Nonlinear Aspects of High Heat Flux Nucleate Boiling Heat Transfer

1995 ◽  
Vol 117 (4) ◽  
pp. 981-989 ◽  
Author(s):  
P. Sadasivan ◽  
C. Unal ◽  
R. Nelson
Keyword(s):  
Heat Transfer ◽  
Chaotic Behavior ◽  
Period Doubling ◽  
Thermal Conditions ◽  
Nucleate Boiling ◽  
High Heat ◽  
Heat Transfer Process ◽  
High Heat Flux ◽  
Heater Surface ◽  
Nucleation Sites

This paper deals with potential nonlinear effects in nucleate boiling systems as a result of the behavior of individual nucleation sites on the heater surface. This requires detailed microscopic modeling of the surface. A computational model has been formulated for this purpose. The model addresses the three-dimensional transient conduction heat transfer process within the problem domain comprised of the macrolayer and heater. Hydrodynamic effects are represented through boundary conditions. Individual nucleation sites are activated or deactivated depending on the thermal conditions that prevail at the site. The model has been used to examine the behavior of sites on a realistic heater surface. The results indicate that significant spatial and temporal temperature variations can occur on the surface, and that thermal interactions among sites can result in some sites operating intermittently. Surface-averaged temperatures show nonlinear period-doubling behavior. A chaotic case was found. Qualitative comparisons are made to both local instantaneous temperature measurements and recent experiments that showed chaotic behavior. We believe that such nonlinear behavior is one of the reasons that mechanistic predictive capabilities for the boiling process have remained elusive.

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

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.

Heat Transfer in Supercritical Steam Flowing Through Spiral Tubes

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Deepak Kumar Kanungo ◽  
Sachin Kumar Shrivastava ◽  
Nand Kumar Singh ◽  
Kirti Chandra Sahu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Three Dimensional ◽  
Tangential Velocity ◽  
Thermal Conditions ◽  
Strong Relationship ◽  
High Heat ◽  
High Heat Flux ◽  
Straight Tube ◽  
Spiral Tube

Abstract We investigate heat transfer in supercritical steam flowing in a spiral tube by conducting three-dimensional numerical simulations. The current numerical solver has been validated with the existing experimental results, and simulations are performed by varying different geometric parameters of a spiral tube. The flow dynamics and heat transfer in a spiral tube are compared against those in a straight tube. For the parameters range considered in the present study, it is found that the heat transfer coefficient (HTC) in the spiral tube is 29% higher than that in the case of a straight tube for the same flow and thermal conditions. Our results indicate that the tangential velocity component resulting due to the spiraling effect of the steam is the primary reason for the enhancement of the HTC value. It is observed that while the HTC in a spiral tube is inversely related to the spiral diameter, it does not exhibit a strong relationship with the spiral pitch. Moreover, three existing heat transfer correlations are evaluated under the spiral flow condition and it is observed that none of them can calculate the HTC value accurately in spiral tubes. Using the Buckingham π-theorem, three modified correlations are proposed for the low, moderate, and high heat flux regimes, which accurately predict the wall temperature and HTC of supercritical steam in spiral tubes in all the heat flux regimes. The correlations have an error band of less than ±20%.

Flow Boiling Enhancement in Microchannels With Diffusion Bonded Wire Mesh

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.

Nucleate Boiling of Dielectric Liquids on Hydrophobic Patterned Surfaces

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.

Mechanistic Considerations for Enhancing Flow Boiling Heat Transfer in Microchannels

2015 ◽  
Author(s):  
Satish G. Kandlikar
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Flow Boiling ◽  
Electronics Cooling ◽  
High Heat ◽  
High Heat Flux ◽  
Nucleation Sites ◽  
Flow Boiling Heat Transfer ◽  
Underlying Mechanisms

Research efforts on flow boiling in microchannels were focused on stabilizing the flow during the early part of the last decade. After achieving that goal through inlet restrictors and distributed nucleation sites, the focus has now shifted on improving its performance for high heat flux dissipation. The recent worldwide efforts described in this paper are aimed at increasing the critical heat flux (CHF) while keeping the pressure drop low, with an implicit goal of dissipating 1 kW/cm2 for meeting the high-end target in electronics cooling application. The underlying mechanisms in these studies are identified and critically evaluated for their potential in meeting the high heat flux dissipation goals. Future need to simultaneously increase the CHF and the heat transfer coefficient (HTC) has been identified and hierarchical integration of nanoscale and microscale technologies is deemed necessary for developing integrated pathways toward meeting this objective.

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.

Enhanced Boiling Heat Transfer From Micro-Porous Cylindrical Surfaces in Saturated FC-87 and R-123

1997 ◽  
Vol 119 (2) ◽  
pp. 319-325 ◽  
Author(s):  
J. Y. Chang ◽  
S. M. You
Keyword(s):  
Heat Transfer ◽  
Boiling Heat Transfer ◽  
Nucleate Boiling ◽  
High Heat ◽  
Bulk Liquid ◽  
High Heat Flux ◽  
High Flux ◽  
Boiling Enhancement ◽  
Nucleate Boiling Heat Transfer ◽  
Enhanced Boiling

The present research is an experimental study of pool boiling heat transfer from cylindrical heater surfaces immersed in saturated FC-87 and R-123. The baseline heater surfaces tested are plain, integral-fin with 709 fins/m, and commercial enhanced (High-Flux and Turbo-B). In addition, a highly effective micro-scale enhancement coating is applied to the plain and integral-fin surfaces to augment nucleate boiling heat transfer. Experiments are performed to understand the effects of surface micro- and macro-geometries on boiling heat transfer. The boiling performance of the micro-porous enhanced plain and integral-fin surfaces are compared with the High-Flux and the Turbo-B surfaces. At high heat flux conditions, the break down of the bulk liquid feed mechanism reduces boiling enhancement from the cylindrical surfaces.

Enhanced Flow Boiling Over Open Microchannels With Uniform and Tapered Gap Manifolds

2013 ◽  
Vol 135 (6) ◽  
Author(s):  
Satish G. Kandlikar ◽  
Theodore Widger ◽  
Ankit Kalani ◽  
Valentina Mejia
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Heat Transfer Performance ◽  
Flow Boiling ◽  
Nucleate Boiling ◽  
High Heat ◽  
High Heat Flux ◽  
Transfer Performance ◽  
Transfer Coefficients ◽  
Heat Transfer Coefficients

Flow boiling in microchannels has been extensively studied in the past decade. Instabilities, low critical heat flux (CHF) values, and low heat transfer coefficients have been identified as the major shortcomings preventing its implementation in practical high heat flux removal systems. A novel open microchannel design with uniform and tapered manifolds (OMM) is presented to provide stable and highly enhanced heat transfer performance. The effects of the gap height and flow rate on the heat transfer performance have been experimentally studied with water. The critical heat fluxes (CHFs) and heat transfer coefficients obtained with the OMM are significantly higher than the values reported by previous researchers for flow boiling with water in microchannels. A record heat flux of 506 W/cm2 with a wall superheat of 26.2 °C was obtained for a gap size of 0.127 mm. The CHF was not reached due to heater power limitation in the current design. A maximum effective heat transfer coefficient of 290,000 W/m2 °C was obtained at an intermediate heat flux of 319 W/cm2 with a gap of 0.254 mm at 225 mL/min. The flow boiling heat transfer was found to be insensitive to flow rates between 40–333 mL/min and gap sizes between 0.127–1.016 mm, indicating the dominance of nucleate boiling. The OMM geometry is promising to provide exceptional performance that is particularly attractive in meeting the challenges of high heat flux removal in electronics cooling applications.

Integrated Eco-Thermal Management for Aerospace

2005 ◽  
Author(s):  
Lev Reznikov
Keyword(s):  
Heat Transfer ◽  
Thermal Management ◽  
High Performance ◽  
Waste Heat ◽  
Space Station ◽  
Nucleate Boiling ◽  
High Heat ◽  
Novel Technologies ◽  
Related Substances ◽  
Nucleation Sites

Thermal Management System developed for aerospace carriers (missile, aircraft, space station), bounds processes of generation and dissipation, transfer and conversion of power, refrigeration, and of bio-metabolism related substances. Local ecosystem of the carrier combines technological and biological subsystems, interacting with internal and outer spaces. The conceptual IETM System performs recovery of waste thermal energy, generation of “free” refrigeration, and recovery of byproducts into safe coolants (ammonia - water). Thermal Management solutions include novel technologies of intensification of the heat transfer and of conversion of the waste resources into refrigeration for extension of cooling capabilities for high heat radars, lasers and microwave generators. The IETM includes Vacuum-Evaporative Refrigeration (VER) utilizing “free natural” vacuum and waste heat-activated refrigeration circuits. VER generates ~1000 Btu of “free” cold per pound of wastewater or ammonia. The introduced high performance microstructure of compound electrohydrodynamic (EHD) boundary microsystems intensifies nucleate boiling, preventing dryout. The coils of the microwires adjoin to the boiling surface and form precision microstructure of heat sink with microchannels between the coils and the surface. The microcavities form the active bubbling nucleation sites along the spiral zones of contacts of the microwires and basic surfaces. The fins-microelectrodes develop additional heat transfer surface and evenly distributed spiral zones of the nucleation sites. Like fibers of a fine wick, the electric forces in EHD capillary structures of the microelectrodes retain the liquid and push out generated vapor bubbles from the surface. Good manufacturability and performance of novel MEMS are based on well-developed materials and common winding technology “borrowed” from electrotechnical industry. Conversion of waste resources into refrigeration and EHD activation of boiling allow meeting strong limitations in weight, reliability and consumption of energy. These conceptual approaches provide diversities in refrigeration capabilities for IETM.

Ultra-Cooling Heat Transfer Characteristics Using Cryogenic Micro-Solid Nitrogen Spray

2012 ◽  
Author(s):  
U. Oh ◽  
Jun Ishimoto ◽  
Naoki Harada ◽  
Daisuke Tan
Keyword(s):  
Heat Transfer ◽  
Heated Surface ◽  
Spray Cooling ◽  
High Heat ◽  
Heat Transfer Process ◽  
Solid Particles ◽  
High Heat Flux ◽  
Heat Transfer Characteristics ◽  
Solid Nitrogen ◽  
New Type

The fundamental characteristics of heat transfer and cooling performance of micro-solid nitrogen particulate spray impinging on a heated substrate were numerically investigated and experimentally measured by a new type of integrated computational-experimental technique. The employed CFD based on the Euler-Lagrange model is focused on the cryogenic spray behavior of atomized particulate micro-solid nitrogen and also on its ultra-high heat flux cooling characteristics. Based on the numerically predicted performance, a new type of cryogenic spray cooling technique for application to a ultra-high heat power density device was developed. In the present integrated computation, it is clarified that the cryogenic micro-solid spray cooling characteristics are affected by several factors of the heat transfer process of micro-solid spray which impinges on heated surface as well as by atomization behavior of micro-solid particles.

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