Experimental investigation of surfactant-enhanced ammonia-water absorption in a shell-and-tube absorber

Abstract

• Surfactants used to demonstrate system level improvements in ammonia-water absorption. • 500 PPM of 1-octanol used as additive. • Reduction in working fluid thermal resistance by 37% observed. • Suppression of low-side pressure in the presence of surfactants. • Benefits include improved system COP and operation at adverse ambient conditions. The use of surfactants for passive enhancement of ammonia-water absorption is experimentally investigated. A vertically-oriented, baffled shell-and-tube absorber with a tightly packed tube bundle for a 10.5 kW absorption chiller is considered. An experimental facility is fabricated to closely simulate the operating conditions in an absorption chiller. Experiments are performed at different solution flow rates, coupling fluid temperatures, and surfactant concentrations. The results demonstrate significant improvements in absorber performance due to the addition of 1-octanol as the surfactant. Mass transfer enhancement by interfacial turbulence and higher heat transfer coefficients due to increased wettability are identified as the mechanisms responsible for the enhancement. The impact of surfactants on the system level parameters including the low-side pressure is investigated. It is also shown that there is no significant impact on desorber performance by the addition of surfactants. The results indicate that surfactants are beneficial and can result in a smaller absorber and allow for system operation at higher ambient temperatures. The results from this study can help guide the development of surfactant-enhanced compact, efficient absorption heat pumps.