In-Vessel Retention (IVR) is one of the existing strategies of severe accident management of LWR, which intends to stabilize and isolate corium & fission products inside the reactor pressure vessel (RPV) and prima...In-Vessel Retention (IVR) is one of the existing strategies of severe accident management of LWR, which intends to stabilize and isolate corium & fission products inside the reactor pressure vessel (RPV) and primary containment structure. Since it has become an important safety objective for nuclear reactors, it is therefore needed to model and evaluate relevant phenomena of IVR strategy in assessing safety of nuclear power reactors. One of the relevant phenomena during accident progression in the oxidic pool is non-uniform high heat generation occurring at large scale. Consequently, direct experimental studies at these scales are not possible. The role computer codes and models are therefore important in order to transpose experimental results to reactor safety applications. In this paper, the state-of-the-art ANSYS FLUENT CFD code is used to simulate Non-uniform heat generation in the lower plenum by the application of Cartridge heating under severe accident conditions to derive the basic accident scenario. However, very few studies have been performed to simulate non-uniform decay heat generation by Cartridge heaters in a pool corresponding lower plenum of power reactor. The current investigation focuses on non-uniform heating in the fluid domain by Cartridge heaters, which has been done using ANSYS FLUENT CFD code by K-epsilon model. The computed results are based on qualitative assessment in the form of temperature and velocity contour and quantitative assessment in terms of temperature and heat flux distribution to assess the impact of heating method on natural convective fluid flow and heat transfer.展开更多
The present work focus on the thermal performance of a horizontal concentric heat exchanger, which is numerically investigated to evaluate the heat transfer enhancement process by adding fins with different configurat...The present work focus on the thermal performance of a horizontal concentric heat exchanger, which is numerically investigated to evaluate the heat transfer enhancement process by adding fins with different configurations. As a part of this investigation, the melting process is simulated from the onset of phase change to the offset involving physics of natural convection in PCM fluid pool. The investigation is carried out by ANSYS Fluent code, which is an efficient numerical analysis tool for investigating fluid flow and convective heat transfer phenomena during PCM melting process. The attention is mainly focused on the extension of contact area between the PCM body and cylindrical capsule to enhance heat transfer rates to PCM bodies during the melting process by employing longitudinal fins in the enclosed capsule. Two commercial PCMs: RT50 and C58, are introduced in a 2D cylindrical pipe with their thermo-physical properties as input for modelling. The selected modelling approach is validated against experimental result with respect to the total enthalpy changes that qualify our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (373 K) is applied to the inner pipe throughout the series of simulation cases and the corresponding Rayleigh number (Ra) ranges from 104 - 105 and Prandtl number (Pr) 0.05 - 0.07. Finally, parametric study is carried out to evaluate the effect of length, thickness and number of longitudinal fins on the thermal performance of PCM-LHTES (Latent Heat Thermal Energy Storage) system associated with the physics of natural convection process during PCM melting.展开更多
In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerica...In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerical analysis is performed for hemispherical 3-D vessel slice to investigate the physics of the effect of Pr number on convective heat transfer characteristics in the melt pool. The investigation is based on ANSYS FLUET, where natural convection heat transfer effect is taken into consideration by Phase-change Effective Convectivity Model (PECM), which is implemented with FLUENT CFD as User Defined Function (UDF), programed by the user. The PECM is tested first by a benchmark test against CFD to gain confidence in its applicability as an analysis tool. Different simulant materials are used with their thermo-physical properties representing different Pr number as input for modelling for both single and double layer melt pool configuration. The selected modelling approach is validated against RASPLAV experimental result with respect to the inner temperature distribution that qualifies our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (343 K) is applied along vessel outer wall throughout the series of simulation cases. The corresponding Rayleigh number (Ra) ranges from 1014 - 1015 and Prandtl number (Pr) 3 - 5. It is found that the fluid Pr number has small effects on the averaged Nu numbers in the convection-dominated regions. The decrease in the Pr number may cause a decrease in the Nu numbers on the top and sidewalls of cavities. In the conduction dominated regions (stably stratified bottom parts of enclosure), the effect of fluid Pr number on heat transfer is more significant and it grows with increasing Ra number.展开更多
文摘In-Vessel Retention (IVR) is one of the existing strategies of severe accident management of LWR, which intends to stabilize and isolate corium & fission products inside the reactor pressure vessel (RPV) and primary containment structure. Since it has become an important safety objective for nuclear reactors, it is therefore needed to model and evaluate relevant phenomena of IVR strategy in assessing safety of nuclear power reactors. One of the relevant phenomena during accident progression in the oxidic pool is non-uniform high heat generation occurring at large scale. Consequently, direct experimental studies at these scales are not possible. The role computer codes and models are therefore important in order to transpose experimental results to reactor safety applications. In this paper, the state-of-the-art ANSYS FLUENT CFD code is used to simulate Non-uniform heat generation in the lower plenum by the application of Cartridge heating under severe accident conditions to derive the basic accident scenario. However, very few studies have been performed to simulate non-uniform decay heat generation by Cartridge heaters in a pool corresponding lower plenum of power reactor. The current investigation focuses on non-uniform heating in the fluid domain by Cartridge heaters, which has been done using ANSYS FLUENT CFD code by K-epsilon model. The computed results are based on qualitative assessment in the form of temperature and velocity contour and quantitative assessment in terms of temperature and heat flux distribution to assess the impact of heating method on natural convective fluid flow and heat transfer.
文摘The present work focus on the thermal performance of a horizontal concentric heat exchanger, which is numerically investigated to evaluate the heat transfer enhancement process by adding fins with different configurations. As a part of this investigation, the melting process is simulated from the onset of phase change to the offset involving physics of natural convection in PCM fluid pool. The investigation is carried out by ANSYS Fluent code, which is an efficient numerical analysis tool for investigating fluid flow and convective heat transfer phenomena during PCM melting process. The attention is mainly focused on the extension of contact area between the PCM body and cylindrical capsule to enhance heat transfer rates to PCM bodies during the melting process by employing longitudinal fins in the enclosed capsule. Two commercial PCMs: RT50 and C58, are introduced in a 2D cylindrical pipe with their thermo-physical properties as input for modelling. The selected modelling approach is validated against experimental result with respect to the total enthalpy changes that qualify our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (373 K) is applied to the inner pipe throughout the series of simulation cases and the corresponding Rayleigh number (Ra) ranges from 104 - 105 and Prandtl number (Pr) 0.05 - 0.07. Finally, parametric study is carried out to evaluate the effect of length, thickness and number of longitudinal fins on the thermal performance of PCM-LHTES (Latent Heat Thermal Energy Storage) system associated with the physics of natural convection process during PCM melting.
文摘In the framework of this research, the principle focus is to analyze the effects of fluid Prandtl number (Pr) on natural convection heat transfer in a volumetrically heated molten pool. As a part of the work, numerical analysis is performed for hemispherical 3-D vessel slice to investigate the physics of the effect of Pr number on convective heat transfer characteristics in the melt pool. The investigation is based on ANSYS FLUET, where natural convection heat transfer effect is taken into consideration by Phase-change Effective Convectivity Model (PECM), which is implemented with FLUENT CFD as User Defined Function (UDF), programed by the user. The PECM is tested first by a benchmark test against CFD to gain confidence in its applicability as an analysis tool. Different simulant materials are used with their thermo-physical properties representing different Pr number as input for modelling for both single and double layer melt pool configuration. The selected modelling approach is validated against RASPLAV experimental result with respect to the inner temperature distribution that qualifies our model to run in the proceeding calculation. It is ensured that an isothermal boundary condition (343 K) is applied along vessel outer wall throughout the series of simulation cases. The corresponding Rayleigh number (Ra) ranges from 1014 - 1015 and Prandtl number (Pr) 3 - 5. It is found that the fluid Pr number has small effects on the averaged Nu numbers in the convection-dominated regions. The decrease in the Pr number may cause a decrease in the Nu numbers on the top and sidewalls of cavities. In the conduction dominated regions (stably stratified bottom parts of enclosure), the effect of fluid Pr number on heat transfer is more significant and it grows with increasing Ra number.
