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High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel.

紀錄類型:	書目-電子資源 : Monograph/item
正題名/作者:	High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel./
作者:	Saini, Nadish.
出版者:	Ann Arbor : ProQuest Dissertations & Theses, : 2020,
面頁冊數:	242 p.
附註:	Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
Contained By:	Dissertations Abstracts International81-11B.
標題:	Nuclear engineering. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28004219
ISBN:	9798643182542

High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel.
Saini, Nadish.

High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel. - Ann Arbor : ProQuest Dissertations & Theses, 2020 - 242 p.

Source: Dissertations Abstracts International, Volume: 81-11, Section: B.

Thesis (Ph.D.)--North Carolina State University, 2020.

This item must not be sold to any third party vendors.

In the dispersed flow film boiling (DFFB) regime, which exists under post loss-of-coolant accident (LOCA) conditions in PWRs, droplet dynamics play a critical role in heat transfer. The DFFB regime is characterized by a very high void fraction, such that the flow regime is akin to a mist type flow. Consequently, the dominant heat transfer pathway under these conditions is to the entrained droplets, which is a strong function of the surface area of the droplets. The major heat transfer mechanisms include radiation from rods to droplet surface and convective heat transfer from bulk vapor to droplets. Evaporation of droplets also results in an increase in the local vapor velocity, further enhancing the heat transfer coefficients. Spacer grids and mixing vane structures play an especially critical role in the DFFB regime. Collision of the droplets with these structures results in an increase in their surface area, which causes a sharp increase in heat transfer immediately downstream of the mixing vanes. Thus, a detailed study of the droplet dynamics - its morphology, average diameter, interaction with surrounding flow and spacers, is indispensable to understanding the intricacies of the DFFB regime. With the advent of supercomputing and the development of highly scalable computer codes, it is becoming increasingly economical to run high fidelity, high resolution simulations of flow phenomena, wherein all relevant scales of the flow are resolved. PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis), a finite element method based Navier-Stokes solver, is one such numerical tool, used herein, with proven strong scaling on leading supercomputers. With the level-set method for interface capturing, PHASTA provides the capability of resolving two-phase flow phenomena. The level-set method implicitly captures the interface between the phases, allowing for resolution of inherent complexities of the flow including droplet collision, breakup and coalescence. In this research, detailed interface-resolved simulations are performed for simulating droplet dynamics in a prototypal reactor sub-channel with spacer grid and mixing vanes, under conditions representative of DFFB regime. Several ad-hoc functionalities are incorporated in PHASTA to enable the DFFB simulations and to enable high-resolution data collection from the simulations. Subsequent post-processing of the data provides the evolution of interfacial area, volume and Sauter mean diameter (SMD) of droplets along the axial length of the sub-channel domain. The SMD of the droplets at the downstream location of the mixing vanes is compared with existing empirical correlations, showing good agreement. Further, a comparative study of the upstream and downstream mean velocity and Reynolds stress tensor profile is presented to emphasize the effect of spacer-grid and mixing vane structures on the bulk flow, with and without the presence of droplets. The high spatial and temporal resolution database from both single-phase and two-phase simulations enable the prospect of data driven turbulence and system thermal hydraulic modeling. Recognizing the prospect of level-set formulation for two-phase flows to simulate complex nuclear reactor regimes, efforts were made in this research to incorporate the formulation in another strong scaling flow solver, Nek5000. A spectrally vanishing viscosity (SVV) approach was implemented to stabilize the re-distancing equation. An improved multi-dimensional filter kernel for SVV is formulated and shown to provide adequate stabilization for liner/non-linear hyperbolic problems. Finally, the level-set formulation was coupled with an existing low Mach number solver in Nek5000 and demonstrated for the solution of 2D two-phase flow problems.

ISBN: 9798643182542Subjects--Topical Terms:

595435
Nuclear engineering.
Subjects--Index Terms:

Dispersed flow film boiling (DFFB)

High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel.
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100 1 $a Saini, Nadish. $3 3547692
245 1 0 $a High-Fidelity Interface Capturing Simulations of the Post-LOCA Dispersed Flow Film Boiling Regime in a Pressurized Water Reactor Sub-channel.
260 1 $a Ann Arbor : $b ProQuest Dissertations & Theses, $c 2020
300 $a 242 p.
500 $a Source: Dissertations Abstracts International, Volume: 81-11, Section: B.
500 $a Advisor: Bolotnov, Igor A.
502 $a Thesis (Ph.D.)--North Carolina State University, 2020.
506 $a This item must not be sold to any third party vendors.
520 $a In the dispersed flow film boiling (DFFB) regime, which exists under post loss-of-coolant accident (LOCA) conditions in PWRs, droplet dynamics play a critical role in heat transfer. The DFFB regime is characterized by a very high void fraction, such that the flow regime is akin to a mist type flow. Consequently, the dominant heat transfer pathway under these conditions is to the entrained droplets, which is a strong function of the surface area of the droplets. The major heat transfer mechanisms include radiation from rods to droplet surface and convective heat transfer from bulk vapor to droplets. Evaporation of droplets also results in an increase in the local vapor velocity, further enhancing the heat transfer coefficients. Spacer grids and mixing vane structures play an especially critical role in the DFFB regime. Collision of the droplets with these structures results in an increase in their surface area, which causes a sharp increase in heat transfer immediately downstream of the mixing vanes. Thus, a detailed study of the droplet dynamics - its morphology, average diameter, interaction with surrounding flow and spacers, is indispensable to understanding the intricacies of the DFFB regime. With the advent of supercomputing and the development of highly scalable computer codes, it is becoming increasingly economical to run high fidelity, high resolution simulations of flow phenomena, wherein all relevant scales of the flow are resolved. PHASTA (Parallel Hierarchic Adaptive Stabilized Transient Analysis), a finite element method based Navier-Stokes solver, is one such numerical tool, used herein, with proven strong scaling on leading supercomputers. With the level-set method for interface capturing, PHASTA provides the capability of resolving two-phase flow phenomena. The level-set method implicitly captures the interface between the phases, allowing for resolution of inherent complexities of the flow including droplet collision, breakup and coalescence. In this research, detailed interface-resolved simulations are performed for simulating droplet dynamics in a prototypal reactor sub-channel with spacer grid and mixing vanes, under conditions representative of DFFB regime. Several ad-hoc functionalities are incorporated in PHASTA to enable the DFFB simulations and to enable high-resolution data collection from the simulations. Subsequent post-processing of the data provides the evolution of interfacial area, volume and Sauter mean diameter (SMD) of droplets along the axial length of the sub-channel domain. The SMD of the droplets at the downstream location of the mixing vanes is compared with existing empirical correlations, showing good agreement. Further, a comparative study of the upstream and downstream mean velocity and Reynolds stress tensor profile is presented to emphasize the effect of spacer-grid and mixing vane structures on the bulk flow, with and without the presence of droplets. The high spatial and temporal resolution database from both single-phase and two-phase simulations enable the prospect of data driven turbulence and system thermal hydraulic modeling. Recognizing the prospect of level-set formulation for two-phase flows to simulate complex nuclear reactor regimes, efforts were made in this research to incorporate the formulation in another strong scaling flow solver, Nek5000. A spectrally vanishing viscosity (SVV) approach was implemented to stabilize the re-distancing equation. An improved multi-dimensional filter kernel for SVV is formulated and shown to provide adequate stabilization for liner/non-linear hyperbolic problems. Finally, the level-set formulation was coupled with an existing low Mach number solver in Nek5000 and demonstrated for the solution of 2D two-phase flow problems.
590 $a School code: 0155.
650 4 $a Nuclear engineering. $3 595435
653 $a Dispersed flow film boiling (DFFB)
653 $a Loss-of-coolant accident (LOCA)
653 $a Pressurized water reactor sub-channel
690 $a 0552
710 2 $a North Carolina State University. $3 1018772
773 0 $t Dissertations Abstracts International $g 81-11B.
790 $a 0155
791 $a Ph.D.
792 $a 2020
793 $a English
856 4 0 $u http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=28004219