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Space Processes & Experiments

Fluid Physics and Transport Branch

Two-Phase Flow

The Fluid Physics and Transport Branch of the Space Processes and Experiment Division at NASA Glenn Center has conducted research on the effects of microgravity on two-phase flow.

Flow is essential to many processes, and there are seven kinds of flow distinguishable on earth due to forces imposed by gravity. Microgravity is able to simplify flow due to the almost non-existent amount of gravity present; there are three principal types of flow regimes in microgravity: bubbly, slug, and annular.

Select an image to view a movie (.mpg).
Type of Flow	Microgravity	Normal Gravity
Bubbly
Slug
Annular

However, flow systems do not consist of entirely straight pipes. The following pictures and movies have been taken in microgravity for a variety of tubing configurations.

The following set of movies involves flow through tees.

Select an image to view a movie (.mpg).
Bubbly	Slug	Annular

The flow enters the tee at the bottom of the image and is split between the "side-arm" branch and the "run." The tee has a 1.27 cm inner diameter.

A contraction is a reduction in the tubing size. Within the contraction, there is a fluid recirculation zone called a "vena contracta." The "wet" image is when the liquid is recirculating with the vena contracta; however, there are conditions whereby the gas phase gets caught in the vena contracta and dries out the wall.

Select an image to view a movie (.mpg).
Wet	Dry

Wet flow through vena contracta is a bubbly slug flow from a 25mm diameter tube into a 19mm tube; as the liquid is forced to contract, the flow changes from bubbly flow to slug flow. Dry flow through vena contracta is an annular flow from a 25mm diameter tube into a 12.7mm diameter tube.

An expansion is an increase in the tube size. Again, there is an area of fluid recirculation near the "corner" of the sudden expansion. Depending on the flowrates, either a bubbly liquid or gas phase is trapped in this region.

Select an image to view a movie (.mpg).
Normal
Gap
Jet

At the inlet, fluid moves from a 12.7mm diameter pipe to a 25mm pipe. Normal expansion takes place at the beginning of flow, and soon a gap expansion occurs as the flow is recirculated and flow velocity continues to increase. A two-phase jet is created eventually, with regions of air flowing above and beneath a region of bubbles.