Steady-State Subcooled Nucleate Boiling on a Downward-Facing Hemispherical Surface

Steady-state nucleate boiling heat transfer experiments in saturated and subcooled water were conducted. The heating surface was a 0.305 m hemispherical aluminum vessel heated from the inside with water boiling on the outside. It was found that subcooling had very little effect on the nucleate boiling curve in the high heat flux regime where latent heat transport dominated. On the other hand, a relatively large effect of subcooling was observed in the low-heat-flux regime where sensible heat transport was important. Photographic records of the boiling phenomenon and the bubble dynamics indicated that in the high-heat-flux regime, boiling in the bottom center region of the vessel was cyclic in nature with a liquid heating phase, a bubble nucleation and growth phase, a bubble coalescence phase, and a large vapor mass ejection phase. At the same heat flux level, the size of the vapor masses was found to decrease from the bottom center toward the upper edge of the vessel, which was consistent with the increase observed in the critical heat flux in the flow direction along the curved heating surface.

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Development of Advanced High Heat Flux Cooling System for Power Electronics

ASME 2009 InterPACK Conference, Volume 2 ◽

10.1115/interpack2009-89082 ◽

2009 ◽

Cited By ~ 1

Author(s):

Yasuhisa Shinmoto ◽

Shinichi Miura ◽

Koichi Suzuki ◽

Yoshiyuki Abe ◽

Haruhiko Ohta

Keyword(s):

Heat Flux ◽

Power Electronics ◽

Critical Heat Flux ◽

Heating Surface ◽

Narrow Channel ◽

High Heat ◽

High Heat Flux ◽

Gap Size ◽

Narrow Channels ◽

Very High

Recent development in electronic devices with increased heat dissipation requires severe cooling conditions and an efficient method for heat removal is needed for the cooling under high heat flux conditions. Most researches are concentrated on small semiconductors with high heat flux density, while almost no existing researches concerning the cooling of a large semiconductor, i.e. power electronics, with high heat generation density from a large cooling area. A narrow channel between parallel plates is one of ideal structures for the application of boiling phenomena which uses the cooling for such large semiconductors. To develop high-performance cooling systems for power electronics, experiments on increase in critical heat flux (CHF) for flow boiling in narrow channels by improved liquid supply was conducted. To realize the cooling of large areas at extremely high heat flux under the conditions for a minimum gap size and a minimum flow rate of liquid supplied, the structure with auxiliary liquid supply was devised to prevent the extension of dry-patches underneath flattened bubbles generated in a narrow channel. The heating surface was experimented in two channels with different dimensions. The heating surfaces have the width of 30mm and the lengths of 50mm and 150mm in the flow direction. A large width of actual power electronics is realizable by the parallel installation of the same channel structure in the transverse direction. The cooling liquid is additionally supplied via sintered metal plates from the auxiliary unheated channels located at sides or behind the main heated channel. To supply the liquid to the entire heating surface, fine grooves are machined on the heating surface for enhance the spontaneous liquid supply by the aid of capillary force. The gap size of narrow channels are varied as 0.7mm, 2mm and 5mm. Distribution of liquid flow rate to the main heated channel and the auxiliary unheated channels were varied to investigate its effect on the critical heat flux. Test liquids employed are R113, FC72 and water. The systematic experiments by using water as a test liquid were conducted. Critical heat flux values larger than 2×106W/m2 were obtained at both gap sizes of 2mm and 5mm for a heated length of 150mm. A very high heat transfer coefficient as much as 1×105W/m2K was obtained at very high heat flux near CHF for the gap size of 2mm. This paper is a summary of experimental results obtained in the past by the present authors.

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The Steady-State Modeling and Analysis of a Two-Loop Cooling System for High Heat Flux Removal

Volume 9: Heat Transfer, Fluid Flows, and Thermal Systems, Parts A, B and C ◽

10.1115/imece2009-11500 ◽

2009 ◽

Cited By ~ 1

Author(s):

Rongliang Zhou ◽

Juan Catano ◽

Tiejun Zhang ◽

John T. Wen ◽

Greg J. Michna ◽

...

Keyword(s):

Heat Flux ◽

Steady State ◽

Heat Exchangers ◽

Cooling System ◽

High Heat ◽

System Structure ◽

High Heat Flux ◽

Vapor Compression ◽

Vapor Compression Cycle ◽

Compression Cycle

Steady-state modeling and analysis of a two-loop cooling system for high heat flux removal applications are studied. The system structure proposed consists of a primary pumped loop and a vapor compression cycle (VCC) as the secondary loop to which the pumped loop rejects heat. The pumped loop consists of evaporator, condenser, pump, and bladder liquid accumulator. The pumped loop evaporator has direct contact with the heat generating device and CHF must be higher than the imposed heat fluxes to prevent device burnout. The bladder liquid accumulator adjusts the pumped loop pressure level and, hence, the subcooling of the refrigerant to avoid pump cavitation and to achieve high critical heat flux (CHF) in the pumped loop evaporator. The vapor compression cycle of the two-loop cooling system consists of evaporator, liquid accumulator, compressor, condenser and electronic expansion valve. It is coupled with the pumped loop through a fluid-to-fluid heat exchanger that serves as both the vapor compression cycle evaporator and the pumped loop condenser. The liquid accumulator of the vapor compression cycle regulates the cycle active refrigerant charge and provides saturated vapor to the compressor at steady state. The heat exchangers are modeled with the mass, momentum, and energy balance equations. Due to the projected incorporation of microchannels in the pumped loop to enhance the heat transfer in heat sinks, the momentum equation, rarely seen in previous refrigeration system modeling efforts, is included to capture the expected significant microchannel pressure drop witnessed in previous experimental investigations. Electronic expansion valve, compressor, pump, and liquid accumulators are modeled as static components due to their much faster dynamics compared with heat exchangers. The steady-state model can be used for static system design that includes determining the total refrigerant charge in the vapor compression cycle and the pumped loop to accommodate the varying heat load, sizing of various components, and parametric studies to optimize the operating conditions for a given heat load. The effect of pumped loop pressure level, heat exchangers geometries, pumped loop refrigerant selection, and placement of the pump (upstream or downstream of the evaporator) are studied. The two-loop cooling system structure shows both improved coefficient of performance (COP) and CHF overthe single loop vapor compression cycle investigated earlier by authors for high heat flux removal.

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Study on onset of nucleate boiling with screw tube for fusion reactor application

Nuclear Fusion ◽

10.1088/1741-4326/ac44ae ◽

2021 ◽

Author(s):

Ji Hwan Lim ◽

Minkyu Park

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Flow Boiling ◽

Nucleate Boiling ◽

High Heat ◽

Transfer Mechanism ◽

High Heat Flux ◽

Heat Transfer Mechanism ◽

System Parameters ◽

Smooth Tubes

Abstract The onset of nucleate boiling (ONB) is the point at which the heat transfer mechanism in fluids changes and is one of the thermo-hydraulic factors that must be considered when establishing a cooling system operation strategy. Because the high heat flux of several MW/m2, which is loaded within a tokamak, is applied under a one-side heating condition, it is necessary to determine a correlative relation that can predict ONB under special heating conditions. In this study, the ONB of a one-side-heated screw tube was experimentally analyzed via a subcooled flow boiling experiment. The helical nut structure of the screw tube flow path wall allows for improved heat transfer performance relative to smooth tubes, providing a screw tube with a 53.98% higher ONB than a smooth tube. The effects of the system parameters on the ONB heat flux were analyzed based on the changes in the heat transfer mechanism, with the results indicating that the flow rate and degree of subcooling are proportional to the ONB heat flux because increasing these factors improves the forced convection heat transfer and increases the condensation rate, respectively. However, it was observed that the liquid surface tension and latent heat decrease as the pressure increases, leading to a decrease in the ONB heat flux. An evaluation of the predictive performance of existing ONB correlations revealed that most have high error rates because they were developed based on ONB experiments on micro-channels or smooth tubes and not under one-side high heat load conditions. To address this, we used dimensional analysis based on Python code to develop new ONB correlations that reflect the influence of system parameters.

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High-heat flux tests of tungsten divertor mock-ups with steady-state plasma and e-beam

Nuclear Materials and Energy ◽

10.1016/j.nme.2020.100816 ◽

2020 ◽

Vol 25 ◽

pp. 100816

Author(s):

V.P. Budaev ◽

S.D. Fedorovich ◽

A.V. Dedov ◽

A.V. Karpov ◽

A.T. Komov ◽

...

Keyword(s):

Heat Flux ◽

Steady State ◽

High Heat ◽

High Heat Flux ◽

State Plasma

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The dynamics of nucleate boiling of salt solutions at a high heat flux

EPJ Web of Conferences ◽

10.1051/epjconf/201919600003 ◽

2019 ◽

Vol 196 ◽

pp. 00003

Author(s):

Vladimir Morozov ◽

Dmitriy Elistratov

Keyword(s):

Wall Temperature ◽

Mass Concentration ◽

Heating Surface ◽

Nucleate Boiling ◽

High Heat ◽

High Heat Flux ◽

Salt Solutions ◽

Working Surface ◽

Aqueous Salt Solutions ◽

Heat Of Evaporation

In this paper, experimental results are obtained for the desorption of layers of aqueous salt solutions of LiBr and CaCl2 at a temperature of nucleate boiling on a horizontal heating surface. The wall temperature is 130 °C. The required volume of the solution with a given mass concentration is placed on the working surface using the Thermo Scientific dispensers. After that, the desorption rate continuously decreases over time. A decrease in the wall temperature leads to a drop in the intensity of the bubbling boiling. The effect of gas convection during evaporation and thermal radiation is small in comparison with the heat of evaporation.

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Flow Boiling Enhancement in Microchannels With Diffusion Bonded Wire Mesh

ASME/JSME 2007 Thermal Engineering Heat Transfer Summer Conference, Volume 1 ◽

10.1115/ht2007-32119 ◽

2007 ◽

Author(s):

Hailei Wang ◽

Richard Peterson

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Flow Boiling ◽

Nucleate Boiling ◽

High Heat ◽

Wire Mesh ◽

Working Fluid ◽

High Heat Flux ◽

Vapor Quality ◽

Heating Wall

Flow boiling and heat transfer enhancement in four parallel microchannels using a dielectric working fluid, HFE 7000, was investigated. Each channel was 1000 μm wide and 510 μm high. A unique channel surface enhancement technique via diffusion bonding a layer of conductive fine wire mesh onto the heating wall was developed. According to the obtained flow boiling curves for both the bare and mesh channels, the amount of wall superheat was significantly reduced for the mesh channel at all stream-wise locations. This indicated that the nucleate boiling in the mesh channel was enhanced due to the increase of nucleation sites the mesh introduced. Both the nucleate boiling dominated and convective evaporation dominated regimes were identified. In addition, the overall trend for the flow boiling heat transfer coefficient, with respect to vapor quality, was increasing until the vapor quality reached approximately 0.4. The critical heat flux (CHF) for the mesh channel was also significantly higher than that of the bare channel in the low vapor quality region. Due to the fact of how the mesh was incorporated into the channels, no pressure drop penalty was identified for the mesh channels. Potential applications for this kind of mesh channel include high heat-flux electronic cooling systems and various energy conversion systems.

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Nucleate Boiling of Dielectric Liquids on Hydrophobic Patterned Surfaces

Volume 8B: Heat Transfer and Thermal Engineering ◽

10.1115/imece2014-37513 ◽

2014 ◽

Author(s):

Nihal E. Joshua ◽

Denesh K. Ajakumar ◽

Huseyin Bostanci

Keyword(s):

Heat Transfer ◽

Heat Flux ◽

Nucleate Boiling ◽

High Heat ◽

Copper Surface ◽

Dielectric Liquid ◽

Working Fluid ◽

Patterned Surfaces ◽

High Heat Flux ◽

Dielectric Liquids

This study experimentally investigated the effect of hydrophobic patterned surfaces in nucleate boiling heat transfer. A dielectric liquid, HFE-7100, was used as the working fluid in the saturated boiling tests. Dielectric liquids are known to have highly-wetting characteristics. They tend to fill surface cavities that would normally trap vapor/gas, and serve as active nucleation sites during boiling. With the lack of these vapor filled cavities, boiling of a dielectric liquid leads to high incipience superheats and accompanying temperature overshoots. Heater samples in this study were prepared by applying a thin Teflon (AF400, Dupont) coating on 1-cm2 smooth copper surfaces following common photolithography techniques. Matching size thick film resistors, attached onto the copper samples, generated heat and simulated high heat flux electronic devices. Tests investigated the heater samples featuring circular pattern sizes between 40–100 μm, and corresponding pitch sizes between 80–200 μm. Additionally, a plain, smooth copper surface was tested to obtain reference data. Based on data, hydrophobic patterned surfaces effectively eliminated the temperature overshoot at boiling incipience, and considerably improved nucleate boiling performance in terms of heat transfer coefficient and critical heat flux over the reference surface. Hydrophobic patterned surfaces therefore demonstrated a practical surface modification method for heat transfer enhancement in immersion cooling applications.

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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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