The vertical bubbling jet region in a cylindrical vessel can be classified into four subregions. They are named the momentum, transition, buoyancy and surface regions from the nozzle exit toward the bath surface. However, the bubble characteristic in each region is not clear even in air-water bubbling jets. The present paper proposes empirical correlations for the bubble frequency and gas holdup in the momentum region in air-water bubbling jet. The momentum region is defined as the region where the gas holdup on the centerline decreases from 100 to 10%. These correlations are applicable to bubbling jets of the modified Froude number from about unity to 2 × 105.
