Abstract
Absorption heat pump water heaters are expected to be more efficient than conventional gas-fueled water heaters. However, such absorption systems are large and not widely accepted in the market. In this paper, we propose the use of adiabatic absorbers as smaller alternatives to conventional shell-and-tube or plate-fin-type absorbers to downsize absorption heat pump water heaters using H2O/NH3. The adiabatic absorption system consists of two components: a subcooler and an adiabatic absorber. The absorption performance and size of the adiabatic absorber are important for achieving higher efficiency. In this study, three types of adiabatic absorbers are proposed: atomizing-spray, spreading-tray, and packed-column absorbers. They are modeled and their absorption performances are analyzed.
In modeling the atomizing-spray absorber, we discuss the breakup position of the liquid film and the diameter of the generated droplets on the basis of the instability theory of liquid films. In analytically modeling the spreading-tray absorber, we discuss the breakup length of the liquid column and the diameter of the generated droplet. In the case of the packed-column absorber, we discuss the effective interfacial area of the dumped packings. Based on the simulation results, we develop design guidelines and compare the expected sizes of the absorbers.
