A plunging jet sparger for injecting gas into downflowing liquids

Previous work has shown the existence of a large bubble beneath devices (called spargers) used to inject gas into a liquid flowing down a vertical pipe with the intention of forming a bubbly flow. The large bubble is undesirable not least because it reduces the driving force for liquid circulation in loop fermenters/reactors. In this paper the performance of a new design of sparger is described. This 'plunging jet sparger' deliberately channels the liquid to the centre of the pipe and injects the air at the wall. The liquid forms a jet which falls down the centre of the pipe and then plunges into the bubbly region below and entrains gas into the bubbly flow. Results for air and water and air and two viscous water/glycerol solutions are reported for a plunging jet sparger in a 0.056 m diameter pipe. Results for air and water in a 0.105 m diameter pipe are also given. The plunging jet sparger is shown to have a generally superior performance to other spargers in respect of 'bubble' length and in respect to resistance to stall at low flow rates. The superiority of the plunging jet sparger is greater for more viscous liquids.