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.

Study on the Critical Heat Flux Mechanism Model under the Condition of Low Velocity and Subcooled Boiling in the Narrow Channel

2011 ◽  
Vol 130-134 ◽  
pp. 3962-3966
Author(s):  
Ming Zhang ◽  
Tao Zhou ◽  
Ping Liu ◽  
Ke Ran ◽  
Cheng Sheng ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Narrow Channel ◽  
Low Velocity ◽  
Mechanism Model ◽  
Leading Role ◽  
Ultimate Cause ◽  
Low Mass

Based on the bubble dynamics, the generation and separation of bubble plays a leading role in the heat transfer of boiling condition. Before the bubble separation, micro liquid layer below bubbles is evaporated to dryness and heat transfer deterioration is the ultimate cause of boiling crisis, proposed a critical heat flux mechanism in the conditions of low velocity and narrow channel. A critical heat flux mechanism model is established. By calculation, in the low mass flow range the mechanism model has a high precision to predict CHF in a larger pressure and export dry degree ranges. Using the model the relationship of parameters is studied.

CFD Study on Specifics of Flow and Heat Transfer in Vertical Bare Tubes Cooled With Water at Supercritical Pressures

2017 ◽  
Author(s):  
Alexander Zvorykin ◽  
Nataliia Fialko ◽  
Sherenkovskyi Julii ◽  
Sergey Aleshko ◽  
Natalia Meranova ◽  
...  
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Mass Flux ◽  
Cfd Simulation ◽  
Operating Conditions ◽  
Temperature Fields ◽  
Coolant Temperature ◽  
Flow And Heat Transfer ◽  
Medium Mass ◽  
Experimental Values

The paper presents results of a study on flow and temperature fields in bare tubes cooled with SuperCritical Water (SCW). This study is based on a Computational Fluid Dynamics (CFD) simulation with the FLUENT code for upward flows in vertical tubes with heated length of 4 m and an inner diameter of 10 mm. Operating conditions were: Mass flux – G ≈ 500 and 1000 kg/m2s; heat flux – q = 189 – 826 kW/m2; and inlet coolant temperature – Tin = 320–360°C. CFD predictions were compared with experimental data in this study. All three heat-transfer regimes: 1) normal heat transfer; 2) improved heat transfer; and 3) deteriorated heat transfer; were considered. The obtained results show that within normal and improved heat transfer CFD predicts experimental values reasonably well. However, within conditions of deteriorated heat transfer CFD predictions are less satisfactory. The CFD outcomes of the heat flux effect on the flow and heat transfer of SCW are presented. Specifics of flow within the pseudocritical region (i.e., approximately ±25°C around a pseudocritical point) are discussed. The buoyancy effect is investigated by axial velocity profiles at the medium mass flux of 500 kg/m2s and heat flux of 287 kW/m2.

Assessment of CFD Models for Multiphase Heat Transfer in Different Boiling Regimes

2021 ◽  
Author(s):  
Cosimo Bianchini ◽  
Riccardo Da Soghe ◽  
Lorenzo Mazzei ◽  
Giuseppe Caggiano ◽  
Maddalena Angelucci
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Full Range ◽  
Saturation Temperature ◽  
Nucleate Boiling ◽  
High Energy ◽  
Operating Conditions ◽  
Liquid Oxygen ◽  
Cfd Models

Abstract Cryogenic propellant rockets, designed to exploit the high energy densities of liquid hydrogen and liquid oxygen, are equipped with turbopumps that deliver liquid fuel to the engine at high pressure levels. Due to the very low saturation temperature of the cryogenic propellant, it is common during the transient operation to have portion of pump walls that achieve boiling conditions. The effect of boiling on the heat transfer between the solid and the fluid needs to be well characterized in order to correctly predict the pump metal temperature evolution and the necessary amount of propellant. This paper presents an investigation about the capabilities of currently available CFD models for boiling to reproduce correctly the phenomenon under various flow conditions. The analysis, conducted with Ansys Fluent CFD solver, focuses on the Eulerian multiphase approach coupled with the mechanistic nucleate boiling model extended to consider the wall boiling regime transition from the nucleate boiling to the critical heat flux regime (CHF). Several test cases are presented to cover the full range of boiling regimes and flow characteristics: the first test focuses on nucleate boiling of sub-cooled water in an upward heated cylindrical pipe, second one deals with 3D boiling water in a rectangular-sectioned duct, the third one considers again nucleate boiling but with a different fluid, namely the R-113 refrigerant, whereas the last investigates the critical heat flux and post dry-out regimes in vertical pipes. Selected tests span over different operating conditions and consider alternative fluids in order to provide a preliminary validation propaedeutic for future investigations focused on more complex applications representative of cryogenic turbopumps.

scholarly journals Enhancement of Heat Transfer With Pool and Spray Impingement Boiling on Microporous and Nanowire Surface Coatings

2010 ◽  
Author(s):  
Suraj Joottu Thiagarajan ◽  
Sreekant Narumanchi ◽  
Charles King ◽  
Wei Wang ◽  
Ronggui Yang
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Jet Impingement ◽  
Operating Conditions ◽  
Working Fluid ◽  
Transfer Coefficients ◽  
Nanowire Surface ◽  
Plain Surface ◽  
Spray Impingement

The National Renewable Energy Laboratory (NREL) is leading a national effort to develop next-generation cooling technologies for hybrid vehicle electronics, as part of the Advanced Power Electronics and Electrical Machines program area in the U.S. Department of Energy’s (DOE’s) Vehicle Technologies Program. The overarching goal is to reduce the size, weight, and cost of power electronic modules that convert direct current from the batteries to alternating current for the motor, and vice versa. Aggressive thermal management techniques help in achieving the goals of increased power density and reduced weight and volume, while keeping the chip temperatures within acceptable limits. The viability of aggressive cooling schemes such as spray and jet impingement in conjunction with enhanced surfaces is being explored as part of the program. In this work, we present results from a series of experiments with pool and spray boiling on enhanced surfaces, such as a microporous layer of copper and copper nanowires, using HFE-7100 as the working fluid. Spray impingement on the microporous coated surface showed an enhancement of 100%–300% in the heat transfer coefficient at a given wall superheat with respect to spray impingement on a plain surface under similar operating conditions. The critical heat flux also increased by 7%–20%, depending on the flow rates. Heat transfer coefficients obtained on the nanowire-grown surface are considerably better than those obtained on the plain surface, although the enhancement is lower than those obtained on the microporous surface. The critical heat flux is also considerably lower for the nanowire surface than for the plain surface.

scholarly journals Predicting Critical Heat Flux With Multiphase CFD: 4 Years in the Making

2017 ◽  
Author(s):  
Emilio Baglietto ◽  
Etienne Demarly ◽  
Ravikishore Kommajosyula
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Bubble Dynamics ◽  
Flow Boiling ◽  
Heated Surface ◽  
Force Balance ◽  
Modeling Framework ◽  
Lift Off ◽  
Limiting Condition

Advancement in the experimental techniques have brought new insights into the microscale boiling phenomena, and provide the base for a new physical interpretation of flow boiling heat transfer. A new modeling framework in Computational Fluid Dynamics has been assembled at MIT, and aims at introducing all necessary mechanisms, and explicitly tracks: (1) the size and dynamics of the bubbles on the surface; (2) the amount of microlayer and dry area under each bubble; (3) the amount of surface area influenced by sliding bubbles; (4) the quenching of the boiling surface following a bubble departure and (5) the statistical bubble interaction on the surface. The preliminary assessment of the new framework is used to further extend the portability of the model through an improved formulation of the force balance models for bubble departure and lift-off. Starting from this improved representation at the wall, the work concentrates on the bubble dynamics and dry spot quantification on the heated surface, which governs the Critical Heat Flux (CHF) limit. A new proposition is brought forward, where Critical Heat Flux is a natural limiting condition for the heat flux partitioning on the boiling surface. The first principle based CHF is qualitatively demonstrated, and has the potential to deliver a radically new simulation technique to support the design of advanced heat transfer systems.

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