Benchmark DEBORA: Assessment of MCFD compared to high-pressure boiling pipe flow measurements

Kód výsledku v IS VaVaI

<a href="https://www.isvavai.cz/riv?ss=detail&h=RIV%2F46356088%3A_____%2F24%3AN0000019" target="_blank" >RIV/46356088:_____/24:N0000019 - isvavai.cz</a>

Nalezeny alternativní kódy

RIV/68407700:21340/24:00376190

Výsledek na webu

<a href="https://www.sciencedirect.com/science/article/pii/S0301932224001976" target="_blank" >https://www.sciencedirect.com/science/article/pii/S0301932224001976</a>

DOI - Digital Object Identifier

<a href="http://dx.doi.org/10.1016/j.ijmultiphaseflow.2024.104920" target="_blank" >10.1016/j.ijmultiphaseflow.2024.104920</a>

Jazyk výsledku

angličtina

Název v původním jazyce

Benchmark DEBORA: Assessment of MCFD compared to high-pressure boiling pipe flow measurements

Popis výsledku v původním jazyce

A benchmark activity on two-fluid simulations of high-pressure boiling upward flows in a pipe is performed by 12 participants using different MCFD (Multiphase Computational Fluid Dynamics) codes and closure relationships. More than 30 conditions from DEBORA experiment conducted by CEA are considered. Each case is characterised by the flow rate, inlet temperature, wall heat flux and outlet pressure. High-pressure Freon (R12) at 14 bar and 26 bar is boiled in a 19.2 mm pipe heated over 3.5 m. Flow rates range from 2000 kg m(-2) s(-1) to 5000 kg m(-2) s(-1) and exit quality x ranges from single-phase conditions to x = 0.1 which leads to a peak void fraction of alpha = 70%. In these high pressure conditions, bubbles remain small and there is no departure from the bubbly flow regime (Francois et al., 2011; Hosler, 1968). However, different kind of bubbly flows are observed: wall-peak, intermediate peak or core-peak, depending on the case considered. Measurements along the pipe radius near the end of the heated section are compared to code predictions. They include void fraction, bubble mean diameter, vapour velocity and liquid temperature. The benchmark covered two phases. In the first phase of the benchmark activities, experimental data were given to the participants, allowing to compare the simulation results and to develop, to select or to adjust the models in the CMFD codes. The second phase included blind cases where the participants could not compare to the measurements. In between the two phases, possible additional model adjustments or calibrations were performed. Overall, the benchmark involved very different closures and a wide range of models' complexity was covered. Yet, it is extremely difficult to have a robust closure for all conditions considered, even knowing experimental measurements. The wall-to-core peak transition is not captured consistently by the models. The degree of subcooling and the void fraction level are also difficult to assess. We were not capable of showingsuperiority of some physical closures, even for part of the model. The interaction between mechanisms and their hierarchy are extremely difficult to understand. Although departure from nucleate boiling (DNB) was not considered in this benchmarking exercise, it is expected that DNB predictions at high-pressure conditions depend strongly on the near-wall flow, temperature, and void fraction distributions. Therefore, the suitability of the closures also limits the accuracy of DNB predictions. The benchmark also demonstrated that in order to progress further in models development and validation, it is compulsory to have new measurements that include simultaneously as many variables as possible (including liquid temperature, velocity, cross-correlations and wall temperature); also, a better knowledge of the local bubble sizes distributions is the key to discriminate performances of interfacial area modelling (IATE, MUSIG or iMUSIG models, considering for instance the possibility of two classes of bubbles having totally different behaviour regarding the lift force). Following this benchmark impulse, we hope that future activities will be engaged on high-pressure boiling water experiments with a continuation of models' comparisons and development.

Název v anglickém jazyce

Benchmark DEBORA: Assessment of MCFD compared to high-pressure boiling pipe flow measurements

Popis výsledku anglicky

A benchmark activity on two-fluid simulations of high-pressure boiling upward flows in a pipe is performed by 12 participants using different MCFD (Multiphase Computational Fluid Dynamics) codes and closure relationships. More than 30 conditions from DEBORA experiment conducted by CEA are considered. Each case is characterised by the flow rate, inlet temperature, wall heat flux and outlet pressure. High-pressure Freon (R12) at 14 bar and 26 bar is boiled in a 19.2 mm pipe heated over 3.5 m. Flow rates range from 2000 kg m(-2) s(-1) to 5000 kg m(-2) s(-1) and exit quality x ranges from single-phase conditions to x = 0.1 which leads to a peak void fraction of alpha = 70%. In these high pressure conditions, bubbles remain small and there is no departure from the bubbly flow regime (Francois et al., 2011; Hosler, 1968). However, different kind of bubbly flows are observed: wall-peak, intermediate peak or core-peak, depending on the case considered. Measurements along the pipe radius near the end of the heated section are compared to code predictions. They include void fraction, bubble mean diameter, vapour velocity and liquid temperature. The benchmark covered two phases. In the first phase of the benchmark activities, experimental data were given to the participants, allowing to compare the simulation results and to develop, to select or to adjust the models in the CMFD codes. The second phase included blind cases where the participants could not compare to the measurements. In between the two phases, possible additional model adjustments or calibrations were performed. Overall, the benchmark involved very different closures and a wide range of models' complexity was covered. Yet, it is extremely difficult to have a robust closure for all conditions considered, even knowing experimental measurements. The wall-to-core peak transition is not captured consistently by the models. The degree of subcooling and the void fraction level are also difficult to assess. We were not capable of showingsuperiority of some physical closures, even for part of the model. The interaction between mechanisms and their hierarchy are extremely difficult to understand. Although departure from nucleate boiling (DNB) was not considered in this benchmarking exercise, it is expected that DNB predictions at high-pressure conditions depend strongly on the near-wall flow, temperature, and void fraction distributions. Therefore, the suitability of the closures also limits the accuracy of DNB predictions. The benchmark also demonstrated that in order to progress further in models development and validation, it is compulsory to have new measurements that include simultaneously as many variables as possible (including liquid temperature, velocity, cross-correlations and wall temperature); also, a better knowledge of the local bubble sizes distributions is the key to discriminate performances of interfacial area modelling (IATE, MUSIG or iMUSIG models, considering for instance the possibility of two classes of bubbles having totally different behaviour regarding the lift force). Following this benchmark impulse, we hope that future activities will be engaged on high-pressure boiling water experiments with a continuation of models' comparisons and development.

Druh

J_imp - Článek v periodiku v databázi Web of Science

CEP obor

—

OECD FORD obor

20305 - Nuclear related engineering; (nuclear physics to be 1.3);

Projekt

—

Návaznosti

V - Vyzkumna aktivita podporovana z jinych verejnych zdroju

Rok uplatnění

2024

Kód důvěrnosti údajů

S - Úplné a pravdivé údaje o projektu nepodléhají ochraně podle zvláštních právních předpisů

Název periodika

International Journal of Multiphase Flow

ISSN

0301-9322

e-ISSN

—

Svazek periodika

179

Číslo periodika v rámci svazku

September

Stát vydavatele periodika

GB - Spojené království Velké Británie a Severního Irska

Počet stran výsledku

31

Strana od-do

1-31

Kód UT WoS článku

001292650300001

EID výsledku v databázi Scopus

2-s2.0-85200219647