Prediction of Adiabatic Bubbly Flows in TRACE Using the Interfacial Area Transport Equation
NURETH-14 - 2011 September 25-30

Presented at:
2011 September 25-30
Toronto, Canada
Session Title:
A9-3 Interfacial Area Transport - Computational

Justin Talley (The Pennsylvania State University)
Ted Worosz (The Pennsylvania State University)
Seungjin Kim (The Pennsylvania State University)
John H. Mahaffy (U.S. Nuclear Regulatory Commission)
Stephen M. Bajorek (U.S. Nuclear Regulatory Commission)
Kirk Tien (U.S. Nuclear Regulatory Commission)


The conventional thermal-hydraulic reactor system analysis codes utilize a two-field, two-fluid

formulation to model two-phase flows. To close this model, static flow regime transition criteria

and algebraic relations are utilized to estimate the interfacial area concentration (

ai). To better

reflect the continuous evolution of two-phase flow, an experimental version of TRACE is being

developed which implements the interfacial area transport equation (IATE) to replace the flow

regime based approach. Dynamic estimation of

ai is provided through the use of mechanistic

models for bubble coalescence and disintegration. To account for the differences in bubble

interactions and drag forces, two-group bubble transport is sought. As such, Group 1 accounts

for the transport of spherical and distorted bubbles, while Group 2 accounts for the cap, slug, and

churn-turbulent bubbles. Based on this categorization, a two-group IATE applicable to the range

of dispersed two-phase flows has been previously developed. Recently, a one-group, onedimensional,

adiabatic IATE has been implemented into the TRACE code with mechanistic

models accounting for: (1) bubble breakup due to turbulent impact of an eddy on a bubble, (2)

bubble coalescence due to random collision driven by turbulent eddies, and (3) bubble

coalescence due to the acceleration of a bubble in the wake region of a preceding bubble. To

demonstrate the enhancement of the code’s capability using the IATE, experimental data for


void fraction, and bubble velocity measured by a multi-sensor conductivity probe are compared

to both the IATE and flow regime based predictions. In total, 50 air-water vertical co-current

upward and downward bubbly flow conditions in pipes with diameters ranging from 2.54 to

20.32 cm are evaluated. It is found that TRACE, using the conventional flow regime relation,

always underestimates

ai. Moreover, the axial trend of the ai prediction is always quasi-linear


ai in the conventional code is predominantly determined by the pressure. It is found that

TRACE with the IATE significantly improves prediction results, yielding a ±10.3% difference

with the data. In addition, the IATE always predicts the correct axial trend of

ai and can also

predict non-linear axial development that reflects the bubble interactions along the flow.

Additional studies are being performed to implement a two-group IATE to further expand the

capability of the code.

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