EXPERIMENTAL STUDY ON AQUEOUS LITHIUM BROMIDE HOZIZONTAL MOTIONS AT SMOOTH COOPER TUBE AND POCKMARK TUBE BOTTOMS
Heat and mass transfer enhancement is one of the major research topics of absorption heat pumps. Two liquid spreading phenomena are discovered in practical engineering: dry patches, and droplets/jets horizontal motions. Both phenomena have great impact on falling film liquid distribution. This paper studies falling film phenomena of aqueous lithium bromide in absorbers, and investigate heat and mass transfer characteristic of smooth copper and pockmark copper tube bundles in falling film absorption. A vacuum experimental section is built to reproduce the phenomena. Cold mode experiments are conducted to reproduce the falling film phenomena and observe the droplets/jets spreading and horizontal motions. The tube diameters are 16mm. The liquid density of lithium bromide solution is between 0.07~0.14kg/m/s. Absorption-evaporation experiments are conducted using smooth copper tubes and pockmark tubes to measure the heat and mass transfer coefficients of different tubes. The results show that spreading lengths of lower layers are generally wider than those of upper layers. However, as the layers raise, spreading lengths tend to be stable. Two kinds of horizontal motions are described and distinguished. As for the absorption-evaporation experiment, under the same liquid spreading density, pockmark tubes have better wettability than smooth copper tubes. The absorption heat transfer coefficient for smooth copper tube is 1.16kW/m2·K, while for pockmark copper tube is 1.45 kW/m2·K. The mass transfer coefficient for the smooth copper tube is 7.0×10-5m/s, while for the pockmark copper tube is 9.1×10-5m/s.