CFD modelling of two-phase critical flow with different length to diameter ratio horizontal tubes : master’s thesis

Singh, Sharandeet (author), Hyvärinen, Juhani (mentor), Tiselj, Iztok (comentor), Patel, Giteshkumar (comentor), Pyy, Lauri (comentor)

In this master's thesis, two-phase critical flow in a separate effect test facility is investigated using computational fluid dynamics (CFD). This topic is being conducted as part of the C-FLOW SAFER 2028 (National Nuclear Safety and Waste Management Research Program 2023–2028) project, which attempts to improve nuclear reactor safety and security. It is reasonably necessary to understand the behavior of two-phase critical flow for the design and analysis of nuclear power systems, especially in emergency situations such as loss-of-coolant accidents. The prediction and understanding of fluid dynamics in nuclear power plants is quite essential for the safe and secure operation of the plants. The main purpose of the thesis is to develop a comprehensive CFD model capable of simulating the flashing flow in pipes with different length-to-diameter ratios and to know the inception of flashing. To do this, ANSYS-FLUENT software, a commercial CFD simulation program, has been employed. Moreover, we performed in-depth analyses and examine the effects of various geometrical parameters, operational conditions, and turbulence models on the flow behavior. Results from the simulations give us an insight into the inception of the flashing conditions along with the temperature, pressure and mass flow changes happening through the length of the pipe of different length-to-diameter ratios. Further, a comparison between the CFD and APROS results has been made to analyze the difference and similarities between these two different codes.

• Language: English
• Keywords: fluid dynamics, computational modelling, two-phase flow, critical flow, horizontal tubes, nuclear reactors, safety analysis, heat transfer, pressure drop
• Work type: Master's thesis/paper
• Typology: 2.09 - Master's Thesis
• Organization: FMF - Faculty of Mathematics and Physics
• Place of publishing: Lappeenranta
• Publisher: S. Singh
• Year: 2024
• Number of pages: 1 spletni vir (1 datoteka PDF (123 str.))
• PID: 20.500.12556/RUL-170939
• UDC: 532
• COBISS.SI-ID: 243370499
• Publication date in RUL: 22.07.2025

Secondary language

• Language: Slovenian
• Title: CFD modeliranje dvofaznega kritičnega pretoka z različnim razmerjem dolžine in premera vodoravnih cevi

Abstract

V magistrskem delu smo z uporabo računalniške dinamike tekočin (CFD) raziskali dvofazni kritični tok. Raziskava je potekala v okviru projekta C-FLOW SAFER 2028 (Finski Nacionalni raziskovalni program za jedrsko varnost in ravnanje z odpadki 2023–2028), ki cilja na izboljšave v varnost jedrskih reaktorjev. Za načrtovanje in analizo jedrskih energetskih sistemov je razumno potrebno razumeti obnašanje dvofaznega kritičnega toka, zlasti v izrednih razmerah, kot so izlivne nesreče. Napovedovanje in razumevanje dinamike tekočin v jedrskih elektrarnah je bistvenega pomena za varno in varno delovanje elektrarn. Glavni namen magistrskega dela je bil razvoj CFD (CFD = Computational Fluid Dynamics = Računska Dinamika Tekočin) modela, ki je sposoben simulirati kritični tok z uparjanjem v ceveh z različnimi razmerji dolžine in premera ter napovedati začetek uparjanja. Za to smo uporabili programsko opremo ANSYS-FLUENT. Poleg tega smo izvedli poglobljene analize in preučili učinkov različnih geometrijskih parametrov, obratovalnih pogojev in modelov turbulence na obnašanje toka. Rezultati simulacij nam dajejo vpogled v območje toka, kjer se začne uparjanje kapljevine skupaj s spremembami temperature, tlaka in masnega pretoka. Na masni pretok ter obliko toka vplivata dolžina in premer cevi. Nadalje smo opravili primerjavo med rezultati CFD programa ter enostavnejšega sistemskega programa APROS, ter analizirali razlike in podobnosti med obema različnima programoma.

• Keywords: dinamika tekočin, računalniško modeliranje, dvofazni tok, kritični tok, vodoravne cevi, jedrski reaktorji, varnostne analize, prenos toplote, padec tlaka