Estimation of peak heat flux onto the targets for CFETR with extended divertor leg

The stability of a gas jet in a surrounding viscous liquid is studied. An expression is developed for the critical velocity at which the jet becomes unstable in a returning viscous liquid. The stability analysis is made to correspond with the geometrical configuration of gas jets and liquid columns similar to those observed near the peak pool boiling heat flux. The critical velocity of the gas jet is then used to obtain the functional form of the peak heat flux on flat plates and cylindrical heaters. The expressions are compared with original observations of the peak heat flux in very viscous liquids on flat plate, and cylindrical, heaters at both earth-normal, and elevated, gravities.

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Rewetting Velocity of High-Temperature Vertical-Narrow-Annular Flow Passages Under Counter-Current Flow Condition

Volume 1: Fora, Parts A, B, C, and D ◽

10.1115/fedsm2003-45378 ◽

2003 ◽

Author(s):

Yasuo Koizumi ◽

Hiroyasu Ohtake ◽

Masanori Tsukudo ◽

Naoki Sakamoto

Keyword(s):

Heat Flux ◽

Annular Flow ◽

Pool Boiling ◽

Outer Wall ◽

Heat Fluxes ◽

Annular Gap ◽

Wall Superheat ◽

Peak Heat Flux ◽

Inner Diameter ◽

Counter Current

Quenching of a thin gap annular flow passage by gravitational liquid penetration was examined experimentally by using R-113. The outer wall was made of copper. The inner wall was made of copper or glass. The inner diameter of the outer wall of the annular flow passages was 40 or 41 mm and the annular gap clearance δ was 0.5, 1.0, 2.0 and 5.0 mm. The outer wall was heated initially up to 250 °C and also the inner wall was heated when the copper inner wall was used. The quenching was observed in δ ≥ 1.0 mm. When δ = 0.5 mm, the wall was just gradually cooled down. The relation between the wall superheat and the heat flux during quenching process was similar to the boiling curve of pool boiling. However, the peak heat flux as well as the heat flux in the film and the transition boiling was lower than those in the pool boiling. These heat fluxes became lower as the gap clearance became narrow. The rewetting velocity became slow as the gap clearance became narrow. The rewetting velocity seemed to have a unique relation for the Peclet number Pe = (ρSCSδSU/λS) and the Biot number Bi = hδs/λs ; Pe ∝ Bi which was the same as that of the Yamanouchi correlation. A decrease in the heat flux (the heat transfer coefficient) in the rewetting front region, which corresponds to the peak heat flux, results in a decrease in the rewetting velocity as the gap clearance becomes narrow.

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Gas Turbine Combustor Liner Wall Heat Load Characterization for Different Gaseous Fuels

Volume 8: Heat Transfer and Thermal Engineering ◽

10.1115/imece2019-11283 ◽

2019 ◽

Author(s):

Kishore Ranganath Ramakrishnan ◽

Shoaib Ahmed ◽

Benjamin Wahls ◽

Prashant Singh ◽

Maria A. Aleman ◽

...

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Load ◽

Recirculation Zone ◽

Flame Temperature ◽

Conduction Model ◽

Steady State Condition ◽

Gaseous Fuels ◽

Peak Heat Flux ◽

Combustor Liner

Abstract The knowledge of detailed distribution of heat load on swirl stabilized combustor liner wall is imperative in the development of liner-specific cooling arrangements, aimed towards maintaining uniform liner wall temperatures for reduced thermal stress levels. Heat transfer and fluid flow experiments have been conducted on a swirl stabilized lean premixed combustor to understand the behavior of Methane-, Propane-, and Butane-based flames. These fuels were compared at different equivalence ratios for a matching adiabatic flame temperature of Methane at 0.65 equivalence ratio. Above experiments were carried out a fixed Reynolds number (based on the combustor diameter) of 12000, where the pre-heated air temperature was approximately 373K. Combustor liner in this setup was made from 4 mm thick quartz tube. An infrared camera was used to record the inner and outer temperatures of liner wall, and two-dimensional heat conduction model was used to find the wall heat flux at a quasi-steady state condition. Flow field in the combustor was measured through Particle Image Velocimetry. The variation of peak heat flux on the liner wall, position of peak heat flux and heat transfer, and position of impingement of flame on the liner have been presented in this study. For all three gaseous fuels studied, the major swirl stabilized flame features such as corner recirculation zone, central recirculation zone and shear layers have been observed to be similar. Liner wall and exhaust temperature for Butane was highest among the fuel tested in this study which was expected as the heat released from combustion of Butane is higher than that of Methane and Propane.

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Pellet triggering of edge localized modes in low collisionality pedestals at DIII-D

Nuclear Fusion ◽

10.1088/1741-4326/ac3b8b ◽

2021 ◽

Author(s):

Robert S Wilcox ◽

Larry R Baylor ◽

Alessandro Bortolon ◽

M Knölker ◽

C J Lasnier ◽

...

Keyword(s):

Heat Flux ◽

Stability Boundary ◽

Localized Modes ◽

Energy Fluence ◽

Alpha Emission ◽

Large Pressure ◽

Peak Heat Flux ◽

Edge Localized Modes ◽

Pellet Injection ◽

Infrared Cameras

Abstract Edge localized modes (ELMs) are triggered using deuterium pellets injected into plasmas with ITER-relevant low collisionality pedestals, and the resulting peak ELM energy fluence is reduced by approximately 25-50% relative to natural ELMs destabilized at similar pedestal pressures. Cryogenically frozen deuterium pellets are injected from the low-field side of the DIII-D tokamak at frequencies lower than the natural ELM frequency, and heat flux is measured by infrared cameras. Ideal MHD pedestal stability calculations show that without pellet injection, these low collisionality pedestals were limited by their current density (peeling-limited) rather than their pressure gradient (ballooning-limited). ELM triggering success correlates strongly with pellet mass, consistent with the theory that a large pressure perturbation is required to trigger an ELM in low collisionality discharges that are far from the ballooning stability boundary. For sufficiently large pellets, both instantaneous and time-integrated ELM energy deposition measured by infrared cameras is reduced with respect to naturally occurring ELMs at the inner strike point, which is the position where it is largest for natural ELMs. Energy fluence at the outer strike point is less effected. Cameras observing both heat flux and D-alpha emission often find significant toroidally asymmetric striations in the outboard far scrape-off layer resulting from ELMs that are triggered by pellets. Toroidal asymmetries at the inner strike point are similar between natural and pellet-triggered ELMs, suggesting that the reduction in peak heat flux and total fluence at that location is robust for the conditions reported here.

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Experimental Study of Thermal Performance of a Reduced Scale Cavity Equipped With Phase Change Material: Study of the Optimal Phase Change Material Layer Location

Journal of Solar Energy Engineering ◽

10.1115/1.4039331 ◽

2018 ◽

Vol 140 (4) ◽

Cited By ~ 1

Author(s):

Ayoub Gounni ◽

Mustapha El Alami ◽

Mohamed Tahar Mabouk ◽

Abdelhamid Kheiri

Keyword(s):

Experimental Data ◽

Heat Flux ◽

Phase Change ◽

Phase Change Material ◽

Phase Change Materials ◽

Peak Heat Flux ◽

Building Walls ◽

Change Material ◽

Reduced Scale ◽

Material Study

Phase change materials (PCMs) used in the building walls constitute an attractive way to reduce the energy consumption and to increase the occupant's thermal comfort. However, there are some challenges to be faced among which the critical one is the PCM layer location allowing the greater heat flux reduction. In this work, the potential of PCM wallboards is evaluated experimentally using a heated reduced scale cavity including walls with or without PCM in a laboratory conditions. The cavity at reduced scale provides the flexibility to test most kinds of wall constructions in real time and allows faster installation and dismantling of the test walls. Three different PCM layer locations inside the walls are examined in terms of heat flux reduction and outside surface temperatures. The results confirm that the PCM layer reduces the peak heat flux compared to a reference wall (wall without PCM). Indeed, the PCM layer hugely affects the peak heat flux when it is placed on the inner face of the walls, near to the heat source. At this location, the peak heat flux reduction, compared to the reference wall, is 32.9%. Furthermore, for numerical validation purpose, the outside overall heat coefficient of the cavity outside walls is determined based on the experimental data.

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Transient Heat Flux Measurements in a Divided-Chamber Diesel Engine

Journal of Heat Transfer ◽

10.1115/1.3247434 ◽

1985 ◽

Vol 107 (2) ◽

pp. 439-444 ◽

Cited By ~ 36

Author(s):

A. C. Alkidas ◽

R. M. Cole

Keyword(s):

Heat Flux ◽

Diesel Engine ◽

Fluid Motion ◽

Local Heat ◽

Relative Increase ◽

Heat Fluxes ◽

Main Chamber ◽

Peak Heat Flux ◽

Flux Measurements ◽

Local Heat Flux

Transient surface heat flux measurements were performed at several locations on the cylinder head of a divided-chamber diesel engine. The local heat flux histories were found to be significantly different. These differences are attributed to the spatial nonuniformity of the fluid motion and combustion. Both local time-averaged and local peak heat fluxes decreased with decreasing speed and load. Retarding the combustion timing beyond TDC decreased the peak heat flux in the antechamber but increased the peak heat flux in the main chamber. This is attributed to the relative increase in the portion of fuel that burns in the main chamber with retarded combustion timing.

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An Induced-Convection Effect Upon the Peak-Boiling Heat Flux

Journal of Heat Transfer ◽

10.1115/1.3449633 ◽

1970 ◽

Vol 92 (1) ◽

pp. 1-5 ◽

Cited By ~ 11

Author(s):

J. H. Lienhard ◽

K. B. Keeling

Keyword(s):

Heat Flux ◽

Pool Boiling ◽

Reduced Pressure ◽

Flux Data ◽

Peak Heat Flux ◽

Variable Gravity

An induced-convection effect upon the peak pool-boiling heat flux is identified and described. A method is developed for correlating this effect under conditions of variable gravity, pressure and size, as well as for various boiled liquids. The effect is illustrated, and the correlation verified, with a large number of peak heat-flux data obtained on a horizontal ribbon heater. The data, obtained in a centrifuge, embrace an 87-fold range of gravity, a 22-fold range of width, a 15-fold variation of reduced pressure, and five liquids.

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Effect of Velocity on Heat Transfer to Boiling Freon-113

Journal of Heat Transfer ◽

10.1115/1.3244243 ◽

1980 ◽

Vol 102 (1) ◽

pp. 26-31 ◽

Cited By ~ 45

Author(s):

Salim Yilmaz ◽

J. W. Westwater

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Atmospheric Pressure ◽

Nucleate Boiling ◽

High Heat ◽

Heat Fluxes ◽

Forced Flow ◽

Film Boiling ◽

Square Root ◽

Peak Heat Flux

Measurements were made of the heat transfer to Freon-113 at near atmospheric pressure, boiling outside a 6.5 mm dia horizontal steam-heated copper tube. Tests included pool boiling and also forced flow vertically upward at uelocities of 2.4, 4.0 and 6.8 m/s. The metal-to-liquid ΔT ranged from 13 to 125° C, resulting in nucleate, transition, and film boiling. The boiling curves for different velocities did not intersect or overlap, contrary to some prior investigators. The peak heat flux was proportional to the square root of velocity, agreeing with the Vliet-Leppert correlation, but disagreeing with the Lienhard-Eichhorn prediction of an exponent of 0.33. The forced-flow nucleate boiling data were well correlated by Rohsenow’s equation, except at high heat fluxes. Heat fluxes in film boiling were proportional to velocity to the exponent 0.56, close to the 0.50 value given by Bromley, LeRoy, and Robbers. Transition boiling was very sensitive to velocity; at a ΔT of 55° C the heat flux was 900 percent higher for a velocity of 2.4 m/s than for zero velocity.

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The interrelation of geometry, orientation, and acceleration in the peak heat flux problem

AIChE Journal ◽

10.1002/aic.690090518 ◽

1963 ◽

Vol 9 (5) ◽

pp. 663-671 ◽

Cited By ~ 9

Author(s):

C. P. Costello ◽

J. M. Adams

Keyword(s):

Heat Flux ◽

Peak Heat Flux

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