Characteristics of HFC-134a absorption rate with [Bmim][Tf2N] in falling film type absorber

Abstract

To develop an absorption heat pump with a hydrofluorocarbon refrigerant, this study evaluated its absorption rate with a falling liquid film type absorber. The HFC-134a refrigerant and [Bmim][Tf2N] ionic liquid were selected as the absorbent pair. The experimental apparatus was designed using the volumetric method, and the effects of the absorbent mass flow, temperature, and pressure conditions on the absorption rate were evaluated. Additionally, we calculated the absorption rate coefficient using the HFC-134a absorption transport model. The experimental results revealed that the absorption rate affected the desired amount of absorption equilibrium under the given temperature and pressure conditions. The absorption rate increased, while the amount of absorption at the set temperature and pressure decreased. Additionally, the outlet amount of absorption in the absorber increased as the absorbent mass flow down onto the heat exchanger tube increased. However, the amount of absorption was saturated as the absorbent mass flow increased. We monitored the absorbent flow behavior in the heat exchanger tube. The gas–liquid surface area was not changed by the absorbent mass flow, and the thickness of the absorbent liquid film increased. The absorption rate coefficient was determined using the HFC-134a absorption transport model, and the absorber height was calculated for up-scaling. The calculation results revealed that, to achieve 80% of absorption equilibrium, the absorber height must be 4.3 times greater than the experimental value. Thus, the heat exchanger with high wettability must be designed with a high absorption rate.