absorption chiller, absorber, falling liquid films, heat and mass transfer enhancement
It is necessary to improve the energy efficiency of all technical processes due to the uncertainties associated with climate change. One possibility to achieve higher energy efficiency is to utilize waste heat which occurs in many different applications. This heat may be used to replace compression chillers by heat driven absorption chillers which leads to a lower consumption of primary energy. Thus, research on heat driven absorption chillers is important to gain higher energy efficiency. In most cases the absorber is the limiting component of absorption chillers which is often designed as a falling-film absorber with horizontal tubes. This paper gives a brief overview on the latest experimental results of absorption on horizontal tubes published in the literature. All important design parameters and their influence on the efficiency of absorbers are considered. This includes the different working fluids and their additives as well as the various geometrical parameters. Thereby, a special focus is put on the different surface structures of the tubes that are used in absorbers. Also recent trends in research as ionic fluids and nanoparticles are examined. As an important result it can be concluded that some design parameters and their effects on the efficiency of absorbers are still not completely understood. Due to this, possibilities for further investigations are given.