•Numerical simulations in a mixing tee to assess fatigue damage.•Non-dimensional temperature profiles along the centerline show a fairly overlapping behavior.•Case 3 predicts a usage factor of 1 for ...estimated number of around 1.1 million cycles.•The resulting alternating stress is coupled with the flow conditions by a linear profile.•The highest alternating stress has approximately the value 177 MPa.
The present paper depicts a numerical study of flow and thermal features in T-junctions with circular cross-section. The numerical simulation is based on the experimental validated wall-resolved Large-Eddy Simulation method. The Reynolds number in the warm main pipe flow covers a range of Rem=27000 to Rem=134000 and the temperature difference of the mixing fluids is up to ΔT=249 K. The location of maximum fluctuations does not change due to a nearly identical flow pattern type in all simulations. This condition allows the investigation of the flow evolution, mixing process and heat transfer for the same thermal flow pattern type. The numerical simulations are coupled with the heat conduction in the structure due to the thermal fluid-structure-interaction. Further, this study offers a deeper insight into the hidden physics of turbulent mixing flows and the transport as well as damping of thermal fluctuations in the near-wall fluid/solid region. Our study considers also thermal stress analysis by Finite-Element Method by utilizing the wall temperature distribution of previously performed numerical simulations. Therefore, fatigue damage is evaluated based on the stress received from the Finite-Element analysis. The results show that the highest Reynolds number case corresponds to the highest flux intensity and turbulence. This affects the flow field and the thermal features in the core flow and the transport of fluctuations close to the wall. The locations with peak fluctuation intensity in the fluid generates also high fluctuating temperature areas in the structure. The finite element analysis demonstrates that the highest temperature difference case leads to the highest alternating stress intensity which has potential for thermal fatigue. The generated maximal alternating stress is coupled with the flow conditions of the mixing fluids. With an increasing Reynolds number of the main and branch pipe flow as well as temperature difference raises also the resulting maximum alternating stress intensity.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Phenomena of subcooled flow through leaks in thin walls are studied.•Laboratory tests on flow through thin-walled apertures with mass flow and optical measurements are performed.•A ...computational model assuming a jet of metastable liquid water is proposed and applied.•Comparative analysis of leak rates with different models on selected tests.
The modeling and prediction of flow rates through leaks in steam generator tubes requires an understanding of the rapid decompression of a subcooled fluid flowing through a small and short flow path. The thin walls of steam generator tubes may lead to the phenomenon that the coolant water cannot evaporate within the leak flow path, which is a key difference compared to leak flow in thick-walled components. Experimental investigations in the literature were investigated and additional laboratory tests on dedicated specimens were performed, including mass flow measurements and optical measurements, which study the flow pattern at the outlet of the leak. These experiments cover a ratio of flow length (wall thickness) to hydraulic diameter L/dh range from 0.4 to 12. Based on the findings, a metastable jet model is proposed, which is based on the formation of a jet of metastable liquid water. The model parameters are fitted with the experiments. The model is compared with alternative approaches, which demonstrates that it is suitable to approximate the mass flow of leaks in steam generator tubes with a sufficiently large leak width or cross section. Due to the small absolute wall thickness of steam generator tubes only very narrow flaws are found to be successfully modeled with ordinary two-phase flow models.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Under ambient conditions, almost all metals are coated by an oxide. These coatings, the result of a chemical reaction, are not passive. Many of them bind, activate and modify adsorbed molecules, ...processes that are exploited, for example, in heterogeneous catalysis and photochemistry. Here we report an effect of general importance that governs the bonding, structure formation and dissociation of molecules on oxidic substrates. For a specific example, methanol adsorbed on the rutile TiO
(110) single crystal surface, we demonstrate by using a combination of experimental and theoretical techniques that strongly bonding adsorbates can lift surface relaxations beyond their adsorption site, which leads to a significant substrate-mediated interaction between adsorbates. The result is a complex superstructure consisting of pairs of methanol molecules and unoccupied adsorption sites. Infrared spectroscopy reveals that the paired methanol molecules remain intact and do not deprotonate on the defect-free terraces of the rutile TiO
(110) surface.
The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ...(bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and N,N,N',N'-tetramethylethylenediamine copper(ii)acetylacetonate tetraphenylborate (Cu(acac)(tmen)B(C6H5)4), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of (Cu(acac)(tmen)B(C6H5)4), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim+ cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.
The behavior of the interfacial water entrapped in reverse micelles (RMs) that were formed by the ionic liquid-like surfactant 1-butyl-3-methylimidazolium 1,4-bis-2-ethylhexylsulfosuccinate ...(bmim-AOT) was investigated with the use of UV-Vis absorption spectroscopy and nuclear magnetic resonance (NMR) relaxometry. The solvatochromism of two molecular probes, namely, 1-methyl-8-oxyquinolinium betaine (QB) and
N
,
N
,
N
′,
N
′-tetramethylethylenediamine copper(
ii
)acetylacetonate tetraphenylborate (Cu(acac)(tmen)B(C
6
H
5
)
4
), was investigated. As a comparison, the analog RMs formed by sodium 1,4-bis-2-ethylhexylsulfosuccinate (Na-AOT) were also explored. By varying the water content inside the RMs and consequently the different magnitude of the water-surfactant interactions at the interface, interesting properties were observed by comparing bmim-AOT and Na-AOT RMs. From the solvatochromic behavior of (Cu(acac)(tmen)B(C
6
H
5
)
4
), we found that the interface in bmim-AOT RMs shows a smaller electron donating capacity than that in Na-AOT RMs. QB revealed that the interfacial region is a weaker hydrogen bond donor and less polar than the corresponding Na-AOT RMs. NMR experiments showed that the molecular motion of water in bmim-AOT RMs is less restricted than that of the water molecules confined in Na-AOT RMs. In summary, the results show how the nature of the bmim
+
cation affects the interaction between the entrapped water and the RM interface, greatly modifying the interfacial water structure in comparison with the results known for Na-AOT.
Change in the cationic component in the surfactant promotes changes in the electron donating ability and micropolarity of the RMs interface.
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