Heat transfer in nucleate boiling, maximum heat flux and transition boiling

The effect of staggered-array water impinging jets on boiling heat transfer was investigated by a simultaneous measurement between boiling visualization and heat transfer characteristics. The boiling phenomena of staggered-array impinging jets on hot steel plate were visualized by 4K UHD video camera. The surface temperature and heat flux on hot steel plate was determined by solving 2-D inverse heat conduction problem, which was measured by the flat-plate heat flux gauge. The experiment was made at jet Reynolds number of Re = 5,000 and the jet-to-jet distance of staggered-array jets of S/Dn = 10. Complex flow interaction of staggered-array impinging jets exhibited hexagonal flow pattern like as honey-comb. The calculated surface heat transfer profiles show a good agreement with the corresponding boiling visualization. The peak of heat flux accords with the location which nucleate boiling is occurred at. In early stage, the positions of maximum heat flux locate at the stagnation point of each jet as the relatively low surface temperature is shown at their positions. At the elapsed time of 10 s, the flat shape of heat flux profile is formed in the hexagonal area where the interacting flow uniformly cools down the wetted surface. After that, the wetted area continuously enlarges with time and the maximum heat flux is observed at its peripheral. These results point out that the flow interaction of staggered-array jets effectively cools down the closer area around jets and also show an expansion of nucleate boiling and suppression of film boiling during water jet cooling on hot steel plate. [This work was supported by the KETEP grant funded by the Ministry of Trade, Industry & Energy, Korea (Grant No. 20142010102910).]

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Boiling Heat Transfer Characteristics of Rotary Hollow Cylinders with In-Line and Staggered Multiple Arrays of Water Jets

Journal of Heat Transfer ◽

10.1115/1.4051835 ◽

2021 ◽

Author(s):

Mohammad Jahedi ◽

Bahram Moshfegh

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Stagnation Point ◽

Surface Heat Flux ◽

Surface Heat ◽

Maximum Heat ◽

Water Jets ◽

Maximum Heat Flux ◽

Inner Surface ◽

Hollow Cylinders

Abstract Transient heat transfer studies of quenching rotary hollow cylinders with in-line and staggered multiple arrays of jets have been carried out experimentally. The study involves three hollow cylinders (Do/d = 12 to 24) with rotation speed 10 to 50 rpm, quenched by subcooled water jets (ΔTsub=50-80 K) with jet flow rate 2.7 to 10.9 L/min. The increase in area-averaged and maximum heat flux over quenching surface (Af) has been observed in the studied multiple arrays with constant Qtotal compared to previous studies. Investigation of radial temperature distribution at stagnation point of jet reveals that the footprint of configuration of 4-row array is highlighted in radial distances near the outer surface and vanishes further down toward the inner surface. The influence of the main quenching parameters on local average surface heat flux at stagnation point is addressed in all the boiling regimes where the result indicates jet flow rate provides strongest effect in all the boiling regimes. Effectiveness of magnitude of maximum heat flux in the boiling curve for the studied parameters is reported. The result of spatial and temporal heat flux by radial conduction in the solid presents projection depth of cyclic variation of surface heat flux in the radial axis as it disappears near inner surface of hollow cylinder. In addition, correlations are proposed for area-averaged Nusselt number as well as average and maximum local heat flux at stagnation point of jet for the in-line and staggered multiple arrays.

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High Heat Flux Phase Change on Silicon Wick Structures

Volume 7: Fluids and Heat Transfer, Parts A, B, C, and D ◽

10.1115/imece2012-88302 ◽

2012 ◽

Cited By ~ 1

Author(s):

Qingjun Cai ◽

Avijit Bhunia ◽

Yuan Zhao

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Phase Change ◽

Test Chamber ◽

Nucleate Boiling ◽

High Heat ◽

High Heat Flux ◽

Maximum Heat ◽

Wick Structure ◽

Silicon Pillars

Silicon is the major material in IC manufacture. It has high thermal conductivity and is compatible with precision micro-fabrication. It also has decent thermal expansion coefficient to most semiconductor materials. These characteristics make it an ideally underlying material for fabricating micro/mini heat pipes and their wick structures. In this paper, we focus our research investigations on high heat flux phase change capacity of the silicon wick structures. The experimental wick sample is composed of silicon pillars 320μm in height and 30 ∼ 100μm in diameter. In a stainless steel test chamber, synchronized visualizations and measurements are performed to crosscheck experimental phenomena and data. Using the mono-wick structure with large silicon pillar of 100μm in diameter, the phase change on the silicon wick structure reaches its maximum heat flux at 1,130W/cm2 over a 2mm×2mm heating area. The wick structure can fully utilize the wick pump capability to supply liquid from all 360° directions to the center heating area. In contrast, the large heating area and fine silicon pillars 10μm in diameter significantly reduces liquid transport capability and suppresses generation of nucleate boiling. As a result, phase change completely relies on evaporation, and the CHF of the wick structure is reduced to 180W/cm2. An analytical model based on high heat flux phase change of mono-porous wick structures indicates that heat transfer capability is subjected to the ratio between the wick particle radius and the heater dimensions, as well as vapor occupation ratio of the porous volume. In contrast, phase change heat transfer coefficients of the wick structures essentially reflect material properties of wick structure and mechanism of two-phase interactions within wick structures.

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Effect of Liquid Properties on Phase-Change Heat Transfer in Porous Wick Structures

Journal of Heat Transfer ◽

10.1115/1.4031929 ◽

2015 ◽

Vol 138 (3) ◽

Cited By ~ 1

Author(s):

Steve Q. Cai ◽

Avijit Bhunia

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Phase Change ◽

Transfer Coefficient ◽

Mode Transition ◽

Maximum Heat ◽

Maximum Heat Flux ◽

Phase Change Heat Transfer ◽

The Heat Transfer Coefficient

In a heat pipe, operating fluid saturates wick structures system and establishes a capillary-driven circulation loop for heat transfer. Thus, the thermophysical properties of the operating fluid inevitably impact the transitions of phase-change mode and the capability of heat transfer, which determine both the design and development of the associated heat pipe systems. This article investigates the effect of liquid properties on phase-change heat transfer. Two different copper wick structures, cubic and cylindrical in cross section, 340 μm in height and 150 μm in diameter or width, are fabricated using an electroplating technique. The phase-change phenomena inside these wick structures are observed at various heat fluxes. The corresponding heat transfer characteristics are measured for three different working liquids: water, ethanol, and Novec 7200. Three distinct modes of the phase-change process are identified: (1) evaporation on liquid–vapor interface, (2) nucleate boiling with interfacial evaporation, and (3) boiling enhanced interface evaporation. Transitions between the three modes depend on heat flux and liquid properties. In addition to the mode transition, liquid properties also dictate the maximum heat flux and the heat transfer coefficient. A quantitative characterization shows that the maximum heat flux scales with Merit number, a dimensionless number connecting liquid density, surface tension, latent heat of vaporization, and viscosity. The heat transfer coefficient, on the other hand, is dictated by the thermal conductivity of the liquid. A complex interaction between the mode transition and liquid properties is reflected in Novec 7200. In spite of having the lowest thermal conductivity among the three liquids, an early transition to the mode of the boiling enhanced interface evaporation leads to a higher heat transfer coefficient at low heat flux.

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RELAP5-3D Sensitivity Studies of Incorporating Axial Boron Gradients Into a Heater Tube Experiment for Pool Boiling CHF Testing in TREAT

Volume 3: Student Paper Competition; Thermal-Hydraulics; Verification and Validation ◽

10.1115/icone2020-16758 ◽

2020 ◽

Author(s):

Richard Hernandez ◽

Nicholas R. Brown ◽

Charles P. Folsom ◽

Nicolas E. Woolstenhulme ◽

Colby B. Jensen

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

National Laboratory ◽

Pool Boiling ◽

Nucleate Boiling ◽

Coupling Factor ◽

Design Parameters ◽

Coolant Temperature ◽

Axial Region ◽

Maximum Heat

Abstract Nuclear reactor designs are governed by postulated accident events that may occur during their operational lifetime. One type of incident is a reactivity-initiated accident (RIA), during which a sudden surge of power in the fuel components within the core may result in the latter exceeding its cooling capabilities. This could lead to a departure from nucleate boiling (DNB) event which results in a significant decrease in heat transfer capabilities. Preventing the occurrence of a DNB crisis requires a fundamental understanding of the cladding-to-coolant heat transfer under fast transient conditions, as well as the governing hydrodynamic and design parameters that influence when the critical heat flux (CHF) will be exceeded. Presently, large uncertainties in computer models used to predict CHF have led to conservative safety limits governing light-water reactor (LWR) designs. The Idaho National Laboratory (INL) is currently leading a combined effort that takes advantage of the restart of the Transient Reactor Test (TREAT) facility, to better understand the mechanism of CHF under in-pile pool boiling conditions. The goal of this laboratory directed project is to use the unique capabilities of TREAT coupled with a non-fueled nuclear heated borated stainless-steel 304 tube experiment within an experimental capsule. The borated tube will induce CHF in the surrounding coolant when subjected to a power pulse within the TREAT. The impacts of rapid surface heating effects as well as radiation-induced surface activation (RISA) will be experimentally investigated. This feature is a continuation to previous thermal hydraulics analysis that was conducted to inform on a test matrix for the design of the borated heater experiment. The borated tube was used in place of a solid rod so that the center axial region can be instrumented to allow for better experimental analysis. Therefore, it is desirable to design this rodlet so that the maximum heat flux occurs at the center of the axial length of the rod. The work presented here analyzes the potential to integrate axial boron gradients within this tube to shape its power curve. Several generic axial power shapes were initially considered. Natural boron concentrations between 0.1–2.0 wt.% were analyzed and a power coupling factor (PCF) was calculated for each. A self-shielding study was conducted to develop radial power profiles for several boron concentrations. These were then applied to three different power pulses to determine how these two parameters influence the chosen axial heat flux curve. Variations in the initial coolant temperature were investigated. Lastly, how the shape of the generic curve is affected following a DNB event was also studied. Two different CHF cases were included within the scope of this analyses; one during which CHF was exceeding along the entire axial region of the rod, and another where the former occurred at the center region only. The behavior of the curve overtime was investigated.

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Live Experimental Results of Melt Pool Behaviour in the PWR Lower Head With Insulated Upper Lid and External Cooling

Volume 3: Nuclear Safety and Security; Codes, Standards, Licensing and Regulatory Issues; Computational Fluid Dynamics and Coupled Codes ◽

10.1115/icone21-15204 ◽

2013 ◽

Cited By ~ 4

Author(s):

Xiaoyang Gaus-Liu ◽

Alexei Miassoedov

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Experimental Results ◽

Melt Temperature ◽

Maximum Heat ◽

Melt Pool ◽

Cooling Conditions ◽

External Cooling ◽

Maximum Heat Flux

In-vessel melt retention has drawn renewed concern as an important severe accident management measure in existing and advanced light water reactors. Despite numerous studies the central question whether the maximum heat flux in a melt pool could exceed the critical heat flux (CHF) is not fully answered. The uncertainty comes from the variety of accident scenarios and the corresponding melt pool configurations, as well as from the applicability of the experimental results to the reactor case. It is therefore necessary to examine the melt heat transfer under different pool configurations and cooling conditions, as well as to compare the experimental results coming from different test vessel geometries and cooling regimes. This study investigates the heat transfer characteristics of an oxidic pool in the PWR lower plenum in the case when the vessel wall is externally cooled by water, and the melt upper surface is free in a closed insulated environment. Thus the melt pool cooling conditions are quasi-isothermal at the inclined sidewall and at the upper surface free surface with thermal radiation. This pool configuration can occur before the melt layer stratification begins or the melt pool is composed only of oxide melt under certain melt relocation sequences. A non-eutectic nitrate mixture with the composition of 20% NaNO3−80% KNO3 in mole relation is used as the simulant melt. Besides the determination of melt temperature and heat flux in their global average values, emphasis are given on the characterization of the axial distribution of melt temperature and heat flux at different power densities and pool heights. Results obtained in hemispherical geometry are analyzed and compared with other studies conducted under similar boundary conditions. The characterization of the heat flux distribution provide important data for the prediction of the maximum heat flux in the reactor case with similar boundary conditions and the evaluation of the concept of in-vessel melt retention by external cooling.

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Experimental Study on Aerodynamic Heating Induced by Dual Injections into Hypersonic Cross Flow

International Journal of Aerospace Engineering ◽

10.1155/2017/7287586 ◽

2017 ◽

Vol 2017 ◽

pp. 1-16 ◽

Cited By ~ 1

Author(s):

Masato Taguchi ◽

Koichi Mori ◽

Yoshiaki Nakamura

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Single Injection ◽

Surface Heat ◽

Aerodynamic Heating ◽

Temperature Sensitive ◽

Maximum Heat ◽

Short Spacing ◽

Surface Heat Transfer ◽

Maximum Heat Flux

In this study, the distribution of surface heat transfer induced by dual side-jets injected into a hypersonic flow has been visualized using a temperature sensitive paint. The experiments were performed in both tandem and parallel injector arrangements, and the spacing between the injection holes was taken as a parameter in each arrangement. As a result, the aerodynamic heating in the separated region of the boundary layer and in the horseshoe vortex was clearly visualized. In the tandem arrangements, heat transfer remarkably increased immediately upstream of the front injector. The distributions and the intensity of surface heat transfer were similar to those caused by the single injection. On the other hand, in the parallel arrangements, the extent of the separation nearly doubled, and the maximum heat flux decreased to less than half of that from the single injection. The global distribution of heat transfer varied significantly as the injector spacing was changed. When the injectors were positioned with a large spacing, the interaction between the side-jets was relatively lowered, and thus distribution, as for the single injector, was induced around each injection hole individually. In contrast, with a short spacing, the dual injection behaved as a single obstacle. The most effective reduction of maximum heat flux was achieved with an intermediate injector spacing.

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Wetting Front Tracking During Metal Quenching Using Array of Jets

2010 14th International Heat Transfer Conference, Volume 5 ◽

10.1115/ihtc14-22080 ◽

2010 ◽

Author(s):

Khalid H. M. Abdalrahman ◽

Umair Alam ◽

Eckehard Specht

Keyword(s):

Heat Flux ◽

Nucleate Boiling ◽

Temperature Data ◽

Film Boiling ◽

Wetting Front ◽

Inverse Algorithm ◽

Maximum Heat ◽

Water Jets ◽

Maximum Heat Flux ◽

Hot Surface

Metal quenching is a commonly used heat treatment technique, e.g. Direct Chill aluminum casting, quenching of steel for obtaining desired micro-structures. Film boiling, transition boiling, nucleate boiling and forced convection are the mechanisms of heat transfer during quenching. When the coolant strikes the hot metal surface during quenching, the surface can be divided into two distinct zones which are dry and wet zones. Heat transfer in dry zone is dominated by film boiling and the wet zone is influenced by transition boiling, nucleate boiling and forced convection. Wetting front is the boundary zone which separates the dry and wet regions. Wetting front is a thin region of coolant in which the transition and nucleate boiling occurs. Within a wetting front, the heat flux leaving from the hot surface reaches it global maximum. The speed of the wetting front indicates the quench ability of the hot surface for the corresponding flow conditions and the coolant. Wetting front tracking is more important for the prediction of surface temperature during quenching. This research works presents the combined numerical and experimental aspects of the heat flux estimation during the quenching process. At any instant, the position of the wetting front is simply assumed as the location of maximum heat flux. This assumption implicitly treats the wetting front as a line instead of area. The location of wetting front and its velocity at every instant are determined by using the experimental temperature data and the inverse algorithm. Experimental setup and temperature measurement technique are explained in detail. The developed inverse algorithm predicts the quenched side temperature and heat flux from the measured side temperature. A two-dimensional Inverse Heat Conduction Problem (IHCP) is solved through the non iterative Finite Element Method (FEM). The considered quenching technique for the study, based on the method of coolant supplied which is array of water jets. One kind of coolant used in this study is tap water. Aluminum 2024, Inconel, and Nickel are the three different materials considered for the analysis. A rectangular plate made of Nickel with dimension 140 × 70 × 2 mm, using the same dimensions of the Inconel. As in the case of the use of Aluminum, the thickness is the only change to 3 mm, the plate quenched by array of water jets with velocities 0.9 m/s, 1.2 m/s, 1.5 m/s and 1.8 m/s. The measured temperature data are further processed through the inverse finite element technique for the estimation of heat flux leaving from the quenched surface. The position of maximum heat flux changes with time which indicates the movement of wetting front. In this work, four different coolant velocities are employed, and the change in coolant velocity strongly affects the heat flux and wetting front movement.

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Microporous Coatings to Maximize Pool Boiling Heat Transfer of Saturated R-123 and Water

Journal of Heat Transfer ◽

10.1115/1.4030245 ◽

2015 ◽

Vol 137 (8) ◽

Cited By ~ 13

Author(s):

Joo Han Kim ◽

Ajay Gurung ◽

Miguel Amaya ◽

Sang Muk Kwark ◽

Seung M. You

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Boiling Heat Transfer ◽

Pool Boiling ◽

Nucleate Boiling ◽

Transfer Coefficients ◽

Maximum Heat ◽

Microporous Coating ◽

Plain Surface ◽

Improved Performance

The present research is an experimental study for the enhancement of boiling heat transfer using microporous coatings. Two types of coatings are investigated: one that is bonded using epoxy and the other by soldering. Effects on pool boiling performance were investigated, of different metal particle sizes of the epoxy-based coating, on R-123 refrigerants, and on water. All boiling tests were performed with 1 cm × 1 cm test heaters in the horizontal, upward-facing orientation in saturated conditions at atmospheric pressure and under increasing heat flux. The surface enhanced by the epoxy-based microporous coatings significantly augmented both nucleate boiling heat transfer coefficients and critical heat flux (CHF) of R-123 relative to those of a plain surface. However, for water, with the same microporous coating, boiling performance did not improve as much, and thermal resistance of the epoxy component limited the maximum heat flux that could be applied. Therefore, for water, to seek improved performance, the solder-based microporous coating was applied. This thermally conductive microporous coating, TCMC, greatly enhanced the boiling performance of water relative to the plain surface, increasing the heat transfer coefficient up to ∼5.6 times, and doubling the CHF.

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Boiling of FC-72 on Surfaces with Open Copper Microchannel

Energies ◽

10.3390/en14217283 ◽

2021 ◽

Vol 14 (21) ◽

pp. 7283

Author(s):

Robert Kaniowski ◽

Robert Pastuszko

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Heat Transfer Coefficient ◽

Transfer Coefficient ◽

Pool Boiling ◽

Fold Increase ◽

Heat Transfer Process ◽

Cross Sectional ◽

Maximum Heat ◽

Maximum Heat Flux

The paper presents the results of experimental research on pool boiling heat transfer of dielectric liquid FC-72. Measurements were made at atmospheric pressure on open surfaces with microchannels. Heat transfer surfaces, in the form of parallel milled microchannels, were made of copper. The rectangular cross-sectional microchannels were 0.2 to 0.5 mm deep and 0.2 to 0.4 mm wide. The surfaces, compared to a smooth flat surface, provided a five-fold increase in the heat transfer coefficient and a two-fold increase in the critical heat flux. The article analyses the influence of the width and height of the microchannel on the heat transfer process. The maximum heat flux was 271.7 kW/m2, and the highest heat transfer coefficient obtained was 25 kW/m2K. Furthermore, the experimental results were compared with selected correlations for the nucleate pool boiling.

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