Fluid Flow
TWO-PHASE FLUID FLOW
TWO-PHASE FLUID FLOW
Water at saturation conditions may exist as both a fluid and a vapor.
This mixture of steam and water can cause unusual flow
characteristics within fluid systems.
EO 1.31
DEFINE two-phase flow.
EO 1.32
DESCRIBE two-phase flow including such phenomena
as bubbly, slug, and annular flow.
EO 1.33
DESCRIBE the problems associated with core flow
oscillations and flow instability.
EO 1.34
DESCRIBE the conditions that could lead to core flow
oscillation and instability.
EO 1.35
DESCRIBE the phenomenon of pipe whip.
EO 1.36
DESCRIBE the phenomenon of water hammer.
Two-Phase Fluid Flow
All of the fluid flow relationships discussed previously are for the flow of a single phase of fluid
whether liquid or vapor. At certain important locations in fluid flow systems the simultaneous
flow of liquid water and steam occurs, known as two-phase flow. These simple relationships
used for analyzing single-phase flow are insufficient for analyzing two-phase flow.
There are several techniques used to predict the head loss due to fluid friction for two-phase
flow.
Two-phase flow friction is greater than single-phase friction for the same conduit
dimensions and mass flow rate. The difference appears to be a function of the type of flow and
results from increased flow speeds. Two-phase friction losses are experimentally determined by
measuring pressure drops across different piping elements. The two-phase losses are generally
related to single-phase losses through the same elements.
One accepted technique for determining the two-phase friction loss based on the single-phase loss
involves the two-phase friction multiplier (R), which is defined as the ratio of the two-phase head
loss divided by the head loss evaluated using saturated liquid properties.
(3-18)
R
Hf , two phase
Hf , saturated liquid
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