Experimental development of a lithium bromide absorption power cycle

Absorption cycles have been proposed not only for cooling but also for power generation, benefiting from temperature glide in heat exchangers, lowering exergy destruction. They can effectively utilise low-temperature solar, geothermal or waste heat. Apart from water-ammonia mixture, alternative working fluids may provide further advantages. Specifically attractive is an aqueous solution of salts such as lithium bromide (LiBr), also known from absorption cooling. Previous theoretical works found thermodynamic benefits of this concept mainly for heat sources around 100 degrees C and technical feasibility even for kW scale systems, but experimental works were limited. This work fills the gap by reporting on the world's first absorption power cycle (APC) using LiBr solution to convert low-temperature heat to power directly. A proof-of-concept system was built and operated with a 360 W design power output, featuring a nylon 3D printed turbine or measurement of temperature glide during phase change in the heat exchangers. This work includes extensive review of considerations for experimental system, design, commissioning and experimental performance. The measured turbine efficiency reached 25%, with a potential for significantly higher values. Over the range of explored conditions, if 65% expander performance was assumed, the maximal cycle efficiency could be around 5% and utilisation efficiency 0.5%.

Automated summary

Absorption cycles can be used for cooling and power generation, benefiting from temperature glide in heat exchangers and utilising low-temperature heat sources. This study presents the world's first absorption power cycle (APC) using a LiBr solution to directly convert low-temperature heat to power. A proof-of-concept system was built and operated with a 360 W design power output, achieving a turbine efficiency of 25% with potential for higher values. The maximal cycle efficiency could be around 5% and utilisation efficiency 0.5%.