Računski model stenskega in volumetričnega uparjanja v toplotni cevi : doktorska disertacija

Štrucl, Jure

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Title:	Računski model stenskega in volumetričnega uparjanja v toplotni cevi : doktorska disertacija
Authors:	ID Štrucl, Jure (Author) ID Zadravec, Matej (Mentor) More about this mentor... ID Marn, Jure (Comentor)
Files:	DOK_Strucl_Jure_2026.pdf (7,72 MB) MD5: 2B00EA64DE885C19FB0EB7CC0FEF8858
Language:	Slovenian
Work type:	Doctoral dissertation
Typology:	2.08 - Doctoral Dissertation
Organization:	FS - Faculty of Mechanical Engineering
Abstract:	Doktorska disertacija obravnava razvoj in validacijo novega kombiniranega modela vrenja (CBM), namenjenega numeričnemu izračunu stenskega in volumetričnega uparjanja in kondenzacije v toplotnih ceveh brez kapilarne strukture oziroma dvofaznih zaprtih termosifonih (TPCT). CBM v enoten okvir poveže razširjeni RPI-model stenskega vrenja z drsečimi mehurčki, volumetrični model uparjanja in kondenzacije po Leeju ter poenostavljen model filmske kondenzacije na osnovi Nusseltove teorije laminarnega filma. Model je v celoti implementiran v okviru metode Euler–Euler in konjugiranega prenosa toplote (CHT) v programskem okolju AVL FIRE™ M, z možnostjo uporabe tudi v kombinaciji z metodo VOF za natančnejšo lokalno analizo dvofaznega toka. Za dokaz koncepta je CBM najprej validiran na preizkusnem kanalu z nadtlačno vodo/glikolom, kjer poteka podhlajeno stensko vrenje. Izvedena je bila obsežna študija vpliva mreže in časovnega koraka ter simulacij pri različnih hitrostih toka, tlakih in toplotnih tokovih, skupaj več kot 96 simulacij. Napovedane temperature stene in nastajanje pare se z eksperimentalnimi podatki ujemajo znotraj približno 5 %, CBM pa v vseh pogojih bolje zajame vpliv prisilne konvekcije kot klasični RPI-model. V drugi fazi je model uporabljen za numerično analizo TPCT z vodo pri različnih toplotnih obremenitvah (100–376 W) in razmerjih polnitve (0,5 in 1,0). Simulacije uspešno opišejo zagon termosifona, nastanek in transport parnih žepov ter tvorbo stenskega kondenzatnega filma v kondenzatorju. V primerjavi z eksperimentom in predhodnimi VOF–Lee-jevimi simulacijami se povprečna absolutna odstotna napaka temperature zmanjša na približno 1,55 %, ob bistveno nižjem računskem strošku (simulacija 60 s obratovanja v nekaj dneh namesto tednov). CBM tako predstavlja energijsko skladen in računsko učinkovit pristop za inženirsko toplotno analizo toplotnih cevi in termosifonov.
Keywords:	toplotna cev, dvofazni zaprti termosifon, uparjanje in kondenzacija, konjugiran prenos toplote (CHT), stensko vrenje
Place of publishing:	Maribor
Place of performance:	Maribor
Publisher:	[J. Štrucl]
Year of publishing:	2026
Number of pages:	XIII, 132 str.
PID:	20.500.12556/DKUM-96016
UDC:	[532.54:536.423]:519.6(043.3)
COBISS.SI-ID:	288824835
Publication date in DKUM:	24.07.2026
Views:	283
Downloads:	10
Metadata:
Categories:	KTFMB - FS
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Licences

License:	CC BY-NC-ND 4.0, Creative Commons Attribution-NonCommercial-NoDerivatives 4.0 International

Link:	http://creativecommons.org/licenses/by-nc-nd/4.0/
Description:	The most restrictive Creative Commons license. This only allows people to download and share the work for no commercial gain and for no other purposes.
Licensing start date:	21.11.2025

Secondary language

Language:	English
Title:	Computational wall and flow evaporation model for heat pipe simulations
Abstract:	This dissertation presents the development and validation of a new Combined Boiling Model (CBM) for numerical prediction of wall and flow evaporation and condensation in wakeless heat pipes or two-phase closed thermosyphons (TPCT). The CBM integrates an extended RPI wall boiling model with sliding bubbles, a volumetric Lee-type evaporation–condensation closure, and a simplified wall film condensation model based on Nusselt’s laminar film theory. The model is fully implemented within an Euler–Euler multiphase framework coupled with conjugate heat transfer (CHT) in AVL FIRE™ M, and can also be combined with a Volume of Fluid (VOF) interface-capturing approach for detailed local two-phase flow analysis. As proof of concept, the CBM is first validated on a heated rectangular channel with pressurised water–glycol flow under subcooled flow boiling conditions. A comprehensive mesh and time-step sensitivity study, together with simulations over a wide range of mass fluxes, pressures, and heat fluxes, was carried out, for a total of more than 96 simulations. Predicted wall temperatures and vapour generation show good agreement with experimental data, with deviations typically within 5 %, while CBM clearly improves the representation of forced-convective boiling compared to the classical RPI model. In the second part, the model is applied to a water TPCT for various heat inputs (100–376 W) and filling ratios (0.5 and 1.0). The simulations successfully reproduce start-up, formation and transport of vapour slugs and the development of a condensate film in the condenser. Comparison with experiments and previous VOF–Lee simulations shows a reduction of the average absolute percentage error of wall temperature to about 1.55 %, while significantly lowering computational cost (about 60 s of physical time obtained in a few days instead of weeks). The CBM thus provides an energy-consistent and computationally efficient tool for engineering thermal analysis and design of two-phase heat pipes and thermosyphons.
Keywords:	heat pipe, two-phase closed thermosyphon (TPCT), evaporation and condensation, conjugate heat transfer (CHT), wall boiling

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