A theoretical model for the process of bubble and drop formation in fl
owing liquids, applicable for both terrestrial and microgravity enviro
nments, has been developed by using a force balance. The contact angle
variation at the nozzle due to the bubble motion and the added mass c
oefficient of the bubble moving through a pipe have been theoretically
analyzed, considering bubble motions during its expansion and detachm
ent stages. Predictions of bubble size of the model show satisfactory
agreement with available experimental results in the case of normal gr
avity. The effects of the nondimensional variables on bubble and drop
size are evaluated in microgravity conditions. In microgravity, the bu
bble is detached from the nozzle only by the liquid flow drag, and in
the region of low liquid velocity the bubble size becomes much larger
than that in normal gravity.