Direct vapor ammonia generation inside a concentrating parabolic trough solar collector for an ammonia/lithium nitrate absorption machine. Theoretical study.

Among the renewable energy technologies, concentrating solar collectors are receiving growing interest as power source for heat and electricity production worldwide. The recent development of small scale parabolic trough collectors, PTCs, suggests extending their application to medium and low temperature facilities configuring solar integrated absorption machines for heating and cooling purposes. The innovative solution considered in this work uses the PTCs as a direct vapor generator/separator forming part of an absorption machine using ammonia/lithium nitrate dissolution as working fluid, thus flowing the dissolution inside the collector absorber tube. The gravity driven flow stratification and separation obtained inside the receiver tube ensures a continuous desorption of the refrigerant and enables a simplified system layout, reducing the overall costs and complexity. The 1-D steady-state numerical model of the PTC vapor generator proposed is suitable for approaching a first characterization of the system operation and supports its design and optimization. A theoretical analysis is carried out to identify the influence of the main constructive and operating parameters on the performance of the PTC as direct vapor generator/separator. The results presented evidence its suitability for the indicated purpose.