Experimental study of critical heat flux in flow boiling under subatmospheric pressure in a vertical square channel

Colgan, Nathan; Bottini, Joseph L.; Martínez‐Cuenca, Raúl; Brooks, Caleb S.

doi:10.1016/j.ijheatmasstransfer.2018.10.082

Cited by 17 publications

(5 citation statements)

References 19 publications

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“…In their work, Colgan et al [11] established a relationship for critical heat flux (CHF) under subatmospheric system pressure conditions using a vertically oriented square channel. Their study identified the density ratio, Weber number, and Boiling number as the primary factors governing the correlation.…”

Section: Htff 184-2mentioning

confidence: 99%

Heat Transfer And Wall Temperature Distribution During Flow Boiling In Conventional And Mini Channels

Kumar,

Kothadia

2023

Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering

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The fluctuation of pressure in flow boiling is affected due to liquid-vapor phase interaction, and thus the flow and wall temperature are influenced. The temporal and spatial variation of wall temperature and the heat transfer coefficient are investigated experimentally at atmospheric system pressure. The two mini-tubes of 2×300 and 4×600 mm inner diameter× heated length are used for analysis. The thermal image technology is used to show the wall temperature distribution. The experimental setup is validated by comparing the heat transfer coefficient with Dittus-Boelter and Gnielinski correlations. The boiling heat transfer coefficient in both tubes are compared to get the effect of diameter, mass flux and heat flux. The radially as well as axially variation of wall temperature during flow boiling is represented. The wall temperature during liquid-phase flow is identical in the radial direction and increases linearly in the axial direction. The wall temperature exhibits significant axially as well as radially variation in two-phase flow. The wall temperature fluctuates vigorously in mini-channels. The influence of subatmospheric system pressure on subcooled flow boiling is examined in the conventional channel with a diameter of 11.7 mm. An increase in the subcooled flow boiling heat transfer coefficient is observed when the system pressure is lower than atmospheric pressure. At subatmospheric system pressure, the wall temperature exhibits radial symmetry across all Froude number values. Furthermore, the mass flux does not significantly impact the subcooled boiling heat transfer coefficient, when subjected to constant heat flux.

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Section: Htff 184-2mentioning

confidence: 99%

Heat Transfer And Wall Temperature Distribution During Flow Boiling In Conventional And Mini Channels

Kumar,

Kothadia

2023

Proceedings of the 9th World Congress on Mechanical, Chemical, and Material Engineering

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“…Their experimental observations indicated that the rate at which heat transferred from the heated surface to the main flow stream is dependent on the heat flux and vapour quality, and it increases with increasing mass flux. Recent work on flow boiling by Colgan et al, [8] studied the Critical Heat Flux (CFH) under subatomic atmospheric conditions. Based on their findings, the mass flux and the inlet subcooling do not have any substantial effect on the critical heat flux, and also the wall superheat is prolonged at the subatmospheric conditions compared to the atmospheric conditions.…”

Section: Experimental Frameworkmentioning

confidence: 99%

Flow boiling heat transfer characteristics using the modified eulerian and wall heat balance model

Okon

Turan

2020

Heat Mass Transfer

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Flow boiling heat transfer is routinely encountered in nuclear reactors, steam engines and other engineering applications. Although several researchers have carried out different numerical and experimental investigations on flow boiling, the underlying physics of the interfacial interaction is still a complex phenomenon to understand in detail. Hence, the numerical simulation and optimisation regarding the adoption of engineering flow boiling parameters have been conducted in this study using the Modified Eulerian-Eulerian Model (MEEM) and Wall Heat Balance Model (WHBM). To predict interpenetrating flow fields and to provide detailed relevant information on the flow behaviour, this study considered a uniform axial heating profile for a cylindrical flow channel. The Raynolds Average Navier Stokes (RANS) equation with an appropriate turbulence model are used to predict the effect of turbulence on the mean flow field, while the MEEM multiphase sub-models are employed to predict the temperature distribution along the wall, the average void fraction, tracking of the single bubble detachment diameter, heat balance at the wall, effect of surface roughness on heat transfer, the effect of aspect ratio, and the critical heat flux. The results obtained from this study are compared with the selected numerical investigation and experimental data presented in the open literature. The present study shows a better approximate prediction (with minimal uncertainties) of both the subcooled boiling heat transfer and the saturated boiling heat transfer. In summary, this study agrees with extant theories and experimental predictions. Thus, it has provided more profound insights into flow boiling heat transfer particularly for flow in a vertical pipe.

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“…Similarly, other studies were also carried out that predicted DNB type CHF at lower mass flux and operating pressure conditions (Kim et al , 2018; Demarly, 2020). Colgan et al (2019) have conducted experiments to predict CHF over the pressure range of 20 ≤ p (kPa) ≤ 108 and observed that CHF increases with increase in inlet subcooling and mass flux. However, the magnitude of influence of these parameters on CHF differs from the studies carried for CHF at higher pressure.…”

Section: Introduction and Literature Reviewmentioning

confidence: 99%

CFD study of DNB in a hexagonal sub-assembly using MuSiG model

Chowrasia,

S.N.,

Pothukuchi

et al. 2023

HFF

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Purpose Subcooled flow boiling phenomenon is characterized by coolant phase change in the vicinity of the heated wall. Although coolant phase change from liquid to vapour phase significantly enhances the heat transfer coefficient due to latent heat of vaporization, eventually the formed vapor bubbles may coalesce and deteriorate the heat transfer from the heated wall to the liquid phase. Due to the poor heat transfer characteristics of the vapour phase, the heat transfer rate drastically reduces when it reaches a specific value of wall heat flux. Such a threshold value is identified as critical heat flux (CHF), and the phenomenon is known as departure from nucleate boiling (DNB). An accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Therefore, the present study aims at the prediction of DNB type CHF in a hexagonal sub-assembly. Design/methodology/approach Computational fluid dynamics (CFD) simulations are performed to predict DNB in a hexagonal sub-assembly. The methodology uses an Eulerian–Eulerian multiphase flow (EEMF) model in conjunction with multiple size group (MuSiG) model. The breakup and coalescence of vapour bubbles are accounted using a population balance approach. Findings Bubble departure diameter parameters in EEMF framework are recalibrated to simulate the near atmospheric pressure conditions. The predictions from the modified correlation for bubble departure diameter are found to be in good agreement against the experimental data. The simulations are further extended to investigate the influence of blockage (b) on DNB type CHF at low operating pressure conditions. Larger size vapour bubbles are observed to move away from the corner sub-channel region due to the presence of blockage. Corner sub-channels were found to be more prone to experience DNB type CHF compared to the interior and edge sub-channels. Practical implications An accurate prediction of CHF and its location is critical to the safe operation of nuclear reactors. Moreover, a wide spectrum of heat transfer equipment of engineering interest will be benefited by an accurate prediction of wall characteristics using breakup and coalescence-based models as described in the present study. Originality/value Simulations are performed to predict DNB type CHF. The EEMF and wall heat flux partition model framework coupled with the MuSiG model is novel, and a detailed variation of the coolant velocity, temperature and vapour volume fraction in a hexagonal sub-assembly was obtained. The present CFD model framework was observed to predict the onset of vapour volume fraction and DNB type CHF. Simulations are further extended to predict CHF in a hexagonal sub-assembly under the influence of blockage. For all the values of blockage, the vapour volume fraction is found to be higher in the corner region, and thus the corner sub-channel experiences CHF. Although DNB type CHF is observed in corner sub-channel, it is noticed that the presence of blockage in the interior sub-channel promotes the coolant mixing and results in higher values of CHF in the corner sub-channel.

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Experimental study of critical heat flux in flow boiling under subatmospheric pressure in a vertical square channel

Cited by 17 publications

References 19 publications

Heat Transfer And Wall Temperature Distribution During Flow Boiling In Conventional And Mini Channels

Heat Transfer And Wall Temperature Distribution During Flow Boiling In Conventional And Mini Channels

Flow boiling heat transfer characteristics using the modified eulerian and wall heat balance model

CFD study of DNB in a hexagonal sub-assembly using MuSiG model

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