an overview of available heat driven thermodynamic cycles for the production of cooling and power. Absorption machines and organic Rankine cycles are identified as mature and efficient technologies and their combination is envisaged to achieve higher efficiencies and to increase the operating flexibility. Then, the development of a prototype is undertaken by integrating an impulse axial turbine into an existing absorption chiller rig. The special characteristics of the expander as well as the simplified architecture of the absorption cycle make the prototype unique. Despite challenges encountered in the development of the system, first experimental results have been obtained giving important insights on the functioning of the cycle.Experimental data from the prototype was also used for the development of accurate numerical models. First, a detailed model of the absorption chiller is developed based on the use of heat and mass exchangers' effectiveness, modelled using dimensionless operating parameters, and adjusted on experimental measures. Subsequently, a 1D real-gas turbine model is developed including a description of the supersonic expansion in the injector and a simplified rotor loss model, whose coefficients were adjusted based on CFD simulations. Experimental tests on the turbine with fluids other than ammonia have proved to model to be robust and applicable to different working fluids. The turbine 1D model is then integrated into the cycle model for parametric analysis of the operating conditions. Since the cycle produces two different useful products, particular attention is paid to its study from an exergetic point of view. Exergoeconomics was used to calculate separately the cost of each product generated by the system, understanding the cost formation process and optimising the overall system. Finally, different possibilities for improving the system are addressed. In particular, its scale-up with the size effect and various architectures that could increase its flexibility such as the use of an ejector for a better regulation of the mass flow.