What is the primary use of excess water heat in absorption refrigeration systems?

In absorption refrigeration systems, the primary use of excess water heat is to evaporate water from the weak lithium bromide solution. This process is essential for the functioning of the absorption cycle, wherein heat is used as the energy source instead of mechanical energy typically provided by a compressor in vapor-compression systems.

When the weak lithium bromide solution is heated, it allows water to evaporate from it, thereby increasing the concentration of lithium bromide in the solution. This concentrated solution then flows to an absorber where it can absorb more water vapor, which is crucial for the cycle's refrigerating capability. Thus, harnessing excess water heat to facilitate the evaporation process directly supports the efficiency and effectiveness of the absorption refrigeration cycle.