Thermal stress analysis of a Water-Molten Salt Heat Exchanger: Computational Fluid Dynamics with Fluid-Structure Interaction
Translated title
Thermal stress analysis of a Water-Molten Salt Heat Exchanger
Author
Naider, Jakub
Term
4. semester
Education
Publication year
2023
Submitted on
2023-05-31
Pages
71
Abstract
This thesis uses computer simulations to study a heat exchanger designed for molten sodium hydroxide. We modeled two common configurations - a double-pipe heat exchanger and a U-tube heat exchanger - with water as the working fluid at three pressures (1, 2, and 5 bar). Computational Fluid Dynamics (CFD) was used to predict flow and heat transfer, and the resulting thermal stresses were evaluated with the Finite Element Method (FEM). In most simulations we assumed the design allowed the tubes to expand thermally without creating extra stress. In one scenario, however (the U-tube at atmospheric pressure), we assumed a baffle (a support plate that holds the tubes) pressed against the tubes so that their thermal expansion was constrained. For each case we calculated a Factor of Safety to check whether the computed stresses exceeded the tensile yield strength, meaning the material would leave the elastic range. Under identical properties and boundary conditions, the double-pipe design produced higher thermal stresses than the U-tube, but its Factors of Safety remained acceptable. When tube expansion was constrained by the baffle, the Factor of Safety fell below 1, indicating yielding and irreversible damage. This shows that provisions to accommodate thermal expansion are necessary.
Dette projekt bruger computersimuleringer til at undersøge en varmeveksler til smeltet natriumhydroxid. Vi modellerede to almindelige konfigurationer - en dobbelt-rørs varmeveksler og en U-rørs varmeveksler - med vand som arbejdsvæske ved tre tryk (1, 2 og 5 bar). Computational Fluid Dynamics (CFD) blev anvendt til at forudsige strømning og varmeoverførsel, og de resulterende termiske spændinger blev vurderet med Finite Element Metoden (FEM). I de fleste simuleringer antog vi, at designet tillod rørernes termiske udvidelse uden at skabe ekstra spændinger. I ét scenarie (U-rør ved atmosfærisk tryk) antog vi derimod, at en baffel (en støtteplade, der holder rørene) pressede mod rørene, så deres udvidelse blev begrænset. For hver sag beregnede vi en sikkerhedsfaktor for at kontrollere, om de beregnede spændinger oversteg flydespændingen, hvilket betyder, at materialet forlader det elastiske område. Under identiske egenskaber og randbetingelser gav dobbelt-rør designet højere termiske spændinger end U-røret, men sikkerhedsfaktoren forblev på et acceptabelt niveau. Når rørudvidelsen blev begrænset af baffelen, faldt sikkerhedsfaktoren til under 1, hvilket indikerer flydning og uoprettelig skade. Dette viser, at der er behov for foranstaltninger, der kan optage termisk udvidelse.
[This apstract has been rewritten with the help of AI based on the project's original abstract]
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