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

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.

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

2015 ◽  
Vol 137 (8) ◽  
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.

Boiling Heat Transfer and Critical Heat Flux Enhancement of Upward- and Downward-Facing Heater in Nanofluids

2013 ◽  
Vol 135 (7) ◽  
Author(s):  
Muhamad Zuhairi Sulaiman ◽  
Masahiro Takamura ◽  
Kazuki Nakahashi ◽  
Tomio Okawa
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Critical Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Flux Enhancement ◽  
Optimum Configuration ◽  
Wall Superheat ◽  
Nucleate Boiling Heat Transfer

Boiling heat transfer (BHT) and critical heat flux (CHF) performance were experimentally studied for saturated pool boiling of water-based nanofluids. In present experimental works, copper heaters of 20 mm diameter with titanium-oxide (TiO2) nanocoated surface were produced in pool boiling of nanofluid. Experiments were performed in both upward and downward facing nanofluid coated heater surface. TiO2 nanoparticle was used with concentration ranging from 0.004 until 0.4 kg/m3 and boiling time of tb = 1, 3, 10, 20, 40, and 60 mins. Distilled water was used to observed BHT and CHF performance of different nanofluids boiling time and concentration configurations. Nucleate boiling heat transfer observed to deteriorate in upward facing heater, however; in contrast effect of enhancement for downward. Maximum enhancements of CHF for upward- and downward-facing heater are 2.1 and 1.9 times, respectively. Reduction of mean contact angle demonstrate enhancement on the critical heat flux for both upward-facing and downward-facing heater configuration. However, nucleate boiling heat transfer shows inconsistency in similar concentration with sequence of boiling time. For both downward- and upward-facing nanocoated heater's BHT and CHF, the optimum configuration denotes by C = 400 kg/m3 with tb = 1 min which shows the best increment of boiling curve trend with lowest wall superheat ΔT = 25 K and critical heat flux enhancement of 2.02 times.

Comparison of Droplet Evaporation and Nucleate Boiling Mechanisms on Nanoporous Superhydrophilic Surfaces

2019 ◽  
Author(s):  
Samuel Cabrera ◽  
Van P. Carey
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Droplet Evaporation ◽  
Transfer Performance ◽  
Nanostructured Surface ◽  
Nanostructured Surfaces ◽  
Droplet Vaporization

Abstract Recent studies have indicated that at slightly superheated surface temperatures, droplet evaporation on a nanoporous superhydrophilic surface exhibits onset of nucleation and nucleate boiling effects similar to pool boiling processes. This paper discusses water droplet evaporation experiments and pool boiling experiments conducted on nanostructured surfaces of a 45° downward facing pyramid copper and aluminum substrate. The nanostructured surfaces were used to conduct both droplet evaporation experiments and pool boiling experiments and thus allow direct comparison of the underlying heat transfer performance and mechanisms for these two different processes. The four surfaces tested were the following: bare copper surface, nanostructured surface on copper, bare aluminum surface, and nanostructured surface on aluminum. Mean heat flux values at varying superheats were obtained through temperature and time measurements. To better understand the heat performance of each surface, the wetting and wicking characteristics of each surface were also tested. Experimental results indicate that many of the mechanisms associated with pool boiling may also play a role in droplet vaporization, and their presence can produce levels of heat transfer performance comparable to, or even higher than, that observed in pool boiling at a comparable wall superheat. The results demonstrate that the nanostructured surface affects onset of nucleate boiling and maximum heat flux in both droplet vaporization and nucleate boiling on these surfaces. The implications of these results for strategies to enhance spray cooling and pool boiling are also discussed.

Subcooled Pool Boiling Experiments on Horizontal Heaters Coated With Carbon Nanotubes

2009 ◽  
Vol 131 (7) ◽  
Author(s):  
V. Sathyamurthi ◽  
H-S. Ahn ◽  
D. Banerjee ◽  
S. C. Lau
Keyword(s):  
Heat Transfer ◽  
Carbon Nanotubes ◽  
Heat Flux ◽  
Pool Boiling ◽  
Type A ◽  
Nucleate Boiling ◽  
Film Boiling ◽  
Test Fluid ◽  
Type B ◽  
Coated Surfaces

Pool boiling experiments were conducted with three horizontal, flat, silicon surfaces, two of which were coated with vertically aligned multiwalled carbon nanotubes (MWCNTs). The two wafers were coated with MWCNT of two different thicknesses: 9 μm (Type-A) and 25 μm (Type-B). Experiments were conducted for the nucleate boiling and film boiling regimes for saturated and subcooled conditions with liquid subcooling of 0–30°C using a dielectric fluorocarbon liquid (PF-5060) as test fluid. The pool boiling heat flux data obtained from the bare silicon test surface were used as a base line for all heat transfer comparisons. Type-B MWCNT coatings enhanced the critical heat flux (CHF) in saturated nucleate boiling by 58%. The heat flux at the Leidenfrost point was enhanced by a maximum of ∼150% (i.e., 2.5 times) at 10°C subcooling. Type-A MWCNT enhanced the CHF in nucleate boiling by as much as 62%. Both Type-A MWCNT and bare silicon test surfaces showed similar heat transfer rates (within the bounds of experimental uncertainty) in film boiling. The Leidenfrost points on the boiling curve for Type-A MWCNT occurred at higher wall superheats. The percentage enhancements in the value of heat flux at the CHF condition decreased with an increase in liquid subcooling. However the enhancement in heat flux at the Leidenfrost points for the nanotube coated surfaces increased with liquid subcooling. Significantly higher bubble nucleation rates were observed for both nanotube coated surfaces.

High Heat Flux Phase Change on Silicon Wick Structures

2012 ◽  
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.

scholarly journals Discussion of the Heat Flux Calculation Method During Pool Boiling on Meshed Heaters

2020 ◽  
Vol 2 (1) ◽  
pp. 247-252
Author(s):  
Łukasz J. Orman ◽  
Norbert Radek ◽  
Jacek Pietraszek ◽  
Dariusz Gontarski
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Distilled Water ◽  
Determination Method ◽  
Nucleate Boiling Heat Transfer ◽  
Calculation Results ◽  
Very High

AbstractThe paper discusses nucleate boiling heat transfer on meshed surfaces during pool boiling of distilled water and ethyl alcohol of very high purity. It presents a correlation for heat flux developed for heaters covered with microstructural coatings made of meshes. The experimental results have been compared with the calculation results performed using the correlation and have been followed by discussion. Conclusions regarding the heat flux determination method have been drawn with the particular focus on the usefulness of the considered model for heat flux calculations on samples with sintered mesh layers.

Optimization Study for Uncertainty Reduction of In-Pile CHF Experiments in TREAT

2020 ◽  
Author(s):  
Seokbin Seo ◽  
Nicholas R. Brown ◽  
Robert J. Armstrong ◽  
Charles P. Folsom ◽  
Colby B. Jensen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Energy Deposition ◽  
Nuclear Reactor ◽  
National Laboratory ◽  
Nucleate Boiling ◽  
Surface Heat ◽  
Idaho National Laboratory ◽  
Optimization Study ◽  
Reactor Test

Abstract Reactivity-initiated accidents (RIAs) are one of the postulated incidents that can threaten the operational safety of a nuclear reactor. During a RIA, a rapid increase of energy deposition in the fuel can lead to a departure from nucleate boiling (DNB) occurrence which refers to the point where a drastic decrease in heat transfer capabilities occurs and the surface heat flux exceeds the critical heat flux (CHF). Aiming to understand the fundamentals beneath CHF and to predict it, the Transient Reactor Test (TREAT) facility at the Idaho National Laboratory (INL) is a unique facility that will be used to experimentally investigate the transient CHF under in-pile pool boiling condition. As part of a comprehensive effort to utilize TREAT for this project, this study analyzed the expected uncertainties in the experimental data by identifying the key inputs for the uncertainty in the temperature measurements and quantifying their priorities. The sensitivities of key inputs from neutronics modeling, the clad-to-coolant heat transfer, thermophysical properties of the tube, and coolant conditions were quantified using Sobol sensitivity analysis methods, and the significant effect of the occurrence of the CHF on the sensitivity of input was found.

Effect of Heat Flux on Pool Boiling Heat Transfer Enhancement (Numerical Investigation Approach)

2020 ◽  
Author(s):  
T. S. Mogaji ◽  
O. A. Sogbesan ◽  
Tien-Chien Jen
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Coefficient ◽  
Transfer Coefficient ◽  
Heat Transfer Enhancement ◽  
Numerical Investigation ◽  
Boiling Heat Transfer ◽  
Pool Boiling ◽  
Nucleate Boiling ◽  
Transfer Enhancement

Abstract This study presents numerical investigation results of heat flux effect on pool boiling heat transfer enhancement during nucleate boiling heat transfer of water. The simulation was performed for five different heated surfaces such as: brass, copper, mild steel, stainless steel and aluminum using ANSYS simulation software at 1 atmospheric pressure. The samples were heated in a domain developed for bubble growth during nucleate boiling process under the same operational condition of applied heat flux ranged from 100 to 1000 kW/m2 and their corresponding heat transfer coefficient was obtained numerically. Obtained experimental data of other authors from the open literature result is in close agreement with the simulated data, thus confirming the validity of the CFD simulation method used in this study. It is found that heat transfer coefficient increases with increasing heat flux. The results revealed that in comparison to other materials tested, better heat transfer performance up to 38.5% and 7.11% is observed for aluminum and brass at lower superheated temperature difference conditions of 6.96K and 14.01K respectively. This behavior indicates better bubble development and detachment capability of these heating surface materials and could be used in improving the performance of thermal devices toward producing compact and miniaturized equipment.

Boiling Heat Transfer Characteristics of Staggered-array Water Impinging Jets on Hot Steel Plate

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Sang Gun Lee ◽  
Jin Sub Kim ◽  
Dong Hwan Shin ◽  
Jungho Lee
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Surface Temperature ◽  
Boiling Heat Transfer ◽  
Steel Plate ◽  
Nucleate Boiling ◽  
Impinging Jets ◽  
Heat Transfer Characteristics ◽  
Maximum Heat ◽  
Maximum Heat Flux

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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