INVESTIGATION OF FUNDAMENTAL THERMAL-HYDRAULIC PHENOMENA IN ADVANCED GAS-COOLED REACTORS Page: 4 of 205
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driven DTHT and the laminar to turbulent transition regimes and carbon dioxide data
covered the returbulizing buoyancy driven DTHT and non-returbulizing buoyancy
induced DTHT. A newly observed phenomenon, namely "returbulization", occurs when
the buoyancy driven DTHT regime recovers back to the normal forced convection heat
transfer due to the strong dependency of gas properties on the temperature. The validity
of the data was established using heat balance and the uncertainty analysis. Based on the
experimental data, the traditional threshold for the DTHT regime was updated to account
for phenomena observed in the facility and a new heat transfer regime map was proposed.
Overall, substantial reduction of the heat transfer coefficient was observed in the DTHT
regime, which will have significant impact on the core and DHR design of passive GFRs.
The MIT data were compared to a large number of existing correlations. None of the
mixed convection laminar correlations agreed with the data. The forced turbulent and the
DTHT regime, Celeta et al.'s correlation showed the best fit with the data. However, due
to the larger L/D ratio of MIT's facility compared to Celeta et al.'s facility and the
returbuliziation due to the gas characteristics, the correlation sometimes under predicts
the heat transfer coefficient. Also, since Celeta et al.'s correlation requires information
about the wall temperature to evaluate the heat transfer coefficient, it is difficult to apply
this correlation directly for predicting the wall temperature.
Three new sets of correlations that cover all heat transfer regimes were developed. The
basic idea of the new correlation is to use the best available and most widely
recommended Gnielinski correlation for forced turbulent convection and modify its
empirically fitted constant (the Re-1000 part) by an empirically fitted function that
accounts for physical phenomena driving the DTHT regimes. Thus, the function is
dependent on the acceleration parameter or the buoyancy parameter depending on the
heat transfer regime. Type-1 correlation set is the most accurate fit suitable for scientific
applications, Type-2 simplifies the calculations by eliminating an iteration process on the
wall temperature and Type-3 is the simplest form suitable for industrial applications. The
first two types show very good fit with the data, while the third type exhibits slightly less
accuracy, which was traded off for simplicity. Three correlations cover most of the MIT
experimental data within 20%range.
Finally, it is noted that more data on the laminar-turbulent transition are required to
understand the flow phenomena more thoroughly. A number of research issues for future
work are listed, based on the phenomena uncovered in this project.
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PHE, INVESTIGATION OF FUNDAMENTAL THERMAL-HYDRAULIC. INVESTIGATION OF FUNDAMENTAL THERMAL-HYDRAULIC PHENOMENA IN ADVANCED GAS-COOLED REACTORS, report, September 1, 2006; [Idaho Falls, Idaho]. (digital.library.unt.edu/ark:/67531/metadc877333/m1/4/: accessed January 23, 2019), University of North Texas Libraries, Digital Library, digital.library.unt.edu; crediting UNT Libraries Government Documents Department.