Sub-channel analysis of a hexagonal sub-assembly: Influence of blockage and axial power distribution on critical heat flux

2021 ◽  
pp. 1-27
Author(s):  
Harish Pothukuchi ◽  
Prasad Patnaik ◽  
B.V.S.S.S Prasad
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Power Distribution ◽  
Operating Conditions ◽  
Transfer Model ◽  
Safe Operation ◽  
Channel Analysis ◽  
Flow Maldistribution ◽  
Early Occurrence

Abstract Study of thermal hydraulics of a hexagonal sub-assembly is essential to ensure safe operation of liquid metal cooled fast reactors. Identifying the dryout location in fuel sub-assembly (FSA) is a precursor to the determination of safe Critical Heat Flux (CHF) margins. In this study, a sub-channel analysis code coupled with a film thickness model is employed to predict the CHF location in a hexagonal sub-assembly. A simple post-CHF heat transfer model is proposed and validated against the experimental data. The nature of flow resistance changes and operating conditions would significantly influence the occurrence of CHF. To this end, the effect of blockage (0.0 ≤ b ≤ 0.3) and axial power distribution (APD) on CHF is systematically investigated in a hexagonal sub-assembly. It was observed that, the presence of blockage causes coolant flow maldistribution which results in an early occurrence of CHF for higher mass flux (G > 1500 kgm−2s−1) and lower inlet subcooling (ΔTsub ≤ 30 K) conditions for b = 0.3. Furthermore, a comparative study of uniform and sinusoidal heat flux distributions are performed. It was noticed that sinusoidal APD causes early occurrence of CHF compared to uniform APD.

On the Nature of Critical Heat Flux in Microchannels

2005 ◽  
Vol 127 (1) ◽  
pp. 101-107 ◽  
Author(s):  
A. E. Bergles ◽  
S. G. Kandlikar
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Flow Boiling ◽  
Flow Distribution ◽  
High Heat ◽  
Operating Conditions ◽  
High Heat Flux ◽  
Clear Understanding ◽  
Wide Range ◽  
Parallel Microchannels

The critical heat flux (CHF) limit is an important consideration in the design of most flow boiling systems. Before the use of microchannels under saturated flow boiling conditions becomes widely accepted in cooling of high-heat-flux devices, such as electronics and laser diodes, it is essential to have a clear understanding of the CHF mechanism. This must be coupled with an extensive database covering a wide range of fluids, channel configurations, and operating conditions. The experiments required to obtain this information pose unique challenges. Among other issues, flow distribution among parallel channels, conjugate effects, and instrumentation need to be considered. An examination of the limited CHF data indicates that CHF in parallel microchannels seems to be the result of either an upstream compressible volume instability or an excursive instability rather than the conventional dryout mechanism. It is expected that the CHF in parallel microchannels would be higher if the flow is stabilized by an orifice at the entrance of each channel. The nature of CHF in microchannels is thus different than anticipated, but recent advances in microelectronic fabrication may make it possible to realize the higher power levels.

Main Results of Na-K Alloy Boiling Investigation

2002 ◽  
Author(s):  
G. A. Sorokin ◽  
G. P. Bogoslovskaya ◽  
E. F. Ivanov ◽  
A. P. Sorokin
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Numerical Modeling ◽  
Liquid Metal ◽  
Critical Heat Flux ◽  
Liquid Metals ◽  
Operating Conditions ◽  
Coolant Temperature ◽  
Low Velocity ◽  
Experimental Conditions

Boiling experiments on eutectic sodium-potassium alloy in the model of fast reactor subassembly under conditions of low-velocity circulation carried out at the IPPE call for further investigations into numerical modeling of the process. The paper presents analysis of pin bundle liquid metal boiling, stages of the process, its characteristics (wall temperature, coolant temperature, flow rate. pressure void fraction and others), that allowed the pattern map to be drawn. The problem of conversion of the data gained in Na-K mock-up experiments to in-pile sodium reactor operating conditions is analyzed here, as well as thermodynamic similarity of liquid metal coolants and eutectic Na-K alloy. Data on bundle boiling in Na-K are presented in comparison with those in different liquid metals. Analysis of data on liquid metal heat transfer in cases of pool boiling, boiling in tubes, in slots, and in pin bundles, as well as data on critical heat flux in tubes was performed and discussed in the paper. The relationship for calculation of critical heat flux in liquid metal derived by the authors is presented. Results of numerical modeling of liquid metal boiling heat transfer during accident cooling of reactor core applied to experimental conditions of going from forced to natural circulation are presented, too.

Subcooled critical heat flux: an assessment of the risk to front-end and beamline components of synchrotron light sources

2010 ◽  
Vol 1 (MEDSI-6) ◽  
Author(s):  
B. Brajuskovic ◽  
D. Capatina ◽  
J. Collins ◽  
P. Den Hartog ◽  
J. Reneker
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Water Saturation ◽  
Saturation Temperature ◽  
Operating Conditions ◽  
Light Sources ◽  
Operational Conditions ◽  
Front End ◽  
Synchrotron Light ◽  
Synchrotron Light Sources

X-ray absorbers in the front ends and beamlines of synchrotron light sources are exposed to very high thermal loads. Many facilities, such as the Advanced Photon Source, are investigating upgrades that will further increase the thermal load. The likelihood of exceeding the limit of subcooled critical heat flux (CHF) in these components was examined. The assessment was performed for both currently possible off-normal operational conditions, such as might occur in the event of a failure of multiple safety interlocks, and the anticipated operating conditions that may result from future upgrades. The subcooled CHF values were calculated using empirical equations frequently cited in the literature and then compared with the computed values of the heat flux at the walls of the component cooling channels in cases where the cooling wall temperature exceeded the water saturation temperature at local hydraulic conditions. Having in mind that the great majority of the available empirical correlations were developed for the conditions characteristic for the operation of heat exchangers in the nuclear power industry, the limitations of this approach are discussed and an experimental study of the subcooled CHF values in the conditions similar to those expected in the front-end and beamline components is proposed.

Heat Transfer Characteristics of a Radial Jet Reattachment Flame

1997 ◽  
Vol 119 (2) ◽  
pp. 258-264 ◽  
Author(s):  
J. W. Mohr ◽  
J. Seyed-Yagoobi ◽  
R. H. Page
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Combustion Process ◽  
Local Heat ◽  
Operating Conditions ◽  
Recirculation Region ◽  
Heat Transfer Characteristics ◽  
Transfer Characteristics ◽  
Impingement Surface

A Radial Jet Reattachment Combustion (RJRC) nozzle forces primary combustion air to exit radially from the combustion nozzle and to mix with gaseous fuel in a highly turbulent recirculation region generated between the combustion nozzle and impingement surface. High convective heat transfer properties and improved fuel/ air mixing characterize this external mixing combustor for use in impingement flame heating processes. To understand the heat transfer characteristics of this new innovative practical RJRC nozzle, statistical design and analysis of experiments was utilized. A regression model was developed which allowed for determination of the total heat transfer to the impingement surface as well as the NOx emission index over a wide variety of operating conditions. In addition, spatially resolved flame temperatures and impingement surface temperature and heat flux profiles enabled determination of the extent of the combustion process with regards to the impingement surface. Specifically, the relative sizes of the reaction envelope, high temperature reaction zone, and low temperature recirculation zone were all determined. At the impingement surface in the reattachment zone very high local heat flux values were measured. This study provides the first detailed local heat transfer characteristics for the RJRC nozzle.

Effect of Thermophysical Properties of the Heater Substrate on Critical Heat Flux in Pool Boiling

2017 ◽  
Vol 139 (11) ◽  
Author(s):  
Pruthvik A. Raghupathi ◽  
Satish G. Kandlikar
Keyword(s):  
Thermal Conductivity ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Pool Boiling ◽  
Temperature Fluctuations ◽  
Operating Conditions ◽  
Force Balance ◽  
Heater Surface ◽  
Monel 400

While the role of the liquid properties, surface morphology, and operating conditions on critical heat flux (CHF) in pool boiling is well investigated, the effect of the properties of the heater material is not well understood. Previous studies indicate that the heater thickness plays an important role on the CHF phenomenon. However, beyond a certain thickness, called the asymptotic thickness, the local temperature fluctuations on the heater surface caused by the periodic bubble ebullition cycle are evened out, and the CHF is not influenced by further increasing the thickness. In the present work, data from literature and pool boiling experiments conducted in this study with seven substrates—aluminum, brass, copper, carbon steel, Monel 400, silver, and silicon—are used to determine the effect of the thermophysical property of the material on CHF for thick heaters that are used in industrial pool boiling applications. The results indicate that the product of density (ρ) and specific heat (cp) represents an important substrate property group that affects the CHF, and that the thermal conductivity is not an important parameter. A well-established force-balance-based CHF model (Kandlikar model) is modified to account for the thermal properties of the substrate. The predicted CHF values are within 15% of the experimental results.

An Experimental Study on the Critical Heat Flux for Low Flow of Water in Bilaterally Heated Vertical Annuli Under Low Pressure Conditions

2014 ◽  
Author(s):  
Lei Zhou ◽  
Guangxu Liu ◽  
Yuanfeng Zan ◽  
Xiao Yan
Keyword(s):  
Experimental Study ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Nuclear Power ◽  
Low Pressure ◽  
Operating Conditions ◽  
Low Flow ◽  
Plant Design ◽  
Water Reactors ◽  
Vertical Annuli

Critical heat flux (CHF) has been widely studied in the past decades because of its importance for nuclear power plant design. But most of the studies are based on flow under normal operating conditions for light water reactors. CHF under low flow and low pressure is of significance when considering operating transients and accidents. In this study, experimental study has been carried out on CHF for low flow rate and low pressure water flow in vertical bilaterally heated annuli. Parameter trends on CHF is discussed and a new predictive correlation was fitted based on the CHF data points. This study is meaningful for concerned nuclear engineering and similar experiment design.

Investigation of Critical Heat Flux for Plutonium-Based Mixed Oxide Advanced Fuel Bundle Design

2021 ◽  
Author(s):  
Lanqin Yuan ◽  
Jun Yang ◽  
Bruce Addicott ◽  
Matthew Dickerson ◽  
Vinson Gauthier
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Mass Flow ◽  
Mixed Oxide ◽  
Natural Uranium ◽  
Operating Conditions ◽  
Working Fluid ◽  
Mox Fuel ◽  
Uranium Fuel ◽  
Power Profile

Abstract The critical heat flux performance of an advanced plutonium-based mixed oxide fuel for potential use in a pressure tube heavy water reactor has been studied experimentally at Canadian Nuclear Laboratories with an electrically-heated string simulator of 43-element fuel bundles. The fuel simulator has a uniform axial power profile and a radial power profile representative of the plutonium-based MOX fuel. The CHF measurements were made in the MR-3 heat transfer loop facility using R-134a refrigerant as the working fluid. The test matrix included system pressures from 1.47 to 2.11 MPa, mass flow rates from 12.7 to 14.7 kg/s and inlet temperatures from 31 to 59°C, which are representative of the water-equivalent reactor operating conditions of 9 to 12.5 MPa pressure, 13.5 to 21.3 kg/s mass flow rate and the desired inlet subcoolings. Compared to conventional natural uranium fuel, the radial power profile of a MOX fuel exhibits a steeper and uneven distribution across the fuel element rings, with a higher value in the outer ring. It was found that CHF values of the MOX fuel are significantly lower than those of the natural uranium fuel. Based on the experimental data, a correlation has been derived to account for the effect of radial power profile on CHF. This correlation can be used to evaluate the relative CHF values of advanced/non-conventional fuel designs with radial power profiles deviating from that of natural uranium fuel.

EXPERIMENTAL DETERMINATION OF CRITICAL HEAT FLUX

2019 ◽  
Vol 22 (1) ◽  
pp. 29-57
Author(s):  
Arnab Dasgupta ◽  
A. K. Vishnoi ◽  
Dinesh K. Chandraker ◽  
Arun Kumar Nayak
Keyword(s):  
Heat Flux ◽  
Experimental Determination ◽  
Critical Heat Flux

Theoretical study on critical heat flux with non-uniform axial power distribution

2017 ◽  
Author(s):  
Wenxing Liu ◽  
Dawei Zhao ◽  
Yuanfeng Zan ◽  
Wanyu Xiong ◽  
Jun Huang
Keyword(s):  
Heat Flux ◽  
Critical Heat Flux ◽  
Power Distribution ◽  
Theoretical Study
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