HYDRODYNAMICS OF GAS-LIQUID COUNTERCURRENT-FLOW IN INTERNALLY FINNED MONOLITHIC STRUCTURES

The flooding behaviour of gas-liquid countercurrent flow was studied i n a set of small diameter internally finned tubes that were bundled in a hexagonal arrangement so that a monolith like structure was obtaine d. The liquid outlet of the tubes was bevelled at an angle of 70 degre es to enhance the countercurrent flow. In order to investigate the eff ect of the fins, the flooding behaviour was compared with countercurre nt flow in a bundle of unfinned tubes, having almost the same cross-se ctional area. It was found that because of the stabilising effect of t he fins, a transition regime exists between the wavy annular film flow regime and the total flooding regime. This regime, which is character ised by pressure drop fluctuations that are in the order of 10%, is co mpletely reversible without hysteresis to occur. Experiments with vari ous liquid outlets demonstrated that not the liquid drainage but the w ay of feeding the gas has the largest effect on the flooding limits. ( C) 1997 Elsevier Science Ltd.